:es on Heating Ventilation Book . Copyright}!^. \^\\ COPYRIGHT DEPOSIT. NOTES ON HEATING and VENTILATION BY JOHN R. ALLEN W PROFESSOR MECHANICAL ENGINEERING University of Michigan Member American Society Heating and Ventilating Engineers Member American Society Mechanical Engineers Member American Society Promotion Engineering Education THIRD EDITION DOMESTIC ENGINEERING COMPANYI CHICAGO 443 So. Dearborn Street 1911 ^ A COPYRIGHT DOMESTIC ENGINEERING CO. 1911 \ ■% cP ©aA^954G7 TABLE OF CONTENTS. Introduction. Theory of heat and measurement of tempera- ture 1 Chapter I. Heat losses from buildings and rules for deter- mining the heat-losses in different construc- tions 7 Chapter II. Different forms of heating systems; their ad- vantages, disadvantages and relative economy. 28 Chapter III. The design of a direct steam-heating system and the properties of steam; steam-tables; loss of heat from radiators; rules for direct heating.. 38 Chapter IV. Design and installation of an indirect steam- heating system; rules for indirect heating.... 65 Chapter V. Steam-boilers and steam-piping. Determination of size and details of construction 76 Chapter VI. The connection of mains to risers and risers to radiators, with illustrations of different ar- rangements in practical use; steam-piping, piping systems, size of return-mains, valves and piping-connections 82 Chapter VII. The design of a hot-water heating system; radi- ator heat-losses, rules for direct and indirect system 120 Chapter VIII. Hot-water boilers and piping. Determination of size and details of construction 127 Chapter IX. Ventilation and pollution of air by human be- ings, artificial lighting and chemical processes; systems of ventilation 141 Chapter X. Design of hot-air heating systems, construction and rules 152 Chapter XI. Fan system of heating, with tables of fan capac- ities and condensation in heater-coil; air-mix- ing systems 164 Chapter XII. A central heating system; its design and instal- lation, with discussion of different methods of carrying pipes underground; specific ap- paratus; combination system of steam and hot water 187 Chapter XIII. Pipe coverings, pipe, air-valves and fittings 209 Chapter XIV. Auxiliary devices for heating systems, regula- tion of humidity and draft; air-washers and vacuum-heating systems 218 SUBJECT INDEX Page A Air change, ordinary as- sumption for 146 changes necessary 144 dilution 143 inlets and outlets 148 mixing systems 182 piping system 220 pollution tests 142 quantity to be supplied. 166 valves 202, 212 valves, pitch and sup- port of pipes 139 washers 223 Anchors and hangers 201 B Boiler horse-pov/er 80 Boilers 188 fire tube 76 hot-water 127 proportion of 78 steam 76 water tube 76 C Carbon dioxide 144 Central heating systems.. 187 Chemical processes 143 Circuits, multiple and single 129 Coils, heating 172 Cold-air duct 155 Combination of heating systems 36 Combination system 87 Combustion, products of.. 142 Conduction 10 Connections of radiators. 109 Connection to mains and risers 99 Convection 13 Page Convection, losses, calcula- tion of 13 Covering for pipes 209 D Damper regulators 221 Dams 83 Determination of building heat-loss 21 Direct and indirect com- binations 73 Direct heating, rules for.. 55 Direct hot- water heating. 32 Direct steam-heating 32 Disc fans 184 Drainage, pipe 94 Drip connections 101 Duct, cold-air 155 E Economy of different sys- tems 36 Expansion joints 97 Expansion of pipes 96 Expansion tank 129 F Factors for exposure 21 Fan-heating systems ....164 Pan, size, speed and horse-power 167 Fan system of heating.... 34 Fittings 217 Fittings, resistance of.... 137 Flow mains and risers. . . .128 Flow, velocity of 186 Flue proportion, hot-air. . .157 radiators 50, 75 Flues, foul air 157 hot-air 156 materials of 184 Furnaces, hot-air 153 HI Page Furnaces, hot-air, opera- tion of 159 Grate surface, proportion of 79 Grates 28 Gravity system 90 Gravity systems 189 H Hangers and anchors 201 Heat 1 Heat generated by human beings 143 Heat generated by illumi- nation 144 Heat-loss for buildings determined 21 Heat-loss from building. . 7 Heat-loss from indirect steam radiators 65 Heaters, cast-iron 176 Heating and power sys- tem, combination of 191 Heating apparatus, classi- fication of 28 Heating systems, auxiliary devices for 218 High -pressure systems. . . . 190 Hot-air furnaces 30, 153 furnaces, operation of. .159 leaders and flues 156 pipe, size of 73 system 152 system rules 160 systems, proportions of. 158 Hot-water boilers and piping 127 direct 32 heating indirect 34 heating rules 124 heating system 120 piping 128 Humidity regulations ....221 Indirect heating rules.... 71 hot-water heating 34 Page hot- water radiators ....122 radiators, heating effect of 70 radiators, installation of 68 steam heat losses 65 steam-heating 33 steam-heating design... 65 Insulation 195 J Joints, expansion 97 L Leaders, hot-air 156 Legs of the system 129 Loss of heat from build- ings 14 Low-pressure pump return system 191 M Mains 82 and risers, location of. . 99 size of steam return... 91 steam, rules for sizes of. 92 Materials, specific heat in. 3 Measurement of work 2 Moisture -supply to heated air 154 Multiple circuit system... 129 One-pipe system 85 Open and closed circuits. .134 Overhead distribution.... 89 Overhead system 132 Paints for radiators, val- ues of 53 Pipe 216 and fittings, resistance of 137 covering 209 drainage 94 IV Page expansion 96 sizes 138, 199 supports 119 Pipes, method of cariy- ing 194 Pipes, pitch and support. .139 Piping, hot-water 128 steam 82 systems 84, 129 Pitch 83, 129 Power and heating sys- tems combined 191 R Radiation 8 Radiator connections . . . .109 heat-losses 121 installation 53 sizes 47 Radiators, different types of relative efficiency. . 44 flue 50, 75 heat loss under varying temperatures 51 indirect hot-water 122 loss of heat from 42 Relation between heat and work 2 Reliefs or drips 82 Resistance of pipe and fittings 137 Respiration, products of.. 142 Return 82 mains and risers 128 mains, sizes of steam.. 91 system, pump 191 Risers 82 Risers and mains, location of 99 Rules for determining heat-losses 22 S Single circuit system 131 Single-pipe system 135 Siphon 83 Specific heat 3 Steam and hot-water sys- tems combined 206 heating direct 32 Page indirect 33 nature and properties of 38 piping 82 system indirect design.. 65 Stoves 30 Supporting of pipes 119 Tables air dilution 143 air-pollution tests 142 capacity of mains 138 capacity of risers 13t* condensation and heat given off by heater- coils 173 condensation chart ....177 conduction power 10 dimensions and heat . losses 57 disc-fan efficiency 183 fan capacities 168 fan efficiency 169 fans, disc 184 heat given off by illumi- nants 144 heat-loss from flue radi- ators 50 heat-losses from indi- rect radiators 67 heat-transmission 52 heat-transmission for varying pressures .... 211 heater dimensions 176 hot-air figuring 161 indirect hot- water radi- ators 124 indirect radiators — tem- peratures of leaving air 68 loss from wrought iron- pipe and cast-iron radiators 42 pipe-size practice 93 pollution by lighting. .. .143 properties of steam 40 proportion of cast-iron hot-water boilers ....129 proportions of hot-air heating systems 159 pressure losses 181 Page radiating power 9 radiator tappings 54 rate of transmission 121 rating of house-heating boilers 80 relative effectiveness of different thicknesses of covering 210 relative size of steam and return main 94 relative temperatures of air and room 63 relative value of differ- ent pipe coverings. .. .210 relative value of radia- tor paints 53 results of computation, direct system 58 results of computations, indirect system 72 results of computations. direct hot- water 125 size of hot-w^ater mains.137 size of flues for indirect radiators 70 specific heats 3 specific heat of gases... 6 speeds, capacities and horse-powers of single inlet, fans at various pressures 171 steam 39 temperature chart 178 temperatures assumed in heating 25 values of air-conditions. 17 values of E 18 values of K 20 values of material and surface 18 Page values of temperature difference 18 velocity of hot-water circulation 137 wrought iron and steel steam, gas and water pipe 215 Tank, expansion 129 Temperature 1 Temperature regulation . . . 219 Thermostat, Johnson 219 Transmission of heat un- der various conditions.. 64 Traps, steam 84 Tunnels for steam sys- tems 197 Two-pipe systems 86 U Unit of heat 2 V Vacuum heating systems. 225 Valves 98, 217 Valves, air 139 Velocity of flow^ 13^ Ventilating ducts 177 Ventilation 141 Ventilation, effects of poor 147 Ventilation systems 147 W Water-hammer 83 Water-line ... 83 Water-seal 83 VI PREFACE THE subject matter originally contained in this book was a reprint from a series of articles pub- lished in Domestic Engineering-. In this edi- tion the original text has been rewritten and a large amount of additional information included. This book wa-s written primarily to show that the subject of Heating and Ventilation could be developed in a logical way from the fundamental principles of en- gineering. The great lack has been in the amount of scientific information available regarding the actual laws of heat and the value of the constants entering into these laws. The University of Michigan has car- ried on, under the direction of ]\I. E. Cooley, Dean of the Engineering Department, a series of experiments for over twenty years. The results of these experi- ments are given in various tables and serve to give the designer data from actual experiments upon which he can base his calculations. There has been included in this edition a resume of the results of the German experiments and these meth- ods of determining lieat losses from buildings. This matter is largely reprints from a book published by the "Metal Worker" under the title, "Formulae and Tables for Heating'' by J. H. Kinealy. This book has been written primarily for the steamfitter and designer of heating systems. It presupposes some elementary knowledge of the details of construction and opera- tion of the sim])ler forms of heating plants. The author has used the previous editions as a text for his classes in Heating and Ventilation. The pres- ent edition has been written with a view to making the book more desirable as a college text. July 1, 1911. John R. Allen. INTRODUCTION Heat. — Heat is a form of motion. In modern sci- ence, all matter is conceived as being made up of small particles called molecules. These particles do not exist in a state of rest, but are in constant vibra- tion. If these particles move slowly the body is at a low temperature ; if they move more rapidly the body is at a higher temperature, the temperature of the body being determined by the rapidity of the motion of the particles. In measuring heat there are two properties to be considered — the intensity and the quantity. This may be compared to measuring water in a pipe. We measure the pressure of the water in the pipe by means of a gauge in pounds per square inch. The quantity of water is measured in pounds. In the same way the intensity of heat is measured by the thermometer in degrees and the quantity of heat is measured by comparison with the quantity of heat which a pound of water will absorb. Temperature. — Temperature, which is a measure of the intensity of the heat of a body, might also be con- sidered as measuring the velocity of the molecules of the body. In mechanical engineering all measure- ments of temperature are made on the Fahrenheit scale. On this scale the freezing point is taken at 32° and the boiling point as 212°, the tube of the ther- mometer between these points being divided into 180 equal parts called degrees. We never know the total amount of heat in a body. Notes on Heating and Ventilation As it is impossible to bring any body to a condition of absolutely no heat, the heat in any body must al- ways be measured from some assumed zero point and in the Fahrenheit scale this assumed zero point is 32° below the freezing point. For theoretical purposes, however, it is highly desirable to have some absolute standard of heat. A perfect gas at 32° contracts about 1/493 of its volume for each degree Fahrenheit that it is reduced in temperature. If, then, we keep on de- creasing the temperature of a perfect gas from 32°, until it reaches a point 493^ below 32° Fahrenheit, it would have, theoretically, no volume. If it has rro volume, the amount of heat which it contains must be zero. This point, then, is called the absolute zero. This point is manifestly an ideal one. To find the absolute temperature in degrees it is necessary to add to the Fahrenheit temperature 461 degrees, that is, 32° Fahrenheit corresponds to 493° absolute. Unit of Heat. — Heat is not a substance and it can not be measured as we would measure water in pounds or cubic feet, but it must be measured by the effect which it produces. Suppose it requires a certain amount of heat to raise a pound of water from 39° to 40° Fahrenheit. It would require three times that quantity of heat to raise a pound of water from 39° to 42.° Fahrenheit. The heat required to raise a pound of water one degree Fahrenheit is called a British thermal unit, and is designated by letters B. t. u. Relation Between Heat and Work. — Work is meas- ured in foot-pounds. The imit of work is the work required to raise one pound through a height of one foot. Ten units of work or ten foot-pounds would be the amount of work done in raising ten pounds one foot high or one pound ten feet high. Heat is a form of motion, hence there must be some definite relation be- 2 Notes on Heating and Ventilation tween heat and work. This relation was first deter- mined by Joule. By a series of experiments Joule found that one heat unit was equivalent to 778 foot-pounds. It is possible, then, to express heat either in heat units or in foot-pounds. Specific Heat. — Different substances require very different quantities of heat to produce the same change of temperature for the same weight. As for example, to raise one pound of water one degree requires one B. t. u. ; to raise one pound of ice one degree requires .504 B. t. u. ; to raise one pound of wrought iron one degree rcquires(^J^138 B. t. u. The heat necessary to raise one pound of a substance one degree, expressed in British thermal units, is called specific heat. The following table gives the specific heat of the principal substances which we meet with in engineering work: TABLE I. SPECIFIC HEATS. Substance. B. t. u. Liquids. Water 1.000 Alcohol 622 Turpentine 472 Petroleum 434 Olive Oil 309 Metals. Cast iron , 1298 Wrought iron 1138 Soft steel 1165 Copper 0951 Brass 0939 Tin 0569 Lead 0314 Aluminum 2185 Minerals. Coal 2777 Marble - 2159 Chalk 2149 Stones ffenerally 2100 Limestone 2170 Building Materials. Brick work 1950 Masonry 2159 Plaster 2000 Pine wood 467 Oak wood 670 Birch 480 Glass 1977 3 Notes on Heating and Ventilation 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 the table we see that it would require to raise one pound of cast iron one degree .1298 heat units, then to raise one pound 142° would require 142 times .1298 or 18.43 heat units, and to raise 300 pounds one degree would require 300 times this amount or 5,529 B. t. u., the heat required to heat the radiator. This is important in heating as the walls of a cold building must be heated. Example.— A church 80'xl00' with walls 2y2 feet thick for 10 feet above the ground and for the re- maining 20 feet 2 feet thick. The roof has a ^ pitch and is made of 2"x8" rafters, 16 inches on centers, covered with 1 inch of pine boarding, tar paper and slate ^ inch thick. Main floor composed of two 1-inch thicknesses of boards laid on 2"xl2" joists, 16-inch centers. Ceiling is of plaster ^ in thick. The church has 20 windows, 6 feet wide and 15 feet high, 12 win- dows, 4 feet wide and 6 feet high, and 2 doors, 8 feet wide and 12 feet high. Allowing an addition of 15% of furnishings, find the heat required to raise the tem- perature of the church from 0° to 50°. Weight of stonework, stone weighing 160 pounds per cubic foot. 370x10x2^x160=1,480,000 pounds 268x20x2 xl60=2,350,000 80 — x40x2x2 xl60--=l,024,000 2 Total weight of masonry assuming I building to be without openings f *.»5)4,uuu Notes on Heating and Ventilation Weight of wood work. Weight per cubic foot taken as 40 pounds. 2x8 x56. 2x75x2x40.= 37,600 pounds of rafters. 144 56.2x104x2x1/12x40= 39,000 pounds of roof boards. 80x100x2x2/12x40=107,600 pounds of joists. 2x12 ^x80x75x2x40...= 80,000 pounds of floor boards. 144 Total weight of wood- work 263,600 pounds. Slate — Weight per cubic foot taken as 170 pounds. 56.5x104x2x1/48x170=41,600 pounds. Plaster — Weight per cubic foot taken as 90 pounds. (360x30x80x40^100x80) %xl/12x90=124,000 pounds. Air — Weight per cubic foot taken as .08 pounds. 80 (80x30x100-1 x40xl00) .08=32,000 pounds. Heat required. 2 4,854,000x50x.2159=52,300,000 B. t. u. 263,600x50x.65 = 8,580,000 B. t. u. 41,600x50x.2159= 448,000 B. t. u. 124,000x50x.2 = 1,240,000 B. t. u. 32,000x50x.2375= 379,000 B. t. u. 62,947,000 B. t. u. Adding 15% for furnishing = 9,440,000 B. t. u. Total to raise building and fur- nishing 50 degrees =72,389,000 B. t. u. This item is a large one in determining the size of the heating plant to be installed in a building inter- mittently heated. In solid substances the change in volume when they are heated is so small that it is not considered. In gases, however, the change in volume when the gas is heated without being confined, depends directly upon the absolute temperature and may be very large. When air is confined and is heated, it cannot expand ; if it does not expand there is no work done because, from our definition of work, it is necessary when work is done, that the body have some movement. On the other hand, when air receives heat and is free to ex- pand it does work. For instance, if air were confined in a cylinder by a piston, and this air were heated, the air would expand and the piston would be moved out. 5 Notes on Heating and Ventilation As the piston is moved through a certain space there must be work done. On the other hand, if the piston were blocked so that it could not move, then the air on being heated would do no work. Then in these two cases different amounts of heat will be required to raise the substance one degree, depending upon whether there is external work done or not. It is nec- essary then in gases that we consider two specific heats, the specific heat of constant volume and the spe- cific heat of constant pressure. For air the specific heat of constant volume is .1689, for constant pressure it is .2375. It is seldom that we use air in a confined space, so that, so far as this work is concerned, we shall in most cases consider the specific heat of air as .2375 — that is, to raise one pound of air one degree requires .2375 B. t' u., the pressure being constant. TABLE lA. SPECIFIC HEATS OF GASES. Constant Constant Substance. Pressure. Volume. Air .2375 .1689 Oxygen 2175 .1550 Hvdrogen 3.4090 2.4122 Nitrogen 2438 .1727 Steam 5000 .S500 Carbonic Acid Co, 2479 .1758 Ammonia 508 .299 Notes on Heating and Ventilation CHAPTER 1 Heat Loss from Buildings. — Heat is lost from a room in three ways — by the direct transmission of the heat through the walls and windows ; by the passage of air up the foul-air Hues, and„by the filtration of air through the walls and air leakage around doors and windows. The first two losses are easily determined, but the de- termination of the loss by filtration must always in- volve a large factor of judgment and experience. All building construction is more or less porous. This is well exemplified by the old experiment made with a common brick. Two cornucopias of paper are pasted on opposite sides of a common brick, the larg« end of the cornucopias being fastened to the brick. Op- posite the small end of the cornucopia at one side is placed a lighted candle. By blowing into the cornucopia on the opposite side, the candle may be blown out, the air having passed directly through the brick. The experiments which have been made in order to determine the loss generally tend to show that in the ordinary well-constructed building the air in the room will change about once per hour, when all doors and windows are closed. In order to study the other heat losses from a room it will be necessary to study the laws of cooling. A body may be cooled in three different ways — by radia- tion, by conduction and by convection (contact of Notes o n Heating and Ventilation air). In order to understand these losses more thor- oughly, each will be considered separately. Radiation. — The heat that passes from a body by radiation may be considered similar to the light which is given off by a lamp. There is always a transfer of radiant heat from the body of a higher temperature to the body of lower temperature. The amount of heat Fig. 1. radiated will depend upon the difference in tempera- ture between the bodies and the substance through which this heat passes and the material composing the surface from which the heat is radiated. The losses by radiation may be better understood by referring to Fig. 1. Suppose the plate PP to be of 8 Notes on Heating and Ventilation cast iron 1 foot square and 1 inch thick. Let us sup- pose this plate to be on both sides at a temperature of 60°. Let this plate form one side of a room, the walls WWW being non-conducting substances and at a temperature of 59°, the air in this space being at a temperature of 60°. Since the plate and the air in the space are at the same temperature, there will be no loss of heat from the air to the walls, but all the heat that passes from the plate PP to the walls must pass by radiation. For ordinary temperatures of heat- ing surfaces, say 60 or 70°, the loss by radiation will equal the difference in temperature between the hot body and the cold body multiplied by a factor repre- senting the radiating power of the body. The follow- ing table gives the radiating power of different sub- stances : TABLE IT. RADIATING POWER. Radiating power of bodies, expressed in heat units, given off per square foot per hour for a difference of one degree Fahrenheit. (Peclet.) Copper, polished 0327 Iron, sheet 0920 Glass 595 Cast iron, rusted 648 Building stone, plaster, wood, brick 7358 Woolen stuffs, any color 7522 Water 1.085 Heat is radiated in straight lines exactly as light is given off from the source of light. We may have heat shadows the same as we have light shadows and the intensity of the heat is inversely proportional to the square of the distance from the source. Some bodies are transparent to heat and other bodies absorb heat, the same as some bodies are transparent to light and others absorb light. The transparency of bodies to heat is called diathermancy. Gases, such as air, oxy- gen, nitrogen, and hydrogen, are almost perfectly 9 Notes on Heating and Ventilation transparent to heat, while wood, hair, felt and other non-conducting bodies are almost perfectly opaque to the transmission of heat. The loss of heat by radia- tion is independent of the form of a body so long as it does not radiate heat to itself. The color or condition of the surface of different bodies affects their radiant power. Smoothly polished surfaces radiate less heat than rough surfaces. As, for instance, a surface painted with lamp black will radiate over 13 times as much heat as a polished copper surface. Example. — Suppose we have a glass surface five square feet in area. The glass surface is at a tempera- ture of 70° and the objects surrounding it are at a temperature of zero. From the table we see that one square foot of glass (surface) loses .595 heat units in an hour for a difference of one degree between it and the surrounding objects. For a difference of 70°, then, each square foot of glass would lose 70 times that amount, or 41.5 heat units, and 5 square feet of glass would lose 5 times that amount, or 207.5 heat units per hour by radiation only. Conduction. — The heat transmitted by conduction is the heat which is transmitted through the body itself. TABLE III. CONDUCTING POWER. The conducting power of materials, expres.sed in the quantity of heat units transmitted per square foot per hour by a plate one Inch thick, the surfaces on the two sides of the plate differing in temperature by one degree. (Peclet.) B. t. u. Copper 515 Iron 233 Lead 113 Stone 16.7 Glass 6.6 Brick work 5.6 Plaster 3.7 Pine wood -76 Sheep's wool .323 10 Notes o n Heating and Ventilation For example, take the condition shown in Fig. 2. PP is a plate, one side of which is enclosed by the walls WW. Let the temperature of the plate outside be 59°, the temperature on the inside of the plate be 60° ; the temperature of the walls be 60°, and the temperature of the air in the room be 60°. Then all the heat that '///////////A \N60 I Air 60' I vt i i i \N60 I Fig. 2. is lost by the room must be lost by direct conduction through the plate PP. The amount of heat conducted will depend upon the material of which the conductor is composed and in addition it will also depend upon the difference in temperature between the two sides of the plate and upon the thickness of the plate. The 11 Notes o n Heating and Ventilation conduction through any plate may be calculated as fol- lows: Multiply the factor given in Table III by the difference in temperature between the two sides of the plate and divide the result by the thickness of the plate in inches. The quotient will be the heat transmitted" by conduction per square foot of surface. V^ 60 Air 59 4 60"$ \N60' J "^mmmmmmmmm^A Fig. 3. Example. — Suppose a boiler plate 5 feet square, Vi- inch thick, to have a temperature of 70° on one side and a temperature on the opposite of 200°. The dif- ference in temperature of the two sides of the plate would be 130°. The amount of heat conducted would then be 233 X 130 ^ >^ = 15,145 B. t. u. per square 12 Notes on Heating and Ventilation foot of plate per hour. Then five square feet would transmit five times this amount, or 75,725 B. t. u. in one hour. Convection. — Loss by convection is sometimes termed loss by contact of air. Take, for example, the condition shown in Fig. 3. Let P be a vertical plane of metal one foot square, having its surfaces main- tained at 60° temperature. Let the walls WW also be at a temperature of 60°. Let the air in the room be 59°. In this case there will be no loss of heat from the walls to the plate by radiation and there will be no loss through the plate by conduction, but heat will be transmitted from the walls and the plate to the air of the room. The air which comes in contact with the warmer walls will be heated. As air is heated it be- comes lighter and rises and a current is formed. This produces a circulation of air, and this circulation of air gives rise to a loss of heat by convection or contact of air. The loss of heat by convection is independent of the nature of the surface, wood, stone or iron losing the same quantity of heat, but it is affected by the form of the body — that is, a cylinder and a sphere would lose different amounts of heat per square foot. Take