(Qarnell Httioeraity ffitbratg Stljata, 5Jetn $nrk BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND THE GIFT OF HENRY W. SAGE 1891 Cornell University Library TH 7223.A432 Heating and ventilation 3 1924 003 892 233 K Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003892233 HEATING AND VENTILATION l\h Qraw-TlillBook Qx 7m PUBLISHERS OF BOOKS F O R_^ Coal Age v Electric Railway Journal Electrical World v Engineering News-Record American Machinist v The Gontractor Engineering 8 Mining Journal v Power Metallurgical 6 Chemical Engineering Electrical Merchandising IniBffiliMlfflilfflf HEATING AND VENTILATION BY JOHN R. ALLEN DEAN OF THE DEPARTMENT OF ENGINEERING AND ARCHITECTURE UNIVERSITY OF MINNESOTA; MEMBER AMERICAN SOCIETY OF HEATING AND VENTILATING ENGINEERS; MEMBER AMERICAN SOCIETY OF MECHANICAL ENGINEERS AND J. H. WALKER SUPERINTENDENT OF CENTRAL HEATING, THE DETROIT EDISON COMPANY ; MEMBER AMERICAN SOCIETY OF HEATING AND VENTILATING ENGINEERS First Edition McGRAW-HILL BOOK COMPANY, Inc. 239 WEST 39TH STREET. NEW YORK LONDON: HILL PUBLISHING CO., Ltd. 6 & 8 BOUVERIE ST., E. C. 1918 LL Copyright, 1918, by the McGraw-Hill Book Company, Inc. THE MAFLE PRESS YOHK PA PREFACE This book is offered as a text-book upon the subject of heating and ventilation for use in the engineering and architectural schools. It is also believed that the development of working methods of design and the including of the various tables and charts make the book of some value as a handbook for the practicing engineer and architect. Calculus has been employed to some extent in the develop- ment of certain expressions, this having been deemed desirable for the sake of completeness. For architectural students and others not equipped with higher mathematics, such parts may be omitted, however, without destroying the structure of the book. Problems have been included at the end of many of the chapters in order to illustrate the principles involved, but it is felt that they can be profitably supplemented by the actual designing by the student of complete heating and ventilating systems for representative buildings of various types. Acknowledgment is made to the American Blower Company and the Buffalo Forge Company for the use of various charts and tables. Information as to the typographical errors which are doubtless present in this initial edition will be gratefully received. J. R. A. March, 1918. J. H. W. CONTENTS Page Preface v CHAPTER, I Heat Measurement of Heat 1 Measurement of Temperature 2 Unit of Heat 4 CHAPTER II Heat Losses prom Buildings Radiation 9 Conduction 10 Convection 11 Loss of Heat from Buildings , 12 Heat Lost Due to Infiltration 18 Calculation of Heat Loss 20 Approximate Rules 21 CHAPTER III Different Methods of Heating Grates 25 Stoves 26 Hot-air Furnaces 26 Direct Steam Heating 27 Direct Heating by Hot Water 28 Indirect Heating 29 Economy of Heating Systems 31 CHAPTER IV Properties of Steam The Formation of Steam 33 Properties of Steam 34 Steam Tables 36 Mechanical Fixtures 37 vii viii CONTENTS CHAPTER V , Radiators Page Direct Cast-iron Radiators . . . 45 Pressed Metal Radiators 50 Heat Transmission from Radiators 51 Location of Radiators 56 Proportioning Radiation 57 Indirect Radiators ■ 60 CHAPTER VI Steam Boilers Fuel .... . 69 Combustion 71 Smoke 72 Types of Boilers 74 The Downdraft Boiler 77 Boiler Rating 81 Draft and Chimney Construction 83 CHAPTER VII Steam Heating Systems Single-pipe Systems . 87 Two-pipe Systems ... . . 89 Overhead System 91 Vapor System . .93 Vacuum Return Line System . 99 CHAPTER VIII Pipe, Fittings, Valves, and Accessories Pipe 102 Fittings 104 Valves .... 106 Pipe Covering 109 Air-valves Ill Traps 112 Reducing Valves ... 115 CHAPTER IX Steam Piping Principles Involved in Piping Design .119 Expansion . . 119 CONTENTS IX Drainage ... Mains and Branches Risers . Pipe Hangers . . Radiator Connections. Flow of Steam in Pipes Selection of Pipe Sizes Page . 120 121 122 . 124 128 131 . 134 CHAPTER X Hot-water Systems Theory of Flow in a Gravity System 142 Types of Gravity Systems 146 Method of Computing Pipe Sizes 151 Forced Circulation . . . • 158 Pumpage, Friction, and Temperature Drop ... 159 Calculation of Pipe Sizes 161 CHAPTER XI Automatic Temperature Control Manual Control 163 Automatic Control Applied to Boiler . 164 Automatic Control of Radiators 166 Advantages of Automatic Control 167 CHAPTER XII Air and Its Properties Composition of Air 169 Water Vapor . ... 170 Measurement of Humidity 173 Psychrometric Chart 175 ■ CHAPTER XIII Ventilation Ventilation Standards Amount of Air Required Methods of Measuring Air Supply Temperature and Humidity . Air Movement Odors. . . ... Dust and Bacteria 179 181 182 184 187 187 188 x CONTENTS CHAPTER XIV Hot-air Furnace Heating Page Furnaces 192 Cold-air Pipe 196 Hot-air Pipes 197 Test of a Hot-air Furnace 204 CHAPTER XV Design of Fan Systems General Arrangement 207 Calculation of Air Quantities ... 208 Flow of Air in Ducts 209 Proportioning Duct Systems 218 Theory of the Centrifugal Fan .... ... 223 Fan Performance 226 Selection of a Fan . . 228 Heaters. . . . 233 Transmission of Heat from Fan Coils . 236 CHAPTER XVI AlR-WASHERS AND AlR CONDITIONING The Air-washer . . . 244 Air Conditioning . 246 Humidity Control 248 Cooling and De-humidification 249 CHAPTER XVII Fan Systems for Various Types op Buildings Heating of Public Buildings 252 Factory Heating . . . 253 Heating of Theatres and Auditoriums .... 255 Estimating Heating Requirements . . . . 255 CHAPTER XVIII Central Heating Location of Power Plant . ... 258 Systems of Distribution 260 Methods of Carrying Pipes .... 262 Expansion Fittings 265 Tunnels 266 Index 301 HEATING AND VENTILATION CHAPTER I HEAT 1. Heat. — Heat has long been known to be a form of energy. Modern theories as to the exact nature of heat conceive it to be a motion or agitation of the molecules, or extremely small particles, of which every body is composed. The intensity of the heat in a body is believed to be dependent upon the violence of this molecular disturbance. Every substance on the earth contains some heat and to say that a body is "cold," means simply that it contains a relatively small amount of molecular motion. Heat and many other forms of energy are mutually convertible. For example, heat energy is converted into electrical energy in a generating plant and electric energy is re-converted into heat energy in an electric stove. Heat energy is converted into mechanical energy in a steam locomotive and some of this mechanical energy is re-converted into heat energy by the fric- of the locomotive brakes. 2. Measurement of Heat. — In measuring heat there are two quantities to be considered : the intensity of heat and the amount of heat. A small piece of white-hot metal may not contain as great a quantity of heat as a pail of warm water, but the intensity of the heat in the former is much greater. The intensity of heat is expressed by the word temperature. The temperature of a body is most easily measured by noting its effect upon some other substance. One measure of the intensity of heat in a body is its ability to transmit heat to a body of lower temperature. Heat will flow from a body of higher temperature to one of lower temperature but will never flow, of itself, from one body into another of higher temperature. When two bodies of different temperatures are placed in thermal contact a heat exchange takes place until the two bodies are at the same temperature and thermal equilibrium l 2 HEATING AND VENTILATION is reached. We may, therefore, state that two bodies are at the same temperature when there is no tendency for heat to flow from the one to the other. 3. Measurement of Temperature. — The measurement of temperature is usually based upon some arbitrary scale which is standardized by comparison with some well-established phys- ical "fixed points." In mechanical engineering most measure- ments of temperature are made on the Fahrenheit scale. On this scale the freezing point of water is taken at 32° and the boiling point at sea level barometer at 212,° the tube of the thermometer between these points being divided into 180 equal parts or degrees. There is, however, an increasing use of the Centigrade scale among engineers. In the Centigrade scale the distance between the freezing point and the boiling point is divided into 100 equal parts. The freezing point on the scale is marked and the boiling point is marked 100°. Both the Fahrenheit and the Centigrade scales assume an arbitrary point for the zero of the scale. If the temperature Fahrenheit is denoted by t f and the tempera- ture Centigrade by l C) then the conversion from one scale to the other may be made by the following equations: i, = jU + 32 L = I (t f - 32) The most common instrument for measuring temperature is the mercury thermometer. Mercury like most other substances undergoes an increase in volume when heated, and is particularly useful because the amount of its expansion for equal increments in temperature is nearly constant over a wide range in tempera- ture. The thermometer is a glass tube of very fine bore with a bulb blown on one end and filled with mercury, as shown in Fig. 1. The air is expelled from the tube by boiling the mercury and the tube is sealed. The space above the mercury then contains mercury vapor at a very low pressure. The 32° and the 212° points of the Fahrenheit scale are located on the tube or stem by immersing the bulb in a freezing mixture and in boiling water. The distance between these points is then divided into 180 equal parts. HEAT 3 To do accurate work with the thermometer is much more difficult than is generally supposed. The mercury of the ordinary glass thermometer does not expand in exactly equal amounts for equal increments of temperature and the bore of the thermometer is never absolutely uniform throughout the length of the tube. All of these irregularities produce errors in observation. When measuring the temperature of liquids the depth to which the thermometer is immersed affects the reading and the thermometer should be calibrated at the depth at which it is to be used. It is really its own temperature that the thermometer indicates and the accuracy with which the temperature of a substance is measured depends upon the complete- ness with which its temperature is reached by the ther- mometer. The thermometer must therefore be brought into intimate thermal contact with the substance to be measured. In measuring the temperature of fluids in pipes, a brass or steel well is inserted into the pipe and filled with some liquid such as oil or mercury, in which the thermometer is immersed. If the thermometer is used to measure the temperature of the air in the room in which there are objects of a higher temperature than the thermometer, its bulb must be protected from the radiant heat of these hot bodies; otherwise the ther- mometer will not read the temperature of the air sur- rounding it but will be affected by the radiant heat absorbed by it. When accurate temperature measure- ments are desired a careful study should be made of the thermometer and its errors and all inaccuracies should be allowed for by careful calibration. The mercury thermometer can be used up to tempera- tures of 500°F. and for temperatures as low as —40°. Where lower temperatures must be measured it is cus- tomary to use thermometers filled with alcohol, and for temperatures higher than 500°F. some form of pyro- meter must be used. High temperatures may be deter- mined approximately by color. For each temperature there is a corresponding color and an approximation to the actual temperature can be made by an observation of the color of the heated substance. Table I gives the temperature colors. TV HEATING AND VENTILATION Table I. — Temperature Colors Color Temp. C. Temp. F. Faint red Dark red Faint cherry. . . Cherry Bright cherry. . Dark orange . . . Bright orange . White heat Bright white . . Dazzling white 525 977 700 1,292 800 1,472 900 1,652 1,000 1,832 1,100 2,012 1,200 2,192 1,300 2,372 1,400 2,552 ,500-1,600 2,732-2,912 4. Absolute Temperature. — In any theoretical consideration of heat it is necessary to have some absolute scale of temperature. The point at which the molecules of a substance would have no motion is considered to be the absolute zero point. According to Marks and Davis this point is theoretically at 491.64° below the freezing point of water on the Fahrenheit scale, or 459.64° below the Fahrenheit zero. On the Centigrade scale- the absolute zero is at —273.1°. To convert any temperature on the Fahren- heit or Centigrade scale to absolute temperature the following formulae are used: Tf = t f + 460 T c =t c + 273 (approximately) (approximately) in which the absolute temperatures on the Fahrenheit and Cen- tigrade scales are represented by T f and T c . These expressions are sufficiently accurate for ordinary work. No one has as yet been able to produce a temperature as low as the absolute zero. The lowest temperatures ever attained have been produced in the heat laboratory at Leyden, Holland, at which there has been produced a temperature of 489° below the Fahrenheit freezing point. 5. Unit of Heat. — Heat must be measured by the effect which it produces upon some substance. The unit of heat used in mechanical engineering is the heat required to raise the tempera- ture of a pound of water one degree Fahrenheit. This is called the British thermal unit and is denoted by B .t.u. As this quantity HEAT 5 is not exactly the same at all temperatures it is necessary to specify further a definite temperature at which the unit is to be established. The practice of different authorities varies in this regard, but the mean B.t.u. established by Marks and Davis is becoming generally used. This is denned as the one hundred and eightieth part of the heat necessary to raise the temperature of one pound of water from 32° to 212°F. 6. Specific Heat. — Specific heat may be denned as the heat necessary to raise the temperature of a unit weight of a sub- stance through one degree. It represents the specific thermal capacity of a body. In English units the specific heat is the quantity of heat necessary to raise a pound of a substance one degree Fahrenheit, expressed in British thermal units. Since the British thermal unit is the quantity of heat necessary to raise a pound of water one degree Fahrenheit, we may say that the specific heat represents the ratio between the heat necessary to raise a unit weight of a body one degree and the heat neces- sary to raise the same weight of water one degree. When a substance is heated at constant pressure its volume increases against that pressure and external work is done as a consequence. The external work may be computed by multiply- ing the pressure by the change in volume. When heated at constant volume no external work is done as no movement is made against an external resistance. In any substance, such as a gas, which, has a large coefficient of expansion due to heat, it is therefore necessary to distinguish between the two specific heats, the specific heat of constant pressure and the specific heat of con- stant volume. The difference between the two specific heats in any particular gas must be equal to the heat equivalent of the external work done when a unit weight of the gas is raised one degree at a constant pressure. The quantity of heat added to or removed from a body is equal to WC(t 2 - h) in which W = weight of the body in pounds. C = specific heat of the material. h = lower temperature Fahrenheit. U = higher temperature Fahrenheit. 6 HEATING AND VENTILATION Table II. — Specific Heats Substance Specific heat Liquids: Water 1 . 0000 Alcohol 0.6220 Turpentine 0.4720 Petroleum 0.4340 Olive oil 0.3090 Metals: Cast iron 0. 1298 Wrought iron 0.1138 Soft steel 0.1165 Copper 0.0951 Brass 0.0939 Tin : 0.0569 Lead 0.0314 Aluminum . 2185 Zinc 0.0953 ' Minerals : Coal 0.2777 Marble 0.2159 Chalk 0.2149 Stones generally . 2100 Limestone. 0.2170 Building Materials: Brickwork 0. 1950 Masonry 0.2000 Plaster . 2000 Pine wood . 4670 Oak wood . 5700 Birch 0.4800 Glass 0. 1977 Specific Heat of Gases Constant Constant Substance pressure volume Air 0.2415 0.1729 Oxygen 0.2175 0.1550 Hydrogen 3.4090 2.4122 Nitrogen . 2438 . 1727 Steam 0.5000 0.3500 Carbonic acid, C0 2 0.2479 0. 1758 Ammonia 0.5080 0.2990 Example. — It is required to raise the temperature of a cast-iron radiator weighing 300 pounds from 70° to 212°. The temperature through which the iron would be raised would then be 212° minus 70° or 142°. From Table HEAT 7 II we see that to raise 1 pound of cast iron 1° would require 0.1298 heat units. To raise 1 pound 142° would require 142 times 0.1298 or 18.43 heat units, and to raise 300 pounds 1° would require 300 times this amount or 5529 B.t.u., the heat required to heat the radiator. Example. — A church 80 by 100 feet inside has stone walls 2J^ feet thick for 10 feet above the ground and for the remaining 20 feet 2 feet thick. The roof has a H pitch and is made of 2 by 8-inch rafters, 16 inches on centers, covered with 1 inch of pine boarding, tar paper and slate y± inch thick. Main floor composed of two 1-inch thicknesses of boards laid on 2 by 12- inch joists, 16-inch centers. Ceiling is of plaster % inch thick. The church has 20 windows, 6 feet wide and 15 feet high, 12 windows 4 feet wide and 6 feet high, and 2 doors, 8 feet wide and 12 feet high. Allowing an addition of 15 per cent, for furnishings, find the heat required to raise the tempera- ture of the structure from 0° to 50° Weight of stonework, stone weighing 160 pounds per cubic foot: 370 X 10 X V/2 = 9,250 cubic feet 368 X 20 X 2 = 14,720 cubic feet 84 + 2X40X2X2 = 6,720 cubic feet Deduction for windows and doors : 20 X 6 X 15 X 2 = 3,600 12 X 4 X 6 X 2 = 576 2 X 8 X 12 X 2Y 2 = 480 30,690 cubic feet 4,656 4,656 26,034 X 160 = 4,165,440 pounds. Weight of woodwork, weight per cubic foot taken as 40 pounds : ^rrr X 56 - 2 X 75 X 2 X 40 = 37,600 pounds of rafters. 56.2 X 104 X 2' X H2 X 40 = 39,000 pounds of roof boards. 80 X 100 X K2 X 40' = 53,500 pounds of floor boards. 2 J*- 12 x 80 X 75 X 40 = 40,000 pounds of roof joists. Total weight of woodwork = 170,100 pounds. Slate, weight per cubic foot taken as 170 pounds: 56.5 X 104 X 2 X Ms X 170 = 41,600 pounds. Plaster, weight per cubic foot taken as 90 pounds : (seoxso+soxio+iooxse^x^Mx^xoo = 142,460 pounds. Air, weight per cubic foot taken as 0.08 pounds: (80 X 30 X 100 + 80 X 4p X 100 )0.08 = 32,000 pounds. - - : v " ' ' Z Heat required : HEATING AND VENTILATION 4,165,440 X 50 X 0.2100 = 43,737,000 B.t.u. 170,100 X 50 X 0.5700 = 4,850,000 B.t.u. 41,600 X 50 X 0.2159 = 448,000 B.t.u. 142,400 X 50 X 0.2000 = 1,424,000 B.t.u. 32,000 X 50 X 0.2415 = 386,000 B.t.u. 50,845,000 B.t.u. Adding 15 per cent, for furnishings 7,627,000 B.t.u. Total to raise to 50° 58,572,000 B.t.u. The heating of the building structure may be very important in determining the size of the heating plant when a building is intermittently heated. 7. First Law of Thermodynamics. — When mechanical energy is produced from heat a definite quantity of heat is used up for every unit of work done and, conversely, when heat is pro- duced by the expenditure of mechanical energy the same definite quantity of heat is produced for every unit of work spent. This first law of thermodynamics might also be called the law of the Conservation of Energy. The relation between work and heat has recently been determined with great accuracy and the results show that one British thermal unit is equivalent to 778 foot-pounds. This factor is called the mechanical equivalent of heat or Joule's equivalent. Problems 1. Convert 50°F. to degrees Centigrade. Convert 150°C. to degrees Fahrenheit. Convert 219°F. to degrees Centigrade. Convert 225°F. to absolute temperature on the Fahrenheit scale. 2. A copper ball weighing 10 pounds is heated in a fire and immediately placed in a vessel of water having an equivalent water weight of 10 pounds. The water was raised in temperature from 50° to 100°. What was the temperature of the ball when it was removed from the fire ? CHAPTER II HEAT LOSSES FROM BUILDINGS 8. Sources of Heat Loss. — When the interior of any building is maintained at a temperature higher than that of the outside air there is a continual loss of heat from the building. The functions of a heating system are, first, to raise the temperature of the interior of the building to the point desired and, second, to maintain this temperature by supplying sufficient heat to replace that lost from the building. The determination of the amount of heat lost from the building under maximum condi- tions is the first step in designing the heating system. Before taking up the methods of calculating heat loss it is necessary to consider first the manner in which heat may be given up by any body. There are three ways in which heat can be transmitted from a body: by radiation, by conduction, and by convection. Each of these will be discussed separately. 9. Radiation. — Heat is transmitted, or radiated, through space by what is supposed to be a motion or vibration of the ether which is believed to pervade all space. Radiant heat follows the same physical laws as radiant light, being radiated, like light, in straight lines. We may have heat "shadows" just as we have light shadows and the intensity of radiant heat is inversely proportional to the square of the distance from the source. Some substances are transparent to heat rays and others absorb them. Gases are almost perfectly transparent to radiant heat while such substances as wood, hair felt, and mineral wool are almost perfectly opaque to it. Radiant heat does not affect the medium through which it passes. When heat is radiated through the atmosphere, for example, the atmosphere is not perceptibly warmed by it. The rate at which heat is radiated increases as the absolute tem- perature of its source is raised. It has been determined experi- mentally that the amount of heat radiated from a body varies as the 4th power of the absolute temperature, or Qr = KT* 10 HEATING AND VENTILATION in which Q r is the quantity of heat radiated, T the absolute tem- perature of the body, and K a constant depending upon the nature of the substance composing it. Radiant heat is given off by all bodies, the net amount of heat radiated by a body being the difference between the total amount radiated from it and the amount radiated from other bodies which is absorbed by it. If one body of absolute temperature 7\ is surrounded by another body of the same material at temperature T 2 , then the heat which will pass between them is Q r = X7Y - KT t * = K{TS - T 2 4 ) This is known as Stefan's law. 10. Conduction. — As has already been stated, heat will pass from any body to a body at a lower temperature which is brought into contact with it. It is further true that if one part of a body is at a higher temperature than another part there will be a flow of heat through the body. The transmission of heat in this manner is known as conduc- tion. A familiar example of this phenomenon is the flow of heat along an iron bar, one end of which is heated in a fire. The ability of different materials to conduct heat differs considerably. Metals are the best conductors of heat, while such materials as wood, felt, asbestos, etc., are very poor conductors. The conduction of heat which takes place through the walls of a building may be best understood from Fig. 2 in which PP is a plate, one side of which is enclosed by the walls WW. Let the temperature of the outside of the plate be 59° and let 60° be the temperature of the inside of the plate, of the inside walls WW, and of the inside air. Then all the heat that is lost by the room must be lost by conduction through the plate PP. The amount of heat lost will be dependent upon the material of the plate PP, upon the difference in temperature of its two sides, and upon its thickness. Fig. 2. HEAT LOSSES FROM BUILDINGS 11 Let E = the "specific conductivity" of the material. t\ = the temperature of the warmer side of the plate. U = the temperature of the cooler side of the plate. A = the area of surface in square feet. I = the thickness of plate in inches. Q = the total quantity of heat transmitted. Then = AE{h - U) I A E the conductivity of the heat path is then —j- and the resistance of the heat path is its reciprocal -ps" A.E Exam-pie. — Suppose a boiler plate, 5 feet square, and 3^ inch thick, to have a temperature of 70° on one side and 200° on the other side. Assume the specific conductivity of the metal to be 240 B.t.u. per hour per square foot of area per inch in thickness per degree difference in temperature. The total heat transmitted per hour is then Q = 25X240 g °- 70) - 1,560,000 B.t.u. per hour. 11. Convection. — When a body is in contact with a fluid at a lower temperature, the envelope of fluid surrounding it becomes heated by conduction of heat from the body. As this fluid envelope is heated its density decreases and it is forced to rise, giving place to the colder fluid from below. A continuous current is thus created and maintained over the surface of the body. This process of heat transfer is called convection. It should be noted that the heat actually leaves the hot body by con- duction from its surface to the fluid in contact with it. The essential characteristic of the process of convection is the continu- ous renewal of the fluid layer at the surface of contact. The loss of heat from a body by convection is independent of the nature of the surface of the body, and of the material com- posing it, but is greatly affected by the form of the body, a cylinder and a sphere, for example, transmitting different amounts . of heat per square foot of surface. The velocity of the fluid over the surface also affects the rate of heat transmission. In the case of convection by air the air movement is often produced by some external force, as when the wind blows against a building or when a fan in an indirect heating system forces air over the surface of steam coils. An increase in the velocity produces a 12 HEATING AND VENTILATION more frequent renewal of the layer of air in contact with the body and augments the rate of heat transmission. Heat may also be transmitted from a fluid to a solid by con- vection as well as from a solid to a fluid. An example of this process is the transfer of heat from the warm air of a room to the cold outside walls. The air, upon giving up its heat, increases in density and falls, giving place to warmer air from above and producing a continuous downward current. 12. Loss of Heat from Buildings. — The heat which is lost from a building may be divided into two parts : (a) the heat which passes by conduction through the building structure; and (b) the heat which is lost due to air infiltration. A third factor, the heat lost in warming air introduced for ventilation, might also be here mentioned. The heat which flows by conduction through the walls and roof of the building is transmitted from the outer surface of the structure partly by radiation and partly by convection. The calculation of the heat lost by convection is very difficult. Methods of arriving at the loss by convection from bodies of various shapes were developed by Peclet and are given in Box's " Treatise on Heat," but these methods cannot, as a rule, be applied to the loss of heat from buildings. They assume, for example, that the air surrounding the object is, except for the influence of the heat from the body itself, in a perfectly quiescent state. In the case of buildings this is far from true, for the air surround- ing a building is- always circulated more or less rapidly by the winds. Because of the necessity of taking into account variable factors of this nature, the heat loss from a building could not be stated in any simple expression and the practical rules that are used for such calculations are therefore largely empirical. The common method of treating the conduction of heat through building walls as given in the following pages was translated by J. H. Kinealy from the work of Rietschel and published in the Metal Worker. In the simplest form of building the walls consist of one solid piece of a single material and the transmission of heat takes place from the air of the room by convection, through the wall by con- duction, and from the outer surface of the wall by convection and by radiation. Such a wall is shown in Fig. 3. In order that heat may flow through the wall it is necessary that the room tempera- ture ti be higher than the temperature of the inside of the wall £/, HEAT LOSSES FROM BUILDINGS 13 that the temperature of the outside of the wall to' be lower than ti; and that the temperature of the outside air t be lower than to. The amount of heat which will be transferred from the air of the room to a unit area of the wall will be ai (h — h') in which a x is a constant. The amount of heat flowing through a unit area of the wall will be — (ti — to) in which e x is a constant which represents the specific conductivity of the material composing the wall. Similarly the heat transfer from a unit area of the outside wall surface is a (to — to). When the rate of heat flow through the wall has reached a stable condition the quantity of heat flowing through successive ti to Fig. 3. fy h ix Y % x s* to «-*,-> Fig. 4. Fig. 5. points of the wall thickness must be the same and we have, therefore, ai(*i - ti) = ^(ti - W) = a (to' - to) A wall may be made up of a series of layers of different ma- terials, as shown in Fig. 4. The transmission of heat takes place in the same way except that the conductivity of the successive layers may be different. In a wall such as shown in Pig. 5 the heat passes through the inside wall to the air in the air space and thence through the outside wall to the outside -air, the temperature at each successive point from the inside to the out- side being lower, as before. If a u a 2 , a 3 and a are the constants representing the conductivity of heat between the air and the wall surfaces (Fig. 5) and e\ and e 2 are the specific conductivities of the materials composing the two walls, then the heat trans- mitted through the walls may be expressed in any of the following equal forms: ai(ti - ti) = - (ti - ti) = a 2 (ti - h) = a 3 (t 2 - ti') {ti — to) = flo(^o — ^o) 14 HEATING AND VENTILATION In order to use these expressions it would be necessary to know the temperature of all the wall surfaces. These temperatures are not known. The only known temperatures are the tempera- tures of the air inside the room and of the air outside of the build- ing. Therefore, let us assume that the heat transmission through the wall may be represented by the expression k(fa — fa), in which A; is a constant to be determined. We then have for Fig- 3:^ C,£* C v £ % Cite k(fa - fa) = oi(*i - fa') = - (fa' - to) = a a (fa' - fa) And for Fig. 5: k(fa - to) = a,(fa - fa') = - (fa' - V) = a,(h' - U) Xi = a>s(ti — h") = — (fa" — to) = ao(to' — fa) . Xi Solving for k we have, for Fig. 3: ax e% a a And for Fig. 5: k = 1 d\ ei a% a 3 e 2 Q,o x For thin glass or thin metal walls - is a very small quantity and may be neglected. The values of a and e must be known before k can be determined. The value of the convection factor, a, is determined by Grashof by the following equation: j_ a _i_ (40c + 30d) T a - c + a+ 10000 in which c is a factor depending on the condition of the air, whether at rest or in motion. Rietschel gives the following values for c: Table III. — Values of c c Air at rest, air in rooms . 82 Air with slow motion, air in rooms in contact with windows 1 . 03 Air with quick motion, air outside of a building 1 . 23 HEAT LOSSES FROM BUILDINGS 15 The factor d depends upon the material composing the wall and on the con- dition of the surface. The values for d may be taken as follows: Table III. — Values op d Substance d Substance d Brickwork 0.740 Sheet iron 0.570 Mortar and similar materials . 740 Sheet iron polished . 092 Wood 0.740 Brass polished 0.053 Glass 0.600 Copper 0.033 Cast iron 0.650 Tin 0.045 Paper 0.780 Zinc 0.049 T is the difference between the temperature of the air and that of the surface of the wall. For walls composed of materials of low conductivity or very thick walls it may be taken as zero. In approximate calculations it is usually taken as zero. The following values of T are given by Rietschel: Table IV. — Values op T Brickwork 5 inches thick 14 . 4 Brickwork 10 inches thick 12.6 Brickwork 15 inches thick 10 . 8 Brickwork 20 inches thick 9.0 Brickwork 25 inches thick 7.2 Brickwork 30 inches thick 5.4 Brickwork 40 inches thick ' 1.8 For single windows 36.0 For double windows 18 . For wooden doors 1.8 Table V gives values of e. These values, as given by different authorities, vary considerably. Table V. — Values op e e Brickwork 5 . 60 Mortar, plaster 5. 60 Rubble masonry 14.00 Limestone 15 . 00 Marble, fine-grained 28 . 00 Marble, coarse-grained 22.00 Oak across the grain 1.71 Pine, with the grain 1 . 40 Pine, across the grain . 76 Sandstone 10.00 Glass 6.60 Paper 0.27 16 HEATING AND VENTILATION For example, assume a brick wall as shown in Fig. 6. There are four air contact surfaces and two walls through which conduction takes place, then: k is the same as in equation (2). Bietschel assumes a u a 2 , and a 3 equal and he uses the same value of T as for a solid of thickness equal to the brickwork with- out the air space. nM , . _. , (40 X 0.82 + 30X0.74)10 d! = a 2 = a 3 = 0.82 + 0.74 + ^ 10000 = a = j.23 + 0.74 + (40X1 - 23 10 + 3 o X074)1 ° = 2M t'l ~i 3 i- W/// Fig. 6. Since both walls are of brickwork Zi 4.75 ei 5.6 x 2 e 2 8.25 5.6 ■8>^- H — Xoi — : 0.85 1.47 Substituting in equation (2) k = = 0.214 0.62 + 0.85 + 0.62 + 0.62 + 1.47 + 0.49 Making this same calculation, assuming T = 0, gives k = 0.210 In Table VI are given the values of k for various building materials which have been determined either experimentally or by methods similar to the foregoing, by different author- ities. A more complete table of values of k is given in the Appendix. HEAT LOSSES FROM BUILDINGS 17 Table VI. — Coefficients of Heat Transmission for Various Materials k B.t.u. per square foot, per hour per degree Wnlln- difference in n °" s - temperature Brick wall 4 inches thick, plain . 52' Brick wall 8% inches thick, plain . 37 Brick wall 4 inches thick, furred and plastered . 28 Brick wall 8K inches thick, furred and plastered . 23 Concrete wall 4 inches thick, furred and plastered 0.31 Concrete wall 6 inches thick, furred and plastered . 30 Clapboard wall with paper, sheathing, studding, and lath and plaster . 23 Ceilings and Roofs: Lath and plaster, no floor above . 32 Lath and plaster, single floor above . 26 Tin or copper roof on 1-inch boards . 45 Shingle roof 0.33 Windows, Skylights and Doors: Ordinary windows 1 . 09 Double windows 0.45 Single skylight 1.50 Pine door % inch thick . 47 Oak door % inch thick 0.63 13. Temperatures Assumed in Heating. — In determining the heat transmission through the walls of a building, it is necessary to assume certain temperatures for the outside air and for the inside air. In the latitude of New York City it is customary to assume 0° for the outside temperature. In the latitude of Washington it is customary to assume 20° above, and in the latitude of St. Paul 20° below. The assumed outside tempera- ture is ordinarily taken as the temperature which might exist for a period of at least 24 hours. The inside temperature to be assumed depends upon the type of building. The tempera- ture maintained in many classes of buildings is largely a matter of custom. In residences this temperature is higher in the United States than in any other country in the world, with the possible exception of Germany. In England and many other countries a temperature of from 55° to 60° is a perfectly proper temperature for a room; while in this country the temperature ordinarily ranges from 65° to 70°. The following are the inside temperatures usually assumed : 18 HEATING AND VENTILATION Table VII. — Inside Temperatures Degrees Residences 70 Lecture rooms and auditoriums 65 Factories for light work 65 Factories for heavy work 60 Offices and schools 68 to 70 Stores 65 Prisons 65 Bathrooms 72 Gymnasiums 55 to 60 Hot houses 78 Steam baths 110 Warm air baths 120 The following assumptions are ordinarily made for unheated spaces : Table VIII Degrees Cellars and closed rooms 32 Vestibules frequently opened to the outside 32 Attics under a roof with sheathing paper and metal or slate covering 25 Attics under a roof with paper sheathing and tile covering 32 Attics under a roof with composition covering 40 14. Heat Lost Due to Infiltration. — No building is ever air- tight; there is a large amount of leakage through the walls, the windows, and other openings. The amount of this infiltration depends largely upon how well the building has been constructed and upon the type of construction. For this reason no definite rule can be given for the determination of infiltration, and the allowance made for this loss must be a matter of judgment and experience. Usually the volume of infiltration is expressed as a certain ratio of the cubic contents, and experiments go to show that the air of the average room is changed about once an hour because of infiltration. In rooms where doors are frequently opened to the outside, or where the windows are loosely fitted and the construction is faulty, the change of air may be as fre- quent as twice an hour. Strictly speaking, however, the amount of infiltration does not depend upon the volume of the room but upon the nature and size of the windows. Experiments 1 have shown that the amount 1 See "Window Leakage" by S. F. Voorhees and H. C. Meyer, Trans. A. S. H. & V. E., 1916. HEAT LOSSES FROM BUILDINGS 19 of air leakage varies considerably for different types of windows. Some forms of metal sash allow a large amount of leakage to take place. Weather strips are very effective in reducing air leakage. As the principal source of leakage is around the window sash the amount of leakage may be considered as varying directly with the perimeter of the windows. It is customary to assume a leakage of from 1.0 to 1.5 cubic feet of air per minute per foot of sash perimeter for windows equipped with weather strips. For windows without weather strips a considerably higher factor should be used. In large buildings the amount of infiltration should be computed in this manner, especially in the case of a tall or exposed building. The heat required to supply these infiltration losses must be sufficient to warm the air from the temperature of the outside air to that of the room. If the infiltration is figured on the basis of a certain number of air changes per hour the loss from this source may be expressed as follows : Let H a = heat required per hour to supply loss due to infiltration. C = cubic contents of the room. n = number of changes per hour. t T = temperature of the room. t = temperature of the outside air. „ C(t r - h)n 55.2 The factor 55.2 = (10415 X 0749 = heat re( ^ uired to raise the temperature of 1 cubic foot of air 1° where 0.2415 is the specific heat of air at constant pressure and 0.0749 is the weight of a cubic foot of air at 70°. 15. Heat Required for Ventilation. — The heat required for ventilation can easily be computed when the amount of air supplied per hour is known. Let H = heat required for ventilation. Q = quantity of air supplied in cubic feet per minute. Then, 60 X Q(U - k) H 55.2 Besides supplying heat to replace that lost through the walls and by infiltration of air, a heating system must supply the heat 20 HEATING AND VENTILATION which is stored in the structure and its contents and in the inside air. In heavy buildings the effect of the heat stored in the walls may have a material effect upon the amount of heat which must be supplied to warm the building initially. If the building is intermittently heated the effect is decidedly appreciable. The best illustration is in the cathedrals of Europe in which no heating systems are used and the heat stored in the walls during the summer serves to keep the building warm throughout the year. The heat which is required initially to warm the inside air and the building structure affects the rapidity with which the build- ing can be heated to the desired temperature. It is often desirable to investigate this question in designing a heating system which is to be operated intermittently and to increase the radiation, if necessary, so that the building can be warmed within a reasonable time. 16. Calculation of Heat Loss from a Building. — In determining the heat loss from a room all surfaces should be considered which have on the outside a lower temperature than the temperature to be maintained in the room. If the room is over a portion of the basement which is unheated or below an unheated attic, the loss through the floor or ceiling should be considered. Similarly, if an adjacent room is liable to be unheated at times, the additional heat loss through the wall should be taken into account. Ordinarily it is assumed that there is no loss through inside walls where the surrounding rooms are heated. The conditions under which the room is to be used should be studied in determining the amount of heat necessary. In certain rooms such as restaurants in the basements of buildings, for example, where there are no outside windows, the problem is often one of cooling rather than heating. In designing any heating system, careful consideration should be given to the conditions existing, and to the exposure of each room in the building. The first step in computing the heat loss is to determine for every room the gross surface of exposed wall, and the window surface, from which the net wall surface is obtained by subtraction. The heat loss through the walls can then be computed from the expression, H w = Wk(t r -t a ) in which HEAT LOSSES FROM BUILDINGS 21 H w = heat loss in B.t.u. per hour. W = exposed wall surface in square feet. U = inside temperature. to = outside temperature. k = coefficient of heat transmission. A similar expression must be worked out for the walls, ceilings and floors next to unheated spaces. The value of t r in such cases may be taken from Table VII. The heat loss through the glass surface is computed from the expression, E g = Gk(t r - t ) in which G is the area of the glass surface in square feet and k is the heat transmission for glass. The heat lost due to air infiltration is next determined by one of the methods given on pages 18 and 19. The total heat loss from the room in B.t.u. per hour is then H = H w + H g -f- H a 17. Correction Factors. — The heat losses determined by this method are for rooms not exposed to prevailing winter winds. For exposed rooms it is customary to add certain percentages to the heat losses to allow for extreme exposures. Also, when a building is intermittently heated, an allowance should be made to insure that the building can be heated within a reasonable time. The correction factors commonly used are given in Table VIII. Table VIII. — Factors foe Exposure and Intermittent Heating Percentage to be added For exposure in direction of prevailing winter winds (usually north and northwest) 15 Same, severe conditions 20 For west exposure 10 For building heated during the day only and closed at night 15 For buildings heated during the day and open at night 30 For buildings heated intermittently 50 18. Approximate Rules for Determining the Loss of Heat.— A common rule for the loss of heat from a building is that given by Prof. R. C. Carpenter in his book on "Heating and Ventilation." This rule is developed from the following consideration: Refer- ring to Table VI we notice that 1 square foot of glass conducts 22 HEATING AND VENTILATION approximately four times as much heat as a plastered brick wall 4 inches thick. If, then, we divide the wall surface by 4, the result will give us the number of square feet of glass surface, which would lose the same quantity of heat. Adding to this the actual glass surface would give us the total equivalent glass surface. As the heat loss per square foot of glass surface per degree difference in temperature is approximately 1 B.t.u. per hour, this total equivalent glass surface multiplied by the temperature difference gives the heat lost through the walls. In considering the infiltration losses it is assumed that for ordinary-sized rooms the air in the room will be changed once an hour. One cubic foot of air weighs, approximately, K3 pound. To raise a pound of air 1° would require about 0.0183 B.t.u. or one heat unit will heat in round numbers about 55 cubic feet of air 1°. If, then, we divide the contents of a room by 55 we will have the heat lost by filtration through the walls per degree difference in temperature. Adding these factors together will give the total heat lost from the room. This rule may be concisely expressed as follows : Let H = B.t.u. loss per hour. G = glass surface in square feet. W = net exposed wall surface in square feet. C = cubic contents of room. n = number of times the air in the room is changed per hour. H=(^ + ^ + G)(U-t ) The quantity n ordinarily varies from 1 to 3; for ordinary rooms n = 1; for corridors 1J^; for vestibules 2 to 3. This rule will indicate an excessive heat loss where a room has large cubic contents and small window surface and will show heat losses that are too small where the room has a very large amount of exposed surface in proportion to its cubic contents. As the infiltration loss in a room depends upon the outside wall and window surface, the following rule seems somewhat more rational. Using the same notation as before, H = (^ + (?) (U - t )n where n is the infiltration factor. The factor n has been determined by comparison with many successful plants that have been installed and it has been found to vary from 1}4 to 2)4- For ordinary rooms n = 1^; for HEAT LOSSES FROM BUILDINGS 23 corridors n = 2; for vestibules and rooms where doors are opened frequently n = 2 to 2}$. 19. Heat Given Out by Persons and Processes. — In consider- ing the amount of heat necessary to heat a room attention must be given to the amount of heat that will be given off by the occupants of the room or by the processes which go on in it. But these sources of heat cannot always be depended upon, as it may sometimes be necessary to heat a room when there are no people in it or when the processes ordinarily going on are not in operation. On the other hand, it may be necessary to cool the room instead of heat it. Often in large auditoriums the greatest source of heat in a room are the people in it. The following table shows the heat given off by the human body under various conditions in a room at a temperature of 70°. Table IX Adults at rest .. Adults at work Adults at violent exercise . Children Infants B.t.u. per hour 380 450 600' 240 63 Example 1. — Assume a room, as shown in Fig. 7. Let the temperature be maintained in the room at 70°, the temperature of the outside air be 0°. Let the walls be of brick, 18 inches thick, plastered on the inside, the win- dows be 2% by 6 feet, the ceiling of the room be 10 feet high. Let the room be on the second floor of the building, the rooms above and below heated. The window surfaces are 2 X 1}/% X 6 = 30 square feet. The gross wall surface is 20 X 10 = 200 square feet. The net wall surface is 200 — 30 = 170 square feet. The cubic contents is 20 X 14 X 10 = 2800 square feet. Then the heat lost from the room would be determined as follows. By the B.t.u. method: %^^>%%m^%%-^%^^ ._ H'o'i- 70 L i v///////////;//////;/////////////J //////%. 70" 70° Fig. 7. H w = 170 X 0.24 (70 E g = 30 X 1.09 (70 2800 (70 - 0) H a — 55.2. H = - 0) = 2856 - 0) = 2289 X 1.0 = 3551 8696 B.t.u. per hour. 24 HEATING AND VENTILATION By Carpenter's rule : / 2800 XI , 170 , on \ „. n . H = ^ gg + -j- + 30] (70 - 0) = (50.9 + 42.5 + 30) X 70 = 8638 B.t.u. per hour. By Allen's rule : H = (~ + 3(A (70 - 0) 1.5 = (42.5 + 30) X 70 X 1.5 = 7613 B.t.u. per hour. Problems 1. Compute the value of k for a wall consisting of 2 inch pine boards. Assume T = 3. 2. Compute the heat loss per hour, per square foot of area, of a wall consisting of two thicknesses of 1 inch pine boards with an air space of 2 inches between. Room temperature 60°, outside temperature 10°- Assume T = 1.8. 3. Compute the heat loss per hour, per square foot of area, of a wall consisting of 1 inch oak boards, an air space of 1 inch, and 4 inches of brickwork. 4. In the room of Fig. 7 (Example 1) find the percentage of the heat loss which would be saved during a heating season of 8 months if double windows were used. Assume average temperature of the room and the surrounding rooms to be 65° and the average outside temperature to be 40°. 6. Taking the same room as in Example 1, heated to a temperature of 60°, with the surrounding rooms at 70° and the air outside at 10°, how much heat must be supplied to the room per hour? Inside walls are of lath and plaster. Ceiling is of lath and plaster, with single floor above, and the room below has its ceiling plastered. 6. Take the same room as Example 1, except that the room is covered by a fiat tin roof. The air space between the ceiling of the room and roof should be assumed to be at a temperature of 32°. CHAPTER III DIFFERENT METHODS OF HEATING 20. Classification of Heating Systems. — The different types of heating systems may be classed under two general heads: direct and indirect. In direct heating the heating surfaces are placed in the rooms to be heated. Under this head come grates, stoves, steam radiators, and hot-water radiators. In indirect heating systems the heating surfaces are placed outside the rooms to be heated and air 'passes over them, is heated, and flows to the various rooms through pipes or flues. Hot-air furnaces would be included under this head, together with various systems of heating in which fresh cold air is made to pass over steam or hot-water radiators on its way to the rooms. Indirect systems may be subdivided into two classes: those in which the air circulates by gravity and those in which the cir- culation is produced by a fan or some other mechanical device. A good example of the gravity or "natural" systems is the hot-air furnace in which the circulation of air through the furnace and air ducts is produced by the difference in temperature, and con- sequently in density, between the air in the hot-air ducts and the cold air outside. The fan systems of heating used in schools and churches are examples of the forced-circulation type in which the circulation is produced by a disc fan or a pressure blower. Before studying the design of the various systems of heating it is desirable to understand in general their advantages and disadvantages. 21. Grates. — The most primitive form of heating apparatus is the grate. In the grate the air which passes through the fire, and is heated by the fire, all passes up the chimney and only the heat given off by radiation to the walls and objects in the room and the small amount given off by the chimney walls is effective in heating the room. In grates of better construction this condition is somewhat improved by surrounding the grate with firebrick so arranged that it becomes highly heated and radiates heat to the room. But the fact that all the air heated by the grate passes up 25 26 HEATING AND VENTILATION the chimney makes the grate a very uneconomical form of heat- ing. In the best forms of open grates only about 20 per cent, of the heat of the fuel is effective in heating the room. This form of heating, however, is highly recommended by many and is a very popular method of heating throughout England and Scotland. The feeling of a grate-heated room is quite different from that of a room heated by other means. All of the heat is given off by radiation and the air is at a considerably lower temperature than the objects in the room, owing to the fact that the radiated heat does not heat the air through which it passes. The air of the room being at a much lower temperature, its capacity for moisture is not increased as much as it would be were the air heated to a higher temperature. The result is that the air contains proportionately more moisture than is the case with most other forms of heating, which, no doubt, is an advantage. On the other hand, it is impossible to heat the room uniformly and a person is either hot or cold, depending on his distance from the fire. Heating by means of grates is practised only in the more moderate climates. Grates are useful in houses heated by other means, as the open chimney forms a most effi- cient foul-air flue and greatly improves the ventilation. 22. Stoves. — The stove is a marked improvement over the grate, particularly from the standpoint of economy. The modern base- burner stove is one of the most efficient forms of heating appara- tus, making use of from 70 to 80 per cent, of the heat in the fuel. In heating a room, the hot surface of the stove, being at a higher temperature than that of the surrounding objects in the room, radiates heat directly to those objects. In addition, heat is given to the air of the room by contact with the hot surface of the stove. In selecting a stove to heat a given room care should be taken to choose one of ample size so that only in the coldest weather would it be necessary to keep the drafts wide open in order to heat the room. At the present time the stove as a general source of heat is being rapidly discarded because of the attendance required, the space occupied, the unsightly appearance of the stove, and the fact that a separate stove is required in every room for satisfactory results. Another objection to the stove is the fact that it does not provide ventilation to the room which it heats. 23. Hot-air Furnaces. — The hot-air furnace is the natural outgrowth of the stove. In this system one large furnace is placed in the basement of the building, and the air is taken DIFFERENT METHODS OF HEATING 27 from the outside or recirculated from the house, passed over the surfaces of the furnace, and carried up through the flues to the rooms to be heated. The principle advantages of the hot-air furnace are that it provides a cheap method of furnishing both heat and ventilation, requires little attendance, and does not deteriorate rapidly when properly taken care of. The greatest disadvantage of this system is that the circulation of the heated air depends entirely upon natural draft; that is, it depends upon the difference in weight between the air inside the flues and the air outside the flues. This difference is extremely small, so that the force producing circulation in the flue is always small. When a very strong wind blows against one side of the house, air from the outside enters through the window cracks and other small openings, forming a slight pressure in the rooms and pre- venting the warm air from entering, thus making it difficult to heat the rooms on that side "of the house. If the system is carefully designed, however, this difficulty can be overcome in a measure. Another serious objection to the hot-air furnace is that it is seldom dust-tight, and dust, ashes, and gases from the fire are carried into the rooms. In general, the hot-air furnace may be considered as a very good type of heating plant for small residences, but because of the small force available for producing circulation its use is limited to buildings where the length of the horizontal flues does not exceed 15 feet. In the case of the hot-air furnace, the heat is carried from the furnace by the air which passes around the furnace and then enters the rooms through the flues. This air circulates in the room and heats the contents of the room and supplies the heat which is lost through the walls. The economy of the hot-air system will vary, depending on the relative proportions of the air taken from the outside and from the rooms. If the air enter- ing the furnace is taken from the house and not from the outside, the economy of the hot-air furnace will be about the same as that of the steam system. If, however, cold air be taken from the outside, an additional amount of heat will be used in heating this cold air up to the temperature of the rooms. Control of the heat supply, with a hot-air furnace, is readily obtained by adjusting the dampers at the registers in each room and by manipulating the furnace drafts. 24. Direct Steam Heating. — From the standpoint of ventila- tion, direct steam heating, without other means for ventilation, 28 HEATING AND VENTILATION is not as desirable as the hot-air furnace. Mechanically, how- ever, it has many advantages. The modern radiator is easily adapted to almost any location in the room and its operation is not affected by the winds. The circulation of the system is positive and a distant room can be heated as easily as those close to the boiler. In the older forms of direct steam-heating systems control of the heat supply is difficult because the radiators, being large enough to heat the room on the coldest days, give off too much heat for average conditions. Since the entire radia- ting surface is heated to a high temperature when the radiator is turned on, much manipulation of the valves is required in order to keep the room at a comfortable temperature. In recent years these disadvantages have been overcome in the so- called "vapor" systems which make use of steam at pressures but slightly higher than atmosphere, and in some cases below atmosphere. In these systems the steam supply to each radia- tor can be controlled at the inlet valve so that only the quantity actually required is admitted to the radiator, and much better regulation is therefore possible. The efficiency of the direct steam-heating system in a well-designed plant is from 60 to 70 per cent. 25. Direct Heating by Hot Water. — The application of direct hot-water radiators as a method of heating is similar to that of steam, with the exception that the surfaces are usually at a much lower temperature and more radiating surface is there- fore required. Hot-water systems are preferable to ordinary steam systems in that the temperature of the radiating surfaces can be easily controlled, and can be anywhere from the tem- perature of the room to 190°, or even higher in the case of certain forms of hot- water systems. Another advantage is that the surface of the radiator, being at a lower temperature, gives off more heat by convection and less by radiation, which tends to keep the room at a more uniform temperature throughout and makes it more comfortable to the occupants. The principal disadvantage of the hot-water system lies in the fact that the circulation of the system is ordinarily produced only by the difference in weight between the water in the hot leg of the system and that in the cold leg of the system. The difference in tem- perature between the two legs is small, being usually about 10° to 20°, so that the resulting force producing circulation is there- DIFFERENT METHODS OF HEATING 29 fore Small. It is necessary to be very careful in designing the piping for a hot-water system as the circulation may be easily affected by the friction in the piping and the height of the radia- tor above the boiler. The greater the height above the boiler the greater will be the difference in weight between the two col- umns of water and the stronger will be the force producing cir- culation. This system in general requires more careful design and construction than the steam system. Another disadvantage is that, because of the great thermal capacity of the water con- tained in the system, considerable time is necessary to change its temperature and the system cannot be made to respond quickly to sudden changes in the demand for heat. The effi- ciency of the hot-water system is practically the same as that of a steam system and we may expect to obtain in the rooms about 60 or 70 per cent, of the heat in the fuel. Where hot-water heating is used in large buildings the circula- tion is produced by a pump. The difficulty of circulation is then done away with and the flow of water is certain and rapid. 