the steam radiator, for example. The air nearest the radi- ator becomes heated and rises ; as it rises its place is taken by other colder air coming off the floor so that a current of air is established. In the ordinary type of radiator, the loss by contact of air represents about half the loss of heat, the balance being loss by radia- tion. Calculation of Convection Losses. — The calculation of the heat lost by convection is quite complicated and 13 Notes on Heating and Ventilation different expressions have been derived for this loss for different forms of surfaces. Those developed by Peclet are given in Box's treatise on Heat. The rules given for convection in the text-books on heat cannot, as a rule, be applied to the loss of heat from buildings. All these rules assume that the air surrounding the object is in a perfectly quiescent state. In buildings this is not the case, for the air surround- ing a building is rapidly circulated by the winds. The- oretically a high building would lose proportionally less heat than a low building, because in the upper stories there would be a smaller difference in temper- ature between the air inside the room and the air out- side than in the lower stories. This, however, is not the case, as the wind circulates the air outside the building and makes the temperature of the air sur- rounding the building on the outside practically the same at all levels. Inside the room, however, the air at the top of the room is much warmer than that at the floor. The re- sult is that the rate of transmission of heat in rooms with high ceilings is appreciabty higher than in rooms with low ceilings, as in the room with a high ceiling we have a greater difference of temperature between the inside and the outside air at the ceiling. This dif- ference is not ordinarily considered unless the height of the room exceeds ten feet. If the height of the room does not exceed ten feet the temperature taken five feet above the floor line may be assumed as the average temperature of the room. The loss of heat from buildings was first investi- gated both experimentally and theoretically by Peclet. The greater part of his work is given in Box's treatise 14 Notes on Heating and Ventilation on Heat. The results obtained by Peclet are difficult to apply practically and nearly all the rules that are used to determine the loss of heat from a building are largely empirical. The constants determined by the German government are probably the most reliable we have. The German formulas and tables w^ere translated by J. H. Kinealy and published under the title "Formu- las and Tables for Heating," by the "Metal Worker." The following pages outline the German method as given in the pamphlet mentioned. In the simplest form of building the walls consist of one solid piece of the same material and in this case the transmission of heat is from the air of the room to the wall by convection, through the wall by conduction and from the surface of the wall to the cold air outside by convection. Such a wall is shown in Fig. 4. A solid wall may be ^made up of a series of layers of different materials, as shown in Fig. 5. The trans- mission of heat, however, goes on in the same way. In a wall such as is shown in Fig. 6, the heat passes through each of the consecutive w^alls just as it does through a solid wall. Heat always passes from a warmer to a colder body. Hence t/, the temperature of the inside of the wall, must be less than the tem- perature of the room t, and the temperature to' must be greater than the temperature of the outside of the wall to'. Each particle in a section of the wall must have a different temperature, the temperature dimin- ishing as the particle is nearer and nearer to the out- side wall. The quantity of heat transmitted through a given area of wall must be the same for each point in the sec- 15 Notes on Heating and Ventilation tion when the wall has once reached a stable condition. The quantity of heat which passes per hour from the warm air of the room to a square foot of wall will be in Figs. 4, 5 and 6 a^ (t^ — t^'), and the heat which passes from the outside wall to the cold outside air is ^0 (to' — to). If the wall has an air space as in Fig. 6, the heat Avhich passes to the air space will be a/(t2' — - r„ "1^ J' f/6 5 ta), and the heat given by the air space to the outer wall will be a/(t2— t/')- The heat that passes through the wall by conduc- tion; as stated before, will be in Fig. 4 — (t^' — t^,'), and in Fig. 6 for the inner wall — ^ (t^' — tg')? and for Xi 62 the outer wall — (tj" — to'). If the layers of this wall ^reof similar material, e^ and eo will be equal. In order to use these expressions it is necessary to know the temperature of the wall surface. These tem- peratures are not known. The only known temperatures are the temperature of the air inside the room and the air outside the building. Let us assume that the heat 16 Notes on Heating and Ventilation transmission through the wall may be represented by the expression k (t^ — t^), where k is a constant to be determined. The amount of heat passing through the wall at each point is constant, hence we have for Fig. 4: K (ti— to)-ai(t,— t/)=a,(t,/— t„) = — (ti'— to') (1) X and for Fig. 6 : K (ti— to)=a,(ti— ti')=a,'(t,'— t,)=a,'(t2— t2")=a,(t/— to) ei 62 =— (ti'— 12')=— (ta"— to') (2) Xl X2 Solving for k in equation (1) K = (3) 1 1 X — + — + — ai ao e , and in equation (2) K = (4) 11 1 1 X, X2 ai a/ a2' ao ei 62 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: (40 c + 30d) T a = c -!- d H 10,000 c as a factor depends on the condition of the air, whether at rest or in motion. Rietschel gives the fol- lowing values for c : TABLE IV. VALUES OF c. e. 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 17 Notes o n Heating and Ventilation d is a factor depending upon the material compos- ing- the wall and on the condition of the surface. The values for d ma}^ be taken as follows : Substance. Brickwork 74 Mortar and similar materials .74 Wood 74 Glass 60 Cast iron 65 Paper 78 TABLE V. VALUES OF d. d. Substance. d. Sheet iron 57 Sheet iron polished 092 Brass polished 053 Copper 033 Tin 045 Zinc 049 T is the difference between the temperature of air and that of the surface of the wall. For poor con- ductors or very thick walls it mav be taken as zero. riGj In approximate calculations it is usually taken as zero. The following values of T are given by Rietschel : TABLE VI. VALUES OF T. Brick work 5 inches thick 14.4 Brick work 10 inches thick 12.6 Brick work 15 inches thick 10. 8 Brick work 20 inches thick 9.0 Brick work 25 inches thick 7.2 Brick work 30 inches thick 5.4 Brick work 40 inches thick 1.8 For single windows 36. For double windov/s 18. For wooden doors 1.8 Table VII gives values of e. These values vary considerably for different authors. TABLE ^ai. VALUES FOR e. e. Brick work 5.6 Mortar, plaster 5.6 Rubble masonry 14. 18 Notes on Heating and Ventilation Limestone 15. Marble, fine grained 28. Marble, coarse grained 22. Oak across the grain 1.71 Pine, with the grain 1.4 Pine, across the grain .76 Sandstone 10. Glass 6.8 Paper 27 For example, assume a brick wall as shown in Fig- ure 7. Tliere are four air contact surfaces and two walls through which conduction takes place, then : K is the same as in equation 4. Rietschel assumes a/, a/' and ao' equal and he uses the same value of T as for a solid of thickness equal to the brick work without the air space. (40X.82+30X.74)10 a^ = a,'=a/=.82+.74H =1.62 10,000 (40X1.23+30X74)10 a,— 1.23+.74H =2.04 10,000 Since both walls are of brick work Xi 4.75 Ci 5.6 X, 8.25 = =1.47 e 5.6 Substituting in equation (5) 1 k = =.214 .62+.62+.624-.49+.85-J-1.47 Making this same calculation, neglecting T gives k=.210 19 Notes on Heating and Ventilation The following- values of k have been determined by using equations (3) and (4) as shown in the example. TABLE VIII. VALUES OF k ADOPTED BY PRUSSIA. Inches thick 492 thick 348 thick 266 thick 226 Brick . work. 4.72 inches 9.85 inches 15 inches 20.1 inches 25.2 inches 30.2 inches 35 inches 40.5 inches 45.6 inches thick, thick, ihick, thick, thick. .184 ,164 .133 .123 .113 Masonry, sandstone. k. 11.8 inches thick 451 15.7 inches thick 39 19.7 inches thick 348 23.8 inches thick 318 27.6 inches thick 287 31.6 inches thick 266 35.4 inches thiclc 246 39.4 inches thick 226 43.3 inches thick 205 47.2 inches thick 195 For limestone masonry the values of k should be taken 10% larger than those given for sandstone. TABLE IX. Values of k for various forms of brick walls. 81/4x4x2, laid with %-inch mortar joints, thick Brick are assumed Plastering % of an inch Outside Walls. Inside Walls. Plaster One Side Board Plastered and Air Plas- and 2.4 Air Space Be- tered Thickness No One Side Spaces in tween Wall Both of Wall. Plaster. Plastered. the Wall. and Board. Sides. k k k k k % brick .52 .49 , , .29 .43 1 .37 .36 .25 .24 .33 1% " .29 .28 .21 .21 .26 2 .25 .24 .19 .20 2% " .22 .21 .16 3 . .19 .18 .14 3^ " .16 .16 .13 4 .14 .14 .12 41/^ " .12 .12 .. For doors, wooden walls and windows, the values of k are given in Tables X, XI and XII. TABLE X. DOOR OR WOODEN WALLS. Thickness — Pine Inside, k inch 52 inch 44 inch 39 inch 34 l^ inch 31 2 inch 26 V2 % 1 11/4 Outside, k .56 .47 .41 .36 .32 .27 Inside, k .64 .59 .54 .50 .47 .41 Oak Outside, k .70 .63 .58 .54 .50 .43 TABLE XI. WINDOWS' AND WALLS. Single window 1.03 Single window, double glass 62 Double window 46 20 Notes on Heating and Ventilation Single skylight 1.16 Double skylight 48 Stud partition, lath and plaster one side 60 Stud partition, lath and plaster both sides 34 Lath and plaster ceiling space above unheated 62 Floor % inch thick, cold space below 45 Floor % inch thick, lath and plaster on under side, cold space below 26 Floor double 1% inches thick, cold space below 31 Floor double 1*/^ inches thick, lath and plaster on under side, cold space below 18 TABLE XII. OUTSIDE WALLS. Walls having lath and plaster on the inside, and outside is covered as described. Outside covering — k: Overlapping clapboard 7-16 inch thick 44 Paper and clapboards 31 % inch sheathing and clapboards 28 % inch sheathing, paper and clapboards 25 Factors for Exposure.— -The heat losses given in the tables should be increased as follows : Where the room has a north or northwestern exposure and the winds are severe, add 20 to 30 per cent. When the building is heated in the day time only and allowed to cool during the night, add 20 per cent. When the building is heated occasionally — for example, a church — add from 40 to 50 per cent. Where a room has a northerly exposure and is subjected to extremely high winds, add 30 per cent. It is usually advisable to assume for unwarmed spaces, such as cellars and attics, a temperature of about 32°. For vestibules and entrances unheated, which are being frequently opened to the outer air, a temperature of 20° may be assumed. Determination of the Loss of Heat from a Build- ing. — In determining the loss of heat from a building all surfaces should be considered which have on the outside a lower temperature than the temperature in the room.' If a room is situated over a portion of the cellar which is not heated, the loss of heat through the floor should be considered. If the room has over it an unheated ^ttig the loss through the ceiling should 91 Notes on Heating and Ventilation be considered. In most cases where the attic has no window it is warm enough so that the heat loss through the ceiling may be neglected. The loss through the sides of a room which is surrounded by rooms at the same temperature may be neglected. Doors entering directly into a room from outside are roughly considered to lose the same amount of heat per square foot as windows. Rules for Determining the Loss of Heat. — A com- mon rule for the loss of heat from a building is that given by Professor R. C. Carpenter in his book on "Heating and Ventilation." This rule is developed from the following consideration : Referring to Table IV, we notice that one square foot of glass conducts approximately four times as much heat as a brick wall 20 inches thick. If, then, we divide the wall sur- face by 4, the result will give us the number of square feet of glass surface, which would lose the same quan- tity of heat. Adding to this the actual glass surface would give us the total equivalent glass surface. In addition to this heat transmitted through the walls we must add the heat which is lost by the air which passes directly through the walls themselves. It is assumed that for ordinary sized rooms the air in the room will be changed about once an hour, so that we must figure on heating the entire air in the room about once per hour. One cubic foot of air weighs, approximately, 1/13 of a pound. To raise a pound of air one degree requires .238 B. t. u. Then to raise one cubic foot of air one degree would require .238 X 1/13 = .0183 B. t. u. or one heat unit will heat 1~.0183=54.6 cubic feet, or in round numbers say 55. If, then, we divide the contents of a room by 55 we 22 Notes on Heating and Ventilation will have the heat lost by filtration through the walls. Adding these factors together will give the total heat lost from the room. This rule may be expressed more concisely as follows: Rule 1. — Divide the contents of the room by 55 ; add the glass surface and add to this sum the zvall surface di- I'ided by 4. The sum zmll be the heap lost from the room per degree difference of temperature between the air in the room and the air outside the room. Multiply this sum by the difference in temperature betzveen the air in- side the room and that outside of Vhe room and the product zvill be the heat lost from the room. This rule can be expressed algebraically as follows : Let^ C represent the volume of the room, W the zvall surface, G the glass surface and d the difference of tem- perature between the air outside and the air inside the room. The heat loss from the room per hour expressed Cn W 1 \- G y d, zvhere n 55 4 is a factor which depends upon the tightness of the room and varies in value from 1 — 3. For ordinary room n=l, for corridors 1.5, for vestibules 2 Po 3. It is quite customary to assume the difference in temperature between the air in a room and the air outside to be 70°. Where the windows are poorly fitted or the house loosely built the loss by filtration should be doubled, and in halls where the doors are being opened and closed frequently this should be multiplied by three. There is one criticism on this method of figuring the heat loss in the room. The diffusion loss is as- sumed to depend upon the cubic contents of the room. 23 /';/ B. t. u.'s zi'ould be Notes on Heating and Ventilation This of course is manifestly not correct, as the diffu- sion loss occurs through the walls and windows and must depend upon the area of the walls and windows. The rule, however, will work very well for rooms of average size, but where the rooms have excessive wall and window surfaces, or where the cubic contents of the room is large compared to the wall and window surfaces, this rule will give inconsistent results. The following rule seems to the author to be capable of a much wider application : Rule 2. — Divide the wall surface by 4; add the glass surface; mnlPiply this sum bv the difference in tempera- ture betzveen the air in the room and the air outside, and then multiply the result by ly^. This rule is for a well constructed building. If the building is old and poorly built then instead of multiplying by 1^^ t^he result should be multiplied by 2;- entrance halls multiplied by 2^. This rule may be expressed algebraically as follows : Let W represent the wall surface, G the glass surface, and d the difference of temperature between the air out- side and the air inside the room. Then the heat loss from the room per hour expressed in B. t. u.'s would \ w \ be < h G Yd n, where n is a factor which depends upon the construction of the house or location of the room and varies in value from 1.5 to 2.5, as stated above. In figuring the radiating surface for any room the cubic contents should always be taken into consideration. In a large room with a small exposed wall surface, if only enough radiation is put in to cover the loss from walls and windows, the room will be slow to heat. In ^(j^ition to taking care of the loss from walls and vyiri- 84 Notes on Heating and Ventilation dows it is necessary for the radiator to heat the air in the room itself. In order to do this a large proportion of this air must either pass through the heating device or be carried out by the ventilating flues, so that where the cubic contents of a room is large it is advisable to add from 10 to 20 per cent to the radiating surface to allow for the heating of the air in the room itself. The above remark applies only when the building is inter- mittently heated ; when the building is continuously heated it is not necessary to consider the volume of the room. The following temperatures are usually assumed in determining the heat losses : TABLE XIII. TEMPERATURES ASSUMED IN HEATING. Degrees. Temperature of stores 68 Temperature of residences 70 Temperature of halls and auditoriums 64 Temperature of prisons 65 Temperature of factories 60 to 68 Temperature of cellars not warmed 32 Temperature of outside entrances 20 Temperature of attics not warmed 32 ^^ The average temperature for the period of the year during which buildings are heated throughout the Cen- States may be assumed to be approximately 35°. The following examples will show the method to be l^ - pursued in determining the heat lost from a building: Example 1. — Suppose a room, as shown in Fig. 8. Let the temperature be maintained in the room at 70 degrees, the temperature of the outside air be 0. Let the walls be of brick, 8 inches thick, plastered on plaster board on the inside, the windows be 2)4x6 feet, the ceil- ing of the room be 10 feet high. Let the room be on the second floor of the building, the rooms above and b^low heated- The window surfaces are 22x2^2x6=30 25 Notes o n Heating and Ventilation square feet. The total wall surface is 20x10=200 square feet. The net wall surface is 200 — 30^170 square teet. Then the lieat lost from the room per degree difference Fig. 8. of temperature by rule 2 would be lT0^4-|-30=:72>4. As the difiference between the outside and inside tem- perature is 70°, the total heat lost is 72>^x70=5,07o B. t. u. per hour. 26 Notes on Heating and Ventilation Example 2. — Take the same room as Example 1, except that the room is covered by a flat tin roof. The air space between the ceiling of the room and roof should be assumed to be at a temperature of 32°. Then, in addition to the loss figured in Example 1, there will have to be added the loss due to the tin roof. The area of the ceiling of the room would be 14x20=280 square feet. Referring to Table IV we find the loss per hour through ceilings of plaster con- struction to be .62 B. t. u. per degree difference of temperature; then the loss through this ceiling would be, per degree of temperature, .62X280=173.0 B. t u. The room being at 70° and the attic space 32°, the difference in temperature would be 70 — 32=38 degrees. The total loss through the ceiling would then be 29.1X38=6,574 B. t. u. Adding this to the loss found in Example 1 we have a total loss from the room, 5,070+6,574=11,649 B. t. u. A more accurate method is to figure the actual loss through the walls and windows from the constants in tables IX and X. The loss from walls (.24X170) 70= 2,856 The loss from windows (1.03X30) 70= 2,163 Total loss from walls and windows= 5,019 To allow for diffusion this sum must be multiplied by Ij/, making a gross loss of 7,528. 27 CHAPTER II. DIFFERENT FORMS OF HEATING. Classification of Heating Apparatus. — The different 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, as, for instance, stoves, steam radiators or hot water radiators. In indirect heating systems the heating apparatus is placed in some other room and the heat carried to the room to be heated by means of pipes. Under this head would be included hot air furnaces and the various systems of heating in which fresh cold air is made to pass over steam or hot water radi- ators on its way to the room. The indirect systems of heating naturally divide themselves into two other classes, those using natural draft and those using forced draft. A good example of natural draft indirect heating is the hot air furnace, where the circulation of air through the house is pro- duced by the difference in temperature between the air in the hot air flues and the cold air outside the flues. The fan system of heating, used in heating school buildings and churches, are good examples of the forced draft system. In this case the draft is largely produced by mechanical means, usually a disc fan or a pressure blower. In order to understand better a discussion of the various forms of heating which will come later, it is desirable to understand in general the advantages and disadvantages of the various forms of heating. Grates. — The most primitive form of heating ap- Notes on Heating and Ventilation paratus 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 ofif by radiation to the walls and objects in the room is effective in heating the room. In grates of better construction this is somewhat improved by surrounding the grate by fire brick so arranged that the brick will become highly heated and radiate heat to the room. But the fact that all the air heated by the grate passes up the stack makes this a very uneconomical form of heating. In the best form 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, has been defended by many. It is a very popular form of heating through- out England and Scotland. The feeling of a grate- heated room is quite different from that of a room heated by other systems. All the heat is given off by radiation and the air in a grate-heated room is at a considerably lower temperature than the objects and persons in the room, owing to the fact that radiated heat does not heat the air through which it passes. The air of the room being at a lower temperature, its capacity for moisture is not increased as much as it would be were the air heated to a higher tem- perature. The result is that the air contains propor- tionally more moisture than is the case in other forms of heating. This, no doubt, is an advantage. On the other hand, it is impossible to heat the room uni- formly, and a person is hot or cold, depending upon his distance from the grate. Heating by means of grates is practiced only in the more moderate climates. The grate is useful in the houses heated by other forms of heating, as it serves as a most efficient foul 29 Notes on Heating and Ventilation air flue. The introduction of a large number of grates into a house adds materially to the ease with which the house may be ventilated. Stoves. — The stove is a marked improvement over the grate as a form of heating, particularly from the standpoint of economy. The modern base burner stove is one of the most economic and efficient forms of heating, making use of from 70 to 80 per cent of the heat in the fuel. In heating by a stove the heat is given off both by radiation and by convection. The hot surface of the stove being at a higher tempera- ture than the surrounding objects in the room, radiates its heat directly to these objects. In addition the air surrounding the stove is heated and rises, passing along the ceiling to the cold wall and window sur- faces where it is cooled, drops to the floor and passes along the floor back to the stove to be again heated. In selecting a stove to heat a given room care should be taken to select one of ample size so that only in the coldest weather would it be necessary to crowd it; that is, keep on the drafts 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 and the itnsightly appearance of the stove. Another serious ob- jection to the stove is the fact that it does not furnish ventilation to the room which it heats. Hot Air Furnaces. — The hot air furnace is a natural outgrowth of the stove. In this system one large stove is placed in the basement of the building, the air is taken from the outside, passed over the sur- faces of the stove or furnace, carried up through the flues to the rooms to be heated. The principal ad- 30 Notes on Heating and Ventilation vantage of the hot air furnace is that it provides a cheap method of furnishing both heat and ventilation, it requires little attendance and does not deteriorate rapidly when properly taken care of. The greatest disadvantage of this system is in the fact 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 flue and the air outside the flues. This difiference of weight is ex- tremely small, so that the force producing circulation in the flue is always small. This force is easily over- come either by the winds or by the resistance of the piping. When a very strong wind blows against one side of the house it is difficult to heat the rooms on that side of the. house. If the system is carefully de- signed, 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 and ashes are carried into the room. In general, how- ever, the hot air furnace may be considered as a very good type of heating plant for small residences. In the case of the hot air furnace the heat is carried to the room by convection, as all heat is carried from the furnace by the air which passes around the fur- nace and enters the rooms from the flues. This air circulates in the room and heats the objects and air in the room. The efficiency of the hot air system will vary, depending on the relative proportion of the air taken from outside and upon the temperature of the air entering the room. If the cold air entering the furnace is taken from the house itself and not from outside, the efficiency of the hot air furnace will be almost the same as that of a steam furnace; that is, 31 Notes on Heating and Ventilation from TO to To per cent of the heat of the coal will go into the rooms. If, however, the cold air is taken from outside, then the heat used in heating the air from the temperature of the outside air to the tem- perature of the room will be lost, and under ordinary conditions of operation the efficiency would be from 50 to 60 per cent. Steam Heating Direct. — From the standpoint of ventilation direct steam heat has little advantage over a stove, as it gives no means of supplying fresh air. Its use in general should be confined to rooms which require little or no ventilation. Mechanically, how- ever, it has many advantages over the stove or the hot air furnace. The boiler for a building having this form of heating can be located anywhere in the basement, and the rooms are free from dirt or gas. The modern radiator is easily adapted to almost any location in the room, it is not affected by wind or local conditions, and a distant room may be heated as easily as one close to the furnace. The efficiency of the direct steam heating system is less than that of a stove, with a well-installed plant from 60 to 70 per cent of the heat of the fuel will be delivered by the radiator to the room. Hot Water, Direct. — 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 at a much lower temperature and hence more radiating surface will be required. It has an advan- tage over steam in that the temperature of the heat- ing surface can be controlled easily, and can be any- where from the temperature of the room to 180 degrees. It also has the advantage that the surface 33 Notes on Heating and Ventilation of the radiator being at a lower temperature gives off more heat by convection and less by radiation. This gives the room more nearly the condition of Summer and the heating is not apparent to the occupants of the room. In the steam radiator the surface is usu- ally not less than 212 degrees. The principal disad- vantage of this system is in the fact that the circula- tion of the system is by natural circulation ; that is, the circulation is produced by a difference in weight between the water in the hot leg of the system and in the cold leg of the system. This difference in tem- perature is usually about 10 degrees, so that the difference in weight between these two columns of water is small and the resulting force producing circu- lation is, of course, small. It is necessary to be very careful in designing the piping for the hot w^ater sys- tem, as the circulation may be easily affected by the height of the radiator above the boiler; the greater the height above the boiler, the greater will be the difference in weight between the two columns of water and the stronger will be the force producing circula- tion. This system in general requires more careful design and construction than the steam system. The efficiency of the hot water system is practically the same as that of steam, and we may expect to obtain in the room from GO to TO per cent of the heat in the coal. Indirect Steam Heating. — In heating with indirect steam radiation cold air is drawn from the outside, passed through and around the hot radiator, which is usually situated in the basement, and delivered by pipes to the rooms to be heated. The rules governing the introduction of air into the rooms and the method 33 Notes on Heating and Ventilation of running pipes is similar to that employed with hot air furnaces. The principal advantages of indirect steam over hot air are: 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 air entering the room will always be as pure as the air which furnishes the source of supply. The source of heat being independent of the position of the boiler, it is possible to place the indirect radiator any- where in the building and long hot air pipes are not necessary. This makes the indirect radiator much more efficient and more certain in operation than the hot air furnace. The efficiency of this system, from the standpoint of coal consumption, will be much less than in direct forms of heating and about the same as the hot air furnace; that is, from 50 to 60 per cent of the heat of the coal will be used effectively in heating. Indirect Hot Water Heating. — The application of hot water indirect is similar to that of steam and the efficiency is practically the same. The use of hot water indirects has been much more limited than the use of steam indirects. The installation of hot water indirects must be done with great care so that each radiator will at all times have the proper amount of hot water circulation through it. In the hot water indirect radiators, if for any reason the water in the radiator becomes cooled, the radiator will be in danger of freezing. In mild climates this difficulty would not be as serious as in locations where the weather is extremely cold. Fan System of Heating. — In buildings of a public or semi-public character, where a large number of 34 Notes on Heating and Ventilation people are to be assembled in a relatively small space, it is necessary to provide adequate ventilation. In the systems that have been previously described it is im- possible to introduce into the room sufficient quanti- ties of air to ventilate the rooms 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 means of mechanically circulating the air. This is done in the fan system by means of a pressure blower or a disc fan. In the fan system the pressure produced by the fan makes the circulation so positive that it is not aflfected by winds or by the distance of the room from the fan itself. The air is taken from the outside, passed through the heating coils and forced into the building by the fan. There are two general methods of heating and ven- tilating with the fan system. In one system the air is first passed through a tempering coil, 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 chamber. The temperature of the air in the room is adjusted by taking the air either from the hot air chamber or from the tempered air chamber. In the second system the rooms them- selves are heated by means of direct radiation and the fan delivers air to the rooms only for the purpose of ventilation. In this case no heating coils would be necessary. In the first method the economy of the system is low, as owing to the large amount of air required for ventilation and the quantity of air introduced into 35 Notes on Heating and Ventilation the room is ordinarily greater than is necessary for the purpose of heating the room. The economy of this form of fan system depends very largely upon the amount of air necessary, but in most cases its effi- ciency would not exceed from 40 to 50 per cent; that is, only 40 to 50 per cent of the heat units in the coal would be effective in heating. In the combined fan system, where direct radiation is used for heat- ing and the fan system for ventilation, the economy of the system is better, probably from 50 to 60 per cent. The increase in economy of this system is due to the fact that it is necessary to run the fans only when it is necessary to ventilate the building. Combination of Different Systems. — In addition to the combination just described, of direct radiation and fan ventilation, there have been devised innumerable combinations, combinations of direct and indirect steam, direct and indirect water, water and hot air, steam and hot air. Probably the combinations which have been most used have been combinations of direct and indirect steam and the combinations of hot water and hot air. The Economy of Different Systems. — The economy of any heating system depends upon the completeness with which the coal in the furnace is burned and the heat lost by the chimney and the ventilating flues. If, with each of the above systems the coal was com- pletely burned and all the heat given off were used, then each one of the systems would have perfect efficiency. The losses from any system, given in detail, are as follows : Loss through imperfect combustion of coal, through the escape of hot gases up the chimney and the 36 Notes on Heating and Ventilation loss of Jieat in the air passincr up the ventilating fine. If the furnace is properly constructed and insures good combustion, the loss due to imperfect combustion is small. The loss of heat passing up the chimney will depend upon the temperature at which the gases leave the chimney and the amount of air used to burn a pound of coal. The loss bv the ventilating flue will depend upon the amount of air it is necessary to supply to the rooms for ventilation. If the hot gases leave the heating apparatus at the same temperature and the same amount of air is used for ventilation, then the efficiency of each system will be practically the same. If the rooms are not ventilated, then, of course, the loss due to the heat passing up the ventilating flues will be saved and the system will be more economical. In fact, strictly speaking, the loss by ventilation should not be considered as entering into the efficiency of the svstem. This loss is entirely independent of the system used and depends entirely upon the amount of air which must be supplied for purpose of ventilation. It is quite obvious that any system involving ventilation will require a greater amount of coal. The loss due to ventilation is due to the fact that all the heat which is given to the air between the temperature of the air out- side the building and the air in the room is ineflFective in heating and is lost up the ventilating flues. It would be poor policy, however, for the designers of heating systems to cut down the amount of ventilation in a room in order to save coal. In several states there are general state laws which require that a certain amount of air be furnished each person per hour in school buildings and other buildings of a public character. The necessity and importance of ventilation will be discussed under another head. 37 CHAPTER III. THE DESIGN OF A DIRECT STEAM-HEATING SYSTEM. Steam heating is usually done by direct or by indirect radiation or by combination of both direct and indirect radiation. In small residences occupied by only three or four persons it is customary to use only direct radiation. The practice, however, is a questionable one, and it seems desirable, even in small residences, that some indirect radiation be used so as to provide a means of ventila- tion. Oftentimes only one indirect radiator is used, bringing its air either into the room most used or into the main hall so that it may be distributed throughout the house. In factories and office buildings where a large amount of air is introduced by the opening and closing of doors it is customary to use only direct radia- tion, and in such buildings this is permissible. Nature and Properties of Steam. — In order to under- stand thoroughly the operation of a steam heating system the nature and properties of steam should be studied. Steam is a watery vapor, and as used in ordinary radiator practice always contains a certain amount of water in suspension, as does the atmosphere in foggy weather. When water is heated in a steam boiler the tempera- ture is slowly increased from the initial temperature of the water to the temperature of the boiling point. When the water reaches the boiling point small particles of the water are changed from water to steam, rise through the mass of water and escape to the surface ; the water is then said to boil. The temperature at which the water boils depends entirely upon the pressure in the boiler and 38 Notes on Heating and Ventilation obviously, as the boiling point increases more and more, heat is required to produce steam. Take, for instance, a given case. Suppose we start with water in the boiler at 40 degrees and the pressure in the boiler at atmospheric pressure, that is, 14.7 pounds. Under this condition it will be necessary to increase the temperature of the water in the boiler to 212 degrees, at which point water will commence to boil. It will be nec- essary to add 212 — 40^172 B. t. u. for every pound of water in the boiler. In order to convert all the water into steam it will be necessary to supply 965.7 heat units for each pound, in addition to the 172 heat units con- sumed in raising the water to the boiling point. During the operation of boiling, however, the temperature of the water remains constant and the 966 heat units added in order to change the water at the temperature of the boiling point into steam are consumed in separating the molecules of water and changing the water from a liquid into a gas. This last quantity is termed the latent heat and it is the latent heat of water which is used primarily in furnishing heat to the room in steam heating. As the pressure in the boiler increases the latent heat diminishes. The relation of these various quantities has been very carefully determined by Regnault and compiled in the form of steam tables. The following is an abbreviated steam table. More complete tables will be found in Pea- body's Steam Tables, or in any of the mechanical engi- neering handbooks. STEAM TABLES. Column 1 of the Steam Table gives the pressure of the steam above the atmosphere in pounds per square inch and below the atmosphere in inches of mercury. Column 2 gives the corresponding temperature of the steam. 39 Notes on Heating and Ventilation Column 3 gives the heat of the liquid or the heat neces- sary to raise one pound of water from 32 degrees to the temperature of the boiling point, corresponding to the pressure. Column 4 gives the latent heat necessary to change a pound of water at the temperature of the boil- ing point into steam at the same temperature. Column 5 is the sum of columns 3 and 4, and represents the amount of heat necessary to raise a pound of water from 32° to the boiling point and then change it into steam at the temperature of the boiling point. The quantities given in this column are called total heat. Column 6 gives the volume of one pound of steam at the differ- ent pressures. Pressure TABLE XIV— PROPERTIES OF STEAM. or Vacuum. Volume of Inches Tempera- Heat of Latent Total 1 lb. of Mercury ture the Liquid Heat Heat Steam —24 137 105 1,019 1,124 135 —20 160 128 1,003 1,131 78.3 —16 175 143 992 1,135 55.9 —14 387 155 984 1,139 43.6 — 8 197 165 977 1,142 35.8 — 2 205 173 971 1,144 30.6 Pounds per sq. in. 212 180.9 965.7 1,146.6 26.36 1 215 184 964 1.148 25 2 219 188 961 1,149 23 8 222 191 959 1,150 22.3 4 224 193 957 1.150.5 21.2 5 227 196 955 1,151 20.16 10 239 208 946 1,154 16.3 15 249 218.8 939.3 1,158.1 13.7 20 . 258.7 228 932.5 1,161 11.85 25 266.7 236.2 927.1 1,163.3 10.36 30 273.9 243.5 922 1,165.5 9.34 35 280.5 250.2 917.3 1,167.5 8.45 40 286.5 256.3 913 1,169.3 7.73 45 292.2 262.1 909 1,171.1 7.11 50 297.5 267.5 905.2 1,172.7 6.61 55 302.4 272.6 901.6 1,174.2 6.16 60 307.1 277.2 898.4 1,175.6 5.77 65 311.5 281.8 895.1 1,176.9 5.43 70 315.8 286.1 892.1 1,178.2 5.13 75 319.8 290.3 889.1 1,179.4 4.86 80 323.7 294.3 886.3 1,180.6 4.63 85 327.4 298.1 883.6 1,181.7 4.41 90 330.9 301.8 881 1,182.8 4.20 95 334.4 305.4 878.5 1,183.9 4.02 100 337.6 308.9 876 1,184.9 3.83 110 343.9 315.4 871.4 1,186.8 3.57 120 349.8 321.5 867.1 1,188.6 3.33 130 355 327.5 863 1,190.3 3.1 140 360 333.5 8"59.1 1,191.9 2.92 150 365.7 338.3 855.4 1,193.4 2.75 40 Notes on Heating and Ventilation EXAMPLES IN USE OF STEAM TABLE. Example 1. — It is required to convert 10 pounds of water at 32° into steam at 100 pounds gauge pressure. Solution. — We see from column 5 that the total heat of 1 pound of steam at 100 pounds pressure is 1,184.9 heat units. Then to form 10 pounds of steam would require 10 times this amount, of 11,849 heat units. 2. How many heat units will be required to form 5 pounds of steam from feed water at 100° in tempera- ture into steam at 10 pounds gauge pressure? Solution. — The total heat of steam at 10 pounds pres- sure above 32° is 1,154 heat units. In this case the feed water already contains in it above 32°, 100 — 32 = G8 heat units. The specific heat of water being 1, the heat units required to form a pound of steam will be 1,154 — 68 ^ 1,086, and to form 5 pounds of steam would re- quire 5 X 1,086 = 5.430. 3. A steam pipe is 8 inches in diameter. The pressure of steam in the pipe is 10 pounds gauge. The steam pipe is to transmit 1,600 pounds of steam per hour. What will be the velocity of steam in the pipe? Solution. — From column 6 of the table we see that the volumn of 1 pound of steam at 10 pounds gauge pres- sure is 16.3 cubic feet. Then 1,600X16.3=26,080 cubic feet, the volume of steam passing per hour. This divided by 3,600 equals 72, the number of cubic feet passing per second. An 8-inch pipe has an area of 50 square inches ; 50^144=.347 square feet; 72-^.347=208 feet per sec- ond, which represents the velocity of the steam passing through the pipe. This velocity is very high. Ordinarily the velocity in steam pipes should not exceed 100 feet per second, even in very large pipes. 41 Notes on Heating and Ventilation LOSS OF HEAT FROM RADIATORS. In designing a direct steam system it will be necessary first to compute the heat losses from the various rooms by the rules previously given. After these losses are determined it will be necessary to place sufficient radi- ating surface in the room to supply these losses. In order to know the amount of surface that should be placed in a room it is necessary to know the amount of heat given off per square foot by the different forms of radiators. Heat losses for the different forms of direct radiators are given in the following table: TABLE XV— LOSS FROM WROUGHT IRON PIPE AND CAST IRON RADIATORS. o B, ^ "H *" '^t ^ ^ 5c ° "S ftp Cast Iron Radiators, 38 1 column 48 sq. ft. 226 2 column 48 sq. ft. 226 3 column 45.3 sq. ft. 226 6 column 36 sq. ft. 225 Wrought Iron Radiators, 1 column 12 sq. ft. 221 2 column 42 sq. ft. 222 3 column 48 sq. ft, 229 4 column 48 sq. ft. 226 1" wall coil, 1 pipe high 212 1" wall coil, 4 pipes high 228 Colonial wall coil 212 Column 5 is the column which shows the relative effec- tiveness of the various types of radiators. It is obtained in the following manner: Take, for example, the two- column cast iron radiators, results of which are given in line 2 of the table. A pound of steam at 226°, as we see from the steam tables, gives up its latent heat in con- densing which amounts to 965 heat units. This radiator 42 S cr r -M hr 1 rQ o^ T! •^Oj d- (D m £o3 5 P P3 u Oi .-o o ^i57=259jieat units per square foot per hour. Di- vidmg the heat loss as given by the rule for loss of heat, by 259 gives the number of square feet of radiation to be used. This is the only method that can be used at all in rooms where conditions are exceptional. For rooms of ordi- nary construction, heated to 70 degrees, and an outside temperature of 0°, a large number of thumb rules are used. Some of these thumb rules are as follows : In the following rules the expression wall surface means exposed wall surface, that is, those surfaces which have outside air temperature on one side and room temperature on the other side. Rule 1. Dh'ide the volume of the room by 55. Add 55 v^ Notes on Heating and Ventilation one-fourth of the exposed zvall surface; add the glass surface, and multiply the sum of these t^hree quantities by .28. The product zvill be the direct radiation in square feet. Rule 2. — For ordinary rooms. Divide the exterior zi^all surface by 4, add the glass surface and multiply the sum by .4. B. — For entrance halls. Diznde the exterior zvall sur- face by 4, add the glass surface and multiply the sum by .54. C. — For the zi^all surface in basement rooms below the ground line. Divide the zvall surface by 4 and multiply the result- by .17. D. — For floors having unheated space beloK'. Divide the -floor space by 4 and multiply the residt by .23. Rule 3. Divide the volume of the room in cubic feet by the factors given below and the quotient zmll be the radiating surface in square feet. First Hoor rooms, tzvo sides exposed 50 First floor rooms, three sides expose 45 Sleeping rooms, second floor 60 t^o 70 Halls and bath rooms 50 First Hoor rooms, one side exposed 55 Offices 50 to 75 Factories and stores 75 to 150 Assembly halls and cJiurches 75 to 150 Rule 4. (Baldwin's Rule). — Divide tJie differences betzt'een the temperature at zvhicJt the room is to be kept and i^hat of the coldest outside temperature by the differ- ence betzt'een the temperature of the steam in the radiator and that at zuhich you zvish to keep the room and the quo- tient zvill be the square feet of radiating surface to be allowed for each square foot of equivalent glass surface, 56 Notes on Heating and Ventilation By equivalent glass surface is meant the wall surface divided by 4 plus the glass surface. In all of these rules the factors to be allowed for ex- posure should be applied. These factors are given under the head of "Factors for Exposure." Where the rule does not involve the contents of the room it will be neces- sary in very large rooms or in rooms where the wall surface is very small in proportion to the contents of the room, to add a certain proportion of radiation, usually not more than 20 per cent, to allow for heating the air in the room quickly when it has once been allowed to cool. Example (Direct Radiation). — In order to under- stand better the methods of determining the heating surface required for a given house, it would be best to consider a concrete example. Figs. IG, 17 and 18 repre- sent the basement, first and second floors of a residence. The house is constructed of wood, sheathed, papered and clap-boarded on the outside and plastered on the inside. On the first floor the rooms are 9 feet 6 inches high and on the second floor 8 feet 6 inches high. The windows are .6 feet high and the standard size is 3 feet wide. Table XX gives the general dimensions of the room and the heat losses from the various rooms, assuming the temperature of the outside air to be zero and the tem- perature of the inside to be 70 degrees. TABLE XX.— DIMENSIONS' AND HEAT LOSSES. Room. Dimensions. Parlor 13'9"xl2'9"x9'6" Sitting room 14'3"xl5'6"x9'6" Dining room 12'6"xl3'9"x9'6" Kitchen 13'0"xl3'0"x9'6" Hall 12'9"xl0'0"x9'6" Second Floor. W. oliamber Il'6"xl3'6"x8'6" 1,320 172 48 10,050 57 B.t.u. Lost Wall Window Per Volume. Surface. Surface. Hour. 1.665 216 36 9,450 2,100 95 48 7,035 1,640 145 36 7.350 1,610 249 36 10,300 1,210 197 18 7,035 Notes o n Heating and Ventilation Alcove 10'0"x 9'6"x8'6" 810 130 40 7,560 So. chamber 12'6"xl4'9"x8'6" 1,560 172 24 7,035 N. chamber 13' xl3' x8'6" 1,440 188 24 7,455 Bath 6' x 8' x8'6" 410 50 18 3,150 E. chamber 13' x 8' x8'6" 880 160 18 5,250 Front hall 14' x 4' x8'6" 885 33 18 2,730 8' X 6' x8'6" TABLE XXI.— RESULTS OP COMPUTATION, DIRECT SYSTEM. Radiating B.t.u. B.t.u. Surface. Two Radiating from Corrected for Column Cast Surface Table XXI. for Exposure. Iron Sq. Ft. by Rule 3. First Floor. Parlor 9,450 10,395 39 33.5 Sitting room.. 7,035 7,035 27 38 Dining room... 7,350 8,085 30 30 Kitchen 10,300 10,300 39 32 Hall 7,035 7,770 29 24 Second Floor. W. chamber... 10,050 11,055 42 22 Alcove 7,560 8,316 31 13 S. chamber 7,035 7,035 27 26 N. chamber.... 7.455 8,190 31 24 Bath ,150 3,465 13 7 E. chamber... 5,250 5,250 20 14.7 Halls 2,730 • 3,003 12 14.7 The method used in determining the British thermal units lost from the room is as follows : In Table XII a wall constructed as described loses .25, Table XI gives the loss from the glass surfaces as 1.03. Then multiply- ing the wall surface by .25 will give the B. t. u. lost per square foot per degree difference and each square foot of glass surface loses about one B. t. u. per square foot. Take, for example, the parlor. The wall surface is 216 square feet. Multiply this by .25; the result, 54 B. t. u. lost per square foot per degree difference of temperature. Add the loss from the glass surface, 36 B. t. u., makes a total loss of 90 B. t. u. Multiply- ing this by the difference between the outside and the inside temperature, gives the heat lost, or 90 X '^0=6,300 B. t. u. lost from the room per hour. To this must be added the loss through the wall by leakage which has been assumed to be 50 per cent, making the total loss 9,450 B. t. u. In Table XXI the second column gives the B. t. u. 58 Notes o n Heating and Ventilation as determined in Table XX ; the third column the B. t. u. corrected for exposure, 10 per cent being- added to rooms having north and west exposures, as, in this case, the prevailing v^inds are from the west. Column 4 gives Fig. 16. Basement Plan. the radiating surface required to heat the rooms with a two-column cast iron radiator. Column 5 gives the radiating surface as determined by Rule 3. 59 Notes o n Heating and Ventilation The quantities in column 4 are obtained in the fol- lowing manner. The steam pressure to be carried in the radiator is 5 pounds. The corresponding temperature Fig. 17. First Floor. of steam is 227 degrees. The temperature of the room is 70 degrees. The difference in temperature between the room and the steam will be 157 degrees. In the last 60 Notes o n Heating and Ventilation column of Table.^VJJLthe heat lost for a two-column cast iron radiator is given as 1.65 B. t. u. per degree differ- ence per hour. Then the total heat lost per square foot per hour will be [l57Xl-65=2G0 B. t. u.T that is, each square foot of radiator surface will give to the room Fig. 18. Second Floor. 260 heat units per hour. Dividing the heat lost from the room, as given in column 3, by 260, will give the results shown in column 4. In column 5 th& radiating surface has been deter- mined by Rule 3, which is sometimes called the Volume 5** ^ 61 Notes on Heating and Ventilation Rule ; that is, the cubic contents of the rooms are divided by a certain factor, depending upon the location of the room. A careful comparison of columns 4 and 5, together with an inspection of the plans, will show the inconsistency of the volume rule. The volume rule can be used only where the room has an average amount of cubic contents, as compared with its wall surface. To get the best results it is better to employ the method that has been used in determining the results in column 4. The case often arising where a contractor guarantees to heat a building to 70° when the outside temperature is zero. When the plant is finished the temperature out- side is many degrees above zero. What temperature should the rooms heat to under this higher outside tem- perature in order to have the room heat to 70° in zero weather? Assume ti=temperature of the outside air from con- tract conditions usually 0°. t2=temperature of air in the room which was guaranteed by contractor. t3=temperature of steam in the radiator during test. t4=actual temperature outside air during test. tg^computed temperature of room for test con- ditions. The heat loss from the room under contract conditions is W +G n(t-tO (1) 4 Heat loss from room under test conditions is W +G n(t,-t,) (2) 62 Notes on Heating and Ventilation Heat loss from radiator under contract conditions = (U—U)c (3) where c is coefficient of transmission. Heat loss from radiator under test conditions = (t-t.)c (4) Then equation (1) must equal (3) and equation (2) must equal (4), hence (vv \ '.La— i2;c ^G )n= and (5) 4 / t -t, ( +G)n= . (6) V 4 / t.— t. Equating the right-hand member of equations (5) and (6) we have t.— 12 t — t. (V to— tl t,— t. Assuming t^ = 0° and t^=70° and solving for t- t,=.695t,+70° (8) The following Table XXH has been computed from equation 8 and shows the room temperature for dif- ferent outside temperature with the same radiation in the room and the same steam temperature. TABLE XXTI. Room Temperaturf! Corresponding' to Temperature of Outside Air. Temperature of Temperature of room Temperature of room outside air. 2-column 1 radia tor. 3 column radif. tor, —30 52 53 —20 58 59 —10 64 64 70 70 10 77.5 75 20 83 83 30 90 89 40 97 95 50 103.5 105.5 60 110 108 70 117 115 80 123.5 121.5 90 130 128 100 137 134.5 63 Notes on Heating and Ventilation Table XXII shows the temperature that should be obtained in a room for various outside temperatures, the original guarantee being to heat the house to 70 degrees in zero weather. Transmission of Heat Under Various Conditions. — The German engineers use the following method of cal- culating the amount of heat which will pass through a square foot of heating surface per hour. Assume H to be the total heat transmitted per hour ; t the difference between the average temperature of the hot and cold fluids ; c a constant depending upon the kind of surface, the hot fluid and the cold fluid and let a ecjual the area of the surface. Then H = c t a. Rietschel gives the following values for the heat trans- mitted : c From air or smoke through a clay plate about ^ inch thick to air 1.00 From air or smoke through a cast or sheet iron plate to air 1.4 to 2.0 From air or smoke through a cast or sheet iron plate to water or the opposite. . . . 