26. Indirect Steam and Hot-water Heating by Natural Circu- lation. — In heating with indirect steam or water radiation cold air is drawn from the outside, passed through and around the hot radiator, which is usually situated in the basement, and delivered through flues to the rooms to be heated. The rules governing the introduction of air into the rooms and the method of running the pipes are similar to those employed in the installation of the hot-air furnace. The principal advantages of indirect steam and water heating over the hot-air furnace are that each room has a separate source of heat, the system is not affected by the winds, and no dust or obnoxious gases are carried to the rooms. The source of heat being independent of the position of the boiler, it is possible to place the indirect radiators anywhere in the building and long air flues are not necessary. This makes the indirect radiator much more certain in operation than the hot-air furnace. The application of in- direct hot-water radiators is similar to that of steam radiators and the economy is practically the same, although the use of hot water for indirect heating has been much more limited than the use of steam. The installation of hot-water radiators must be done with great care so that each radiator will at all times have the proper amount of water circulating through it, for if for any reason the circulation is stopped the water in the radiator will be 30 HEATING AND VENTILATION in danger of freezing. In mild climates this difficulty would not be as serious as in locations where the weather is extremely cold. 27. Fan Systems of Heating. — In buildings of a public or semi-public character, where a large number of people are gathered in a relatively small space, it is necessary to provide adequate ventilation. With the systems that have been pre- viously described it is impossible to introduce sufficient quanti- ties of air to ventilate such buildings properly. It may be said in general that no system of natural circulation has ever produced satisfactory ventilation in a room occupied by a large number of people; it is necessary to provide some mechanical means for introducing the air. In fan systems the pressure produced by the fan makes the circulation positive so that it is not affected by winds or by the distance of the room from the source of heat. The air is taken from the outside, or sometimes recirculated from the inside, and is passed through the heating coils and forced into the building by the fan. There are three general methods of heating and ventilating with the fan system. In one system the air is first passed through a tempering coil and then taken by the fan and delivered through a heating coil. Each room has a connection both to the hot air and to the tempered air chambers. The temperature of the air in the room is adjusted by taking the air partly from the hot-air chamber and partly from the tempered-air chamber. In the second system the rooms themselves are heated by means of direct radiation and the fan delivers air to the rooms only for the purpose of ventilation. In this case a much smaller amount of heating surface in the fan system is necessary as the air is heated to only about 70°. The economy of this system is also better, due to the fact that it is necessary to run the fan only when it is necessary to ventilate the building. In the third system both the heating and ventilating is done by means of the fan system but only one system of ducts is installed. The temperature of the air leaving the heating coils is adjusted so as to maintain the proper room temperature. This method is applicable only in factory buildings, theatres, and other build- ings which are divided into only a few rooms, making it possible to utilize air of the same temperature throughout the entire building. 28. Combinations of Different Systems. — In addition to the combination just described, of direct radiation and fan ventila- DIFFERENT METHODS OF HEATING 31 tion, there have been devised innumerable combinations — com- binations of direct and indirect steam systems, direct and in- direct hot water, water and hot air, and steam and hot air. The combinations which have been most used are those of direct and indirect steam systems and of hot water and hot air. 29. Economy of Heating Systems. — The economy of any heat- ing system depends upon the completeness with which the heat in the fuel is effectively utilized in heating the building. The principal sources of loss and the manner in which the heat is utilized in any type of heating system are as follows : Losses: Imperfect combustion. Sensible heat in the chimney gases. Combustible in the ash. Radiation from boiler or furnace. Radiation from flues or piping. Losses through excessive temperature in the building. Heat utilized: Heat utilized in supplying the heat losses from the building. Heat used for ventilation. Of the losses, the first three are dependent rather upon the design of the grates and firepot than upon the type of heat- ing system. The radiation from the boiler or furnace is partially recovered as it serves to warm the basement and de- creases the heat loss to the basement from the rooms above. The loss from this source is fairly constant, regardless of the amount of heat delivered by the boiler or furnace and if a very low fire is carried, as in mild weather, it may become quite appreciable in comparison with the heat delivered. The loss from the flues or piping is also partially utilized in warming the building. The heat used to supply the heat losses from the building is the principal product of any heating system. A part of this heat may be considered as a loss, however, if excessive temperatures are maintained either during the hours when the' building is occupied, or during the night or other times when a low tempera- ture could be carried. The amount of heat used for ventilation will depend upon the amount of fresh air supplied. The air introduced for ventilation is discharged from the building at room temperature, and the heat contained in this air in excess of the heat in the outside air 32 HEATING AND VENTILATION is evidently the amount chargeable to ventilation. While this item might, from the standpoint of heating only, be considered as a loss, it is really the price that must be paid for good ventila- tion which is essential to health and comfort. In many States there are laws which specify the minimum amount of air which must be furnished per hour for each occupant in theatres and other buildings of a public character. The necessity and impor- tance of ventilation will be discussed in later chapters. CHAPTER IV PROPERTIES OF STEAM 30. The Formation of Steam. — The different types of heating systems discussed in the previous chapter owe most of their characteristic features to the element used to transmit the heat from the boiler or furnace to the rooms. The most important is the steam system in which steam serves as the medium for carrying the heat from the boiler to the radiators. Before tak- ing up the design of steam-heating systems it is necessary to study the nature and properties of steam. Steam as produced in the ordinary boiler contains a certain amount of water in suspension as does the atmosphere in foggy weather. Let us suppose that we have a boiler partly filled with cold water, and that heat is applied to the outside of the boiler. As the water in the boiler is heated its temperature slowly rises until a certain temperature is reached at which small particles of water are changed into steam. The steam bubbles rise through the mass of water and escape from the surface. The water is then said to boil. The temperature at which the water boils depends entirely upon the pressure in the boiler. The steam produced from the boiling water is at the same temperature as the water, and under this condition the steam is said to be saturated. If we close the steam outlet the pressure in the boiler and the temperature of the water and steam will increase rapidly. If we continue to apply heat to the boiler with the outlet partly closed so that a constant pressure is maintained, the temperature of the steam and water will remain constant until all of the water is evaporated into steam. Any further addition of heat will raise the temperature of the steam above the boiling point and it will then be superheated. 31. Superheated Steam. — Superheated steam is steam at a temperature higher than the temperature of the boiling point corresponding to the pressure. If water were to be intimately mixed with superheated steam some of the heat in the steam would be used in evaporating the water and the temperature of 3 33 34 HEATING AND VENTILATION the steam would be lowered. If sufficient water were added the superheat would be entirely used up in evaporating the water and the steam would then be saturated. Superheated steam can have any temperature higher than that of the boiling point. When raised to any temperature considerably above the boiling point it follows very closely the laws of a perfect gas and may be treated as a perfect gas. 32. Saturated Steam. — When steam is at the temperature of the boiling point corresponding to its pressure it is said to be saturated. If this saturated steam contains no suspended. mois- ture it is said to be dry saturated steam, or in other words, dry saturated steam is steam at the temperature of the boiling point and containing no water in suspension. If heat is added to dry saturated steam, not in the presence of water, it will become super- heated. If heat is taken away from dry saturated steam it will become wet steam. The steam used in a heating plant is saturated steam and nearly always contains moisture, so that the substance used as a heating medium is really a mixture of steam and water. Steam at a pressure equal to or slightly above atmosphere is commonly known as vapor. It should be remembered, however, that the difference between vapor and steam is merely one of pressure, and that vapor is in no sense a separate state of the substance. Dry saturated steam is not a perfect gas and the relations of its pressure, volume, and temperature do not follow any simple law but have been determined by experiment. The properties of dry saturated steam were originally determined by Regnault between 60 and 70 years ago, and so carefully was his work done that no errors in his results were apparent until within very recent years, when the great difficulty of obtaining steam which is exactly dry and saturated became appreciated, and new experiments by various scientists proved that Regnault's results were slightly high at some pressures and slightly low at others. 83. Properties of Steam. — The heat used in the formation of 1 pound of superheated steam at any pressure from water at 32° may be divided into three parts : (a) the heat of the liquid, which is the heat required to raise the temperature of the water from 32° to the temperature of the boiling point; (b) the latent heat of vaporization, which is the amount required to change the 1 pound of water at the temperature of the boiling point to dry saturated steam at the same temperature; and (c) the "heat of superheat " or, more simply, the superheat, which is the heat added PROPERTIES OF STEAM 35 to 1 pound of steam to raise it from the boiling point temperature to the final temperature. 34. Heat of the Liquid. — The heat of the liquid may be deter- mined for any boiling point temperature by the expression h = c(t - 32) in which h = the heat of the liquid. t = the boiling point temperature. c = the specific heat of water. For approximate results c may be taken as = 1. The change in the volume of the water during the increase in temperature is extremely small, and the amount of external work done may be neglected and all of the. heat of the liquid may be considered as going to increase the heat energy of the water. The heat of the liquid, together with the other properties of saturated steam, is given in Table X for various steam pressures. This table is condensed from Marks and Davis' complete tables which are generally accepted as being accurate. 35. Latent Heat. — The latent heat of steam has been defined as the heat required to convert 1 pound of water at the temperature of the boiling point into dry saturated steam at the same tem- perature. Experiments show that the latent heat, usually designated by L, diminishes as the pressure increases. When water is changed into steam, the volume is greatly increased, so that a considerable portion of the latent heat is used in doing external work. The remainder may be considered as being utilized in changing the physical state of the water. Let P be the pressure at which the steam is generated, V the volume of 1 pound of steam, and v the volume of 1 pound of water; then the external work done is equal to P(V - v) At 212° the external work done in producing 1 pound of steam is equivalent to 73 B.t.u. or about one-thirteenth of the latent heat. Experiments show that the latent heat of steam diminishes about 0.695 heat units for each degree that the temperature of the boiling point is increased. If t be the temperature of the boiling point, then, approximately, L = 1072.6 - 0.695(Z - 32) 36 HEATING AND VENTILATION When steam condenses the same amount of heat is given up as was required to produce it. 36. Total Heat of. Steam. — The total heat of dry saturated, steam is the heat required to change 1 pound of water at 32° into dry saturated steam. This quantity will be designated by H, and H = h + L The experimental results given in the table for the value of the total heat may be approximated very closely by means of the formula H = 1072.6 + 0.305(« - 32) It is more accurate, however, to take the values of the total heat from the tables than it is to compute them from the formula. The total heat in 1 pound of steam under any condition of mois- ture or superheat is the amount of heat required to change it from water at 32° to its existing condition. When steam contains entrained water the percentage by weight of dry steam in the mixture is termed the quality of the steam. If we let q represent the quality of the steam, then the latent heat in 1 pound of wet steam equals 100 and the total heat in 1 pound of wet steam equals ft + ioo 37. Steam Tables. — The following table shows the properties • of dry saturated steam. More complete tables will be found in Marks and Davis' "Steam Tables" and in the engineering handbooks. Column 1 gives the absolute pressure of the steam •in pounds per square inch. Absolute pressure is the pressure shown on the steam gage plus the atmosphere or barometric pressure. For sea-level barometer the atmospheric pressure is 14.7 pounds per square inch. Column 2 gives the corresponding temperature of the steam in degrees Fahrenheit. Column 3 gives the heat of the liquid, and column 4 gives the latent heat. Column 5 gives the total heat of the steam and is the sum of the quantities in columns 3 and 4. Column 6 is the volume of 1 pound of dry saturated steam at the different pressures. Column 7 is the weight of 1 cubic foot of steam at the different pressures. PROPERTIES OF STEAM 37 Table X. — Properties op Saturated Steam 1 1 2 3 4 5 6 7 Absolute Temp., deg. F. Heat Latent Total Sp. vol., Density, pressure, of the heat of heat of cu. ft. lb. per lb. per liquid evap. the steam per lb. cu. ft. sq. in. V t h L H D 1/v 10 193.22 161.1 982.0 1,143.1 38.38 0.02606 11 197.75 165.7 979.2 1,144.9 35.10 0.02849 12 201.96 169.9 976.6 1,146.5 32.36 0.03090 13 205.87 173.8 974.2 1,148.0 30.03 0.03330 14 209.55 177.5 971.9 1,149.4 28.02 0.03569 15 213.00 181.0 969.7 1,150.7 26.27 0.03806 16 216.30 184.4 967.6 1,152-. 24.79 0.04042 17 219.40 187.5 965.6 1,153.1 23.38 0.04279 18 222.40 190.5 963.7 1,154.2 22.16 0.04512 19 225.20 193.4 961.8 1,155.2 21.07 0.04746 20 228.00 196.1 960.0 1,156.2 20.08 0.04980 21 230.60 198.8 958.3 1,157.1 19.18 0.05213 22 233.10 201.3 956.7 1,158.0 18.37 0.05445 23 235.50 203.8 955.1 1,158.8 17.62 0.05676 24 237.80 206.1 953.5 1,159.6 16.93 0.05907 25 240.10 208.4 952.0 1,160.4 16.30 0.0614 30 250.30 218.8 945.1 1,163.9 13.74 0.0728 35 259.30 227.9 938.9 1,166.8 11.89 0.0841 40 267.30 236.1 933.3 1,169.4 10.49 0.0953 45 274 . 50 243.4 928.2 1,171.6 9.39 0.1065 50 281.00 250.1 923.5 1,173.6- 8.51 0.1175 55 287.10 256.3 919.0 1,175.4 7.78 0.1285 60 292.70 262.1 914.9 1,177.0 7.17 0.1394 65 298.00 267.5' 911.0 1,178.5 6.65 0.1503 70 302.90 272.6 907.2 1,179.8 6.20 0.1612 75 307.90 277.4 903.7 1,181.1 5.81 0.1721 80 312.00 282.0 900.3 1,182.3 5.47 0.1829 85 316.30 286.3 897.1 1,183.4 5.16 0.1937 90 320.30 290.5 893.9 1,189.4 4.89 0.2044 95* 324.10 294.5 890.9 1,185.4 4.65 0.2151 100 327.80 298.3 888.0 1,186.3 4.429 0.2258 105 331.40 302.0 885.2 1,187.2 4.230 0.2365 110 334.80 305.5 882.5 1,188.0 4.047 0.2472 115 338.10 309.0 879.8 1,188.8 3.880 0.2577 120 341.30 312.3 877.2 1,189.6 3.726 0.2683 125 344.40 315.5 874.7 1,190.3 3.583 0.2791 130 347.40 318.6 872.3 1,191.0 3.452 0.2897 135 350.30 321.7 869.9 1,191.6 3.331 0.3002 38. Mechanical Mixtures. — Problems involving the resulting temperature and final condition when various substances at i From Marks and Davis' "Steam Tables and Diagrams." 38 HEATING AND VENTILATION different temperatures are mixed mechanically are often met with in heating work. They are best treated by first determining the heat in B.t.u. that would be available for use if the temperature of all of the substances were brought to 32°F., and using this heat (positive or negative) to raise (or lower) the total weight of the mixture to its final temperature and condition. Another method of solving such problems is by equating the heat ab- sorbed to the heat rejected and solving for t, the resulting tem- perature. It is often difficult to decide upon which side of the equation a material should be placed. In such a case a trial cal- culation should be made, and the temperature determined by the trial will settle this question. In a mixture of substances which pass through a change of state during the mixture process it is almost necessary to make a trial calculation. Take for example a mixture of steam with other substances. The steam may all be condensed and the resulting water cooled also; the steam may be condensed only; or the steam may be only partially condensed. The equations in each case would be different. If 1 pound of dry saturated steam at a temperature tiis con- densed and then the temperature of the condensed steam is lowered to a temperature t 2 , the amount of heat H' given off would be H' =L t + c(h - h) where L r is the latent heat corresponding to the temperature h and c is the specific heat of Water. If the steam were condensed only, the heat given off would be H' =Li and the temperature of the mixture is the temperature corre- sponding to the pressure. If the steam is only partly condensed let q' equal the per cent, of steam condensed. Then "100 and the temperature of the mixture is the temperature corre- sponding to the pressure. The general laws of thermodynamics do not apply in the case of mixtures as the equations become discontinuous. The general expression for heat absorbed in passing from a solid to a gaseous state may be stated as follows: PROPERTIES OF STEAM 39 Let Ci, C2, cz be the specific heats of the material in the solid, liquid, and gaseous states, respectively. Let w be the weight of the material, t the initial temperature, t\ the temperature of the melting point, t 2 the temperature of the boiling point, t 3 the final temperature, H f the heat of liquefaction, and L the heat of vaporization. Then H' = w[d(ti -t) + H f + afa -h)+L + c 3 (h - t 2 )] Example. — Find the final temperature and condition of the mixture after mixing 10 pounds of ice at 20°, 20 pounds of water at 50° and 2 pounds of steam at atmospheric pressure. Mixture takes place at the pressure of the steam. The specific heat of ice may be taken as 0.5 and the heat of liquefaction as 144 B.t.u. First Method Solution. — Heat to raise ice to 32° = 10 X 0.5(32 - 20) =60.0 Heat to melt ice = 10 X 144 = 1440 Total heat necessary to change the ice to water at 32° = 1500 B.t.u. Heat given up by water when temperature is lowered to 32° = 20 X (50 - 32) = 360.0 Heat in steam above 32° (from tables) = 2 X 1150.3 . = 2300.6 Total heat given up in lowering water and steam to 32° = 2660 . 6 B.t.u. Heat available for use = 2660.8 - 1500 = USE/. 6 B.t.u. Degrees this heat will raise the mixture 1160 . 6 +32 = 36 . 3 .'. Final temperature of mixture = 36.3 + 32 = 68.3°F. Ans. 32 pounds water at 68.3°F. Second Method Assume that the steam is all condensed and that the final temperature of the mixture is t. Then the heat necessary to raise the ice to the melting point equals 10 X 0.5(32 - 20) The heat necessary to melt the ice equals 10 X 144; the heat necessary to raise the melted ice to the temperature of the mixture equals 10 (t — 32); the heat necessary to raise the water to the temperature of the mixture equals 20 (t — 50); the heat given up by the steam in changing to water at the temperature of the boiling point equals 2 X 970.4, and the heat given up by the condensed steam when its temperature is lowered to the temperature of the mixture equals 2(212 — t). Combining the preceding parts into one equation, we have 10X0.5(32-20) + 10X144 + 10(4-32) +20(«-50) =2X970.4+2(212-*) 40 HEATING AND VENTILATION 60 + 1440 + lOi - 320 + 20* - 1000 = 1940.8 + 424 - 2t 32< = 2184.8 t = 68.3° Since t is less than the temperature of the boiling point corresponding to the pressure at which the mixture takes place, all the steam is condensed. Ans. 32 pounds water at 68.3°F. Example.— 1 Find the resulting temperature and condition after mixing 10 pounds of ice at 20°, 20 pounds of water at 50°, 40 pounds of air at 82°, and 20 pounds of steam at 100 pounds gage pressure and containing 2 per cent, moisture. Mixture takes place at the pressure of the steam. Solution. — ■ 10 X 0.5(32 - 10 X 144 20) First Method 60 = 1440 1500 B.t.u. = heat to raise ice to water at 32°. 20 X (50 - 32) = 360 40 X 0.2415(82 - 32) = 483 20(308.8 + 0.98 X 880.0) = 23,424 24,267 B.t.u. = heat given up by air, water, 1,500 and steam. 22,767 B.t.u. = heat available. 40 X 0.2415(337.9 - 32) = 2,955 B.t.u. = heat to raise air to 337.9°. 19,812 B.t.u. = heat available to raise the water. 50 X 308.8 = 15,440 B.t.u. = heat to raise water to 337.9°. 4,372 B.t.u. = heat available to evaporate water. 4372 SofTTi = 4.97 pounds steam. Ans. 40.00 pounds air 45.03 pounds water \ at 337.9°. 4.97 pounds dry saturated steam . Second Method Assume the steam to be all condensed and let the temperature of the mixture be t°. Equating the heat gained by the ice, water, and air, and the heat lost by the steam, we have 10 X 0.5(32 - 20) + 10 X 144 + 10(< - 32) + 20(« - 50) + 40 X 0.2415 (t - 82) = 20 X 0.98 X 880^0 + 20(337.9' - t) 60 + 1440 + 10< - 320 + 20* - 1000 + 9.7* - 792 = 17,248 + 6758 - 20< PROPERTIES OF STEAM 41 59.5* = 24,618 t = 413.7°F. This result is of course absurd, as the temperature of the mixture cannot be higher than the temperature of the boiling point corresponding to the pressure at which the mixture takes place. Therefore, our assumption that all the steam is condensed must be wrong, and we know that part of it remains in the form of steam, and hence the temperature of the mixture is equal to the temperature of the boiling point corresponding to the pressure at which the substances are mixed. Then, substituting for t its value, and letting x represent the number of pounds of steam condensed, we have 10 X 0.5(32 - 20) + 10 X 144 + 10(337.9 - 32) + 20(337.9 - 50) + 40 X 0.2415(337.9 - 82) = 880.0a; 60 + 1440 + 3059 + 5758 + 2472 = 880.0a; 880.0s = 12,789 x = 14.53 pounds condensed. 20 X 0.98 = 19.6 pounds = original weight of dry steam. Ans. 40 pounds air 1 10 + 20 + (20 - 19.6) + 14.53 = 44.93 pounds water \ at 337.9°. 19.6 — 14.53 = 5.07 pounds dry saturated steam J The difference between the results obtained in these two methods of work- ing this problem is due to the fact that in the first method we took account of the variation in the specific heat of water by using the heat of the liquid, h, from the tables, in place of (t — 32) wherever possible, while in the second method we assumed this specific heat to be constant and equal to 1. Example. — Find the resulting temperature and condition after mixing 10 pounds of ice at 20°, 20 pounds of water at 50°, and 30 pounds of steam at 100 pounds pressure and 400° temperature. Mixture takes place at 25 pounds pressure. First Method Solution. — 10 X 0.5(32 - 20) 60 10 X 144 = 1,440 1,500 B.t.u. = heat to raise ice to water at 32°. 20 X (50 - 32) = 360 30^X 0.53(400 - 3a7,9) 987 30 X 1188.8 = 35,664 37,013 B.t.u. = heat given up by water and steam. 1,500 60 X 235.6 35,513 B.t.u. = heat available. 14,136 B.t.u. = heat to raise water to 266.8°. 21,377 B.t.u. = heat available to evaporate water. 42 HEATING AND VENTILATION 21 377 qqo fi = 22.89 pounds steam. 22.89 pounds dry saturated steam } at 266.8°F. Second Method Assume the steam to be all condensed and let the temperature of the mixture be t°. Then 10 X 0.5(32 - 20) + 10 X 144 + 10(1 - 32) + 20(t - 50) = 30 X 0.53 (400 - 337.9) + 30 X 880.0 + 30(337.9 -t) 60 + 1440 + 10i - 320 + 20t - 1000 = 987 + 26,400 + 10,137 - 30« 60i = 37,344 t = 622.4° This result is, of course, impossible and we see at once that only part of the steam is condensed, and that the temperature of the mixture must be that of the boiling point corresponding to the pressure at which the mixture takes place. This problem differs from the previous ones in that the pressure of the mixture is different from the original steam pressure, and we must proceed in a slightly different manner. Assume for the moment that the steam has all been condensed and that we have 60 pounds of water at 622. 4°F. Then assume that the temperature of the water is dropped to the temperature of the boiling point (266.8°) corresponding to the pressure (25 pounds) at which the mixture is made. Each pound will give up, approximately (622.4 — 266.8) B.t.u. This heat can then be used to re-evaporate part of the water. Therefore, since the latent heat corresponding to 25 pounds is 933.6, we have 60(622.4 - 266.8) 60 X 355.6 21,330 no or 9T3T6 = "" 933T6~~ = 933^ = 22 ' 85 pounds ^-evaporated. Ans. 37.15 pounds water \ 22.85 pounds dry saturated steam / Problems 1. Required the temperature after mixing 3 pounds of water at 100°F., 10 pounds of alcohol at 40°F., and 20 pounds of mercury at 60°F. 2. Required the temperature and condition after mixing 5 pounds of ice at 10°F. with 12 pounds of water at 60°F.' 3. Required the temperature and condition after mixing 10 poundsof ice at 15°F. with 1 pound of water at 212°F. 4. Required the temperature and condition of the mixture after mixing 5 pounds of steam at 212°F. with 20 pounds of water at 60°F. 5. One pound of ice 2 at 32° is mixed with 10 pounds of water at 50° and 1 Specific heat of ice equals 0.5. 2 Latent heat of fusion of ice = 144 B.t.u. 's. PROPERTIES OF STEAM 43 20 pounds of steam at 212°. What is the temperature and condition of the resulting mixture? 6. Ten pounds of steam at 212° are mixed with 50 pounds of water at 60° and 2 pounds of ice at 32°. What will be the resulting temperature and condition of the mixture? 7. Ten pounds of steam at atmospheric pressure, 5 pounds of water at 50° and 10 pounds of ice at 32° are mixed together, (a) What will be the resulting temperature of the mixture? (6) What will the condition of the mixture be? (c) If the steam is not all condensed, determine what per cent, of the steam will be condensed. 8. Five pounds of steam at atmospheric pressure, 10 pounds of water at 60°, and 2 pounds of ice at 20° are mixed at atmospheric pressure. What will be the resulting temperature? 9. Ten pounds of ice at 10°, 20 pounds of water at 60° and 5 pounds of steam at atmospheric pressure are mixed at atmospheric pressure. Find the resulting temperature and condition of the mixture. 10. Twenty pounds of steam at atmospheric pressure, 10 pounds of water at 60° and 50 pounds of air at 100° are mixed together at the pressure of the steam, (a) What will be the resulting temperature? (b) If the steam is not all condensed, determine what per cent, of the steam will be condensed. 11. A mixture is made of 10 pounds of steam at atmospheric pressure, 5 pounds of ice at 20°, 10 pounds of water at 50°, 30 pounds of air at 60°. (o) What will be the temperature of the resulting mixture? (6) What will be the percentages by weight of air, steam, and water in the mixture? 12. What would be the resulting temperature and condition of a mixture of 10 pounds of water at 40°, 20 pounds of water at 60°, and 8 pounds of steam at 5 pounds pressure? Mixture takes place at 5 pounds pressure. 13. Ten pounds of steam at 5 pounds pressure, 1 pound of ice at 32°, and 20 pounds of water at 60° are mixed at 5 pounds pressure. What will be the temperature and condition of the resulting mixture? 14. Five pounds of ice at 5°, 10 pounds of water at 50°, 20 pounds of air at 80°, and 5 pounds of steam at 20 pounds pressure are mixed at the pres- sure of the steam. Find the resulting temperature and condition of the mixture. 15. Required the temperature and condition of the mixture after mixing 10 pounds of steam at a pressure of 30 pounds absolute and a temperature of 250.3°F., 2 pounds of ice at 10°F., and 20 pounds of water at 40°F. Mix- ture takes place at the pressure of the steam. 16. Fifty pounds of air at 100°, 10 pounds of steam at atmospheric pres- sure, and 10 pounds of water at 60° are mixed at atmospheric pressure. What is the temperature of the mixture and how much steam is condensed? 17. Required the final temperature and condition after mixing at the pressure of the air 100 pounds of air at a temperature of 500° and a pressure of 100 pounds absolute, and 2 pounds of steam at 100 pounds absolute having a quality of 98 per cent. 18. Five pounds of steam at 5 pounds gage pressure are mixed at atmos- pheric pressure with 10 pounds of water at 60°. What is the temperature and condition of the resulting mixture? 19. Thirty pounds of water at 60°, 10 pounds of steam at 115 pounds 44 HEATING AND VENTILATION absolute and a temperature of 400°F., and 10 pounds of ice at 20° are mixed at atmospheric pressure. What will the resulting temperature be? What is the condition of the mixture? 20. Ten pounds of ice at 20°F., 18 pounds of water at 80°, and 10 pounds steam at 75 pounds pressure and 90 per cent, quality, are mixed at atmos- pheric pressure. What is the resulting temperature and condition of the mixture? 21. Two pounds of steam at 150 pounds absolute and a temperature of 400°, 5 pounds of ice at 22°, and 10 pounds of water at 60° are mixed at atmospheric pressure. Find the final temperature and condition of mixture. 22. Required the final temperature and condition after mixing at atmos- pheric pressure 3 pounds of ice at 22° and 3 pounds of steam at 100 pounds pressure and containing 2 per cent, moisture. 23. Find the resulting temperature and condition of a mixture of 10 pounds of steam at 150 pounds absolute and a temperature of 400°F., 10 pounds of water at 60°F., and 50 pounds of air at 112°F. Mixture takes place at atmospheric pressure. 24. Five pounds of ice at 0°, 20 pounds of water at 75°, and 15 pounds of steam at 50 pounds absolute and 95 per cent, quality are mixed at 20 pounds absolute. What is the resulting temperature and condition of the mixture? 25. How many pounds of water will 10 pounds of dry steam heat from 50° to 150° if the steam pressure is 100 pounds gage? 26. If 10 pounds of steam at 100 pounds gage raised 93 pounds of water from 50° to 140°, what per cent, of moisture is in the steam, radiation being zero? 27. A pound of steam and water occupies 3 cubic feet at 110 pounds absolute pressure. What is the quality of the steam? CHAPTER V RADIATORS 39. Classification. — In a steam or hot-water heating system the conveying medium absorbs heat at the boiler and then flows to the radiators whose function is to transmit the heat to the air, walls, etc. of the room. There are several forms of radiation, the proper one to be used in any particular case depending upon the nature and use of the building. The selection of radiators of the proper size for each room in the building is very important. If the radiators are too small it will be impossible in the coldest weather to warm the building to the required temperature within a reasonable time, if at all. On the other -hand, the installation of radiators of too large a size adds unnecessarily to the cost of the heating system, and tends to cause the rooms to be overheated during a large part of the time. In order to compute intelligently the amount of radiating surface required, it is necessary to study the various forms of radiation and the factors affecting the rate of heat transmission from each. Radiators may be divided into three classes: (a) direct ra- diators, (6) indirect radiators, and (c) semi-indirect radiators. Direct radiators, as explained in Chapter III, are located in the rooms to be heated, while indirect radiators are located elsewhere and a current of air conveys the heat from them to the rooms. Semi-indirect radiators are a combination of the other two forms, the radiators being installed in the rooms but delivering a large proportion of their heat output by means of a current of air which passes through them. 40. Direct. Cast-iron Radiators. — Direct radiators are made of cast iron, pressed iron, and wrought iron or steel pipe, the cast-iron radiator being by far the most widely used. It is composed of several sections cast separately and assembled, the number of sections being fixed by the amount of surface required. The sections are made in several different widths and heights so that for a radiator of a given surface, a wide range of shapes and 45 46 HEATING AND VENTILATION sizes is available. The wider sections are divided through most of their length by vertical slots into from two to six segments or Single Column Radiator Two Column Radiator Three Column Radiator Four Column Radiator Window Type Fig. 8 "columns." The standard heights vary from 15 to 45 inches but the 38-inch height is the one most often used. In Fig. 8 are RADIATORS 47 shown several forms of cast-iron radiators. Radiators are fin- ished in several designs to harmonize with room decorations. In general appearance the form of radiator used for steam is quite similar to that used for water. The two designs are funda- mentally different, however, in that the sections of the steam radiator are joined together at the bottom only, while those in a hot-water radiator are connected at both top and bottom. Hot- water radiation may be used for steam but steam radiation could not be satisfactorily used in a hot-water system because air would become trapped in the top of each of the sections, pre- venting the water from filling them. Fig. 9. — Methods of assembling cast-iron radiators. The sections are joined by means of nipples. One method is to use a smooth tapered "push nipple," fitting into tapered holes in the adjacent sections. Draw-bolts extending the full length of the radiator are used to force the joints to a tight fit. Another method is to use nipples threaded with "right and left " threads. These nipples are cast with internal lugs and are turned up by means of a special wrench. The two methods of assembling are shown in Fig. 9. Cast-iron radiators are usually given a hydraulic pressure test at the factory of about 120 pounds per square inch. They are therefore suitable for working pressures approaching this figure but are seldom subjected to any such pressure except in the case of hot-water systems in tall buildings where the hydrostatic 48 HEATING AND VENTILATION head is high. The weight of cast-iron radiators averages about 7 pounds per square foot of surface and the internal volume is about 30 cubic inches per square foot of surface. This internal volume is largely fixed by the requirements of manufacture, the only stipu- lation from an engineering standpoint being that the passages must not be so small as to restrict the flow of the water or steam. Cast-iron radiation is also furnished in the form of "wall radiators" as illustrated in Fig. 10. This type of radiation is so Fig. 10. — Wall radiator. proportioned that it takes up very little lateral space and is intended to be hung from brackets. It is well adapted for use in factory buildings. The rated external surface of radiators of various widths and heights is given in Table XI in square feet of surface per section. Table XI. — Heating Surface per Section — Cast-iron Radiation Height, One- Two- Three- Four- Six-column or inches column column column column ' ' window ' ' pattern 45 5 6 10 38 3 4 5 8- 32 2K 3Ys 4^ 6K 26 2 2% 3M 5 23 1% 2H 22 2H 3 4 20 iji 2 5 18 m 3 16 3M 15 IX 14 13 3 RADIATORS 49 Wall Radiatoks Size of section, Heating surface, inches (approx.) square feet 14 by 16 5 14 by 22 7 14 by 29 9 It should be noted that the height of a radiator is taken as the total height above the floor for radiators having legs of standard height. The rated surface given in the table does not correspond exactly with the actual surface, but the difference may be neg- lected as the heat transmission from radiators is usually given in terms of rated surface. 41. Radiator Tappings. — The end sections of cast-iron radia- tors are usually tapped for a 2-inch pipe thread and furnished with bushings having openings whose size depends on the size of the radiator. The sizes of the reduced openings for radiators intended for use with different systems of piping are as follows : Table XII. — Radiator Tappings Single-pipe Work Size of radiator, square feet Inches Up to 24 1 24 to 60 IK, 60 to 100 IK Above 100 2 Two-pipe Work, supply and return Up to 48 1 by % 48 to 96 IK by 1 Above 96 IK by IK Water radiators, supply and return Up to 40 1 by 1 40 to 72 IK by IK Above 72 IK by IK For vapor systems supply, j^inch, return, K inch. Air valve tapping, K inch on all radiators. 42. Pressed-metal Radiators. — In recent years radiators made of pressed metal have been introduced and are now some- times used. Fig. 11 illustrates the appearance of one design of this form of radiator, and Fig. 12 is a cross-section. The sections are made of two sheets of metal pressed to shape and welded at the edges. In other designs the joint is a lapped seam. A special alloy- or soft steel selected for its non-corroding qualities is used. The radiator is assembled by welding the sectors 50 HEATING AND VENTILATION together or by joining them with lapped seams. Pressed-metal radiators are made in a variety of sizes corresponding to those of cast-iron radiation. The sections are very narrow and occupy much less space than do cast-iron radiators of equal surface. The weight per square foot of surface is also much less than that of cast-iron radiation, averaging about 2 pounds. The cost is about the same as that of ordinary cast-iron radiation. The radiating surface of pressed-metal sections of various heights and widths is given in Table XIII. Because of its light weight this -.Welded Fio. 11. — Pressed metal radiator. Fig. 12. — Section of pressed metal radiator. form of radiation is especially suitable for hanging on wall brackets. Table XIII. — Pressed-metal Radiation, Square Feet of Surface per Section Width of section, inches ty 2 SM 45 6 38 3 5 32 2H 4M 26 2 3% 22 1% 3 18 m 2M 14 i 43. Pipe Radiation. — In factories and other industrial buildings radiators built of pipe are often used and are a very satisfactory RADIATORS 51 form of radiation. These pipe coils usually consist of a pair of cast-iron headers connected by four or more pipes of either 1 inch or \y± inches diameter. Pipe coils are usually made in the mitre form as shown in Fig. 13. The vertical lengths of pipe provide sufficient flexibility to allow the longer horizontal members to expand freely. Some such provision is essential. The openings in one of the headers or the elbows are tapped si nflc -TjOn- 3flC nflr nflc nfln -nOn- 3flC nfln Fig. 13. — Mitre pipe coil. with a left-hand thread so that the coil can be readily assem- bled. Pipe coils of the form shown in Fig. 14 are also some- times used, especially in hot-water work. Radiators were formerly made of vertical pipes screwed into a cast-iron base. This form of radiation is little used at present. 44. Heat Transmission from Radiators. — Heat flows from the water or steam in a radiator into and through the metal wall Continuous pipe coil. and is transmitted from the outer surface partly by radiation and partly by convection. The resistance to heat flow offered by the walls of the radiator is so slight that the temperature of the outer surface is practically the same as that of the water or steam. It is very difficult to measure accurately the portions of the total amount of heat which are transmitted by radiation and by convection. Rough tests, however, indicate that about one- half of the total amount is given off in each manner. The total 52 HEATING AND VENTILATION amount of heat transmitted per square foot of radiating surface is affected by several factors, such as the temperature difference between the radiating surface and the surrounding air, the nature of the surface, the height and shape of the radiator, and the location of the radiator in the room. 45. Effect of Shape of Surface. — The form or shape of the radiator has a marked effect on the heat transmission, affecting both the amount radiated and that given off by convection. A greater amount of heat per square foot of surface is given off by radiation from a pipe coil or a single-column radiator than from a radiator of a wider pattern. This can be clearly understood from a study of Fig. 15 which represents horizontal cross-sections of a single-column and a three- column radiator. The rays of heat from points on the single-column radiator can travel in nearly any direction without interruption, while the rays emanating from many points such as A, on the surface of the inner columns of the Fio. 15. three-column radiator, are largely intercepted by the other portions of the radiator. The transmission of heat by convection is dependent upon the difference in temperature between the surface of the radiator and the air. The upper part of a radiator will transmit less heat per square foot by convection than will the lower part because of the increase in the temperature of the air as it ascends along the surface. Hence the average heat transmission per square foot is greater for short than for tall radiators, and for the same reason a radiator or pipe coil laid on its side will give off more heat than when in a vertical position. 46. Effect of Painting. — The effect of the decorative painting on the heat transmission is sometimes considerable. Experi- ments made at the University of Michigan indicate that (a) if several paints of different kinds are applied successively the effect on the heat transmission is due entirely to the final coat, and (b) the aluminum or bronze paints have the greatest effect, reducing the heat transmission almost 25 per cent, in some cases. The relative effect of different kinds of paints is given in Table XIV. RADIATORS 53 Table XIV. — Relative Effect of Radiator Paints Kind of paint } Relative transmission Bare iron surface 1 . 000 Copper bronze . 760 Aluminum bronze . 752 Snow-white enamel 1 . 010 No-luster green enamel . 956 Terra-cotta enamel 1 . 038 Maroon glass Japan . 997 White lead paint '. . 0.987 White zinc paint 1.010 47. Coefficients of Heat Transmission. — The amount of heat transmitted from a radiator may be represented by the expression, 1.9 °1.8 m V 1 m en 1 1.6 § H fh-6 w 1.4 1,3 ^^^1 Column -"-"^■-2. Column -^~^3 Column ~~^-i Column 20 24 28 48 Fig. 16.- 30 36 40 44 Height of Radiator - Inches -Coefficient of heat transmission from radiators. H = SK(t, - t r ) in which S = the area of the radiating surface in square feet. K = the coefficient of heat transmission in B.t.u. per square foot per hour per degree difference between radiator and room temperature. t s = temperature of the steam or water in the radiator. t r = room temperature. The values of K, the coefficient of heat transmission for ordinary cast-iron radiation of various heights and widths, is given by the curves in Fig. 16 which are based on the results of 54 HEATING AND VENTILATION recent- experiments. For other forms of radiation the values of K given in Table XV may be taken as average figures. Table XV. — Coefficient of Heat Transmission from Radiators k B.t.u. per square foot per hour per degree difference in temperature Cast iron, height 38 inches: One-column 1 . 75 Two-column 1 . 65 Three-column 1 . 55 Four-column 1 . 45 Wall Coil: Heating surface 5 square feet, long side vertical 1 . 92 Heating surface 5 square feet, long side horizontal 2.11 Heating surface 7 square feet, long side vertical 1.70 Heating surface 7 square feet, long side horizontal 1 . 92 Heating surface 9 square feet, long side vertical 1 .77, Heating surface 9 square feet, long side horizontal 1 . 98 Pipe Coil: Single horizontal pipe 2 . 65 Single vertical pipe 2 . 55 Pipe coil 4 pipes high 2 . 48 Pipe coil 6 pipes high .' 2 . 30 Pipe coil 9 pipes high 2.12 This data is based on a temperature difference between the radiator and the air of about 150° which represents ordinary- conditions. The rate of heat transmission increases slightly with an increase in the temperature difference. In Table XVI are given the results of a test on a 38-inch two-column radiator Table XVI. — Coefficient of Heat Transmission for Varying Tem- perature Difference Between the Radiator and Room Difference in temperature, degrees Coefficient of heat transmission, K 80 1.560 100 1.580 120 1.615 140 1.645 150 1.650 160 1.675 170 1.690 180 1.705 190 1.720 RADIATORS 55 showing this change in the value of K with an increasing tempera- ture difference. For ordinary conditions, that is, when the system is to be designed for a steam pressure of from 1 to 5 pounds and the room temperature is 70° or thereabouts, there will be no necessity for considering the change in the heat transmission with varying temperature differences. Occasionally, however, there are 80 40 700 60 m | 20 .5 GOO g 80 O i-l « 40 •a 500 3 £60 I 20 «400 e 80 | 40 £ 300 .9 20 200 80 40 100 60 \ ^ •**** i i i v °t- • ~^< Eoo n T< nip. > • **'j S % » c AS ^ V ni ij 1 / i i i 1 il i i 1 I i // 1 J i i / \ ' i / \ ^ C ond< nsal ioir i / X \ Ca Bt II on / s >~ i . ( < 1 , P resst d Ir on 1 1 / / u 8.00 20 30 Time 40 50 74 72 70 68 66 64 8 62 1 60 g 68 a 56 | 54 52 50 48 46 9.00 Fig. 17. — Result of a comparative test of a cast iron and a pressed iron radiato. conditions such as in drying rooms and similar places that are to be kept at a very high temperature where it will make an appreci- able difference in the amount of radiation required. In some vacuum systems, also, where a very high vacuum is to be carried even in the coldest weather, it is desirable to take this factor into consideration. The heat transmission from pressed-metal radiation is practi- cally the same as that from cast iron. This is illustrated in Fig. 56 HEATING AND VENTILATION 17 which shows the results of a test 1 to determine the relative performance of the two forms of radiation under the same condi- tions. A radiator of each kind was placed in either of two similar rooms and the condension formed in each radiator was weighed at 10-minute intervals and the room temperatures were measured. While the rate at which the room was warmed was nearly the same in both cases it will be noted that in the case of the cast-iron radiator the initial condensation of steam is con- siderably greater. 48. The Location of Radiators. — The location of the radiators is of considerable importance from several standpoints. Unless Effect of locating radiator beneath window. there are columns or other permanent structures in the interior of the room, it is necessary, at the outset, to place the radiators around the walls. The piping is also simplified by placing the radiators near the walls. If the radiators are placed against an interior wall there is a tendency for uncomfortable draughts to be formed by the cooling effect of the windows and outer wall tending to form a downdraught on one side of the room, together with the effect of the upward movement created by the radiator on the other side. If the radiator is placed under the window, 1 See " Coefficient of Heat Transmission in a Pressed-Metal Radiator " by John R. Allen, Trans. A. S. H. & V. E., 1914. RADIATORS 57 the current of air rising from the radiator will counteract this tendency and will produce an air movement as illustrated in Fig. 18. The downward current caused by the cooling effect of the window causes a secondary circulation of the air between the radiator and the window. The location of the radiators beneath the windows if possible is, on the whole, the most desirable. Recent tests 1 have indicated that the transmission of heat is slightly greater when the radiators are located in other positions, but the slight gain in effectiveness is greatly overbalanced by the other considerations noted above. Radiators are often located under seats and shelves or behind grilles of various designs, the object being either to conceal the radiator or to conserve space. The heat transmission from the radiator is usually decreased by such enclosures, because of the restriction imposed on the circulation of the air through the radiator. Where it is necessary to place a radiator in such a location, an addition of from 10 to 30 per cent, should be made to its heating surface according to the degree to which the circula- tion is retarded by the enclosure. 49. Proportioning Radiation. — The heat loss from the various rooms of a building having been calculated by the methods given in Chapter II, it is then necessary to determine the amount of radiating surface which will be required to supply the heat losses. It is necessary first to know the temperature of the steam or water in the radiator. If steam is the heat carry- ing medium the temperature will be that corresponding to the pressure to be carried. In many heating systems it is possible to carry a pressure of at least 5 pounds when necessary and for such systems the radiation is commonly figured on the basis of this pressure. If, however, special conditions require that a lower pressure be used the temperature of the steam which is assumed should be that corresponding to the pressure. Some types of vapor heating systems are designed to operate at nearly atmospheric pressure, and the radiation is consequently figured for 212°. If hot water is used the temperature will range between 160° and 200°. The factors affecting the temperatures carried in hot-water systems will be discussed later. The type of radiation and the height must next be selected from 1 See report of Committee on Best Position of a Radiator, Trans. A. S. H. & V. E., 1916. 58 HEATING AND VENTILATION a consideration of the nature of the building and of the space available. Prom the chart in Fig. 16 or from Table XV the heat transmission per square foot of surface for the type of ra- diation selected can be found and the total surface necessary to transmit the heat required can then be computed. For example, consider that the room shown in Fig. 7, page 23, is to be heated by a heating system which is to operate at a pressure of 2 pounds. The heat loss from the room was found by the B.t.u. method to be 8696 B.t.u. per hour with room temperature 70°. Assume that 38-inch, two-column radiation is to be used. The tempera- ture of steam at 2 pounds pressure is 218.2 and the difference in temperature between the steam and the air is 218.2° — 70° or 148.2°. From the chart in Fig. 16 we see that the value of K for 38-inch, two-column radiation is 1.65. For a temperature difference of 148.2° the heat transmission would be 244 B.t.u. per square foot per hour. Dividing 8696 by this figure we find that 35.6 square feet of radiation would be required. Since 38-inch, two-column radiation contains 4 square feet of surface per section, a radiator of nine sections would be used. 50. Approximate Rules for Calculating Radiation. — The method outlined above should be followed when accurate results are necessary or when the conditions are exceptional. For rough calculations the average rate of heat transmission per degree difference in temperature per hour may be assumed to be 1.65 B.t.u. If the steam pressure is assumed to be 5 pounds the temperature will be 227° and the temperature difference be- tween the radiator and the room, assuming the room temper- ature at 70°, would be 157°. The heat transmission per square foot of radiation per hour would then be 1.65 X 157 = 259 B.t.u. Having computed the heat loss by either of the methods given in Chapter II the radiation required can be approximately determined by dividing the computed heat loss by 259. 51. Checking a Contractor's Guarantee. — The case often arises in which a contractor has guaranteed that the heating system as installed is capable of heating the building to 70° in zero weather and it is desired to prove that this is true without waiting for extremely cold weather. By means of the following method it is possible to determine the temperature to which the building must be heated in the warmer weather if the heating system is capable of heating it to the' guaranteed temperature in the coldest weather. RADIATORS 59 Let h = temperature of outside air under contract conditions, usually 0°. t 2 = temperature of air in building under contract con- ditions. t 3 = temperature of steam in radiator at pressure specified. Test made with steam at same pressure. ti = temperature of outside air during test. t$ = inside temperature to be maintained during test if system fulfills guarantee. h = computed heat loss from building per degree dif- ference in temperature. The heat loss from the building under conditions specified in guarantee would be h(U - h) (1) The heat loss from the building under test conditions is Kh - U) (2) The heat loss from the radiators under contract conditions would be K(f, - h) (3) in which K is the coefficient of heat transmission from the radiator. The heat transmission from the radiator under test conditions is K{U - h) (4) Then the quantity (1) must be equal to the quantity (3) and the quantity (2) must be equal to (4), hence and Equating the right-hand members of equations (5) and (6), we have £3 — t% _ ts — t& t<\ — t\ t a — £4 (7) Assuming h = 0°, t 2 = 70°, and h = 228°, the temperature corresponding to 5 pounds steam pressure, and solving for h we have If, = 0.695*4 + 70 (8) 60 HEATING AND VENTILATION The following table has been computed from equation (8) and shows the room temperature, for different outside temperatures existing during the test, which must be maintained to fulfill a guarantee which specifies the temperatures and steam pressure given above. For other conditions equation (7) must be solved for U. Table XVII. — Room Temperature for Various Outside Temperatures Outside temperature during test Room temperature, two-column radiation Room temperature, three-column radiation -30 52.0 53.0 -20 58.0 59.0 -10 64.0 64.0 70.0 70.0 10 ■77.5 75.0 20 83.0 83.0 30 90.0 89.0 40 97.0 95.0 50 103.5 105.5 60 110.0 108.0 70 117.0 115.0 80 123.5 121.5 90 130.0 128.0 100 137.0 134.5 52. Indirect Radiators. — Indirect radiators are so named be- cause they are located outside of the room to be heated and the heat is conveyed from the radiator to the room by a current of air. Indirect radiators are of two classes: gravity indirects, in which the circulation of the air over the radiating surface is produced by the difference in weight of the heated and unheated columns of air, and fan coils, over which the air is forced by a fan. Only the former will be considered here, the various types of fan systems being discussed in Chapter XV. There are two reasons for the use of gravity indirect radiators. Their chief advantage is that they can be arranged to introduce fresh air from outside and they are therefore desirable from a standpoint of ventilation. Another advantage is that the radia- tors are out of sight, which is desirable in any room or apartment where appearance is an important factor. It is seldom that indirect radiators are installed throughout an entire building because of the increased cost both of installation and operation as compared with direct radiation. In a residence, indirect RADIATORS 61 radiation is often installed in the living rooms where ventilation is most desired and where the appearance of the radiators would be objectionable, and direct radiation is used in the bed- rooms, halls, etc. The increased operating cost where indirect radiation is used is due to the fact that the large quantities of air which are brought in from outside must be heated up to room temperature or above. 53. Forms of Indirect Radiation. — As indirect radiators are concealed, their appearance is not an important factor and they are therefore designed and installed from a standpoint of effect- iveness rather than appearance. Since the resistance to heat transmission between the outer surface of the radiator and the air is greater than that from the steam or water to the inside surface of the radiator wall, it is desirable to make the external Fig. 19a. Fig. 196. Forms of indirect radiators. surface of greater area than the internal. This is accomplished by adding projections in the form of pins or fins. Two forms of indirect radiation are illustrated in Figs. 19a and 19&. The sections are joined together in the same manner as are the sections of direct radiators. The form shown in Fig. 196 is of the so-called short-pin type. A similar form having longer pins can also be obtained. 54. Arrangement of Indirect Radiators. — Two common arrange- ments for indirect radiators taking air from outside are illus- trated in Fig. 20 and Fig. 21 . The radiator is placed in a chamber or box usually situated in the basement of the building, as close as possible to the base of the flue leading to the room to be heated. The air is admitted to the radiator chamber by a duct or flue from 62 HEATING AND VENTILATION an opening in the outside wall or from the room above. This duct should be provided with a suitable damper, arranged if Cold Air (~ Duot r from 1 Outside jL ®, >Q£i£i Warm Air JOOO OOOOOOOOOOOO oooo lOOOOOOOOO ooooooooooooc lOOOOOOOOOOOOOOOO oooo o oooooooooooooooooooooc DOOOOO 0000000000000: __ OOOOOOOOOQOOOOOOOOOOOt 000000000000000 00 001 V Oleanout Fig. 20. — Indirect radiator with bypass. possible to close when the steam or water supply to the radiator is shut off. A bypass damper should also be provided, with a means of controlling it from the room, so that the tem- perature of the air can be readily adjusted. The casing surrounding in- direct radiators is usually built of galvanized iron and it should be bolted together with stove bolts, so that the sections can be easily removed. A much better method of construction, though a more expensive one, is to enclose the radiator in a brick chamber of sufficient size to permit access to the radiator. The duct leading from an indirect radiator should be carried to the room as directly as possible. Long horizontal pipes should be avoided. 1 From "Pipe-fitting Charts" by W. G. Snow. Fia. 21. — Indirect radiator. 1 RADIATORS 63 The indirect radiators are usually suspended in the box or chamber on iron pipes supported by rods from the joists. There should be at least 10 inches clearance between the radiator and the bottom and top of the casing, but the sides of the casing should fit the radiator as closely as possible, so that all of the air must pass through the radiator. Indirect radiators should be placed at least 2 feet above the water line of the boiler if they are to be operated on a gravity steam system, and should be so arranged that the condension will drain from them by gravity. The tappings of these radiators are the same as for two-pipe direct steam radiators. The following table gives the size of flues required for indirect radiators of various sizes. Table XVIII. — Size op Flttes for Indirect Radiators Heating surface, square feet Area of cold- air supply, square inches Area of hot- air supply, square inches Size of brick flue for hot air, inches Size of register, inches 20 30 40 8X8 8X8 30 45 60 8 X 12 8 X 12 40 60 80 8 X 12 10 X 12 50 75 100 12 X 12 10 X 15 60 90 120 12 X 12 12 X 15 80 120 160 12 X 16 14 X 18 100 150 200 12 X 20 16 X 20 120 180 240 14 X 20 16 X 24 140 210 280 16 X 20 20 X24 Indirect radiators are sometimes arranged to re-circulate the air from the room instead of drawing in fresh air from outside. No ventilation is obtained by such an arrangement and the only advantage of the indirect radiator so installed is that it is concealed. 65. Heat Transmission from Indirect Radiators. — Heat is transmitted from indirect radiators almost entirely by convec- tion. The amount of heat which will be transmitted from a given indirect radiator depends upon the temperature of the entering air, the temperature of the radiator, and the quantity of air passing through the radiator. The last quantity depends in turn upon the relative temperatures of the heated air and the unheated air, and upon the friction in the air ducts. In Fig. 22 let h! be the average vertical distance from the radiator to the 64 HEATING AND VENTILATION point of delivery to the room. The force effective in producing the flow of air is then V = h' (Dr - D t ) in which D x = density of outside air. D 2 = density of heated air. During a state of constant flow the quantity of air passing through the radiator will always be just sufficient so that the friction loss due to the air passing through the system will equal the available head producing flow. Owing to the impossi- bility of determining in advance the resistance of the duct, because of lack of a standard type of construction, it is very diffi- cult to compute accurately the quantity of air which will pass Fig. 22. through the system. The action is also complicated by the stack effect of the heated room above. Accordingly the methods used in designing indirect radiators are based on experimental data. Table XIX gives the amount of heat transmitted from standard and long-pin radiators under various conditions. It will be noted that the temperature to which the air is heated by the long-pin radiator is less than that to which it is heated by the short-pin radiator with the same quantity of air passing. This is undoubtedly due to the fact that the pins are so long that the rapid removal of heat by the air causes the ends to become cooled. The long-pin type, however, is very desirable for use when large quantities of air are required, as the air passages are ample. This is the work for which it is primarily designed. The RADIATORS 65 short-pin type gives better results for ordinary residences and other buildings where only small quantities of air pass through the radiator. Table XIX. — Heat Tbansmission from Pin Radiators Cubic feet of air passing per square foot of radiation per hour Rise in temperature of the air Pounds of steam condensed per square foot of radiation B.t.u. transmitted per square foot of radiation per degree difference in temperature between steam and air Standard pin Long pin Standard pin Long pin Standard pin Long pin 50 75 100 125 150 175 200 225 250 275 300 147 143 140 138 135 132 130 127 123 121 119 140 137 135 132 129 126 123 120 118 115 112 0.125 0.170 0.240 0.295 0.355 0.410 0.470 0.530 0.585 0.645 0.700 0.150 0.210 0.260 0.310 0.360 0.405 0.450 0.490 0.530 0.570 0:610 0.80 1.17 1.51 1.85 2.22 2.57 2.90 3.25 3.60 3.90 4.22 0.95 1.27 1.60 1.90 2.20 2.47 2.72 3.00 3.20 3.40 3.60 56. Calculation of Indirect Radiation. — In order to determine the required size of an indirect radiator it is necessary to assume the quantity of air that will pass through the radiator. In school buildings and other buildings where a large air supply is desired and where the flues will be of ample size, the amount of air passing per square foot of radiation may be assumed to be 200 cubic feet per hour. In residences and buildings where the flues are usually small, the amount of air passing per square foot of surface per hour does not exceed 150 cubic feet. The air should be assumed to enter the radiator at the minimum outside tempera- ture for which the system is to be designed. If this temperature is 0°, for example, and the quantity of air passing is taken as 200 cubic feet per hour per square foot of radiation, the air will be heated according to figures given in Table XIX to about 130°. The air which enters the room at this temperature gives up its heat to supply the heat lost by conduction through the walls, and finally finds its way out of the room through the window cracks, foul air flues, etc. Each cubic foot of air, therefore, gives up enough heat to lower its temperature from 130° to 70°, s 66 HEATING AND VENTILATION if the latter is the room temperature. This amount of heat is equal to (13 ° 5 ~ ?0) X 200 = 218 B.t.u. per square foot of radiator surface. This amount is available for supplying the heat losses through the walls and the amount of surface in the indirect radiator for the case given above would be equal to the computed heat loss through the walls divided by 218. 57. Approximate Rules for Indirect Heating. — The following approximate rules may be used to compute the amount of indirect heating surface required. This quantity in each case is desig- nated by R. Rule 1. — For ordinary rooms: R = ( j- f- glass surface) X 0.6 For entrance halls: R = ( -r (- glass surface) X 0.75 Rule 2. — Figure the heating surface the same as for direct heating and add 40 per cent. Rule 3. — For rooms on first floor: „ volume of room, cubic feet R= 40 For second and third floor rooms : „ volume of room, cubic feet R= 50 For stores and large rooms : „ volume of room, cubic feet R = 60 58. Combination of Direct and Indirect Radiators. — A very common arrangement is to install enough indirect radiation to give the proper amount of air for ventilation and to install direct radiation to supply the heat losses. The direct radiation would then be computed in the ordinary manner, as if there were no other source of heat. This system has the advantage of being more economical, as less cold air need be heated per hour. RADIATORS 67 Further, when the rooms are unoccupied, the indirect radiators may be entirely shut off, resulting in a considerable saving of fuel. 59. Semi-direct Radiators. — When only a small quantity of air is needed for ventilation semi-indirect or "flue" radiators may be used in place of indirect radiators. A radiator of this form is shown in Fig. 23. The air enters through a grating in the wall behind the radiator and passes into a metal box which en- closes the lower part of the radiator and thence up through the spaces between the sections. Dampers in the fresh air open- ing and in the base may be ad- justed to allow part or all of the air to re-circulate from the room. Radiators used for this purpose are of a special design, the sections being so shaped that the passages between them are divided into a number of vertical flues. A test recently conducted on a flue radiator showed that about 45 per cent, of the ttoal heat transmitted is carried off by the" air passing through the flues, the remaining 55 per cent, being given off by radiation and by convection from the outer surfaces. When flue radiators are used the amount of surface allowed should be about 25 per cent, greater than if direct radiation were used. Eig. 23. — Flue radiator. Problems. 1 To be properly heated, a certain building requires 5627 square feet of 30-inch, one-column radiation. How much would be required if wall coil, of sections containing 9 square feet of surface, long side horizontal, were used? How much would be required if pipe coils, 9 pipes high, were used? 2. A heating system is guaranteed to heat a building to 70° in zero weather at 5 pounds pressure. A test is made with the outside tempera- ture at 10". What inside temperature must be reached to fulfill the guarantee? 68 HEATING AND VENTILATION 3. A heating system is guaranteed to heat a building to 65° with the outside temperature at 10° and at a steam pressure of 1 pound. A test is made with the outside temperature at 15°. What inside temperature must be maintained to fulfill the guarantee? 4. Assume that the room in Fig. 7, p. 23, is to be heated by indirect radiation. Inside temperature 70°, outside temperature 0°. How much radiation would be required and what would be the proper size for the flues and registers'? 5. Take the same room as in Prob. 4 and figure the amount of indirect radiation. required by each of the approximate rules in Par. 57. 6. Take the same room as in Prob. 4 and figure the amount of in- direct radiation required if the inside temperature is 65° and the outside temperature 10°. CHAPTER VI STEAM BOILERS 60. Fuel. — Before taking up the subject of boilers, it is desir- able to study the various kinds of fuel and the general principles of combustion. Coal, coke, wood, oil, and gas are used as boiler fuels. Coal is by far the most widely used fuel in the United States, being found in varying amounts in no less than thirty States in the Union. It is of vegetable origin, being the remains of vegetation which existed during a former geological period and which gradu- ally reached its present state through the action of decay and of earth pressure. The chief constituents of coal are carbon, hydrogen, oxygen and nitrogen. The carbon exists partly in an uncombined or "fixed" state and partly in combination with the hydrogen and oxygen as hydrocarbon compounds which are given off as gases when the coal is heated. Coals are classified as anthracite, bituminous, etc., according to the relative pro- portions of fixed carbon and volatile matter as given in Table XX. Table XX. — Classification of Coals Composition per pound of combustible Calorific Kind of coal Volatile matter Fixed carbon value per pound of combustible 3.0- 7.5 7.5-12.5 12.5-25.0 25.0-40.0 35.0-40.0 97.0-92.5 92.5-87.5 87.5-75.0 75.0-60.0 65.0-50.0 14,900-15,300 15,300-15,600 15,600-15,900 15,800-14,800 15,200-13,700 Bituminous — Eastern Bituminous — Western All coals contain more or less non-combustible matter, con- sisting principally of moisture and ash. The nitrogen in the coal is also a non-combustible but it is customary to treat it as combustible matter. The moisture content of different coals varies from 2 per cent, to as much as 20 per cent, and the ash content from 4 to 20 per cent, by weight of the coal as mined. 69 70 HEATING AND VENTILATION It will be noted that the percentages in Table XX are based on 1 pound of combustible. The bituminous and semi-bituminous coals are the most abundant and are the kinds used for most industrial purposes. Many bituminous coals are of the variety known as "caking" coals because, when heated, the lumps fuse together into a solid crust, while the so-called "non-caking" or free-burning coals do not possess this quality. Bituminous coals burn with a char- acteristic yellow flame and emit smoke unless burned under favorable conditions. They are sold in the sizes given in Table XXI and as "run-of-mine" or ungraded. Table XXI. — Commercial Sizes of Bituminous Coal Kind of coal Will pass through bars spaced Will not pass through bars spaced \Vi inches Nut 1J4 inches % inch % inch Slack The slack coal does not command as high a price as the larger sizes because of its higher ash content and the difficulty of burning it. Anthracite or hard coal is principally used for domestic pur- poses and for other conditions where a smokeless coal is required. It ignites slowly but burns steadily with a short blue flame. It is of relatively great density and does not crumble easily. It is marketed in the sizes given in Table XXII. Table XXII. — Commercial Sizes op Anthracite Coal Kind of coal Will pass through Will not pass through Rice Buckwheat. . . Pea Chestnut Stove or range Egg Large egg J^-in. mesh H-in. mesh . 24-in. mesh lM-in. mesh 1%-in. mesh 2 L 2-in. mesh 4-in. mesh Jij-in. mesh Ji-in. mesh J^-in. mesh 24-in. mesh lJ4-in. mesh 1%-in. mesh 2%-in. mesh 61. Composition and Analysis of Coal. — Coal consists of carbon , hydrogen, sulphur, oxygen, and nitrogen combined in various STEAM BOILERS 71 ways, together with moisture and ash. The moisture includes both that originally contained in the coal and that added during storage and shipment. The moisture content of a given coal is determined by subjecting a finely powdered sample to a tempera- ture of about 220°F. for about 1 hour and noting the loss in weight during that time. This method, while not giving an absolutely accurate result, is the one universally employed. The amount of volatile matter is determined by subjecting a sample of dried coal to a high temperature out of contact with air until there is no further loss of weight, and noting the de- crease in weight. The residue left after distilling off the volatile matter consists of the fixed carbon and ash. By burning the sample in an uncovered crucible the fixed carbon can be removed , leaving the ash. There are two forms of coal analysis — the "Proximate Analy- sis"and the " Ultimate Analysis." The former consists of a deter- mination of the moisture, volatile matter, fixed carbon, and ash in the manner just described. This is the more useful form of analysis and is the one generally used by engineers. The ulti- mate analysis, which consists of a determination of the carbon, hydrogen, oxygen, nitrogen, and sulphur, is usually made in a chemical laboratory. In the proximate analysis, the percentages may be reckoned either on a basis of dry coal or coal "as received." In the former case the moisture content is given in addition. The heat value or calorific value of a fuel is the amount of heat developed by its combustion, expressed in B.t.u. per pound of fuel. The heat value of coal is determined by igniting a sample of known weight in a closed vessel surrounded by water and noting the rise in temperature of the water. From the pre- viously determined thermal capacity of the vessel and water the heat developed can be computed. The calorific value of the various kinds of coal was given in Table XX. 62. Coke. — Coke is the residue left after the volatile matter is driven off from bituminous coal and consists mainly of carbon. It is produced as a byproduct in the manufacture of artificial gas and is also manufactured for various industrial purposes. It is of relatively low density and is consumed rapidly so that when used as a boiler fuel frequent firing is required unless a very deep bed of fire is maintained. 63. Combustion. — Combustion may be defined as the chemical combination of a substance with oxygen which proceeds at such 72 HEATING AND VENTILATION a rate that a high temperature is produced. Carbon is the principle combustible in coal. When its combustion is complete, it forms carbon dioxide (C0 2 ); when it is incomplete it forms carbon monoxide (CO). The hydrogen in the coal unites with oxygen to form water vapor and the nitrogen, which is an inert substance, is set free. For economy in fuel consumption it is necessary that combustion be complete and to this end the supply of air must be ample. In order to insure a sufficient supply to all parts of the fuel bed, it is necessary to supply from 150 to 300 per cent, of the theoretical requirements. As all of this excess air leaves the boiler at the flue-gas temperature, it is evident that in the interest of economy the amount of excess air used should be reduced to the minimum required for complete combustion. The best index of the amount of excess air in the percentage of C0 2 in the flue gases. If exactly enough air is supplied the C0 2 content, by volume, of the flue gases would be 21 per cent. In practice, however, the best results are obtained with a CO2 content of from 10 to 15 per cent., the higher figure being attain- able only with mechanical stokers. In the ordinary hand-fired furnaces of heating boilers the C0 2 content of the flue gases ranges between 5 and 13 per cent. 64. Smoke. — Smoke consists principally of unburned carbon in finely divided particles set free by the splitting up of unburned hydrocarbon gases. While the waste represented by the visible products themselves is not great, smoke is an indication of incom- plete combustion and consequently of wasted fuel. A great deal of damage is caused annually by smoke and in most communities the making of excessive smoke is prohibited by law. Smoke may be avoided by the use of anthracite coal, coke, or the semi-bituminous coals, which have little volatile matter, and by insuring complete combustion when coals high in volatile matter are used. When coal containing much volatile matter is placed on a hot bed of fuel, the volatile matter is distilled off. In order that complete combustion of this gas may take place, sufficient air must be supplied and intimately mixed with the combustible gases. Furthermore, the combustion space must be of sufficient size so that combustion can be completed before the gases come into contact with the relatively cold surfaces of the boiler. The air supply must not be so copious or at such a low temperature as to chill the mixture below the temperature required for combustion. These requirements are met by the STEAM BOILERS 73 use of various appliances and of furnaces of special design which will be discussed later. 65. Comparison of Different Fuels. — It might be reasonably assumed that from the standpoint of economy that coal is the most desirable which has the greatest calorific value per dollar of cost. This is not strictly true, however, as there are other factors which affect the actual economy. Moisture in the coal is undesirable, principally because of the fact that it absorbs heat when the coal is burned and passes up the stack as super- heated steam. An excessive amount of ash is objectionable be- cause the cost of its transportation from the mine must be paid and because of the trouble which it causes in the furnace. It obstructs the passage of air through the fuel bed and fuses together into clinkers which must be broken up and removed from the furnace. The formation of clinker is the most trouble- some when the ash is fusible at a comparatively low temperature and also is thought to be aided by the presence of sulphur. The latter should therefore not exceed 3^ per cent. Coals high in volatile matter are undesirable unless the fur- nace is designed to burn them, for reasons which have been previously stated. For the smaller sizes of coal and for coals which cake heavily a greater draft is necessary and if not avail- able the desired rate of combustion may be impossible of attain- ment. In general, the smaller sizes of coal cost less per heat unit because of the less demand for them. When purchased in large quantities the price of coal is often based upon the calorific value and ash content. This is a very desirable way to purchase coal. Where smokeless combustion is desirable or compulsory, an- thracite coal is perhaps the most suitable fuel. The facts that it is the cleanest coal to handle and that it requires little atten- tion render it especially desirable for domestic use. Coke is a very good fuel when the firepot of the boiler is of sufficient depth to hold a large quantity of it. Otherwise, a good fire cannot be maintained without more frequent attention than can conveniently be given. Semi-bituminous coals, such as "Poca- hontas" and "New River" are capable of being burned in an ordinary furnace with little smoke because of the small amount of volatile matter which they contain. The bituminous coals contain the greatest heat value per unit of cost, but have some marked disadvantages. Bituminous coal 74 HEATING AND VENTILATION is particularly dirty to handle, which is a strong argument against its use in residences. It is also difficult to burn it with- out smoke except in furnaces of special design, intelligently and carefully operated. With the increasing cost of coal and growing scarcity of anthracite, it is becoming more widely used, however, in all classes of work and many special furnaces are being developed for it. 66. Boilers. — Strictly speaking, a boiler is a vessel in which steam is generated by the application of heat. The furnace in which the heat is developed is often practically an integral part of the boiler, however, and the term "boiler" therefore often refers to the combination of boiler and furnace. The primary requirement in a boiler is that it be of sufficient strength to withstand the pressure which is to be carried in it. In boilers used for heating purposes only, this is comparatively simple as the pressure carried rarely exceeds 10 pounds. Secondly, the heating surface must be sufficient in proportion to the grate surface so that the heat will be largely removed from the flue gases before they leave the boiler; and the boiler should be so designed that the flue gases are made to impinge upon and rub along the heating surfaces to the greatest possible extent as this "scrubbing" action increases the rate of heat transfer. The boiler must be so designed that the water may circulate freely to the heating surfaces and the steam pass away from them without restriction. Also, the area of the surface of the water must be sufficient so that the bubbles of steam rising through the water can escape without excessively disturbing the water level. If the liberating surface is restricted or if the steam space is too small, there is a tendency for priming (i.e., the carrying of water into the steam pipes) to take place, particularly when the boiler is being forced. This consideration is more important in a low- pressure boiler than in a high-pressure boiler as the bubbles of steam have a greater volume at the lower pressure. In boilers used for heating purposes, it is desirable to have a large storage of water so that steam will be continuously generated in spite of slight variations in the condition of the fire. A very large volume of water is not desirable, however, when the boiler is operated intermittently as the entire mass of water must be heated when- ever the boiler is put into service. 67. Types of Boilers. — The most common type of boiler for Keating residences and small buildings is the round cast-iron STEAM BOILERS 75 boiler shown in Fig. 24. This type of boiler consists of from three to five main castings such as A, B, and C (Fig. 24). The castings are joined by the tapered nipples N, N, and are drawn and held together by vertical bolts. For a boiler of a given diameter, the amount of heating surface can be varied by the size or number of the intermediate sections such as B in the figure. It is reason- able to suppose that the "taller" boilers are somewhat the more efficient since the ratio of heating surface to grate area is the greater. Round boilers may be obtained having rated capacities up to about 1600 square feet of radiation. Fig. 24. — Round oast-iron boiler. Sectional oast-iron boiler. The "sectional" boiler, as shown in Fig. 25 is obtainable in rated capacities up to about 9000 square feet of radiation. It consists of from five to ten sections joined with nipples. In the larger sizes the sections are made in halves, the idea being to make the boiler capable of being easily transported and erected. One of the advantages of sectional boilers is the possibility of erecting them in an existing building without the necessity of cutting holes in the floor or walls. Steel boilers are frequently used for heating, particularly in large buildings. A common type is the return-tubular boiler illustrated in Fig. 26. The return-tubular boiler (so named 76 HEATING AND VENTILATION because the gases flow through the flues toward the front of the boiler) is desirable for heating purposes because of its large water storage, ample circulating areas, and large liberating Damper , tfti. q Iff" I Fig. 26. — Horizontal return-tubular boiler. surface. Another type of horizontal fire-tube boiler is the firebox boiler shown in Fig. 27. Boilers of this type in which the furnace is incorporated with the boiler are known as portable boilers as Fig. 27. — Firebox boiler. distinguished from brick-set boilers of which that in Fig. 26 is an example. Steel boilers of the return-tubular and firebox types are suitable for working pressures up to 100 pounds. The marine-type boiler shown in Fig. 28 can be used for higher pressures as the fire does not touch the outer shell. Water-tube boilers, in which STEAM BOILERS 77 the water circulates through the tubes and the flue gases over the outside of them, are used for capacities of over 150 horsepower and for high-pressure work. Uptake Fig. 28. — Marine-type boiler. 68. Grates. — For heating boilers the grates are usually of the shaking type, consisting of a number of toothed bars as shown in Fig. 29, having a bearing at either end and connected to a rocking link. The free area through the grate is about 50 per cent, of the gross area and the width of the openings varies from %6 to M inch, depending upon the size of fuel to be used. In large steel boilers the grates are often stationary and the ashes are removed through the firing door. 69. The Downdraft Boiler. — Owing to the difficulty of burning bituminous coal without smoke in the ordinary boiler, many boilers have been designed with special furnaces for this purpose, chief among which is the downdraft boiler illustrated in Fig. 30. The furnace consists of two separate grates placed one above the other. Coal is fed to the upper grate only and the air, instead of passing upward through the fuel bed as in the ordi- nary furnace, enters at the top and passes downward through it. Combustion is most active at the bottom of the fuel bed, and to prevent it from being burned out, the grate is made of hollow bars Fig. 29. — Shaking grate bar. 78 HEATING AND VENTILATION through which the water in the boiler circulates. The volatile matter is freed from the coal on the top of the fuel bed and passes down through the incandescent fuel where most of it is ignited. The lower grate contains an incandescent fuel bed consisting of small pieces of coke from which the gases have been driven and which have fallen down through the bars of the upper grate. In the hot combustion chamber between the grates the gases de- scending from the upper fuel bed mingle with the hot air which enters through the lower grate and complete and smokeless com- bustion takes place. In addition to the important feature of burning any grade of coal without smoke and with complete combustion of the volatile Fig. 30. — Sectional downdraft boiler. matter, the downdraft furnace has other advantages. No trouble is experienced from clinkers, if the boiler is properly fired, and the performance is uniform as there are no cleaning periods to disturb the fuel bed. In firing a downdraft furnace, it is important that the main fuel bed be not seriously disturbed. It should be frequently sliced, but just sufficiently to crack the caked mass of fuel so that air can find its way through it. No green coal should ever be fed to the lower grate; it should contain only such material as falls through from the upper grate. The main air supply of course enters through the firing door of the upper grate and the fire is controlled by the regulation of this air opening. The one STEAM BOILERS 79 great disadvantage of the downdraft furnace is the necessity for fairly careful firing, without which the smokeless feature is lost. If green coal is shovelled on the lower grate, if the lower grate is not properly covered, or if the upper fuel bed is violently dis- turbed by poking, much smoke will be formed. Any of these things are very liable to be done by a careless attendant. 70. Other Special Furnaces. — Another means of promoting the thorough mixing and combustion of the air and volatile matter necessary for smokelessness is by the use of some form of brick ignition arch or wall. In the boiler shown in Fig. 31 the gases are made to pass from the fuel bed into the "mixing" Combustion Chamber .Mixing Chamber Fig. 31. — Smokeless boiler with brick ignition wall. chamber and thence through the vertical slot in the ignition wall to the combustion chamber. The ignition wall becomes highly heated and serves to assist in the ignition of the gases, the narrow slot causing a thorough intermingling of the gases and air. The air supply enters principally through the fuel bed and an auxiliary air supply is provided above the fuel bed. With a boiler of this type, some smoke is unavoidable during the firing periods when the doors are open, admitting great volumes of cold air and when the green coal thrown upon the fire is giving off a large amount of hydrocarbon gases. For the greater part of the time, however, smokeless combustion is obtained. 80 HEATING AND VENTILATION Other devices for the prevention of smoke consist of ignition arches of various designs, and of steam jets directed into the furnace so as to cause a thorough mixing of the air and gases. An interesting type of special boiler which is coming into wider use is the magazine-feed type designed primarily for burn- ing the small sizes of anthracite coal and coke. These fuels cannot be burned successfully in an ordinary boiler because of the difficulty of getting air through a fuel bed of any considerable thickness, while a thin fuel bed requires very frequent firing. Fig. 32. — Magazine feed boiler. With the magazine feed such as illustrated in Fig. 32 the fresh fuel is fed by gravity as required and the fuel bed is at all times sufficiently thin to allow air to pass through it. The magazine holds sufficient fuel so that the boiler needs attention only at much less frequent intervals than does the ordinary boiler. 71. Proportions of Boilers. — The heating surfaces in a boiler are defined as those surfaces which have water on one side and hot gases on the other side. In order that the boiler may be efficient the ratio of heating surface to grate surface should be large. The ratio is limited, however, by such factors as the cost 182 HEATING AND VE. of buildings. For buildings such as theatres and schools, it is customary to provide a certain volume of air per minute for each occupant. For rooms where the number of occupants is vari- able or where there is pollution from sources other than respira- tion, sufficient fresh air is provided to renew that in the room a certain number of times per hour. For ordinary conditions of temperature and humidity, Table XXXIX gives the usual practice as to the amount supplied. 167. Methods of Measuring Air Supply. — When the air enters a room through but one or two ducts, the quantity can be directly measured by a pitot tube or anemometer, the use of which will be discussed in Chapter XV. Another method which in many cases is more convenient is based on the measurement of the carbon dioxide content of the air combined with our knowledge of the rate at which the carbon dioxide is added by the exhalation from the occupants. Let V = volume of air admitted to the room in cubic feet per hour. a = volume of CO2 contained in a unit volume of the air admitted. r-i = amount of C0 2 per unit volume of air in the room at the beginning of the test. r 2 = amount of C0 2 per unit volume of air in the room at the end of the test. r = amount of CO2 per unit volume of air in the room at any time during the test. R = volume of room in cubic feet, c = amount of CO2 produced in the room, in cubic feet per hour. t = time of experiment in hours. During any small period of time dt, the amount of air enter- ing the room is Vdt and the amount of CO2 contained in the entering air is aVdt. The amount of C0 2 produced during the time dt is cdt. During the same interval, an equal volume Vdt leaves the room through the exhaust flues and its CO2 content is rVdt. The net increase in the volume of CO2 in the room is then (aV + c)dt - rVdt = (aV - rV + c) dt Let the increase in the CO2 content of the air in the room per r ujiy j ±uxx 7I0N 183 cubic foot during the interval di be represented by dr. Then the total net increase is Rdr. Equating the two Rdr = (aV - rV + c)dt (1) and dt = . — r w (2) (aV + c) — Vr dr = B\ - Jn a V + c-Vr I 7 * 2 1 t = R\ = log, (aV + c - Vr) R , Wi - aV - c t= V l ° S °Vr 2 -aV-c V = 2.303 7 log 10 Vr2 _ aV _ c (3) If r-i = r 2 , which means that there is no increase in the C0 2 content of the air in the room, then the amount entering the room, plus the amount produced must equal the amount leaving the room, or aV + c= Vr 2 from which V = and r 2 = rx = a + y> (4) r 2 — a V lie = 0, then from (3) V = 2.303 f \og 10 r -^^ (5) t r 2 a Equation (4) is applied practically by assuming a certain production of C0 2 per hour per person, which figure is usually taken as 0.6 cubic foot. Equation (4) then becomes in which C.F.H. = cubic feet of air per hour supplied to the room per occupant. C0 2 = carbon dioxide content of the room air in parts per 10,000. x = carbon dioxide content of the outside air in parts per 10,000. . This formula is recommended by Dr. E. V. Hill and is used by the Health Department of the City of Chicago. The chart in STEAM BOILERS 83 A steam pressure gage similar to that in Fig. 35 is also required. To facilitate the control of the drafts and to maintain an even steam pressure some form of damper regulator operated by the pressure in the boiler is very desirable. The form shown in Fig. 36 consists of a corrugated metal bellows which expands under pressure, closing the ashpjt damper and opening the check damper in the flue by means of chains or rods connected to the lever. The pres- sure at which the action takes Pig. 34. — Water column. Fig. 35. — Steam pressure gage. place depends upon the location of the weight on the lever arm. 74. Draft and Chimney Construction. — In order to maintain combustion in a furnace a continuous supply of air must be moved Fig. 36. — Damper regulator. through the fuel bed. In the ordinary heating boiler, the air is drawn through by means of a chimney, which also serves to dispose of the smoke and other products of combustion. The chimney produces a "draft" or movement of the air because of the difference in weight between the column of hot gases in 84 HEATING AND VENTILATION the chimney and the cold outside air. The intensity of the force produced depends upon the average difference in temperature be- tween the hot gases in the stack and the outside air and upon the height of the stack. This force must be sufficient to move the required amount of air and gases through the boiler and stack against the frictional resistances interposed by the various obstructions. These resistances consist of (a) the resistance of the fuel bed, (6) the resistance of the flues of the boiler, (c) the resistance of the damper and breeching, and (d) the resistance of the stack itself. The first three items are fixed by the kind of fuel used and by the design of the boiler. The last item depends upon the height, cross-section, and construction of the stack. If the cross-sectional area of the stack is too small, the friction in the stack itself will be great and the sum of the various re- sistance factors may be greater than the available draft produced by the stack. Increasing the area of the stack results in a re- duction of its frictional resistance and therefore in an increase in the net amount of draft available at the foot of the stack for overcoming the boiler and breeching losses. Increasing the height of the stack obviously increases the available draft. Table XXIII. — Size op Chimney Flues Direct radiation Height of chimney flue (feet) Diameter of chimney flue (inches) Steam in square feet Water in square feet 30 ft. 40 ft. 50 ft. 60 ft. 80 ft. 250 500 750 1,000 1,500 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 375 750 1,150 1,500 2,250 3,000 4,500 6,000 7,500 9,000 10,500 12,000 13,500 15,000 7.0 9.2 10.8 12.0 14.4 16.3 18.5 22.2 24.6 26.8 28.8 30.6 32.4 34.0 6.7 8.8 10.2 11.4 13.4 15.2 18.2 20.8 23.0 25.0 27.0 28.6 30.4 32.0 6.4 8.2 9.6 10.8 12.8 14.5 17.2 19.6 21.6 23.4 25.5 26.8 28.4 30.0 6.2 8.0 9.3 10.5 12.4 14.0 16.6 19.0 21.0 22.8 24.4 26.0 27.4 28.6 6.0 6.6 8.8 10.0 11.5 13.2 15.8 17.8 19.4 21.2 23.0 24.2 . 25.6 27.0 The dimensions of a chimney can be computed from a consider- ation of the principles stated above, 1 but for ordinary cases 1 For methods of chimney design see Gebhakdt, "Steam Power Plants." STEAM BOILERS 85 they can be determined by empirical rules. Table XXIII by Prof. R. C. Carpenter gives the dimensions of chimneys for various amounts of steam or water radiation. If the flue is square, the sides should be equal in length to the diameter for a round flue given in the table, it being assumed that the corners of a square flue are not effective. The available draft of such chimneys, as measured with an ordinary draft gage, should approximate the values given in Table XXIV. Table XXIV. — Dkaft in Small Chimneys 1 Temperature of chimney gases, deg. F Height in feet 200 250 300 Draft — inches of water 60 0.27 0.32 0.35 55 0.25 0.29 0.32 50 0.23 0.26 0.29 45 0.21 0.23 0.26 40 0.18 0.21 0.23 35 0.16 0.19 0.20 30 0.14 0.16 0.17 ,25] 0.12 0.14 0.14 20 0.09 0.11 0.12 In measuring the available draft the gage should be connected to the breeching on the chimney side of the damper. The fire should be regulated so that the temperature of the stack gases will approximate working conditions and the damper should be quickly closed immediately before the reading is taken. A chimney must be so constructed that the wind, deflected by surrounding buildings, will not blow down into it and thus im- pede the draft. An illustration of two common sources of trouble is given in Fig. 37. The wind striking the sloping roof is de- flected over the peak and down into the chimney. The chimney should be extended well above the top of all adjacent buildings. The round flue is the most effective per square foot of area but is somewhat difficult to construct. For small buildings a square or rectangular flue is used. It should be lined with tile and should be smooth and free from leaks. Offsets should always be avoided, if possible, and when unavoidable should 1 From "Chimneys: Their Design and Construction," by Harold L. Alt, Heating & Ventilating Magazine, March, 1917. 86 HEATING AND VENTILATION be made with gradual bends. No other openings of any sort should be made in the flue to which the boiler is connected. In large buildings the stack is often constructed of steel, lined with brick. Fig. 37.- -Effect of wind on chimneys of insufficient height, proper construction. Dotted lines show 75. Hot-water Heaters. — For hot-water systems the heater used is very similar to the steam boiler. In cast-iron water heaters of both the round and sectional type a smaller casting is substituted for the steam dome. For large buildings ordinary steel boilers are often used, although in many cases the water is heated by the exhaust steam from generating units in some form of "surface" heater. The water column, safety valve, and pressure gage are of course omitted from a water heater. PROBLEMS 1. A boiler evaporates 1749 pounds of water per hour from a tempera- ture of 180° into steam at 10 pounds gage pressue and 98 per cent, quality. What is the equivalent evaporation "from and at" 212°, and what boiler horsepower is developed? 2. A boiler containing 820 square feet of heating surface evaporates 2600 pounds of water per hour, from a temperature, of 190° into steam at 50 pounds gage pressure and 97 per cent, quality. What per cent, of rating is developed? CHAPTER VII' STEAM HEATING SYSTEMS 76. Class'fication of Systems. — In a steam heating system the piping and radiators must be arranged with a view to perform- ing successfully three functions : (1) the conveying of steam to the radiators, (2) the removal of air from the radiators, and (3) the draining off of the condensation from the radiators. The many types of steam heating systems in use differ from one another mainly in the manner in which these operations are accomplished. It is the purpose of this chapter to discuss these various types and their relative merits for different classes of buildings. Steam heating systems may be divided roughly into two gen- eral classes according to the manner in which the connections are made to the radiators. In the single-pipe systems the steam is conveyed to the radiator through a pipe which enters the radiator at the bottom of one of the end sections. The con- densation which forms in the radiator flows back through this same pipe. In the two-pipe systems a separate system of piping is provided to carry away the condensation, and in some cases the air, from the radiators. 77. Single-pipe System. — The simplest form of single-pipe system is that shown in Fig. 38. The nearly horizontal pipes leaving the boiler are called the steam mains. The vertical pipes extending to the upper floors are called risers. Steam is generated in the boiler and flows through the mains and risers into the radiators, forcing the air out ahead of it through some kind of an air valve on the end of the radiator opposite the sup- ply connection. In the system shown in Fig. 38 the condensation formed in the radiators drains down the risers into the mains and back to the boiler. The direction of the flow of the condensation is thus opposite to the direction of the steam flow. In the risers this is not objectionable if the system is small. In the mains, however, the water and steam flowing in opposite directions are very liable to interfere with each other, unless the mains are of such a diameter that the steam will travel at a very low velocity. 87 88 HEATING AND VENTILATION If the pipes are small so that such interference takes place the water is picked up by the steam and driven to the end of the main with a characteristic loud cracking noise known as "water- hammer." A better design of a single-pipe system is shown in Fig. 39. The main pitches away from the boiler and the condensation Fig. 38. — Single-pipe system — mains pitching toward boiler. entering the main from the risers flows along with the steam. The main circles the basement and a drip connection carries the condensation from the end of it to the boiler, entering below the water line. This is the most common form of single-pipe system. Fig. 39. — Single-pipe system — mains pitching away from boiler. Another form of single-pipe system is the single-pipe re- lief system shown in Fig. 40. The connections to the risers are taken from the bottom of the main and a drip connec- tion is taken from the foot of each riser to a "wet" return main, so called because it is below the water line of the boiler. The STEAM HEATING SYSTEMS 89 advantage of this method is that no condensation from the radia- tors is carried by the main. It also has the advantage of allow- ing the main to be placed close to the basement ceiling, which is desirable if the basement is used for any purpose for which full head room is desired. This system is sometimes referred to as a two-pipe system because of its return main. It will be noted, however, that there is only one connection to each radiator, as in the other single-pipe systems. The single-pipe system is simple in design and can be installed at a low cost. It is especially suitable for residences and small buildings where a low-priced system is desired. In large build- ings, however, a single-pipe system is less desirable, on account of the large quantities of water which must be carried in the steam o Of Of c~> D Q GL a. Fig. 40. — Single-pipe relief system. mains and risers. Another objection is the trouble .which is sometimes experienced due to the radiators not draining properly. If the inlet valve is not closed tightly when the radiator is shut off, or if the valve leaks, some steam will continue to flow into the radiator and because of the small area of the opening it is impossible for the condensation to drain out against the inflowing steam. As a result the radiator becomes partly filled with water and when the valve is again opened an annoying cracking and pounding takes place as the water pours out against the inrushing steam. 78. Two-pipe Systems. — -Fig. 41 shows a typical two-pipe dry return system. As the term indicates, the return mains are above the water line of the boiler and are filled with steam. The supply mains and risers are installed and connections taken from them to each radiator in much the same manner as in the 90 HEATING AND VENTILATION single-pipe system. A "return" connection is made from each radiator to the return main, through which the condensation from the radiator flows. As the steam has a free passage through the radiator from the supply main to the return main, it is evident that the latter will be filled with steam at a pressure approaching that in the supply mains, a slight pressure drop taking place through the radiator and its connections. The end of each supply main is dripped into the return main through a 4 or 5-foot seal as at b,b, which serves to prevent the full steam pressure from entering the return main. One of the chief faults of the two- pipe, dry return system is the tendency for the steam to enter the radiator through the return connection, especially if the fit -Efcfi Q a a E3 Fie. 41. — Two-pipe dry return system. return valve is opened first when turning on the radiator, and thus trap air in the center of the radiator. In the "wet return" system this trouble is eliminated. The return main is below the water line of the boiler and separate connections are made to it from each radiator and from the low points in the supply mains. A wet return system is shown in Fig. 42. It is evident that no steam can enter the radiator through the return connection, as the lower end of each connection is sealed with water. The water level in the return pipes is sometimes con- siderably higher than that in the boiler, as will be evident upon consideration of Fig. 42. If the pressure on the surface of the water in the boiler is the same as that on the surface of the water in the return lines, then the water levels will be the same. But if a pressure of 2 pounds, for example, exists in the boiler and there is a drop due to friction, of }i pound along the main, then the water at (6) will rise to a height sufficient to balance the drop STEAM HEATING SYSTEMS 91 between the boiler and the point (&). It is necessary, therefore, to use pipes sufficiently large so that the pressure drop will not be excessive; and futhermore, no radiators should be located less than 2 feet above the water line of the boiler. The wet return system will usually operate with less noise than a dry Fig. 42. — Wet return system. return system as the condensation does not flow in horizontal pipes containing steam. A disadvantage of two-pipe systems is the cost of a double set of radiator valves, and the nuisance of having to operate both valves. Sometimes a check valve is used instead of a shutoff valve on the return end of the radiator. &L St J& £3 S-J3 s p U. Fig. 43. — Overhead distribution — single-pipe system. 79. Overhead System. 1 — In buildings over three or four stories high the overhead system illustrated in Fig. 43 is nearly always used. The main circles the attic and risers extend down from it to the basement, supplying the radiators on the successive 92 HEATING AND VENTILATION floors. The steam is carried to the attic main by a main riser from which no radiators are supplied. The chief advantage of the overhead system of distribution lies in the fact that the steam and condensation in the risers are both moving downward. Smaller risers can therefore be used without causing noise or interfering with the circulation of the system. The fact that the large piping is in the attic rather than the basement is also an advantage when the matter of head room and appearance in the basement is a consideration. The overhead method of distribution may be applied to either the single-pipe or two-pipe system. In the latter case, the return risers and the return main are arranged in the same manner as in the ordinary upfeed system. 80. Air-line Systems. — In the systems previously described, the air is discharged from the radiators through some kind of an air valve to the atmosphere. In order to force the air out of the radiators the steam must be at some pressure above atmosphere, and the temperature of the water in the boiler must be higher than 212°. Consequently, when the fire dies down or is banked at night, no steam is delivered to the radiators. Furthermore, when pressures only slightly above atmosphere exist in the boiler, the radiators near the boiler are wholly or partially filled with steam while those farthest from the boiler may be cold, resulting in an uneven heating of the building. Another objection to the ordinary means of air removal is the disagreeable odor of the air discharged and the noise and frequent leakage of steam and water which are characteristic of most ordinary air valves. To overcome these objections a system of air lines is sometimes provided to convey the air from all of the radiators to a pump or ejector located in the basement. In place of an ordinary air valve, an "air-line valve" is used, having a pipe connection on the discharge side, and designed to allow air to pass through it but to close against steam. By the suction of the pump or ejector a partial vacuum is maintained in the air-line system and as the steam output of the boiler falls off the vacuum extends into the radiators, piping, and boiler. The boiling temperature is consequently reduced to the temperature corresponding to the existing pressure and the boiler continues to generate steam for a considerable time after the fire is banked. The circulation of the entire system is also improved and a more even heating is secured. In some cases no attempt is made to maintain a vacuum on the STEAM HEATING SYSTEMS 93 air lines and they are used only to eliminate the ordinary air- valve troubles. 81. Vapor Systems. — A form of two-pipe system having many desirable features is the vapor system, which with slight modifica- tions is also variously termed "vacuo-vapor, " "atmospheric," etc. These names are derived from the fact that such systems are intended to operate on pressures but little above, and in some cases below atmosphere. The essential features of vapor systems are: » I. The use of radiators of the hot-water type with supply valve at the top a"nd with return connection which carries off both the air and condensation. II. The use of a graduated supply valve by means of which the amount of steam admitted to the radiator can be controlled. III. Absence of steam in the return lines, which are either open to the atmosphere or under a pressure less than atmosphere. The arrangement of a radiator in a vapor system is shown in Fig. 44. By means of a graduated supply valve the steam supply can be controlled so that only the amount required to heat the room [f|=%H is admitted to the radiator. The steam flows into the successive sections of the radiator at the top and fills them through part or all of their length, depending upon the degree of valve opening, in the manner shown in Fig. 44. The surface of the part of the radiator which is filled with steam is at nearly the steam temperature. The remainder of the surface is warmed by the condensation which trickles down the inside sur- faces, the temperature decreasing toward the bottom. The temperature of the discharged condensation is thus materially lowered and in cases where the condensation is not returned to the boilers this is an advantage from an economic standpoint. An important characteristic of vapor systems is that there is normally no steam in the return lines. They carry both the air and condensation from the radiators and are often open to Fig. 44. — Radiator in a vapor system. 94 HEATING AND VENTILATION the atmosphere. The steam is prevented from flowing into the return line from the radiators by either of two means : (a) By some device such as a trap or an orifice installed on the return end of the radiator. (6) By limiting the maximum area of opening of the inlet valve so that at no time will more steam be supplied to the radiator than can be condensed in it. Fig. 45c. Various forms of thermostatic traps. 82. Radiator Traps. — In most vapor systems some kind of a trap is used. The most common is the thermostatic trap which is so constructed as to allow the comparatively cool air and STEAM HEATING SYSTEMS 95 condensation to pass but to close when the steam at higher temperatures reaches it. Several forms of thermostatic traps are illustrated in Figs. 45a, b, and c. All consist fundamentally of a thin-walled metal chamber A (Fig. 45c) containing a volatile liquid, such as alcohol, which vaporizes when heated and forms sufficient pressure inside the chamber, at a temperature of about 210°, to expand it and bring the valve B against the seat C. In operation the trap remains open while air and condensation pass through it but when steam reaches it and heats the thermo- static element it closes, and remains closed until condensation accumulating in it cools a few degrees, causing it to open again and discharge the condensation. i r i — i By-pass Fig. 46. — Radiator trap of float type. Outlet Another type of radiator trap is the float trap in which the open- ing and closing of the valve is dependent entirely upon the flow of condensation into the trap. A common form is that illus- trated in Fig. 46. The valve A is normally closed against the seat B and the air from the radiator is discharged through the passage C in the center of the float. When condensation has accumulated to a sufficient height in the body of the trap, it raises the float D, opening the valve and allowing the condensa- tion to flow out until the normal level is reached . The chief ob j ec- tion to float traps is that they are sometimes noisy in operation and are then a source of annoyance to the occupants of the room. Also, there is a tendency for some leakage of steam through the trap to take place. 96 HEATING AND VENTILATION 83. Retarders. — "While the thermostatic and float traps are designed to close positively against the steam, another type of return fitting is used which only restricts its passage, allowing a small amount to pass into the return line when the radiator is filled with steam. This is not objectionable as the leakage is usually so slight that it is condensed in the return lines. Retard- ers are usually in the form of an orifice as in Fig. 47. These fittings have the advantages of being of low cost, of simple construction, and of requiring no adjustment. For systems of moderate size they are quite satis- factory. If, however, the pressure regulation is such that a pressure ,. ,-= .,,, of over a few ounces may exist in the system there is a possibility of an excessive amount of steam leak- ing into the return lines, which is Fig. 47.-Retarder. Ver y Undesirable. Such fittings are often used in connection with a supply valve having a restricted opening such as those used in the atmospheric system described in the next paragraph. 84. Atmospheric Systems. — The primary function of the return fittings previously described is to prevent or restrict the leakage of steam into the return line. In the so-called atmos- pheric system this is accomplished in another way — by restricting the supply so that there will be no uncondensed steam to overflow into the return line. In such systems no special return fitting is provided and the return line is connected direct to the radiator. The maximum area of opening of the supply valve when in its wide open position is restricted by means of an orifice disc, for example, so that with an assumed pressure in the supply pipe ■ — usually about 5 ounces — only the amount of steam which the radiator will condense can enter it. It is evident that the amount of steam which will pass through the maximum opening of the supply valve will vary with the pressure in the supply pipe. Therefore any pressure less than that for which the system is designed will not cause sufficient steam to enter the radiator in the coldest weather. Any considerable increase in pressure above this amount will force more steam through the valve than the radiator will condense and the excess will enter the return piping. If the system has been carefully designed, so that at any one time nearly the same pressure exists at the supply connections of all the STEAM HEATING SYSTEMS 97 radiators, and if the pressure is closely regulated at the boiler, the atmospheric scheme is quite successful in systems of moderate size. When the water of condensation is not returned to the boiler, as often happens when steam is obtained from a central heating plant, it is always desirable to utilize the sensible heat in the condensation. Atmospheric systems accomplish this very effect- ively, the heat being removed as the condensation flows down the walls of a partly filled radiator and through the uncovered return pip- ing. In systems where the steam supply is restricted at the inlet valves the radiators are sometimes given from 10 to 20 per cent, more surface than is required, so that at no time will they be entirely filled and the lower portions are always available for removing the sensible heat of the condensa- tion. 85. Supply Valves. — The supply valves of vapor systems are of two classes — those which limit and those which do not limit the amount of steam which can enter the radiator when the valve is in the wide open position. In Fig. 48 is shown a valve of the Fig. 48. — Supply valve — maximum opening not restricted. Fig. 49. — Supply valve — maximum opening restricted. second type. The full opening can be obtained by a half turn of the lever handle and the degree of opening is always readily discernible. The valve can be partly opened according to the amount of heat required. Fig. 49 shows one form of valve 98 HEATING AND VENTILATION whose maximum opening may be restricted according to the size of the radiator on which it is to be used. The maximum movement of the handle is fixed by the stop (d) which is adjusted when the system is first put into service. 86. General Arrangement of Vapor Systems. — The arrange- ment of the supply and return piping of a vapor system is shown in Fig. 50. The air is forced out of the radiators by the entering steam and passes through the return piping to the air vent located near the boiler. The supply main pitches away from the boiler and is dripped at the end by means of a trap similar to those used, on the radiators or by a seal. Fig. 50. — Vapor system. 87. Removal of Air from Return Piping. — Many different methods are employed for venting the air from the return piping. The simplest arrangement is to leave the return line open at all times to the atmosphere; but to provide against leakage of steam in case of the failure of a radiator trap to close, a special vent valve is often provided which is normally open and closes only when steam reaches it. These vent valves are quite similar in principle to the ordinary thermostatic radiator trap. Float valves, or combination float and thermostatic valves, are fre- quently used, their function being to close when water reaches them and thus to guard against leakage in case of the accidental flooding of the return piping. Some vent valves include also a check-valve arrangement which allows air to escape from the system but prevents it from reenter- ing. The air is driven out of the system when the radiators and piping fill with steam; and as the steam output of the boiler de- creases, the pressure falls below atmosphere and the boiler con- STEAM HEATING SYSTEMS 99 tinues to generate steam after the temperature of the water in it has dropped below 212°, as is the case in a vacuum system. 