2.0 to 4.0 From steam through cast iron or wrought iron plate to air 2.2 to 3.6 From steam through a metal wall to water. IfiO.O to 200.0 64 CHAPTER IV. Design of Indirect Steam Heating System. — It is seldom that indirect radiators only are installed. This is due chiefly to the increased cost of installation and operation of such a plant, as compared with a plant using both direct and indirect radiation. In a resi- dence heated by indirect radiation alone, it will be necessary to introduce an' excess of air over that re- quired by ventilation. This materially increases the cost of operation. In designing an indirect heating plant the loss of heat from the building is figured in the same way as with the direct system. In using indi- rect radiation alone it will be necessary to introduce enough air so that the heat left in the room will be suf- ficient to take care of the losses from the walls and win- dows. In order to determine the amount of surface to be placed in the room, it is necessary to know the tem- perature to which the radiator will heat the air and the amount of heat given off by the indirect radiator under different conditions of operation. Heat Lost from Indirect Steam Radiators. — The amount of heat that may be obtained from a given indi- rect radiator will depend upon the temperature at which the air is taken in, the temperature of the radi- ator, and the cubic feet of air passing through the radiator. The following table gives the relation be- tween the above quantities, assuming the temperature of the air entering the radiator to be zero, the tempera- ture of the steam in the radiator 227 degrees, the tem- perature corresponding to 5 pounds gauge pressue: In school buildings and in buildings where the flues 65 Notes o n Heating and Ventilation are of ample size the amount of air passing per square foot of radiating surface 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 Fia. 19. Extended Surface Indirect Radiator. per square foot of surface per hour does not exceed 150 cubic feet. ^ From the results of the tests on indirect radiators given, the following points may be noted : Fig. 20. Long Pin Indirect Radiator. If the temperature of the air entering the radiator is constant, then the temperature of the air leaving 66 Notes on Heating an d Ventilation the radiator will decrease as the amount of air passing through the radiator is increased. In order to determine the amount of heat trans- milted by the radiator it is necessary to assume the number of cubic feet of air that will pass through the radiator per square foot of radiation. You will also note the difference between the extended surface radiator and the long pin radiator (Fig. 20). As shown in Table XXIII, the temperature at which the air is heated by the long pin is less than the tem- perature to which the air is heated by the short pin with the same quantity of air passing. This is un- doubtedly due to the fact that the pins are so long TABLE XXIII. HEAT LOSSES FROM INDIRECT RADIATORS. X B. t. u. trans- mitted per sq. ft. Cubic feet Increase In of radiation per of air j^;> temperature Pounds of degree dlff. In passing 'i'"/ of the air steam con- temper, of air per sq. ft. , f passing densed per passing through of <^{ the X , sq. ft. of radiator and the radiation. '^ _ \ radiator. > radiation. steam. - — -- Stan- ^^^^^"""^ Stan- . Stand- \ dard Long dard Long dard Long A Pin. Pin. Pin. Pin. Pin. Pin. 50 147 140 .125 .15 .80 .95 75 143 137 .17 .21 1.17 1.27 100 140 135 .24 .26 1.51 1.60 125 138 132 .295 .31 1.85 1.90 150 135 129 .355 .36 2.22 2.20 175 132 126 .41 .405 2.57 2.47 200 130 123 .47 .45 2.90 2.72 225 127 120 .53 .49 3.25 3.00 250 123 118 .585 .53 3.60 3.20 275 121 115 .645 .57 3.90 3.40 300 119 112 .700 .61 4.22 3.60 that the ends become cooled. On the other hand, the long pin type is a very desirable type to use when one wishes to pass large quantities of air, as the radiator has ample air passage. This is primarily the work for which it is designed. The short pin gives better results for ordinary houses where small quantities of air pass through the radiator. 67 Notes o n Heating and Ventilation Installation of Indirect Radiators. — Indirect radi- ators are placed in a chamber or box, usually situated in the basement of the building, as close as possible to the vertical flue leading to the room which they are to heat. The air is admitted to the radiator by a duct or flue, connected with the outside air. This duct should be supplied with a suitable damper and, if pos- sible, be so arranged as to close automatically when the steam pressure is taken off the radiator. The cold air is usually admitted directly beneath the radiator and the heated air on leaving the room is taken off at one side. TABLE XXIV. INDIRECT RADIATORS— TEMPERATURES OF LEAVING AIR. Temperature of air Temperature of air Temperature leaving the radiator leaving the radiato^r of air enter- with a velocity of with a velocity o'f ing the radl- 200 cu. ft. of air 150 cu. ft. of air ator. per sq. ft. surface. per sq. ft. surface. Standard Long Standard Long Pin Pin Pin Pin 130 125 135 128 10 134 128 139 132 20 139 132 144 136 30 144 136 149 140 40 148 141 153 144 50 153 144 158 146 The casing surrounding indirect radiators is usually built of galvanized iron and it should be bolted to- gether with stove bolts, so that the casing may be easily removed. A much better method, but one which is more expensive, is to enclose the radiator in a small brick chamber with cement floor. This chamber should be large enough so that the radiator is accessible for repairs. Sometimes a duct is pro- vided in the radiator casing so that cold air may be taken around the radiator and mixed with the heated air through a suitable damper, controlled from the room which is heated. This is a very common ar- 68 Notes on Heating and Ventilation rangement in school buildings. Fig. 21 shows a sketch of an arrangement of this kind. The pipes or ducts leading from an indirect radi- Fig. 21. 69 Notes on Heating and Ventilation ator should be carried to the room as directl}^ as possible. It is better to have a long cold air pipe than a short hot air pipe. A long horizontal hot air pipe should be avoided. Where the air from the indirect radiator is to be used primarily for ventila- tion it is best to place the hot air register near the ceiling. The indirect radiators are usually suspended in the radiator chamber on iron pipes supported by rods hanging from the ceiling. There should be at least 10 inches clear space between the radiator and the bot- tom and top of the casing. The casing of the radi- ator should fit the radiator as closely as possible, so that very little air is allowed to pass around the radi- ator without being heated. 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 system of circulation, and should be so arranged that the condensed water will drain from them without trap- ping. The tappings of these radiators are the same as for double pipe direct steam radiators. The following table gives the general proportions for an indirect ra- diator system : TABLE XXV.— SIZE OF FLUES FOR INDIRECT RADIATOR. Heating Area of Cold Area of Hot Size of Surface, Air Supply, Air Supply, Brick Flue for Size of Sq. Ft. Sq. In. Sq. In. Hot Air. Register. 20 30 40 8x 8 8x 8 30 45 60 8x12 8x12 40 60 80 8x12 10x12 50 75 100 12x12 10x15 60 90 120 12x12 12x15 80 120 160 12x16 14x18 100 150 200 12x20 16x20 120 180 240 14x20 16x24 140 210 280 16x20 20x24 Heating Effect of an Indirect Radiator. — It is usual to assume that the air enters the radiator at zero 70 Notes on Heating and Ventilation degree of temperature, in which case it will leave the radiator at about 130 degrees, the steam pressure in the radiator being 5 pounds and the velocity through the radiator being 200 cubic feet per hour per square foot of radiator. Under the above conditions an ordi- nary pin radiator will give ofif 470 B. t. u. per square foot, or, say approximately, 450 B. t. u. Under these conditions the air entering the room will be at a temperature of 130 degrees, and if the tempera- ture of the room is TO degrees this air will be capable of losing to the room 60 degrees, or, in other words, there 'is. 60 degrees of temperature available in this air for heating purposes, or of 450 B. t. u. given out by the radiator 210 B. t. u. are available for heating the room. SOME RULES FOR INDIRECT HEATING. Rule 1. — For ordina/ry rooms. Divide the ivall sur- face by 4, add the glass surface, and multiply the sum by .6. The quotient will be the amount of indirect radiation necessary to heat the room. B. — For entrance halls. Diznde the exterior wall sur- face by 4, add the glass surface and multiply the sum by .75, the product ivill be the number of square feet of indi- rect radiation. Rule 2. — Figure the heating surface the same as for direct heating. Add 40 per cent. Rule 3. — Divide the volume of the room by 40. The quotient is the square feet of indirect surface required to heat the rooms on the first floor. For second and third -floor rooms divide by 50, and in stores and large rooms divide by 60. Example of Indirect Heating. — Take the same house 71 Notes on Heating and Ventilation that was used in the problem for direct heating. In this case all rooms are to be heated by indirect radiation. It is in actual practice an unusual arrangement, but it is fig- ured out in this way as an illustration merely. The heat loss in this house will, of course, be the same in both direct and indirect heating and is given in Table XXI (p. 58). Assume that the air enters the radiator at zero degrees and leaves at 130 degrees ; that the steam in the radiator is at 5 pounds pressure and that 200 cubic feet of air is passed through the radiator per square foot of surface. From the results determined in paragraph headed ''Heating Effect of the Indirect Radiator" each [ square foot of radiation gives approximately 450 B. t. u. If the temperature of the room is 70 degrees only \\,-> 60 degrees of the heat given to the air is effective in heat- ^ ing the room. As the total amount of increase in tem- perature is 130 degrees, only approximately 60-i-130, or p 45 per cent, is available for heating. Each square foot ' ^ of indirect radiation gives off .450 B. t. u., 45 per cent of 450, or 200 B. t. u., will be available for heating y ' the room. The heat loss as given m the table for the parlor is 10,395 B. t. u. Dividing this by 200 gives 52, the number of square feet of radiation required for the room. TABLE XXVI.— RESULTS OF COMPUTATION, INDIRECT STSTEM. B. t. u. Size of Volume Lost Radiator Area Hot Area of Per Hour. in. Sq. Ft. Air Blue. Vent Flue. Room. First Floor — Parlor 10,395 50 100 12x12 900 Sitting room 7,035 35 70 8x12 700 Dining room 8,085 40 80 8x12 720 Kitchen 10,300 50 100 12x12 1,000 Hall, 2d floor... 15, 800 73 145 12x12 1,500 Second Floor — W. chamber, alcove 19,370 93 180 12x20 1,600 So. chamber.... 7,035 35 70 8x12 700 N. chamber 8,190 40 80 8x12 750 Bath 3,465 17 40 6x 8 800 E. chamber 5,250 24 50 6x8 600 72 Notes on Heating and Ventilation Size of Hot Air Pipe. — Fifty-two square feet of radiation passing 240 cubic feet of air per square foot will pass 12,480 cubic feet of air per hour; 12,480 is 3.47 cubic feet per second. Allowing a velocity of 5 feet per second, the area of the hot air pipe is 3.47-i-5=.69 square feet. This equals 99 square inches, which is the proper area of the pipe. The size of the cold air pipe leading to the radiator is usually made the same size of the hot air pipe. Table XXVI gives the results for the whole house computed in the same manner as given above. In the table the odd figures and decimals have been left ofif. In selecting the size of radiator for a room, it is neces- sary to select those that vary by 10 square feet or more, as indirect radiator sections are not made smaller than 10 square feet per section. In a house where the radi- ators would be less than three sections, it is necessary to put two or three rooms on the same radiator, as it is not desirable to make very small indirect stacks. There is always danger, however, in taking the heat for two sep- arate rooms ofif the same radiator, that the heat will not distribute equally between the two rooms. When sep- arate rooms are heated from the same radiator, care should be taken to see that pipes leading to the two rooms have about the same length and as nearly as pos- sible the same resistance. Combination of Direct and Indirect. — A much more common arrangement of indirect radiators is to put in just enough indirect radiation to give the proper amount of air for ventilation and supply the additional heat for the room with direct radiation. Each system is installed as though the two were separate, except that they take 73 Notes on Heating and Ventilation their .steam from the same steam mains and return into the same return pipes. In this system the direct radi- ators can be installed on the one-pipe system, but the in- direct should be installed on the two-pipe system, as in- direct radiation does not work well on a one-pipe system. Fig. 22. Arrangement of Flue Radiator. It is not necessary to put indirect radiation into all the rooms of a residence. They are put into the princpial living rooms, the hall and the large bedrooms. Where the house is small it may be necessary to put indirect ra- diation only in the sitting room and in the hall. An ex- 74 Notes on Heating and Ventilation ample of this kind will be taken up under the head of ventilation. Flue Radiators. — Where only a small quantity of air is needed for ventilation flue radiators may be used in place of indirect radiators as shown in figure 22. The damper in the outside wall regulates the amount of air passing into the room and in extremely cold weather this may be entirely closed. Table XVI on page 50 shows the heat loss from this type of radiation and the amount of air that the flues will pass. In figuring this type of radiation figure the same as for direct radiation and add 25%. Each 30 square feet of flue radiation will furnish ventilation sufficient for one person. 75 CHAPTER V. STEAM BOILERS. Types. — Boilers are divided into two general classes — fire tube or tubular, and water tube or tubulous boilers. The commonest form of boiler used for heating purposes in this country is what is known as the return flue fire tube boiler. These boilers are adapted to plants of over 30 and under 150 horsepower and where the pressure does not exceed 100 pounds. For pressures above 100 pounds it is customary to use water tube boilers. There is one exception, that is the Scotch marine boiler, which is a fire tube boiler and which can be made to with- stand pressures of 200 pounds and over in large sizes, as in this boiler the fire does not come in contact with the outside shell. For heating purposes there have been introduced a number of special forms of boiler, a great many of these forms being built of cast iron. Cast iron boilers are not usually operated at pressures exceeding 10 pounds. Any of these forms of boilers may be used for heat- ing, the selection and the proper form will depend upon the conditions in each particular case. In selecting a boiler the following points should be taken into consid- eration : The boiler must be of sufficient strength to withstand the maximum pressure to be carried. This does not usually exceed 10 pounds. It must have suffi- cient heating surface in proportion to the grate surface to be economical. The stack temperature in a low pres- sure boiler should not exceed 500 degrees. The boiler must have sufficient liberating surface so that the steam formed in the water may escape from the surface of the 70 Notes on Heating and Ventilation water, without carrying a large quantity of water with it. The boiler must have large circulating areas so that the water may be circulated freely to the heating surfaces and the steam formed may pass away from the heating surfaces without restrictions. The steam that forms o« the heating surfaces rises in bubbles and is liberated from the surface of the water. If the boiler has insufficient liberating surfaces or the circulating areas are contracted the steam cannot rise rapidly enough and bubbles of steam remain on the heated surfaces. These bubbles pre- vent the water from reaching the heating surfaces and as steam is a poor conductor of heat this results in an over- heating of these surfaces. This trouble may be very serious, especially in the water tube type of boiler, and results in the burning out of the tubes. In cast iron boilers the lack of proper liberating surfaces and suffi- cient steam space often causes excessive priming. The question of circulating area and liberating surface is of more importance in a low pressure boiler plant than in a high pressure plant, as steam at 5 pounds pressure has about six times the volurne of steam at 100 pounds pres- sure ; so that to have relatively the same circulating area and liberating surface in a low pressure boiler, we should have five times as much as in a high pressure boiler. In boilers for heating purposes it is desirable that they should have sufficient steam space, and a large storage of water, particularly if the plant is to be continuously oper- ated. In boilers having large water storage it is possible to maintain a steam pressure on the boiler all night un- der banked fires. Where boilers are to be operated only occasionally, it may be desirable to have a small quanti- ty of water, as each time the boiler is started it is nec- essary to heat all tlie w^ater in the boiler before steam is 77 Notes on Heating and Ventilation formed. The ordinary fire tube return flue boiler, on ac- count of its large water storage, liberal circulating areas and large liberating surface, is a desirable one for heat- ing purposes in large buildings. Proportion of Boilers. — The heating surfaces in a boiler are those surfaces which have water on one side and hot gases on the other. A boiler should be so pro- portioned as to transmit as much of the heat generated by the fuel to the water as possible. Experience has de- termined that for best results in boilers of 50 horse- power and over a square foot of heating surface should evaporate not more than three pounds of water per square foot of heating surface. For small houses, where heating boilers of but a few horsepower are used, it is not usual to allow a square foot of heating surface to evaporate more than 2 pounds of water and when a square foot of heating surface evaporates more than the amounts given above, the transmission of heat through the plate becomes so rapid that all the heat is not re- moved ; the result is an excessively high stack tempera- ture and a corresponding los^ of heat. Surfaces that have steam on one side and hot gases on the other are called superheating surfaces. It is not advisable to have superheating surfaces in a boiler. Small heating boilers are distinctly different from power boiler or heating for large plant. In large plants coal is being fed to the boiler almost continu- ously and the flues are carrying a large quantity of gases. Small house heating boilers are fed at infre- quent intervals and the flues of these boilers do very little of the work of transmitting heat. In small boil- ers a distinction must be made between the flue sur- face and the fire surface. The fire surfaces are those 78 Notes on Heating and Ventilation heating surfaces upon which the rays of radiant heat from the fire impinge directly. During the periods r/hen the drafts are closed most of the steaming in the boiler is produced by the fire surface, it is there- fore important in a "house heating boiler to have a large amount of fire surface as compared with the flue surface. It is good practice to have 60 per cent fire surface and 40 per cent flue surface in cast-iron house heating boilers. The proportion of grate surface to heating surface depends upon the kind of fuel and the intensity of the draft. In small boilers used for heating purposes it is usual to allow one square foot of grate surface to every 15 to 30 square feet of heating surface. For boilers 50 horsepower and over it is usual to allow from 30 to 40 square feet of heating surface per square foot of grate surface and in very large boilers the ratio is 50 to 60 square feet of heating surface per square foot of grate. The rate of combustion for anthracite coal will vary from 2 to 6 pounds of coal per square foot of grate surface per hour with average draft. With bituminous coal under similar circumstances, 3 to 8 pounds will be burned in the smaller boilers and 8 to 15 pounds in the larger sizes. The air opening to be allowed in the grates depends upon the kind of coal, but usually does not exceed 50 per cent of the area of the grate. Anthracite and the better grades of bituminous coal do not require as large opening as do the slack coals. The term boiler horsepower as applied to boilers has no definite value and varies with local customs, and the opinion of the manufacturer. 79 Notes o n Heating and Ventilation Boiler Horsepower. — The rating of a boiler should be the amount of steam it can evaporate with good economy and without producing wet steam. In pur- chasing a boil*er specify the number of square feet of grate surface the boiler should contain. This is a better criterion of the work that the boiler will do than the horsepower rating. The American Society of Mechanical Engineers has adopted the following rating for the horsepower of a boiler: A boiler horsepower is 34^ pounds of wat^r evap- orated from feed zvater at 212 degrees, to steam at 212 degrees, which is called the from and at evaporation. According to this rule, if three pounds of water are evaporated per square foot of heating surface, we would allow from, 10 t^o 12 square feet of heating surface for each boiler horsepoiver. The American Society of Heating and Ventilating Engineering recommended the following ratings for cast-iron house-heating boilers : TABLE XXVII. Rating of Hovise- ■Heating Boilers. Area Coal Burned Total Coal of per Hour Burned Rating of Grate. per sq. ft. of Grate per Hour. Boiler. Sq. Ft. Lbs. Lbs. 1 2.67 2.67 82 1.5 2.96 4.44 140 2 3.59 7.18 226 3 4.21 12.63 390 4 4.55 18.20 585 5 4.88 24.40 780 6 5.06 30.36 975 7 5.24 36.68 1,165 8 5.36 42.88 1,405 9 5.48 49.32 1,650 10 5.60 56.00 1,890 11 5.71 62.81 2,125 12 5.82 69.84 2,360 13 5.93 77.09 2,595 14 6.08 85.12 2,915 15 6.23 93.45 3.235 16 6.35 101.60 3,485 17 6.46 109.82 3,730 18 6.51 117.18 4,010 19 6.55 124.45 4,285 20 6.58 131.60 4,545 21 6.61 138.81 4.800 80 Notes on Heating and Ventilation In compiling the table it is assumed — 1. That the area of the grate shall be the area of the opening in which the grate is placed, measured to the outermost limits of air openings. 2. That the boiler is to be used under average working conditions, carrying steam at 2 pounds pres- sure; that the draft shall be sufficient to burn the number of pounds of coal per hour given in the table, and that the coal used shall be a good quality of anthracite coal having a heating power of 13,000 B. t. u. per pound of dry coal. 3. That the rating as given in the table means the number of square feet of direct radiation steam sur- face that can be carried by the boiler, based upon the supposition that each square foot of direct radiation steam surface emits 250 B. t. u. per hour with steam at two pounds pressure in the radiator and with air surrounding the radiator at a temperature of 70 de- grees. CHAPTER VI. STEAM PIPING. In designing a system of steam piping the three fol- lowing considerations are the most important : First, that the piping shall be so arranged that all condensed water shall drain from it ; second, that it shall be free to expand, that is, so arranged that the joints shall not be strained when the piping is heated ; third, that all points in the piping at which air would accumulate shall be provided with some means of removing the air. In this text the different parts of the piping system referred to will have the following meaning: Mains. — Mains are those pipes which lead from the boiler or boiler header to the submains or risers. Usu- ally there are no radiators tapped from these mains. Risers. — Risers start from the mains in the base- ment or attic, and extend up or down through the build- ing. From the risers the connections to the individual radiators are taken. Returns. — All piping carrying condensed water from the steam mains to the boiler is included in the return system. The terms return riser, return main, etc., have the same significance as in the steam system. Reliefs or Drips. — A small pipe connecting the steam to the return system so as to carry condensed wa- ter to the returns is called a relief or drip. Drips are used at all points where water would collect in the steam system. These drips are sometimes made of large pipe and called equalizing pipes, serving to equalize the pres- sure between steam and return mains in gravity return systems. 