88. Advantages of Vapor Systems. — It is apparent that for many classes of buildings vapor systems have some advantages over the other systems of heating, which may be summarized as follows : 1. Control of the Heat Supply. — This is accomplished by the manipulation of the supply valves and is therefore dependent for its effectiveness upon the attention of the occupants of the room. The improved design of inlet valve and its accessible location at the top of the radiator render it convenient to operate, but in many classes of buildings the occupants are not inclined to make use of this means of heat control. 2. Circulation on Very Low Pressures. — This is of some ad- vantage from the standpoint of economy, but is shared by the various kinds of vacuum systems. 3. Noiseless Operation.- — As the steam and water flow in sepa- rate systems of piping there is no opportunity for water-hammer. 4. Discharge of Air into the Basement Instead of into the Rooms.- — ■ This eliminates the noise, smell, and drip which accompany the action of the ordinary air valve. 5. Economy of Operation. — The opportunity afforded for accu- rate temperature regulation coupled with the possibility of cir- culation on very low pressures are productive of some economy. The measure of saving obtained, however, is rather uncertain. The disadvantages of vapor systems are the cost of the special fittings and appliances and the maintenance of the radiator traps. 89. Vacuum Return Line Systems. — In a "vacuum return line" system radiators of the hot water type may be used, the arrangement being similar to that of a vapor system, or steam radiation can be used with the inlet valve at the bottom. In either case some form of trap is provided on the radiators and a vacuum pump is connected to the return main. Various kinds of "exhausters" have been devised for use on vacuum return systems but the most satisfactory apparatus is a simple pump. If a high-pressure steam supply is available, a steam-driven pump exhausting into the heating system is the most economical as regards the energy consumed, but motor- driven pumps have the advantage of requiring much less atten- tion and maintenance. A simple plunger pump is shown in Fig. 51. Pumps of this type can be built to operate on steam 100 HEATING AND VENTILATION pressures as low as 10 pounds but this necessitates a very large steam cylinder. In general, unless steam of at least 25 pounds pressure is available, it is better to use a motor-driven pump. For the proper operation of a vacuum system it is essential that the traps on the radiators be in good condition and close tightly. If they do not close tightly a leakage of steam into the return pipes will occur which will make it very difficult to main- tain the vacuum. A water spray at the vacuum pump suction is often used to condense any steam which may be present, but the use of an excessive amount of spray water is a source of considerable loss, as the spray water must necessarily be wasted, carrying with it the latent heat of the steam which it has condensed. Fig. 51. — Steam-driven vacuum pump. One of the advantages of vacuum systems — the continued generation of steam at temperatures below 212° — has already been brought out (Par. 80). Another important advantage is the better circulation in both supply and return pipes produced by the greater pressure differential. If, for example, a vacuum system is operated with a steam pressure of 2 pounds and a vacuum of 10 inches of mercury, the total differential is about 7 pounds. A more rapid warming up of the system, better removal of air from the radiators, and better circulation in return lines having air or water pockets are other advantages which might be mentioned. In case some radiators are located, perforce, below the water line of the boiler a vacuum pump must be used to drain them properly. From the standpoint of STEAM HEATING SYSTEMS 101 economy vacuum systems are of some advantage because of the lower radiator temperatures which exist if a vacuum is carried on the entire system at times when less heat is needed. When exhaust steam is used for heating a vacuum system permits of a lower back pressure on the engines and turbines and therefore tends to better the economy of the plant. Vacuum systems are best suited to large buildings where the advantages to be gained will justify the initial cost and the operating cost of the special equipment. CHAPTER VIII PIPE, FITTINGS, VALVES, AND ACCESSORIES 90. Pipe. — The pipe used for the conveying of steam and water is made of either cast iron, wrought iron, or steel. Because of the low tensile strength of cast iron, pipe made of this material is suitable only for low pres ures, and must .have a relatively thick wall. Owing to its ability to withstand corrosion it is especially adaptable for use where it must be buried in soil. Cast-iron pipe is seldom used in heating work. The pipe ordinarily used in heating and power plants is made from wrought iron or mild steel Steel pipe is much more widely used than wrought iron pipe at the present time being somewhat lower n price and for many purposes equally as desirable as wrought-iron pipe. The pipe commonly furnished to the pur- chaser under the name of wrought-iron pipe is likely to be steel pipe,- so that if wrought-iron pipe is desired it must be clearly specified. It is rather difficult to distinguish between the two materials except by a chemical test. The threads cut upon steel pipe with an ordinary threading die are usually some- what the more ragged, however, and this affords a rough means of identification. Wrought-iron pipe is believed by many to be more resistant to corrosion than steel pipe, but the degree of superiority in this respect, if both kinds are well made, is problematical. In the manufacture of wrought pipe the strips of metal, cut to the proper width, are drawn through a bell to the cylindrical form and the edges welded together. In pipe of the smaller diameters a "butt" weld is used and in the larger sizes a "lap" weld. Wrought-iron and steel pipe are furnished in sizes ranging from % inch to 30 inches nominal diameter. In the sizes up to 14 inches the nominal diameters correspond approximately with the inside diameter of the pipe, while in the larger sizes the pipe is designated by its outside diameter. The nominal and actual dimensions of wrought-iron and steel pipe are given in Table 102 PIPE, FITTINGS, VALVES, AND ACCESSORIES 103 XXVI. Ordinarily it is not desirable to use the 3}4, 4J^> 7, 9, and 11-inch sizes unless necessary, as these are regarded as odd sizes and their use is being gradually discontinued. For working pressures of over 150 pounds "full-weight" pipe should be specified. Such pipe is selected as being of full card weight per running foot, while ordinary pipe varies somewhat from the standard weight because of slight variations in the thickness of Table XXVI. — Standaed Wrought Steam, Gas and Water Pipe Table of Standard Dimensions Diameter Circum- ference Transverse areas Length of pipe per square foot of exter- nal surface feet Length of pipe contain- ing 1 cubio foot, feet Nomi- nal weight per foot, plain ends Nomi- # nal inter- nal, inches Exter- nal, inches Ap- proxi- mate inter- nal diam., inches Exter- nal, inches Inter- nal, inches Exter- nal, square inches Inter- nal, square inches Number of threads per inch of screw H 0.405 0.269 1.272 0.845 0.129 0.057 9.431 2,533.775 0.244 27 H 0.540 0.364 1.696 1.144 0.229 0.104 7.073 1,383.789 0.424 18 n 0.675 0.493 2.121 1.549 0.358 0.191 5.658 754.360 0.567 18 H 0.840 0.622 ' 2.639 1.954 0.554 0.304 4.547 473.906 0.850 14 H 1.050 0.824 3.299 2.589 0.866 0.533 3.637 270.034 1.130 14 1 1.315 1.049 4.131 3.296 1.358 0.864 2.904 166.618 1.678 11H Hi 1.660 1.380 5.215 4.335 2.164 1.495 2.301 96.275 2.272 U)5 M 1.900 1.610 5.969 5.058 2.835 2.036 2.010 70.733 2.717 11W 2 2.375 2.067 7.461 6.494 4.430 3.355 1.608 42.913 3.652 11H 2H 2.875 2.469 9.032 7.757 6.492 4.788 1.328 30.077 5.793 8 3 3.500 3.068 10.996 9.638 9.621 7.393 1.091 19.479 7.575 8 3H 4.000 3.548 12.566 11.146 12.566 9.886 0.954 14.565 9.109 8 4 4.500 4.026 14.137 12.648 15.904 12.730 0.848 11.312 10.790 8 m 5.000 4.506 15.708 14.156 19.635 15.947 0.763 9.030 12.538 8 5 5.563 5.047 17.477 15.856 24.306 20.006 0.686 7.198 14.617 8 6 6.625 6.065 20.813 19.054 34.472 28.891 0.576 4.984 18.974 8 7 7.625 7.023 23.955 22.063 45.664 38.738 0.500 3.717 23.544 8 8 8.625 8.071 27.096 25.356 58.426 51.161 0.442 2.815 24.696 8 8 8.625 7.981 27.096 25.073 58.426 50.027 0.442 2.878 28.554 8 9 9.625 8.941 30.238 28.089 72.760 62.786 0.396 2.294 33.907 8 10 10.750 10.192 33.772 32.019 90.763 81.585 0.355 1.765 31.201 8 10 10.750 10.136 33.772 31.843 90.763 80.691 0.355 1.785 34.240 8 10 10.750 10.020 33.772 31.479 90.763 78.855 0.355 1.826 40.483 8 11 11.750 11.000 36.914 34.558 108.434 95.033 0.325 1.515 45.557 8 12 12.750 12.090 40.055 37.982 127.676 114.800 0.299 1.254 43.773 8 12 12.750 12.000 40.055 37.699 127.676 113.097 0.299 1.273 49.562 8 13 14.000 13.250 43.982 41.626 153.938 137.886 0.272 1.044 54.568 8 14 15.000 14.250 47.124 44.768 176.715 159.485 0.254 0.903 58.573 8 15 16.000 15.250 50.265 47.909 201.062 182.654 0.238 0.788 62.579 8 104 HEATING AND VENTILATION the sheets from which it is made. For extremely high pressures, "extra strong" and "double extra strong" pipe may be obtained. The extra thickness of the walls is added on the inside of the pipe, reducing the internal area and not affecting the outside diameter. These heavier grades are seldom used in heating work. 91. Pipe Threads. — In order that they may be screwed to a tight joint, pipe threads are made with a taper of 1 in 32 with the axis of the pipe, and the threads in the fittings are tapped to the same taper. Pipe threads are commonly made to conform to 90 Elbow Reducing Elbow Cross Reducing Coupling Plug Cap Bushing Close Nipple Fig. 52.- Y Bend Coupling Shoulder Nipple -Screwed fittings. the so-called Briggs standard which calls for a thread having a 60-degree angle, with the top and bottom slightly flattened. The number of threads per inch varies for the different sizes of pipe. 92. Screwed Fittings. — The common forms of screwed fittings used in heating work are shown in Fig. 52. All except the ordinary coupling are made of cast iron. In designating reducing tees the size of the openings opposite each other is given first and then the size of the branch opening. For example, the reducing tee in Fig. 52 is a l}i by 1 by ^-in'ch tee. For pressures over 125 pounds, an "extra heavy" pattern is PIPE, FITTINGS, VALVES, AND ACCESSORIES 105 available which is suitable for working pressures up to 250 pounds. Extra heavy fittings are made with a greater wall thickness and are of larger dimensions throughout. 93. Unions. — Where screwed fittings are used, provision should be made, at intervals in the line, for disconnecting the piping for repairs, etc. "Right and left" couplings or "unions" are used for this purpose. The former, as the name indicates, are couplings tapped at one end with a left-hand thread, so that both Lip Union Iron, and Brass Union Fig. 53. Iron Union with Brass Seat King -Pipe unions. threads can be screwed up simultaneously. Longitudinal ridges are cast on right and left couplings so that they can be identified after installation. For pipe sizes up to 2 inches, nut unions, consisting of two pieces screwed to the ends of the pipe and held together by means of a threaded nut are used. Flanged unions are used with larger sizes of pipe. In Fig. 53 are shown these various types of pipe connections. The ground-joint union is superior .Screwed Flange Welded Flange Fig. 54. — Various forms of flanges Improved Van Stone Flange to the gasket union in that it can be disconnected repeatedly without trouble, whereas the gasket in the latter type must be frequently replaced. 94. Flanged Fittings. — Piping of the larger sizes is usually designed with flanged connections, in order that any section of pipe or any fitting can be readily removed. With screwed fittings it is necessary, in order to remove any member, to take 106 HEATING AND VENTILATION down all of the line from the nearest union or flanged connection. Flanges are commonly screwed to the pipe, especially for low- pressure work. For high-pressure work they may be welded to the pipe or attached by the "Van Stone" method in which the pipe extends through the flange and is formed to a flat face as shown in Fig. 54. Some forms of standard weight flanged fittings are shown in Fig. 55. These fittings are suitable for pressures up to 125 pounds. There is an extra heavy pattern of flanges and flanged fittings which differ both in general dimensions and in the number and spacing of the bolts. 90 Elbow 45 Elbow Reducer Reducing Tee Tee Fig. 55. — Flanged fittings. 95. Gaskets. — In bolting together flanged fittings it is neces- sary to insert a gasket between the faces in order to insure a tight joint. Gaskets are made of sheet rubber for water and low-pressure steam lines; for high-pressure lines gaskets of corrugated copper or of various compositions containing asbestos are used. Gaskets are preferably cut in a plain ring to fit inside of the flange bolts. 96. Valves. — In Fig. 56 are shown the various types of valves. The gate valve is the form ordinarily used in steam piping. Globe valves are not permissible in horizontal steam lines as they are so constructed as to dam up the water and cause it to accumulate in the bottom of the pipe, but on vertical steam pipes and on PIPE, FITTINGS, VALVES, AND ACCESSORIES 107 water pipes they are permissible and are especially desirable when the flow of steam or water is to be throttled." The angle valve is a very good type of -valve for locations where it can be used. Iron body gate valve non-ris- ing stem. Iron body globe valve rising stem. Angle valve. All brass gate valve. All brass globe valve. Fig. 56. Swing cheek valve. Valves in sizes up to 3 inches are made entirely of brass and the larger sizes are usually made of cast iron, with the gates and seats faced with bronze to give a non-corroding surface. The bronze mountings can be replaced when worn. -The cover or 108 HEATING AND VENTILATION "bonnet" of these larger valves is bolted instead of screwed to the body. Gate valves are made either with a "rising" or "non-rising" stem. With a rising, stem valve the amount to which the valve is open is always apparent, which is often of great advantage but the space occupied by the valve is somewhat greater. Check valves are frequently used in heating work. The swing check illustrated in Fig. 56 is the most satisfactory form. 97. Radiator Valves. — The ordinary radiator valve for steam is of the angle pattern and is provided with a union for connecting to, the radiator, as shown in Fig. 57. The valve disc is made of Fig. 57. — Ordinary radiator valve. Fig. 58. — Packless valve. hard rubber and is renewable. These valves are also made in the "corner" pattern. The stem of the ordinary radiator valve is packed to prevent leakage with a soft stranded packing. The packing is seldom permanently tight, however, and the resulting leakage is often a source of considerable annoyance. In the more modern valves the packing is replaced by a grooved hard-rubber washer which is held against a seat by a spring. The construction of these so-called "packless" valves is shown in Fig. 58. Valves so con- structed are much superior to the ordinary type, as all leakage and the necessity of renewing the packing are eliminated. The ordinary steam-radiator valve may be used in hot-water work. A special hot-water valve is made, however, which PIPE, FITTINGS, VALVES, AND ACCESSORIES 109 consists of a sleeve having an orifice equal to the pipe area. By a half turn of the hand-wheel the sleeve is turned so that the orifice is brought opposite the opening to the radiator. When closed, the valve allows enough circulation through the radiator to prevent freezing. Fig. 59 shows a valve of this type. 98. Pipe Covering. — The piping of a heating system which is not intended to serve as radiating surface is insulated with some material of low heat conductivity. Most insulating materials owe their useful property to air enclosed in extremely small volumes. If the material is to be an efficient insulator these air volumes must be so minute that the circulation of the air in them is re- duced to a minimum and in addition, the material itself must be of low con- ductivity. A satisfactory pipe cover- ing must also be able to withstand the effect of high temperature and vibration, and to retain its insulating qualities throughout a long period of years. The material which is probably the most widely used as an insulator is magnesium carbonate. It is in the form of a white powder, and some fibrous material such as asbestos fibers must be used with it as a binder, the aggregate being molded into blocks or into segments curved to fit the various sizes of pipe. Infusorial earth, which consists of the siliceous shells of minute organisms, is also combined with various binding materials to form a very efficient covering. Many forms of pipe covering are made of asbestos in combina- tion with some cellular material. The compound is rolled into sheets and the covering built up in corrugations so as to enclose air spaces. While not the most efficient type, these coverings are often the most suitable because of their low price. Fig. 60 shows a covering of this type. Hair felt, composed of matted cattle hair, is very efficient but cannot be placed in direct contact with steam pipes owing to its tendency to char at steam temperatures. In the selection of a pipe covering the cost of the pipe covering Fig. 59.- -Hot water radiator valve. 110 HEATING AND VENTILATION should be balanced against the saving which is effected by the reduction of the heat loss from the piping. The most recent tests made on the commercial grades of pipe covering are those Fig. 60. — Cellular pipe covering. 0.95 p 0.90 a C 0.85 3 O H fe 0.80 B 0.70 c m u a 0.65 Return Main Fig. 86. — Drip connection to riser, vapor or vacuum system. Steam mains are dripped into the return line in a similar manner. Bypasses are sometimes provided for the most important traps to enable them to be easily cleaned or inspected and dirt strainers are also sometimes used. 114. Valves. — The location of valves in a heating system should be given careful consideration. While valves are desirable 128 HEATING AND VENTILATION in many locations, there are also some places where they should never be used unless the plant is in the hands of a competent engineer, because of the possibility of accidents resulting from ignorant handling of them. In a small system as few valves should be installed as possible. Indeed for residence systems it is seldom necessary to install any valves except at the radiators. Valves should never be installed on the steam outlet of the boiler or on the return connection unless the plant is under careful supervision or unless two boilers are used in parallel, in which case valves are necessary in order to enable one boiler to be cut out of service for repairs. In large buildings a valve should be provided on each riser, if possible, so that the riser can be shut off for repairs, etc., without necessitating the shutting down of the entire system. Valves should also be provided on each branch main and return line in such buildings. Gate or angle valves should be used in preference to globe valves. 115. Radiator Connections. — The connections to a radiator must be sufficiently flexible so that the main or riser is perfectly P Fig. 87. — Connection to first floor radiator. £. K —». Branch Exposed La Boom Below Fig. 88. — Connections from risers where vertical movement is small. free to expand without straining the fittings. They must also be designed to allow the radiator to drain properly and must be free from water pockets. Figs. 87, 88, and 89 show some proper methods of connecting radiators in a single-pipe system. That shown in Fig. 87 is used for first-floor radiators connected directly to the main. The connection in Fig. 88 is suitable for risers whose vertical movement is small enough to be absorbed by the spring of the horizontal pipe. An objection to this ar- STEAM PIPING 129 rangement is the fact that the connection is under the floor and inaccessible unless the horizontal branch is exposed in the room below as shown by the dotted lines. In the connection shown in n Fig. 89. — Flexible connection, plan view — used when riser has considerable vertical movement. Fig. 89 a radiator valve of the "corner" pattern is used and the use of the elbows gives a very flexible combination which is well Fig. 90. — Radiator connections — vapor system. suited for tall buildings where the movement of the risers is considerable. Wrong method. The connections to a radiator of a vapor system are shown in Fig. 90. These connections are also very flexible and the use of 45-degree elbows reduces the frictional resistance. In no case should a radiator be connected as in Fig. 91. The short, stiff connection allows no free vertical movement of the riser and causes severe strains on the fittings. 9 130 HEATING AND VENTILATION 116. Pipe Coils. — Pipe coils may be connected in the manner shown in Figs. 92a and 926. The arrangement in Fig. 92a is used for a two-pipe system and that in Fig. 926 for a single-pipe system. A return connection is always used on pipe coils be- cause of the difficulty of draining the large amount of condensa- Fig. 92a. Fig. 926. Methods ofconnecting pipe coils. tion formed in radiation of this type back through the inlet connection. The check valve in Fig. 926 prevents steam from entering the coil through the return connection. In order to open the check valve against the pressure of the steam in the riser a water head must be built up above it equivalent to the drop in pressure through the coil, which may be quite appreciable. Return Main Water Connection Blow-off Valve Fig. 93. — Boiler connections. Therefore, a short length of vertical pipe should be installed above the check valve as shown, to receive the water column which would otherwise occupy the lower part of the pipe coil. 117. Boiler Connections. — The usual method of arranging the connections to a steam boiler is shown in Fig. 93. In "i l\ o j \! .. < — \l « STEAM PIPING 131 addition to the supply and return connections there is re- quired a blowoff cock and a city water connection with a shutoff valve and a check valve. It is sometimes necessary to connect two boilers in parallel. This must be carefully done so that there will be no chance of either boiler losing water to the other. Connections of ample size between both steam and return connec- tions should be made so that the pressure and water levels in both boilers will be always the same. 118. Flow of Steam in Pipes. — When any fluid flows through a pipe a certain pressure is necessary to move it against the resistance caused by the friction of the fluid against the inner surface of the pipe. The following laws governing the friction of fluids in pipes have been established by experiment: 1. The total amount of frictional resistance is independent of the absolute pressure of the fluid against the pipe wall. 2. The frictional resistance varies nearly as the square of the Fig. 94. velocity. 3. The frictional resistance varies directly as the area of contact between the fluid and the pipe wall. 4. The frictional resistance varies directly as the density of the fluid. Consider a condition of steady flow in a pipe and let pi (Fig. 94) be the unit static pressure of the fluid, at one point and let p 2 be the pressure at another point at a distance L from the first. The drop in pressure due to the friction of the fluid in passing through the distance L is then P = Pi ~ P2 Expressing the laws of friction stated above in algebraic form we have Pa = FSDv 2 (1) in which P = drop in unit pressure in pounds per square foot. a = cross-sectional area of the pipe in square feet. F = a constant depending on the nature of the fluid and the nature of the pipe surface. S = area of contact between the fluid and the pipe in square feet. D = density of the fluid in pounds per cubic foot. v = velocity of the flow in feet per second. 132 HEATING AND VENTILATION Then P = -FSDv* (2) a f Let F be made arbitrarily = sr Then equation (2) becomes This is done simply to bring into the expression the ternr ^z which is the usual form for expressions of this nature. For round pipes of diameter d and length L, S = ird L and a = 4 ' ™ r, 4/LDu 2 ... Then P = i— (4) Let w = the weight of steam flowing in pounds per minute. Then m = ^ X»Xi)X60 = 47.12d 2 yD and „ = -^^ (5) P Let p be the pressure drop in pounds per square inch = j^~. and let di be the diameter in inches = 12d. Substituting in (4) these values for v, P and d we have V = 0.04839 £jg (6) The coefficient / was found by Unwin to be = K ( 1 + jtt-,) The value most commonly used for K for steam is that de- termined by Babcock which = 0.0027. Substituting in (6) we have p = 0,0001306 w 2 L (l + ^) (7) Ddi s in which p = pressure drop in pounds per square inch. w = weight of steam flowing in pounds per minute. L = length of pipe in feet. di = diameter a|^pipe in inches. D = average density of steam in pounds per cubic foot. STEAM PIPING 133 The value of the coefficient / given above has been found to be correct for small pipes and comparatively low velocities. For large pipes and high velocities the value of / is considerably lower. l 119. Factors Affecting the Size of Pipes. — The sizes of pipes to be used in a heating system depend upon several factors. The fundamental requirement as regards the supply pipes is that they must be of sufficient capacity to transmit the required quantities of steam with the pressure differential which is available. The latter depends somewhat upon the source of the steam supply. When exhaust steam from an engine or turbine is used for heating, it is best, from the standpoint of economy, to make possible the carrying of a low back-pressure by designing the heating system to operate with an initial pressure of not over 2 pounds per square inch. The same practice should usually be followed when steam is taken direct from a boiler, as it may be desired at some future time to use exhaust steam. The circulation will also be much better and the system more satisfactory if the pipe sizes are ample. When a vacuum pump is used the greater pressure differential thus set up makes possible the use of smaller pipes but it is well, nevertheless, to design the supply piping to operate as a gravity system with a moderate pressure drop so that the pump can be shut down at times if desired. The return pipes, however, can be made somewhat smaller if a vacuum pump is to be used. Another factor which makes an extreme reduction in the size of the supply pipes un- desirable is the noise caused by the resulting high velocity of the steam flowing through them. On the other hand, to make the pipes of excessive size increases unnecessarily the cost of the system. From a consideration of these various factors and of modern practice, a safe standard for the rate of pressure drop in the supply piping may be taken as from 0.03 to 0.10 pounds per 100 feet of pipe. There are other factors beside that of pressure drop which, affect the size of the supply pipes, such as the provision for the carrying of condensation. In general all steam pipes in which the con- densation drains in the opposite direction to the flow of steam should be larger than if both flow in the same direction. This 1 See "The Transmission of Steam in a Central Heating System" by J. H. Walker, Trans. A. S. H. & V. E., 1917. 134 HEATING AND VENTILATION applies particularly to single-pipe radiator connections and branches and to the risers of single-pipe systems. The proper size of return pipes is based upon experience and good practice as there is no definite law upon which their size can be computed. They must first of all be sufficiently large to carry the condensation. Second, they should be large enough so that they will not become plugged with dirt; and third, they must, in a vapor or vacuum system, be large enough to handle the air from the radiators as well as the condensation, when the radiators are first turned on. 120. Selection of Sizes of Supply Pipes. — In a large or impor- tant system it is very desirable to make a detailed calculation of the pressure drop through the system. Besides insuring ample pipe sizes this will enable the pipe sizes to be reduced in some cases below those which would be chosen arbitrarily. In a large build- ing a considerable saving may be effected by judiciously choosing the pipe sizes for the risers and mains. In a vapor system the ideal condition would be to have approximately the same pressure at all radiator valves. To accomplish this fully would be of course an impossibility, but such a condition can be approxi- mated by careful design. In selecting the pipe sizes by the "exact" method, the desired pressure drop through the system is chosen and the approximate average drop per unit length of pipe is found, after which the exact drop can be computed by means of formula (7), Par. 118. In order to facilitate the cal- culations, the logarithmic chart in Fig. 95 has been prepared, from which the pressure drop per 10 feet of pipe can be read directly. The chart is based on an average density of the steam corresponding to a pressure of 2 pounds gage, which is sufficiently accurate for the range of pressure which occurs in a heating system. In figuring the capacities of the pipes no allowance need be made for condensation in the pipes themselves as this will ordinarily be negligible if the pipes are covered, but if the pipes are to be left bare their radiating surface should be included with that of the radiators. The scales at the bottom of the sheet read directly in square feet of radiation having an assumed heat transmission of 245 B.t.u. per square foot per hour, which is the amount which would be transmitted from 38-inch, two- column radiation with a room temperature of 70° and a steam temperature corresponding to the pressure of 2 pounds. The scales at the top of the sheet read in B.t.u. delivered per hour, STEAM PIPING 135 and are convenient for use when the B.t.u. to be delivered by- each radiator is known. As an example of the use of the chart, consider a riser 218 feet long supplying 3000 square feet of radiation. If the drop through the riser is to be not more than 0.1 pound, find the proper pipe size. The drop of 0.1 pound in 218 feet is equivalent to a drop of 0.0046 pound in 10 feet. Passing vertically from the 3000-square feet point on the horizon- Use upper scale for pipe sizes 5 and over Heat Delivered per Hour Thousands of B.t.u. s. 2,000 3,000 4,000 6,000 -8,000 10,000 20,000 40,000 60.000 80,000100,000 200,000 20 30 40 SO 60 70 80 90100 200 300 400 500 600 800 1,000 2,000 ',' I ill I l* . i . I I I i I ■ 2 I I I I i I 'PRESSURE DROP IN STEAM PIPES Based on the Formula n - . 00 01306 w a J(l+M ) ZIZ. Steam Pressure 2 lbs.gage 7 Steam Temp. 218.5 deg. Heat Transmission of Kadiatiol .

n ■ + u D1 + D2 A ■ wn Ds + Di the water in BC is then = = and m EG = 2 2 Now consider the forces acting on each side of the plane A-A passed through the pipe GB. The pressure on the left side is evidently due to the column of water BC of density s~ — plus the column CJ of density D 5 which is h pl + Dl) +h > Dt The pressure on the right-hand side is evidently Adding these pressures algebraically, we obtain for the result- ant pressure tending to move A-A to the left A^-*^ 144 HEATING AND VENTILATION Let D , = * + *.,* ».-* + * Then the unit pressure p' available for producing circulation is p' = h(D R - D F ) (1) It is evident that this pressure is the same at any point in the circuit BCEGB. It is independent of the relative lateral positions of the radiator and the boiler and depends only on the height h and the densities D R and D F . It is customary to express this pressure as a "head," i.e., the height of a column of water of the same density as that in the system which will produce the given pressure at its base. Let D be the average density of the water and hi the head equivalent v' to the unit pressure p'; then p' = h x D and hi = jz- Sub- stituting in equation (1) we have , h(D R - D F ) hx = — d — r hi is then the head available for producing circulation. If D, D R , and D F are expressed in pounds per cubic foot and h in feet, then hi will be in feet of water column. To express the head in inches, which is a more convenient unit, the right-hand member is multi- plied by 12, and h> = m(Z Y ^ (2) The density D in equation (2) represents the average density of the water in the system. A close approximation would be to make D = D R + D F Substituting in (2) h! is then the available circulating head in inches of water. 128. Friction. — The general expression for the loss of pressure due to friction for fluids in round pipes according to equation (4), page 132, is P = W^? (4) d2g W HOT-WATER SYSTEMS 145 in which P = loss of pressure due to friction, pounds per square foot. / = a constant depending on the nature of the fluid and of the pipe wall. D = average density of the fluid, pounds per cubic foot. v = velocity, feet per second. d = pipe diameter, feet. g = acceleration of gravity = 32.2. L = length of pipe in feet. To express the frictional resistance in terms of fluid head, let P = h" D in which P is in pounds per square foot and D in pounds per cubic foot, h" being the equivalent head in feet of the fluid at density D. Substituting in (4) ^"-^ < 5 > Let P = 4/, then h" = P \ £- (6) a Ig Now if v is expressed in inches per second, and d in inches, the head h" will be expressed in inches of water, without any change in the form of the expression, the inch unit being the more convenient. Equation (6) gives the frictional resistance to flow through straight lengths of pipe only. The resistance due to elbows and other fittings must also be taken into account. The resistance of such obstructions has been found to be nearly proportional to the square of the velocity of flow, and may therefore be expressed in the form av 2 in which a is a constant to be determined. The summation of all such "single resistances" may then be expressed as v 2 s * h «) and the entire frictional resistance will be h "=4f g +^4 9 ® In order to impart to the mass of water in the system the 10 146 HEATING AND VENTILATION velocity v, a certain head must be used up in overcoming this v 2 "starting resistance" which is equal to ^—,' in which g', the acceleration of gravity, is expressed in inches per second per second so that this last term will be expressed in inches of water head as are the others. The complete expression for the head required to start and to maintain flow may then be written h" - L v2 _i_ t y2 m v * h ->d2} + * a 2} + W . In which h" is in inches of water head. d is in inches. L is in feet. v is in inches per second. g is in feet per second per second. g' is in inches per second per second. In considering only the force required to maintain a steady flow, the last term does not enter, however. 129. Condition of Steady Flow. — When the circulation in a heating . system has become constant, the head available for producing flow must be exactly equal to the frictional resistance. This condition must invariably be fulfilled. If the available head increases or decreases, the velocity will change also until it assumes such a value that the frictional resistance will equal the available head. The relation 1 may be expressed by equating the right-hand members of equations (3) and (8) 24h DV+D- F - p d2g + * a 2g (10) 130. Types of Gravity Systems. — Two-pipe Multiple-circuit System. — There are several different ways of arranging the piping in a gravity system. The most common method for installations of moderate size is the tworpipe multiple-circuit system shown in Fig. 99. The water leaves the boiler through the flow main, passes through the radiators and into the return main. A single pair of mains may be installed to circle the basement, but a better method is to install two or more pairs which extend in different directions. In order to insure a 1 For further discussion see "Heating and Ventilation" $>y A. H. Barker, to whom the foregoing analysis is due. HOT-WATER SYSTEMS 147 sufficient flow of water to each radiator, it is best to provide sepa- rate supply and return risers to each radiator from the mains. Both the supply and return mains are given a pitch toward the boiler of about % inch in 10 feet, so that no air will accumulate in the piping and so that the system can be drained at the boiler. Two-pipe systems are often installed with a "reversed" return main, as shown in Fig. 100. The flow in the return main is in the same direction as in the supply main and is so arranged that the length of the circuit through each radiator is the same. This tends to equalize the resistance to flow through all the radiators and the system therefore operates more uniformly throughout. D .ft jQ D ^ a &Jg R__R { 1=1 Fig. 99. — Two pipe multiple circuit system. Fig. 100. — Reversed return. A modification of the two-pipe system was formerly used, in which separate supply and return pipes were provided for each radiator. Although such an arrangement gives good results, the complication and cost of the piping have rendered it prac- tically obsolete. 131. Expansion Tank. — The change of volume of the water in a hot-water system under varying temperatures is quite appreciable and an expansion tank must always be provided. The tank is located well above the highest radiator in the system and is provided with a vent and an overflow to the sewer, as illustrated in Fig. 101. If located in an unheated room, a connection should be made to it from both supply and return mains to insure sufficient circulation to prevent freezing. If possible, the connection to the tank should be taken from the supply main as near the boiler as possible so that the air which is liberated from any fresh water which is fed to the boiler will rise 148 HEATING AND VENTILATION to the expansion tank and escape rather than accumulate in the radiators. The required capacity of the expansion tank is evidently a function of the quantity of water in the system and may be de- termined by computing the volumetric expansion, for the maxi- mum temperature range, of the es- timated quantity of water in the system. A rough rule is to make the capacity of the expansion tank in gallons equal to the radiation in square feet divided by 40. Overflow and Vent 2* .14 .12 .10 .08 .06 .04 .02 140° 150° 160° 170° 180° 190° 200° 210° 220° .Temperature -of Flow Fig. 108. above the boiler. The height h should be taken from a point midway between the flow and return connections of the boiler. If both of the radiator connections are at the bottom, the distance h is measured to the connections. If the inlet connection is at the top, the height h is usually measured to a point located at a distance above the bottom connection equal to one-fourth the height of the radiator. */ <« $/ o / A ?/ vy r /o 70 oo 50 40 -fi- -"'f-^ -~~h- -!-->■ :::7E -y— /—, L - J "oL ^ m f" : "/^=7 fczZ z__ —f - l V &3>. 1 ^7 - ^ ,7- ^:^ /- -/ -V- 2*2; 'W -?- ?~^ s ^ y— Z-7-- y ^vj ?'w ■*^ /'\. / * v -~y " ^ / / __J^ ?*, >/ -/- ft -?£ A/ , Q'j — /- -^ Ar — ^ ^ % t ~k' ^ a / / ? v - / ■'*>■ v > v / / v ^ / ^y ■ *>Mr ?>/ i * / / f^i - "/- / "" zs&f »»" i „/ , -L I z^ . / "•>r b---- j. lZ i ~t / "*- i V _,^ 7- / <>c ~^ A* / .- _ ^ ?v / y / f / 1 7 /- .' "V v y / ;( ' / / -*hU zz-A 7f / / v • ¥ ■^ L_y_ -t / v $*•&/- i ? IS* "■j, 4 '■ 1 — y~r "-V - -/ —j / ' 7^ ^ : ^Jr«- ' 1 1 / -^y 1 / 7 _) *> <%L 7"-/ / -; A -z / I_ 1^ /-7- /'•' / nL / l joss of Head by Fricti for Water in Iron Pipes Temp. 160Deg.F. Based on the Formula K d 217 in which P = .01439 + -=2595 V V as given .by Weisbach mi i 1 I i i i i i m ~^zzt '-::;L :,z.. / ^ ^./ f 7 ■J—/- EKF -7^ /-?- -■/- ZZ i T / s .7 ?:;v / 1 / v - U , -/- t - t ?:::3 ^ ; /-*^f / ~7__ 1 Z l / " V / / / /^ \L- J. - /.- / t - / I 7 ' / /' / / / / ~7T ' / 1 Z> w to ■* 000 soo 1,000 o o pT uantlty = = § of Wate o o c FlowJ o ng-Pc a o oesc o « not unds pel II 1 58 § Hour 200,000 300,000 400,000 500,000 600,000 Fig. 109. plify the determination of frictional resistance under various con- ditions of flow, the chart in Fig. 109 has been constructed, based on Weisbach's value for p. 1 Having given the weight of water 1 The results of later researches, not fully confirmed, indicate that the Weisbach coefficient is somewhat high and also somewhat in error in that it does not take into account any variation of the friction with the pipe diam- eter. However, the results obtained from its use are sure to be on the safe 154 HEATING AND VENTILATION flowing and the pipe size, the resistance in inches of water can readily be taken from the chart. For the computation of the resistance of the fittings or "single resistances," it is very convenient to consider that the resistance so introduced is equal to that of a certain length of pipe of the same diameter. Approximate determinations of the value of a indicate that at the average velocities occurring in heating work, the length of pipe in feet equivalent to a 90-degree elbow is equal to twice the number of inches diameter of the pipe. For example, a 3-inch elbow is equivalent in resistance to 6 feet of 3-inch pipe. Values for the various single resistance are given in Table XXXI. Table XXXI. — Values of Single Resistances Equivalent length in feet equals diameter in inches multiplied by 90-degree elbow 2 90-degree elbow — long sweep 45-degree elbow Radiator 1 1 4* Boiler 4* Valve lto2 * Diameter of pipe connections. The procedure in calculating the pipe sizes according to the accurate method is then as follows: The piping is completely laid out according to the system chosen, i.e., whether overhead or with basement mains, etc. The circuit supplying the most unfavorably situated radiator is the first to be considered. The pipes in this circuit are assigned tentative sizes and the single resistances noted and the equivalent lengths obtained from Table XXXI. The total equivalent length of each section of the cir- cuit is then computed and the friction drop taken from the curves in Fig. 109. The available circulating head must next be corn- side and it has been used in the design of many successful installations. For further discussion see : "The Determination of Pipe Sizes for Hot Water Heating Systems," by F. E. Geisecke, Trans. A. S. H. & V. E., 1915. "The Friction of Water in Iron Pipes and Elbows," by F. E. Geisecke, Trans. A. S. H. & V. E., 1917. "The Mechanics of Heating and Ventilat- ing," by Konrad Meier. "Heating and Ventilating" by A. H. Barker. HOT-WATER SYSTEMS 155 puted. From the curves in Fig. 108, the value of 24 -pr — - , n is found for the flow and return temperatures which have been assumed. This value, multiplied by the height in feet of the radiator Under consideration, above the boiler, gives the circulat- ing head in inches of water. If the friction head does not agree within about 5 per cent, with the circulating head, as it probably will not in the first calculation, the size of some of the pipes in the circuit must be changed and the total friction drop again computed. By successive refinements the two quantities can be made nearly equal. This circuit having been established, the circuits to the other radiators are worked out in a similar manner, the parts in common with the circuit first computed being left as first set down. In the case of a single-pipe system, the cir- culation to the most unfavorably situated riser is first computed, with the circulating head taken as that due to the riser. 138. Necessity of Accurately Choosing the Pipe Sizes. — Let us examine the effect of an improper selection of pipe sizes. There are three possible ways in which errors can be made. I. By making all the parts of the system too small but of the proper relative size. II. By making all of the pipes too large. III. By making the resistance of some circuits much greater than that in the others. If the pipe sizes are all too small, the primary effect will be to decrease the quantity of water passed through the entire system in unit time. If the temperature of the water leaving the boiler is kept constant, the effect of the decrease in the quantity will be to increase the temperature drop in the radiators. This will increase the available circulating head which will in turn increase the velocity of flow. Unless the error is extreme, ijhe system will therefore approach the performance set for it. If the pipes are. too large throughout, the primary effect will be to increase the flow of water through the system. This will cause a decrease in the temperature drop through the radiators, a reduc- tion in the circulating head, and a consequent reduction of the flow to some value approaching the proper one. The same action takes place in the case of the individual circuits or radiators. If the pipes are too small, the reduction in flow causes an increase in the temperature drop and- the net result is usually but a slight decrease in the heat delivered to the room. 156 HEATING AND VENTILATION It is thus apparent that gravity hot-water systems are to some extent self -regulating. It is due to this property that the ordinary hot-water systems, installed without exact design, operate with satisfaction. Indeed, for the usual small system it is not practi- cable to make exact calculations of the pipe sizes, experience having evolved "rules of thumb" which give pipe sizes which are on the safe side and produce entirely acceptable results. While the heat delivered to the rooms may vary by several per cent, from the theoretical requirements, the error is well within that due to inaccuracies in computing the heat losses from the room. In large installations, the exact method has some distinct advantages. The liberality with which the pipe sizes of a small system are selected cannot be practised on a large system without a considerable increase in the cost of the installation, while any pipes which may be chosen too small can be replaced only at great expense. Throttling valves, while they should be placed on the branch circuits as a precaution, are difficult to adjust and are easily tampered with. A calculation of the pipe sizes in the manner outlined is therefore desirable for large or important installations. 139. Approximate Rules for Pipe Sizes. — Table XXXII gives the capacity of mains of various pipe sizes for different kinds of systems. Table XXXII. — Size op Mains Assumed Length 100 Feet, Temperature Drop in Radiators 20° Capacity, square feet of direct radiation Pipe diam. Two-pipe upfeed One-pipe upfeed Overhead m 75 45 130 IX 110 65 190 2 200 121 340 w 310 190 530 3 540 330 920 SX 780 470 1,330 4 1,100 650 1,800 5 1,900 1,100 3,200 6 3,000 1,800 5,000 7 4,300 2,700 7,200 8 5,900 3,500 9,900 Table XXXIII gives the capacity of risers in square feet of radiation. HOT-WATER SYSTEMS Table XXXIII. — Size of Risers Assumed Temperature Drop in Radiators, 20° 157 Pipe size Upfeed Downfeed risers, not exceeding four floors First floor Second floor Third floor Fourth floor 1 33 46 57 64 48 m 71 104 124 142 112 m 100 • 140 175 200 160 2 187 262 325 375 300 2K 292 410 492 580 471 3 500 755 875 1,000 810 The following schedule of tappings is used for hot-water radiators : Table XXXIV. — Radiator Tappings Size of radiator Supply and return tappings Up to 40 square feet 1 inch 40 to 72 square feet \\i inches Over 72 square feet IK inches 140. Piping. — Many of the principles governing the design of steam piping apply to hot-water work. Expansion must be provided for with care, although it is less in amount. Connec- tions and fittings must be installed so as to interpose as little resistance to flow as possible. The venting of the air from the system is important. In addition to a vent at the expansion tank, a small pet-cock should be provided at each radiator and at any other points at which air may accumulate. Mains should be given a pitch of at least }4, i nc h in 10 feet toward the boiler and provision should be made for draining the water from the entire system as is necessary when the plant is shut down in cold weather. 141. Closed Systems. — In the open-tank systems which have been described, the water temperature is limited to 212° because the pressure at the top of the system is at atmosphere; but if the pressure of the water at the top of the system is raised above atmosphere, its boiling point and consequently the allowable temperature is raised, increasing the heat output of the system For maintaining the increased pressure on the system, some device such as a mercury seal is inserted in the pipe leading to the expansion tank. One form of these so-called "generators" is 158 HEATING AND VENTILATION shown in Fig. 110. The water from the system, as its tempera- ture rises, exerts an increasing pressure on the surface of the mercury in the chamber B, forcing mercury up the tube A until it bubbles out of the top of the tube. A pressure equivalent to the height of the mercury column thus formed may be built up at the top of the system and the water may be heated nearly to the corresponding boiling point. As the water in the system cools and decreases in volume, the mercury falls down the tube and more water enters the system from the expansion tank. To Expansion Tank Fig. 110. — Mercury seal "generator." Generators are especially useful for increasing the output of a heating system which has been inadequately designed or which has become inadequate. 142. Forced Circulation. — When hot-water heating is used in large buildings or groups of buildings, the circulating power is ob- tained from a pump and smaller pipes are used, the water flowing at much higher velocities than in a gravity system. In systems employing forced circulation, the water usually passes through the pump, then to the heater, and to the radiators. The piping is arranged in the same general manner as in the gravity systems. The action is somewhat different from that in the gravity systems HOT WATER SYSTEMS 159 in that the force producing circulation is from the pump and not from the cooling action of the radiators; for although the tempera- ture difference in the system has some effect, it is so far over- balanced by the force exerted by the pump as to be negligible. The flow through the various parts of the system is therefore governed to a greater extent by the frictional resistance, as the system does not possess the self-regulating qualities of the gravity system. 143. Pumpage, Friction, and Temperature Drop. — The quan- tity of heat delivered per hour may be expressed by the equation H = Q (h- t 2 ) (1) in which H = quantity of heat delivered per hour. Q = weight of water pumped per hour. h — t 2 = drop in temperature of water. It is evident that the quantity of water and the temperature drop may vary, the requirement being that their product remain constant. As the temperature drop is increased, however, the average temperature of the radiators is lowered and somewhat more surface must be installed. It is common practice to allow a temperature drop under maximum conditions of about 20°. Before a circulating pump can be intelligently selected, it is necessary to choose the differential pressure at which the system is to be operated. If a large pressure drop is allowed, the pipes can be made relatively small, but the power required for pumping the water will be greater. Although it is true that the energy used up in friction is converted into heat and is therefore utilized, the energy thus recovered is only a portion of the energy input to the pumping unit. The cost of the power must therefore be taken into consideration. If the pump is steam-driven and the exhaust used for heating the water, the cost of power will be lower than if current is purchased for a motor-driven pump. In each case a study should be made, balancing the annual invest- ment charges of the piping system against the cost of power to determine the most economical combination. The pressure drop usually allowed is from 10 to 30 pounds. The velocity of flow in the pipes is limited to about 40 inches per second in build- ings where the noise produced by a higher velocity would be objectionable. In industrial buildings, no such limit is imposed. 144. Calculation of Pipe Sizes. — The calculation of the pipe sizes in a forced circulation system is much more im- 160 HEATING AND VENTILATION portant than in a gravity system, because the former does not possess the "self -regulating" property of the gravity system. If any one circuit is unfavorably designed, there will be a tendency for it to be short-circuited. Furthermore, the resistance of the entire system must be made approximately equal to the rated head of the pump. The procedure in designing a forced cir- culation system is as follows. The heat loss from the building having been computed, the temperature drop in the radiators is chosen and the amount of water to be supplied per hour is com- 3 til.SCO Lbs.per Hr. 4 Fig. 111. puted from formula (1), Par. 143. From a consideration of the various factors mentioned in the preceding paragraph, the dif- ferential head is chosen and a pump is selected which will operate most efficiently under the given conditions. The piping must then be designed so that this differential pressure is used up in friction. The general scheme followed in choosing the pipe sizes is similar to that used for a gravity system, the available circulating head, which in this case is produced by the pump, being balanced by the pipe friction. HOT-WATER 'SYSTEMS 161 The method can best be explained by working out a specific installation. In Fig. Ill is shown diagrammatically one part of an overhead two-pipe system. The weight of water flowing per hour is indicated for the circuit which supplies the radiator marked 30-41, the assumption being made that these water quantities have been computed in the manner previously ex- plained. The circuit through this radiator is the longest and should therefore be computed first and the other parallel circuits designed to give the same resistance. In column 2, Table XXXV, the actual length of each section of the circuit is given. The system will be designed on a basis of a pressure differential of 10 pounds. The length of the circuit is 481 feet. The average Table XXXV. — Calculation of Pipe Sizes — Forced Circulation System a o O 31 U a a 3 55 1-3 M 14-, O o ft 3-B-S 3 O 0J e 03 '■V 13 OJ O a o t. Ph J3 M '3 u CO "o SI 3 a m oj CJ O 03 -p 'ta oj u 0J "Si a in a > -P r-H M a c t£ Eh O 0) rH ft ft O .s* CO 0J OJ m OJ CJ a 03 -p CO 'ta 0> Is o E-i OJ a 'S .s a E o3 09 d) © "to 0) N 03 % a OJ > '3 o 1 « S 1 -p 3 O OJ O 4) ,-h a k'S. 0Jm_ P.O 5| _(/:" 'co oj OJ S P3"— QJ a ' n o H 1 2 3 4 5 6 7 8 9 10 11 12 13 1-2 2-3 3-4 4-5 5-6 6-30 30-41 41-42 42-13 43-44 44-45 45-46 46-47 47-48 48-49 49-50 50-51 51-52 52-53 53-54 54-29 29-55 106,470 106,470 91,260 76,050 60,840 15,210 1,667 1,667 3,000 4,333 5,667 7,000 8,333 9,667 11,000 12,333 13,667 15,210 60,840 76,150 91,360 106,470 Total. . . 4 4 3 3 3 2 1 1 1 1 IK m IK m m IK VA 2 3 3 3 4 21 158 22 22 22 10 8 12 12 12 12 12 12 12 12 12 12 3 22 22 22 29 1X8 3 X S 1 X 4 2X2 1 X 4 3X8 29 182 22 22 22 14 12 12 12 12 12 12 12 12 12 12 12 7 22 22 22 53 4.0 4.0 9.4 6.8 4.6 2.4 0.9 0.9 2.8 5.2 2.7 3.9 5.3 3.3 4.1 4.9 5.9 2.4 4.6 6.8 9.4 4.0 11.6 72.8 20.7 15.0 10.1 3.4 1.1 1.1 3.4 6.2 3.2 4.7 6.4 4.0 4.9 5.9 7.1 1.7 10.1 15.0 20.7 20.2 249.3 8.8 2H 2H t X 3 22 13 22 9.0 7.5 9.0 19.8 9.8 19.8 275.1 Pounds 9.7 11 162 HEATING AND VENTILATION friction loss per 10 feet of pipe in inches of water column at a 10 X 1728 temperature of 160° will be . fi - = 5.9 inches of water. With the given quantities of water flowing, and using a friction loss of approximately 5.9 inches per 10 feet, the pipe sizes can be chosen from the chart in Fig. 109, page 153. They are set down in column 3. The length equivalent to the single resist- ances is computed and the total equivalent lengths set down in column 6. From the friction chart the resistance per 10 feet for each section is found. These are multiplied by the equiva- lent lengths and the results set down in column 8. The sum of all of them is found to be 249.3 inches of water which is equal to 8.8 pounds as against the 10 pounds originally specified. The sections 5-6, 6-30, and 52-53 may be decreased one pipe size to increase the resistance, as given in columns 9 to 13. The total resistance will then be 275.1 inches or 9.7 pounds which is sufficiently close to the desired resistance. The circuit 2-3-5- 53-29-55 and all of the remaining circuits must then be worked out in a similar manner to give an equal resistance, the parts which have already been computed being left as they stand. It is desirable to install a "lock and shield" valve on each riser and at each radiator in order that the distribution can be ad- justed after the system is completed. 145. Pumps. — Either the centrifugal or the reciprocating pump may be used to produce the circulation; but the centrifugal type is by far the more suitable. It possesses the advantages of pro- ducing a uniform flow of water, does not transmit jars or vibration to the piping, requires little attendance, and is economical in operation. Centrifugal pumps may be driven by either a steam turbine or a motor, the former drive being used when high-pres- sure steam is available. CHAPTER XI AUTOMATIC TEMPERATURE CONTROL 146. Manual Control. — In every heating system the radiators, boiler, and other component parts are selected on the basis of the maximum requirements, i.e., for the lowest outside temperature which is to be expected. Consequently the capacity of the sys- tem is much greater than is required in average winter weather. In many localities, for example, where heating plants are de- signed for a minimum outside temperature of 0°, the average temperature for the heating season is from 35° to 40°. In order to prevent excessive room temperatures the heat output of the system must be regulated, either manually or automatically, to correspond approximately with the heat losses from the building. Temperature control is accomplished in different ways accord- ing to the kind of heating system and the nature of the building. In many cases manual control of the radiators or of the furnace drafts is all that is necessary; in other cases, automatic tem- perature control, applied to the individual radiators, is very de- sirable. In hot-air furnace installations and in small steam and hot-water systems the universal method is to regulate the heat output of the boiler or furnace by adjusting the drafts. When the building is large, however, it is often impossible to regulate accurately the temperature throughout the building by this means and control of the radiators must be resorted to. In vapor systems equipped with graduated inlet valves accurate control is possible if sufficient attention is given by the occupants of the room to the adjustment of the valves. In single-pipe steam systems the supply of steam. to each radiator cannot be controlled and it is therefore sometimes desirable to provide at least two radiators in each room so that one or both can be used as required. In a vacuum steam system the heat output can be varied within certain limits by varying the steam pressure. For example, if the -steam pressure could be varied from 10 inches of vacuum to 10 163 164 HEATING AND VENTILATION Fig. 112.