82 ' ^ Notes on Heating and Ventilation Pitch. — The pitch of a pipe refers to its indination from the horizontal pipe lines. It is best that pipes should pitch with the current of the steam, so that the steam will assist in the removal of the condensation. Return pipes are usually pitched toward the boiler so that the system may be drained at that point. Water Line. — The water line is the height at which the water stands in the return pipes. In a well designed gravity system it is seldom more than twelve inches above the water line of the boiler. Siphon. — When a vertical bend is made in the return main so that the return dips down and returns to its former level, it is called a siphon. All siphons should be provided with a drain (or pet cock). Dams. — Sometimes the water level in the boiler is lower than that desired in the piping system and an in- verted siphon is placed in the return pipe. No return will then take place until the water has reached the highest point of this bend in the return. A dam should be provided with an air cock. Water Seal. — Where a return pipe enters the return main below the water line it is said to be sealed. It is customary to seal all main riser drips and returns from indirect radiatprs and pipe coils. Water Hammer. — The rattling and the hammering often heard in pipes is called water hammer. It is caused by steam coming in contact with water or surface in the pipes which is colder than itself. A sudden condensa- tion results and a vacuum is produced into which the water rushes. The blow is often so severe as to crack the fittings and spring the valves. It is most apt to oc- cur when the plant is first started. Accidents from this cause may be avoided by admitting the steam very slow- 83 Notes o n Heating and Ventilation ly at first and draining low points in the piping system. Steam Traps. — Steam traps are vessels usually placed between the steam and the return system to allow the water of condensation to be carried to the return sys- tem without steam entering the returns. Bv the use of Fij. 23. steam traps the steam and return mains may have a wide difference of pressure. Steam traps are objection- able as they are liable to get out of order and require frequent repairs. Systems of Piping. — The systems of piping may be grouped under three general heads. First, the one- 84 Notes on Heating and Ventilation pipe system. In this system the pipe carrying the steam to the radiator also returns the condensed water from the radiator to the boiler. Second, two-pipe system, in which one set of pipes is used to carry the steam to the radiator and an entirely separate set of pipes is used to carry the return water to the boiler. Third, a com- bination of these two systems. The usual arrangement in the combination system is to run the mains on a two- pipe system, but the connection between the mains and the radiators is on the single pipe system. The one- pipe system has certain fundamental advantages over the two-pi])e system. In the one-pipe system the steam and condensed water are always at the same temperature and as a result there is very little opportunity for water hammer. In the two-pipe system the steam and water being separate the water may become considerably cooled below the temperature of the steam, and if at any point in the system it again comes in contact with the water we have condensation of the steam, vacuum forms, caus- ing water hammer. In large plants, however, the one- pipe system is not desirable, as it necessitates carrying a very large quantity of water in the steam mains. One-Pipe System. — The simplest of all piping sys- tems used in steam heating is what is known as the one- pipe gravity system. In this system, the steam gener- ated in the boiler flows through the pipes to the radia- tors where it is condensed. The condensed steam in the radiators flows back through the same piping system to the boiler. This arrangement necessitates the condensed steam flowing back against the current of the steam. This is objectionable, as there is a tendency to trap the water. Because of this tendency it is good practice to make the pipes larger in size than would be the case 85 Notes o n Heating and Ventilation if the steam and water flowed in the same direction. In the one-pipe gravity system the pipe should always be given a good pitch toward the boiler. Figure 23 shows in diagram the piping and radiator connections for a one-pipe system. Two-Pipe System. — In the two-pipe system one sys- tem of pipes supplies the steam and another system car- Fig. 24. ries off the water of condensation. The principal object in the two-pipe system is to avoid the accumulation of any great amount of water in the radiators or mains and in that way give a more positive circulation. Fig- ure 24 shows the general arrangement used in the two- Notes o n Heating and Ventilation pipe system. The indirect radiators and pipe coils should always be connected on the two-pipe system. Combination System. — In ordinary buildings the most satisfactory method is to use a combination of the one-pipe and the two-pipe systems. In this system, as Fig. 25. diagram in Figure 25, the radiators on the one-pipe system, while on tne two-pipe sys- shown in and risers are the mains are installed on the tem. The system has this advantage over the one- pipe system of mains, that the mains are not obliged to carry so much water of condensation and can be freecl 87 Notes o n Heating: and Ventilation from water from time to time. The one-pipe radiator connections of this system are more desirable than the two-pipe radiator connections in that there is but one valve to get into trouble instead of two and the steam and the water of condensation are always in contact with Fig. 26. each other — thus avoiding the danger of water hammer. The risers may be one-pipe, as it is very seldom that we have difficulty with the circulation in using vertical risers. In most cases the one-pipe radiator connections and two-pipe mains will be found to giv^ the best satisfac^ tion. 88 Notes o n Heating and Ventilation Overhead Distribution. — In office buildings and buildings where the basement space is valuable for rental purposes, it is desirable to place the steam mains where they will occupy the least desirable space. It is custo- mary to run a vertical steam main to the attic. A set of distributing mains is run through the attic, from which Fig. 27. vertical risers extend down through the building with drip pipes connecting to the return system at their low- er ends. The radiators are connected to the risers by means of single-pipe radiator connections. This system gives very satisfactory results as in all cases the cur- rents of steam and water are in the same direction. In buildings exceeding four stories in height it is usually necessary to provide some form of flexible connection 39 Notes on Heating and Ventilation to allow for expansion. A system of this kind is shown in Figure 26. Gravity System. — Figures 23-26, inclusive, are all shown for gravity return system and this system is the one commonly used for all small buildings and for resi- dences. In this system the steam and return mains are connected to the boiler without the introduction of pumps or traps, so that the condensed steam flows back to the boiler by gravity. Figure 27 gives a diagrammatic sketch of such a system. If the pressure at the surface of the water in the boiler is the same as the pressure of the surface of the water in the return mains, then the water level in the return mains and in the boiler will be the same. But if, as shown in Figure 27 by the dotted lines, the pressure in the boiler is 5 pounds and the pres- sure is only 4 pounds when it gets to the ends of the system, then the system is no longer balanced. It is nec- essary for the water to rise in the return mains until the column of water in the return mains is of sufficient height so that its weight will equal a pressure of 1 pound per square inch, or approximately, it must rise about 2.31 feet so that the water in the return main will be 2.31 feet higher than the water in the boiler, and this will be true for each 1 pound difference in pressure between the steam at the boiler and the steam at the ex- tremities of the system. It is necessary, then, to be very careful to have ample sized piping in this system so that the pressure at all points of the return main will be about equal. In addition, it is necessary that the steam radia- tors, both direct and indirect, be at least 2 feet above the water line. For the reasons given above it is not desir- able to operate large plants on the gravity return sys- tem, as this system requires larger expense for steam do Notes on Heating and Ventilation mains and more or less difficulty will always be experi- enced in starting up the system. The systems of circu- lation involving traps and pump circulation will be taken up under the head of Central Heating Systems. Size of Steam Return Mains. — There are a great many rules given for determining the size of steam and return mains, all of which must be more or less modified to meet the particular case in hand. In fact, a very careful determination of the size of main is not necessary, as, no matter how carefully we calculate the size of the main, it is necessary to take the nearest pipe size. In determining the size of the main two conditions must be considered. First, it must be of sufficient capacity to al- low of free circulation. This is the principal considera- tion in smaller buildings. Second, the mains must not produce more than a certain drop of pressure. This point is of particular importance in the design of central heating systems. In the case of residences, the size is determined by rules determined by practice. In the second place, the laws governing the amount of pressure in steam pipes are fairly well known. They will be treated under the head of Central Heating Systems. The most rational method of finding the size of mains is by determining the velocity of steam passing in the main. Knowing the weight of steam passing in the main and having the pressure, the volume of steam passed through the main is known. This volume divided by the allow- able velocity in feet gives the area of the pipe in square feet. The velocities allowed in various forms of mains are as follows: In the steam engine connections from 75 to 100 feet per second. In exhaust steam mains from 75 to 150 feet per second. n Notes on Heating and Ventilation For steam heating work on the one pipe system, pipes 2 inches and nnder 10 feet per second. For two- pipe work, pipes 2 inches and under 15 feet per second. For two-pipe work, pipes 2 to 4 inches 25 feet per second. For single-pipe work, low pressure, pipes 2 to 4 inches 15 feet per second. For single-pipe work, low pressure, pipes 4 inches and over 30 feet per second. Example. — Assume that a main is to supply 2,000 feet of radiation. This radiation gives off approximately 1.70 B. t. u. per square foot of radiating surface per degree difference of temperature. Let the tempera ture of the steam be 220°, the temperature of the room 70°. Then the total B. t. u. transmitted per hour will be 220—70X1.70X3,000=510,000. At 220° the latent heat of steam taken from the steam tables equals 966 B. t u. Then the steam used per hour will be 510,000^966=527 pounds of steam. At 220° each pound of steam has a volume of 22.95 cubic feet. Hence we have 527X22.95=12,000 cubic feet per hour or 3.3 cubic feet per second. For a velocity of 25 feet per second we must have a pipe with an area of .132 square feet or 19 square inches. This is approxi- mately the area of a 5-inch pipe. Miscellaneous Rules for Size of Steam Main. Rule 1. — The following is a very common rule for gravity return systems: To determine the diameter of the main leading from the boiler, point off two places in the number expressing the radiating surface and take the square root of the remainder. To apply the above rule for indirect surfaces, multiply the indirect sur- , 98 Notes o n Heating and Ventilation face by seven-fifths and proceed as for direct sur- face. As an example, suppose we are to supply 2,000 sq^uare feet of direct radiation. We point off two places, which gives us 20. The square root of 20 is 4.48, which would make the size of the main 4^ inches. Table XXVIII gives the common practice in pipe sizes : TABLE XXVIII. No. of Sq. Ft. Steam of Radiation Single Steam Main Steam Riser Steam Riser on the Pipe Two Pipe Single Pipe Two Pipe Main or Riser. System, System. System. System. 50 11/^ inch liA inch 1 14 Inch liA inch 100 2 inch 1% inch 1% inch 1% inch 150 2 inch 1% inch 2 inch 1% Inch 200 2^ inch 2 inch 2^4 inch 2 inch 250 21/^ inch 2 inch 2V2 inch 2 inch 300 3 inch 2^ inch 3 inch 2h■/ ;/ Fig. 31. The Simplest Form of Connection. Not Desirable if Ex- pansion at Riglit Angle is Great. by having frequent risers with shorter radiator con- nections. Where risers are concealed in a building of wooden construction they should be carefufly protected from the woodwork, CONNECTIONS TO MAINS AND TO RISERS. In making the connections from mains to risers in a steam system there are three things to be considered — the drip, the expansion, and free circulation. The sim- 99 Notes on Heating and Ventilation plest form of connection in shown in Fig. 31, and for general purposes it is perhaps the best form of con- nection. The expansion of the main in the direction of its length is taken care of by turning in the threads of the vertical pipes. The expansion at right angles to the main, which is ordinarily very small, is taken care of by the spring of the pipes. If the expansion occurring at right angles were very large, then some other form of connection would be desirable. y?/ser '"n\ mill" iiWBijiiiiiiLi Bii]»«/uy<) WWWWMWWMIlilHHlMilli nnMiiimrmi iWIKrii l^«ll\ /^a //? Fig. 32. Using a 45° Ell Instead of a 90°, as Shown in Fig. 31. Fig. 32 shows a similar connection, but using a 45- degree elbow in space of a 90-degree elbow at the main, as shown in Fig. 31. This connection offers less resist- ance to the passage of steam than the connection shown in Fig. 31 ; on the other hand, it does not allow of as much expansion. The pipe rising from the main be- ing at 45 degrees, there is a limited opportunity for any turning in the threads of the pipe and expansion is taken up by the spring of the pipe. In this figure a drip is shown at the bottom of the riser. A drip is often placed at this point, particularly in large buildings. In smaller 100 Notes on Heating and Ventilation plants condensation is carried back through the steam connection itself, as in Fig. 31. In larger buildings it is undesirable to carry so much condensation through the horizontal pipes and a drip is placed at the bottom of the riser, as shown in Fig. 32. Fig. 33 shows a connection similar to that in Fig. 31. It allows free expansion of the main, the same as Fig. 31. In Fig. 3'^ all the condensation which has occurred Fig. 33. Allows for Expansion of the Main; Requires a Drip at the Point where Riser Starts. in the main up to this connection will drain into the connection and it is therefore necessary to place a drip at the point where the riser starts. A connection of this kind is often used where it is desired to meter different riser connections for different consumers, then the con- densation for each riser or each set of risers can be col- lected and metered with very little possibility of its com- ing back into the main. This is, in some respects, an undesirable form of connection. If for any reason the water level rises in the return system above the hori- zontal pipe connection to the riser, then the riser will be 101 Notes on Heating and Ventilation entirely sealed from the main and it will be impossible to get steam into the riser. The writer has experienced this difficulty in places where it was necessary to use this Af^j. Tf^ser ^ *:.*!■ :.<'jittllfJI,i,UI/ll/lJJl,,,,,,,,,,,,,,,n,..,,,.,,,.,,,.,,,ijj,ji.j,....,,,j,,,n,,,,,,..,,^ WilH/itJNUti Fig. 59. of streams in different directons throughout the room. This arrangement of inlet and outlet registers is the usual one for school buildings. It is preferable to have the inlet and outlet register on the inside walls opposite the window surfaces and both registers on the same wall. This, however, is not absolutely necessary. The inlet and outlet registers should never be on the outside walls. Where the inlet register is placed, on the floor J50 Notes on Heating and Ventilation and the outlet register at the ceiling then the air com- ing from the inlet register will pass directly to the outlet register and a large proportion of the heated air be lost ; in addition there will be very little circulation of air in the room, as shown in Fig. 58. In rooms for restaurant purposes, where smoking is allowed or in smoking rooms or in kitchens, the air must be taken ofif the ceiling, as, the foul air, being warmer, rises to the ceiling. In this case it is necessary to bring the ventilating air in at the baseboard, at a very low velocity and at a number of places and take the air out at definite points near the ceiling, as shown in Fig. 59. In theaters and churches special means must be employed for securing ventilation. It is customary to admit the air in a large number of places. Some- times this is done by means of a large number of small registers placed directly under the seats. Care, how- ever, must be used in doing this to avoid drafts. An- other method is to employ a large number of openings around the sides of the room. The air is usually taken oflf near the stage at the lowest point in the auditorium. There should be provided in all auditoriums some means of taking the air ofif the ceiling, as oftentimes the heat given ofif by the occupants of the room is more than sufficient to heat the room, and in addition we have the heat given ofif by the sources of illumination. This heat can be best taken care of at the ceiling line, which is naturally the warmest point in the room. 151 CHAPTER X. DESIGN OF HOT AIR HEATING SYSTEM. Design of Hot Air System. — In a hot air furnace the cold air from the outside is passed over heated iron surfaces, usually enclosed in galvanized iron or brick walls. The space between the walls and hot surfaces of the furnace is connected to the outside air at the bottom and at the top. to the flues leading to the rooms. The amount of air circulating through the furnace will depend upon the temperature of the hot air leaving the furnace and the height and resistance of the flues. In order that the air in a room may be quickly replaced by warm air it is necessary that the room be provided with a foul air flue. A great many of the difficulties that have been expe- rienced with the hot air system as ordinarily installed are due to the sharp competition in business, which has resulted in the erection of plants of inferior workman- ship and design. One of the commonest mistakes is the installation of a furnace much too small to do the work properly. The result of putting in a small fur- nace is that the fire must be continually crowded so that the heating surface is at high temperature and a large amount of the heat of the coal is wasted in excessive stack temperature. The hot air system with natural draft should not be used in houses where the horizontal portion of the hot air flues would exceed 20 feet in length. In very large houses two or more furnaces may be used to avoid excessive pipe resistance. 152 Notes on Heating and Ventilation Hot Air Furnaces. — Hot air furnaces are as varied in types as are steam boilers. They are made either of cast iron or steel. It is difficult to decide between the merits of these two materials. Cast iron is less lia- ble to be rapidly deteriorated by rust when the boiler stands in the summer, but it is more easily broken either by misuse or shrinkage strains in the castings. There is no essential difference between the metals in their conducting capacity as applied in these furnaces. It is very important to see that the furnace is so con- structed that the joints between the fire-box and hot-air chamber are tight, so that the air entering the rooms may not be mixed with gases of combustion. This is one of the most difficult things to prevent in the hot air furnace. Joints should be as few as possible and ver- tical joints should be avoided. The introduction of mois- ture into the air passing through the furnace is an im- portant consideration and will be treated in a separate paragraph. The builders rate their furnaces at about their maxi- mum capacity-. The rating being expressed as the num- ber of cubic feet of building volume the furnace will heat. In selecting a furnace it is wise to have 25 to 50 per cent excess capacity in the furnace over the build- er's rating. The fire pot of a furnace should be slightly conical in shape and should be large enough to contain sufficient fuel to last eight hours. The rate of combustion on the grate should be taken at not to exceed 4 pounds of coal per hour. A high temperature of combustion is usually desirable for the best economy, but the stack gases should not exceed 500°. The air space between the furnace and the outside 153 Notes on Heating and Ventilation casing should have at least 25 per cent more cross- sectional area than the leader pipes taken from it. A furnace should be proportioned so that the air leaving it should not exceed 180° in temperature. There should be one square foot of grate for every 30 to 50 square feet of heating surface in the furnace. Each square foot of heating surface may be assumed to give off 1,000 to 1,500 B. t. u. per hour. A furnace should be provided with some form of shaking and dumping grate which is easily cleaned. In addition to draft doors admitting air below the grates, the furnace is usually provided with a check damper in the smoke pipe. The draft door and check damper are arranged so that they may be controlled by chains situated in some convenient point in the room above. Necessity of Supplying Moisture to Heated Air. — It is very important that air after being heated by the furnace pass over the surface of a pan of water so that it can take up moisture. One pound of air at 32° F. will hold in the form of a vapor .003 of a pound of water, and at 150 degrees it will hold .22, or about 70 times as much. If then we take air saturated with moisture at an outside temperature of 32 degrees and heat it up to 150 degrees we have increased its capacity for moisture 70 times. On entering the rooms if the air has not been given opportunity to take up moisture it will take it up from the objects of the room. This drying effect of the air injures the furniture and wood- work and affects the persons occupying the room, pro- ducing a dry throat and a feeling of cold due to rapid evaporation from the skin. The usual method of overcoming this is to have a pan 154 Notes on Heating and Ventilation filled with water situated in the furnace near the fire- box. This, however, is the wrong end of the furnace to place the pan, as the air entering is coolest at this point. The water should be added to the air as it leaves the furnace. In some hot air installations every pipe leaving the furnace has a trough in it, which is filled with water, and from this water the air takes up its moisture. Cold Air Duct. — The cold air supplied to the fur- nace is usually taken from one of the basement win- dows and brought to the furnace through a tile or wooden duct lined with galvanized iron ; where a tile duct is used it is placed below the level of the cellar floor. The cold air should be taken from the side of the house that 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 area of the hot air leaders leaving the furnace. It is well to provide some means of recirculation of the air in the house through the furnace. The air for recirculation is usually taken from the Hall. If it is desired to recirculate partially and take the balance of the air from outside, the recirculating pipe should be brought to the furnace separately, and a deflecting plate placed in the air space under the furnace. If this is not done the air will come in from the outside and may pass up the recirculating pipe instead of going to the furnace. If, however, the recirculating pipe is only to be used when the cold air pipe from outside is closed, then the recirculating pipe can be conducted into the cold air 155 Notes on Heating and Ventilation pipe directly. In this case the cold air pipe and recircu- lating pipe must both be provided with dampers. The cold air pipe should have at least three-fourths of the combined areas of the hot air pipes. It is a common error to make the recirculating pipe of a furnace system too small. The recirculating pipe -should be not less than three-fourths the area of the cold air pipe. It is better to have it equal in area to the cold air pipe. Hot Air Leaders and Flues. — The furnace should be centrally located, or if the coldest winds come from a certain direction, it can be located more on that side of the house from which the cold winds come. The hot air flues leading from the furnace should be as short and direct as possible ; long horizontal pipes should be avoided. Horizontal pipes should pitch sharply towards the furnace, three-quarter inch to the foot is good prac- tice. All hot air pipes should have nearly equal resist- ance to the passage of the air. The hot air flues should have as few and as easy turns as possible. They should never be placed in the outside walls. Uptake flues of any kind in outside walls seldom draw satisfactorily. The hot air flue should enter the room in most cases opposite the largest exposed glass surface or some dis- tance from it. The circulation of air in the room would be best if the hot air entered near the ceiling. The prin- cipal objection to this is that the register in the wall is apt to blacken the wall and it does not allow people to warm themselves over it. Floor registers are very objectionable as they always serve as receptacles for all kinds of rubbish and sweepings. Dampers should be provided in all pipes leading to 156 Notes on Heating and Ventilation rooms above the first floor. If all the registers are pro- vided with dampers there is danger of burning the fur- nace, due to shutting off all the passages for removing hot air and preventing circulation in the furnace. It is good practice to have no valve in the hall register so one pipe will always be open. Proportions of Hot Air Flues. — The velocity of air for first floor leaders may be calculated as three or four feet per second, second floor four to five feet per second, third floor and floors above five to six feet per second. The flues leading to the second and third floor room may have a velocity as high as 400 feet per minute. In the best installations the leads and flues are double walled with asbestos between the walls. The cross- sectional area of all the leaders should be from 1.1 to 1.5 times the area of the grate. The registers should be proportioned so as to give a velocity of two to three feet per second on the first floor and three to four feet per second on the floors above. The effective area of the ordinary registers is about 50 per cent of the actual area, taking outside di- mensions. H. B. Carpenter, in a paper before the Society of Heating and Ventilating Engineers (Transactions, vol. 5, p. 77), gives the following rule for finding the cubic feet of air passing through pipes per minute : To the first floor multiply the area in inches by 1.25. To the second floor multiply the area in inches by 1.66. To the third floor multiply the area in inches by 2.08. It is good practice to figure on changing the air in the principal rooms five times per hour in hot air heating. Foul Air Flues. — The foul air flues should be placed 157 Notes on Heating and Ventilation in the inside walls and with foul air registers at the baseboard. The reason being that the hot air entering the room opposite the window surfaces rises to the ceihng, passes along the ceiling to the windows and is cooled. It then drops to the floor line, passes along the floor and out the foul air register. The hot air reg- ister should be a sufficient distance from the foul air register so that the hot air will not pass directly to the foul air flue. A cheap foul air flue can be made by having a register in the baseboard opening into the spaces between the studs, selecting a space that is open to the attic, a ventilator is placed on the attic space and discharges foul air out of doors. No two rooms should open into the same studding space. A still better draft can be produced by extending each flue separately by galvanized iron pipe to the ventilator. If no ventilating flues are provided, it is very difficult, especially if the house is tight, to get a proper circulation of hot air from the furnace; you cannot put hot air into a room if there is no provision for taking cold air out. The area of these foul air flues should be not less than 80 per cent of that of the warm air flues and they are often made equal in area to the area of the warm air flues. A fireplace makes one of~ the best forms of foul air flue. In a house well provided with fireplaces, it is often not necessary to provide any other foul air flues. General Proportions of Hot Air Systems. — The size of the hot air flue, vent flue, hot air register, heating surface and grate surface in the furnace is given in Table XLI. This table is given for rooms of average proportion and under average conditions. 