— Bellows thermostat. pounds pressure, the temperature of the radiating surfaces would be increased from 193.2° to 240.1°, which, if the room temperature is 70°, would give a range of heat output of about 38 per cent. This is about the maximum range which could be secured by this means. 147. Automatic Control Applied to Boiler or Furnace. — Tem- perature control by adjusting the drafts of the boiler or furnace can be accomplished automatically by means of any one of several designs of thermostats. The simplest of these con- sists of a bellows containing a volatile liquid which causes an expansion and con- traction of the bellows with changes of temperature. The bellows is installed at the point from which the temperature is to be controlled and its movement is trans- mitted by means of a cable to the dampers on the boiler or fur- nace in such a way that a lowering of the room temperature causes an increase in the air supply to the fuel bed and a result- ing increase in the heat output. This form of thermostat is shown in Fig. 112. In another form of thermostat the dampers are operated by a motor located in the basement and started electrically from a controller placed in the room above. Fig. 113 illustrates the controller of such a thermostat. The member A consists of two strips of metals, having different coefficients of expansion, brazed together. This member is fixed at point B and the end C is deflected to the right or left by the unequal expansion of the metals with changes of tempera- ture. The controller is connected electrically with the motor in such a way that, as the temperature drops and the strip C makes a contact with D, a current of low voltage is transmitted through the circuit, and, by means of a relay, starts the motor, which opens the drafts on the boiler. Similarly, a slight increase Fig. 113. — Controller for damper thermostat. AUTOMATIC TEMPERATURE CONTROL 165 of temperature above the established point causes a contact to be made between C and E and the motor is started, closing the drafts. The temperature for which the controller is set can be changed by moving the knob F which shifts the position of D and E. The controller can be obtained with a clock mechanism which will cause the drafts to close at night and to open in the early morning at some predetermined time. The motor may be a clock mechanism, in which the energy is obtained from a spring which is wound periodically by hand. "Wire Fig. 114. — Method of connecting thermostat. The electric motor is more desirable, however, as it requires no winding. The method of connecting the motor to the dampers is shown in Fig. 114. In installing this form of thermostat the location of the con- troller is of prime importance. As the heat supply for the entire building is to be controlled from one point, it is essential that the controller be installed in some central location where the tem- perature is approximately an average of that in the entire building. It is the difficulty of controlling the temperature satisfactorily from a single point that limits the use of such thermostats to residences and small buildings. 166 HEATING AND VENTILATION Air Inlet 148. Automatic Control Applied to Individual Radiators. — In large buildings, in order to regulate the temperature auto- matically, the radiators in the various rooms must be operated as separate units, by means of a controller located in each room. The power for operating the radiator valves is obtained from compressed air, supplied from a central source, and the air sup- ply to the individual radiator valves is regulated by a small valve operated by the expansion element in the controller. The system may be designed so that the radiator valves are either fully open or fully closed, or the amount of opening may be graduated according to the room temperature. The former arrangement is necessary on single-pipe radiators and is known as the "positive" type, while the latter or "graduated" type is applicable to steam radiators having a separate re- turn connection and to hot-water radiators. The type of radiator valve used is shown in Fig. 115. The valve is closed when air under sufficient pressure is admitted above the diaphragm A. When the air pressure is released the springs BB force the valve open. If a pressure less than that re- , . quired to close the valve exists above the valve for compressed air diaphragm the valve will take an inter - system of temperature me diate position depending on the amount regulation. of that pressure. In the graduated system the intermediate positions of the radiator valve are obtained by creating this partial pressure. A common design of compressed-air thermostat of the gradu- ated type is shown in Fig. 116. The thermostatic element is the hard-rubber cylinder A. The valve G is closed while the room temperature is up to normal and the full air pressure is transmitted through the inlet C, the restricting valve S, and the outlet D to the diaphragm chamber in the radiator valve, keeping the valve closed. When the tube A contracts, due to a lowering of the room temperature, a downward force is exerted on the rod K and the block L, moving the valve lever to the right against the pressure of the spring N, and opening the valve G slightly. Because of the restricted passage at S the air pressure in the passage Y and in the diaphragm chamber of the radiator valve, is lowered, allowing the latter to open and to admit some AUTOMATIC TEMPERATURE CONTROL 167 steam to the radiator. A further contraction of the tube A causes a further lowering of the air pressure at Y and an increase in the opening of the radiator valve. A thermostat of the posi- tive type is so constructed that an opening of the valve corre- sponding to G causes a complete reduction of the pressure at Y, allowing the radiator valve to open wide. 149. Compressors. — The air supply is obtained from a small compressor, usually motor-driven, located in the basement. A storage tank is required and a constant pressure is maintained in the tank by means of a governor which automatically starts jS ^|6a |7D| 7zl74^ Fig. 116. — Compressed air thermostat-graduated type. carried and stops the compressor, as required. The pressure on the tank is usually about 25 pounds per square inch. The mixing dampers and the heating coils of a fan system can be readily controlled by thermostats, through the use of a dia- phragm motor as shown in Fig. 117. The control of humidity is also possible by the use of similar devices. These applications will be considered more fully under "Fan Systems." 150. Advantages of Automatic Control.— The advisability of installing a system of thermostatic control depends largely upon the type of building under consideration. The principal advan- 168 HEATING AND VENTILATION tages of thermostatic control are the convenience and the in- creased comfort which it affords the occupants. Without any manipulation of the radiator valves, the temperature of the rooms is maintained at the most comfortable point, regardless of the outside temperature. In many cases a considerable saving in fuel can be effected by the use of automatic control, due to the fact that with manual control there is always a tendency for the rooms to become overheated through lack of attention to the radiator valves. This may be true even when graduated valves or other means of facilitating hand control are provided. The Fig. 117. — Diaphragm motor. actual amount of the saving in fuel is problematical, being given by many as from 10 to 30 per cent. In the average case it is probable that the lower figure is the more nearly correct. The objections to the compressed-air systems of thermostatic control are the rather high initial cost of the apparatus and the cost of maintaining and of keeping in adjustment the various parts of the system. Thermostatic control is especially desirable for hotels, schools, office buildings, and other buildings of a public character. For fan systems, automatic control of the dampers and coils is very much to be desired, and in most cases is abso- lutely necessary if satisfactory results are to be obtained. CHAPTER XII AIR AND ITS PROPERTIES 151. Composition of Air. — -The atmosphere of the earth is a mixture of several gases and vapors, the proportions of which vary somewhat in different localities and under different weather conditions. In general the proportions of nitrogen and oxygen, the two most important constituents of dry air, are approxi- mately as follows: By weight By volume Nitrogen 76.9 79.1 Oxygen 23.1 20.9 Carbon dioxide and water vapor are also contained in air in varying amounts and there are in addition small quantities of other gases, such as argon, ozone, and neon, which are of less importance. Air is not a chemical combination but is a mechan- ical mixture of these gases. 152. Oxygen. — Oxygen, (0), which constitutes about one-fifth of the air by volume, is the element upon which animal life is dependent for its existence. In the process of respiration the lungs draw in and expel periodically a small quantity of air and a portion of the oxygen unites chemically, while in the lungs, with impurities of the blood, and thereby cleanses it. Some of the resulting products of this chemical reaction are exhaled in the form of gases and vapors. Our health and bodily comfort are dependent upon the proper performance of this process. 153. Nitrogen. — Nitrogen, (N), which constitutes nearly all of the remaining four-fifths of the air by volume, is a relatively inert gas. It performs the important function of diluting the oxygen. As the human body is organized this dilution is essen- tial; an atmosphere of pure oxygen would soon burn up and destroy the body tissues. 154. Carbon Dioxide. — Carbon dioxide, (C0 2 ), exists in small amounts in the open air, the purest air containing from 3 to 4 parts of C0 2 by volume in 10,000. Carbon dioxide is also known as car- bonic acid gas, as it forms a weak acid when dissolved in water. 169 170 HEATING AND VENTILATION Being one of the products of respiration it is found in larger quantities in the air of occupied rooms. Carbon dioxide was for a long time believed to have a poisonous effect when taken into the lungs, but is now known to be quite harmless, of itself, even in appreciable amounts. It has the effect, however, of diluting the oxygen content of the air. This necessitates an increase in the rate of breathing and under extreme conditions causes great discomfort. Haldane and Priestly found that with 2 per cent, of CO2 the lung action was increased 50 per cent.; with 3 per cent, of C0 2 about 100 per cent.; with 4 per cent, of C0 2 about 200 per cent. ; and with 6 per cent, of C0 2 about 500 per cent. With 6 per cent, breathing becomes very difficult, while with more than 10 per cent, there occurs a loss of con- sciousness, but no immediate danger to life. Exposure to an atmosphere containing even 25 per cent, of C0 2 does not result in immediate death. Being a product of respiration the amount of C0 2 present in the atmosphere of a room is an indication of the amount of air being supplied to the room. The measurement of the C0 2 content of air is therefore of importance in ventilating work. There are several methods of measurement in use, the most accurate of which is that devised by Petterson and Palmquist. The apparatus is provided with a graduated chamber into which a sample of air is drawn and measured. It is then made to flow into a burette containing a saturated solution of caustic potash which absorbs the C0 2 . The air is then forced back to the measuring chamber and the decrease in volume noted. The apparatus is calibrated to read directly in parts per 10,000. Another method sometimes used is that of Wolpert. A solu- tion of sodium carbonate of known concentration is made up and a small quantity of phenolphthalein indicator is mixed with it. A suitable piston arrangement is used to force a known volume of the air to be analyzed into contact with the solution and the apparatus is shaken to promote the reaction between the acid CO2 and the alkaline solution. The process is repeated several times until the original pink color of the solution dis- appears. The number of charges of air necessary to cause the color change gives an indication of its C0 2 content. 155. Water Vapor. — Water vapor is an important constituent of the atmosphere. It is the most variable in quantity of , any of the atmospheric elements, its amount depending largely AIR AND ITS PROPERTIES 171 on the weather conditions. In the northern part of the United States the range of the moisture content of the atmosphere is very great. In New York, for example, it varies at different times from 0.5 grain to 7 grains per cubic foot. Water vapor, strictly speaking, is nothing other than steam at very low pressures, and its properties are similar to those of steam. This fact should always be -borne in mind when dealing with the subject of atmos- pheric moisture. Another conception that should be thoroughly understood is that of Dalton's law of partial pressures. Accord- ing to this law, in any mechanical mixture of gases, each gas has a partial pressure of its own which is entirely independent of the partial pressures of the other gases. For example, consider a cubic foot of hydrogen gas at an absolute pressure of 5 pounds per square inch. If a cubic foot of nitrogen at an initial pressure of 10 pounds per square inch be injected into the same space, the resulting total pressure will be 15 pounds per square inch and the volume 1 cubic foot. In air, therefore, the oxygen, nitrogen, water vapor, and other gases each have their own partial pressure, the sum of all of them being equal to the total or barometric pressure. For every temperature there is a corresponding partial pres- sure of water vapor at which the vapor is in a saturated state, its condition then being exactly similar to that of saturated steam, i.e., with the maximum number of molecules occupying a unit space. When the water vapor is in a saturated condition the air is also spoken of as being saturated since it then contains the maximum weight of vapor which it can hold at that temperature. If the temperature of the air is higher than that corresponding to the partial pressure of the water vapor, the vapor is superheated ; if the temperature drops below the saturation point some of the vapor is condensed and the vapor pressure is lowered to that corresponding to the new temperature. The saturation tem- perature is termed the dew point. The partial pressure of satu- rated vapor increases as the temperature increases. Conse- quently air at higher temperatures is capable of holding a greater weight of water per cubic foot. It should be remembered that the water vapor exists independently of the air except for the tem- perature effect of the latter; and the vapor may be thought of as occupying the given volume at its own partial pressure. The state of intimate mixture of the air and vapor causes their tem- peratures to be always the same. 172 HEATING AND VENTILATION 156. Relative and Absolute Humidity.- — Atmospheric mois- ture is termed humidity. Absolute humidity is the actual vapor content expressed in grains per cubic foot or per pound of air. The ratio of the vapor content to the vapor content of saturated air at the same temperature, expressed in per cent., is called the relative humidity. For example, given a sam- ple of air at 70° having an absolute humidity of 4 grains per cubic foot. Since saturated air at 70° contains 8 grains per cubic foot, the relative humidity is 50 per cent. 157. Total Heat of Air.— The total heat above 0° of air containing aqueous vapor is the sum of the heat of the air and the heat of the vapor. The latter has three components: the heat of the liquid, the heat of vaporization, and the superheat. In dealing with air containing vapor it is often convenient to use the units of weight instead of volume as a basis for calculations. The total heat above 0° in 1 pound of dry air at temperature t a is equal to H = C va (ta ~ 0) in which t a is the air temperature and C pa = 0.2415, the specific heat of air at constant pressure. Let W w = the weight of water vapor contained in 1 pound of a mixture of air and water vapor. Then for saturated atmosphere H = (1 - W w ) X C pa (t a - 0) + W a (h' + r) in which h! = heat of the liquid above 0° for the water vapor. r = latent heat of the water vapor. For atmosphere below saturation at temperature t a H = (1-TT„) X C pa (t a - 0) + W w {h' + r + C' ps (t a - t d )) in which t d is the temperature at the dew point and C' p , is the specific heat of water vapor at constant pressure. 158. Adiabatic Saturation. — When air below saturation is brought into intimate contact with water there is always a tendency for some of the water to vaporize, adding to the mois- ture content of the air. If no heat is added from an outside source and none removed, the heat of vaporization for the mois- ture which is added will be supplied entirely at the expense of the heat of the air and of the superheat of the original quantity of water vapor. The process will continue until the saturation point is reached. A process of this nature taking place without AIR AND ITS PROPERTIES 173 a transfer of heat to or from an outside source is called adiabatic and the final temperature which is reached is therefore termed the temperature of adiabatic saturation. Its depression below the original temperature of the air will depend upon the amount of moisture which was added to bring the air to saturation. The heat used in the vaporization of the moisture which was added is exactly equal to the heat given up by the air and by the water vapor which it contained originally, assuming that the water which was added was at the temperature of adiabatic saturation. The action may be expressed algebraically as follows: 1 Let t = temperature of the air. t' = temperature of adiabatic saturation. W = weight of water vapor mixed with 1 pound of dry air at saturation at temperature t'. W = weight of water vapor mixed with 1 pound dry air at temperature t. W — W = weight of water added per pound of dry air. r = latent heat of vaporization at temperature t. C P s = specific heat of water vapor at constant pressure. C V a = specific heat of dry air at constant pressure. (W - W)r = C ps W (t - t') + C pa (t - t') (1) W= r + CUt - F) (2) 159. Measurement of Humidity. — The principle stated in the preceding paragraph affords a convenient means for measuring humidity, through the use of the wet- and dry-bulb thermometer. The instrument consists of two mercury ther- mometers, the bulb of one of which is covered with cotton wick- ing. The end of the wicking extends into a bottle of water and the entire length is kept wet by absorption. As the water is evaporated from the wicking its temperature is lowered to the temperature of adiabatic saturation or "wet-bulb" temperature. By reading both thermometers when they have reached a con- stant point the wet-bulb depression is obtained and the moisture content of the air (W) can be found from equation (2), Par. 158. Distinction should be drawn between the wet-bulb temperature and the dew point, which was defined in Par. 155. The former 1 From "Rational Psychrometric Formula" W. H. Carrier, Trans. A. S. M. E., 1911. 174 HEATING AND VENTILATION temperature is produced by adding moisture to the air and causing its temperature to drop by reason of the giving up of heat to vaporize the water. The dew point, on the other hand, is reached by removing heat from the air without changing its moisture content. In order to obtain accurate results it is necessary that the air surrounding the wet-bulb thermometer be in motion so that the maximum evaporation may be secured. For this reason the best form of wet- and dry-bulb thermometer is the "sling psy chrome ter" illustrated in Fig. 118. In this instrument the wet- and dry-bulb thermometers are mounted on a metal strip pivotted to a handle. In using the instrument the wick surrounding the wet bulb is moistened and the instrument is whirled rapidly and read at intervals until there is no further drop in the wet-bulb tem- perature. Somewhat more accurate results are obtained with the "aspira- tion" psychrometer in which a con- tinuous current of air is drawn over the wet-bulb thermometer by means of a small fan driven by clockwork. It is necessary that the water used to moisten the wet bulb of the sling psychrometer be at approximately the wet-bulb temperature; otherwise the time required to bring the water to the wet-bulb temperature might be so great that parts of the wicking would become dry. The ideal psychrometric chart in Fig. 119 is constructed for use with the sling psychrometer. 1 This chart gives the moisture content of air in grains per cubic foot, the volume basis being the more convenient for ordinary ventilating work. In Figs. I and II, in the Appendix, are given the psychrometric charts which give the properties of air on the basis of 1 pound of air. 160. Example of Use of Psychrometric Chart. — Given a dry-bulb temperature of 80° and a wet-bulb temperature of 70°, 1 From "Fan Engineering," Buffalo Forge Company. Fig. 118. — Sling psychro- meter. AIR AND ITS PROPERTIES 175 find the relative and absolute humidity and the dew point. From the 80° point on the horizontal scale follow the vertical line to its intersection with the diagonal line representing the wet-bulb temperature of 70°. Passing horizontally to the left from this point to the left-hand scale we find that the absolute humidity is 6.65 grains per cubic foot. To find the relative humidity we note that this same point lies between the 60 and 70 per cent, relative humidity lines (the curved lines extending o q p* 3 5 o s 3 V 2 100ff90#80ff 70# C0# , 1 -> 7 / *•. / / ■< 7 a •> / ' -x */x ■7 A v>, / > '- i A ^7^? v/ v 7 tJ^Z~ A- 7^7 2 < *• V 2*** ie<® ZT^r > >( w-4 %> > 5f 's. Jt/$ ZM-^$< 250? j ; --KlJsSL^L. ^4 X^2 -*.. / v v . ->< ** / ^< tC^X^*** N <' " \ '^fe x S^ x x > X ,x jSj^Sc \ 5*;>^= ^•s^ ^L< 5><< tf\ 3l§|^<^ S^ <ls \ f^"~ -^^>v^3^ Ss^^ ■^ rr i-j" ,s t 50* 40? +-• a 20 Si 105* 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 Dry Bulb Temperature Fig. 119. — Psychrometric chart. upward to the right) and that the relative humidity is 62 per cent. To find the dew point, follow left horizontally from this same point to the curved line of wet-bulb temperatures, called the saturation line. The dew point is 64.5°. The relation between the wet- and dry-bulb temperatures and the dew point should be thoroughly understood. 161. Application to Air Conditioning. — If water is sprayed continuously into the path of a current of air and the same water is recirculated repeatedly the temperature of the water will approach the wet-bulb temperature of the air. The latter will not change but the dry-bulb temperature of the air will be lowered until it approaches the wet-bulb temperature, and at saturation the two will coincide. The wet-bulb temperature depends upon 176 HEATING AND VENTILATION the total heat of the air and vapor and will be constant so long as the total heat of the mixture of air and vapor is constant. In the process mentioned the heat of the air above the wet-bulb temperature and. the superheat of its original water vapor content go to supply the heat of vaporization for the added moisture, as ex- pressed by equation (1), Par. 158. This means is often employed to cool the air for ventilation. If a spray of artificially cooled water be used the air can be cooled to within a few degrees of the water temperature. If this temperature is below the dew point of the air some of the moisture content will be condensed and the resulting condition will be one Table XXXVI. — Properties op Dry Air 1 Barometric Pressure 29.921 Inches Tem- per- ature, deg. F. Weight per cu. ft., pounds Ratio to volume at 70° F. B.t.u. absorbed by 1 cu. ft. dry air per deg. F. Cu. ft. dry air warmed 1° per B.t.u. Tem- pera- ature, deg. F. Weight per cu. ft., pounds Ratio to volume at 70° F. B.t.u. absorbed by 1 cu. ft. dry air per deg. F. Cu. ft. dry air warmed 1° per B.t.u. 0.08636 0.8680 . 02080 48.08 130 0.06732 1.1133 0.01631 61.32 5 0.08544 0.8772 . 02060 48.55 135 0.06675 1.1230 0.01618 61.81 10 0.08453 0.8867 0.02039 49.05 140 0.06620 1.1320 0.01605 62.31 15 0.08363 0.8962 0.02018 49.56 145 0.06565 1.1417 0.01592 62.82 20 0.08276 0.9057 0.01998 50.05 150 0.06510 1.1512 0.01578 63.37 25 0.08190 0.9152 0.01977 50.58 160 0.06406 1 . 1700 0.01554 64.-35 30 0.08107 0.9246 0.01957 51.10 170 0.06304 1.1890 0.01530 65.36 35 0.08025 0.9340 0.01938 51.60 180 0.06205 1.2080 0.01506 66.40 40 0.07945 0.9434 0.01919 52.11 190 0.06110 1.2270 0.01484 67.40 45 0.07866 0.9530 0.01900 52.64 200 0.06018 1.2455 0.01462 68.41 50 0.07788 0.9624 0.01881 53.17 220 0.05840 1.2833 0.01419 70.48 55 0.07713 0.9718 0.01863 53.68 240 0.05673 1.3212 0.01380 72.46 60 0.07640 0.9811 0.01846 54.18 260 0.05516 1.3590 0.01343 74.46 65 0.07567 0.9905 0.01829 54.68 280 0.05367 1.3967 0.01308 76.46 70 0.07495 1.0000 0.01812 55.19 300 0.05225 1.4345 0.01274 78.50 75 0.07424 1.0095 0.01795 55.72 350 0.04903 1.5288 0.01197 83.55 80 0.07356 1.0190 0.01779 56.21 400 0.04618 1.6230 0.01130 88.50 85 0.07289 1.0283 0.01763 56.72 450 0.04364 1.7177 0.01070 93.46 90 . 07222 1.0380 0.01747 57.25 500 0.04138 1.8113 0.01018 98.24 95 0.07157 1.0472 0.01732 57.74 550 0.03932 1.9060 0.00967 103.42 100 0.07093 1.0570 0.01716 58.28 600 0.03746 2.0010 0.00923 108.35 105 0.07030 1.0660 0.01702 58.76 700 0.03423 2 . 1900 0.00847 118.07 110 0.06968 1.0756 0.01687 59.28 800 0.03151 2.3785 0.00782 127.88 115 0.06908 1.0850 0.01673 59.78 900 0.02920 2.5670 0.00728 137.37 120 0.06848 1.0945 0.01659 60.28 1000 0.02720 2.7560 0.00680 147.07 125 0.06790 1 . 1040 0.01645 60.79 1200 0.02392 3.1335 0.00603 165.83 From "Fan Engineering," Buffalo Forge Company. AIR AND ITS PROPERTIES 177 of saturation at the final temperature. These principles are applied practically in the cooling and dehumidifying of air which will be discussed in Chapter XVI. 162. Properties of Dry and Saturated Air. — The properties of dry air are given in Table XXXVI and the properties of saturated air in Table XXXVII, at the standard barometric pressure of 29.92 inches of mercury. Table XXXVII. — Propeeties op Saturated Air 1 Weights of Air, Vapor of Water, and Saturated Mixture of Air and Vapor at Different Temperatures, Under Standard Atmospheric Pressure of 29.921 Inches of Mercury Temper- ature, deg. F. Vapor pres- sure, inches of mercury Weight in a cu. ft. of mixture B.t.u. ab- sorbed by 1 cu. ft. sat. air per deg. F. Cubic feet Weight of the dry air, pounds Weight of the vapor, pounds Total weight of the mixture, pounds sat. air warmed 1° per B.t.u. 0.0383 0.08625 0.000069 0.08632 0.02082 48.04 10 0.0631 0.08433 0.000111 0.08444 0.02039 49.05 20 0.1030 0.08247 0.000177 0.08265 0.01998 50.05 30 0.1640 0.08063 0.000276 0.08091 0.01955 51.15 40 0.2477 0.07880 0.000409 0.07921 0.01921 52.06 50 0.3625 0.07694 0.000587 0.07753 0.01883 53.11 60 0.5220 0.07506 0.000829 0.07589 0.01852 54.00 70 0.7390 0.07310 0.001152 0.07425 0.01811 55.22 80 1.0290 0.07095 0.001576 0.07253 0.01788 55.93 90 1.4170 0.06881 0.002132 0.07094 0.01763 56.72 100 1.9260 0.06637 0.002848 0.06922 0.01737 57.57 110 2.5890 0.06367 0.003763 0.06743 0.01716 58.27 120 3.4380 0.06062 0.004914 0.06553 0.01696 58.96 130 4.5200 0.05716 0.006357 0.06352 0.01681 59.50 140 5.8800 0.05319 0.008140 0.06133 0.01669 59.92 150 7.5700 0.04864 0.010310 0.05894 0.01663 60.14 160 9.6500 0.04341 0.012956 0.05637 0.01664 60.10 370 12.2000 0.03735 0.016140 0.05349 0.01671 59.85 180 15.2900 0.03035 0.019940 0.05029 0.01682 59.45 190 19.0200 0.02227 0.024465 0.04674 0.01706 58.80 200 23.4700 0.01297 0.029780 .004275 0.01750 57.15 163. Specific Heat of Air. — The specific heat of a gas may be expressed in either of two ways: i.e., the specific heat of constant •From "Fan Engineering," Buffalo Forge Company. 12 178 HEATING AND VENTILATION pressure, and the specific heat of constant volume. The reason for this has already been stated (Par. 6). In ventilating work the former quantity is the one involved. Its value as determined by Carrier is 0.2415 B.t.u. ProbI ems 1. Given wet-bulb temperature 66°, dry-bulb temperature 80°. Find dew point, per cent, saturation, and moisture content. 2. Given air at a temperature of 60° and containing 5 grains of water vapor per cubic foot. What is its relative humidity? 3. The air outside of a building is at a temperature of 31° and has a rela- tive humidity of 84 per cent. On being drawn into the building it is heated to 70°. What is its relative humidity at the higher temperature? 4. Air at 80° is 87 per cent, saturated. When cooled to 55° what is its ' new moisture content? 6. Air at 25° has a humidity of 90 per cent. How much moisture must be added to give it a humidity of 50 per cent, when heated to 70°? 6. A room has a volume of 1800 cubic feet. The air is changed once per hour. The incoming air has a temperature of 35° and a relative humidity of 75 per cent. It is desired to maintain a humidity of 50 per cent, in the room, the temperature being 70°. How many gallons of water must be evaporated in 24 hours to do this? CHAPTER XIII VENTILATION 164. Ventilation Standards. — 'While the art of ventilating occupied rooms has advanced greatly during recent years, there are as yet no fixed standards as to what constitutes satisfactory ventilation. It is only very recently that many of the physio- logical effects of certain atmospheric conditions have been under- stood, and a satisfactory explanation of other phenomena is still lacking. The formulation of standard requirements has there- fore been very difficult and further progress now depends upon their establishment rather than upon the mechanical problems involved in fulfilling them. The most agreeable atmosphere that we know of is undoubtedly that which exists outdoors on a sunny spring day; but the specific qualities which make it agreeable have not been definitely discovered. It is well known, however, that many other things beside the mere supplying of a sufficient quantity of air are necessary to provide comfortable conditions. The effect of the atmospheric conditions upon the human body is twofold: namely, its effect upon the skin, and its effect when taken into the lungs. The former is largely a matter of removing heat from the body at the proper rate, while the latter is a ques- tion of supplying sufficient air of the proper cleanliness. In the maintaining of what is now considered as satisfactory ventilation, the following factors must be taken into account: 1. Sufficient air supply, properly distributed. 2. Reduction of odors and impurities. 3. Removal of dust and bacteria to an acceptable amount. 4. Proper temperature. 5. Proper humidity. 6. Proper amount of air motion. The first three of these factors concern the effect of the in- haled air, while the last three affect the rate of heat removal from the skin. 165. Sources of Air Pollution. — -The percentage of oxygen absolutely necessary for human existence has been shown, in the preceding chapter, to be quite low, and a considerable reduction of oxygen may take place without even causing great 179 180 HEATING AND VENTILATION discomfort. In general, it may be stated that the quantity of air to be supplied for proper ventilation is governed by other factors which necessitate a greater quantity than that required to maintain a sufficient oxygen content. The air of occupied rooms becomes the recipient of many polluting elements, the most important of which are the products of respiration. The average person breathes at the rate of about. 17 respirations per minute while at rest. At each respiration, about 30}-^ cubic inches of air are inhaled or about 18 cubic feet per hour, which amounts to about 34 pounds of air in 24 hours or a little over 7 pounds of oxygen. The inhaled air loses about 5 per cent, of its oxygen content while in the lungs and gains from 3}i to 4 per cent, of carbon dioxide. The percentage com- position of free air and of expired air, by volume, is about as follows : Free atmosphere, per cent, (approximately) Expired air, per cent. (approximately) Oxygen Nitrogen Carbon dioxide . 20. 9 79. 1 0.03 to 0.04 15.4 79.2 4.03 to 4.04 In addition to carbon dioxide, water vapor is an important product of respiration. The moisture thus added to the air will increase the humidity above the comfort point unless the atmos- phere is renewed with sufficient frequency. There are also emanations from the mouth, lungs, and skin which give rise to disagreeable odors and which are believed by some to have a poisonous effect when taken into the lungs. Al- though this belief is not universally accepted, and although the exact effect of this organic matter is not known, common clean- liness alone demands that sufficient fresh air be supplied to dilute such impurities considerably. There are other sources of air pollution, such as the products given off by the combustion in gas and oil lamps and from manufacturing processes. Gas lights give off carbon dioxide, water vapor, and traces of sulphuric acid. If the burners are not properly adjusted, carbon monoxide, which has a poisonous and sometimes a fatal effect, may also be generated. Table XXXVIII gives the amount of combustible consumed and the amount of carbon dioxide emitted per candlepower from gas lights. VENTILATION 181 Table XXXVIII. — Air Pollution by Gas Lighting Consumption of combustible per candlepower in oubic feet per hour Carbon dioxide per candle- power in cubic feet per hour Fishtail burner 0.802-0.527 0.0 -0.445 0.053-0.024 0.494-0.304 0.254 Welsbach burner 0.030-0.057 Manufacturing and chemical processes give off various gas- eous impurities, but such conditions require individual study and no set rules can be given. 166. Amount of Air Required. — The proper amount of air supply has been determined from experience for different classes Table XXXIX. — Air Supplied to Various Classes of Buildings Cubic feet per hour per occupant No. pf renewals of air per hour Churches, auditoriums and assembly rooms Theatres Grade schools High schools College class rooms Hospitals for ordinary diseases Hospitals for children Hospitals for contagious diseases Hospitals for wounded Barracks Living rooms in residences Stairways and halls Bedrooms Work shops Public waiting rooms Public toilet rooms Small convention halls General offices Private offices Public dining rooms Banquet halls Basement restaurants Hotel kitchens Public libraries Textile mills Engine rooms Boiler rooms Railroad roundhouses 1,200-1,800 1,000-1,200 1,000-1,500 1,200-1,800] 1,500-2,000 2,500-3,500 2,000-2,500 5,000-5,500 3,500-5,000 1,000-1,800 1,200 600 1,000 600-2,000 1-2 1H 4 10 4 3 4 4 5 8-12 4-6 3 4 3-6 2-6 12 182 HEATING AND VENTILATION of buildings. For buildings such as theatres and schools, it is customary to provide a certain volume of air per minute for each occupant. For rooms where the number of occupants is vari- able or where there is pollution from sources other than respira- tion, sufficient fresh air is provided to renew that in the room a certain number of times per hour. For ordinary conditions of temperature and humidity, Table XXXIX gives the usual practice as to the amount supplied. 167. Methods of Measuring Air Supply. — When the air enters a room through but one or two ducts, the quantity can be directly measured by a pitot tube or anemometer, the use of which will be discussed in Chapter XV. Another method which in many cases is more convenient is based on the measurement of the carbon dioxide content of the air combined with our knowledge of the rate at which the carbon dioxide is added by the exhalation from the occupants. Let V = volume of air admitted to the room in cubic feet per hour. a = volume of CO2 contained in a unit volume of the air admitted. ri = amount of C0 2 per unit volume of air in the room at the beginning of the test. r 2 = amount of C0 2 per unit volume of air in the room at the end of the test. r = amount of C0 2 per unit volume of air in the room at any time during the test. R = volume of room in cubic feet. c = amount of C0 2 produced in the room, in cubic feet per hour. t = time of experiment in hours. During any small period of time dt, the amount of air enter- ing the room is Vdt and the amount of C0 2 contained in the entering air is aVdt. The amount of C0 2 produced during the time dt is cdt. During the same interval, an equal volume Vdt leaves the room through the exhaust flues and its C0 2 content is rVdt. The net increase in the volume of C0 2 in the room is then (aV + c)dt - rVdt = (aV - rV + c) dt Let the increase in the C0 2 content of the air in the room per VENTILATION 183 cubic foot during the interval dt be represented by dr. Then the total net increase is Rdr. Equating the two Rdr = (aV - rV + c)dt (1) and dt - (aV+c)-Vr (2) t = R r r ° * aV + c - Vr t = R \ ± loge (aV + c - 7r) , fi, Vn - aV - c t= V l ° S °Vr 2 -aV-c y = ^^ ^f^ (3) If r - ! = r 2 , which means that there is no increase in the C0 2 content of the air in the room, then the amount entering the room, plus the amount produced must equal the amount leaving the room, or aV + c = Vr 2 from which V = and r 2 = ri = a + = (4) 7- 2 — a K If c = 0, then from (3) V = 2.303 f log 10 ?:i — ^ (5) Equation (4) is applied practically by assuming a certain production of C0 2 per hour per person, which figure is usually taken as 0.6 cubic foot. Equation (4) then becomes CF.fl.-^ (6) UU 2 —x in which C.F.H. = cubic feet of air per hour supplied to the room per occupant. C0 2 = carbon dioxide content of the room air in parts per 10,000. x = carbon dioxide content of the outside air in parts per 10,000. This formula is recommended by Dr. E. V. Hill and is used by the Health Department of the City of Chicago. The chart in 184 HEATING AND VENTILATION Fig. 120 shows the air supply per person when any given C0 2 content exists in the room. The above method of determining the air supply does not apply when there is any source of carbon dioxide other than the lungs of the occupants. 168. Air Distribution. — Merely to supply enough air to a room is not sufficient for good ventilation; it must be distributed in a fairly uniform manner so that each occupant receives approxi- mately the specified amount. The methods of distribution will be dealt with later. To determine the uniformity of distribu- tion, the common method is to take measurements of the C0 2 con- tent in different parts of the room and thus determine the varia- tion of the quantity supplied per occupant at the different points from the average quantity. a 3.000 ta u fc 2,500 u Formula CO 2 6000 +x p* W 2.000 u a> ft ]§ 1,500 ft a d ™ 1,000 < °- 500 3 100 CFH per occupant \ C02~X X may be taken as 4 if an analysis of outside air ia not made \ V 15 20 25 30 35 40 45 C02Content in 10,000 PartB of Air 50 55 65 Fig. 120. — Chart showing air supply per person for various amounts of C02 169. Temperature and Humidity. — One of the chief objects sought when air for ventilation is provided is the establishment of such conditions that heat will be removed from the human body at a rate which is favorable for comfort and health. Heat is lost from the body in three ways : by radiation, by convection, and by the evaporation of moisture from the skin. A relatively large amount of heat is lost by convection and consequently the temperature of the surrounding air and the amount of air movement are important factors. The amount of heat lost due to the evaporation of perspira- tion from the skin depends upon the relative humidity of the air and upon the amount of air motion. It is also dependent, of course, upon the amount of perspiration which is given off by VENTILATION 185 the pores of the skin, more heat being lost by evaporation from the skin of a person who perspires freely than from a dry skin. Comfortable conditions can exist through a rather wide range of temperature and relative humidity -provided that the combina- tion of the two is such as to cause the proper rate of heat loss from the body. The air motion may also vary, but within rather narrow limits. The chart in Fig. 121 showing the proper relation between the temperature and humidity was constructed by Dr. E. V. Hill from a series of tests made by Prof. J. W. Shepherd. From the center line of the "Comfort Zone" shown in the chart, it will be noted that equally comfortable conditions can be had with a 73 71 f» 69 ti "67 8 65 | 63 I 61 £59 57 " ■- ~S~ 3i(T V, "T &5- ■4T '"— — ■-- ,. '.Too Wt on ""^ JZ otie Of -My r Q i°rt *~" -"-- •~. ?< >o f ■~~, ~~ 30 32 34 36 38 40 42 44 46 48 50 52 64 56 58 60 62 64 66 68 70 72 74 76 78 Relative Humidity Per Cent Fig. 121.- 'Comfort Zone" showing the temperature and humidity required to produce comfortable conditions. temperature of 65° and a humidity of.56 per cent, as with a tem- perature of 70° and a humidity of 36 per cent. Low humidities such as ordinarily exist in most buildings during the heating season are known to be detrimental to health, as the membranes of the throat and nose become dry and irritated. There is little doubt but that the proper humidification of the air of residences and other heated buildings is very beneficial from a physiological standpoint but there have been certain difficulties in the way of its universal application. Many of the devices intended for the purpose are entirely inadequate to supply the moisture required by even a moderate-sized room. There is also a general lack of appreciation of the quantities of moisture required, some idea of which was brought out in the preceding chapter. Another drawback is the tendency for moisture to be deposited on the 186 HEATING AND VENTILATION windows when even a moderate humidity is maintained in very cold weather. For these reasons, the application of artificial humidity has been limited to buildings of sufficient size and of such a character as to make practicable the use of an air washer or other rather elaborate means for humidification. Excessive humidity, on the other hand, is undesirable, as it causes a feeling of intense discomfort, especially when accom- panied by high temperature, because of its effect in lowering the rate of evaporation from the skin and therefore retarding the process of heat removal from the body. According to Prof. Foster, about 4 pounds of water are given off by an adult man under extreme conditions in 24 hours, of which 2}£ pounds are evaporated from the skin and the remainder is contained in the expired air. Under average conditions, the amount given off is about one-half the above. The heat given off from the body will vary from about 335 to 460 B.t.u. per hour depending upon the age, sex, diet, amount of exercise, etc. About 15 B.t.u. of this amount are given off with the expired air and 35 B.t.u. are contained in the moisture with which the expired air is saturated. Approximately 70 B.t.u. are contained in the mois- ture which is evaporated from the skin, leaving about 250 B.t.u. to be lost by convection and radiation. The last two quantities especially are extremely variable under different atmospheric conditions. In a hot, dry atmosphere, for example, the air temperature may be higher than that of the body and no heat can be given off by convection or radiation. The evaporation of perspiration from the skin must then be depended upon to remove all of the excess heat from the body. In crowded rooms, the heat and moisture given off from the bodies and from the exhalations of the occupants may render the atmosphere extremely uncomfortable, so that cooling and de- humidifying are required. It has been demonstrated repeatedly that the depressing effect of a so-called stuffy atmosphere is due to its action on the skin as much as or even more than to its effect on the lungs. When the air is artificially cooled, it has been found that the inside temperature must be raised somewhat as the outside temperature increases, so that the shock to the sensations of one entering from the outside will be minimized. The inside tem- perature should not be more than 10° or 12° below the outside, as a maximum. VENTILATION 187 170. Air Movement. — The rate of evaporation of moisture from the skin depends, in addition to the temperature and humidity of the atmosphere of the room, upon the continuous renewal of the aerial envelope surrounding the body. Unless this renewal takes place, the air immediately surrounding the body increases in temperature and moisture content to such an extent that the skin evaporation is retarded to an uncomfortable degree. A proper circulation of the air within a room also pre- vents the immediate reinspiration of the air expired from the lungs and diffuses it throughout the room. The motion of the air, however, should never be such as to cause uncomfortable drafts. In general, a movement toward the face is greatly preferable to one from the rear. An air movement of about 2 feet per second is considered to be permissible, but a much greater velocity is uncomfortable. Air movement may be directly measured by injecting into the air clouds of smoke and timing their movement across the room. Toy balloons are also used for this purpose. Cubic space is an important factor in ventilation, particularly in crowded rooms, for with too small a volume per person it may be impossible to move the required amount of air through the room without giving rise to unpleasant drafts. Dr. Billings recommends the following as the minimum amount of space to be allowed per occupant. Lodging or tenement house . . 300 cubic feet per person School room 250 cubic feet per person Hospital ward 1,000-1,400 cubic feet per person Auditoriums 200 cubic feet per person In computing the cubic space for this purpose, all space over 12 feet above the floor should be neglected. 171. Odors. — Another function of ventilation is the removal or reduction of odors, the most common and most objectionable of which arise from the bodies of the occupants. The sources of these odors are emanations from the throat and lungs, the perspiration from the skin, and soiled clothing. In factories, odors are created by industrial operations of various sorts. The so-called "crowd smell" is not harmful of itself, for it has been shown that healthful existence is quite possible in such an atmosphere. Repulsive odors are indirectly harmful, how- ever, in that they cause the occupants of the room to breathe 188 HEATING AND VENTILATION less deeply; but regardless of their actual physiological effect, modern standards of cleanliness require that sufficient air be supplied to occupied rooms to maintain a wholesome atmosphere. As yet, no satisfactory standard has been found for the meas- urement of odors. 172. Ozone. — Ozone is used to some extent as a means for counteracting odors and bacteria. Ozone is simply a form of oxygen in which the molecule consists of three instead of two atoms. The additional atom is readily liberated and the sub- stance is consequently an active oxidizing agent. Ozone is present in very minute amounts in the atmosphere. When injected into the atmosphere of a room with a con- centration of not more than 1 part per million, ozone is capable of obliterating even very marked odors. The exact action which takes place is at present a matter of debate. By some it is believed that ozone actually destroys the odors through its oxidizing action. It is known, however, that it is quite possible to compensate one odor with another so that its effect upon the olfactory membrane is neutralized, and it may be that the real action of the ozone is a masking of the odors by what is called "olfactory compensation" rather than a destroying of them. It is very essential that the concentration of the ozone be. kept very low, for in an atmosphere of more than about 1 part per million of ozone, serious irritation of the throat and lungs is liable to result. The common method of producing ozone is by means of an elec- trical discharge at high voltage. Several commercial machines are available for the purpose. 173. Dust and Bacteria. — The air, especially that of cities, contains a large amount of dust in very finely divided particles. These particles consist of many different substances, most of which are mineral. In large cities, tons of cinders and smoke particles are cast out into the air annually, which adds to the production of dust from other sources. Dust in itself is not particularly injurious to health but it serves as a carrying me- dium for all sorts of bacteria. Several methods of determining the dust content of air have been devised. The most successful scheme is to draw a sample of air into a suitable cylinder containing a glass disc coated with an adhesive varnish and so placed that the indrawn air impinges upon it. The number of dust particles determined by microscopic VENTILATION 189 count affords an indication of the amount of dust in the air. Dust can be quite thoroughly removed from air by means of the air washer, to be described later. 174. Methods of Introducing Air. — In providing ventilation for a room, it is necessary to adopt a definite scheme for the intro- duction of fresh air and the removal of the vitiated air. When the air quantities are small the leakage around the windows may be relied upon as a means for permitting the escape of the air, but in general, it is necessary to install a system of vent flues. There are two general methods of circulating the air through a room. In the upward system, the air is introduced through the floor or through the side walls near the floor and is removed near the Fig. 122. — Effect of various locations of inlet and outlet. ceiling. In the downward system, the air is introduced through registers in the side walls located from 7 to 10 feet above the floor and is removed near the floor. The former method is especially adapted to theatres and auditoriums where a large number of small openings can be provided in the floor, thus securing a very even distribution. The upward system is also suitable for restaurants and rooms where there is smoking or where other impurities or odors are created which have a natural tendency to rise. The downward system is used in schools, hospitals, etc. where the occupants are not many and where it is not practicable to have openings in the floor. The relative location of the inlet and outlet openings greatly 190 HEATING AND VENTILATION affects the thoroughness of the air renewal throughout the room. It has been demonstrated that the most effective scheme is to place the outlet near the floor and on the same side of the room as the inlet. The effects of various locations of the inlet and outlet are shown in Fig. 122. Problems 1. A test made in a room in which there are several people shows a CO2 content of 12 parts per 10,000. What quantity of air is being supplied per hour per occupant? 2. A test of the air of an occupied room shows a C0 2 content of 13 parts per 10,000. Outside air contains 33^ parts per 10,000. How much air is being supplied per hour per occupant? CHAPTER XIV HOT-AIR FURNACE HEATING 175. Furnace Systems. — The hot-air furnace is widely used throughout the country in the heating of residences of moderate size. In addition to its simplicity and relatively low cost, it has the great advantage of providing fresh air for ventilation. It is especially well adapted to moderate climates where, for a large part of the winter, heat is needed only in the morning and evening. As brought out in Chapter III, the greatest disadvantage in a furnace system is the fact that the force producing circulation, being dependent upon the relatively slight difference in density between the heated and unheated air, is quite small and is often insufficient to overcome the resistance of the piping or the pres- sure of a very strong wind blowing against the building. These difficulties can often be overcome, however, by intelligent design of the system. The size of the building which a hot-air furnace can serve is limited because of the friction in the horizontal piping. The practical limitation to the length of horizontal ducts which can convey the required volumes of air is about 20 feet. It is sometimes feasible to install two separate furnaces and thus avoid pipes of excessive length. There are many forms of furnaces on the market, some of which are of indifferent design and workmanship. The non- success of many furnace installations is usually due to this fact and to the lack of intelligent planning of the piping system. A common mistake, brought about by the endeavor to minimize the cost of the installation, is the use of a furnace of insufficient size. As a result, a very hot fire must be maintained and the flue gases leave the furnace at a high temperature, necessitating the use of an excessive amount of fuel. In a furnace system the heat is absorbed by the air as it passes through the furnace and is carried by the air to the rooms above. The air circulates through the rooms, giving up heat to the objects in the room and to the walls. The walls and the con- 191 192 HEATING AND VENTILATION tents of the room remain at a slightly lower temperature than the air. If no foul-air flues are provided, the air entering the room must eventually find its way out through the cracks around the windows, through the walls themselves, or through the doors into other rooms; for otherwise the flow of air into the room could not be maintained. It sometimes happens, in a tightly constructed building, that this leakage is insufficient, and the flow of air to the room is retarded. A foul-air flue from each room is there- fore desirable, although in the average residence its initial cost is seldom deemed warranted. The air entering the furnace may come either from outside or may be partially or wholly re-circulated from the house. It is best to provide both means of air supply, so that either may be used as conditions demand. When only a few people are in the building, the air may be re-circulated, but for a number of people it is very desirable that an ample supply of fresh air be introduced. The economy of a hot-air system is affected by the proportion of the air taken from each of these sources. When all the air is re- circulated from the house, then the economy of the hot-air furnace is about the same as that of a steam or hot-water plant ; but when air is taken from outside, then a certain amount of heat is used in warming it up to the temperature of the room, and this heat is not available for supplying the heat losses from the build- ing. But heat used in this way should be considered as the price of ventilation and should not be charged against the effi- ciency of the system. 176. Furnaces. — The hot-air furnace consists fundamentally of a firepot and a series of passages for the flue gases, surrounded by a metal or brick casing. The air circulates through the space between the furnace proper and the casing, absorbing heat from the hot surfaces of the firepot and gas passages. The gas pas- sages are usually formed by a simple casting called a "radiator." Hot-air furnaces are quite varied in design. In general there are two types: those with the radiator at the top of the furnace, as in Fig. 123; and those with the radiator near the bottom of the furnace, as in Fig. 124. Occasionally, in cheap furnaces, the radiator is left off entirely. For the best possible efficiency in any furnace the entering air should first come into contact with the surfaces behind which are the coldest flue gases and the air leaving the furnace should pass over the hottest surfaces. This ideal condition is difficult of realization, for mechanical HOT-AIR FURNACE HEATING Radiator 193 Fig. 123. — Furnace with radiator at the top (easing removed). Fig. 124. — Furnace with radiator near bottom (casing removed). 13 194 HEATING AND VENTILATION reasons, but the furnace which most nearly approaches it will in general be the most efficient. The heating surfaces of a furnace may be divided into two classes: (a) direct heating surfaces, which are those which are in contact with the fire or which receive heat by direct radiation from the fire ; and (b) indirect heating surfaces, which are heated only by the hot gases. In addition there are some surfaces which receive heat only by conduction from the heating surfaces proper, such as projections and braces, these being called "ex- tended" surfaces. The parts of such surfaces which are more than about 2 inches from actual heating surface are of doubtful effectiveness, however. All of the heating surfaces give up heat to the air entirely by convection. The amount of heat transmitted through the heat- ing surfaces of course increases as the difference in temperature between the air and the products of combustion increases. The effectiveness of the heating surfaces decreases as the distance from the fire increases and direct heating surfaces are naturally more effective than indirect heating surfaces. The more rapid the flow of air over the heating surfaces, the greater will be the amount of heat removed. Since the effectiveness of the heating surfaces depends upon the design of the furnace, it is impossible to base the capacity of the furnace upon the amount of heating surface. Roughly, however, the heat transmission may be assumed to be, on an average, from 1000 to 1500 B.t.u. per hour per square foot of surface. 177. Furnace Construction. — The firepot and radiator are usually made of cast iron, although steel is sometimes used. There is no appreciable difference in the thermal conductivity of the two materials. It is essential that the joints between the different castings be air-tight so that the products of combustion cannot escape and be carried to the rooms above. The joints, therefore, are of a modified tongue and groove design, the grooves being filled with a special cement and the castings drawn and held together with draw bolts. Joints should be as few as possible and vertical joints should be avoided. The firepot is usually slightly conical and should be deep enough to contain sufficient coal to last for 8 hours, leaving enough unburned coal on the grates at the end of that time to ignite the fresh charge of fuel. With hard coal this means that HOT-AIR FURNACE HEATING 195 the depth should be sufficient to allow for 50 pounds of coal being placed on the grate per square foot of grate. Coke or soft coal will require a greater depth of firebox than anthracite coal. The grate area should be from 1 :25 to 1 : 12 of the area of the heating surface, the proportion depending upon the kind of fuel and the size of the furnace — the larger the furnace, the smaller the ratio. If anthracite coal is used the ratio should not exceed 1 :25. If bituminous coal is used it should be 1 :20 and for coke about 1 :15 for furnaces of average size. For burning soft coal some furnaces are provided with an auxiliary air supply so arranged that heated air is introduced into the firepot above the fuel bed, mixing with the combustible gases and promoting complete and smokeless combustion. The furnace casing is usually of galvanized iron, although large furnaces are sometimes enclosed by brickwork. When a galvanized-iron casing is used, insulation is obtained by providing an inner casing of black iron or tin with an air space between the inner casing and the outer casing of about 1 inch. The area between the furnace and casing should be sufficient so that no appreciable resistance is interposed to the circulation of air through the furnace. In .small furnaces the velocity should not exceed 250 feet per minute and in larger furnaces 300 to 250 feet per minute. These figures apply only to gravity circulation. Furnaces are rated by the manufacturers either upon a basis of the volume of the building to be heated or upon the total cross-sectional area of the warm air ducts. Inasmuch as these ratings usually represent about the maximum capacity of the furnace, it is well to choose a furnace of 25 to 50 per cent, excess capacity. 178. Humidification. — The hot-air furnace system affords a particularly favorable opportunity for humidification, but unfor- tunately most of the manufacturers have been extremely backward in providing adequate apparatus for adding the necessary amounts of moisture to the air. Most furnaces are equipped with some sort of a "water pan" which is usually installed near the bottom of the furnace. This location is entirely wrong, for the air as it enters at the bottom of the furnace has the least capacity for absorbing moisture. To be effective, the humidifying apparatus should be placed where the hottest air will pass over it, i.e., at the furnace outlet. Few realize that in order to maintain a proper humidity in even a small house there must be evaporated 196 HEATING AND VENTILATION hourly a quantity of water of the order of 10 pounds. To be satisfactory, the water pan must therefore be kept filled auto- matically from the water-supply system. Fig. 125 shows a humidifier which is located at the top of the furnace and is automatically filled. The amount of water evaporated increases with the amount of air passing through the furnace and with the temperature of the air, making the apparatus to some extent self-regulating. Accurate automatic regulation is impossible, however, without a system of humidity control such as will be described later. Fig. 125. — Humidifier. 179. Cold-air Pipe. — The air supply to the furnace may be taken from outside or can be re-circulated from the house. It is also quite feasible to take only a certain amount of air from outside and to supply the remainder by re-circulation. With complete re-circulation the advantage of ventilation is entirely lost but the system is somewhat more economical. The cold- air duct may be of galvanized iron or may be constructed of tile and placed beneath the basement floor. It should come from the side of the house which is subject to the prevailing winds. It is sometimes desirable to have cold-air ducts leading to different sides of the house so that the supply of cold air may be taken from the windiest side. The cross-section of the cold-air duct should be 80 per cent, of the aggregate area of the supply ducts leaving the furnace. The re-circulating duct should be brought from the coldest part of the house and from some room such as the hall which has other rooms leading into it. The side of the stairway, the lower stairway risers, or the space in front of large windows are good locations for the re-circulating register. If it is desired to re-circulate partially and to take the balance of the air from outside, the re-circulating pipe should be brought to the furnace independently of the fresh-air pipe, and a deflect- ing plate placed in the air space under the furnace. If this is not done, the air may come in from the outside and pass up HOT-AIR FURNACE HEATING 197 the re-circulating pipe instead of through the furnace. Both the fresh-air pipe and the re-circulating pipe must be provided with dampers. It is a common error to make the re-circulating pipe of a furnace system too small. The area of the re-circulating pipe should be not less than three-fourths the combined area of the hot-air pipes, and it is better to have it equal tp their combined area. 180. Hot-air Pipes.— The furnace should be centrally located, or if the coldest winds come from a certain direction, it can be located toward that side of the house. The pipes leading from the furnace should be as short and direct as possible; long hori- zontal pipes should be avoided. The horizontal pipes are called leaders; the vertical pipes flues or risers. Leaders are usually made of round pipe. All leaders should be given the same pitch of at least 1 inch per foot and should leave the furnace at the same elevation. They should be insulated with asbestos paper, or if extending through a very cold part of the basement, with an air-cell covering. It is desir- able to provide a damper in each pipe so that the distribution of the air among the different rooms can be adjusted. The risers should in every case be installed in an inside partition, as the cooling effect, when placed in an outside wall, would greatly retard circulation, besides causing an excessive waste of heat. It is usually necessary to limit the depth of the riser to 4 inches, so that it may be enclosed in the studding. The width also is sometimes limited by the distance between the studding and many furnace systems suffer from this source. It is some- times necessary to run two risers to large second-floor rooms when space is not available for a single riser of sufficient size. Architects often fail to realize the importance of providing suf- ficient space for this purpose. Risers, when made of single-walled pipe must be insulated with asbestos paper to protect the woodwork and a clearance on all sides of at least J4 inch must be left. Double-walled pipe which has an air space between the walls is becoming widely used. The air space serves as an insulator and greatly decreases any possible fire hazard as well as reducing heat loss from the pipe. When double-walled pipe is used the proper size should be selected so that the net inside area will not be reduced below the computed requirements. Bright tin is ordinarily used for all piping. 198 HEATING AND VENTILATION The leader is connected to the riser by means of p, fitting called a "boot" shown in Figs. 126a and 1266. The form shown in Fig. 126a is preferable as it interposes less resistance to the flow of air. The air is delivered into the room through a register of the form shown in Figs. 127 and 128. Floor registers have the advan- tage that they may be made of any size and may be placed in any part of the room. They are often favored because the air / Fig. 126a.— Boot of im- proper design. Fig. 1266. — Boots of good design. leaving them does not deposit dust on the walls as does the side- wall register. Floor registers, however, are very insanitary as they collect great quantities of dirt; and they also frequently necessitate cutting the carpets or rugs. On the whole, the side- wall register is much to be preferred. Registers are provided with means of cutting off the flow of air in the form of louvres or, Fig. 127. — Floor register. Fig. 128.— Wall register. in the side-wall type, a single shutter of sheet metal. The shutters in some of the registers should be omitted, so that by no possible chance could all of the air supply be cut off; for with no air circulating through the furnace, the danger of overheating and burning out the firepot is great. It is often convenient to supply a first-floor register and a riser from a single leader. This can be very satisfactorily accomplished by means of the arrange- ment shown in Fig. 129. The free area of an ordinary register HOT-AIR FURNACE HEATING 199 is only about half of its gross area and its size must therefore be about double that of the pipe which supplies it. For a floor Fig. 129. — Method of connect- ing first floor register and riser to a single leader. Fig. 130. — Box for floor register. Fig. 131. — Stack and register frame — double walled pipe. register a box of the form shown in Fig. 130 is provided and for a wall register a frame of the form shown in Fig. 131 is used. Fig. 132 shows the general arrangement of a furnace system. 181. Size of Hot-air Pipes. — There are two methods of 200 HEATING AND VENTILATION figuring the size of the hot-air pipes, the B.t.u. method and the volume method. The former is the more rational and is the one recommended. Example of B.t.u. Method. — -Assume that the heat loss from the given room is 12,000 B.t.u. per hour and that the air enters at 140°, room temperature being 70°. Each cubic foot of air entering the room will give up enough heat to ,lower its tem- perature from 140° to 70°. The amount of heat given up when a cubic foot of air is cooled 1° is approximately }is B.t.u. Fig. 132. — General arrangement of furnace system. 140-70 Therefore, the heat given up per cubic foot is — ~ — = 1.27 B.t.u. The volume of air required per hour = 12,000 -h 1.27 = 9460 cubic feet. Allowing a velocity of 250 feet per minute in the hot-air pipe, the required area of the hot-air pipe is _ ^OU X OU = 0.63 square foot. The velocity of air for first-floor leaders may be taken as 3 to 4 feet per second, for second-floor leaders 4 to 5 feet per second, and for third-floor leaders 5 to 6 feet per second. The risers leading to second- and third-floor rooms may have a velocity as high as 400 feet per minute. Registers should be proportioned so as to give a velocity of 2 to 3 feet per second on the first floor and 3 to 4 feet per second on the floors above, on the basis of the effective area of the register. Volume Method. — In the volume method the area of the hot- HOT-AIR FURNACE HEATING 201 air pipe is assumed to be purely a function of the size of the room, no account being taken of the heat losses. This method is manifestly inaccurate as the amount of air required depends of course upon the heat lost from the room. For rooms of average proportions and of ordinary construction, the volume method is usually successful, however, if carefully applied. The chart in Fig. 133 gives the size of leaders and risers required for rooms of various dimensions. It is permissible to reduce the size of the leader to which a riser is connected, as indicated by the chart, because of the acceleration of the circulation due to the stack effect of the riser. 8 9 10 4» 11 V V >y «v -J ^v /;< ]r > & >•* y / ' #?:■ V y * .3 13 1 14 o K ir 7\ ^ /. *« y / I* 1 , ^ r J j>° 3* > •j, v •4 ■ . f s a* v -j - > *> ^ w ^> *jS a*' v' J < / V' / V* *^5 4 >°°< ^ =\ n- V N?° ,s> ' 3 12 20.4 35.3 45.5 4 16 17.7 30.5 39.4 46.6 5 20 15.5 27.2 35.3 41.7 47.4 6 24 14.5 25.0 32.3 38.2 43.3 47.9 7 28 13.4 23.1 29.9 35.3 40.1 44.3 48.2 8 32 12.5 21.6 28.0 33.2 37.6 41.5 45.1 48.4 and accurate results cannot be obtained by averaging the pressure readings. The method outlined above is the standard method adopted by the American Society of Heating and Ventilating Engineers. 1 Fig. 138. — Anemometer. 192. The Anemometer. — For very approximate results, the anemometer, Fig. 138, is a convenient instrument for measuring the flow of air at the duct outlets. For very low velocities it is not suitable, as the friction required to revolve the propeller is 1 Report of Committee on Standardization of Use of Pitot Tube, Trans. A. S. H. & V. E., 1914. 214 HEATING AND VENTILATION the source of a considerable error. In using the anemometer the face of the register is divided into a number of equal areas and the readings taken at the several areas are averaged. The dial is calibrated to read directly in feet and the velocity is obtained by taking the registration of the instrument during a definite period of time. 193. Friction Loss. — The general expression for the friction of fluids in pipes (equation (3), page 132) is applicable to the flow of air: a 2g or for round ducts of perimeter R and length L p _fRL W _jRL v* a 2g a 2g in which P = pressure required to overcome friction, pounds per square foot. a = cross-sectional area of duct, square feet. D = density of air, pounds per cubic foot. v = velocity, feet per second. / = coefficient of friction. h a = height in feet of a column of air equivalent to P. It is more convenient to express the friction head in terms of inches of water. If the density of air at 70° be taken as 0.075 and the density of water as 62.3 pounds per cubic foot then the head in inches of water is h -™™X}*f*k* = o.00022^ 62.3 a 2g a The value of / was found by Reitschel and other to be about 0.0037 for smooth iron ducts. Prof. J. E. Emswiler 1 reports values for /ranging between 0.004 and 0.006 for velocities of 800 feet per minute and over, the coefficient decreasing slightly as the velocity increases. For practical purposes a somewhat higher coefficient is used, giving larger duct sizes. Allowance is thereby made for roughness of the duct surfaces and for accidental obstructions. The chart in Fig. 139, which is published by the American 1 See "Coefficient of Friction of Air Flowing in Round Galvanized Iron Ducts," by J. E. Emswiler, Trans. A. S. H. & V. E., 1916. DESIGN OF FAN SYSTEMS 215 Blower Co., gives the friction in inches of water per 100 feet length of duct for various quantities of air. The chart is for round ducts; to figure the friction in a square or rectangular duct, it is necessary first to obtain the diameter of the equivalent round duct, which can be done by means of Table XLII. Friction in Inches Water Gage per 100 Eeef- Fig. 139. — Frictional resistance in round air ducts. Example. — Find the friction loss in a 20 by 10-inch duct 67 feet long, carrying 2000 cubic feet of air per minute. From Table XLII-we find that the diameter of the equivalent round duct is 15.4 inches. From the chart, in Fig. 139 the friction drop per 100 feet of duct for the given flow and for a diameter of 15.4 inches is readily found to be 0.31 inches of water. For a length of 67 feet the drop would be 0.3 X 0.67 = 0.201 inches of water. 216 HEATING AND VENTILATION Table XLII. — Diameter op Round Ducts Equivalent to Rectangular Ducts of Various Dimensions Side 4 6 8 10 12 14 15 16 18 20 22 24 rectangular duct Equivalent diameters 3 4 4.4 5 4.9 6 5.4 6.6 7 5.8 7.0 8 6.1 7.6 8.8 9 6.5 8.0 9.3 10 6.8 8.4 9.8 11.0 11 7.1 8.8 10.2 11.5 12 7.4 9.2 10.7 12.0 13.2 13 7.6 9.6 11.1 12.5 13.7 14 7.6 9.9 11.5 12.9 14.3 15.4 15 8.2 10.2 11.9 13.4 14.7 16.0 16.5 16 8.4 10.5 12.3 13.8 15.2 16.5 17.1 17.6 17 8.6 10.8 12.6 14.2 15.7 17.0 17.6 18.2 18 8.9 11.1 13.0 14.6 16.1 17.4 18.1 18.7 19.8 19 9.1 11.4 13.3 15.0 16.5 17.9 18.6 19.2 20.4 20 9.3 11.6 13.6 15.4 17.0 18.4 19.0 19.7 20.9 22.0 22 9.7 12.1 14.2 16.1 17.8 19.2 19.9 20.6 21.9 23.1 24.2 24 10.0 12.6 14.8 16.8 18.5 20.0 20.8 21.5 22.8 24.0 25.2 26.4 26 10.4 13.1 15.4 17.3 19.2 20.8 21.6 22.3 23.8 25.1 26.3 27.5 28 10.8 13.5 15.9 18.0 19.8 21.5 22.4 23.1 24.6 26.0 27.3 28.5 30 11.0 13.9 16.4 18.5 20.5 22.2 23.1 23.9 25.4 26.8 28.2 29.5 32 11.3 14.3 16.9 19.1 21.1 22.9 23.8 24.6 26.2 27.7 29.1 30.5 34 11.6 . 14.7 17.3 19.6 21.6 23.5 24.4 26.3 26.9 28.5 30.0 31.3 36 11.9 15.1 17.7 20.1 22.2 24.2 25.1 26.0 27.7 29.3 30.8 32.2 38 12.2 15.4 18.2 20.6 22.8 24.8 25.8 26.7 28.4 30.0 31.5 33.1 40 12.5 15.7 18.6 21.1 23.3 25.4 26.4 27.3 29.1 30.8 32.4 33.9 42 12.7 16.1 19.0 21.6 23.8 25.9 26.9 27.9 29.8 31.4 33.0 34.5 44 13.0 16.4 19.4 22.0 24.3 26.5 27.5 28.5 30.3 32.1 33.7 35.3 46 13.3 16.7 19.8 22.4 24.8 27.0 28.1 29.1 31.0 32.8 34.6 36.2 48 13.5 17.0 20.1 22.8 25.2 27.5 28.6 29.6 31.6 33.4 35.2 37.0 50 13.7 17.3 20.4 23.2 25.7 28.0 29.2 30.3 32.2 34.1 35.9 37.6 52 13.9 17.6 20.8 23.6 26.2 28.5 29.6 30.7 32.9 34.7 36.5 38.3 54 14.1 17.9 21.1 24.0 26.6 29.0 30.1 31.2 33.4 35.3 37.2 38.9 56 14.3 18.2 21.5 24.4 27.0 29.5 30.6 31.7 33.9 35.9 37.8 39.6 58 14.6 18.4 21.8 24.7 27.4 30.0 31.1 32.2 34.4 36.4 38.4 40.3 60 14.7 18.7 22.1 25.1 27.8 30.5 31.6 32.7 34.9 37.1 39.1 40.9 62 15.0 19.0 22.4 25.5 28.2 30.9 32.1 33.2 35.4 37.7 39.6 41.6 64 15.1 19.2 22.7 25.9 28.6 31.3 32.6 33.7 35.9 38.2 40.2 42.2 66 15.3 19.5 23.0 26.2 29.0 31.7 33.0 34.2 36.4 38.7 40.8 42.8 68 15.5 19.7 23.3 26.5 29.4 32.1 33.4 34.7 36.9 39.2 41.4 43.4 194. Pressure Loss Due to Obstructions. — The loss of pressure caused by various obstructions, such as elbows, branches, etc., is usually expressed as a multiple of the velocity head. The actual loss, however, is of course a loss of static head, since the velocity head at all points in a pipe, for a given quantity of DESIGN OF FAN SYSTEMS 217 air flowing, depends entirely upon the cross-sectional area at each point. The center line radius of elbows should be equal to at least 1}4 times the width of the duct, as demonstrated by Frank L. Busey, 1 who obtained the following results for elbows of square cross-section : Center line radius in per cent, of pipe width Per cent, of velocity head lost 50 95 75 34 100 17 150 8 200 7 Another method is to add to the actual length of straight pipe a certain length which will have the same friction loss as that due to the resistance in question. The following table gives the loss of pressure due to various obstructions. Table XLIII. — Pressure Loss Due to Various Obstructions Equivalent length of straight pipe Round elbow (c. 1. radius 1J^ X width) ■ Sharp elbow Square tee Branch from main duct Angle, 15 degrees (per cent, of v. p. in branch).. 30 degrees 45 degrees Abrupt entrance to pipe Coned entrance to pipe Registers (free area = duct area = }4 total area of register). 10 X width ir washers: Velocity through washer, feet per minute Pressure loss, inches of water 400 0.15 500 0.25 600 0.35 700 0.45 Example. — Given an air duct of square cross-section carrying air at a velocity of 900 feet per minute, and at a temperature of 70°. Find the loss 1 See "Loss of Pressure Due to Elbows in the Transmission of Air through Pipes or Ducts," by Frank L. Busey, Trans. A. S. H. & V. E., 1913. 218 HEATING AND VENTILATION of head due to an elbow of diameter l}4 X width. From formula (2), page 210, the velocity head = (j^g) * X 0.07495 = 0.0505 inches. The pressure loss is 0.08 X 0.0505 = 0.004 inches. 195. Proportioning Duct Systems. — It is highly desirable that the size of the ducts be intelligently selected and that the pres- sure loss in the system be computed as accurately as possible. The principal reason for doing this is to insure the selection of a fan of the proper characteristics; for in order that the required quantity of air be delivered it is necessary that a fan be selected with working head sufficient to overcome the resistance of the system. Furthermore, the proper proportioning of the various branches will result in the delivery of the proper air quantities to the various rooms without too great a dependence upon the use of the dampers. In designing a duct system it is necessary first to select the static resistance against which the fan is to operate. Since the power consumption depends upon the resistance, the cost of power is a consideration in air-duct design. A reduction in the power required can be obtained by increasing the duct sizes; but the increased cost of the larger ducts and the greater space required are the opposing factors. There are two general systems of air distribution and the method of choosing the duct sizes depends upon the type of system. In public buildings, particularly in schools, the single- duct system is used, in which the air is delivered to a plenum chamber by the fan and separate ducts radiate to the various rooms. In such a system the duct having the greatest resistance is first designed, which fixes the pressure to be carried in the plenum chamber. The other ducts are then so designed as to deliver the required quantities with the given pressure differential. The longest duct is designed on a basis of certain assumed velocities; Table XLIV gives those recommended by W. H. Carrier: Table XLIV. — Velocities in Single-duct Systems Velocity, feet per minute Vertical flues 400-750 Horizontal runs 700-1200 Wall registers 1 200-400 Floor registers 1 125-175 1 Over- gross area. DESIGN OF FAN SYSTEMS 219 In industrial buildings the trunk duct system is used, consist- ing of one or more main ducts with branches taken off at inter- vals. Such ducts are so proportioned as to give an equal friction loss per foot of length. The outlets are designed for certain velocities depending upon the size of the room and upon the distance through which it is desired to blow the air, the possi- bility of objectionable drafts being considered. It is customary to assume an outlet velocity of from 700 to 1500 feet per minute, an average figure being 1000 feet per minute. The branches from the main duct should be so proportioned as to deliver the re- quired air quantities and it is usually best to provide dampers on the outlets so that any inequalities in distribution can be ad- justed after the system is installed. It is desirable to design all airxlucts on a basis of an air density corresponding to the maximum air temperature to be expected. i i fit i i hi. W. m » ' I P ]4y 1600 C.F.M. - 250'- * J-J- Fig. 140. 196. Example of Single Duct System. — Assume that a single duct system is to be designed and that the longest duct is ar- ranged as in Fig. 140, the air temperature being 70°. We will figure the horizontal run on a basis of 1000 feet per minute and a duct of rectangular section will be used. The area of the horizontal duct will be 1600 -f- 1000 = 1.6 square feet and a 12- by 19-inch duct will be used. For the riser a velocity of 600 feet per minute will be used and the required area is 1600 -r- 600 = 2.75 square feet, requiring a 16- by 24-inch duct. From Table XLII we find that the diameter of a round pipe equivalent to a 12- by 19-inch rectangular duct is 16.5 inches and for a 16- by 24-inch duct 21.5 inches. From the chart in Fig. 139 we find 220 HEATING AND VENTILATION that a pipe of 16.5 inches diameter will transmit 1600 c.f.m. with a friction loss of 0.14 inches per 100 feet, and the loss for a 21.5-inch pipe is 0.034 inches per 100 feet. To the actual length of straight pipe we must add the equivalent of the elbows, which may be taken (see Table XLIII) as ten times the actual width of the duct measured on the radius of the elbow. The total friction drop due to the straight pipe is then as follows : (250 + 10) X ^ + (40 + 13.3) X ^ = 0.382 inch The resistance of the register may be taken as 1.25 times the velocity head corresponding to a register velocity of 300 feet per minute, upon which basis the size of the register will be selected. The velocity head we may compute by means of formula (2), page 210, hv = (tJSV) * X 0.07495 = 0.0056 inch M096.5/ The loss through the register is 0.0056 X 1.25 = 0.007 inch. The loss at the entrance to the duct from the plenum chamber we will take as 80 per cent, of the velocity head corresponding to the velocity of 1000 feet per minute. 0.80 X K = 0.80 X (ij^j) 2 X 0.07495 = 0.050 inch. The total resistance of the duct is then 0.382 + 0.007 + 0.050 = 0.439 inch and the total pressure in the plenum chamber must be equal to this plus the velocity head corresponding to 1000 feet per minute or 0.439 + 0.062 = 0.501 inch. The remaining ducts must then be of such a size as to use up this available total pressure of 0.501 inch. Assume the following data for one of the ducts: Quantity of air delivered, 1150 c.f.m. Register velocity, 300 feet per minute. Velocity, throughout entire length, 800 feet per minute. Total equivalent length, including resistance of elbows, 110 feet. The following quantities can be computed : / 300 \ 2 Resistance of register = (jo965/ X °' 07495 = 0-0056 inch. DESIGN OF FAN SYSTEMS 221 / 800 \ 2 Loss at entrance to duct = 0.80 X L nnc g ) X 0.07495 = Vl096 - 5/ 0.032 inch. (800 \ 2 1 nQfi g ) X 0.07495 = 0.040 inch. Static head to be used up by friction = 0.501 — (0.0056+ 0.032 + 0.040) = 0.423 inch. The friction loss per 100 feet of duct must then be 0.423 -r- 1.10 = 0.385 inch. From the chart in Fig. 139 the diameter of the round pipe which will give this friction loss for 1150 c.f.m. is 12.0 inches. This is equivalent (see Table XLII) to a rectangular pipe 10 by 12 inches or 8 by 15 inches, either of which could be used. The equivalent length allowed for the elbows, which must necessarily have been estimated, should be revised if the computed width of the duct is greatly different from the assumed width upon which the equivalent lengths were estimated, and the calculation repeated. 197. Correction for Temperature. — The quantities for which the duct sizes are computed are the volumes at the actual temperature of the air flowing. On the other hand, the volumes fixed by the heating and ventilating requirements are on a basis of room temperature, i.e., about 70°. The volumes upon which the air ducts are designed must therefore be de- termined by multiplying the volumes at 70° by the ratio : Density of air at 70° Density of air at duct temperature These ratios are given in Table XXXVI, page 176, in the column headed "Ratio to Volume at 70°F." 198. Trunk-line System. — In a trunk-line system, the pro- cedure would be as follows : Assume a system laid out as in Fig. 141, in which the quan- tities as given are on a basis of 70°. The system will be de- signed for a temperature of 135° and the actual quantities flowing in the various sections are as follows; A-B 11,100 X 1.1230 = 12,465 B-C 5,800 X 1.1230 = 6,513 C-D 1,800 X 1.1230 = 2,021 B-E 3,300 X 1.1230 = 3,706 E-F 1,500 X 1.1230 = 1,684 The total head at point A must be equal to the friction loss in the trunk duct plus the velocity head at D, the end of 222 HEATING AND VENTILATION the trunk duct. The method of proportioning by a uniform friction loss leads to a reduction in the velocity toward the end of the trunk and a consequent conversion of some of the velocity head to static head. The absolute values of the veloc- ity and static heads at A are not important, the require- ment being that their sum be equal to the friction loss plus the velocity head at D. On a basis of velocity of 1000 feet per minute the velocity head atD will be equal to [ tkqo r ) X 0.06675 = 0.055 inch on a basis of 135°. The friction drop may be fixed arbitrarily and we will choose it in this case as 0.20 inch per 100 feet, giving a total pressure at point A of 0.20 X 2.25 + 0.055 = 0.505 inch. For a friction drop of 0.20 inch per 100 k- -75- — *H -100'- 11.100 ^YT •60- -- »l © CO 1.500 JL ogl20 If 100 £*80 1— !■*» (S 1 60 ° 40 o 1 20 Pressure Characteristic of Forward Curved Blade Fans T ressu Stra: Ch ght 1 iractc lade riatlc Fane o( 20 40 60 80 100 Fer Cent of Rated Capacity 120 140 ICO Fig. 144. — Pressure characteristics of straight-blade and multi-blade fans at constant speed. 1 developed will be greater than that corresponding to the pe- ripheral velocity. The two types of fans have inherently different characteristics. In a straight-blade fan operated at constant speed the total pres- sure developed decreases as the output of the fan is allowed to in- crease by reason of a lessened resistance. The multi-blade fan develops an increasing total pressure as its output is increased under the same conditions. In Fig. 144 are shown the pressure characteristics of the two types. The vertical ordinate is in terms of the ratio of the total pressure to the pressure corre- 'From "The Centrifugal Fan," by Frank L. Btjsey, Trans. A. S. H. & V. E., 1915. 228 HEATING AND VENTILATION sponding to the peripheral velocity, this standard being used simply to make the curves comparable. The practical signifi- cance of these differing characteristics is evident when the action of a fan supplying a system of ducts is considered. With a straight-blade fan if one part of the duct system were shut off and the fan speed is unchanged the result would be an increase in the amount of air delivered to the other rooms. With a multi- blade fan, on the other hand, the quantity delivered through the remaining ducts would not be greatly altered. Other advan- tages of fans of the multi-blade type are the smaller space occupied and the fact that their higher speed makes it possible to connect them direct to motors. The higher speed also reduces the cost of the motor in some cases. In general the multi-blade type is the more suitable for ventilating systems. Fig. 145. — Wheel of straight-blade fan. Wheel of multi-blade fan. 206. Commercial Types. — In Fig. 145 are shown the wheels of a straight-blade and of a multi-blade fan and in Fig. 146 is shown the casing of a multi-blade fan. The general appearance of the casings of the two types is quite similar, the multi-blade fan being somewhat smaller in diameter and of greater width for the same capacity. Fans can be obtained with the discharge opening at various angles and with the inlet opening on either side. In some cases fans of double width, having an inlet on both sides, are used. 207. Selection of a Fan. — Before selecting a fan for a given installation it is necessary to know the quantity of air to be handled and the static resistance of the duct system. The total pressure against which the fan must operate is the sum of the DESIGN OF FAN SYSTEMS 229 static resistances on both the suction and the discharge sides of the fan plus the velocity head at the fan outlet, which can be determined from the volume of air delivered and the size of the outlet. The size of fan which will fill the requirements is best obtained from the data published by the various fan manu- facturers. It is usually possible to obtain the same capacity and static head from two or more different size fans. Frequently the fan which operates the most efficiently under the given con- ditions is not the lowest in first cost and the selection must be governed by the relative importance of these factors. Fig. 146. — Casing of multi-blade fan. 208. Fan Tables. — The exact performance to be expected of a fan under any given conditions can be obtained from the tables published by the manufacturers. There are two kinds of fan tables — the "total pressure" tables, which give the speed, ca- pacity, and horsepower for the various size fans at the most efficient paint for various total pressures; and the more complete "static pressure" tables, which give the performance at points on either side of the most efficient point. Tables XLV and XL VI are, respectively, the total pressure table for various sizes of one type of multi-blade fan, and the static pressure table for a multi-blade fan of one particular size, the latter being in a some- 230 HEATING AND VENTILATION what condensed form. More complete static pressure tables for both steel plate and multi-blade fans may be found in the Ap- Table XLV. — Capacities op Buffalo Niagaba Conoidal Fans (Type N) Under Aveeage Working Conditions — at 70°F. and 29.92 Inches Barom.' Fan No. Mean diam. of blast wheel Area of outlet, square feet 9^-in. total press. or 0.217 oz. H-in. total press, or 0.288 oz. R.p.m. Vol. Hp. R.p.m. Vol. Hp. 3 15W 1.31 413 1,490 0.13 478 1,720 0.19 3H 18^ 1.79 354 2,030 0.17 409 2,350 0.26 4 20H 2.33 310 2,650 0.22 358 3,070 0.34 Hi 23H 2.95 276 3,360 0.28 318 . 3,880 0.43 5 26 H 3.64 248 4,150 0.35 287 4,790 0.53 5ii 28?i 4.41 225 5,020 0.42 260 5,800 0.65 6 31?fi 5.25 207 5,970 0.50 239 6,900 0.77 7 36H 7.14 177 8,130 0.68 205 9,400 1.05 8 42 9.33 155 10,610 0.89 179 12,260 1.37 9 47 11.81 138 13,450 1.12 159 15,520 1.73 10 52 14.58 124 16,580 1.39 143 19,160 2.14 11 58 17.64 113 20,070 1.68 130 23,180 2.58 12 63 21.00 104 23,880 2.00 119 27,590 3.08 13 68 24.65 95 28,040 2.35 110 32,370 3.61 14 73 28.68 89 32,520 2.72 102 37,550 4.19 15 78 32.80 83 37,330 3.13 96 43,100 4.80 Static pressure is 77H per cent, of total press. Table XLV. — (Continued) Fan No. Mean diam. of blast wheel Area of outlet, square feet %-in. total press, or 0.360 oz. i^-in. total press, or 0.433 oz. R.p.m. Vol. Hp. R.p.m. Vol. Hp. 3 15^ 1.31 533 1,930 0.27 585 2,110 0.35 3H 18H 1.79 457 2,620 0.37 501 2,870 0.48 4 20H 2.33 4C0 3,430 0.48 439 3,750 0.63 Hi 23M 2.95 356 4,340 0.60 390 4,750 0.80 5 26H 3.64 320 5,350 0.74 351 5,870 0.98 e« 28?i 4.41 291 6,470 0.90 319 7,100 1.19 6 31H 5.25 267 7,710 1.07 292 8,450 1.41 7 36>4 7.14 229 10,490 1.46 251 11,500 1.92 8 42 9.33 200 13,700 1.91 219 15,020 2.51 9 47 11.81 178 17,340 2.41 195 19,000 3.18 10 52 14.58 160 21,400 2.98 175 23,460 3.93 11 58 17.64 146 25,900 3.60 160 28,390 4.75 12 63 21.00 133 30,820 4.29 146 33,780 5.65 13 68 24.65 123 36,180 5.03 135 39,650 6.63 14 73 28.68 114 41,950 5.84 125 45,990 7.69 15 78 32.80 107 48,160 6.70 117 52,790 8.83 Static pressure is 77H per cent, of total press. 1 From "Fan Engineering," Buffalo Forge Co. DESIGN OF FAN SYSTEMS 231 pendix, pages 276 to 299. The static pressure tables are the better adapted for general use. The total pressure can be found for any conditions by adding to the static pressure the velocity pressure as given in the third column in Table XL VI. Table XLVL— No. 10 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barom. 1 Outlet velocity, Capac- ity, cu. ft., air Add for J3-in. s.p. 9i-in. s.p. 1-in. s.p. 154-in. s.p. 2-in. s.p. total ft.-min. per min. press. R.p.m. Hp. R.p.m. Hp. R.p.m. Hp. R.p.m. Hp. R.p.m. Hp. 1,400 20,410 0.122 164 2.92 206 4.61 243 6.59 308 11.1 1,500 21,870 0.141 163 3.13 204 4.78 240- 6.83 305 11.5 1,600 23,330 0.160 164 3.42 202 5.02 238 7.05 302 11.8 357 17.0 1,700 24,790 0.180 165 3.74 201 6.30 235 7.28 299 12.1 353 17.5 1,800 26,240 0.202 166 4.13 200 6.61 233 7.59 295 12.4 350 17.9 1,900 27,700 0.225 168 4.55 200 6.01 232 7.91 293 12.7 347 18.3 2,000 29,160 0.250 171 5.04 200 6.48 231 8.32 291 13.0 343 18.7 2,100 30,620 0.275 174 5.56 201 7.00 231 8.77 288 13.5 340 19.2 2,200 32,080 0.302 177 6.12 203 7.54 230 9.31 286 13.9 338 19.6 2,300 33,540 0.330 180 6.76 205 8.16 231 9.92 285 14.4 336 20.1 2,400 34,990 0.360 183 7.43 207 8.86 232 10.60 284 16.0 332 20.6 2,600 37,910 0.422 190 8.95 213 10.40 235 12.10 282 16.3 329 21.8 2,800 40,830 0.489 198 10.70 219 12.20 240 13.90 283 18.1 327 23.3 3,000 43,740 0.560 206 12.70 226 14.30 246 16.00 285 20.1 326 25.0 3,200 46,660 0.638 215 14.80 234 16.70 251 18.30 288 22.4 327 27.4 Note. — Bold-face figures indicate point of highest static efficiency. The fan tables are based on actual tests made by operating the fan at constant speed against different artificial resistances consisting of plates, having openings of various sizes, placed at the end of a straight pipe about 30 diameters in length. In Fig. 147 are shown the performance curves for a multi-blade fan, based on the percentage of rated capacity, the latter being taken as the point at which the fan operates with the highest total efficiency. It should be borne in mind that these perform- ance curves are based on a constant speed. It is frequently necessary to find the performance of a fan at some pressure different from any given in the tables. The method of doing this can best be shown by a typical example. Assume that 38,000 cubic feet of air per minute is to be delivered by a No. 10 Conoidal fan against a static resistance of 1J4 inches. Find the required speed and horsepower. The data for 1-inch static is given in Table XL VI. The corresponding capac- 1 From " The Centrifugal Fan," by Frank L. Busey, Trans. A. S. H. & V. E., 1915. 232 HEATING AND VENTILATION ity of the fan at 1-inch static may be found by multiplying by the square root of the ratio of 1-inch to lj^-inch, since we know that the pressure varies as the square of the speed and conse- quently as the square of the volume delivered. The capacity on a 1-inch basis is thus found to be 34,100 c.f.m. From Table XL VI we find that the speed and horsepower for 33,540 c.f.m. at 1-inch static are respectively 231 r.p.m. and 9.92 horsepower. The speed and horsepower at 1^ inches static we can compute from our knowledge that the speed varies directly as the capacity and the power as the cube of the capacity. The fan will deliver 200 180 100 140 gl20 o Sioo 80 60 40 AV agjJ nett» t^ o^ oj£ ■r Ce nt of /Ila tprf t $g£ oV"- *&S £l«o ^ ^ V*£ Total Ef icienly > •get (V* 1 - rf* is** ,£fet ^*- -iiSjc y 00 80 100 Per Cent of Eated Capacity 120 160 Fig. 147. — Performance curves of Niagara conoidal fans. 38,000 c.f.m. against lj^ inches static with a speed of 258 r.p.m. and a power consumption of 13.9 horsepower. In selecting a fan for a given installation it is usually possible to fulfill the required conditions with two or even three different- size fans. In such a case the first cost, operating cost, and out- let velocities should be considered in making the selection. The smaller the fan the greater will be the outlet velocity for the same volume. In the case of schools or other buildings where quiet operation is essential the outlet velocity should not be over about 2200 feet per minute. In industrial buildings, how- ever, outlet velocities of about 3000 feet per minute are quite permissible. DESIGN OF FAN SYSTEMS 233 209. Correction for Temperature. — The fan tables are based on an air density corresponding to a temperature of 70°. In a system in which the fan is so located with respect to the heating coils that it handles air at a different temperature, a correction must be made. This can be done by making use of the relations stated in Par. 203. For example: Assume that it is required to handle 11,700 c.f.m. against a static head of 1% inches at 140°. As brought out in Par. 203, at constant capacity and speed, the horsepower and pressure vary inversely as the absolute temperature of the air. Therefore, if we select a fan which will handle 11,700 c.f.m. against a pressure of 1.75 X w = 1.98 inches at 70°, it will de- liver the same quantity against a pressure of 1.75 inches at 140° at the same speed. From the fan tables we find that a No. 90 steel plate fan will do this at a speed of 403 r.p.m. and a power consumption of 7.32 horsepower. The power con- sumption at 140° would be 7.32 X 530 a Aa i. ™^ = 6.46 horsepower. It should be remembered that the volume of air fixed by the heating or ventilating requirements is usually based on the room temperature and the equivalent volume of the same weight of air at the temperature at which it enters the fan must be found by means of the volume ratios given in Table XXXVI, page 176. 210. Disc Fans. — The disc fan as illustrated in Fig. 148 is well adapted for handling considerable quantities of air against very low pressures. It is therefore widely used where the air is moved into or from a room without passing through a system of ducts. While not highly efficient, this type of fan is easily installed, is of moderate cost, and requires little space. Such a fan is usually inserted directly into a wall or partition and is driven by a direct-connected motor. 211. Heaters. — In a fan system the heat is transmitted from the heating units entirely by convection, the air being drawn over them at a fairly high velocity. There are two types of heater Fig. 148. — Disc fan. 234 HEATING AND VENTILATION used for such work — the cast-iron or "vento" heater and the wrought-iron pipe coil. The former is made up of sections, as shown in Pig. 149, connected together at the top and bottom by- right- and left-hand nipples cast with a hexagonal nut at the middle. A row of sections thus connected con- stitutes a stack. The sections are obtainable in nominal lengths of 30, 40, 50, 60, and 72 inches. All sizes are connected at both top and bottom and are therefore suitable for hot water as well as steam. Vento sec- tions are furnished in two widths, the "regular" and the "narrow," and by the use of nipples of different lengths the distance between sections can be made either A%, 5, or h% inches center to center, the 5-inch spacing being standard. The surfaces are broken up by a large number of pro- jections which extend into the air passages and serve to augment the heating surface in an .effec- tive manner. The principal dimensions of the sections of various sizes are given in Table XL VII. iSs* S3 Fig. 149. — Vento heater. Table XL VII. — Dimensions of Vento Sections, Inches Nominal size Square feet of surface Actual height Width 30 8.00 30 9M 40 10.75 4U<4 9H Regular width 50 13.50 50% 2 9M 60 16.00 60% Ws 1 72 19.00 72% 2 9Ys 40 7.50 41^4 m Narrow 50 9.50 502% 2 m 60 11.00 60% 6M Approximate weight 8.2 pounds per square foot of surface. The method of installing the stacks in a sheet-metal casing is shown in Fig. 150. The stacks are staggered so as to break up the stream lines and increase the intimacy of the contact between the air and the heating surface. The spaces left at the DESIGN OF FAN SYSTEMS 235 ends of the stacks due to the staggered arrangement are partially closed by strips of angle iron. Fig. 150. — Vento heater installed in casing. r® ® 0"0 "t F©"©"0 © @" c 0O@©@©©©_ 0©0©©O©@ ©»Q ©0@©0©©@ . L O ©0_0. 0.0-0 @i':Q S-Q_© ©-© ©_ © Fig. 151. — Pipe coil heater. 212. Pipe-coil Heaters. — Heaters made of 1-inch pipes are also widely used. The pipe is made into loops with ordinary 236 HEATING AND VENTILATION elbows, and the loops are screwed into a cast-iron base. The base is so partitioned that the steam flows in at one end of each of the loops. The sections are arranged as shown in Fig. 151, the pipes being staggered with reference to the flow of air through the heater. The sections are built in different sizes and a wide range in heating surface is available. The complete heater is composed of several units in series, as in the case of the cast-iron heaters. 213. Transmission of Heat From Fan-coil Surfaces. — The heating units are arranged in series, the outside air entering the first section and being heated up to the required delivery temperature during its passage through the successive sections. Since the rate of heat transmission varies nearly as the tem- perature difference between the steam and the air, the heat transmitted from the last stacks is much less than from those with which the cold air first comes into contact. The final temperature to which the air is heated depends upon the number of stacks through which the air passes in series and upon the velocity of the air. The cross-sectional area of the heater depends upon the quantity of air delivered, the stacks being chosen of sufficient size so that the free area between the sections will allow that quantity to pass through at the velocity chosen. The free area per section for Vento heaters is given in Table XL VIII. Similar data is published by the manufacturers of pipe-coil heaters. Table XL VIII. — Free Areas op Vento Sections Free area, square inches per section inohes 5;Hj-in. centers 5-inch centers 4%-inch centers 30 0.542 0.460 0.390 40 0.729 0.620 0.525 50 0.905 0.768 0.650 60 1.085 0.921 0.781 72 1.303 1.104 0.937 The velocity to be assumed depends upon the nature of the installation. In public buildings and in other places where^the noise which accompanies high velocities is objectionable, the velocity through the heater should be limited to between 1000 to 1300 feet per minute while in factories and similar buildings a DESIGN OF FAN SYSTEMS 237 Table XLIX. — Final Temperatures and Condensation Regular Section — Standard Spacing, 5-inch Centers of Sections — Steam, 227°, 5 Pounds Gage 3 b os a H Velocity through heater in feet per minute- -measured at 70° © OS •** 600 800 1,000 1,200 1,400 1,600 1,800 2,000 *- P. Oj'O a 3 1? Final temp, of air leav- ing heater Cond. lb. per sq. ft. per hour ft 6 fH d ft 6 ft ft d ft d -20 -10 34 1.69 1 43 1.65 38 1.95 35 2.24 32 2.46 20 58 1.46 54 1.75 51 1.99 49 2.23 47 2.42 45 2.56 43 2.65 42 2.82 30 66 1.39 62 1.64 60 1.92 58 2.17 56 2.33 54 2.46 52 2.54 51 2.69 -20 63 1.60 55 1.92 49 2.22 44 2.46 40 2.69 37 2.92 34 3.12 31 3.27 -10 69 1.52 62 1.85 56 2.12 51 2.35 47 2.56 44 2.77 41 2.94 38 3.08 2 75 1.44 68 1.74 62 1.99 58 2.23 54 2.42 51 2.62 48 2.77 46 2.95 20 87 1.29 81 1.57 76 1.80 72 2.00 69 2.20 66 2.36 64 2.54 62 2.69 30 93 1.21 87 1.46 83 1.70 79 1.89 76 2.06 73 2.21 71 2.37 69 2.50 -20 91 1.42 82 1.74 75 2.03 69 2.28 64 2.51 59 2.70 55 2.88 52 3.08 -10 96 1.36 87 1.66 80 1.92 75 2.18 70 2.39 66 2.60 62 2.77 58 2.90 3 101 1.30 93 1.59 86 1.84 81 2.08 76 2.27 72 2.46 68 2.62 65 2.78 20 110 1.15 103 1.42 97 1.65 92 1.85 88 2.06 85 2.22 82 2.38 79 2.52 30 115 1.09 108 1.33 103 1.56 98 1.75 94 1.91 91 2.08 88 2.23 85 2.35 -20 114 1.29 103 1.58 96 1.86 90 2.12 84 2.34 78 2.51 74 2.71 to 2.88 -10 117 1.22 108 1.51 101 1.78 95 2.02 89 2.22 84 2.41 80 2.60 76 2.76 4 121 1.16 113 1.45 106 1.70 100 1.92 95 2.13 90 2.31 86 2.48 82 2.63 20 130 1.06 122 1.31 115 1.52 110 1.73 105 1.91 101 2.08 97 2.22 94 2.37 30 134 1.00 126 1.23 120 1.44 115 1.63 110 1.80 106 1.95 102 2.08 99 2.21 -20 132 1.17 122 1.46 114 1.72 107 1.95 100 2.15 94 2.34 90 2.54 86 2.72 -10 135 1.13 126 1.40 118 1.64 111 1.86 105 2.06 99 2.24 95 2.42 91 2.59 5 138 1.06 129 1.32 122 1.56 115 1.77 109 1.96 104 2.14 100 2.31 96 2.46 20 144 .95 136 1.19 130 1.41 124 1.60 119 1.78 114 1.93 110 2.08 107 2.23 30 148 .91 140 1.13 134 1.33 128 1.51 123 1.67 118 1.80 115 1.96 112 2.10 -20 146 1.06 137 1.34 129 1.59 121 1.81 115 2.02 110 2.22 105 2.40 100 2.56 -10 149 1-.02 140 1.28 132 1.52 125 1.73 119 1.93 114 2.12 109 2.29 104 2.44 6 152 .97 143 1.22 135 1.44 129 1.65 123 1.84 118 2.02 113 2.17 109 2.33 20 156 .87 148 1.10 142 1.30 129 1.49 130 1.65 126 1.81 122 1.96 118 2.09 30 159 .83 151 1.04 145 1.23 139 1.40 134 1.56 130 1.71 126 1.85 122 1.97 -20 159 .98 150 1.25 141 1.47 134 1.69 128 1.90 122 2.08 117 2.26 113 2.44 -10 161 .94 152 1.19 144 1.41 137 1.62 131 1.81 126 1.99 121 2.16 117 2.33 7 163 .90 154 1.13 147 1.35 140 1.54 135 1.73 130 1.90 125 2.06 121 2.22 20 167 .81 159 1.02 152 1.21 146 1.39 141 1.55 136 1.70 132 1.85 128 1.98 30 169 .76 161 .96 155 1.15 149 1.31 144 1.46 139 1.60 135 1.73 132 1.87 -20 168 .90 159 1.15 151 1.37 144 1.58 138 1.77 133 1.96 128 2.14 123 2.29 -10 170 .87 161 1.10 153 1.31 147 1.51 141 1.69 136 1.87 131 2.04 126 2.18 8 172 .83 164 1.05 156 1.25 150 1.44 144 1.62 139 1.7S 134 1.93 129 2.07 20 175 .75 167 .94 161 1.13 155 1.30 150 1.46 145 1.6C 141 1.74 137 1.87 30 177 .71 169 .89 163 1.07 158 1.23 153 1.38 148 1.51 144 1.64 140 1.76 238 HEATING AND VENTILATION velocity between 1200 and 1600 feet per minute is permissible. For this purpose velocities are based on an air density correspond- ing to 70°, this being merely an arbitrary standard adopted for convenience in making computations. In very cold climates a a velocity of 800 feet per minute or less is advisable because of the tendency for the condensation to freeze in the coils. The velocity thus chosen is used both as a basis for computing the height and width of the heater and also for determining its depth, i.e., the number of stacks to be used. In Table XLIX are given the final temperatures obtainable from heaters of vari- DtHerence between Final Temperature and Tnitlal Temperature of Air N CO CO ** ^S" Swooooo Frictional Resistance in Inches of Water Fig. 152. — Friction curves for pipe coil heaters. ous depths for air at different initial temperatures and velocities. The final temperature for which the heater is designed depends upon the amount of heat to be supplied and upon whether the fan system is to be used for ventilating alone or to supply the DESIGN OF FAN SYSTEMS 239 heating requirements also. The temperature of the entering air used in the computations should be the minimum for which the system is to be designed. Example. — Assume that a factory is to be heated and that 1,400,000 cubic feet of air per hour are required at a temperature of 140°. Minimum out- side temperature 0°. What size Vento heater should be used? Free area (square feet) = volume (cubic feet per minute at 70°) velocity (feet per minute) Free area 1,400,000 1200 X 60 X 1.1320 = 17.17 square feet Difference between Pinal Temperature and Initial Temperature of Air O COS SgOlOo O ©©=5 '-" (M W OT CO 5< ^lOWlD t- GO 35 ^ o • © • © t '© . ■ • • • ' ■ Frictional Resistance in Inches of Water Fig. 153, — Friction curves for vento heaters. Referring to Table XLVIII it is seen that by using eighteen 60-inch sections, spaced 5 inches center to center, the free area will be 18 X 0.921 = 16.58 square feet, which is sufficient, giving a velocity of 1244 feet per minute. From Table XLIX it is seen that a heater seven stacks deep would raise the air from a temperature of 0° to 140° at a velocity 240 HEATING AND VENTILATION of 1200 feet per minute. The heater should therefore be sevnn stacks deep. Ordinarily it would be divided into a tempering coil of three stacks and a heating coil of four stacks. Pipe-coil heaters are chosen in a similar manner from the data furnished by their manufacturers. Recent tests 1 have shown that the heating effect of both Vento and pipe-coil heaters is closely related to the friction loss under- gone by the air in passing through them; and that for the two different types of heaters, the friction loss will be practically identical for the same increase in temperature of the air. This might logically be expected as the heat transmission depends upon the thoroughness of the rubbing action of the air over the heating surfaces. From the curves in Figs. 152 and 153 the friction drop can be determined for either Vento or pipe coil if the other facts are known, and vice versa. These curves are based on the following formula which was developed from the results of tests mentioned above on pipe coils and upon tests made on Vento heaters by L. C. Soule. V(h - U) C = KN in which C = condensation in heater — pounds per square foot per hour. V = velocity of air — feet per minute. t x — t 2 = temperature rise of air. N = number of stacks in heater. K = a constant = 15,307 for pipe coil and 13,130 for Vento. As an example of the use of the charts we will take an assumed case. With five stacks and an entering temperature of 10°, the final temperature for 1200 feet velocity is found from pipe- coil data to be 129°, making the increase in temperature 119°. In Fig. 152 the horizontal dotted line representing 1200 feet velocity intersects the vertical line representing 119° at the point A. From point A we draw the 45° line until it intersects the vertical line for five stacks. From this point we extend a horizon- tal line to the right-hand side of the chart and we see that the 1 See " Comparison of Pipe Coils and Cast-iron Sections for Warming Air," by John R. Allen, Proc. A. S. H. & V. E., 1917. DESIGN OF FAN SYSTEMS 241 condensation per square foot per hour is 1.89 pounds. The frictional resistance is obtained by extending the horizontal line for 1200 feet velocity to the right until it intersects the diagonal line for five stacks; a vertical line from this intersection shows the resistance to be 0.25 inches of water. In Fig. 153 the same case is worked out for Vento heaters as indicated by the dotted lines. The condensation is found to be about 1.94 pounds and the velocity 1068 feet for the same resistance and temperature rise. It will be noted that while the heating effect and resistance of the two heaters are the same, the velocities are quite different. Fig. 154. — Piping connections for vento heaters. 214. Installation and Piping Connections. — The heating units are usually mounted on a brick or concrete pier and enclosed by a metal duct. The proper arrangement of the steam piping connections for Vento heaters is shown in Fig. 154 for a double- tier installation. The center section of a long stack is tapped for an air vent as shown. Separate valves should be provided for each stack or pair of stacks. Special care is necessary in arranging the return connections from fan heaters, as any accumulation of condensation will soon 16 242 HEATING AND VENTILATION be frozen by the cold air. There is always a considerable drop in pressure through the heaters and the inlet connections, so that the pressure at the return connections should not be de- pended upon to lift the condensation; the discharge should be by gravity or a vacuum pump should be used. Thermostatic control is almost essential on fan systems. The diaphragm control valves, similar to those used for radiators, are installed as shown in Fig. 154 and are controlled from thermo- stats whose expansion member projects into the ducts. Problems 1. In the example in Par. 189, assuming that 657,000 cubic feet of air per ho*ur are delivered, if the heat loss as given was computed for 0°, what should be the delivery temperature when the outside temperature is 20°? 2. A factory building is to be heated by a hot-blast system with complete recirculation. With the following data given compute the amount of air which must be handled per hour by the system. Heat loss from building 27,800 B.t.u. per hour per degree difference in temperature. Inside temperature 65° Outside temperature —10° Temperature at which 140° air is delivered. 3. In the single duct system of Fig. 140 assume that the longest duct is to carry 1100 c.f.m. What is the total pressure required in the plenum chamber? 4. Compute the pipe sizes for a trunk duct system similar to that in Fig. 141 except that the air quantities in the different sections on a 70° basis are as follows: Section Air quantity A— B 19,000 c.f.m. B—C 7,500 C—D 2,000 B— E 6,000 E—F 4,000 Maximum air temperature 130°. 5. Find the speed, horsepower, and outlet velocity for three different sizes of steel plate fan 1 delivering 18,000 c.f.m. against a static resistance of 1)4 inches at 70°. 6. .Find the speed, horsepower, and outlet velocity for three different sizes of multi-blade fan 1 delivering 12,000 c.f.m. against a static resistance of 2 inches at 70°. 7. A multi-blade fan is to handle 9000 c.f.m. against a static head of 1M inches at 140°. What is the required speed and horsepower? 1 See tables in Appendix, pages 276 to 299. DESIGN OF FAN SYSTEMS 243 8. What would be the size of vento heater required to heat 800,000 cubic feet of air per hour from an outside temperature of 10° to a delivery tempera- ture of 140°? Assume a velocity through the heater of 1500 feet per minute. 9. What would be the size of vento heater required to heat 1,100,000 cubic feet of air per hour from an outside temperature of 0° to a delivery tempera- ture of 70°? Assume a velocity through the heater of 1100 feet per minute. 10. Find by means of the friction chart in Fig. 153 the frictional resistance of a vento heater, 5 stacks deep, for a velocity of 1500 feet per minute. Find the resistance of a vento heater, 3 stacks deep, for a velocity of 900 feet per minute. CHAPTER XVI AIR WASHERS AND AIR CONDITIONING 215. The Air Washer. — Various methods of filtering or washing air have been in use for many years. In the older forms of apparatus the dust was usually filtered from the air by means of muslin screens; but this method is not very effective and has the disadvantage that the screens soon become clogged with dirt, greatly increasing the resistance to the flow of air through them. Screen filters have been superseded by the modern air washer, in which the dirt is removed from the air by water sprays and by the contact of the air against wet surfaces. A typical air washer is shown in Fig. 155. It consists of three elements — the spray nozzles, the scrubber plates, and the eliminator plates. The nozzles are placed in a bank across the path of the air and the water is forced through them by a pump and is discharged in a fine conical spray or mist in the direction of the air flow. The air, drawn through the washer by the fan, is thus brought into intimate contact with the water and much of the dirt and soluble gases are removed. The final cleansing is done by the scrubber plates which are designed to change the direction of flow so that the dirt will be thrown out from the air by its inertia and by the rubbing of the air over the wet surfaces. The plates are kept flooded either by the spray nozzles or by a separate row of nozzles placed above them. Following the scrubber plates are a series of eliminator plates whose function is to remove the entrained water from the air. The lower part of the washer constitutes a tank into which the water falls and from which it is taken by the circulating pump. A float valve admits fresh water as required to replace that evaporated. Proper provision must be made in an air washer to prevent trouble from the large quantities of dirt which are washed from the air and deposited in the tank. A screen of ample area is necessary on the suction line to the pump to prevent the dirt from being carried into the circulating system, and in some types of washers special devices are necessary to enable the spray 244 AIR WASHERS AND AIR CONDITIONING 245 SIDE VIEW a Strainer Drain-* END VIEW Fig. 155. — Air washer. 246 HEATING AND VENTILATION nozzles to be cleaned periodically by flushing. The accumulated dirt must be removed from the tank at frequent intervals. The air washer is placed between the tempering coils and the heating coils of a fan system, this arrangement being necessary in order to insure that the air entering the washer will be at a temperature sufficient to keep the spray water from freezing. 216. Air Conditioning. — The air washer, in addition to cleans- ing the air, is also used to add to or reduce its moisture content so that the atmosphere in the building will be maintained in accordance with the standard fixed by ventilation or manufactur- ing requirements. In many textile processes, and in the manu- facture of powder, photographic films, etc., the proper "condi- tioning" of the air is of extreme importance. Humidification is accomplished by heating the spray water so that the air will absorb the proper amount of moisture while passing through the spray chamber. Sufficient heat is given up by the spray water, first to evaporate sufficient moisture to bring the air to saturation, at its entering temperature and, second, to add further amounts of heat and moisture until the air leaves the washer at saturation and at such a temperature that it contains the requisite quantity of water vapor. It then passes to the heating coils which raise its temperature without affecting its moisture content. For example, suppose that it is required to deliver air to a room at a temperature of 70° and a relative humidity of 60 per cent., which requires a moisture content of 4.85 grains per cubic foot. We will assume that the outside air has a dry-bulb tem- perature of 25° with a relative humidity of 20 per cent. Referring to Fig. 156, the entering air is heated by the tempering coils to a temperature of 40°, as represented by the line AB. In the washer moisture is absorbed from the spray water until the air becomes saturated at 40° as represented by BC. Both heat and moisture continue to be absorbed from the spray water until the air reaches the condition represented by point D, in which it con- tains 5.0 grain per cubic foot and has a temperature of 56°. It is then heated by the heating coils to the delivery temperature of 70°, at which it will have the required relative humidity of 60 per cent. During this process the moisture content per pound of air remains the same, the weight of the vapor per cubic foot decreasing slightly because of its expansion due to the tempera- ture increase. For approximate calculations this difference may AIR WASHERS AND AIR CONDITIONING 247 be neglected and the line DE representing this last step on the chart in Fig. 156 may be taken as a horizontal line. For very accurate work the charts in Figs. I and II in the Appendix, which are constructed on the basis of 1 pound of air, may be used. Every final condition of the air has a corresponding tempera- ture at saturation, to which the air is brought before it passes to the heating coils. If, in the case given above, the temperature of the outside air were above 56° it would be lowered because of the heat given up by it to evaporate the moisture which it absorbs — - 13 12 ii 3 10 O r o 8 57 u M c i2^Z iizz *l ^ v i tj£*,<5 o*^c n j/ \, ^ J wx2 ^^> ^ ""x "* / ^"l* Ix^-O^.. . ■> &?■}< *%< ^> -<*^ N.' x. - <^>^^ ; -^ ^ r^^ Js?sl : ^^2x ^-„ >v v v • > ^ C^^^^is. ^v ~v ^^^^^^ = 51 60 5« 40^6 30iS ; 20jt , 10 ji g 20 25 30 35 40 50 55 60 65 70 75 Dry Bulb Temperature Fig. 156. 85 90 95 100 105 provided, however, that its original moisture content be con- siderably below saturation. The action would then be repre- sented by the line FD. If the dry-bulb temperature of the enter- ing air were between 40° and 56° no heat would be added by the tempering coil and moisture would be added at a constant dry- bulb temperature until the air reached saturation, after which it would follow the line CD to 56° as before. 217. Spray-water Heater.— In order to supply heat to the spray water, a heater is installed in the water circulating line, usually between the pump and the spray nozzles. If high-pres- sure steam is available it is injected directly into the water 248 HEATING AND VENTILATION through a suitable valve. If low-pressure steam or hot water are used a closed heater, in which the spray water circulates through tubes surrounded by the heating medium, is necessary. 