168 Notes on Heating and Ventilation TABLE XLIII.— PROPORTIONS OF HOT AIR HEATING SYSTEM. Contents of Room in Cubic Feet. 500 1,000 1,500 First Floor — Diameter hot air flue, In 6 8 9 Diameter foul air flue, in 6 8 9 Second Floor — Diameter hot air flue, in 6 7 8 Diameter foul air flue, in 6 7 8 Grate area in furnace, sq. in 25 50 76 Heating surface in furnace, sq. ft 5 10 15 2,000 . 2,500 3,000 3,500 4,000 5,000 6,000 8,000 10,000 10 ' 11 12 13 14 16 17 20 24 10 11 12 13 14 16 17 20 24 9 10 11 11 12 14 15 18 20 8 ■ 9 9 10 10 12 12 14 16 100 125 150 175 200 250 300 350 40U 20 25 30 35 40 50 62.5 SO 100 The following assumptions have been made the above table : Temperature outside air, degree ; temperature of air in the room, 70 degrees ; changes of air in the room, three times per hour. Velocity of air in hot air flues, 1st floor, 3 ft. per second. Velocity of air in hot air flues, 2nd floor, 4 ft. per second. Velocity of air in four air flues, 1st and 2nd floors, 3 ft. per second. Temperature of air entering the room, 160 degrees. Proportion of grate surface to heating surface, 1 to 30. Pounds of coal burned per square foot of grate sur- face per hour, 3. Suggestions for Operating Hot Air Furnaces. — The temperature of the rooms should be regulated by the drafts of the furnace as much as possible. The heating surfaces of the furnace should never be brought to a red heat. If it is necessary to do this to keep the rooms warm, the furnace is too small. Ashes should be frequently removed from the furnace, as an accumulation of ashes may burn out the grate. Never shake the fire more than is necessary to expose 159 Notes on Heating and Ventilation the red coals to the ash pit. The furnace should be cleaned at least once a year. The water pan of the fur- nace should be kept full of water, ROUGH RULES FOR HOT AIR SYSTEM. 1. The volume of the house divided by 50 equals square feet of heating surface in furnace radiator. 2. The volume of the house divided by 20 equals the number of square inches of grate area in the furnace. 3. Divide the volume of the room by 20 and the square root of the quotient will be the diameter of the furnace pipe for the first floor room. For second floor rooms divide the volume by 25 and the square root of the quotient will be the diameter of the furnace pipe. Example of Hot Air System. — As an example of the hot air system applied to the ordinary dwelling, take the same house that was used as an example of direct steam heating. The heat lost from the rooms would be the same as in the case of direct steam. As an example of an individual room take the parlor. From Table XX we see that the volume of the parlor is 1,665 cubic feet and the heat lost 10,395 B. t. u. per hour. In figuring the heating system for the parlor the following assumption will be made : The hot air enters the room at 160°. Cold air enters the furnace at 0°. The temperature in the room is 70°. Then the ^ air entering the room i^s reduced in temperature 160— ^g;>I^ 70=90°. Each pound^of air on having its temperature reduced 90° would give up .2375X90=21.4 B. t. u. Then there will have to be introduced into the room to supply heat lost from the room 10,395-1-21.4=485 pounds of air per hour. At atmospheric pressure a pound of 160 Notes on Heating and Ventilation air occupies approximately 13 cubic feet, hence 485 pounds of air is equal to 6,300 cubic feet. This is the amount of air which must be deHvered to the room per hour; 6,300 cubic feet of air per hour is equal to 1.75 cubic feet per second. Allowing a velocity of 3 feet per second, the area of the pipe would be 1.75^3 = . 58 square feet, which is equivalent to 84 square inches, or approxi- mately the area of a pipe 10.5 inches in diameter. To warm the air going- to the parlor would require 485 X .2375X160=:18,500 B. t. u. In a similar way the same quantities have been calculated for the other rooms. Except that for the second floor room, a velocity of 4 feet per second has been allowed. TABLE XLIV. B.t.u. Cu. ft. Diam- Volume lost. B.t.u. of air eter of from room given air entering of hot room, per hour, per hour. room, air pipe. First Floor. Parlor 1,665 10,305 18,500 6,300 lOVo Sitting room 2,100 7,035 12,500 4,350 9" Dining room 1,640 7,350 12,800 4.500 9 Kitchen 1,610 10,300 18,000 6,250 IOV2 Hall 1,210 7,035 12,500 4,350 9 Second Floor. West Alcove 1,320 10,050 17,900 6,200 9 Alcove 810 7,560 13,400 4,750 8 South chamber 1,560 7,035 12,500 4,400 8 North chamber 1,440 7,455 13,300 4,650 8 Bath 410 3,150 5,600 1,850 G East chamber 880 5,250 • 9,400 3,300 7 Halls 88 2.730 4,800 1,750 6 151.200 Column 3 of Table XLIV shows the heat which is left by the air in the room. Column 4 .shows the heat used to warm the air entering the room. The difference be- tween these two columns is the heat lost up the ventilat- ing flues. This loss should not be charged against the hot air furnace, but should be considered as the loss that must be charged to ventilation. The loss is about 44 per cent if the temperature of the outside air is at 0° 161 Notes o n Heating and Ventilation and the temperature of the air entering the room is 160°. As the temperature of the outside air or the incoming air is increased proportionately more heat enters the room and this loss becomes less. During the average winter weather the outside air is 35°, in which case the per cent of loss by ventilation, that is, through the ven- tilating flues, is about 30 per cent. Fig. 60. Summing up column 4 of the table gives the heat required to warm the air entering the entire house in zero weather or 151,200 B. t. u. If we assume that 80 162 Notes on Heating and Ventilation per cent of the coal goes into the heated air, then there will be required from the coal 151,200-^.8=188,500 B. t. u. per hour. A good anthracite coal contains about 13,500 B. t. u. ; then in zero weather this house would use 188, 500-f-13, 500=14 pounds of coal per hour. As the average loss from a house during the heating season is approximately 50 per cent of the loss during zero weather, the average consumption of coal in this house for the heating season would be 14X -5=7.00 pounds of coal per hour. Assuming the furnace to be operated 24 hours per day and 200 days per year, the coal consumption for this house would be 7 X 24X200 -f- 2,000=16.8 tons. Fig. 60 shows a cross section of a house with the hot air system installed. 163 CHAPTER XI. FAN SYSTEM OF HEATING. Where it is necessary to introduce large quantities of air into a building for the purpose of ventilation a natural system of circulation is out of the question and it is necessary to force the air into the building by some mechanical device. This is usually done by means of a steel plate blower which delivers the air with sufficient pressure to force the air into all rooms in the building. The pressure required in the average building does not usually exceed one-quarter ounce. -The mechanical sys- tem of ventilation has the additional advantage that its operation is entirely independent of the heating of the building and the building may be ventilated as easily in the summer as in the winter. The natural system of ventilation depends entirely upon the air in the flues being heated, and during the summer periods the system is inoperative. Systems of Fan Heating. — There are two general schemes of fan heating, one in which the air is heated to a temperature higher than that in the room, so that it furnishes enough heat to supply the heat lost from the walls and windows, as well as to furnish air for ventila- tion. In the other system the heat loss from walls and windows is supplied by direct radiation situated in the room and the fan supplies only the necessary amount of air for ventilation. In the latter system the air for ventilation is supplied at about the temperature to be maintained in the room. The first system, in which all the heat is supplied by means of a fan, is most applica- 164 Notes on Heating and Ventilation ble in buildings that must be heated and ventilated both night and day. Hospitals and asylums are buildings of this class. It has certain disadvantages, however. When a room has very large glass surfaces it is almost impos- sible with this system to prevent strong cold drafts com- ing down along the window surfaces. The system is in many cases wasteful. In order to heat a building it is often necessary to admit more air than is required for the purpose of ventilation, and all the heat put into the air to raise the temperature of the outside air to the temperature of the room is lost. On the other hand, this system requires but one system of heating, which makes it less expensive to install. The second system mentioned, where direct radiation and a fan are both used, is most applicable in buildings that require ventilation only part of the time. Schools, factories, office buildings are buildings that may be in- cluded in this class. While the buildings are filled with occupants the fan system is operated ; as soon as the occupants leave the building the fan system is closed and the building kept warm by means of direct radiation. The building is thus kept warm at a minimum expendi- ture for fuel. There is no necessity of introducing into the building more air than is necessary for ventilation. But the system is expensive to install, as it involves installing two separate systems of heating. This system is being more and more favorably considered, however, in connection with the class of buildings men- tioned. General Arrangement of the Fan System. — The us- ual arrangement of the fan system is shown in Fig. 61. The air is drawn first through a series of tempering coils 165 Notes o n Heating and Ventilation shown at A. Then it enters a tempered air chamber in which is located the fan. This deHvers the air through a series of heating coils B into the hot air chamber. From this hot air chamber the individual rooms in the buildings take their heat. The tempered coils are usually designed to heat the air to about 70°. The fan takes this air at 70° and passes it to the heating coils. After leaving the heating coils the temperature of the air is from 130° to 140°. Where the air is used for ventilation only the heating coils are omitted and the air is deliv- Fig. 61. ered by the fan from the tempered air chamber directly to the room. Quantity of Air to Be Supplied. — The quantity of air to be supplied to each room will depend upon the system of heating employed. If the heating is done en- tirely by fan enough air must be admitted so that the heat left by the air will be sufficient to heat the room. In audience and school rooms the amount of air necessary to supply proper ventilation is usually sufficient for heat- ing. In offices and living rooms more air will have to 166 Notes on Heating and Ventilation be supplied in order to heat the room than would be necessary for purposes of ventilation. Roughly speak- ing, if the number of cubic feet of air supplied to the room per hour is four times the cubic contents of the room the room will be heated, providing the air be sup- plied at not less than 140°. In a system where direct radiation is used to supply losses from walls and win- dows only enough air is introduced to supply the neces- sary ventilation. The amount of air necessary can be determined by rules previously given under the head of Ventilation. Size, Speed and Horsepower of Fan. — In most cases the type of fan known as the steel plate blower or multi- vane fan is best adapted to the w^ork of fan heat- ing. The theory of this fan has been discussed by Weisbach and Lindner in their treatises, also by vari- ous writers in the Transaction of the Society of Heating and Ventilating Engineers. The results derived are difficult of application. The following general statement may be made, however: The dis- charge capacity of a fan depends upon the speed of the fan tips, the size of the fan blades, and the size of the discharge openings. As the discharge opening of the fan is decreased the velocity of the air leaving the fan increases and the pressure of air in the fan case increases until we get to the maximum pressure that can be produced by a certain velocity of fan tips. This will occur when the area of the outlet equals the effec- tive area of the fan blades. This is the point at which the fan delivers the maximum amount of air correspond- ing to the pressure for a given speed. If we further reduce this discharge outlet the pressure in the fan case 167 Notes o n Heating and Ventilation remains constant, the quantity of air discharged is re- duced and the power to drive the fan is reduced. TABLE XLV.— FAN CAPACITIES. Speeds, Capacities and Horse Powers of "A B C" Steel Plate Fans of "Varying Revolutions. R.P.M. FAN BO 60 70 80 90 100 110 120 140 leo 180 200 3141 280 240 PerV. 785 942 1100 1257 1414 1571 1728 1885 2200 2513 2837 3455 3769 AirV. 685 m) 957 1092 12iW 1867 1503 1640 l."15 2182 2459 2732 8005 3279 100 Pres. .017 .025 .034 .044 .055 .068 .082 .1(K) .134 .175 .231 ,273 .385 .401 Cu. Ft. 682 1121 1870 2652 3840 5475 6395 9.565 14916 21750 S0221 4^608 55201 71941 H. P. .160 ;222 .370 .476 .672 1.01 1.37 2.03 3.46 5.47 7.7 12.0 17.1 25.1 PerV. 981 1178 1375 1571 1768 1964 2160 2356 2750 8141 3533 39?fl 4318 4711 AirV. 853 1025 11P6 1366 1.538 1707 1879 2029 2390 2724 3078 8415 8756 4098 125 Pres. .027 .089 .053 .060 .089 lOH .132 .153 .212 .276 .350 .435 .525 .626 C«. Ft. 852 1402 2338 31.58 4809 6844 7992 11945 18645 27170 37767 5?010 68997 99910 H. P. .175 .284 .439 .5S8 .934 1.34 2.06 2.90 5.00 8.15 12.5 19.3 29.2 435 PerV. 1177 1413 1650 1886 2121 2356 2592 2827 3S00 3770 4240 4711 5182 5653 Air V. 1025 1230 1432 1640 1845 2044 2255 2460 2870 3280 3688 4098. 4500 4928 150 Pres. .039 .056 .075 .100 .1?0 160 190 .230 .800 .400 .503 626 758 .904 Cu. Ft. 1023 1681 2805 3979 5760 8110 (BM> 14360 22374 32610 45325 62412 82811 10812C H. P. .200 -325 .531 .756 1.27 1.86 2.7* 3.10 7.22 11.3 19.6 32,1 46.2 68.6 PerV. 1874 1649 1925 2200 2474 2749 3024 ■3297 3850 438Q 4947 5496 6046 6596 AirV. 1195 1434 1674 1914 2152 2390 2630 2868 8350 3826 4303 4781 5?fiO 574? 175 Pres ,053 .076 .101 .134 .172 .212 .2.58 .WW .420 .554 687 84^ U02 1.21 Cu Ft. 1194 1962 3274 4622 6729 9594 11200 16715 26100 88043 52888 72814 96626 126089 H.'P. .225 .393 .647 1.01 1.74 2.46 3.55 5.52 9.91 17.3 27.9 44.2 67.1 103.0 Per V. 1570 1884 2200 2511 2828 8142 3456 8770 4400 5026 5654 6282 6910 7538 — AirV. 1366 1640 1915 2187 2460 2737 ■mn 3280 38.'^0 ♦375 4918 5465 6011 6558 200 Pres. .069 .101 .184 .175 .225 274 .338 .392 .537 .700 .503 1.12 1.34 a59 Cu. Ft. 1364 2242 3740 5304 7690 10960 128.S0 19150 29850 43520 60442 83331 110422 148902 H. P. .262 .478 .855 1.26 2.05 3.16 4.69 7.01 13.3 23.7 39.2 62.1 96.6 154.5 PerV. 1766 2120 2475 2829 8182 3534 3888 4241 4950 56.54 6360 7065 7774 AirV. 1536 1844 2153 2459 2767 8073 3383 36SH mf, 4919 5583 6148 6762 225 Pres. .0S7 .126 ,172 .225 .285 .351 .421. .507 .690 .601 1 14 1.41 1.69 Cu. Ft. 1534 2523 4207 5968 8655 12334 14385 21500 ;«560 48680 68000 93634 124217 H. P. .300 .581 1.08 1.57 2.61 4.09 5.95 9.29 17.0 31.1 52.8 87.9 142.5 PerV. 1963 2355 2750 3143 3535 8927 4320 4712 5500 6283 7067 7852 Air V. 1708 2048 2392 2784 wno 3416 3758 4100 4780 5450 61 4M 6840 250 Pres. .109 .056 .213 .280 .3fl(> 430 .520 .630 .860 I 12 1.48 1.73 Cu. Ft. 1706 2793 4675 6332 Hfi(X) 13705 16000 23950 37310 54200 75558 104036 H. P. .375 .684 1.22 1.79 8.32 4.97 7« 116 ^2.5 41.2 71.7 121.4 PerV. 2159 2591 3025 3457 8889 4319 4731 5183 6050 6911 7774 AirV. 1878 2258 2632 3008 3388 3755 40tO 4507 5263 6013 6768 875 Pres. .131 .189 ,25H .337 426 .5V6 .623 .7.56 1.04 1.35 1 71 Cu. Ft. 1876 3083 5142 7294 10578 15773 17394 26278 41020 .5K328 88104 H. P. .436 .821 1.45 2.35 3.92 6.oa 909 14.5 29.4 54.7 89.3 PerV. 2355 2826 3300 3771 4242 4712 5184 5654 6600 7539 AirV. 2050 24.58 2H75 3280 3685 41(NI 4510 49£0 5745 6555 300 Pres. :160 .225 mi .401 520 .630 .760 .910 15'6 1.62 Cu. Ft. 2016 3363 5610 7957 11520 16i5<) 19200 28800 44750 63629 H.P. .500 .975 1.73 2.86 4.63 7.U 11.4 18.1 87.5 69.3 Per V. 2747 3297 3850 4399 4949 '^^ 6018 6.597 7700 AirV. 2390 2863 3345 3827 4-295 5262 5724 6680 NOTE 350 Pres. .216 .306 41 H .550 .693 .8.50 .970 1.25 1.68 These 6gures guaranteei 01. 1% 01. IK 01. 2 01. 2 "4 01. 8 01. 60 CU. FT. R P. M. H. P. 2740 380 .80 3900 .540 1.60 4760 6.59 2.66 5490 760 385 6090 847 5 32 6700 930 6.65 73.50 1004 8.22 7750 1075 10.25 8650 1200 14.38 9520 1320 18.85 60 CU. FT R. P. M. H. P. 3,i.T0 317 1.03 5040 449 2.05 5490 549 3.42 7100 633 4.95 7910 706 6.84 8700 776 8.54 9410 838 10.60 10200 895 13.2 11210 1000 18.45 12330 1100 24.3 70 CU. FT. R. P. M. H. P. 5220 271 1.51 7350 383 3.02 9050 471 5.04 10400 .542 7.30 11600 605 10.10 12700 663 12Si; 13750 716 1560 147.50 768 19.40 16.500 857 27. '20 18000 938 35.7 80 CU. FT. R. P M. H. P. 630 238 1.82 8900 836 3.65 10940 412 6.08 125.50 474 8.82 14000 5.30 12.15 153,50 580 15.20 16600 627 18.85 17300 672 23.40 198S0 750 S3.80 21920 825 43.2 90 CU. FT. R. P. M. H. P. 7850 211 2.27 11050 299 4.53 13600 366 7.56 15600 421 1100 17450 470 15.10 19100 515 18.90 20650 557 23.40 22100 5<:6 29.10 •247.50 666 40.70 27300 734 53.5 100 CU. FT. R. P. M. H. P. 9.>t0 1«0 2.76 13.500 268 5.,52 16.500 329 9.a) 19050 380 13.35 21300 424 18.42 23300 464 23.00 2.5200 502 28.60 •27000 .537 ss.to 30.^00 600 49.60 33000 659 65.2 110 CU. Ft. R. P. M. H. P. 11870 173 8.43 16700 244 6.85 20600 800 1144 23600 345 16.60 26400 885 22.W) 28900 422 28.60 31.300 4:)6 35.50 33500 488 44.00 37.500 546 61.7 41200 600 81.2 ]20 CU. FT. R. P. M. H. P. 15030 1.59 4.32 21000 224 8.65 2.5840 274 14.40 29700 816 20.60 33200 3.54 28.80 36400 387 36.00 39400 418 44.60 42^200 448 55.45 47100 500 777 51800 550 102.1 140 CU. FT. R. P. M. H. P. 19800 136 5.72 27900 192 11.42 84200 2:{5 19.00 39400 271 27.60 44000 302 38.10 48200 331 47.60 51200 357 59.00 55800 883 73.30 639C0 439 1027 68400 470 135.5 160 CU. FT. R. P M H. P .2.50:>0 118 7.29 85600 168 14.60 4;i700 206 24.32 502.50 237 35.20 56150 265 48.60 61.500 290 160.75 66500 814 75.30 712.50 336 93.50 79200 373 134.0 87500 412 172.0 180 CU. FT. R. P. M. H. P. S1410 106 9.07 44200 149 18.13 54300 183 30.24 62700 211 43.80 69700 235 60.48 76700 259 75.5 82700 279 93.6 88400 •298 116.^20 99000 834 131.0 108400 866 214.0 200 CU. KT. R. P. M. H. P 38000 95 1102 53700 134 22.20 66000 165 .36.80 75700 189 53.8 84950 212 73.5 93000 2:12 920 100500 •251 1140 107:00 268 1415 r20000 300 1985 134000 830 261.0 220 CU. FT. R. P. M. H. P. 46S0O 87 13.48 66300 123 27.00 80900 150 44.90 93200 173 65.10 104000 193 89.6 113.500 211 112.0 123300 •229 139.0 131400 244 178.0 147100 274 243.0 161500 300 818.0 240 CU. FT. R. P M. H P. 56400 80 1610 79000 112 32.30 96.-)00 137 53. M) 11-2000 1.59 7.H,00 124800 177 107 4 136800 194 1340 147400 209 106 1.5S0OO •224 206.0 176100 194000 2.50 275 2«0.0 3820 of ai * delivered. Mr. M. C. Huyett gives the follow- ing approximate rule for finding the capacity of a fan : The quantity of air in cubic feet delivered per revolu- tion is equal to one-third the diameter of the fan wheel multiplied by the width of the blades at cir- 169 Notes on Heating and Ventilation cumference, multiplied by the circumference of the fan wheel. All dimensions expressed in feet. Professor R. C. Carpenter gives the following rule for determining the horsepower required by the fan : The horsepower required for the fan is equal to the fifth power of the diameter of the fan wheel in feet multiplied by the number of revolutions per second, divided by 1,000,000 and multiplied by one of the fol- lowing coefficients — for free delivery, 30 ; for delivery against 1-ounce pressure, 20 ; for delivery against 2 ounces pressure, 10. The best method of obtaining the horsepower to drive a fan and the capacity of the fan is by reference to the table. Table XLV gives the speed, capacity and horsepower required for various sized fans as determined by the American Blower Co. Table XLVI gives similar results for different sized fans at varying pressure. Table XLVII gives the results for a fan of the multi vane type, such as the Sirocco. The table should be made use of in the following manner: Having determined the quantity of air re- quired for the entire building, we select from the table a fan which would give the proper capacity. In doing this three things must be considered. The fan must have sufficient capacity to deliver the amount of air required. It must deliver this air with the minimum horsepower, and it must rotate with sufficient speed to product a pressure in the fan system sufficient to over- come the resistance of the piping. It is always possi- ble to select either a small fan driven at a high speed or a large fan driven at a low speed, both of which will deliver the same capacity of air. A large fan may be 170 Notes o n Heating and Ventilation TABLE XLVII. Speeds, Capacities and Horse Powers of Single Inlet, Standard Width Fans at Various Pressures. Fisura Giren Retiteaeat Dnumie Prritura in Ounco per Square Inch. Foe Slabc Piewire Deduct 26.9%. For Velodly Pienure Deduct 71.2%. No. o( Uumeter Wheel to.. 10.. 10.. 10.. uo.. li Ol. UO.. 2 0.. 210.. 3 0.. M 3 CU. FT. R.P. M. B. H. P. 38 2290 .005 55 3230 013 67 3960 024 77 4580 037 87 5120 051 95 5600 068 102 6050 085 110 6460 105 122 7232 145 135 7920 190 4i CU. FT. R.P. M. B. H. P. 87 1524 Oil 125 2152 030 152 2640 053 175 3048 084 197 3400 .116 215 3732 .153 232 4OJ0 193 250 4304 .238 277 4816 .330 ;«.5 5280 433 • CU. FT. R.P. M. B. H. P. 155 1U5 .0185 220 1615 052 270 1980 095 310 2290 .147 350 2560 205 380 2800 .270 410 3025 .34 440 3230 .42 490 3616 .58 540 3960 76 n CU. FT. R.P. M. B. HlP. 242 915 029 344 1290 0«2 422 1585 149 485 1830 .230 548 2050 320 594 2240 422 640 2420 532 688 2580 656 768 2890 910 844 3170 1 19 » CU. FT. R.P. M. B. H. P. 350 762 .042 500 1076 .118 610 1320 .216 700 1524 .333 790 1700 .463 860 1866 .610 930 2020 1000 2152 95 1110 2408 1 32 1220 2640 1.73 12 CU. FT. R.P. M. B. H. P. 625 572 .074 880 808 208 1080 990 .381 1250 1145 .588 1400 1280 .82 15J0 1400 1 08 1650 1512 1.36 1770 1615 1 66 1970 1808 2 32 2170 1980 3 05 IS CU. FT. R.P. M. B. H. P. 975 456 115 1380 645 326 1690 790 .600 1950 912 923 2180 1020 1 29 2400 1120 1.69 2590 1210 2.14 2760 1290 2 61 3090 1444 3 65 3390 1580 4 8 18 CU. Fr. R.P. M. B. H. P. 1410 381 .167 1990 538 470 2440 660 862 2820 762 1.33 3160 850 1.85 3450 933 2 43 3720 1010 3.07 3980 1076 3.75 4450 1204 5 25 4880 1320 6 9 21 CU. FT. R.P. M. B H. P. 1925 326 .227 2710 482 .640 3310 565 1 17 3850 652 1 81 4290 730 2 53 4700 800 3 33 5070 864 4 18 5420 924 5 11 6060 1032 7 15 6620 1130 9 4 24 CU. Fr. R.P. M. B. H. P. 2500 286 .296 3540 404 .832 4340 495 1.53 5000 572 2 35 5600 640 3 28 6120 700 4 :g 6620 756 5 44 70BO 807 6 64 7900 904 9.3 8680 990 12.2 27 CU. Fr. R.P. M. B. H. P. 3175 254 373 4J90 359 1 05 5500 440 1.94 6350 508 2 98 7100 568 4 16 7780 622 5.48 8400 672 6 90 8980 718 8.44 10050 804 11 8 J 1000 880 15 5 30 CU. FT R.P. M. B. H. P. 3910 228 460 5520 322 1 30 6770 395 2 40 7820 456 3 68 8750 510 5 15 9600 560 6 75 103^ 604 8 53 11050 645 10 4 12350 722 14 5 13550 790 19 1 36 CU. FT. R. P. M. B. H. P. 5650 190 66.1 7950 269 1 87 9750 330 3 44 11300 381 5 .30 12M0 425 7 40 13!>00 466 9 72 14900 504 12.26 15900 538 15 17800 602 20 9 19500 660 27 5 42 CU. FT. R. P. M. B. H. P. 7700 163 90? 10850 231 2 55 13300 283 4 69 15400 326 7 24 17170 365 10 1 18800 400 13 3 20300 432 16 7 21700 462 20 4 24250 516 28 5 26600 566 37 5 4a CU. FT R. P. .M. B. H. P. 10000 143 1 18 14150 202 3 32 17350 248 6 10 20000 286 9 40 22400 320 13 1 24500 350 17 2 26500 378 21 75 28300 403 26 6 31600 452 37.1 34700 495 48 8 54 CU. FT. R. P. M. B H. P. 12700 127 1 49 17950 179 4 20 22000 220 7 75 25400 254 11 9 28400 284 16 6 31100 311 21 9 33600 336 27 6 35900 359 33 7 40200 402 47 1 44000 440 02 60 CU. FT. R.P. M. B H. P. 15650 114 1 84 22100 161 5 20 27100 198 9 58 31300 228 14 7 35000 255 20 6 38400 280 27 41400 302 34 1 44200 322 41 6 4940O 361 .58 2 51200 396 76 5 66 CU FT. R. P. M. B. H. P. 18950 104 2 23 26800 147 6 30 32850 180 11 6 37900 208 17.8 42300 232 24 9 46400 254 32 7 50100 275 41 2 53600 294 50 4 60000 328 70 4 65700 360 92 6 72 CU. FT. R.P. M. B. H. P. 22600 95 2.66 31800 134 7 48 39000 165 13 7 45200 190 21 2 50600 212 29 6 55200 233 38 9 59600 252 49 63600 269 59 8 71200 301 83 6 78000 330 110 78 CU. FT. R. P M. B H. P. 2t>J00 88 3 10 37350 124 8 77 45800 153 16 1 52800 176 24 8 59100 197 34 7 64700 215 45 6 70000 233 57.5 74700 248 70 2 8350O 278 98 91600 305 129 84 CU. FT. R. P. H. B. H P 308O0 81 3 61 43400 115 10 2 53200 142 18 7 61600 163 28 9 68700 182 40 4 75200 200 53 81200 2I« 66 8 86800 231 81 7 97100 258 114 106400 283 1.S0 90 CU. FT. H. P. M. B. H. P. 35250 76 4 14 49S00 107 11 7 61000 i:{2 21 5 70500 152 33 1 78800 170 46 2 86400 186 60 7 93300 201 76 7 99600 214 93 6 111200 241 131 122000 264 172 171 Notes on Heating and "Ventilation driven at so slow a speed that it will not produce suf- ficient pressure to overcome resistance of the air flues. Choose the largest fan that, driven at sufficient speed to overcome the resistance of the air flue, will deliver a proper quantity of air for the purpose of ventilation. As an example : Suppose we wish to deliver to a build- ing 10,000 cubic feet of air per minute. Referring to the table, we see that we may use an 80-inch fan driven at 400 revolutions, in which case there would be re- quired 5 horsepower to drive the fan and the pressure produced would be .713 ounce or we might use a 120-inch fan driven at 125 revolutions per minute, in which case the power required to drive the fan would be 2.9 horsepowers and the pressure produced would be .153. In the first case the fan is small and being driven at high speed the pressure produced is more than necessary to overcome the resistance required except when the flues are long and have a number of turns. In the case of the 120-inch fan, while the horse- power is much lower the pressure is insufficient to over- come the ordinary resistance. For ordinary purposes the pressure should be about .25-.50. Referring again to the table, we see that the 100-inch fan driven at 200 revolutions per minute would require 3.15 horsepowers and produce a pressure of .274. This would be about the proper size of fan for most cases. The pressure required to overcome the resistance of the building de- pends very largely upon the capacity and design of the flues and the resistance of these flues is largely a mat- ter of judgment and experience. Heating Coils. — The determination of the proper quantity of heating coil to raise the air to a given tem- 172 Notes o n Heating and Ventilation Table XLVIII— Condensation and Heat Given Off by Heater Coils. d TEMPERATURE AIR ENTERING COIL 00-10° Velocity of Air Velocity of Air Velocity of Air Velocity ' of Air .^ j_) ^_ o C o 0)0 == 2 01 o c o o o aaw t;o .istS w ^6 .22 w ^o .22 w ^° . m (/] ^OJ'S -u) bx) W 1^ " ti c Oi c ^ w ^ == o3 c J; a 6 o CO d 2; -a erf*