218. Humidity Control. — The steam supply valve of the heater is controlled — usually by automatic means- — so that the proper amount of heat is added to the water. In a compressed-air system of control, a diaphragm valve is placed on the supply to the water heater and may be operated by means of a "hygrostat" or "humidostat," which corresponds to the thermostat of a temperature control system. In place of the thermostatic element there is used some material such as wood or hair which undergoes a change in length when the moisture content of the surrounding air changes. The "humidostat" is placed either in Steam Supply /Water Inlet Water Outlet ' Fig. 157. — Spray-water heater. the main duct or in the principal room of the building and con- trols the supply valve on the heater. An injector type of heater with a diaphragm control valve is shown in Fig. 157. Another and a more rational method of humidity control is based on the fact that the air always leaves the washer in a saturated condition and therefore its moisture content will depend upon its tempera- ture. From a thermostat placed in the path of the air leaving the washer the heat added to the spray water is controlled so that the exit temperature of the saturated air is at the point fixed by the humidity required. In the example given in Paragraph 216 the thermostat at the washer outlet would be set for 56° and the temperature of the air leaving the washer would be maintained at that point. A special duct-type thermo- stat of the form shown in Fig. 158 is used for the purpose, having a bulb extending into the path of the air and controlling the air supply to the diaphragm valve in the usual manner. Humidification may also be accomplished by steam jets when no washer is used, in which case the jets are located in the same position as the washer and may be automatically controlled. AIR WASHERS AND AIR CONDITIONING 249 Another type of humidifier is located directly in the room and discharges a finely atomized spray which vaporizes after leaving the apparatus. If the steam supply is perfectly free from oil and does not possess a disagreeable odor, humidifiers of the type which discharge steam directly into the room may be employed. They are not always suitable for use in moderate weather, how- ever, as a considerable amount of heat is given up by the steam which might raise the room temperature to an uncomfortable point. The objection to these latter forms of humidifier is the absence of automatic means of regulating the humidity. | To Diaphragm Valve on Spray Water Heater Fig. 158.- Stem, in Path of Air T Air Supply -Duct thermostat for dewpoint method of humidity control. 219. Cooling and Dehumidification. — If no heat is added to the spray water of an air washer some evaporation will still take place but the latent heat of the vaporization in this case is taken from the air itself. It is by the application of this principle that cool- ing by means of an air washer is accomplished, the temperature of the air being lowered because of the heat supplied to vaporize the added moisture. The extent of the cooling effect depends upon the capacity of the entering air for absorbing moisture or, in other words, upon the wet-bulb depression of the entering air. As the air absorbs moisture in the spray chamber its dry- bulb temperature drops but the wet-bulb temperature, which is a measure of the total heat of the mixture, remains unchanged. If the water is re-circulated its temperature soon drops to the wet-bulb temperature. In a perfect washer the dry-bulb tem- perature of the air would be reduced to the same point — i.e., 250 HEATING AND VENTILATION the air would become saturated, but in a commercial washer this limit is never reached. The cooling effect actually obtained averages about 60 per cent, of the wet-bulb depression, this percentage being termed the humidifying efficiency of the washer. Referring to the psychrometric chart in Fig. 159, the point A represents the original condition of the air at 90° dry-bulb temperature and 75° wet-bulb temperature. The cooling and humidifying action is represented by the constant wet-bulb temperature line AB, the point B representing the final condition of 81° dry-bulb temperature. The line AC represents the ac- 13 12 u u 3 10 "3 r y 8 O 7 u <0 a 6 CD U 3 5 CD O a 4 ■8 ' /'n/ I^C^ ^~2^ "^ 4fP > K /N'^/ ^>< ^v< -s >. P" «5 J^ ^ A( S !^ ^ ^"ji ^ ^^ KX*"" ^K.'**' VC ^*C /*. ^^ ^^ X\ ,,N. /~\£ ^«/K- • *»* ^^ >< ^s/^^- V ** /X^yV^v'\ J^ ^v: ^. ~"v ^^xS^X ^^.^s^^ii ^.^>< ^^*^>!' ; * x?5 s.'^'s<^ < -^ ^^^^^"C ^"\ ~>^^-^ ^ ^<><5'C< < >< > '^-' >< ^ ><'^,^ > <' ^^ ^^^-^ ^ ^^ S^-*!^ SS > '^^<' < ' ^-^>< ^" V ^^^,"^i:^ ^ <^S : Ss^>J > ^5 , < : S- >: ^^^ :: '^->«^ "^^ ^^ ~\ (llliliSi^^^^?^^^^^;: 50* 40* 30*| 20*, 10* 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 Dry Bulb Temperature Fig. 159. tion if the air were cooled to efficiency of the washer is then = saturation. 90 - 81 The humidifying q _ -,. = 60 per cent., and the amount of moisture actually added is 1.2 grains per cubic foot, or approximately 60 per cent, of the 2.0 grains which it would be necessary to add to bring the air to saturation. A greater cooling effect can be obtained if the spray water be artificially cooled, in which case heat will be transferred from the air to water by direct contact and no evaporation will take place. Both the dry-bulb and the wet-bulb temperatures will fall until AIR WASHERS AND AIR CONDITIONING 251 they coincide at the dew point. If the spray-water temperature is sufficiently low they will be reduced still further and some of the moisture will be given up by the air. This action is represented by the line ADE in Fig. 159. In a properly designed washer the air can be cooled to within a few degrees of the average water temperature. This method of dehumidification is sometimes employed in industrial work. The cooling of the spray water is usually accomplished by means of a refrigeration plant. The brine coils are placed in the tank of the washer so that the spray water during its cycle passes over them. If a supply of cold artesian well water is available the cost of installation and operation is greatly reduced. CHAPTER XVII FAN SYSTEMS FOR VARIOUS TYPES OF BUILDINGS 220. School Buildings. — In school buildings and in various other public buildings, the fan system may be designed to furnish both the heating and ventilating requirements, or may be used to furnish ventilation only, the heating being done by direct radiation. In the former case, owing to the necessity for adjust- ing the temperature of the air supplied to each individual room, a single-duct system is necessary. When ventilation only is supplied a trunk-duct system may be used as the air is supplied continually at a temperature of about 70°. The arrangement Mixing Dampers Fresh Air Inlet Fig. 160. — Arrangement of single duct system. of the fan and heater in a single-duct system is shown in Fig. 160. The air passes first through the tempering coils, then through the air washer, if one is installed, and to the fan, which forces part of it through the reheating coils into the hot-air chamber and part of it into the tempered-air chamber. The double dampers at the entrance to each duct are controlled from thermo- stats in the respective rooms so that the temperature of the mixture of hot and tempered air is sufficient to supply the heat losses from the room and to maintain it at the proper temperature. The volume of air delivered is approximately constant regardless of the relative proportions of hot and tempered air. A mixing damper is illustrated in Fig. 161. The temperature of the tempered air is maintained at about 70° and that of the heated air at about 140°. Sometimes this arrangement is varied slightly by running double ducts to the foot of each vertical duct and installing a mixing damper at that point which is controlled by hand through a chain or cable from the room above. 252 FAN SYSTEMS FOR BUILDINGS 253 Provision must be made for removing the air from the rooms at the. same rate at which it is supplied and a system of vent flues is provided for that purpose. The flues from the separate rooms join together in a trunk duct and lead to a common discharge at the roof. The attic is sometimes used as a discharge chamber, the flues leading directly to it. Exhaust flues are figured at a velocity of 600 to 750 feet per minute and are assumed to carry off the same amount of air as is delivered to the room. In some cases an exhaust fan is installed to facilitate the removal of the foul air. The velocity in the exhaust flues can then be from 1200 to 1500 feet per minute. In public buildings over three or four stories in height, where the friction in the exhaust flues is appreciable, an exhaust fan is desirable. The ventilation of school rooms is usually done by the downward system, the air entering near the ceiling and be- ing exhausted near the floor. 221. Factory Heating.— The hot-blast system is often the best system for most industrial build- ings as it affords a means of supplying fresh air to replace ~ ^ f , _— —, that containing the fumes or ^k^gS^!^ moisture from manufacturing g processes. It is also desirable in factory buildings where the space required by direct radiation cannot be spared. Owing to the fact that such buildings are seldom divided into many rooms the air can be supplied at a constant temperature through a trunk system of ducts. A draw-through arrangement is almost universally used, the heating coils being placed on the suction side of the fan, which discharges directly into the main duet. For ordinary shop buildings of steel construction, the ducts are of galvanized iron and are suspended from the columns or roof trusses. An example of this arrangement is shown in Fig. 162. In modern reinforced-concrete buildings the columns are fre- quently made hollow and used as the air ducts, the heating ap- paratus and the trunk duct being located on the roof and ar- Fig. 161. — Mixing damper. 254 HEATING AND VENTILATION ranged to discharge the air into the top of each column. Dis- charge openings are made in the columns at each floor. The trunk duct and branch ducts which are on the roof must be well insulated. Details of this method of construction are shown in FAN SYSTEMS FOR BUILDINGS 255 Fan and Heater c Located In Pent House Branch Duct Hoof j ^ EeinioKed Concrete Flat Slab /Construction Fig. 163. The air is sometimes carried underground in brick or concrete ducts, but the heat loss from such ducts is con- siderable. 222. Heating of Theatres and Audi- toriums.- — Theatres and auditoriums are usually both heated and ventilated by the fan system. In a theatre the air is usually admitted through openings in the floor, the space beneath the floor acting as a plenum chamber as shown in Fig. 164. These openings are made adjustable so that the distribution of air throughout the house can be controlled. The foul air is removed through registers near the roof and beneath the galleries. An ex- haust fan is often provided. If it is not possible to introduce the air through the floor, registers in the side walls are pro- vided for the purpose. The former sys- tem provides a much more even distri- bution, however. Air washers are installed in all first-class theatres, both to remove dust from the entering air and to cool it. Direct radia- tion is usually necessary in the lobby, offices, and dressing rooms. Fig. 163. — Hollow column method of distribution. Fig. 164. — Theatre ventilating system. 223. Methods of Estimating Heating Requirements. — It is frequently necessary to estimate the cost of heating a building prior to its construction. It is a very difficult matter to do this accurately, first, because of the inaccuracies that are inevitable in the computation of the heat losses and, secondly, because of 256 HEATING AND VENTILATION the pronounced effect of the manner in which the firing is done and in which the system is handled. The most satisfactory method is to compute the theoretical heat loss and to apply a factor to allow for the manner in which it is believed the plant will be handled. To compute the total heat loss from the building, it is necessary to assume the tempera- ture at which the building is to be carried and the average outdoor temperature. The heat required for ventilation will depend upon the amount of air used and the number of hours of use. Example. — Given a school building heated with direct radiation and equipped with a ventilating system. With the following data furnished, what would be the annual fuel cost? Heat loss from the building per hour per degree difference in temperature between the inside and outside, 12,500 B.t.u., not including ventilation. Average outside temperature for heating season, 38°. Hours use of building, 8:00 a. m. to 4:00 p. m., 5 days per week. Amount of air supplied for ventilating, 40,000 cubic feet per minute. Cubic feet of space, 300,000. The actual time during which the building is used is 8 hours per day. Let us assume that a temperature of 68° is maintained for 10 hours of each of the 5 school days or 50 hours per week. Allowing for vacations, we may assume that the school is occupied for 32 weeks of the heating season, or 1600 hours per year. For the remainder of the 8 months or 5760 hours in the heating season, the temperature may be assumed to average 50°. The heat loss, not including ventilation, would then be as follows : 12,500 X (68 - 38) X 1600 = 1 600,000,000 B.t.u. 12,500 X (50 - 38) X 4160 = 623,000,000 B.t.u. 1,223,000,000 B.t.u. The ventilating fan, if properly handled, would be operated only during the actual hours of occupancy or 40 hours per week, 1280 hours per year. The heat loss from this source would be 60 X 40,000 X 1280 X 0.019(68 - 38) = 1,750,000,000 B.t.u. During the remainder of the time, the air may be assumed to change 1J^ times per hour due to infiltration. 300,000 X 1.5 X 4480 X 0.019(50 - 38) = 460,000,000 B.t.u. The total heat loss is then 3,433,000,000 B.t.u. Assume that the coal used contains 13,000 B.t.u and costs $5 per ton. For a plant of this nature, operated by efficient help, we may safely assume that 65 per cent, of the heat in the fuel is delivered to the building. The total annual cost would then be 3,433,000,000 5 13,000 X 0.65 A 2000 * uio This is the estimated cost on a strict basis. It would be well to add about 10 per cent, for safety, making the final estimate $1116.50. If unskilled help were to have been used or other known factors tending to extravagance in the use of heat, it might be necessary to increase the strict figure by as much as 30 per cent, in extreme cases. FAN SYSTEMS FOR BUILDINGS 257 224. Heating Requirements of Various Types of Buildings. — The variation in the amount of heat used in different types of buildings is shown in Table L, which gives data for a number of steam-heated buildings in Detroit, Michigan. These buildings are all heated from a central station. The heat loss per hour per degree difference in temperature is given for each building. It will be noticed that the steam consumption per B.t.u. of computed heat loss varies greatly for the individual buildings and that the average figures for the different classes of buildings are also quite different. Table L. — Steam Consumption of Buildings at Dbteoit, Michigan Heating Season of 1914-15 Average Temperature for Heating Season (Oct. 1 to May 31) — 38. 9-° a o CO 01 11 ■*-> at ption of in- .on ,1.1) ption cubic 1.2) ption f com- ss 1.3) e8 03 . 1 P CQ a.S R t- rt ' 3 2 a> m « u . agar o 2 o, a o o o o -^ m o-S o o3 ^^ o-** 3 "73 oj a m l-l 2° ■5 p, a o O a o3 GO So." i °° 03 Pi"" his OFFICE BUILDINGS Building No. 1 6,524 549,000 26,600 3,091,264 474 5,630 116.2 2 2,755 326,000 16,000 2,393,000 868 7,330 149.5 3 3,820 273,000 13,100 1,860,676 487 6,810 142.0 4 5,280 367,000 16,700 3,563,200 668 9,700 213.5 5 15,300 1,350,000 65,000 12,632,048 825 9,350 194.2 6 7,940 584,000 29,100 4,942,767 622 8,460 169.8 7 50,0003 3,220,000 120,000 34,209,387 684 10,630 285.0 S 79,500' 4,900,000 205,000 41,850,000 527 8,540 204.2 Totals and weighted aver- 171,119 11,569,000 491,500 104,542,342 610 9,020 212.5 RETAIL STORE BUILDINGS Building No. 1 1,673 160,960 8,715 627,200 375 3,900 71.9 2 1,256 111,500 ■ 6,400 364,700 290 3,270 f 57.0 3 16,1003 2,725,100 104,000 7,254,078 451 2,660 69.8 4 11,3153 1,063,100 42,400 6,012,348 531 5,660 141.9 5 3,864 403,000 18,700 2,110,900 550 5,250 112.9 6 2,684 459,400 18,400 987,000 368 2,150 53.6 7 4,413 325,500 17,700 1,677,800 380 5,140 94.6 8 1,701 199,000 8,690 1,437,600 843 7,210 165.0 9 3,632 613,000 21,600 3,133,650 862 5,110 145.0 10 2,620 393,000 16,500 1,539,560 587 3,910 93.2 11 2,513 350,00(5 11,890 2,214,200 880 6,320 186.1 12 2,162 197,800 8,200 1,072,900 496 5,420 130.8 Totals and weighted aver- 53,933 7,001,360 283,195 28,431,936 527 4,060 100.5 RESIDENCES: Totals and av- erages for 114 GARAGES: 65,421 3,156,800 304,499 37,484,000 573 11,870 123.0 Totals and av- erages for 12 11,414 1,219,700 74,243 9,949,800 870 8,160 134.0 1 B.t.u. per hour per degree difference between inside and outside temperatures. 2 Including steam for heating water. 8 Including equivalent of fan coil. 17 CHAPTER XVIII CENTRAL HEATING 225. Location of Power Plant. — It is not intended in this chapter to discuss the design of heating systems, such as are in- stalled for the purpose of heating parts of a city, but rather to describe the methods used in distributing heat to groups of build- ings such as public institutions; and as the conditions under which different systems are installed differ widely, the suggestions which follow can be but general. Before starting the design of the distribution system it is first necessary to have a careful survey made of the property, showing the location of the buildings to be heated and the elevation of their basements and first floors, together with a general profile of the ground through which the tunnels or pipes are to be run. The profile of the ground will largely determine the proper loca- tion of the power house. In general, the power house should be located as nearly as possible to the buildings to be heated or as nearly as possible to the largest steam load, but the facilities for receiving coal should also be taken into consideration. If it is possible to locate the plant on a siding from which coal can be delivered direct from the cars to the bunkers without trucking, this will often prove to be the most economical arrangement even if it necessitates locating the plant at some distance from the buildings to be heated; for the cost of loading, trucking, and un- loading will usually overbalance the investment charges on the additional length of steam pipes required if the plant is located in the more distant location. If possible the plant should be so located that the condensation from the various buildings can be drained to it by gravity, and it should also be located so that the floor of the boiler room can be drained to the sewer. Considerable difficulty is usually ex- perienced in carrying away the water from the cleaning and blowing down of the boilers if no sewer connection can be made. The question of the soil, the water supply, and the general appear- ance of the power house must also be taken into consideration. 258 CENTRAL HEATING 259 226. Boilers. — The selection of boilers of the proper type and size is of extreme importance in the economical operation of the plant. A thorough study should be made of the heating and electric load, both present and future. The maximum demand for steam for heating should be computed on a basis of the ra- diation installed plus a liberal allowance for transmission losses. The demand for steam due to the lighting and power require- ments should be computed from a knowledge of the maximum current demand and the steam consumption of the electric generating units, allowing also for the energy used by the power- plant auxiliaries. The boiler capacity must be such as to fill whichever of the two requirements proves to be the greater. The exhaust steam should always be utilized insofar as possible for heating. When the available exhaust is not sufficient, some live steam must be used, while if there is more exhaust steam than can be utilized some of it must be discharged to atmosphere. After having determined the maximum amount of steam which the plant might be called upon to furnish, the size of the boilers can be chosen. The steam output per rated boiler horsepower varies considerably according to the type of boiler, type of fur- nace, etc., but a rough rule for small plants is to assume that 1 square foot of heating surface in a boiler will evaporate 3 pounds of water per hour. The total boiler capacity can then be computed upon this basis and it should be divided into units of such sizes that the expected range of loads can be handled by operating the boilers within their range of highest economy. This can best be done by providing a certain boiler or boilers to handle the lightest loads which are expected and other boilers to handle the average operating load and the maximum load. It is de- sirable that there be a sufficient number of boilers in the plant so that the largest one can be cut out of service at any time for clean- ing or repairs. If the boiler pressure to be carried is less than 100 pounds, either fire-tube or water-tube boilers may be used. In general, for this service fire-tube boilers are very satisfactory, as they have large water storage, repairs are easily made, and the boiler may be operated at an output considerably beyond its rated capacity. The principal objection to fire-tube boilers, except those of the Scotch marine type, is the large space which they occupy. If the boilers are to be operated at pressures much over 100 260 HEATING AND VENTILATION pounds as will usually be the case if electric generating units are installed, then only water-tube or Scotch marine boilers should be used. 227. Systems of Distribution — Gravity System. — -The com- mon method of distributing heat is to pipe the steam to the vari- ous buildings and return the condensation to the power house. If the elevation of the power plant with respect to the other buildings will permit, the condensation may be returned by gravity to the boiler and no pumping is necessary. With this system any difference in steam pressure between the boiler and the extreme point in the piping system will result in a correspond- ing elevation of the water level in the return system at the extreme point — each pound of pressure difference producing a difference in level of 2.31 feet. It is essential, then, that with a gravity-return system the difference in pressure between the boiler and the extreme point of the piping system be compara- tively small . The drop in pressure assumed will determine the size of the steam piping. In gravity systems it is usual to allow for a drop in pressure of not over 2 pounds between the boiler and the extreme end of the system. In some cases the gravity-return system has been used over quite an extended area, one building so heated being as far as 2500 feet from the boiler, and the system has given very good satisfaction. In a central heating plant using the gravity-return system, unless the steam mains are from 6 to 8 feet above the return pipes, it is necessary that the steam condensed in the mains be dripped into a separate return line and pumped back to the boilers, by a pump or a return trap. The pump or trap should be of sufficient size to take care of the large amount of conden- sation which occurs when the steam is first admitted to the cold pipes. By returning the condensation of the mains sepa- rately, hammering is avoided and the system can be started much more rapidly. Gravity-return systems are rarely used where the boiler pres- sure exceeds 10 pounds. 228. Low-pressure Pump Return System. — In a very large system where it is difficult to get enough difference in elevation between the steam and return mains, or where the drop in pres- sure exceeds 2 pounds, it is usual to install a pump return system. This will usually be necessary in case any of the buildings are piped with a two-pipe vapor system as the difference in CENTRAL HEATING 261 pressure between the main and return is then quite liable to be over 2 pounds. One of the common arrangements is to dis- charge the condensation from each building through a trap into the return main which carries the water back to a tank in the power house. From this tank the water is returned to the boilers by means of a pump. The drip from the steam main is trapped directly to the return main. 229. High-pressure System. — Steam is sometimes distributed at high pressure and the pressure reduced before entering the building piping systems by means of a reducing valve. This method has some advantages. Because of the higher pressure, the allowable pressure drop in the distributing pipes is greatly increased. This, together with the fact that the specific volume of the steam is less at the higher pressure, allows the use of much smaller pipes in the distribution system and thereby reduces its cost. In determining the srze of the steam mains, a considerable drop may be allowed under maximum conditions, providing the pressure at the most distant building is always sufficient to heat the building. 230. Combination of Power and Heating System.- — In the majority of cases the heating system is combined with an electric lighting and power system. The piping connections may be made in a manner quite similar to the arrangement in Fig. 97, page 140, provision being made to feed live steam to the heating mains to supplement the exhaust steam when the latter is less than the heating requirements. A back-pressure valve should be provided to insure against the building up of an excessive pressure in the heating mains. When the heating load is very large in comparison with the electrical load, part of the boilers can be used as high-pressure boilers and the others can be lower priced low-pressure boilers connected directly to the heating lines. The desirability of such an arrangement, however, is determined entirely by local conditions. 231. Hot-water Heating.- — A hot-water system, using forced circulation, is very satisfactory if properly designed. The water is heated in a tube heater by the exhaust steam and is circulated through the system by means of a centrifugal pump. A vacuum can be carried on the engine exhaust to a degree depending upon the outgoing temperature of the water. To supplement the exhaust steam heater a live steam heater is installed, but in most cases it need be operated only in the coldest weather. The 262 HEATING AND VENTILATION temperature of the outgoing water is adjusted by the operating engineer for the prevailing weather conditions in accordance with a prearranged schedule. The distribution lines in a hot-water system may be arranged according to either of two schemes. In the one-pipe circuit system a single main makes a complete circuit of the territory covered and the supply connection to each building is taken from the top of the pipe and the return connection is made to the bottom of the pipe a few feet further along and a resistance is inserted in the pipe between the connections which has the effect of diverting the water into the building system. In the multiple or two-pipe system both a flow- and a return- main are installed, the water passing from the flow main through the building systems and back to the plant via the return main. The multiple system is the more commonly used although it is somewhat the more expensive to install. The systems in the buildings are arranged in the ordinary manner for either system of distribution. 232. Methods of Carrying Pipes. — The pipe lines serving the buildings should always be carried underground if possible. Fig. 165. — Wood casing. Pipes installed above ground are extremely unsightly and are difficult to support and to insulate. Underground pipes may be installed either in a small conduit or in a tunnel of walking height. The former is a much cheaper method and is quite satisfactory when only one or two pipes are to be installed, but when a greater number of pipe lines must be provided for or when electric cables are also to be installed, a walking tunnel is desirable. There are a large number of designs of conduits ranging from a rough wooden box to a heavily insulated and waterproofed covering. The essential requirements in a conduit for heating pipes are- — good insulating qualities, protection of the pipe from water, provision for free expansion of the pipe, and durability. CENTRAL HEATING 263 A very common form of covering is the wood casing shown in Fig. 165. The casing has a wall 4 inches thick and is built of segmental staves bound tightly together with steel or bronze wire, and the assembled casing is rolled in tar and sawdust to give it a waterproof coating and is lined with bright tin to reduce the radiation loss from the pipe. Wood is a very good insulator and if installed under favorable conditions, this form of conduit is very satisfactory. The wood deteriorates, however, if subjected to continued dampness. The concrete conduit shown in Fig. 166 has the advantage of being very durable and is very easily constructed from common materials. The concrete prevents any considerable amount of Concrete^ :a>.- &"•>:• :^*, "•'.•&;-"•-& Fig. 166. — Concrete conduit. water from reaching the pipe and if desired can be made nearly waterproof by the addition of a waterproofing compound. In building this conduit the concrete bottom is first poured and allowed to set and then the pipe is installed and covered with ordinary pipe covering. The wooden box is then built over it and the remainder of the envelope is poured, the sides of the trench serving as the outer sides of the form if the soil is suffi- ciently cohesive. The supports for the pipe in any form of conduit must be such as to allow it to move freely when it undergoes a change in length. Some form of roller is commonly used and they are placed at intervals of 10 or 15 feet. Another form of conduit is built of vitrified tile split longitudi- nally 'and having insulating material either molded to the walls 264 HEATING AND VENTILATION of the tile or packed around the pipe. The joints are cemented to render them water-tight. Such a conduit is shown in Fig. 167. There are many other types of construction in use but those which Diatomaceous Insulation rnrmrrrTTTiii.ini -Split tile conduit. have been described are representative. The heat loss from underground lines depends upon the steam temperature, efficiency of the insulation, and the soil conditions. Tests made on the district heating mains of the Detroit Edison Company in 1913-14, Fig. 168.— Slip joint. which are laid in conduit of the forms shown in Figs. 165 and 166, gave a result of 0.0511 pounds of condensation per square foot of external pipe surface per hour for steam at 5 pounds pressure. 233. Expansion Fittings. — Owing to the length of the pipe CENTRAL HEATING 265 lines special provision is necessary to take care of the expansion. It is seldom feasible to do so by means of bends, and special fittings are required. The slip joint illustrated in Fig. 168 is a simple means of absorbing large amounts of expansion. It consists of a sleeve which is free to move in the body of the fitting, a packing gland being provided to prevent leakage. Slip joints are located at intervals of from 200 to 300 feet depending upon the steam temperature. They must be installed in manholes or in some other place where they are accessible for packing. The type of expansion fitting shown in Fig. 169 depends upon the Service Outlet Outer Ring'' Fig. 169. — Diaphragm expansion joint. flexibility of a copper diaphragm for absorbing the movement of the pipe. The advantage of such a fitting is that it requires no manhole and does not need to be packed. The amount of travel which can be allowed for each fitting is small, the fittings being usually placed at intervals of 80 to 100 feet and the pipe anchored midway between them. The body of the fitting is also anchored and the expansion of the pipe on either side is taken up by the diaphragms. The cost of a pipe line fitted with diaphragm joints is considerably greater than when slip joints are used. 234. Installation of Underground Lines. — Careful provision should be made for carrying away the ground water from the pipe, particularly if the soil is of clay. A drain tile is installed 266 HEATING AND VENTILATION for the purpose, either directly below or to one side of the con- duit and is surrounded with crushed stone or coarse gravel extending around the lower part of the conduit. Water seeping through to the conduit finds its way into the tile, which carries it away to the sewer. Unless this provision is made, the water will reach the pipe and will corrode it very rapidly. 235. Tunnels. — Tunnels of brick or concrete are used when several pipes are to be carried. The size and shape of tunnel used will depend upon the number of pipes to be carried, the character of the soil, and the depth of the tunnel in the ground. Fig. 170 shows a small tunnel suitable for pipes of about 8 inches diameter or less. It is of brick 4 inches thick and has a layer of Portland cement on the outside which is painted with a thick coat of tar or asphalt over the arch to keep out water. Ribs 4 inches thick and 8 inches wide are placed where the sup- ports are imbedded in the walls. The supports are of ordinary pipe. A drain tile may be placed on either side to carry away the ground water but no such provision is necessary if the tunnel is built in a sand or gravel soil. Owing to the small size of this tunnel and its low head room it is not very suitable for large pipes or when much walking through it is necessary. Missing Page 268 HEATING AND VENTILATION sure work. In underground piping the noise in the pipes is not a factor and advantage can therefore be taken of all of the avail- able pressure drop to decrease the size of the pipes. In a high- pressure system very much greater pressure drops are permissible and the pressure may be allowed to drop, under maximum condi- tions, from the boiler pressure nearly to the pressure required for heating. It should be borne in mind, however, that the pres- sure drop varies as the square of the weight of steam flowing and Fig. 172. consequently a steam flow slightly greater than that estimated will cause a considerably greater pressure drop. It is therefore best to allow a reasonable margin in selecting the pipe sizes. The chart in Fig. 95 is suitable only for pressures of approxi- mately 2 pounds. For higher pressures the capacity of various size pipes for a given pressure drop can be found from the basic formula of Par. 118. For hot-water systems the pipe sizes can be computed by the methods given in Chapter X. APPENDIX Thblb I — Coefficients of Heat Transmission Through Building Materials Walls Brick Walls Coefficient of heat transmission, (k) B.t.u. per square foot per hour per degree difference of temperature. Thickness, inches Plain Plastered on one side Furred and plastered k k k 4 0.52 0.50 0.28' 8M 0.37 0.36 0.23 13 0.29 "0.28 0.20 17H 0.25 ' 0.24 0.18 22 0.22 0.21 0.16 26K 0.19 0.18 Concrete Walls Thickness, inches Plain Furred and plastered Thickness, inches Plain Furred and plastered k k k k 2 0.69 16 0.37 0.24 4 0.55 0.31 20 0.33 0.23 6 0.49 0.30 24 0.30 0.215 8 0.47 0.28 28 0.27 0.20 10 0.45 0.265 32 0.25 0.18 12 0.43 0.25 36 0.23 0.17 Brick Walls, Sandstone Faces Thickness of brick, inches Thickness of sandstone, inches k Thickness of brick, inches Thickness of sandstone, inches k 4 4 0.31 12 8 0.16 8 4 0.22 4 12 0.26 12 4 0.17 8 12 0.19 4 8 0.29 12 12 0.15 8 8 0.20 269 270 HEATING AND VENTILATION Table I. — Coefficients of Heat Transmission Through Building Materials (Continued) Walls Limestone Walls Thickness, inches Furred and plastered Thickness, inches Furred and plastered k k 12 0.49 28 0.31 16 0.43 32 0.28 20 0.38 36 0.26 24 0.35 40 0.24 Tile Walls Thickness, inches Plain tile Tile and stucco Tile, stucco, and plaster k k k 4 0.79 0.75 0.34 8 0.56 0.54 0.27 12 0.44 0.41 0.26 16 0.40 0.37 0.23 20 0.33 0.31 0.20 Wooden Walls Clapboard %6 inch, studding, lath and plaster Clapboard %6 inch, paper, studding, lath and plaster Clapboard %g inch, sheathing % inch, studding, lath and plaster. Clapboard %6 inch, paper, sheathing % inch, studding, lath and plaster k 0.44 0.31 0.28 0.23 Miscellaneous Wooden Walls Thickness of board, inches Pine boards only Double boards, paper between Board and corrugated iron l m 2 2M k 0.77 0.51 0.43 0.35 0.30 k 0.32 0.24 0.19 0.16 0.14 k 0.45 0.36 0.30 0.26 0.23 Inside Partitions:] Lath and plaster, one side . . . Lath and plaster, both sides . k 0.60 0.34 APPENDIX 271 Table I. — Coefficients of Heat Transmission Through Building Materials (Continued) Floors Floors near ground, assuming ground temperature = 50° k Cement or tile, no wood above 0.31 Cement or tile, wood above 0.08 Dirt floor . 23 Single thickness wood, on joists 0.10 Double thickness wood, on joists . 08 Ceilings k Cement or tile, no wood above . 39 Cement or tile, wood floor above 0.10 Lath and plaster, no floor above . 32 Lath and plaster, single floor above . 26 Metal lath and plaster, no floor above . 49 Roofs Metal Roofs: k Tin on 1-inch sap wood roofing boards . 45 Copper on 1-inch sap wood roofing boards . 45 Unlined metal 1 . 30 Corrugated iron 1 . 50 Iron over tongue and groove boards . 20 Iron on wood for framing only 1 . 32 Slate Roofs: Unlined slate 0.82 Slate on 1-inch sap wood roofing boards . 43 Slate over tongue and groove boards . 30 Slate on wood for framing only . 80 Tile Roofs: Tile % to 1 inch thick 0.80 Tile on boards 0.30 Miscellaneous : Shingles on narrow 1-inch wood strips . 33 Tar paper on 1-inch sap wood roofing boards . 44 Tar and gravel over tongue and groove boards 0. 30 Roofs Miscellaneous {Continued) : k Six-inch hollow tile, 2-inch concrete, tar and gravel. ... 0.36 Same, but with 8-inch tile 0. 30 Two-inch concrete, with cinder fill . 80 Four-inch concrete, with cinder fill . 60 Six-inch concrete, with cinder fill 0. 54 272 HEATING AND VENTILATION Table I. — Coefficients of Heat Transmission Through Building Materials (Continued) Windows, Skylights, and Doors Average single windows 1 . 09 Small size windows of ordinary glass 1 . 20 Single large windows of plate glass 1 . 08 Double windows 0.45 Single-frame windows with double glass 0. 72 Single skylight 1.50 Double skylight . 50 Single monitor 1 . 25 Doors Thickness, inches Pine Oak Thickness, inches Pine Oak H l k 0.56 0.47 0.41 k 0.70 0.63 0.58 2 k 0.36 0.32 0.27 k 0.54 0.50 0.43 Table II. — Thermal Properties of Water 1 Temperature, degrees F. Specific volume, cubic feet per pound Density, pounds per cubic foot Specific heat 20 0.01603 62.37 1.0168 30 0.01602 62.42 1 . 0098 40 0.01602 62.43 1.0045 50 0.01602 62.42 1.0012 60 0.01603 62.37 0.9990 70 0.01605 62.30 0.9977 80 0.01607 62.22 0.9970 90 0.01610 62.11 0.9967 100 0.01613 62.00 0.9967 110 0.01616 61.86 0.9970 120 0.01620 61.71 0.9974 130 0.01625 61.55 0.9979 140 0.01629 61.38 0.9986 150 0.01634 61.20 0.9994 160 0.01639 61.00 1.0002 170 0.01645 60.80 1.0010 180 0.01651 60.58 1.0019 190 0.01657 60.36 1.0029 200 0.01663 60.12 1.0039 210 0.01670 59.88 1.0050 220 0.01677 59.63 1.007 230 0.01684 59.37 1.009 240 0.01692 59.11 1.012 250 0.01700 58.83 1.015 1 Condensed from Marks and Davis "Steam Tables.' APPENDIX 273 PSYCHROMETRIC CHARTS The curves in Figs. I and II 1 give the complete properties of air based on the pound of air as a unit. The curves in Fig. I are to be used for dry-bulb temperatures of from 20° to 110° and those in Fig. II for dry-bulb tempera- tures of from 80° to 380°. Having given the wet- and dry-bulb tempera- tures of the air, the moisture content in grains per pound of dry air is found by passing vertically from the dry-bulb temperature on the horizontal scale to the diagonal line corresponding to the wet-bulb temperature and thence horizontally to the scale of moisture content at the left. The dew point is determined by passing horizontally to the left from the intersection of the dry-bulb and wet-bulb temperature lines to the saturation curve, the point of intersection being the dew point. The heat required to raise the tem- perature of 1 pound of air plus its moisture content when saturated, and the corresponding vapor pressure are found by passing vertically from the dew point to the respective curves and thence to the corresponding scales at the left. The total heat is found by passing vertically from the wet-bulb tem- perature on the saturation curve to the total heat curve and thence to the scale at the left. The volume of air in cubic feet per pound for saturated air and for dry air is obtained by passing vertically from the dry-bulb tempera- ture to the respective curves and to the scale at the left. Example. — Assume dry-bulb temperature = 75° relative humidity = 60 per cent. From the chart we obtain : Wet-bulb temperature, 65.25°; dew point, 60°; grains moisture per pound dry air, 77; heat required to raise 1 pound air plus its moisture content when saturated at 60° through 1°, 0.247 B.t.u. Vapor pressure of air saturated at 60°, 0.523 inches mercury. Total heat in 1 pound of air with its moisture content when saturated at 65.25°, 29.75 B.t.u. As to this last quantity, the total heat of saturated air at 65.25° is the same as that of the air under the given conditions, 65.25° being the wet-bulb temperature. 1 From "Fan Engineering," Buffalo Forge Company. 18 274 HEATING AND VENTILATION 0S3 OSS 015 061 Oil ogi 081 OH 06t Oil OST 081 OH 06 APPENDIX 275 ooei oon ooot 006 008 001 009 005 OOt oos 276 HE ATINO AND VENTILATION STATIC PRESSURE TABLES FOR A. B. C. TYPE S, STEEL PLATE FAN CAPACITY TABLE Table III. — No. 50 Single Inlet Steel Plate Fan — Type S s. p. H" S. P. H" S. P. H" S. P. H" S P. H" S P. H" Vol- ume * O > -a a V B TS s •a a T3 a ■o a —4 co ft ja am a ja o. Si a -= ft o a J3 a, J , p, .a ft«s a ja A cq ^s A ffl hS A m C ft tr 1 co a « (-1 a tr* co a m a « 2250 1000 2366 301 .218 2690 343 .291 2940 375 .365 3175 404 .443 3400 433 .523 3610 460 .610 2475 1100 2491 317 .256 2781 354 .337 304(1 387 .417 3267 416 .501 348(1 443 .585 3671 468 .675 2700 1201 260C 331 .305 2925 373 .390 3125 398 .473 3361 427 .563 3575 455 .655 3763 480 .747 2925 13(11. 2736 Ml .360 300(1 382 .446 3237 412 .537 3475 442 .633 3675 468 .730 3865 492 .828 3150 1401 2X46 362 .418 3107 395 .509 3310 422 .603 3573 455 .707 3750 478 .808 3965 505 .914 3375 150(1 2987 381 .490 3226 411 .586 346C 441 .686 3651 465 .790 3860 402 .895 4061 517 1.01 360C KiO( star 391 .563 335C 427 .666 3565 454 .770 3765 48(1 .880 396(1 504 .990 416(1 530 1.11 3825 1701 3271 416 .645 3475 442 .755 3681 46i .864 3S85 495 .978 4055 517 1.10 4251 541 1.22 405C ISO! 341 ( 431 .750 3607 461 .855 381 C 485 .973 4011 510 1.09 4180 533 1.24 4351 554 1.34 4275 1901 3546 452 .838 3731 475 .965 3935 501 1.08 412( 524 1.21 432(1 551 1.34 4455 567 1.46 450C 2001 370( 471 .949 386C 491 1.08 4051 515 1.20 4255 541 1.34 4423 564 1.47 45XC 584 1.61 4725 2101 385C 49( 1.07 400C 511 1.21 4211 536 1.33 4351 554 1.48 4535 57X 1.62 4681 596 1.75 495C '2201 1001 511 1.20 4163 531 1.36 4321 551 1.49 450( 573 1.63 467(1 595 1.78 4X01 611 1.92 5175 2301 4323 551 1.50 4451 56( 1.63 462r 581 1.79 4771 607 1.95 4931 628 2.10 540C 2401 4461 56X 1.62 162( 588 1.82 474( 604 1.97 4921 626 2.13 5045 641 2.285 5625 2501 4601 586 1.83 4721 lilll 1.99 48X1 622 2.16 5036 641 2.32 5171 658 2.485 585( 2601 49H 625 2.20 5001 637 2.36 51X1 66( 2.54 5325 B7& 2. 700 630( 2801 5181 661 2.62 52X( 671 2.81 5435 692 2.98 5511 702 3.180 6750 3000 5485 60S 3.09 5610 714 3.31 5650 720 3.48 5S40 744 3.692 S. P. 1" S. P. IK" S. P. iy 2 " S. P. IK" S. P. 2" S. P. 2J4" Vol- ume co IN o > ■a a ft ft ft aj a ft ft ja ■a a d ■a a ft A a ft d ja -a 0,8 a d d .a il a ST* m A PP il ft r* co A M c^ CO A m r* co A M C ft t" 1 CO A m C^ CO A m 2700 1200 3955 503 .850 4152 529 1.04 4470 570 1.26 4950 630 1.48 5230 667 1.72 5750 732 2.22 2925 13011 4050 515 .927 4380 558 1.13 4550 580 1.35 5024 64(1 1.59 5295 673 1.83 5820 740 2.34 3150 1400 4143 527 1.02 4465 569 1.24 4700 598 1.46 5105 65(1 1.70 535(1 681 1.97 5900 752 2.49 3375 150(1 425(1 541 1.12 4570 582 1.33 48511 617 1.58 51X0 66(1 1.83 545(1 694 2.09 5950 757 2.64 360(1 1600 4325 550 1.22 4652 594 1.47 4950 630 1.71 5245 667 1.96 555(1 707 2.23 6025 767 2.80 3825 17(11 4437 564 1.34 4750 605 1.61 5040 642 1.85 533(1 67U 2.11 5625 717 2.38 6100 777 2.96 4051 1801 4527 576 1.47 4846 616 1.73 51111 652 1.99 541(1 6X1 2.28 570(1 725 2.55 6195 7X8 3.15 4275 1901 4613 5SX 1.60 4945 631 : 1.87 5231! 666 2.14 5520 702 2.44 5780 737 2.73 6265 79X 3.33 4501 2001 4743 604 1.75 .5(175 646 2.03 5325 678 2.32 562(1 715 2.62 5860 746 2.92 6365 X10 3.53 4725 2101 4X51 HIS 1.89 5145 655 2.19 5441 693 2.49 5724 721 2.81 5955 759 3.12 6475 825 3.76 4951 2201 4971 633 2.07 5256 671 2.365 5551 707 2.68 579(1 73X 3.00 6050 769 3.32 6550 835 4.00 5175 2301 5091 643 2.345 5371 684 2.565 5631 717 2.88 590(1 751 3.22 6150 7X3 3.54 6610 844 4.24 5401 2401 5211 663 2.447 5481 698 2.770 5751 732 3.09 6025 767 3.44 6271 79X 3.78 6700 X53 4.50 5625 2501 5341 681 2.655 5610 715 2.970 5851 745 3.32 6101 776 3.67 6343 808 4.04 6800 865 4.76 585C 2601 5485 (HIS 2.875 5741 731 3.22 5981 762 3.56 6201 79( 3.92 6461 823 4.31 6880 8775.04 6301 2X01 5711 727 3.390 5960 759 3.715 6231 794 4.09 6461 822 4.48 665( X47 4.86 7090 903 5.65 6751 3001 5971 761 3.890 6200 790 4.28 6461 X22 4.68 6675 851 5.07 6901 871 5.49 7295 928 6.32 7201 3201 6231 794 4.480 6475 825 4.91 6731 857 5.34 6»2( XXI 5.74 7135 909 6.17 7531 960 7.02 7651 3401 6581 83,' 5.180 6741 8.18 5.62 696( 886 6.06 7151 911 6.51 7355 937 6.93 7750 987 7.83 8101 360( 6815 871 5.900 7001 891 6.37 7201 91616.85 7441 948 7.30 7600 968 7.78 8020 1021 8.69 8550 3800 7105 905 6.730 7350 936 7.25 7475 952j7.72 7060 976 8.21 7840 999 8.67 8220 1047 9.68 APPENDIX 277 CAPACITY TABLE Table IV. — No. 60 Single Inlet Steel Plate Fan — Type S S. P. Yi" S P. %" S P. H" S P. H" S P. %." S P. H" Vol- ume ft 2.60 472(1 502 2.83 488(1 518 3.07 5036 534 3.30 51 7( 54C 3.53 8321 260( 491(1 521 3.13 5001. 531 3.36 518(1 55( 3.61 5325 565 3.84 896( 280( 518(1 BS( 3.71 5281 56(1 3.99 5435 571- 4.23 55K 585 4,53 9600 3000 5485 582 4.40 5610 596 4.71 5650 600 4.96 5840 620 5.25 Vol- 05 S. P. 1" S. P. 1M" S. P. 1H" S. P. l%" S. P. 2" S. P. 2)4" ume 5^ O > T3 ftSi a d d j3 Tl a? a d d A ■a ft QJ a d d J3 -a ft ro a ft d J3 13 ftS a d d ft a d ft H£ rt m (-1 "■ CT 1 to « m C ft tr 1 co P5 ffl ft! u t - " co A m il ft tr 1 co « m 1-1 " tr 1 to rt M 3840 1200 3955 420 1.21 4152 452 1.48 4470 475 1.79 4950 525 2.10 5230 555 2.44 5750 610 3.16 4160 130C 405(1 430 1.32 4380 465 1:61 455(1 483 1.92 5024 533 2.26 5295 561 2.61 5820 617 3.33 448C HOC 4143 43d 1.45 4465 474 1.76 47011 409 2.08 5105 542 2.43 5350 568 2.80 5900 626 3.54 480C 150(1 4250 451 1.59 4570 485 1.91 485(1 515 2.25 518(1 55(1 2.61 5450 578 2.97 5950 631 3.76 512C 160(1 4325 45S 1.74 4652 495 2.09 495(1 526 2.43 5245 557 2.78 5550 580 3.18 6025 640 3.98 544C 170(1 4437 471 1.91 4750 504 2.29 504(1 534 2.63 533(1 566 3.01 5625 598 3.39 6100 648 4.22 576C 180(1 4527 481 2.08 4846 514 2.46 511(1 542 2.83 541(1 574 3.24 570(1 605 3.63 6195 658 4.48 608C loor 4613 490 2.27 4945 525 2.66 523(1 555 3.05 552(1 586 3.47 5780 613 3.89 6265 665 4.74 640C 200f 4743 504 2.48 5075 538 2.89 5325 565 3.29 562(1 597 3.73 5861 621 4.16 6365 676 5.03 6720 210f 4850 515 2.69 5145 545 3.12 544(1 578 3.55 5724 607 4.00 5955 632 4.43 6475 687 5.35 704C 2200 4970 S?f 2.94 5256 Sfif 3.37 5550 588 3.81 579(1 615 4.28 6051 642 4.72 6550 695 5.68 7360 2300 509f 540 3.33 5370 570 3.65 5630 598 4.09 5900 626 4.58 6150 653 5.05 6610 701 6.03 768C 240f 52 If 553 3.48 5480 583 3.93 5750 61(1 4.39 6025 64(1 4.90 6271 666 5.38 6700 711 6.40 800C 250f 5340 567 3.78 561 ( 595 4.23 585(1 621 4.72 610(1 64t 5.22 6343 674 5.74 6800 722 6.77 8320 260f 5485 58? 4.09 5740 60S 4.58 5980 635 5.07 6200 651- 5.57 646( 686 6.13 6880 730 7.17 896C 280f 5710 606 4.82 5960 632 5.28 623(1 661 5.83 646(1 686 6.37 6«5( 706 6.91 7090 752 8.04 960C 3000 5970 633 5.54 6200 658 6.08 646(1 686 6.67 6675 608 7.23 6900 732 7.82 7295 773 8.98 1024C 320f 6230 662 6.37 6475 687 6.98 6730 715 7.58 692( 735 8.17 V135 757 8.80 7530 799 9.98 1088C 340f 6580 698 7.36 6740 715 8.00 69W 73(1 8.62 71 51 761 9.26 7365 781 9.87 7750 823 11.14 1152C 360f 6815 723 8.40 700f 745 9.09 7201. 764 9.75 7441 791 10.39 7601 807 11.08 8020 851 12.37 12160 3800 7105 7.55 9.58 7350 780 10.32 7475 793 10.98 7660 814 11.67 7840 832 12.33 8220 873 13.78 278 HEATING AND VENTILATION CAPACITY TABLE Table V. — No. 70 Single Inlet Steel Plate Fan — Type S S. P. H" S. P. H' g P. H" S. P. H" S. P. K" S. P. H" Vol- ume CD 13 6 13 S 13 s -a S 13 S P. TJ 6 ft _' > a If, ft .a ft* .ft x p. CD p, X ft cd ft X ft ( 5180 471 4.82 52NI. 480 5.19 5435 491 5.50 5510 501 5.88 12480 3000 5485 499 5.71 5610 511 6.12 5650 514 6.43 5840 530 6.82 S. P. 1" S. p. m" S. P. U4" S. p. IK" S. P. 2" S. P. 2W Vol- CD ume 3*3 ft a> S ft ft X T3 & CD s p. ft 13 ft. CD a ft x T3 ftrn S n ft X 13 ft cd s ft ft x 13 ft CD S ft ft X H £ K CQ « m r^ co « m H& « n tr 1 to « m P& « po 4992 1200 3955 359 1.57 4152 37S 1.92 4470 407 2.33 4950 450 2.72 5230 475 3.17 5750 523 4.11 5408 1300 4050 368 1.71 4380 39,S 2.09 4550 415 2.50 5024 457 2.93 5295 481 3.39 5820 529 4.32 5824 1400 4143 376 1.88 4465 406 2.28 4700 427 2.71 5105 465 3.15 5350 487 3.63 5900 536 4.59 6240 1500 4250 3X6 2.07 4570 416 2.48 48511 441 2.91 5180 471 3.38 5450 495 3.86 595(1 541 4,88 6656 1600 4325 393 2.26 (652 424 2.71 4950 450 3.15 5245 476 3.61 5550 505 4.13 6025 548 5.17 7072 1700 4437 404 2.47 4750 432 2.97 5040 45!) 3.42 5330 484 3.90 5620 511 4.41 fiinn 555 5.47 7488 1800 4527 412 2.70 1846 440 3.19 5110 465 3.67 5410 494 4.21 5700 519 4.72 6195 563 5.82 7904 1900 4613 420 2.95 4945 449 3.45 5230 475 3.96 5520 502 4.52 5780 525 5.05 ll"liS 570 6 IS 8320 2000 1743 430 3.22 5075 461 3.75 5325 4S4 4.28 5620 511 4.84 5860 533 5.40 6365 579 6,52 8736 ■lino 4850 441 3.50 5145 468 4.05 5410 494 4.61 5724 521 5.20 5955 541 5.76 6475 588 6 95 9152 v.oa 4970 452 3.81 i25li 477 4.37 5550 505 4.96 5790 527 5.55 6(150 550 6.13 6550 595 7,38 9568 2300 5090 463 4.33 5370 488 4.74 5630 512 5.32 5900 536 5.95 6150 560 6.55 6610 601 7 82 9984 2400 5210 474 4.52 5480 498 5.11 5750 523 5.70 6025 547 6.36 627(1 570 6.98 0,7(10 610 8,39, 10400 WI0 5340 485 4.91 5610 510 5.49 585(1 532 6.13 6100 555 6.78 6343 575 7.46 68(10 618 8 80 10816 2600 5485 498 5.32 5740 522 5.95 5980 544 6.58 6200 564 7.23 646(1 587 7.96 ■■,880 625 9 32 11648 1800 5710 520 6.26 i960 542 6.85 6230 567 7.57 6460 587 8.28 665(1 605 8.98 7090 644 10 44 12480 3000 5970 542 7.19 ■,200 564 7.90 6460 598 8.66 6675 607 9.38 690(1 627 10.13 7295 663 11 65 13312 3200 6230 567 8.27 6475 588 9.07 6730 612 9.86 6921) 629 10.60 7135 648 11.40 7530 685 12 97 14144 3400 ■;.iM, 59S 9.58 HMD 613 10.38 6960 632 11.19 7150 650 12.00 7355 670 12.81 7750 705 14 46 14976 3600 6815 620 10.88 7020 63S 11.77 /200 655 12.66 7440 676 13.48 76(in 691 14.38 8020 729 16 04 15808 3800 7105 646 12.43 7350 668 13.40 H'lb 680 14.25 7660 697 15.14 7840 713 16.00 S220 747 17.88 APPENDIX 279 CAPACITY TABLE Table VI. — No. 80 Single Inlet Steel Plate Fan — Type S S. P. Vi" S. P. %" S. P. H" S. P. H" S. P. K" S. P. H" Vol- ume CD o > S ti ft 43 a d d 43 -d ft a d d 43 f t» « pq M m c 1 co ti pq t 1 co ti pq C* CO ti m t^ CO ti pq 5050 1000 2366 189 .488 2690 214 .654 2940 234 .818 3175 25.3 .994 3400 271 1.17 3610 28R 1.37 5555 11(11 249( 19,' .575 2781 222 .755 304( 242 .935 3267 26( 1.12 348( 277 1.31 3«7( 29? 1.52 6060 1201 2001 207 .685 2925 23? .87; 3125 24!- 1.06 336( 268 1.26 3575 285 1.47 376? 30f 1.68 6565 isor 2786 218 .80S 3001 239 1.002 3237 257 1.21 3475 276 1.42 3675 29? 1.63 3865 308 1.86 7070 140( 2846 227 .94( 3107 248 1.144 33 1( 264 1.35 357? 285 1.58 375( 29! 1.81 3965 316 2.05 7575 isor 2987 238 1.097 3226 257 1.314 346( 27ft 1.54 3fi5( 291 1.77 386( 307 2.01 406C 324 2.26 8080 ioor 313C 25( 1.26i 3351 267 1.497 3505 284 1.73 3765 298 1.97 396f .315 2.22 41 6f 332 2.48 8585 170C 327( 261 1.445 3475 277 1.695 368( 29? 1.94 3885 310 2.19 4055 32? 2.47 4250 339 2.74 9090 180C Mil 272 1.686 3607 287 1.92C 3811 30? 2.18 4011 31! 2.44 4181 33? 2.77 4350 347 3.02 9595 1901. 3546 28:- 1.87! 3731 297 2.165 3935 3 IS 2.42 412( 328 2.71 432C 344 3.00 4455 350 3.28 10100 2001. 3701 295 2.15C 3861 305 2.425 4051. 322 2.71 ♦255 33t 3.01 4423 35? 3.31 4580 365 3.61 10605 2101 3X51 307 2.40C 4I)0( 311 2.71 4211 335 2.99 1351 347 3.33 4535 361 3.64 4680 373 3.94 11110 2201. 4(I0( 31! 2.688 4168 332 3.04 432( 341 3.34 45(11 35>- 3.67 467(1 372 4.00 4800 383 4.32 11615 2301 432? 345 3.36 445C 354 3.67 4628 360 4.02 477(1 38(1 4.37 4930 393 4.71 12120 240! 446( 356 3.63 4621 368 4.08 474C 378 4.42 492(1 393 4.78 5045 402 5.12 12625 250( 460( 367 4.10 472( 376 4.47 (88(1 380 4.85 5036 401 5.20 5170 412 5.57 13130 260( 491C 392 4.94 soor: 3!1> 5.30 5180 413 5.69 5325 423 6.06 14140 280( 51 HC 413 5.85 528(1 421 6.30 5435 433 6.67 5510 439 7.14 15150 3000 5485 437 6.93 5610 447 7.42 5650 450 7.81 5840 465 8.28 S. P. 1" S. P. lVi" S. P. 1M" S. P. 1H" S. P. 2" S. P. 2W Vol- ume +3 CD ft CD a ft d 43 a d d 43 •a a d d 43 Ti p.8 a d 43 ■a ft Qj a d d 43 T} ftS a d d 43 tr* co « m H " ti m cr 1 to « pq tr* co ti pq ft! U tr* co ti pq i! ft T^ CO K pq 6060 1200 3955 315 1.91 4152 331 2.33 ♦470 356 2.83 4950 .394 3.31 5230 417 3.86 5750 458 5.00 6565 1300 4050 32? 2.08 438( 34! 2.54 4551 36? 3.03 5024 401 3.56 5295 421 4.12 5820 464 5.25 7070 1400 4143 32f 2.28 4465 356 2.77 470f 375 3.29 5105 407 3.83 535(1 426 4.42 5900 470 5.58 7575 1500 4250 33f 2.51 457f 364 3.02 4851 386 3.54 51 8C 41S 4.10 545(1 434 4.68 5950 475 5.93 8080 1600 4325 345 2.75 465? 371 3.29 495( 395 3.83 5245 418 4.39 555(1 442 5.02 6026 480 6.27 8585 1700 4437 35S 3.01 4750 378 3.61 504( 402 4.15 5330 424 4.74 5625 44 1- 5.35 6100 48B 6.63 9090 1800 4527 361 3.29 ♦R4fl 3R6 3.89 51lf 407 4.46 54 Id 431 5.10 570(1 455 5.73 6196 493 V.05 9595 1900 4013 368 3.59 4945 394 4.19 523C 417 4.81 552C 440 5.48 5780 460 6.13 6265 499 V.47 10100 anoo 474? 377 3.91 5075 404 4.55 5325 424 5.19 5621 448 5.88 5861 467 6.57 6366 50V 7.92 10605 vnn 4850 386 4.25 5145 41 1 4.92 544I 43? 5.60 5724 456 6.32 5956 475 7.00 6475 516 8.45 11110 2200 4970 396 4.64 5256 41! 5.31 555( 44? 6.02 5791 461 6.74 6051 482 7.45 6550 522 8.96 11615 2300 5090 405 5.36 537f 427 5.75 5631 44r 6.45 5901 470 7.22 6151 491 7.95 6610 527 9.52 12120 2400 5210 416 5.48 548( 437 6.20 5751 458 6.92 6025 481 7.72 6271 601 8.48 6700 534 10.10 12625 2500 5340 425 5.96 561( 447 6.66 5851 466 7.45 BKIC 486 8.23 634:: 505 9.06 6800 542 10.68 13130 SfiOO 5485 437 6.44 574( 457 7.22 598( 477 7.98 B20C 494 8.78 646( 515 9.67 6880 548 11.30 14140 2800 5710 455 7.60 5960 475 8.33 B23( 497 9.19 6461 515 10.05 6650 530 10.90 7090 564 12.68 15150 3000 5970 476 8.73 6200 494 9.60 646( 515 10.53 6675 532 11.38 690C 55( 12.33 7295 581 14.16 16160 3200 6230 497 10.05 6475 517 11.00 673( 537 11.97 6921 551 12.88 7135 568 13.86 7530 600 15.73 17179 3400 6580 524 11.62 674( 537 12.62 6961 555 13.60 715C 570 14.60 7355 5S7 15.55 7760 618 IV. 58 18180 3600 6815 543 13.23 700( 55! 14.30 7201 574 15.40 7441 593 16.38 V600 605 17.48 8020 639 19.50 19190 3800 7105 565 15.10 7350 586 16.27 7475 596 17.30 7660 611 18.38 7840 624 19.44 8220 655 21.73 280 HEATING AND VENTILATION CAPACITY TABLE Table VII. — No. 90 Single Inlet Steel Plate Fan — Type S S P. H" S. P. %" S. P. H" S. P. %" S. P. H" S. P. H" Vol- ume +3 -a aS s d 0, ja -a S d d ja •a a d d .a a d d ja aSi a d d ja a cd a d d J3 HS « m H'i # m HS A m c* to M m :r< to rt pq c^ to « pq 6450 iooo 2366 167 .625 2690 190 .835 2940 208 1.05 3175 224 1.27 3400 240 1.49 3610 255 1.75 7095 nor 249f 176 .735 ?78l 196 .965 30 if 215 1.19 :12li7 231 1.43 3481 246 1.68 3671 251 1.93 7740 120f 2601 184 .876 2925 207 1.11 ;;rv 221 1.35 3361 238 1.61 3575 253 1.88 376? 266 2.14 8385 isor '736 19? 1.03 3000 21? 1.27 3237 22! 1.54 3475 245 1.81 3675 25(1 2.09 3865 27? 2.37 .9030 nor 2846 2111 1.20 3107 ?.?.( 1.46 33 If 234 1.73 357? 25? 2.03 3754 265 2.31 H'.lli.- 28(1 2.61 9675 isor 2987 211 1.40 3226 228 1.68 3460 244 1.97 365( 258 2.26 386(1 273 2.57 4064 287 2.89 10320 lfinr 313f 231 1.61 3350 337 1.91 3565 252 2.21 3765 266 2.52 396(1 28(1 2.84 416(1 294 3.17 10965 170(1 3271 231 1.85 3475 245 2.17 3681 26f 2.48 3885 275 2.81 4055 287 3.15 425(1 30(1 3.40 11610 isor 3410 241 2.15 3607 255 2.45 3811 269 2.79 40 IC 28,1 3.12 4180 296 3.54 435(1 308 3.86 12255 mnr 3546 251 2.40 373(1 264 2.76 3935 278 3.10 412(1 291 3.46 43211 3(15 3.83 4455 315 4.19 12900 200C 3700 262 2.72 3860 27? 3.09 405C 286 3.46 4255 301 3.86 4423 313 4.22 458(1 324 4.62 13545 2 10C 385C 272 3.06 400(1 28? 3.47 421(1 298 3.82 435(1 308 4.25 4535 320 4.64 468(1 331 5.03 14190 220(1 lOOf 38,1 3.43 4168 MS 3.88 432(1 305 4.27 45011 318 4.68 4671] 3311 5.11 480(1 3411 5.52 14835 230(1 4323 306 4.30 445(1 314 4.69 4628 327 5.13 477(1 338 5.59 493(1 348 6.02 15480 ?400 4460 315 4.64 462C 327 5.21 474(1 335 5.65 (92(1 348 6.22 5045 356 6.55 16125 2500 4600 325 5.24 4726 334 5.71 4S8C 347 6.19 5036 356 6.64 517(1 366 7.13 16770 soon 401(1 348 6.31 50011 354 6.77 518(1 366 7.28 5325 376 7.74 18060 2800 518(1 366 7.47 528(1 37? 8.05 5435 384 8.53 551(1 39(1 9.12 19350 3000 548.5 3S7 8.87 5610 397 9.48 5650 400 9.98 5840 414 10.57 S. P. 1" S. P. IK" s. p. m" S. P. IK" S. P. 2" S. P. 2X" Vol- a> ume +3 ■ 3~£ ■o a d ■T3 a d ■a a d ■c a a -a a d ■a a a O > nS; d ja & 8> a ja a S a J3 aSj d X3 aS> d ja a urne ftS a d ft ja ftS a a ja ft ■0 ft o a p. ft ja •a ft m a ft ft a ft ft ja ft S. P. 1" S. P. 1H" S. P. 1H" S. P. 1%" S. P 2" S. P. 2H" ft O T3 a a T3 a a -ai a a •0 a a X! a a T3 a a a 3) ja a oj a X! a£ a -G a J3 a( 174 1.93 3237 187 2.32 3475 201 2.74 3675 213 3.16 3865 224 3.58 13664 1400 2846 165 1.81 3107 18C 2.21 331C 192 2.61 3573 207 3.06 375(1 217 3.50 3965 23(1 3.96 14640 1501) 29X7 173 2.12 3226 187 2.54 346C 200 2.97 365(1 211 3.43 3X60 224 3.88 406(1 235 4.37 15616 1600 313(1 1X3 2.44 335(1 194 2.89 3565 207 3.34 3765 218 3.81 3960 229 4.29 416(1 241 4.80 16592 1700 327(1 189 2.79 3475 201 3.27 3680 213 3.74 3XS5 225 4.24 4055 235 4.76 425(1 246 5.28 17568 1800 Mill 197 3.25 1(107 20(1 3.71 ■Kill 221 4.22 401(1 232 4.72 41X0 242 5.36 4350 252 5.84 18544 19011 1546 206 3.63 1730 216 4.18 3935 228 4.68 412(1 239 5.23 4320 250 5.79 4455 258 6.34 19520 200(1 (70(1 214 4.11 ..,.,1 224 4.68 mw 235 5.22 4255 245 5.82 4423 257 6.39 45X0 265 6.97 20496 2100 IS.-ill 223 4.63 40011 232 5.24 421(1 244 5.77 4350 252 6.42 4535 262 7.02 46X0 271 7.61 21472 2200 400(1 232 5.18 416X 242 5.87 4320 251 6.46 4500 261 7.08 ♦670 271 7.72 4800 27X 8.34 22448 2300 4323 251 6.50 445(1 258 7.10 4628 268 7.76 4770 277 8.45 4930 2X6 9.12 23424 2400 4460 25S 7.02 462(1 268 7.88 4740 275 8.55 4920 2 85 9.24 5045 292 9.92 24400 2500 4600 266 7.93 4720 273 8.63 488(1 283 9.37 5036 292 10.05 5170 300 10.77 25376 2600 49111 284 9.55 5000 290 10.25 51X0 300 11.00 5325 30X 11.72 27328 2W10 51 K0 30(1 11.3 52X0 306 12.17 5435 315 12.88 5510 319 13.80 29280 WOO 5485 317 13.4 5610 325 14.34 5650 327 15.08 5840 338 16.00 S. P. 1" S. P. M" S. P. 1H" S. P. lJJ" S. P. 2" S. P. 2H" Vol- ume ■a a ■z) a ■0 a •0 a -0 a •o a u > a£J a J3 a a J3 a ■a a a d ■3 ft a ft ja ft d> a d d T3 a a> a d d ja ft a ft a ja « « cr" co rt (0 f-l " tr- co « « ir 1 co M m (-1 ft t— * CO M m y p. tr 1 to « m 14340 1200 3955 209 4.52 415? 220 5.52 4470 237 6.69 4950 262 7.83 5230 279 9.12 5750 305 11.73 15535 1300 4050 215 4.92 438C 232 6.02 455C 242 7.18 5024 267 8.43 5295 281 9.75 5820 309 12.4 16730 1400 4143 220 5.40 4465 237 6.57 470C 24S 7.80 5105 271 9.04 535C 284 10.44 5900 313 13.2 17925 150C 4356 226 5.95 457(1 243 7.15 485(1 257 8.40 5180 275 9.73 5450 289 11.10 5950 316 14.0 19120 1600 3325 229 6.50 4652 247 7.80 495C 263 9.08 5245 278 10.40 55511 294 11.87 6025 320 14.8 20315 1700 4437 235 7.12 475C 252 8.55 504C 268 9.84 533(1 283 11.22 5625 298 12.1 6100 324 15.7 21510 1800 4527 240 7.78 4846 257 9.20 511(1 271 10.56 5410 287 12.10 5700 302 13.6 6195 328 16. V 22705 1900 4613 245 8.48 4945 262 9.92 523(1 277 11.33 5520 293 12.9 5780 307 14.5 6266 333 17.7 23900 2000 4743 251 9.27 5075 269 10.77 5325 283 12.3 5620 298 13.9 5860 311 15.5 6365 338 18.7 25095 2100 4850 257 10.07 5145 273 11.67 544(1 289 13.2 6724 304 14.9 5955 316 16.5 6475 344 20.0 26290 2200 4970 264 10.97 5256 279 12.56 555(1 294 14.2 5790 30/ 15.9 6050 321 17.6 6550 348 21.2 27485 2300 5090 270 12.45 5370 285 13.60 563(1 29(J 15.3 5900 313 17.1 6150 326 18.8 6610 351 22.5 28680 2400 5210 276 12.98 5480 292 14.70 575(1 305 16.4 6025 320 18.3 6270 333 20.1 6700 366 23.9 29875 2500 5340 283 14.12 5610 298 15.78 5X5(1 31(1 17.6 6100 324 19.5 6343 336 21.5 6800 361 25.3 31070 2600 5485 291 15.27 5740 304 17.10 598(1 317 18.9 6200 329 20.8 6460 348 22.9 6880 366 26.7 33460 2800 5710 303 18.00 i960 316 19.73 623(1 331 21.7 6460 343 23.8 3650 353 25.8 7090 3/6 30.0 35850 3000 5970 317 20.68 6200 329 22.70 64HI1 343 24.9 6675 354 26.9 6900 366 29.2 7295 387 33.5 38240 3200 6230 330 23.80 6475 344 26.10 6730 357 28.3 6920 367 30.5 /136 378 32.8 7530 399 37.2 40630 3400 6580 349 27.50 6740 357 29.85 6960 320 32.1 7150 379 34.6 (355 391 36.8 7750 411 41.7 43020 3600 6815 362 31.30 7000 372 33.80 7200 382 36.4 7440 394 38.7 /6U0 404 41.4 8020 426 46.2 45410 3800 7105 377 35.80 7350 390 38.50 7475 397 41.0 7660 407 43.6 7840 417 46.0 8220 436 61.4 284 HEATING AND VENTILATION CAPACITY TABLE Table XI. — No. 130 Single Inlet Steel Plate Fan — Type S S. P. X" S. P. %" S. P. H" S. P. %" S. P. H" S. P. ■%" Vol- V ume r> a a a -a aS s a a J3 ■a a o s a a ja ■8 a$ a a a -a a qj a a a T3 a a a ja h u K M H w £ m c* m a m H £ « n H & 05 M « « 14050 1000 2366 116 1.360 2690 132 1.820 2940 144 2.280 3175 156 2.765 3400 166 3.262 3610 177 3.810 15455 1101 2491 122 1.602 278C 136 2.101 304(1 149 2.607 3267 160 3.128 348C 171 3.658 3670 ISC 4.218 1686C 1201 260C 127 1.90S 2925 143 2.433 3125 153 2.952 336C 165 3.516 3575 175 4.091 3763 184 4.668 18265 1301; 2736 134 2.25C :):<7 157 3.351 3475 170 3.950 3675 ISO 4.555 3865 189 5.162 1967C 1400 2X41 m 2.62C 3107 152 3.19C 331(1 162 3.771 3573 175 4.414 (750 184 5.050 3965 194 5.710 21075 1500 29X7 146 3.06C 3226 158 3.66C 3460 170 4.290 3650 179 4.937 3S60 189 5.595 4060 199 6.290 2248C 160IJ 313(1 154 3.515 (351 164 4.168 3565 175 4.807 3765 185 5.500 (960 193 6.190 ♦160 >04 6.918 23885 1700 32 71 160 4.027 3475 170 4.717 3680 ISO 5.408 3885 190 6.102 4055 197 6.868 4250 208 7.620 2529C 18(1(1 341(1 167 4.690 3607 177 5.345 381(1 187 6.078 4010 196 6.800 4180 205 7.715 4350 213 8.423 26695 190(1 3546 174 5.230 373(1 183 6. 026 3935 193 6.752 4120 202 7.550 4320 212 8.350 4455 ?1S 9.147 281O0 200(1 37011 1S1 5.935 386(1 189 6.250 4050 198 7.540 4255 209 8.400 4423 217 9.210 4580 225 10.04 29505 2101) '(85(1 ISO 6.678 400(1 196 7.550 4210 206 8.320 4350 213 9.253 4535 222 10.120 4680 229 10.97 30910 2200 4000 196 7.475 4168 204 8.452 4320 212 9.300 4500 221 10.20 4670 229 11.120 4800 !35 12.02 32315 231)0 4323 212 9.230 4450 218 10.23 llil'S 227 11.18 4770 234 12.170 4930 242 13.12 33720 2400 446(1 219 10.130 4620 226 11.34 4740 232 12.30 4920 241 13.30 5045 247 14.26 35125 2500 4600 226 11.40 4720 231 12.43 4880 239 13.48 5036 247 14.48 5170 253 15.49 36530 2600 491(1 241 13.75 5000 245 14.76 5180 254 15.85 5325 261 16.87 39340 2800 51X0 254 16.29 52X0 259 17.53 5435 ;•..,, 18.60 5410 270 19.87 42150 3000 5485 269 19.30 5610 275 20.66 5650 277 21.74 5840 2S6 23.06 Vol- ume v IN > S. P. 1" S. P. IK" s. p. iy z " S. P. IK" S. P. 2" S. P. 2M" -a a i ■.— a C -1 ume 8 a d ■J3 0,8 a ft J3 •o ft 8 a d d ■a a$ a d ft T3 ft?, S 6 d J3 a d ft ~ £fi PS ffl Bit pS ffl (LJ o. rt ffl PS « [T 1 ta « m PS pq 16000 1000 2366 108 1.550 2690 123 2.072 2940 134 2.596 3175 145 3.150 3400 155 3.715 3610 164 4.337 17600 not 2491 113 1.825 2780 127 2.392 304C IHfi 2.967 3267 14! 3.56C 348(1 158 4.16C 3671 167 4.800 19200 1201 2601 118 2.172 2925 m 2.77C 3125 142 3.36C 336C 153 4.00C 3575 163 4.655 3763 171 5.318 20800 1301 2736 121 2.56C 3000 137 3.175 3237 147 3.817 3475 158 4.500 3675 167 5.187 1865 176 58.80 22400 1401 2846 12!: 2.98C 3107 141 3.63C 331(1 151 4.29S 3573 163 5.025 37.5(1 171 5.750 3965 18f 65.10 24000 1501 2987 136 3.482 3226 147 4. 168 346(1 157 4.885 365C 166 5.620 3860 176 6.370 406C 185 7.160 25600 1601 3131 142 4.00C 335(1 153 4.747 3565 162 5.475 3765 171 6.255 3960 180 7.045 416f IS! 7.870 27200 1701 327( 14! 4.585 3475 15S 5.36S 36XC 168 6.155 3885 177 6.950 1055 184 7.820 425C 193 86.70 288O0 1801 341( 155 5.34C 3607 164 6.087 3810 173 6.92C 101(1 183 7.750 4180 190 8.787 435C W 9.590 30400 1901 3546 161 5.95C 3730 171 6.850 3935 179 7.699 412(1 187 8.600 ♦32(1 197 9.510 1455 203 10.4 32000 2001 3701 16t 6.75C 3860 176 7.690 405(1 1X4 8.580 4255 194 9.560 1423 201 10.5 158(1 20! 11.4 336O0 2101 3851 175 7.60C 4000 182 8.600 421(1 191 9.475 135(1 198 10.5 1535 206 11.5 168(1 213 12.5 35200 22IK 4001 182 8.52C 4168 18!) 9.625 +32(1 197 10.6 150(1 205 11.6 167(1 213 12.7 480(1 219 13.7 3680C 2301 4323 197 10.6 145(1 203 11.6 1628 21(1 12.7 177(1 217 13.9 493(1 224 15.0 38400 2401 446(1 203 11.5 462(1 21(1 12.9 174(1 216 14.0 192(1 224 15.2 5045 228 16.24 4000C 25(l( 46011 2(10 13.0 172(1 215 14.2 188(1 222 15.3 5036 229 16.49 517(1 235 17.62 4160C 260( 491(1 223 15.6 5000 237 16.80 518(1 236 18.05 5325 242 19.20 4480C 280( 5180 236 18.55 528(1 240 19.98 5435 247 21.18 5510 251 22.62 48000 3000 5485 249 21.96 5610 255 23.53 5650 257 24.76 5840 226 26.25 Vol- S. P. 1" s. p. m" S. P. iy 2 " S. P. 1%" S. P. 2" S. P. 2H" ume ftS a d ft ■a a 8 a d d -a ft D a a d ft aj a a a a ft a ja ■a aS a a a -a H& PS ffl C a PS m H ft PS m f-l a PS ffl t-1 a M ffl Hit PS ffl 19200 1200 3955 180 6.045 4152 189 7.400 4470 203 8.965 4950 225 10.5 5230 236 12.2 5750 262 15.8 20300 TROf 405( 184 6.595 438( 19! 8.07C 455( 207 9.637 5024 228 11.3 5295 241 13.0 5820 265 16.64 22400 1401 414.' 18,' 7.247 4465 203 8.808 17()( 212 10.4 5105 232 12.1 5351 243 14.0 59(11 263 17.68 24000 1501 425( 19? 7.957 457( 208 9.56C 485( 221 11.2 518'. 23b 13.0 5451 248 14.9 5951 271 18.80 25600 1601 4325 197 8.7K 4652 212 10.4 495( 225 12.1 .5245 231 13.9 5551 252 15.9 6025 274 19.90 27200 17W 4437 201 9.545 475( 216 11.4 504( 22! 13.2 5331 243 15.0 5625 256 16.98 6100 277 21.00 28800 1800 4527 206 10.4 4846 221 12.3 flllf 232 14.2 5411 246 16.20 5701 25! 18.16 6195 282 22.35 30400 1900 4613 21( 11.4 4945 225 13.3 5231 23fi 15.3 5521 251 17.37 5781 263 19.43 6265 285 23.68 32000 2000 4743 215 12.4 5075 231 14.4 5325 242 16.45 5621 255 18.65 5861 267 20.80 6365 289 25.10 33600 2100 485( 221 13.5 5145 234 15.6 544( 247 17.73 5724 261 20.00 5955 271 22.18 6476 294 26.80 35200 ?2no 4970 226 14.7 5256 23f 16.82 555( 252 19.10 5790 264 21.38 6050 275 23.61 6550 298 28.40 36800 230( 5090 231 16.67 537( 244 18.21 5631 256 20.47 590( 263 22.90 6150 280 25.20 6610 301 30.20 38400 MOO 52H 237 17.39 548f 24! 19.67 5751 261 22.00 6025 274 24.46 6270 285 26.90 6700 306 32.00 40000 2500 5340 243 18.89 56H 255 21.12 5851 266 23.60 6100 277 26.10 6343 289 28.72 6800 309 33.80 41600 2600 5485 24' 20.46 574; 261 22.90 5981 272 25.35 6201 282 27.85 6460 293 30.65 6880 313 35.80 44800 2800 5710 ?6( 24.08 596( 271 26.41 623( 283 29.15 «46( 293 31.85 665U 303 34.60 7090 322 40.10 48000 3000 5970 27? 27.70 6201 28? 30.40 6461 294 33.36 6675 304 36.10 69UI 314 39.08 7295 332 44.90 51200 3200 6230 '83 31.90 6475 294 34.90 673( 306 37.95 6921 315 40.80 7135 324 43.90 7531 343 50.00 54400 3400 6580 •>, 99 36.80 6741 307 39.92 696( 316 43.07 7151 325 46.25 7356 335 49.30 7750 353 55.70 57600 3600 6815 310 41.92 7(120 31! 45.30 72 0( 327 48.07 7441 331 51.99 7600 346 55.38 8020 365 61.80 60800 3800 7105 323 47.90 7350 334 51.60 7475 340 54.92 /660 349 58.37 7840 357 61.60 8220 374 69. 00 286 HEATING AND VENTILATION CAPACITY TABLE Table XIII. — No. 160 Single Inlet Steel Plate Fan — Type S S P. H" S. P. %" S p. y%" S P. H" S. P. H" S. P. %" VoU ume +^> 3N a qj a d •a ~ 01 a oj a a d -3 a m a d d -a a d d J3 a oi a d d aS a a d J3 « pq hU rt pq H a rt pq « pq HS A pq E-l " « M 20250 1000 2366 04 1.957 3690 107 2.615 M40 117 3.28 3175 127 3.98 3400 135 4.69 3610 144 5.48 22275 1100 249( Of 2.31 27SO 111 3.025 3040 121 3.75 3267 136 4.5 3481 13S 5.25 3671 146 6.08 24300 1201 2601 KM 2.75 2925 116 3.505 3125 125 4.25 336C 134 5.06 3575 142 5.89 3763 150 6.72 26325 1301 2731) KIS 3.23 306( 1 1 f 4.01 3237 12* 4.82 3475 138 5.68 3675 146 6.55 3865 154 7.44 28350 140! 2X46 IIS 3.77 3107 124 4.59 33K 132 5.43 357S 142 6.35 375(1 140 7.26 3965 158 8.2 30375 1501 29X7 11! 4.40 3226 12f 5.27 346f 137 6.17 365(1 145 7.1 386(1 154 8.05 4060 162 9.05 32400 16(11 3131 125 5.06 335! 13S 5.99 3565 142 6.92 3765 15(1 7.91 396(1 158 8.9 4160 166 9.94 34425 1701 3271 13(1 5.78 3475 138 6.79 36Xf 147 7.77 38X5 155 8.78 4055 162 9.88 4250 169 10.93 36450 1X01 3411 136 6.75 3607 144 7.68 381(1 152 8.725 401 C 16(1 9.8 418(1 167 10.1 4350 173 12.1 38475 1 !)()( 3546 141 7.52 373C 148 8.67 3935 157 9.71 412(1 164 10.90 432(1 172 12.0 4455 178 13.1 40500 2001 370C 147 8.54 3X6f 154 9.71 4051 161 10.83 4255 170 12.1 4423 176 13.2 4580 183 14.4 42525 2101 385(1 153 9.60 400(1 15S 10.85 42 K 167 11.97 435(1 173 13.3 4535 181 14.6 4680 1X7 15.8 44550 2201 4001 15S 10.74 416(5 166 12.17 4321 172 13.40 450(1 179 14.7 4670 186 16.0 4800 191 17.3 46575 2301 4323 172 13.44 ♦45(1 177 14.70 4623 1X4 16.1 4770 190 17.5 4930 196 18.9 48600 2401 446(1 178 14.55 46211 184 16.30 474(1 1X9 17.7 4920 196 19.2 5045 201 20.5 50625 2501 460(1 1X3 16.40 47:>( m 17.90 4X8(1 194 19.4 5036 200 20.8 5170 206 21.3 52650 2600 49K 196 19.80 5000 199 21.3 51X0 206 22.8 5325 212 24.3 56700 2801 51 Sf 206 23.4 5280 210 25.2 5435 216 26.5 5410 220 2X.6 60750 3000 5485 218 27.8 5610 223 29.7 5650 225 31.3 5840 232 33.1 Vol- ume S. P. 1" S. P. lj-i" S. P. 1H" S. P. XYi." S. P. 2" S. P. 2H" ■a a a Tl a d T3 a a TJ a d ■o a d 13 a d a J a & aS .fl a a 1 . X. a 3! J3 a oi J3 a o J3 H u « « L] a rt pq a! ft a pq r[ a « pq cJ a tf cq l\ IX r* to « pq 24300 1200 3955 158 7.64 4152 166 9.35 4470 178 11.3 4950 197 13.3 5230 208 15.4 5750 229 20.0 26325 130(1 405(1 161 8.33 1381 175 10.2 455( 1X2 12.2 5024 201 14.3 5295 211 16.5 5X21 232 21.1 28350 HOC 41 43 165 9.16 4465 17X 11.1 4701 187 13.2 5105 201- 15.3 5351 213 17.7 5901 235 22.4 30375 150(1 425(1 161 10.04 457I 182 12.1 4851 193 14.2 51 XI 206 16.4 545' 217 18.8 5951 337 23.7 32400 1600 :li ! 172 11.0 4652 1X6 13.2 495( 197 15.3 5245 20! 17.6 5551 222 20.1 6025 24f 25.2 34425 17011 4437 177 12.0 475( 181 14.4 504(1 20(1 16.6 533(1 212 19.0 5625 224 21.5 6100 243 26.6 36450 180(1 ♦527 18(1 13.1 4X46 IDS 15.6 511(1 203 17.9 541(1 211 20.4 570(1 227 22.9 6195 247 28.3 38475 19011 4613 184 14.4 4945 197 16.8 523(1 208 19.3 55211 22(1 21.9 57X(1 23(1 24.5 6265 24S 29.9 40500 1006 4743 181. 15.7 5075 202 18.2 5325 212 20.8 562(1 224 23.5 5X6(1 233 26.3 6365 253 31.8 42525 3106 4X5(1 193 17.0 5145 205 19.7 544(1 216 22.5 5724 228 25.3 5955 237 28.1 6425 257 33.8 44550 2200 497(1 198 18.6 5256 201 21.3 5550 221 24.1 579(1 23(1 27.0 605(1 241 29.8 655C 261 35.9 46575 2306 509(1 203 21.10 537(1 214 23.1 5630 224 25.9 5900 235 28.9 6150 245 31.9 66 Id 263 38.1 48600 240(1 52111 20X 22.0 5481J 218 24.9 5750 229 27.8 6025 24(1 30.9 6270 250 34.0 67011 267 40.4 50625 !50(l 534(1 213 23.9 561(1 224 26.7 5850 233 29.8 61011 243 33.0 6343 252 36.3 680C 271 42.8 52656 ?600 ,54X5 21,8 24.8 574(1 22S 28.9 5980 23X 32.0 620(1 24735.2 6460 257 38.7 6X81 274 45.3 56700 2800 5710 228 30.4 5960 338 33.4 6230 24X 36.8 6460 257 40.3 6650 265 43.7 7096 28? 50.8 60750 3000 597(1 23X 35.0 631111 247 38.4 646(1 357 42.2 6675 265 45.7 6900 274 49.3 7295 29(1 56.7 64800 3200 6330 252 40.3 6475 258 44.2 67HII 368 47.9 6920 276 51.6 71 35 284 55.4 7536 300 63.0 68850 3400 65X0 262 46.5 6740 26X 50.5 6960 277 54.4 7150 285 58.5 7355 293 32.4 7750 30,8 70.3 72900 3600 6X15 272 53.0 7000 279 57.3 7200 287 31.6 7440 296 65.5 7600 303 70.0 8026 32(1 78.0 76950 3S00 7105 283 60.5 7350 292 65.2 7475 297 69.4 7660 305 73.7 7840 312 77.8 8220 32X 87.0 APPENDIX 287 STATIC PRESSURE TABLES FOR NIAGARA CONOIDAL FANS 1 Table XIV. — No. 3 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet Capacity, Add H" 3. P. H" S. P. H" 3. P. «"S.P. H" S. P. 14" S. P. velocity, cu. ft. for ft. per air total a a S a a a mm. per mm. press. O, P, a a p. p, P. a p. P, a M b rt W K B rt B Pi B Pi a 1000 1310 .063 387 .09 483 .15 1100 1440 .076 384 .11 477 .16 1200 1570 .090 387 .12 477 .17 557 .23 1300 1710 .106 393 .14 470 .18 550 .25 623 .32 1400 1840 .122 400 .16 473 .20 547 .26 617 .33 687 42 1500 1970 .141 410 .18 477 .23 543 .28 613 .35 680 .43 743 .52 1600 2100 .160 420 .21 480 .25 547 .31 610 .37 673 .45 733 54 1700 2230 .180 430 .24 490 .28 550 .34 607 .40 670 .48 727 .56 1800 2360 .202 443 .28 500 .32 553 .37 610 .43 667 .51 723 .59 1900 2490 .225 457 .31 510 .35 560 .41 613 .47 667 54 720 62 2000 2630 .250 470 .35 520 .40 570 .45 617 .52 667 .58 720 .66 2100 2760 .275 483 .39 530 .45 580 .50 623 .56 670 .63 720 .71 2200 2890 .302 497 .44 543 .50 590 .55 633 .61 677 .68 723 .76 2300 3020 .330 513 .49 557 .55 600 .61 643 .67 683 .73 727 .81 2400 3150 .360 527 .55 570 .61 610 .67 650 .73 690 .80 733 .87 2500 3280 .390 543 .60 583 .67 623 .74 660 .80 700 .86 740 .94 2600 3410 .422 560 .67 597 .74 633 .81 673 .88 710 .94 747 1.02 2800' 3670 .489 590 .81 623 .89 660 .96 693 1.04 730 1.10 767 1.17 3000 3940 .560 623 .99 657 1.04 687 1.14 720 1.22 753 1.29 780 1.36 3200 4190 .638 717 1 . 33 747 1.42 780 1.50 810 1.58 3400 4460 .721 807 1.75 833 1.84 Outlet velocity, ft. per Capacity, cu. ft. air Add for total 1" S. P. lJi" S. P. WS.P. Wt." S. P. 2" S. P. 2H" S. P. a a" a a a a mm. per mm. a Pi a W p. Pi a B p. Pi a B p. p5 a B p. Pi P, B p, Pi a B 1300 1400 1500 1710 1840 1970 .106 .122 .141 820 810 800 .58 .59 .62 920 913 .80 .81 1027 1017 1.00 1.04 1110 1.25 1600 1700 1800 2100 2230 2360 .160 .180 .202 793 783 777 .64 .66 .68 903 893 883 .84 .86 .89 1007 997 983 1.06 1.09 1.12 1100 1087 1077 1.29 1.32 1.35 1190 1177 1167 1.53 1.58 1.61 1343 1330 2.13 2.16 1900 2000 2100 2490 2630 2760 .225 .250 .275 773 770 770 .71 .75 .79 877 873 867 .92 .95 .99 977 970 960 1.14 1.17 1.22 1067 1057 1050 1.39 1.42 1.46 1157 1143 1133 1.65 1.68 1.73 1317 1303 1297 2.20 2.24 2.29 2200 2300 2400 2890 3020 3150 .302 .330 .360 767 770 773 .84 .89 .95 863 860 860 1.03 1.08 1.13 953 950 947 1.25 1.30 1.35 1040 1033 1027 1.50 1.54 1.59 1127 1120 1107 1.76 1.81 1.85 1287 1270 1263 2.33 2.38 2.43 2500 2600 2800 3280 3410 3670 .390 .422 .489 777 783 800 1.03 1.09 1.25 860 863 870 1.20 1.26 1.43 943 940 943 i:41 1.47 1.63 1023 1020 1013 1.64 1.70 1.84 1103 1097 1090 1.91 1.96 2.10 1253 1247 1233 2.49 2.54 2.67 3000 3200 3400 3940 4190 4460 .560 .638 .721 820 837 863 1.44 1.65 1.90 883 900 920 1.61 1.83 2.06 950 960 980 1.81 2.02 2.26 1020 1023 1033 2.02 2.23 2.47 1087 1090 1093 2.25 2.47 2.69 1227 1217 1213 2.82 3.00 3.21 3600 3800 4000 4730 4990 5250 .810 .900 1.000 883 2.18 943 2.34 997 1017 2.53 2.84 1050 1067 1087 2.76 3.04 3.39 1107 1117 1133 2.96 3.28 3.60 1220 1227 1233 3.48 3.76 4.10 1 From "Fan Engineering," Buffalo Forge Co. 288 HEATING AND VENTILATION Table XV. — No. Z}4 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total X" S. P. H" S.P. K"S.P. H" S.P. K" S. P. K"S.P. a a a a a a min. per mm. press. p, pi 0, a a pi A a a si P. a p. pi A a A pi A a A pi A a 1000 1100 1200 1790 1970 2140. .063 .076 .090 332 329 332 .13 .14 .16 414 409 409 .20 .21 .23 477 .32 1300 1400 1500 2320 2500 2680 .106 .122 .141 337 343 352 .18 .21 .24 403 406 409 .25 .28 .31 472 469 466 .33 .36 .38 534 529 526 .43 .45 .48 589 583 .57 .59 637 .71 1600 1700 1800 2860 3040 3210 .160 .180 .202 360 369 380 .28 .32 .37 412 422 429 .34 .49 .33 469 472 474 .42 .46 .51 523 520 523 .51 .55 .59 577 574 572 .62 .65 .69 629 623 620 .73 .77 .80 1900 2000 2100 3390 3570 3750 .225 .250 .275 392 403 414 .42 .48 .53 437 446 454 .48 .54 .61 480 489 497 .56 .62 .68 526 529 534 .64 .70 .76 572 572 574 .74 .79 .86 617 617 617 .85 .90 .96 2200 2300 2400 3930 4110 4290 .302 .330 .360 426 440 452 .59 .67 .74 466 477 489 .68 .75 .83 506 514 523 .75 .83 .91 543 552 557 .83 .91 .99 580 586 592 .92 1.00 1.09 620 623 629 1.03. 1.10 1.18 2500 2600 2800 4470 4640 5000 .390 .422 .489 466 480 506 .82 .91 1.10 500 512 534 .91 1.01 1.21 534 543 566 1.01 1.10 1.31 566 577 594 1.08 1.19 1.41 600 609 626 1.17 1.27 1.50 634 640 657 1.27 1.39 1.59 3000 3200 3400 5360 5720 6070 .560 .638 .721 534 1.35 563 1.42 589 614 1.56 1.81 617 640 1.65 1.94 646 669 692 1.75 2.05 2.38 669 694 714 1.85 2.16 2.50 Outlet velocity, ft. per mm. Capacity, cu. ft. air per mio. Add for total press. 1" S. P. IK" S.P. IK" S.P. IK" S. P. 2" S. P. 2M" S. P. a A pi A a a A pi A a a A K A a a A pi A a a A pi A a a A A a 1300 1400 1500 2320 2500 2680 .106 .122 .141 703 694 686 .78 .81 .84 789 783 1.08 1.10 880 872 1.36 1.41 952 1.70 1600 1700 1800 2860 3040 3210 .160 .180 .202 680 672 666 .86 .89 .93 774 766 757 1.15 1.17 1.21 863 854 843 1.45 1.48 1.52 943 932 923 1.75 1.79 1.84 1020 1009 1000 2.08 2.14 2.19 1151 1140 2.89 2.94 1900 2000 2100 3390 3570 3750 .225 .250 .275 663 660 660 .97 1.02 1.08 752 749 743 1.25 1.30 1.35 837 831 823 1.56 1.59 1.65 914 906 900 1.89 1.94 1.99 992 980 972 2.24 2.29 2.35 1129 1117 1111 2.99 3.05 3.11 2200 2300 2400 3930 4110 4290 .302 .330 .360 657 660 663 1.14 1.22 1.30 740 737 737 1.40 1.47 1.53 817 814 812 1.70 1.77 1.84 892 886 880 2.03 2.10 2.17 966 960 949 2.40 2.46 2.52 1103 1089 1083 3.17 3.23 3.31 2500 2600 2800 4470 4640 5000 .390 .422 .489 666 672 686 1.40 1.48 1.70 737 740 746 1.63 1.72 1.95 809 806 809 1.91 2.00 2.22 877 874 869 2.23 2.32 2.50 946 940 934 2.60 2.67 2.86 1074 1069 1057 3.38 3.46 3.63 3000 3200 3400 5360 5720 6070 .560 .638 .721 703 717 740 1.96 2.24 2.59 757 772 789 2.19 2.49 2.81 814 823 840 2.46 2.75 3.08 874 877 886 2.74 3.04 3.36 932 934 937 3.06 3.36 3.66 1052 1043 1040 3.84 4.08 4.36 3600 3800 4000 6430 6790 7140 .810 .900 1.000 757 2.97 809 3.19 854 872 3.44 3.86 900 914 932 3.75 4.14 4.61 949 957 972 4.03 4.46 4.90 1046 1052 1057 4.73 5.12 5.59 APPENDIX 289 Table XVI. — No. 4 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H" S. P. H" S. P. H" S. P. H"S.P. Vi." S. P. H" S. P. a a a a a a mm. per mm. press. ft & n ft tn ft ft W ft a W p. « d a ft W 1000 1100 1200 2330 2570 2800 .063 .076 .090 290 288 290 .17 .19 .21 363 358 358 .26 .28 .30 418 .41 1300 1400 1500 3030 3270 3500 .106 .122 .141 295 300 308 .24 .28 .32 353 355 358 .33 .36 .40 413 410 408 .44 .47 .50 468 463 460 .56 .59 .62 515 510 .74 .77 558 .92 1600 1700 1800 3730 3970 4220 .160 .180 .202 315 323 333 .37 .42 .49 360 368 375 .45 .50 .56 410 413 415 .55 .60 .66 458 455 458 .66 .71 .77 505 503 500 .80 .85 .90 550 545 543 .96 1.00 1.05 1900 2000 2100 4430 4670 4900 .225 .250 .275 343 353 363 .55 .62 .70 383 390 398 .63 .71 .80 420 428 435 .73 .81 .89 460 463 468 .84 .92 1.00 500 500 503 .96 1.04 1.12 540 540 540 1.11 1.17 1.26 2200 2300 2400 5130 5370 5600 .302 .330 .360 373 385 395 .78 .87 .97 408 418 428 .88 .98 1.09 443 450 458 .98 1.08 1.19 475 483 488 1.08 1.19 1.30 508 513 518 1.21 1.31 1.42 543 545 550 1.35 1.44 1.55 2500 2600 2800 5830 6070 6530 .390 .422 .489 408 420 443 1.07 1.19 1.44 438 448 468 1.19 1.32 1.58 468 475 495 1.32 1.43 1.71 495 505 520 1.41 1.56 1.84 525 533 548 1.53 1.67 1.95 555 560 575 1.67 1.81 2.08 3000 3200 3400 7000 7460 7930 .560 .638 .721 468 1.76 493 1.86 515 538 2.03 2.37 540 560 2.16 2.53 565 585 605 2.29 2.67 3.11 585 608 625 2.42 2.82 3.27 Outlet velocity, ft. per Capacity, cu. ft. air Add for total 1" S. P. IK" S. P. 1K"S. P. l?i"S. P. 2" S. P. 2)4" S. P. a a a a a a mm. per mm. press. ft tn d, a W ft W ft a W a W a ft M 1300 1400 1500 3030 3270 3500 .106 .122 .141 615 608 600 1.03 1.06 1.09 690 685 1.41 1.44 770 763 1.78 1.84 833 2.23 1600 1700 1800 3730 3970 4220 .160 .180 .202 595 588 583 1.13 1.17 1.22 678 670 663 1.50 1.53 1.58 755 748 738 1.89 1.94 1.94 825 815 808 2.29 2.34 2.40 893 883 875 2.72 2.80 2.87 1008 998 3.78 3.84 1900 2000 2100 4430 4670 4900 .225 .250 .275 580 578 578 1.27 1.33 1.40 658 655 650 1.63 1.70 1.76 733 728 720 2.03 2.08 2.16 800 793 788 2.47 2.53 2.59 868 858 850 2.93 2.99 3.07 988 978 973 3.91 3.99 4.07 2200 2300 2400 5130 5370 5600 .302 .330 .360 575 578 580 1.49 1.59 1.70 648 645 645 1.83 1.92 2.00 715 713 710 2.23 2.31 2.40 780 775 770 2.66 2.74 2.83 845 840 830 3.14 3.22 3.30 965 953 948 4.15 4.23 4.32 2500 2600 2800 5830 6070 6530 .390 .422 .489 583 588 600 1.83 1.94 2.23 645 648 653 2.13 2.24 2.55 708 705 708 2.50 2.61 2.90 768 765 760 2.91 3.03 3.27 828 823 818 3.39 3.49 3.73 940 935 925 4.42 4.51 4.74 3000 3200 3400 7000 7460 7930 .560 .638 .721 615 628 648 2.56 2.93 3.38 663 675 690 2.87 3.25 3.67 713 720 735 3.22 3.59 4.02 765 768 775 3.59 3.97 4.39 815 818 820 4.00 4.39 4.79 920 913 910 5.01 5.33 5.70 3600 3800 4000 8400 8860 9330 .810 .900 1.000 663 3.87 708 4.16 748 763 4.50 5.04 788 800 815 4.90 5.41 6.02 830 838 850 5.27 5.83 6.40 915 920 925 6.18 6.69 7.30 19 290 HEATING AND VENTILATION Table XVII. — No. 4J^ Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total X" S. P. H" S. P. H" S. P. H" S. P. H" S. P. X" S. P. a a a a a a min. per mm. press. a a W ft P. M a ft w ft w p. ft M a ft w 1000 1100 1200 2950 3250 3540 .063 .076 .090 258 256 258 .21 .23 .27 322 318 318 .33 .35 .38 371 .52 1300 1400 1500 3840 4130 4430 .106 .122 .141 262 267 273 .30 .35 .40 313 316 318 .41 .46 .51 367 365 362 .55 .59 .63 416 411 409 0.71 0.75 0.79 458 453 0.93 0.97 496 1.17 1600 1700 1800 4720 5020 5310 .160 .180 .202 280 287 296 .46 .53 .61 320 327 333 .57 .64 .71 365 367 369 .69 .76 .84 407 405 407 0.84 0.90 0.97 449 447 445 1.02 1.07 1.14 489 485 482 1.21 1.27 1.33 1900 2000 2100 5610 5900 6200 .225 .250 .275 305 313 322 .69 .79 .88 340 347 353 .80 .89 1.01 373 380 387 .92 1.02 1.13 409 411 416 1.06 1.16 1.26 445 445 447 1.22 1.31 1.42 4 SO 480 480 1.40 1.48 1.59 2200 2300 2400 6500 6790 7090 .302 .330 .360 331 342 351 .98 1.10 1.23 362 371 380 1.12 1.24 1.38 393 400 407 1.24 1.37 1.51 422 429 433 1.37 1.50 1.64 451 456 460 1.53 1.65 1.80 482 485 489 1.71 1.82 1.96 2500 2600 2800 7380 7680 8270 .390 .422 .489 362 373 393 1.35 1.51 1.82 389 398 416 1.50 1.67 2.00 416 422 440 1.67 1.81 2.17 440 449 462 1.79 1.97 2.33 467 473 487 1.94 2.11 2.47 493 498 511 2.11 2.29 2.63 3000 3200 3400 8860 9450 10040 .560 .638 .721 416 2.23 438 2.35 458 478 2.57 3.00 480 498 2.73 3.20 502 520 538 2.90 3.38 3.93 520 540 556 3.06 3.57 4.13 Outlet velocity, ft. per min. Capacity, cu. ft. air per min. Add for total press. 1" S. P. IK" S. P. 1H" S. P. 1H"S. P. 2" S. P. 2H"S. P. a d ft B a ft d B a d ft B a d ft B a d a d P3 ft B 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2800 3000 3200 3400 3600 3800 4000 3840 4130 4430 4720 5020 5310 5610 5900 6200 6500 6790 7090 7380 7680 8270 8860 9450 10040 10630 11220 11810 .106 .122 .141 .160 .180 .202 .225 .250 .275 .302 .330 .360 .390 .422 .489 .560 .638 .721 .810 .900 1.000 547 540 533 529 522 518 516 513 513 511 513 516 518 522 533 547 558 576 5S9 1.30 1.34 1.38 1.43 1.48 1.54 1.60 1.69 1.78 1.89 2.01 2.15 2.31 2.45 2.82 3.24 3.71 4.27 4.90 613 609 602 596 589 585 582 578 576 573 573 573 576 580 5S9 600 613 629 1.79 1.82 1.89 1.93 2.00 2.07 2.15 2.23 2.31 2.43 2.53 2.69 2.84 3.22 3.63 4.11 4.64 5.27 685 678 671 665 656 651 647 640 636 633 631 629 627 629 633 640 653 665 678 2.25 2.33 2.39 2.45 2.51 2.57 2.63 2.74 2.82 2.92 3.04 3.16 3.30 3.67 4.07 4.54 5.08 5.69 6.38 740 733 725 718 711 704 700 696 689 685 682 680 676 680 682 689 700 711 725 2.82 2.90 2.96 3.04 3.12 3.20 3.28 3.36 3.46 3.59 3.69 3.83 4.13 4.54 5.02 5.55 6.20 6.85 7.61 793 785 778 771 762 756 751 747 738 736 731 727 725 727 729 738 745 756 3.44 3.54 3.63 3.71 3.79 3.89 3.97 4.07 4.17 4.29 4.42 4.72 5.06 5.55 6.06 6.66 7.37 8.10 896 887 878 869 865 858 847 842 836 831 822 818 811 809 813 818 822 4.78 4.86 4.94 5.04 5.14 5.25 5.35 5.47 5.59 5.71 5.99 6.34 6.74 7.21 7.82 8.46 9.23 APPENDIX 291 Table XVIII. — No. 5 Niagara Conoid al Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H" a. P. H" S. P. H" s. P. H" S. P. H" S. P. W S. P. a s a a a a mm. per mm. press. a S ft tfl 0, B a P3 n B ft & p, P. » P. pi n 1000 1100 1200 3640 4010 4370 .063 .076 .090 232 230 232 .26 .29 .33 290 286 286 .41 .44 .47 334 .65 1300 1400 1500 4740 5100 5470 .106 .122 .141 236 240 246 .38 .43 .50 282 284 286 .51 .56 .63 330 328 326 .68 .73 .78 374 370 368 .88 .92 .98 412 408 1.15 1.20 446 1.44 1600 1700 1800 5830 6190 6560 .160 .180 .202 252 258 266 .57 .66 .76 288 294 300 .70 .79 .88 328 330 332 .86 .94 1.03 366 364 366 1.04 1.11 1.20 404 402 400 1.26 1.33 1.40 440 436 434 1.49 1.57 1.64 1900 2000 2100 6930 7290 7660 .225 .250 .275 274 282 290 .86 .97 1.09 306 312 318 .99 1.11 1.24 336 342 348 1.14 1.26 1.39 368 370 374 1.31 1.43 1.56 400 400 402 1.50 1.62 1.75 432 432 432 1.73 1.83 1.96 2200 2300 2400 8010 8380 8750 .302 .330 .360 298 308 316 1.21 1.36 1.51 326 334 342 1.38 1.55 1.70 354 360 366 1.53 1.69 1.86 380 386 390 1.69 1.85 2.03 406 410 414 1.89 2.04 2.22 434 436 440 2.11 2.25 2.41 2500 2600 2800 9100 9480 10200 .390 .422 .489 326 336 354 1.67 1.86 2.25 350 358 374 1.86 2.06 2.46 374 380 396 2.06 2.24 2.68 396 404 416 2.21 2.43 2.88 420 426 438 2.40 2.60 3.05 444 448 460 2.60 2.83 3.25 3000 3200 3400 10940 11660 12390 .560 .638 .721 374 2.75 394 2.90 412 430 3.18 3.70 432 448 3.38 3.95 452 468 484 3.58 4.18 4.85 468 486 500 3.78 4.40 5.10 Outlet velocity, ft. per Capacity, cu. ft. air Add for total 1" S. P. IK" S. P. W" S. P. IVi" S. P. 2" S. P. 2Y % " S. P. a a a a a a mm. ' per mm. press. ft B ft ft B P3 a B ft ft B ft ft B p. P3 ft B 1300 1400 1500 4740 5100 5470 .106 .122 .141 492 486 480 1.60 1.65 1.71 552 548 2.21 2.25 616 610 2.78 2.88 666 3.48 1600 1700 1800 5830 6190 6560 .160 .180 .202 476 470 466 1.76 1.82 1.90 542 536 530 2.34 2.39 2.47 604 598 590 2.95 3.03 3.10 660 652 646 3.58 3.65 3.75 714 706 700 4.25 4.38 4.48 806 798 5.90 6.00 1900 2000 2100 6930 7290 7660 .225 .250 .275 464 462 462 1.98 2.08 2.19 526 524 520 2.55 2.65 2.75 586 582 576 3.18 3.25 3.38 640 634 630 3.85 3.95 4.05 694 686 680 4.58 4.68 4.80 790 782 778 6.10 6.23 6.35 2200 2300 2400 8010 8380 8750 .302 .330 .360 460 462 464 2.33 2.48 2.65 518 516 516 2.85 3.00 3.13 572 570 568 3.48 3.60 3.75 624 620 616 4.15 4.28 4.44 676 672 664 4.90 5.03 5.15 772 762 758 6.48 6.60 6.75 2500 2600 2800 9100 9480 10200 .390 .422 .489 466 470 480 2.85 3.03 3.48 516 518 522 3.33 3.50 3.98 566 564 566 3.90 4.08 4.53 614 612 608 4.55 4.73 5.10 662 658 654 5.30 5.45 5.83 752 748 740 6.90 7.05 7.40 3000 3200 3400 10940 11660 12390 .560 .638 .721 492 502 518 4.00 4.57 5.27 530 540 552 4.48 5.08 5.73 570 576 588 5.03 5.60 6.28 612 614 620 5.60 6.20 6.85 652 654 656 6.25 6.85 7.48 736 730 728 7.83 8.32 8.90 3600 3800 4000 13120 13850 14580 .810 .900 1.000 530 6.05 566 6.50 598 610 7.03 7.88 630 640 652 7.65 8.46 9.40 664 670 680 8.22 9.10 10.0 732 736 740 9.65 10.5 11.4 292 HEATING AND VENTILATION Table XIX. — No. 5)4 Niagaba Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total X" S. P. H" S. P. H" S. P. H" S. P. Yi" S. P. %" S. P. a a a a a a min. per min. press. a d « ft pi ft IK 0, pi 0, K p. 0, W p. p4 P. HI p. ft W 1000 1100 1200 4410 4850 5290 .063 .076 .090 211 209 211 .32 .35 .40 264 260 260 .49 .53 .57 304 .78 1300 1400 1500 5730 6170 6620 .106 .122 .141 215 218 224 .45 .52 .60 257 258 260 .62 .68 .76 300 298 296 .83 .88 .95 340 336 335 1.06 1.12 1.18 375 371 1.40 1.45 406 1.75 1600 1700 1800 7060 7500 7940 .160 .180 .202 229 235 242 .69 .80 .92 262 267 273 .85 .95 1.06 298 300 302 1.04 1.13 1.25 333 331 333 1.26 1.35 1.46 367 366 364 1.52 1.60 1.70 400 397 395 1.81 1.89 1.98 1900 2000 2100 8380 8820 9260 .225 .250 .275 249 256 264 1.04 1.17 1.32 278 284 289 1.19 1.34 1.50 306 311 316 1.38 1.53 1.68 335 336 340 1.59 1.73 1.88 364 364 366 1.82 1.96 2.12 393 393 393 2.09 2.21 2.37 2200 2300 2400 9700 10140 10590 .302 .330 .360 271 280 287 1.47 1.65 1.83 296 304 311 1.67 1.86 2.05 322 327 333 1.85 2.05 2.25 346 351 355 2.05 2.24 2.45 369 373 377 2.28 2.47 2.68 395 397 400 2.55 2.72 2.92 2500 2600 2800 11030 11470 12350 .390 .422 .489 297 306 322 2.02 2.25 2.72 318 326 340 2.25 2.49 2.98 340 346 360 2.49 2.71 3.24 360 367 378 2.67 2.94 3.48 382 387 398 2.90 3.15 3.69 404 407 418 3.15 3.42 3.93 3000 3200 3400 13230 14110 15000 .560 .638 .721 340 3.33 358 3.51 375 391 3.84 4.48 393 407 4.08 4.78 411 426 440 4.33 5.05 5.87 426 442 455 4.57 5.33 6.17 Outlet Capacity, cu. ft. air Add for total 1" S. P. IK" S. P. ws.p. Wi" S. P. 2" S. P . M2" S. P. velocity, ft. per a a a a a a min. per mm. press. Pi P, M p. a W p, pi P. K p, ft K p, pi ft pi p. W 1300 1400 1500 5730 6170 6620 .106 .122 .141 447 442 437 1.94 1.99 2.07 502 498 2.67 2.72 560 555 3.36 3.48 606 4.21 1600 1700 1800 7060 7500 7940 .160 .180 .202 433 427 424 2.13 2.20 2.30 493 487 482 2.83 2.89 2.99 549 544 537 3.57 3.66 3.75 600 593 587 4.33 4.42 4.54 649 642 636 5.14 5.29 5.42 733 726 7.14 7.26 1900 2000 2100 8380 8820 9260 .225 .250 .275 422 420 420 2.39 2.52 2.65 478 476 473 3.09 3.21 3.33 533 529 524 3.84 3.93 4.08 582 576 573 4.66 4.78 4.90 631 624 618 5.54 5.66 5.81 718 711 707 7.38 7.53 7.68 2200 2300 2400 9700 10140 10590 .302 .330 .360 418 420 422 2.82 3.00 3.21 471 469 469 3.45 3.63 3.78 520 518 517 4.21 4.36 4.54 567 564 560 5.02 5.17 5.35 615 611 604 5.93 6.08 6.23 702 693 689 7.84 7.99 8.17 2500 2600 2800 11030 11470 12350 .390 .422 .489 424 427 437 3.45 3.66 4.21 469 471 475 4.02 4.24 4.81 515 513 515 4.72 4.93 5.48 558 557 553 5.51 5.72 6.17 602 598 595 6.41 6.59 7.05 684 680 673 8.35 8.53 8.95 3000 3200 3400 13230 14110 15000 .560 .638 .721 447 456 471 4.84 5.54 6.38 482 491 502 5.42 6.14 6.93 518 524 535 6.08 6.78 7.59 557 558 564 6.78 7.50 8.29 593 595 596 7.56 8.29 9.04 669 664 662 9.47 10.1 10.8 3600 3800 4000 15880 16760 17640 .810 .900 1.000 482 7.32 515 7.87 544 555 8.50 9.53 573 582 593 9.26 10.2 11.4 604 609 618 9.95 11.0 12.1 666 669 673 11.7 12.7 13.8 APPENDIX 293 Table XX. — No. 6 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H" S. P. !«" s. p. W S. P. H" S. P. ?£" S. P. %" S. P. a a a a a a mm. per min. press. p. 0, W a a W a 0, a PS a M a P5 a W a a n 1000 1100 1200 5250 5770 6300 .063 .076 .090 193 192 193 .37 .42 .48 242 238 238 .59 .63 .67 278 .93 1300 1400 1500 6820 7350 7870 .106 .122 .141 197 200 205 .54 .62 .72 235 237 238 .73 .81 .91 275 274 272 .98 1.05 1.13 312 308 307 1.27 1.33 1.41 344 340 1.66 1.72 372 2.08 1600 1700 1800 8400 8920 9450 .160 .180 .202 210 215 222 .82 .95 1.09 240 245 250 1.01 1.13 1.26 274 275 277 1.23 1.35 1.49 305 304 305 1.49 1.60 1.73 337 335 334 1.81 1.91 2.02 367 363 362 2.15 2.25 2.36 1900 2000 2100 9970 10500 11030 .225 .250 .275 228 235 242 1.24 1.40 1.57 255 260 265 1.42 1.59 1.79 280 285 290 1.64 1.82 2.00 307 309 312 1.88 2.06 2.24 334 334 335 2.16 2.33 2.52 360 360 360 2.49 2.63 2.82 2200 2300 2400 11550 12070 12600 .302 .330 .360 248 257 263 1.75 1.96 2.18 272 279 285 1.98 2.21 2.45 295 300 305 2.20 2.43 2.68 317 322 325 2.43 2.66 2.92 339 342 345 2.72 2.94 3.19 362 363 367 3.04 3.23 3.48 2500 2600 2800 13120 13650 14700 .390 .422 .489 272 280 295 2.41 2.68 3.24 291 299 312 2.67 2.96 3.55 312 317 330 2.96 3.22 3.85 330 337 347 3.18 3.50 4.14 350 355 365 3.45 3.74 4.39 370 374 384 3.74 4.07 4.68 3000 3200 3400 15750 16790 17850 .560 .638 .721 312 3.96 329 4.18 344 359 4.57 5.33 360 373 4.86 5.69 377 390 403 5.15 6.01 6.98 390 405 417 5.44 6.34 7.35 Outlet velocity, ft. per Capacity, cu. ft. air Add for total 1" S. P. 1M"S.P. WS.P. l?i"S.P. 2" S. P. 2H" S. P. a a ■ a a a a min. per min. press. a a « a a W a a a a P3 a W a a - M a a W 1300 1400 1500 6820 7350 7870 .106 .122 .141 410 405 400 2.31 2.37 2.46 460 457 3.18 3.24 513 509 4.00 4.14 555 5.00 1600 1700 1800 8400 8920 9450 .160 .180 .202 397 392 389 2.54 2.62 2.73 452 447 442 3.36 3.44 3.56 504 499 492 4.25 4.36 4.47 550 544 539 5.15 5.26 5.40 595 589 584 6.12 6.30 6.45 672 665 8.50 8.64 1900 2000 2100 9970 10500 11030 .225 .250 .275 387 385 385 2.85 3.00 3.16 439 437 434 3.67 3.82 3.96 489 485 480 4.57 4.68 4.86 534 529 525 5.55 5.69 5.83 579 572 567 6.59 6.73 6.91 659 652 649 8.78 8.96 9.14 2200 2300 2400 11550 12070 12600 .302 .330 .360 384 385 387 3.35 3.57 3.82 432 430 430 4.11 4.32 4.50 477 475 474 5.00 5.18 5.40 520 517 514 5.98 6.16 6.37 564 560 554 7.06 7.24 7.42 644 635 632 9.32 9.50 9.72 2500 2600 2800 13120 13650 14700 .390 .422 .489 389 392 400 4.10 4.36 5.00 430 432 435 4.79 5.04 5.73 472 470 472 5.62 5.87 6.52 512 510 507 6.55 6.81 7.34 552 549 545 7.63 7.85 8.39 627 624 617 9.94 10.2 10.7 3000 3200 3400 15750 16790 17850 .560 .638 .721 410 419 432 5.76 6.59 7.60 442 450 460 6.45 7.31 8.24 475 480 490 7.24 8.06 9.04 510 512 517 8.06 8.93 9.86 544 545 547 9.00 9.86 10.8 614 609 607 11.3 12.0 12.8 3600 3800 4000 18900 19950 21000 .810 .900 1.000 442 8.71 472 9.36 499 509 10.1 11.3 525 534 544 11.0 12.2 13.5 554 559 567 11.9 13.1 14.4 610 614 617 13.9 15.1 16.4 294 HE A TING AND V EN TIL A TION Table XXI. — No. 7 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. Capacity, cu. ft. air Add for total H"S.P. M"S. P. H" S. P. %" S. P. U" s. P. K"S. P. a a s a a a per min. per min. press. p. a M p. a iH a a 0. pi a a a pi a W a pi a a 1000 1100 1200 7140 7860 8570 .063 .076 .090 166 164 166 .51 .57 .65 207 204 204 .80 .85 .92 239 1.26 1300 1400 1500 9290 10000 10720 .106 .122 .141 169 172 176 .74 .85 .98 202 203 204 1.00 1.10 1.24 236 234 233 1.34 1.43 1.53 267 264 263 1.73 1.81 1.91 294 292 2.26 2.34 319 2.83 1600 1700 1800 11430 12150 12860 .160 .180 .202 180 184 190 1.12 1.29 1.49 206 210 214 1.37 1.54 1.72 234 236 237 1.68 1.83 2.02 262 260 262 2.03 2.18 2.36 289 287 286 2.46 2.60 2.75 314 312 310 2.93 3.07 3.21 1900 2000 2100 13570 14290 15000 .225 .250 .275 196 202 207 1.68 1.90 2.13 219 223 227 1.93 2.17 2.44 240 244 249 2.23 2.47 2.73 263 264 267 2.56 2.80 3.05 286 286 287 2.95 3.18 3.43 309 309 309 3.39 3.58 3.84 2200 2300 2400 15720 16430 17150 .302 .330 .360 213 220 226 2.38 2.67 2.97 233 239 244 2.70 3.01 3.33 253 257 262 3.00 3.31 3.64 272 276 279 3.31 3.63 3.97 290 293 296 3.70 4.00 4.34 310 312 314 4.13 4.40 4.73 2500 2600 2800 17860 18580 20000 .390 .422 .489 233 240 253 3.27 3.64 4.41 250 256 267 3.64 4.03 4.83 267 272 283 4.03 4.39 5.24 283 289 297 4.33 4.77 5.64 300 304 313 4.70 5.10 5.98 317 320 329 5.10 5.54 6.37 3000 3200 3400 21430 22860 24290 .560 .638 .721 267 5.39 282 5.68 294 307 6.22 7.25 309 320 6.62 7.74 323 334 346 7.01 8.18 9.51 334 347 357 7.40 8.62 10.0 Outlet velocity, ft. per Capacity, cu. ft. air Add for total 1" S. P. 134" S. P. 1)4" S. P. 1 Vi" S. P. 2" S. P. 214" S. P. a a a a a a mm. per mm. press. a pi a K a Pi a W a pi a a a « a B a Pi a a a pi a a 1300 1400 1500 9290 10000 10720 .106 .122 .141 352 347 343 3.14 3.23 3.35 394 392 4.33 4.41 440 436 5.44 5.64 476 6.81 1600 1700 1800 11430 12150 12860 .160 .180 .202 340 336 333 3.46 3.57 3.72 387 383 379 4.58 4.68 4.85 432 427 422 5.78 5.93 6.08 472 466 462 7.01 7.15 7.35 510 504 500 8.33 8.58 8.77 576 570 11.6 11.8 1900 2000 2100 13570 14290 15000 .225 .250 .275 332 330 330 3.88 4.08 4.30 376 374 372 5.00 5.19 5.39 419 416 412 6.22 6.37 6.62 457 453 450 7.55 7.74 7.94 496 490 486 8.97 9.16 9.41 564 559 556 12.0 12.2 12.5 2200 2300 2400 15720 16430 17150 .302 .330 .360 329 330 332 4.56 4.86 5.19 370 369 369 5.59 5.88 6.13 409 407 406 6.81 7.06 7.35 446 443 440 8.13 8.38 8.67 483 480 474 9.60 9.85 10.1 552 544 542 12.7 12.9 13.2 2500 2600 2800 17860 18580 20000 .390 .422 .489 333 336 343 5.59 5.93 6.81 369 370 373 6.52 6.86 7.79 404 403 404 7.64 7.99 8.87 439 437 434 8.92 9.26 10.0 473 470 467 10.4 10.7 11.4 537 534 529 13.5 13.8 14.5 3000 3200 3400 21430 22860 24290 .560 .638 .721 352 359 370 7.84 8.97 10.3 379 386 394 8.77 9.95 11.2 407 412 420 9.85 11.0 12.3 437 439 443 11.0 12.2 13.4 466 467 469 12.3 13.4 14.7 526 522 520 15.3 16.3 17.4 3600 3800 4000 25720 27150 28580 .810 .900 1.000 379 11.9 404 12.7 427 436 13.8 15.4 450 457 466 15.0 16.6 18.4 474 479 486 16.1 17.8 19.6 523 526 529 18.9 20.5 22.4 AFFEND1X 295 Table XXII. — No. 8 Niagaea Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H" a. P. H" S. P. H" S. P. U" S. P. K"S.P. H" S. P. a a a a a a mm. per mm. press. PS d a pi P. w t4 ft a p. ft a ft a n ft a 1000 1100 1200 9330 10270 11200 .063 .076 .090 145 144 145 .67 .74 .85 181 179 179 1.04 1.11 1.20 209 1.65 1300 1400 1500 12130 13060 14000 .106 .122 .141 148 150 154 .96 1.11 1.27 176 178 179 1.31 1.44 1.61 206 205 204 1.75 1.87 2.00 234 231 230 2.25 2.36 2.50 258 255 2.95 3.06 279 3.69 1600 1700 1800 14930 15860 16800 .160 .180 .202 158 161 166 1.47 1.69 1.94 180 184 188 1.79 2.01 2.25 205 206 208 2.19 2.39 2.64 229 228 229 2.66 2.85 3.08 253 251 250 3.21 3.39 3.59 275 273 271 3.82 4.01 4.19 1900 2000 2100 17730 18660 19600 .225 .250 .275 171 176 181 2.20 2.48 2.79 191 195 199 2.52 2.83 3.18 210 214 218 2.91 3.23 3.56 230 231 234 3.34 3.66 3.98 250 250 251 3.85 4.15 4.48 270 270 270 4.42 4.68 5.02 2200 2300 2400 20530 21460 22400 .302 .330 .360 186 193 198 3.11 3.48 3.87 204 209 214 3.53 3.93 4.35 221 225 229 3.92 4.33 4.76 238 241 244 4.33 4.74 5.19 254 256 259 4.83 5.22 5.67 271 273 275 5.40 5.75 6.18 2500 2600 2800 23330 24260 26130 .390 .422 .489 204 210 221 4.28 4.76 5.76 219 224 234 4.75 5.26 6.31 234 238 248 5.26 5.73 6.85 248 253 260 5.65 6.23 7.36 263 266 274 6.13 6.66 7.81 278 280 288 6.66 7.23 8.32 3000 3200 3400 28000 29860 31720 .560 .638 .721 234 7.04 246 7.42 258 269 8.13 9.47 270 280 8.64 10.1 283 293 303 9.15 10.7 12.4 293 304 313 9.66 11.3 13.1 Outlet Capacity, cu. ft. air per min. Add for total press. 1" S. P. 1J4" S. P. W" S.P. lJi" S. P. 2" S. P. 2M" S. P. velocity, ft. per min. a p. ft a a a pi ft , a a d pi 0, a a ft P3 ft a a d pi d a a d Pi ft a 1300 1400 1500 12130 13060 14000 .106 .122 .141 308 304 300 4.10 4.22 4.37 345 343 5.65 5.76 385 381 7.10 7.36 416J8.90 1600 1700 1800 14930 15860 16800 .160 .180 .202 298 294 291 4.51 4.66 4.86 339 335 331 5.98 6.11 6.33 378 374 369 7.55 7.74 7.94 413 408 404 9.15 9.34 9.60 446 441 438 10.9 11.2 11.5 504 499 15.1 15.4 1900 2000 2100 17730 18660 19600 .225 .250 .275 290 289 289 5.06 5.33 5.61 329 328 325 6.53 6.78 7.04 366 364 360 8.13 8.32 8.64 400 396 394 9.86 10.1 10.4 434 429 425 11.7 12.0 12.3 494 489 486 15.6 15.9 16.3 2200 2300 2400 20530 21460 22400 .302 .330 .360 288 289 290 5.96 6.35 6.78 324 323 323 7.30 7.68 8.00 358 356 355 8.90 9.22 9.60 390 388 385 10.6 11.0 11.3 423 420 415 12.6 12.9 13.2 483 476 474 16.6 16.9 17.3 2500 2600 2800 23330 24260 26130 .390 .422 .489 291 294 300 7.30 7.74 8.90 323 324 326 8.51 8.96 10.2 354 353 354 9.98 10.4 11.6 384 383 380 11.7 12.1 13.1 414 411 409 13.6 14.0 14.9 470 468 463 17.7 18.1 19.0 3000 3200 3400 28000 29860 31720 .560 .638 .721 308 314 324 10.2 11.7 13.5 331 338 345 11.5 13.0 14.7 356 360 368 12.9 14.3 16.1 383 384 388 14.3 15.9 17.5 408 409 410 16.0 17.5 19.1 460 456 455 20.0 21.3 22.8 3600 3800 4000 33590 35460 37330 .810 .900 1.000 331 15.5 354 16.6 374 381 18.0 20.2 394 400 408 19.6 21.6 24.1 415 419 425 21.1 23.3 25.6 458 460 463 24.7 26.8 29.2 296 HEATING AND VENTILATION Table XXIII. — No. 9 Niagara Conoidal Fan (Type N) Capacities and Static Pbesstjres at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H"S. P. H" S. P. M" S. P. %" S. P. H" S. P. H"B.F. a a a a a a [min. per mm. press. p, P. b p. PS a B p. PS ft B p. PS a B p. PS P, B p, PS P. B 1000 1100 1200 11810 12990 14170 .063 .076 .090 129 128 129 .84 .94 1.07 161 159 159 1.32 1.41 1.52 186 2.09 1300 1400 1500 15360 16530 17720 .106 .122 .141 131 133 137 1.22 1.40 1.61 157 158 159 1.65 1.82 2.04 183 182 181 2.21 2.37 2.54 208 206 205 2.85 2.99 3.16 229 227 3.74 3.87 248 4.67 1600 1700 1800 18900 20080 21250 .160 .180 .202 140 143 148 1.86 2.14 2.45 160 163 167 2.27 2.54 2.84 182 183 185 2.77 3.03 3.35 203 202 203 3.36 3.60 3.90 225 223 222 4.07 4.29 4.55 244 242 241 4.84 5.07 5.30 1900 2000 2100 22440 23620 24800 .225 .250 .275 152 157 161 2.78 3.14 3.52 170 173 177 3.19 3.58 4.03 187 190 193 3.69 4.08 4.51 205 206 208 4.23 4.64 5.04 222 222 223 4.87 5.25 5.67 240 240 240 5.60 5.92 6.35 2200 2300 2400 25980 27160 28340 .302 .330 .360 166 171 176 3.93 4.41 4.90 181 186 190 4.47 4.97 5.50 197 200 203 4.96 5.48 6.02 211 215 217 5.47 6.00 6.56 226 228 230 6.10 6.61 7.18 241 242 244 6.83 7.27 7.82 2500 2600 2800 29520 30710 33070 .390 .422 .489 181 187 197 5.41 6.02 7.28 195 199 208 6.01 6.66 7.98 208 211 220 6.66 7.25 8.67 220 224 231 7.15 7.88 9.30 233 237 243 7.76 8.42 9.88 247 249 256 8.43 9.15 10.5 3000 3200 3400 35430 37790 40150 .560 .638 .721 208 8.91 219 9.40 229 239 10.3 12.0 240 249 10.9 12.8 251 260 269 11.6 13.5 15.7 260 270 278 12.2 14.3 16.5 Outlet velocity, ft. per Capacity, cu. ft. air Add for total 1" S. P. IX" S. P. iy 2 " S. P. 1K"S.P. 2" S. P. 2J^"S. P. a a a a a a min. per mm. press. ft PS ft n ft . PS ft B d PS ft w PS a B PS ft B a PS ft B 1300 1400 1500 15360 16530 17720 .106 .122 .141 273 270 267 5.18 5.34 5.53 307 304 7.15 7.29 342 339 8.99 9.31 370 11.3 1600 1700 1800 18900 20080 21250 .160 .180 .202 264 261 259 5.71 5.90 6.15 301 298 294 7.57 7.73 8.01 336 332 328 9.56 9.80 10.0 367 362 359 11.6 11.8 12.2 397 392 389 13.8 14.2 14.5 448 443 19.1 19.4 1900 2000 2100 22440 23620 24800 .225 .250 .275 258 257 257 6.41 6.74 7.10 292 291 289 8.26 8.59 8.91 326 323 320 10.3 10.5 10.9 356 352 350 12.5 12.8 13.1 386 381 378 14.8 15.2 15.6 439 435 432 19.8 20.2 20.6 2200 2300 2400 25980 27160 28340 .302 .330 .360 256 257 258 7.54 8.04 8.59 288 287 287 9.23 9.72 10.1 318 317 316 11.3 11.7 12.2 347 344 342 13.4 13.7 14.3 376 373 369 15.9 16.3 16.7 429 423 421 21.0 21.4 21.9 2500 2600 2800 29520 30710 33070 .390 .422 .489 259 261 267 9.23 9.80 11.3 287 288 290 10.8 11.3 12.9 314 313 314 12.6 13.2 14.7 341 340 338 14.8 15.3 16.5 368 366 363 17.2 17.7 18.9 418 416 411 22.4 22.8 24.0 3000 3200 3400 35430 37790 40150 .560 .638 .721 273 279 288 13.0 14.8 17.1 294 300 307 14.5 16.4 18.6 317 320 327 16.3 18.1 20.3 340 341 344 18.2 20.1 22.2 362 363 364 20.3 22.2 24.2 409 406 405 25.4 27.0 28.8 3600 3800 4000 42510 44880 47240 .810 .900 1.000 294 19.6 314 21.1 332 339 22.8 25.5 350 356 362 24.8 27.4 30.5 369 372 378 26.7 29.5 32.4 407 409 411 31.3 33.9 36.9 APPENDIX 297 Table XXIV.— No. 10 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H" S. P. %" S. P. H" S. P. Vs" S. P. H" S. P. 14," S. P. a a a a a a mm. per mm. press. p, ft W ft a ft ft K ft u ft w 1000 1100 1200 14580 16040 17500 .063 .076 .090 116 115 116 1.04 1.16 1.32 145 143 143 1.63 1.74 1.87 167 2.58 1300 1400 1500 18960 20410 21870 .106 .122 .141 118 120 123 1.50 1.73 1.99 141 142 143 2.04 2.25 2.52 165 164 163 2.73 2.92 3.13 187 185 184 3.52 3.69 3.90 206 204 4.61 4.78 223 5.77 1600 1700 1800 23330 24790 26240 .160 .180 .202 126 129 133 2.29 2.64 3.03 144 147 150 2.80 3.14 3.51 164 165 166 3.42 3.74 4.13 183 182 183 4.15 4.45 4.81 202 201 200 5.02 5.30 5.61 220 218 217 5.97 6.26 6.55 1900 2000 2100 27700 29160 30620 .225 .250 .275 137 141 145 3.43 3.88 4.35 153 156 159 3.94 4.42 4.97 168 171 174 4.55 5.04 5.56 184 185 187 5.22 5.72 6.22 200 200 201 6.01 6.48 7.00 216 216 216 6.91 7.31 7.84 2200 2300 2400 32080 33540 34990 .302 .330 .360 149 154 158 4.85 5.44 6.05 163 167 171 5.51 6.14 6.79 177 180 183 6.12 6.76 7.43 190 193 195 6.76 7.40 8.10 203 205 207 7.54 8.16 8.86 217 218 220 8.43 8.98 9.65 2500 2600 2800 36450 37910 40830 .390 .422 .489 163 168 177 6.68 7.43 8.99 175 179 187 7.42 8.22 9.85 187 190 198 8.22 8.95 10.7 198 202 208 8.83 9.73 11.5 210 213 219 9.58 10.4 12.2 222 224 230 10.4 11.3 13.0 3000 3200 3400 43740 46660 49570 .560 .638 .721 187 11.0 197 11.6 206 215 12.7 14.8 216 224 13.5 15.8 226 234 242 14.3 16.7 19.4 234 243 250 15.1 17.6 20.4 Outlet Capacity, cu. ft. air Add for total 1" S. P. 1K"S.P. 1H"S. P. W'S.P. 2" S. P. 2K" S. P. velocity, ft. per a a a a a a nun. per min. press. ft M a W ft a n rt ft w ft K p. ft M 1300 1400 1500 18960 20410 21870 .106 .122 .141 246 243 240 6.40 6.59 6.83 276 274 8.83 9.00 308 305 ii.i 11.5 333 13.9 1600 1700 1800 23330 24790 26240 .160 .180 .202 238 235 233 7.05 7.28 7.59 271 268 265 9.34 9.54 9.89 302 299 295 11.8 12.1 12.4 330 326 323 14.3 14.6 15.0 357 353 350 17.0 17.5 17.9 403 399 23 1 . 6 24.0 1900 2000 2100 27700 29160 30620 .225 .250 .275 232 231 231 7.91 8.32 8.77 263 262 260 10.2 10.6 11.0 293 291 288 12.7 13.0 13.5 320 317 315 15.4 15.8 16.2 347 343 340 18.3 18.7 19.2 395 391 389 24.4 24.9 25.4 2200 2300 2400 32080 33540 34990 .302 .330 .360 230 231 232 9.31 9.92 10.6 259 258 258 11.4 12.0 12.5 286 285 284 13.9 14.4 15.0 312 310 308 16.6 17.1 17.7 338 336 332 19.6 20.1 20.6 386 381 379 25.9 26.4 27.0 2500 2600 2800 36450 37910 40830 .390 .422 .489 233 235 240 11.4 12.1 13.9 258 259 261 13.3 14.0 15.9 283 282 283 15.6 16.3 18.1 307 306 304 18.2 18.9 20.4 331 329 327 21.2 21.8 23.3 376 374 370 27.6 28.2 29.6 3000 3200 3400 43740 46660 49570 .560 .638 .721 246 251 259 16.0 18.3 21.1 265 270 276 17.9 20.3 22.9 285 288 294 20.1 22.4 25.1 306 307 310 22.4 24.8 27.4 326 327 328 25.0 27.4 29.9 368 365 364 31.3 33.3 35.6 3600 3800 4000 52490 55400 58320 .810 .900 1.000 265 24.2 283 26.0 299 305 28.1 31.5 315 320 326 30.6 33.8 37.6 332 335 340 32.9 36.4 40.0 366 368 370 38.6 41.8 45.6 298 HEATING AND VENTILATION Table XXV. — No. 11 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total X" S. P. H" S. P. y 2 "s. P. H" S. P. H" s. P. 14" S.P. a a a a a a mm. per mm. press. p, pi n W p, a W o P. M a ft w ft w x ft w 1000 1100 1200 17640 19410 21170 .063 .076 .090 106 105 106 1.26 1.40 1.60 132 130 130 1.97 2.11 2.26 152 3.12 1300 1400 1500 22930 24700 26460 .106 .122 .141 107 109 112 1.82 2.09 2.41 128 129 130 2.47 2.72 3.05 150 149 148 3.30 3.53 3.79 170 168 167 4.26 4.47 4.72 187 186 5.58 5.78 203 6.98 1600 1700 1800 28230 29990 31750 .160 .180 .202 115 117 121 2.77 3.20 3.67 131 134 136 3.39 3.80 4.25 149 150 151 4.14 4.53 5.00 166 166 166 5.02 5.39 5.82 184 183 182 6.08 6.41 6.79 200 198 197 7.22 7.58 7.93 1900 2000 2100 33520 35280 37050 .225 .250 .275 125 128 132 4.15 4.70 5.26 139 142 145 4.77 5.35 6.01 153 156 158 5.51 6.10 6.73 167 168 170 6.32 6.92 7.53 182 182 183 7.27 7.84 8.87 196 196 196 8.36 8.85 9.49 2200 2300 2400 38810 40580 42340 .302 .330 .360 136 140 144 5.87 6.58 7.32 148 152 156 6.67 7.43 8.22 161 164 166 7.41 8.18 8.99 173 176 177 8.18 8.95 9.80 185 186 188 9.12 9.87 10.7 197 198 200 10.2 10.9 11.7 2500 2600 2800 44100 45870 49400 .390 .422 .489 148 153 161 8.08 8.99 10.9 159 163 170 8.98 9.95 11.9 170 173 180 9.95 10.8 13.0 180 184 189 10.7 11.8 13.9 191 194 199 11.6 12.6 14.8 202 204 209 12.6 13.7 15.7 3000 3200 3400 52910 56450 599S0 .560 .638 .721 170 13.3 179 14.0 187 196 15.4 17.9 196 204 16.3 19.1 206 213 220 17.3 20.2 23.5 213 221 227 18.3 21.3 24.7 Outlet velocity, ft. per mm. Capacity, cu. f$. air_ per min. Add for total press. 1" S. P. 1K"S. P. 1M"S. P. IK" S. P. 2" S. P. 2H" S. P. a X d a d X d a a d X ft M a d x d a d X ft M a d x ft w 1300 1400 1500 22930 24700 26460 .106 .122 .141 224 221 218 7.74 7.97 8.26 251 249 10.7 10.9 280 277 13.4 13.9 303 16.8 1600 1700 1800 28230 29990 31750 .160 .180 .202 216 214 212 8.53 8.81 9.18 246 244 241 11.3 11.6 12.0 275 272 268 14.3 14.7 15.0 300 296 294 17.3 17.7 18.2 325 321 318 20.6 21.2 21.7 366 363 28.6 29.0 1900 2000 2100 33520 35280 37050 .225 .250 .275 211 210 210 9.57 10.1 10.6 239 238 236 12.4 12.8 13.3 266 265 262 15.4 15.7 16.3 291 288 286 18.6 19.1 19.6 316 312 309 22.2 22.6 23.2 359 356 354 29.5 30.1 30.7 2200 2300 2400 38810 40580 42340 .302 .330 .360 209 210 211 11.3 12.0 12.8 236 235 235 13.8 14.5 15.1 260 259 258 16.8 17.4 18.2 284 282 280 20.1 20.7 21.4 307 306 302 23.7 24.3 24.9 351 346 345 31.3 32.0 32.7 2500 2600 2800 44100 45870 49400 .390 .422 .489 212 214 218 13.8 14.6 16.8 235 236 237 16.1 17.0 19.2 257 256 257 18.9 19.7 21.9 279 278 276 22.0 22.9 24.7 301 299 297 25.7 26.4 28.2 342 340 336 33.4 34.1 35.8 3000 3200 3400 52910 56450 59980 .560 .638 .721 224 228 236 19.4 22.1 25.5 241 246 251 21.7 24.6 27.7 259 262 267 24.3 27.1 30.4 278 279 282 27.1 30.0 33.2 296 297 248 30.3 33.2 36.2 335 332 331 37.9 40.3 43.1 3600 3800 4000 63510 67030 70560 .810 .900 1.000 241 29.3 257 31.5 272 277 34.0 38.1 286 291 296 37.0 40.9 45.5 302 305 309 39.8 44.1 48.4 333 335 336 46.7 50.6 55.2 APPENDIX 299 Table XXVI. — No. 12 Niagara Conoidal Fan (Type N) Capacities and Static Pressures at 70°F. and 29.92 Inches Barometer Outlet velocity, ft. per Capacity, cu. ft. air Add for total H" S. P. H" S. P. W S. P. «"S.P. K" S. P. %" S. P. a a a a a a mm. per mm. press. p. p. PS a M p. P3 p. a X 0, p, W a 0. W 1000 1100 1200 21000 23090 25190 .063 .076 .090 97 96 97 1.50 1.67 1.90 121 119 119 2.35 2.51 2.69 139 3.72 1300 1400 1500 27290 29390 31490 .106 .122 .141 98 100 103 2.16 2.49 2.87 118 118 119 2.94 3.24 3.63 138 137 136 3.93 4.21 4.51 156 154 153 5.07 5.31 5.62 172 170 6.64 6.88 186 8.31 1600 1700 1800 33600 35600 37790 .160 .180 .202 105 108 111 3.30 3.80 4.36 120 123 125 4.03 4.52 5.06 137 138 138 4.93 5.39 5.95 153 152 153 5.98 6.41 6.93 168 168 167 7.23 7.63 8.08 183 182 181 8.60 9.02 9.43 1900 2000 2100 39890 41990 44090 .225 .250 .275 114 118 121 4.94 5.59 6.27 128 130 133 5.67 6.37 7.16 140 143 145 6.55 7.26 8.01 153 154 156 7.52 8.24 8.96 167 167 168 8.66 9.33 10.1 180 180 180 9.95 10.5 11.3 2200 2300 2400 46190 48290 50390 .302 .330 .360 124 128 132 6.99 7.83 8.71 136 139 143 7.94 8.84 9.78 148 150 153 8.81 9.74 10.7 158 161 163 9.74 10.7 11.7 169 171 173 10.9 11.8 12.8 181 182 183 12.2 12.9 13.9 2500 2600 2800 52490 54590 58790 .390 .422 .489 136 140 148 9.62 10.7 13.0 146 149 156 10.7 11.8 14.2 156 158 165 11.8 12.9 15.4 165 168 173 12.7 14.0 16.6 175 178 183 13.8 15.0 17.6 185 187 192 15.0 16.3 18.7 3000 3200 3400 62980 67180 71380 .560 .638 .721 156 15.9 164 16.7 172 179 18.3 21.3 180 187 19.5 22.8 188 195 202 20.6 24.1 27.9 195 203 208 21.8 25.4 29.4 Outlet Capacity, cu. ft. air per min. Add for total press. 1" S. P. 1J4" S. P. 1K"S. P. 1K"S. P. 2" S. P. 2K" S. P. velocity, ft. per min. a p. P3 P, a p, a p. a n a a a n a a P. M a a d w 1300 1400 1500 27290 29390 31490 .106 .122 .141 205 203 200 9.22 9.49 9.84 230 228 12.7 13.0 257 254 16.0 16.6 278 20.0 1600 1700 1800 33600 35690 37790 .16Q .180 .202 198 196 194 10.2 10.5 10.9 226 223 221 13.5 13.7 14.3 252 249 246 17.0 17.4 17.9 275 272 269 20.6 21.0 21.6 298 294 292 24.5 25.2 25.8 336 333 34.0 34.6 1900 2000 2100 39890 41990 44090 .225 .250 .275 193 193 193 11.4 12.0 12.6 219 218 217 14.7 15.3 15.8 244 243 240 18.3 18.7 19.5 267 264 263 22.2 22.8 23.3 289 286 283 26.4 26.9 27.7 329 326 324 35.1 35.9 36.6 2200 2300 2400 46190 48290 50390 .302 .330 .360 192 193 193 13.4 14.3 15.3 216 215 215 16.4 17.3 18.0 238 238 237 20.0 20.7 21.6 260 258 257 23.9 24.6 25.5 282 280 277 28.2 29.0 29.7 322 318 316 37.3 38.0 38.9 2500 2600 2800 52490 54590 58790 .390 .422 .489 194 196 200 16.4 17.4 20.0 215 216 218 19.2 20.2 22.9 236 235 236 22.5 23.5 26.1 256 255 253 26.2 27.2 29.4 276 274 273 30.5 31.4 33.6 313 312 308 39.8 40.6 42.6 3000 3200 3400 62980 67180 71380 .560 .638 .721 205 209 216 23.0 26.4 30.4 221 225 230 25.8 29.2 33.0 238 240 245 29.0 32.3 36.2 255 256 258 32.3 35.7 39.5 272 273 273 36.0 39.5 43.1 307 304 303 45.1 48.0 51.3 3600 3800 4000 75580 79780 83980 .810 .900 1.000 221 34.9 236 37.5 249 254 40.5 45.4 263 267 272 44.1 48.7 54.2 277 279 283 47.4 52.4 57.6 305 307 308 55.6 60.2 65.7 INDEX Absolute temperature 4 zero 4 Adiabatic saturation 172 Air and its properties 169-178 Air, composition of 169, 180 conditioning 175, 244-251 cooling 176,186,249-251 distribution 184, 189 -ducts 214-222 flow of, in ducts 209-216 friction of, in ducts. . . 214-216 infiltration of 12, 17 measurement of 210-214 motion 179, 184, 187 pollution 179 properties of 176, 177 psychrometric chart for 174, 175, 273-275 specific heat of 177 supply 179, 181 measurement of .... 182-183 total heat of 172 -valves Ill venting 123 -washers 217, 244-251 Air-line system 92 valves 92, 112 Allen's rule for heat loss 22 Anemometer 213 Anthracite coal 69 Argon 169 Ash 69,73 Atmospheric system 96 Automatic temperature control 163-168 Back pressure valve 141 Bacteria 179 Bituminous coal 69, 73 Body, heat loss from the 179, 185, 186 Boiler connections 130 horsepower 81 301 Boilers 69-86 cast-iron 75 downdraf t 77 firebox 76 magazine feed 80 marine type 77 proportions of 80 rating of 81 requirements of 74 return tubular 76 round 75 sectional 75 selection of 259 smokeless 79 steel 75 types of 74-80 water tube 77 Boot 198 Branches 121 British thermal unit 4 Calorific value of coal 71 Carbon dioxide, 72, 169, 170, 180, 182-183 monoxide 72, 180 Carbonic acid gas. See Carbon dioxide. Carpenter's rule for heat loss ... 22 Centigrade scale 2 Central heating 258-268 Centrifugal fan. See Fans. Check valve 107, 108 Chimneys 83-86 Clinkers 73 CO2. See Carbon dioxide. Coal 69-74 analysis of 70 composition of 70 consumption of 255-257 sizes of 70 Coefficients of heat transmission through walls . . 17, 269-272 from radiators 53 302 INDEX Coke 71 Cold-air pipe 196 Combustion 71-73, 78 Comfort zone 185 Condensation, drainage of, 119, 120 in underground steam lines, 264 Conduction 9-10 Conduit, for pipes 262-263 Contractor's guarantee 58 Convection 11 factor 13, 14 Cost of heating 255-257 Dalton's law of gases' 171 Damper 253 regulator 83 De-humidification 249-251 Dewpoint 171, 174 Diaphragm expansion joint. .. . 265 motor 167 valve 166 Dirt pocket 127 Disc fan 233 Distribution systems 260-262 Downdraf t furnace . 78 Draft 83-86 Drip connections 123, 127 Dry return system 90 Dust 179,188 Dynamic head 209 Economy of heating systems. . . 31 Ejector. 92 Equivalent evaporation 81 Estimating of heating require- ments 255-257 Expansion fittings 264 of pipes 119, 264 tank 147, 148 Exposure, factors for 21 Factory heating 253-255 Fahrenheit scale 2 Fan heaters 233-242 systems 30 arrangement of 207 design of 206-243 types of 206, 252-256 Fans, centrifugal, blades and housings 224-225 efficiency of 226 laws of 226 power required by 225 straight blade 226 theory of 223 Fittings, flanged 105 resistance of 136, 154 screwed 104 Flanges 105 Flow of air. See Air. Flue gases 72 radiators 67 Flues 84 foul-air 202 hot-air 197 Forced circulation hot-water heating 158-162 Friction, of air in pipes 214-216 of fluids in pipes 131 in hot water systems, 144- 146, 152-154, 159-162 Fuels 69-74 Furnace, boiler 77-79 heating 191-205 hot-air 26, 191, 192-195 pipeless 203 test of 204 Gage 83 Gaskets 106 Gate valve 107 Generator 157-158 Glass, heat transmission of . . 17, 272 Globe valve 107 Grate surface 81, 195 Grates .* 25,77 Gravity hot-water heating 142 indirect radiators. See Radiators. system of distribution 260 Guarantee, checking of 58 Heat 1-8 definition of 1 flow of 1 given off by persons 23 latent 35,37 INDEX 303 Heat, loss of, from a body 9 from buildings. . 179, 185-186 Allen's rule 22 ■ approximate' rules. .. . 21 calculation of 20 Carpenter's rule 22 coefficients of. .16, 269-272 from underground pipes. 264 measurement of 1 of superheat 34, 37, 172 of the liquid 34, 35, 37, 172 of vaporization 34, 37, 172 total 36 transmission from radiators 51-55, 63 value of coal 71 Heaters for fan systems .... 233-242 friction in 238-241 installation of 241 pipe coil 235 vento 234 hot-water 86 Heating, central 258-268 different methods of 25-32 direct 25,27 fan systems of 30 furnace 191-205 hot water 28, 142-162, 261 indirect 25 of auditoriums 255 of factories 253 of schools 252 of theatres 255 steam required for 257 surface of boilers 81 systems, economy of. .... . 31 hot-water 142-162 losses in 31 steam 87-101 •Horsepower, boiler 81 Hot-air furnace heating .... 191-205 pipes 197,199-201 Hot-water heaters 86 systems 142-162,261 Humidification 195 See also Air conditioning. Humidifier 196 Humidifying efficiency 250 Humidity, absolute 172 Humidity, control of 248 measurement of 173 relative 172 standards of 179, 184 See also Air conditioning. Infiltration 12, 17 Intermittent heating 21 Joule's equivalent 8 k, values of 16, 269-272 Lamps, pollution from 180 Leaders 197-201 Magazine-feed boiler 80 Mains, steam 87, 121 Mercury seal generator 158 Mixing damper 253 Mixtures of substances 38-44 Moisture, in fuel 71 in air. See Water vapor and Humidity. Neon 169 Nitrogen 169 Odors 179,180,187 One-pipe systems. See Single- pipe systems. Overhead system, steam... 91, 118 water 148,149 Oxygen 169, 179, 180 Ozone 164, 188 Painting of radiators 52 Partial pressures, law of 171 Perspiration 184 Petterson and Palmquist appa- ratus 170 Pipe 102 coil heaters. See Heaters. coils 51, 130 covering 109-111 dimensions of 103 fittings 104, 105 flanges 105 hangers 124-125 304 INDEX Pipe, threads 104 unions 105 Pipes, hot-air 197-201 size of, for steam 133-137, 267-268 water 151-157, 159-162 Piping, for hot water systems. . 157 steam 117-141 underground 262-266 Pitot tube 211-213 Power plants 139-140, 258 Pressure drop in steam pipes 131-136 gage 83 Proximate analysis of coal 71 Psychrometer 174 Psychrometric chart, 174, 175, 273-275 Pumpage 159 Pump-return system 260 Pumps, circulating 162 vacuum 99 Radiation, approximate rules for 58, 66 proportioning of 57,58,65 transmission of heat by. . . 9 Radiators 45-68 cast-iron 45-49 classification of 45 connections to 128-129, 137-138 direct 45 effect of enclosing 57 of painting 52 flue 67 heating surface of 48, 50 heat transmission from. . 51-55 indirect 45,60-67 location of 56 pipe 51 pressed metal 49, 55 semi-indirect 45 tappings 49 wall type 48 Re-circulating duct 196 Reducing valve 115, 141 Registers 198,202 Regulation of temperature . 163-168 Relief system 88, 122 Respiration 169, 180 Retarder 96 Return piping 126 Reversed return 147 Riser vent 112 Risers 87,122,127 hot-air 197-201 Safety valve 82 Saturated steam 33-34 Saturation, adiabatic 172 School buildings 252-253 Semi-anthracite coal 69 -bituminous coal 69, 73 -indirect radiators 67 Separator 115 Single-duct system 219, 252 -pipe systems, steam 87-89, 117 water 149,151 Size of pipes 119, 133 Sling psychrometer 174 Slip joint 264 Smoke 12 Smokeless combustion 73, 78 furnaces 77, 79 Specific heat, definition 5 of substances 6 of water 272 Stacks 82-86 Static efficiency 226 head 209 Steam boilers. See Boilers. consumption of 257 flow of, in pipes 131-136 formation of 33 heating 27 -heating systems 87-101 piping 117-141 properties of 33-44 table 37 saturated 33, 34 superheated 33 Stefan's law 10 Stoves 26 Sulphur.. 73 Tapping of radiators 49 Temperature, absolute 4 INDEX 305 Temperature, colors 4 control of '. ... 163-168 definition of 1 inside 17 measurement of 2-3 standards of 179, 184-185 Theatres, heating of 255 Thermodynamics, first law of . . 8 Thermometer 2-3 wet- and dry-bulb 173 Thermostatic control 163-168 Tile conduit 264 Total efficiency 226 head 209 Traps, bucket 112, 114 float 95,112,113 radiator 94,95,127 thermostatic 94, 127 tilting 114 Trunk line duct system 221 Tunnels 266-268 Two-pipe systems, steam . .87, 89-91 water 147,148 Ultimate analysis of coal , 71 "Underground piping 262-266 Unions 105 Unit of heat 4 Unwin's coefficient 132 Vacuum pump 99 system, 92, 99-101, 108, 126, 163 Valves, air- Ill air-line 112 back-pressure 141 check 107 gate 107 globe 107 location of 127 Valves, radiator 97, 108 reducing 115, 141 Vapor system, 93, 98, 99, 108, 126, 163 water. See Water vapor. Velocity head 209 Ventilation 31, 179-190 heat required for 19, 31 methods of 189 of auditoriums 255 of schools 252 of theatres 255 standards of 179 systems of 30 See also Fan systems. Vento heaters. See Heaters. Volatile matter 69, 72, 73 Walls, coefficients of heat trans- mission through, 17, 269-272 flow of heat through 12-17 Water column 82 pan 195 specific heat of 272 thermal properties of 272 vapor 169, 170-178,180 See also Humidity. Wet- and dry-bulb thermo- meter 173 -bulb temperature. . . . 173, 175 -return system 90 Windows, air leakage through. . 19 heat loss through. . 17, 269-272 Wolpert method of C0 2 deter- mination 170 Wood casing 262 Zero, absolute. 20 llMlil,,« ; , -;;;;,::, III Ml J ■•- jj ... . .1 ,;,;;;;