Jh C Ol 01 i 2 s o t-.S ti— o> 1^ > h 0,05 be '^ ^ 33 = S U 0) t-— > 01 'V > ^ ao3 be c rt ^ rrj o" '-'' o t..5 U 01 > Jh a oi t« o. c^ a 03 a o3 a 03 4 1 2.90 39 2.4 35 2.68 32 2.85 31 8 2 1.92 74 2.21 65 2.46 60 2.65 55 12 3 1.78 94 2.1 82 2.32 77 2.45 73 16 4 1.53 114 1.86 98 2.09 93 2.25 88 20 5 1.31 130 1.68 115 1.88 108 2.10 103 24 6 1.20 143 1.54 128 1.77 122 1.92 117 28 7 1.10 152 1.45 140 1.70 134 1.85 129 32 8 1.05 1.40 148 1.65 140 1.77 133 TEMPE RATURE AIR E NTERING con . 400-50° Velocity ' of Air Velocity of Air Velocity of Air Velocity ' of Air o 1000 fe et per l r_ ■i-i •«-> >-^ o c o ajo ■ c o 0) o C o ^1^ c o 01 o u o o ■ ^ § o o • ^ o o o • '^ S o o • u 3 .X «1H w p "-^ . .S t»-( 03 13 ^ . 3 <^ . p ^ . lU o ?!" = +j bi3 M ct C be w rt c 3^ 1?; = rt 0) 3^ ^2^'S -u he w rt c 0) a o 6 2 CO d o t-.5 p. ^ ftoJ be ^•3 c S o ^ 2 o U.5 a fcH-H 0) > !-, art oc 03 O 01 a t^ ;-, \ \ V N, % \ s N \ s ^^ f- \ \ N. \ \ s ^ '0. \ s \ s N, ^ s s \ s v <;^ 1- \ \ s. S s. ^ if) \ s V N ^ s s. ^ s \ V S, ^ ?.* N s ^ V s. \ s V N s s. V \ 1 ::^ 500 600 700 -800 900 1000 1100 1200 1300 Velocity of Air Through Heater in Feet per Fig. 64. 1024 1072 1121 1170 1219 1267 1316 1365 1414 1462 1511 1560 1608 1657 1706 1755 1804 1852 1901 1950 1999 2047 20% 2145 2194 2242 2291 2340 2389 2437 2486 2535 2584 2632 2681 2730 C/3 X Cu 1400 1500 Minute best form of flue is round, the next best form is square, or, if rectangular, is nearly square as po<;sible. All 177 Notes o n Heating and Ventilation turns and branches should be made with easy curves. The size of the flues is ordinarily determined by the velocity of the air passing in the flues. In main ducts of large size a velocity as high as 1,500 feet per minute may be used. In the branch main- or small main ducts Temperature Chart Initial air temi>erature, o° Fahrenheit. Steam pressure, 5 pounds u^- = = = = = = = 210.° = :=: = 200.° = = = = = p = 190.° 180° 170° 160° 150° ^ ^ ^ ^ ^ = — ^ 1 1 ^ 1 %_ 1 140° 130° 120° 110° 100° 90° ^ :s: 1 i - = ^ F=i ^^ir = S kH 1 ^ =•— 1 =si 1 1 =s frr ^ ^ ^ § = 80.° 70° 60.° 50.° 40.° 30.° 20° 1 1 Y ^ 1 1 1 ^ m ^ aS ITOj — 10° 0° = = = ^ 1 ^ 500. 600 700 800. 900. 1000. 1100. 1200 1300. 1400. 1500. Velocity of Air Through Heater in Feet per Minute. Fig. 65. the velocity should not exceed 800 to 1,000 feet. In flues leading to the individual rooms the velocity should be from 600 to 800 feet per minute, depending upon their size. Where the ducts are of small size this ve- locity is often reduced to 400 feet per minute. The 178 Notes on Heating and Ventilation velocity at the registers should not exceed 300 feet per minute except in very large registers so located that the current of air entering the room will not strike the occu- pants of the room, then the velocity may be 500 feet per minute. In all ordinary buildings, if these propor- tions of air velocities are used the resistance of the sys- tem will be from .3 to .6 of an ounce pressure. The loss of pressure in a piping system of square or round pipe may be determined from the following expression used by the U. S. Navy Department : 1 H, = 4f — Vi^ d . Where H is the loss of pressure due to friction meas- ured in head of air in feet, f is the coefficient of fric- tion, 1 and d are length and diameter of pipe, both in feet or both in inches, and V^ is the velocity of flow through the pipe in feet per second. If V^ is changed to V, or velocity in feet per minute, and f given its proper value, which for good piping is .00008, then 1 V2 H, = d 11,250,000 1 If V = 2,000, Hf = .3556 — d 1 If V = 1,000, H, = .0889 — d For rectangular pipe of short side h and long side nh the formula becomes : 1 + n 1 V^ H, = n h 2,250,000 179 Notes on Heating and Ventilation Where 1 = length of pipe and V is velocity of air through it in feet per minute. If a standard pressure be assumed of 5 pounds per square foot, which corresponds to a head of air of 84.25 ft., then for each foot of head lost there will be a loss in delivery of .6 or 1 per cent. For example, suppose 364 feet per minute are required at a given outlet, where the total head is 69.67, a loss of 15 feet. The corresponding loss of delivery would be 9 per cent and the rated capacity of the pipe to delivery of this air should be 364/91 = 400 cubic feet per minute. In determining the length of a pipe a 90° elbow is equal to 5 diameters of pipe provided the radius to the center of the pipe is not less than 1^ diameters. A smaller radius than this should not be used, as it in- creases the resistance very rapidly. Where branches leave the main ducts it is a common practice to place a deflecting damper at the bend of the branch. This is merely a piece of galvanized iron attached to the point of the branch, which may be adjusted and fastened so that each branch will take its proper supply of air. Dampers controlled by the attendants in the building should be as few as possible. The reductions in the size of a flue should be made gradually. The angle of the reduction should not exceed a taper of 1^" per foot. No round pipes less than 6 inches in diameter are used, and if rectangular, less than 6x8. A common arrange- ment of ducts is to let them radiate from the fan in the form of a tree, with trunk and branches. Another very satisfactory method of distribution is to force all the air from the fan into a large duct or chamber in which the air has a very low velocity. 180 Notes o n Heating and Ventilation The rooms take their air from this chamber by means of vertical flues controlled by proper dampers. These large chambers are called Plenum chambers. A g:ood TABLE L.— PRESSURE LOSSES. Air. — Loss of Pressure in Ounces per S'quare Inch per 100 Feet of of Pipe of Varying Velocities and Varying Diameters of Pipes. Velocity of Aii Feet per Minute. 600 1,200 1,800 2,400 »,000 8,600 4,200 4.800 6,000 Velocity of Air Keet per Minute. 600 1,200 1,800 2,400 8,600 4,200 4,800 6.000 DIAMETER OK PIPE IN INCHES. Velocicy ol Aft Feet per Minute. 1 2 3 4 6 1 6 7 8 Loss OF PrESS(.>KE IK OvsCcs 600 1,200 1,800 2,400 8.000 8,600 4,200 .400 1.600 8.600 6.400 10.000 14/400 .200 .800 1.800 8.200 5.000 7.200 9.800 12.800 20.000 133 .533 1.200 2.133 8.333 4.800 6.5.')3 8.533 13.333 .100 .400 JWO 1.600 2.500 8.600 4.900 6.400 10.000 .080 .820 .720 1.280 2.000 2.880 3.<*20 5120 8.000 .067 .267 .600 1.067 1.667 2.400 3.267 4.267 6.667 .057 .22« .514 .914 1.429 2.057 2.800 8.6.57 5.714 .050 .200 .450 .800 1.250 1.800 2.450 4,800 6,000 8200 &.000 DIAMETER OF PIPE IN INCHES 11 18 14 16 18 Loss OF Pressure i.n Ounces. .044 .040 .036 .033 .029 .028 .022 178 .160 .145 133 .114 .100 .089 400 .360 .327 .800 .257 .225 200 .711 .640 .582 .533 .457 .400 856 1 111 1.600 1.000 .909 1.809 .833 1.200 ■".'900 1.029 .800 2.178 1.960 1.782 1.633 1.400 1.225 1.089 2.844 2.560 2.327 2.133 1.829 1.600 1.422 4 444 4.000 3.636 8.333 2.857 2.500 2.222 DIA.METER OF PIPE IN INCHES. 28 24 28 32 36 40 44 Loss OF Pre.v96 in 33900 46.76 140 2.20 60312 -'85 76300 Vio 363 94240 4^48 Heater R. P. M. H. P. >o59 .300 9t» 409 ,.788 534 636 832 534 1.64 .396 2 14 35' 2 70 322 3 37 264 4 85 6 60 200 8 63 ,'A ..60 ''3 3 1400 Free Cu. Ft. R. P. M. HP. >47S 767 «33 s 4400 570 '3? 6850 460 .,68 9870 38B 530 '3470 327 721 17600 286 942 22270 254 1.19 27500 230 '55 39600 190 53900 289 70300 ■44 , 3 77 '"tit 4 77 109500 "5 589 Heater R. P. M. H. P. i»'3S ■487 to64 .660 .Ul 742 '35 623 '95 2.64 ^^l *'2 438 376 540 ^.88 10. 6 »34 «J8 205 'f 5 21.6 1600 Free Cu. Ft. R. P. M. HP. 2830 875 ■8S 3850 750 25J 5000 656 ■ 330 ,8.0 526 •515 II300 438 ■ 742 15400 375 20050 33= '34 25400 298 I 67 3'40o 264 2 06 45200 220 2 97 61500 168 4 05 80000 16s 101200 146 6.68 125900 Heaier R. P. M. H. P. 1411 735 1J16 1. 00 1050 'if 848 2 04 712 2 94 603 4 00 537 5 23 468 6 62 8 17 .^'8 ',l'i ■ 268 20 9 234 26 5 210 ■3' 7 1800 Free Cu. Ft. R.P.M. H. P. »47 4320 840 336 5*3° 73' 440 8850 II? 12700 490 99' 17300 420 « 35 22600 1.76 28600 3*> 2 22 35200 »94 Siooo 245 397 354 23 90200 185 7 0t 302 30.0 114000 141000 148 It.o Heater H. P. V588 I OS .368 ■ 43 ■ 181 • 87 954 « 93 8^1 4:<>3 679 S 75 595 7 so 5»6 9 50 483 11 7 236 47 Free Cu. Ft. R. P. M. H. P. 35SO 1090 33« 4000 456 6280 815 ■597 9800 655 93' .4'2A 545 •34 '9*4° 470 .83 31800 3«3 3 02 39260 327 3 73 565. 5 38 76960 '31 7 3' 100520 206 9 55 127200 182 157100 3000 4'-o 2 39 164 <4 9 Heaier R. P. M. H. P. .764 I 30 1520 • 77 1312 2 30 ioft> 360 890 5 '5 755 7 05 664 9 '5 585 117 528 '4 5 440 20 8 2!^ 336 37 292 46 8 262 578 2200 Fret Cu Ft. R. P M. H P. 3890 4'4 4300 1050 576 6800 900 754 loSoo 15520 600 I 70 21130 S'5 2 31 97600 450 -3 <» 35000 400 382 •43200 360 4 72 62200 300 6 79 84700 257 9 25 (10500 228 139800 '5 3 172500 iJ!l Heater R P.M. HP, 1940 1 70 1700 a 30 1460 3 00 1163 4-70 97' 6 Bo 830 9 '5 7»7 . 12 I 645 '5 3 .fj 48s «70 .4'5 370 r. 61.0 ,84 tl.O of vertical flues leading to the rooms, at which point there is introduced a mixing damper similar to the mix- ing damper shown in Fig. 62. 183 Notes on Heating and Ventilation Materials of Flues. — The flues for fan systems are ordinarily constructed of galvanized iron with double lap joints riveted or soldered. The ducts should be made as nearly as possible air-tight. The weight of material used for ducts depends upon the size of the duct. It ordinarily varies from No. 26 to No. 20 gauge. Large ducts are also made of sheet iron with close riveting. When ducts are made of sheet iron the ducts are painted and then asphalted. Where it is necessary to build ducts underground they are built of brick or cement. The ce- ment, if anything, is preferable to brick, as it does not absorb odors as easily and may be plastered to make a smooth job. Where possible it is desirable to build the ducts and flues into the building itself, making them of permanent material. Brick or cement ducts built into the building and so arranged that they may be examined and cleaned easily are the most satisfactory. Wood is always a bad material to use for ducts and should be avoided. Where it is used the ducts are lined with tin, owing to the fact that wood usually shrinks, leaving open joints. Vent ducts from closets should be carried out of the buildings separately from the other vent flues. Where these ducts are made of brick they should be lined with galvanized iron to prevent the odors from the closet be- ing absorbed by the brick. It is very desirable that closet vents should be collected at convenient points and then exhausted from the building by means of a fan. This prevents the odors from the toilet rooms being car- ried back into the building. Disc Fans. — Disc fans are used where the resistance to be overcome is very slight or in cases where the ducts 184 Notes on Heating and Ventilation are very large, with easy turns and of very short length. They are extensively used for exhausting the air from the vent flues and where the vent flues are short and large they give good satisfaction. The capacity, speed and horsepower of various sizes of disc fans is shown, in Table LI. Example. — As an example of the fan system consider an auditorium. The dimensions of the room are 40 feet 9 inches by 79 feet G inches by 127 feet 9 inches. The volume of the room is 413,000 cubic feet. It has 203 square feet of glass surface and 5,441 square feet of wall surface. The heat lost from the room, figuring in the same way as we have for previous examples, will be 168,010 B. T. U.'s. The hall has a seating capacity of 2,500 persons. Allowing 2,000 cubic feet of air per per- son, the necessary air to be admitted to the room will be 5,000,000 cubic feet of air per hour. This equals 383.- 000 pounds. In order to heat the room with this quan- tity of air entering, it will be necessary to heat the air but 1.85 degrees so that the air admitted to the room for ventilating purposes will be far more than that nec- essary for heating purposes. It is best, then, to figure on admitting air only for purposes of ventilation. To heat this air from zero to 70° would require 383,000 X .2375X70=6,353,000 B. T. U.'s. Referring to Table XLV, we see that a heater coil 12 pipes deep will heat air having a velocity of 1,250 feet per minute to a tem- perature of 82°, which is probably about the proper assumption to make in this case. The coil will condense 2.1 pounds of steam per square foot per hour. Each pound s:ives up about 970 heat units, so that each square foot of heater coil will give ofif about 2,000 B. T. U.'s per hour. Then the number of square feet of heater coil required would be 6,350,000-^2,000=3,175 square feet. 185 Notes on Heating and Ventilation The heater coils are usually made of 1-inch pipe and each square foot of surface is equivalent to about 3 feet of 1-inch heater pipe, hence there will be required 3,175 X3 or 9,525 feet of 1-inch pipe in the heater coils. The air to be admitted to the hall is 5,000,000 cubic feet per hour or 83,300 cubic feet per minute. The usual velocity allowed for the air passing through the heater coil is 1,200 feet per minute. This will require an air area in the heater coil of 83,000^1,200=69.5 square feet. The area in the various heater coils will be found in the blower company's catalogues and is also given in Table XLVIII. This will determine the size of the heater coil to be used. On account of the size of the hall and the amount of air introduced, it will be best to have two fans for deliv- ering air into the building. Each fan would then need a capacity of 41,650 cubic feet per minute. In order to overcome the resistance of the flues the pressure should be from .4 to .5 of an ounce at least. From the table of fan capacities we see that a 180-inch fan running at 150 revolutions would require 19.6 horsepowers and pro- duce a pressure of .503 ounces and give the air required. Assuming the air to be delivered to the hall by four ducts, these ducts being large, it would be reasonable to allow a velocity of 1,000 feet per minute in the duct. Each duct would have to carry 20,800 cubic feet of air per minute; 20,800-^1,000=20.8 square feet in area. As the registers of these ducts will be large and situated well above the head line, it would be safe to allow a velocity of 400 feet per minute through the register. The area of each register, assuming that there are four en- tering the room, would be 26 square feet. The vent flues leaving the room should have an area about equal to the hot air flues. 186 CHAPTER Xil. A CENTRAL HEATING SYSTEM. Design and Location. — It is not intended in this chapter to discuss the design of heating systems, such as is used in the heating of a city, but systems that are in use for the heating of public institutions, or groups of buildings. The type of system to be used in a given installation depends very largely upon the location and. character of the building to be heated. No two systems, even though designed by the same engineer, will be the same, and the suggestions made in this chapter can be but general. Before starting the design of a general heating sys- tem it is first necessary to have a careful survey of the property. This survey should show the exact location of the buildings to be heated, the elevation of the basement and first floor, together with a gen- eral profile of the ground through which the tunnels or pipes are to be run. The profile of the ground will largely decide the proper location of the power house. The power house should be located as nearly as possible to the buildings to be heated or as near as possible to the largest steam load. It should be low enough, if the profile of the land will permit, so that the condensation of the return mains may be returned to the power house by gravity. If possible, it should be so located that the floor of the boiler room may be drained to the sewer. Considerable difficulty is usu- ■ ally experienced to carry away the water, which re- sults from the cleaning and blowing off of the boilers 187 Notes on Heating and Ventilation if no sewer connection can be made. The question of the soil, the location of the railroad siding, the water supply and the general appearance of the power house must also be taken into consideration. Boilers. — Before designing the power house the type and general form of boilers must be determined. If the power house is to work on a low pressure system with a pressure under 100 pounds, either fire 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 crowded considerably beyond its rating. The economy of water tube and fire tube boilers is prac- tically the same. The principal objection to fire tube boilers, except of the Scotch marine type, is the large space which it oc- cupies. If the power house is to be operated on high pressure, that is, over 100 or 125 pounds, then only water tube or Scotch marine boilers can be used. The size of the boiler must be determined by the amount of steam which is to be used by the radiation and other devices taking steam from the boilers. The steam used by the dififerent forms of radiation can be determined by reference to the radiator tables previously given, and to this must be added the steam used by auxiliaries, by the kitchen, the condensation in the ' main and all other devices using steam. After having once de- termined the quantity of steam the plant is expected to use, it is customary to assume that each square foot of heating surface in a boiler will evaporate about three pounds of water. This deter- mines the total 'imount of heating surface that the 188 Notes on Heating and Ventilation boilers should contain. The boiler units should be so selected that one boiler or one set of boilers will take care of the plant during the light load period of opera- tion, that two boilers or sets of boilers will take care of the average operating load. In addition to this there should be a boiler or set of boilers that will take care of the maximum conditions of load. There should al- ways be a sufficient number of boilers in the plant so that at least one boiler or set of boilers can be out of service for a considerable period of time for cleaning or re- pairing. In a central heating plant using the gravity return system, it is necessary that all boilers have their water line at the same level. Systems of Distribution. The general design of a piping system and its lo- cation will depend upon the system of distribution adopted. Gravity System. — If the gravity return system is used no main feed pump is necessary, the water re- turning by gravity to the boiler, as previously described. With this system any difference in pressure between that in the boiler and that at the extreme point in the piping system will result in a corresponding elevation of the water level in the return system at the extreme point — each one pound drop of pressure in the steam piping corresponds to an increase in the level of the water in the return piping of 2.30 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 comparatively small. The difference of pressure assumed will determine 189 Notes on Heating and Ventilation the size of the piping. In gravity systems it is usual to allow for the drop of pressure not over two 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, the most distant build- ing heated being as far as 2,500 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 six to eight feet above the return it is necessary that the steam condensed in the mains be dripped separately from the main re- turns in the building and this drip pumped back to the boilers, preferably by a pump and receiver, or some other mechanical means, such as a return trap. This pump and receiver should be of sufficient size to take care of the steam condensed in the mains when the steam is being turned on and the condensation is ex- cessive. By returning the condensation of the mains separately, excessive hammering is avoided and the sys- tem can be started much more rapidly. Gravity return is used only where the boiler pressure does not exceed ten pounds. High Pressure System. — The high pressure steam is sometimes used for general heating purposes, but the pressure is reduced through a reducing valve before en- tering the radiators. It has some advantages. The pipes are smaller and circulation is very rapid in this system. It is not possible to use exhaust steam with a high pressure system. When pipe coil radiation is used it would be safe to carry a pressure up to 100 pounds on the radiators, but high. pressure in the radiators is not good practice. In determining the size of steam mains for 190 Notes on Heating and Ventilation such a system a loss of pressure as high as ten pounds would not be considered excessive. In the high pressure system each building usually sends its condensation back- to the return system through a trap so that the pres- sure on the return is only sHghtly above the atmosphere. This condensation returns to a surge tank, from which the feed pumps return it back to the boilers. The drip from the steam mains is dripped directly back into the return system. Low Pressure Pump Return System. — In a very large system where it is difficult to get enough differ- ence in elevation between steam and return mains, or where the drop in pressure exceeds two pounds, it is usual to install some form of pump return. One of the most common forms of pump return is to trap the re- turn condensation of each building into the return main, which carries the return back to a surge tank in the boiler room. From this surge tank the water is re- turned to the boiler by means of a pump. The drip from the steam main is trapped directly to the return main. The most objectionable feature of this system is the constant attendance and the repairs necessary to take care of the traps. Combination of Pov^er and Heating System. — In most cases the heating system is combined with some form of power system. This makes a very economical combination, as the exhaust from the power plant may be used in the heating system. Where the exhaust can be entirely utilized for from six to eight months of the year it is seldom profitable to use condensing engines. There are two general schemes used for combining a power and heating system. In the simplest form the 191 Notes o n Heating and Ventilation boilers are operated at a high pressure. The steam goes from the boilers to the engine, and after the steam leaves the engine it passes directly to the heating sys- tem. A by-pass pipe is carried from the high pressure steam main to the heating main and in this by-pass is located a reducing pressure valve. If for any reason Fig. 67. the engine does not supply sufficient steam to maintain pressure on the heating system, then the reducing valve opens and introduces live steam. The returns from the heating system are carried back to the boiler by means of a pump. Fig. 67 shows the general arrangement of systems of this kind with a by-pass for furnishing live steam to a heating system. This system depends in a measure for its success upon the action of the reducing pressure valve. The cross-section of a reducing pressure valve is 192 Notes o n Heating and Ventilation shown ill J^'ig'. (38. Such valves have been found to be quite reliable when well designed and well made. The principle cause for trouble is when the valve be- comes foul with dirt, in a system of this kind the en- gine exhaust is always provided with a back pressure Fig. 68. valve connected to the atmosphere. This valve is so arranged that if for any reason excessive pressure should accumulate in the heating system the valve would open and exhaust the steam into the atmosphere. The arrangement shown in Fig. 67 is most used in small plants and both the heat and the power can be taken from one boiler. In larger plants the heating boilers are operated on the low pressure and the power boilers on the high pressure system. In the high pressure system steam goes to the engine and pumps and is exhausted through an oil separator into the low pressure system. The pressure of the exhaust is determined by the pres- sure carried on the low pressure system. This system is particularly desirable where the heating load is con- 193 Notes on Heating and Ventilation siderably larger than the power load ; and where at times the engines are entirely shut down and only the low pressure system is operated. Fig. 69 shows a sketch of this arrangement. Fig. 69. Method of Carrying Pipes. — In carrying pipes from owe building to another it is always desirable, if possi- ble, to carry them underground. Carrying underground affords much better heat insulation, the pipes are more easily supported and are less apt to be disturbed. The simplest method of underground distribution and the cheapest is to enclose the pipes in a pine board case, as shown in Fig. 70. This arrangement, however, is not as desirable as a tunnel system, the heat insulation is not as satisfactory and the pipes are more difficult to get at for repairs. Its chief recommendation is that it is cheap. In most cases it should be used for work where the expense of a tunnel system would not be war- ranted. 194 Notes o n Heating and Ventilation A system quite largely used is to enclose pi[)es in pump logs, that is, hollow wooden pipes. These pipes are creosoted and filled with an asphah paint or some other means of preservation. They are often hned with tin or some other form of metal lining. The pipe is passed through the pump log and is usually covered with about one inch of some standard form of pipe cover- £'/ei/a/'^o/i Fig. 70. ing. This method of running the pipes furnishes quite satisfactory heat insulation. It is much more durable than the pine board duct, it is easier to install and easier to replace in case of repairs. It has, however, the dis- advantage of making the pipe quite inaccessible and in case of accident the removal of the entire system is necessary ; this in many places is very expensive. The builders of one of these pipe ducts stated that the loss in the pipes enclosed in this manner is from one-fourth of one per cent to six per cent per mile of pipe deliver- ing steam at its full capacity. The larger the pipe the smaller the proportional heat loss. Fig. 71 shows a cross section of a pipe log with covering. This pipe log construction is most used in central heating systems for building connections and where only one pipe is to be used in supplying the building. Where it is necessary to run a number of pipes the most desirable method is to run through tunnels made 195 Notes o n Heating and Ventilation of brick or cement. The size and form of tunnel used will depend upon the number of pipes to be carried, the character of the soil and the depth into the ground. Where tunnel systems have been installed the general experience has been that they more than paid for them- selves in a short time, as they entirely do away with the necessity of taking up the pipe and allow for repairs '77/7 /./nin^ £'/ev^/'/ ^v^//on P/o. Fig. 71. and frequent inspection. Fig. 72 shows a small sized tunnel. This tunnel has been used for carrying pipes not over 8 inches in diameter. The tunnel is 3 feet 6 inches wide, 4 feet 6 inches high. It is made of brick 4 inches thick, with 1 inch of Portland cement outside. This cement is painted a thick coat of tar or asphalt to below the crown of the arch. Wherever the supports come the tunnel is ribbed with an 8-inch rib of brick 16 inches wide. This rib is placed about every 10 feet. A tunnel of this kind has been in use for some time and has given good satisfaction. It is not desirable to use this sort of timnel for large pipe or where the tunnels are to be frequently inspected. For larger pipes the section shown in Fig. 73 is much more desirable. This tunnel is 5 feet by 6 feet inside dimensions. The tunnel is made of two 196 Notes o n Heating and Ventilation courses of brick or about 9 inches thick. It is plas- tered on the outside with 1 inch of cement and then tarred down to the crown of the arch. At the lowest point of the tunnel on each side is shown a 3-inch tile, which serves to carry away the drainage around the tun- nel. If possible, this 3-inch tile should be brought to some drain. In moist clay soils it is sometimes found Fig. 72. necessary to run a tile under the middle of the tunnel, connecting with the inside of the tunnel so that seepage through the tunnel walls may be carried off either to the sewer or to the ptimping plafit. In sand and in gravel soils this is not necessary, as almost no difficulty X97 Notes on Heating and Ventilation would be experienced from leakage. Fig. 74 shows a tunnel made for carrying two large pipes. The tunnel is 5 feet 6 inches by 6 feet 6 inches and gives ample Fig. 73. passageway between the pipe supports for easy access at all times. The cost of tunnels depends upon the nature of the excavation and the price of materials. To give an ap- proximate idea of what tunnels cost, the tunnel shown in 198 Notes o n Heating and Ventilation Fig. 72 has been constructed, including excavation, back filling and all necessary material, for $7.00 per linear foot. The tunnel shown in Fig. 73 has been constructed for $8.00 per linear foot, and the tunnel shown in Fig. 70 has been constructed for $9.00 per linear foot. '^ %■ ! 4 1 It , [ \j^ Fig. 74. Sizes of Pipes. — The size of the pipe necessary to carry a given quantity of steam is determined by the allowable loss of pressure that the system will permit. In a low pressure system this loss of pressure should not exceed 2 pounds. In a high pressure system it should X99 Notes on Heating and Ventilation not exceed 10 pounds. The rule most commonly used is called Babcock's rule, and is as follows : Let W ^ weight of steam in pounds flowing per minute. w = the weight of a cubic foot of steam. p^ = pressure in pounds per square inch of steam enter- ing pipe. p, =: pressure in pounds per square inch of steam leav- ing the pipe. d = diameter in inches. L = length of pipe in foet. \v (Pi — P2) d, q f Then W = 87 l (1 H — ) d The best way of handling this expression is to assume different diameters of pipe and then try a number of standard pipe sizes. In this way deter- mine the pipe size which approximates most closely the weight of steam which it is desired to carry. In low pressure gravity return systems the return is usually taken as one-half the pipe size of the steam main up to 10 inches. Above 10 inches the size is taken as one-half the size of the steam main minus one size. As, for example, a 10-inch main w^ould require 5-inch return, a 14-inch would require a 6- inch return. The size of drip main for a given steam main depends entirely upon the length of the main. It should never be less than ^-inch and it is seldom necessary to make the pipe over 134-inch. A 134- inch drip main will take care of 2,000 feet of 12-inch pipe, providing the pipe is well covered with stand- ard covering. 300 Notes on Heating and Ventilation Hangers and Anchors. — When pipes are carried through tunnels it is necessary to provide a different form of hanger than in building work. In tunnel work the head room is so limited it is ordinarily im- possible to suspend pipes from above and they must have some form of roller hanger. Fig. 74 shows ball- bearing hangers for 12-inch pipe and roller hangers for the 6-inch pipe. Fig. 72 shows a very simple form of roller hanger. Fig. 73 also shows a form of ball-bearing hanger for 8-inch pipe and roller bearing for 4-inch pipe. The ball-bearing hangers shown in these figures have given very satisfactory results. They are expensive, but the expense is warranted. In tunnel work the clearance is so small that it is necessary to know exactly where the expansion is to be taken up. The only way to be certain of this is to anchor the pipe at the point desired. These an- chors are usually made of heavy cast iron with wrought iron straps enclosing the pipe. The hangers should be built into the tunnel or building walls and should pass entirely through the wall, projecting 4 inches or more on the opposite side of the wall. The anchors should not be built into walls that are less than 12 inches thick, and preferably they should be 16 inches thick. In putting in hangers and supports in tunnel work it is a very important thing to see that a clear space is left through the center of the tunnel which will give easy access to the tunnel. The easier the access and the more comfortable the tun- nel for passage, the more frequent will be the in- spections, and such inspections insure of the piping being kept in the best possible condition. 301 Notes o n Heating and Ventilation Air Valves. — Fig 75 shows an air valve adapted for use on large heating systems. The outlet of this air valve is three-quarters of an inch in diameter. It is particularly designed to take care of the air in the OUTLET J" PIPE Fig. 75. Air Valve for Use on Steam Mains. building and tunnel mains. The ordinary sized valve used in radiators is entirely insufficient to take care of large mains. Piping that is 4 inches and over should have the larger valves. With still larger pip- ing, 10 or 12 inches in diameter, where the mains are 400 or 500 feet long, even this size is hardly sufficient to take care of the air unless a number of them are used. The valve shown in Fig. 7(1 is often used. This consists of a brass pipe ''A" four feet long, to which is screwed a 1^-inch angle valve. This pipe and angle valve are attached by a suitable elbow and 303 Notes on Heating and Ventilation nipple to the main from the point at which the air is to be removed. A yoke is fastened at elbow "B" and to this yoke two iron rods are attached. These ,4i ^ W**f."~-^' ■^"^laeasesHe^J**" Fig. 76. — This Form of Air Valve is Often Used. iron rods are connected at the other end of the yoke "C." Yoke '*C" is attached to the valve stem of the angle valve. The threads are removed from the stem 303 Notes on Heating and Ventilation of the valve so that the valve will pass freely through the stuffing" box. By means of a lock nut on the valve stem the height of the valve disc above the seat may be adjusted. To start with, however, the brass rod "A" will be cold and the valve disc will be off the valve seat and air will be alowed to pass out pipe ''D." As soon as steam comes the brass pipe "A" ex- pands, bringing the valve seat up against the disc and closing the valve so that no steam can escape. Fig. 77. Air Valve to Relieve a Fitting and Line of Pipe from Air. Another arrangement that may be used is shown in Fig. 77. At the point at which it is desired to re- move the air a 1-inch pipe is tapped into the fitting. Into this is tapped a 1-inch nipple, an elbow and a short piece of pipe, as shown. At the end of this short piece of pipe is attached a gate valve. At inter- vals along the inside of the pipe are attached large air valves, such as the one shown in Fig. 75. On start- ing up the system the gate valve is left wide open and remains open until steam begins to blow, then this gate valve is closed and the small air vajves take 304 Notes on Heating and Ventilation care of the accumulation of air that occurs from time *o time. Lack of proper air valves may cause serious acci- dents in the pipe system. In large pipes when steam is turned on it will circulate along the top of the pipe and the cold air remains at the bottom of the pipes ; the upper side of the pipe will then be hotter than the lower and hence will expand more than the under side. The tendency of the pipe is to assume a circular form, as shown in Fig. 78 by dotted lines. In Fig. 78. How Air Collects and Sometimes Breaks a Piping Sys- tem. How it Is Prevented. case of a very large pipe this has been known to wreck the piping system, breaking flanges and spring- ing the valve seats. Such a condition may be pre- vented by running the air pipes on the mains down to the bottom of the main, as shown in the figure, so that the air is removed from the bottom of the main instead of from the top of the main. In long piping systems it is very desirable that at intervals of not more than 100 feet air valves should be placed to remove the air from the bottom of the main. The size of these valves will depend upon the size of the main and they should be of ample capacity. It is not always necessary to use automatic valves. Auto- 205 Notes on Heating and Ventilation matic valves can be replaced by %-inch or ^^^-i^^^ch valves for this purpose. Air valves should be located at all high points on the return main, particularly at points where the return main rises, passes along the horizontal, and then drops down again. At such points air valves should be located at the top of the main. If this is not done the air will accumulate at these high points and prevent passage of water, sometimes almost as effectively as though the main were valved at these points. Surge tanks, traps and other devices where air may accumulate should be provided with air valves. In fact, when trouble is experienced in a steam pipe sys- tem one of the first things that the builder should assure himself of is that the air is being properly removed from all parts of the system. COMBINATION OF STEAM AND HOT WATER SYSTEM. There are a number of systems using a combina- tion of exhaust steam and hot water for use in con- nection with central heating systems. The exhaust from the engine is passed through an exhaust heater and the water heated in this heater is circulated through the heating system by means of a pump. In this way exhaust steam can be used for heating a large territory without producing any back pressure. This form of heating may be used in connection with a condensing engine. The water being circulated by a pump under pressure insures its actual circulation throughout the whole system and makes possible the use of relatively small mains for heating purposes, 206 Notes on Heating and Ventilation smaller than would be required for either low pres- sure steam or exhaust steam. In addition to the ex- haust steam heater there may he used either a hot water boiler or an auxiliary live steam heater, so that in case the exhaust is insufficient for heating the water, the water may be passed through this live steam heater, bringing it up to the proper tempera- ture. In some cases a Greene economizer has been used for furnishing additional heat, thereby making use of the waste from the boiler. Systems of this kind have been installed in a num- ber of cities and as high as one thousand houses heated from a central heating system. In these hot water circulating systems two general forms of pump are used, either a centrifugal pump driven by a mo- tor or engine, or a piston pump of the ordinary type. In most cases unless a high pressure is desired, a centrifugal pump is desirable. The central hot water heating system has one particularly desirable feature — the hot water leaving the system may be adjusted to correspond with the external temperature. The size of hot water mains is determined from the ve- locity of water circulating in the main. In small mains it should not exceed 2 feet per second ; in large mains it may be as high as 4 feet per second. Central heating by means of hot water is particu- larly adapted for residence districts, as the system can be installed with less expense per foot of main, making it possible to cover profitably an area having the houses scattered. Central heating with steam is particularly adapted for close business districts where steam is the usual form of heating and where the piping system will be relatively short for the load carried. 207 Notes on Heating and Ventilation In connection with the systems using pressure there must be used some form of expansion tank. Some of these systems use an open expansion tank, allowing the water in the return system to enter this open tank at practically atmospheric pressure, the suction of the circulating pump being connected to this open tank. Where this system is used a piston type of pump would probably be a desirable form. Where the centrifugal type of pump is used it would be desirable to use a closed tank. In this case the tank is partly filled with water and partly filled w^ith air. The expansion and compression of the air al- lows for the change in the volume of water due to changes of temperature conditions. In this case 'the pump will then only furnish the pressure necessary to overcome the resistance of the piping system. The air side of the expansion tank should be provided with an air pump, so that pressure may be maintained by means of an air pump on the air side of the sys- tem and the proper quantity of air carried in the tank at all times. 208 CHAPTER XIII. PIPING, COVERING AND OTHER APPLIANCES. Pipe Covering. — In all piping installation it is cus- tomary to cover the distributing pipes, except ra- diator connections. It is good practice to cover the risers passing through buildings, together with all steam and return mains. Where the water mains pass through rooms in which any drip from the pipes would be objectionable, such pipes are also covered to prevent the condensation of moisture on the out- side of pipes. In general the best form of non-con- ductor is dry air, which is so confined as to prevent circulation. In all successful forms of covering air is confined in the structure of the covering and the effectiveness of the covering depends largely upon the confining of this air. The effectiveness of differ- ent forms of covering was determined in a series of experiments made under the direction of Prof. M. E. Cooley, University of Michigan. Table LII shows the relative effectiveness of some of the different forms of covering. The results of these tests show that hair felt is the best non-conductor. It is not, however, suited for over 5 pounds pressure, as it chars and breaks down at higher pressure owing to the higher temperature; this is also true of the wool felts. In low pressure work at such temperatures as are ordinarily used, hair felt is found to be quite satisfactory. It is ex- pensive, but its expense is warranted in the saving from condensation in the piping. 209 Notes o n Heating and Ventilation TABLE LII. Relative Value of Different Pipe Coverings. Material of covering Moulding coverings. 1. Asbestos 145 .319 1.23 136. .803 2. Magnesia 119. .224 .94 166. .915 S. Magnesia and asbestos. .125 .300 1.12 118. .879 4. Asbestos and wool felt.. .190 .228 1.12 102. .910 5. Wool felt 117 .234 1.16 110. .904 6. Wool felt and iron with airspace 134 .269 ... 125. .828 Sectional Coverings. 7. Mineral wool 097 .193 .94 91. .952 8. Asbestos sponge 105 .220 1.12 102. .920 9. Asbestos felt 100 .217 1.35 94. .923 10. Hair felt 080 .186 1.45 75. .960 Non- Sectional Coverings. 11. Two layers asbestos paper 388 .777 ... 364. .263 12. Two layers asbestos paper, one inch hair felt and one thickness canvas 070 .150 ... 68. 1.000 Table LIII shows the relative efifectiveness of differ- ent thicknesses of covering. Column 3 of this table shows the relative effectiveness of the various thick- nesses of covering compared with the bare pipe. From this table it is not a difficult matter to figure the amount of saving that may be made by using various TABLE LIII. Heat Transmission for Varying Thicknesses of Covering. Condensation Ratio of Conden- B. T. IT.'S Thickness of per sq. ft. per sation covered transmitted per covering. hour in pounds. to bare pipe. sq. ft. per hour, inches. ; ^] % .120 .281 167. % .117 .255 163. 1 .107 .231 149. lU .099 .219 138. 1% .087 .191 121. 2 .078 .19 108. The covering used in obtaining the above results was a wool felt. 210 Notes on Heating and Ventilation thicknesses of covering. Knowing the amount of steam carried per year and the cost to produce 1,000 pounds of steam, and having the results shown in this table, we can easily compute the financial saving to l^e made in the various thicknesses of covering. In doing this it is usually found that for 1)uilding work an incli covering is sufficiently heavy ; but for tunnel work and all work where the heat loss from the pipe is entirely lost and does not enter the build- ing it is economy to use covering 2 inches thick. Where superheated steam is used at high tempera- tures the covering is from '3 to 5 inches thick. Table LIV' shows the heat lost through a 1-inch wool cover- ing with various steam pressures. In covering a pip- ing system the fittings and valves should be covered the same thickness as the pipe. This also applies to flanges and steam traps. Where flanges and other parts which require removal are covered they should be covered so that the covering can be taken off easily. A satisfactory method of doing this is to form a covering composed of one layer of asbestos paper, 1 inch of hair felt and one thickness of 8- ounce duck. These are quilted together with cord so that the jacket is firmly held in one piece. This cov- ering is then fastened over the pipe to be covered by means of hooks and laces. TABLE LIV. Heat Transmission for Varying Pressures. Condensation Ratio of Conden- B. T. Tf^.'s Trans- Gauge per sq. sation of covered mission per pressure. ft. per liour. to bare pipe. sq. ft. per hour. 5. .3 .108 .239 100. 9.fi .111 .233 104. 1.5.5 .126 .227 110. 20.5 .134 .223 119. The advantage of covering may be shown from the following computation : 211 Notes on Heating and Ventilation Example. — In a given steam plant it was found that the heat lost from bare pipes per hour was 3,355,000 B. t. u. In the particular plant in ques- tion the number of heat units required to make a pound of steam was 990, and this loss of heat would represent a condensation of 3,390 pounds of steam per hour. Assuming an evaporation of 9 pounds of steam per pound of coal this would be equivalent to 376 pounds of coal per hour. If the plant were op- erated 365 days in the year and 20 hours a day, and the coal cost $3.25 per ton, the yearly loss would be $2,069. By covering the pipe 1 inch thick with hair felt the loss which would result from the bare pipe would be reduced to 15 per cent, which equals $314, making a saving of $1,755 by putting on covering. This amount capitalized at .10 per cent would repre- sent an investment of $17,550. In the particular case in question the actual cost of the covering was but $3,500. Air Valves. — In steam piping work it is very im- portant that the piping system be provided with suf- ficient number of properly located air valves. Pri- marily, air valves should be located at the points in the piping at which air accumulates in quantity. We are familiar with the fact that when a radiator is not provided with an air valve steam will not circulate into it and it does not become warm. This is also true of both steam mains and the return system. The writer has seen the entire return system of a building plugged with air on account of there being no air valve on a high point in the return main. For radiators an air valve similar to that shown in Fig. 79 is usually used. You will notice that this 212 Notes o n Heating and Ventilation air valve allows air entering from the connection to the radiator to pass directly to the top of the air valve body and out through a small hole or opening, which may be adjusted by means of a screw plug. If water enters the air valve, the water will rise in the valve body until the copper float, having a pin on its upper end, rises so as to close the exit from the air valve, Fig. 79. Type of Air Fig. 80. Air Valve Fig. 81. Air Valve Valves Commonly Used on Radiators Adapted to Hot Used in Radiators. In Connection with Water Work. Paul Valve. and no water is allowed to escape. When steam en- ters the air valve the expansion plug shown at thr center of the air valve expands, raising the copper float, again closing the outlet from the air valve. Fig. 80 shows an air valve which is used for radi- ators in connection with a system of air piping from the air valves. (1) is a cap screw screwed down on the valve with a lead washer, making a tight seat. (2) is a hollow screw upon which the expansion post (3) sets, closing the valve. The adjustment of the valve is done with screw (2), and this may be done 213 Notes on Heating and Ventilation without disturbing- the valve. (3) is a hollow part fastened at (5) and held in place by the union (6). This should never be disturbed. (4) is the nipple of the valve body, by which it is attached to the ra- diator. This is the union for attaching to the piping of the Paul system or other air piping system. (7) is a nut which forms the union for attaching this pip- ing. The operation of the valve is as follows : The air is drawn in from the radiator through nipple (4) into the valve between the adjusting screw (2) and the composition part (3) passing down through (3) into the pipe. When steam enters the composition part becomes heated and expands, thereby closing the opening between (3) and (2). When air again ac- cumulates and cools this composition part contracts, permitting air to be drawn through the tube. There are two typical forms of air valve, one clos- ing off the air by the action of the float, the other closing off the air by the action of heat expanding a plug. Fig. 79 shows a combination of these two principles, which prevents the throwing of water or the discharging of steam. Fig. 80 exemplifies the simple expansion operation. The valve shown in Fig. 80 would allow cold water to pass. Fig. 81 shows an air valve particularly adapted to hot water work. In this air valve the float principle alone is used. Air enters in through the connection to the radiator, as shown by the arrow in the cut, passes under the float and escapes through a small tube which reaches to a point near the top of the air valve. As soon as the water enters the float lifts, due to the air compressed by the water under the float, 214 Notes o n Heating and Ventilation Table LV. WROUGHT IRON AND STEEL STEAM, GAS AND WATER PIPE TABLE OF STANDARD DIMENSIONS Diameter Circum- ference Transverse Areas Length of Pipe per Sq. Ft. of Length of Pipe Containing One Cubic Foot Nominal Weight Per Foot 11 "re 3 (Q S u <5q c u 0) 4-1 X c u c In. In. In. In. In. Sq. In. Sq. In. Ft. Ft. Ft. Lbs. % .405 .27 1.272 .848 .0573 .0717 9.44 14.15 2513. .241 27 H .54 .364 1.696 1.144 .1041 .1249 7.075 10.49 1S83.3 .42 18 % .675 .494 2.121 1.552 .1917 .1663 5.657 7.73 751.2 .559 18 H .84 .623 2.639 1.957 .3048 .2492 4.547 6.13 472.4 .837 14 H 1.05 .824 3.299 2.589 .5333 .3327 3.637 4.635 270. 1.115 14 1 1.315 1.048 4.131 3.292 .8626 .4954 2.904 3.645 166.9 1.668 111^ m 1.66 1.38 5.215 4.335 1.496 .668 2.301 2.768 96.25 2.244 111^ m 1.9 1.611 5.969 5.061 2.038 .797 2.01 2.371 70.66 2.678 1154 2 2.375 2.067 7.461 6.494 3.356 1.074 1.608 1.848 42.91 3.609 11^ 2^ 2.875 2.468 9.032 7.753 4.784 1.708 1.328 1.547 30,1 5.739 8 3 3.5 3.067 10.996 9.636 7.388 2 243 1.091 1.245 19.5 7.536 8 m 4. 3.548 12.566 11.146 9.887 2.679 .955 1.077 14.57 9.001 8 4 4.5 4.026 14.137 12.648 12.73 3.174 .849 .949 11.31 10.665 8 4H 5. 4.508 15 708 14 162 15.961 3.674 .764 .848 9.02 12.49 8 5 5.563 5.045 17.477 15.849 19.99 4.316 .687 .757 7.2 14.502 8 6 6.625 6.065 20 813 19.054 28.888 5.584 .577 .63 4.98 18.762 8 7 7.625 7.023 23.955 22.063 38.738 6.926 .501 .544 3.72 23.271 8 8 8.625 7.982 27.096 25.076 50.04 8.386 .443 .478 2.88 28.177 8 9 9.625 8.937 30.238 28.076 62.73 10.03 .397 .427 2.29 33.701 8 10 10.75 10.019 33.772 31.477 78.839 11.924 .355 .382 1.82 40.065 8 11 11.75 11. 36. 914 1 34. 558 95.033 13.401 .325 .347 1.51 45.028 8 12 12.75 12. 40.055 37.7 1 113.098 14.579 .299 .319 1.27 48.985 8 Piping is often designated as "Merchant Pipe." This term is used to indi- cate soft steel pipe taken from stock. In sizes from % inch to 6 inch it is about 5-^. under the card weight and about 10^^ under card weight for sizes above 6 inch. Full weight pipe is made of stock that will produce pipe of full card weight. 215 Notes on Heating and Ventilation and the rubber valve held by the rim closes the open- ing through v^^hich the air escapes. The valve as shown here is made for connection to an air valve piping system. A similar valve is made without this connection. In the air valve shown for connection to a piping system there is a three-way plug cock in the air valve, Avhich allows of air and water being drawn directly to the air pipe system and of being en- tirely closed oflf. Pipe. — Piping for heating systems is made either of wrought iron or mild steel. An extra price must be paid for wrought iron pipe. The smaller sized pipes up to and including 1^4 inches are butt welded and are tested to 300 pounds pressure. Large sizes are lap welded and tested to 500 pounds pressure. Pipe is shipped in lengths of from 16 to 20 feet and is threaded at both ends, but a coupling is put on only at one end. The standard size pipes in use are given in ta- ble No. LV. Piping is often designated as ''Merchant Pipe." This term is used to indicate soft steel pipe taken from stock. In sizes from i/s-inch to 6-inch it is about 5 per cent under the card weight and about 10 per cent under card weight for sizes above 6-inch. Full weight pipe is made of stock that will produce pipe of full card weight. Both steel and wrought iron piping is designated as wrought iron pipe. If wrought pipe is desired it should be called "strictly wrought iron pipe." Piping is made in three weights — standard pipe, the dimensions of which are given in Table 42 ; extra 216 Notes on Heating and Ventilation strong pipe, suitable for working pressures up to 2o() pounds ; double extra strong pipe, suitable for work- ing pressures up to 500 pounds. Fittings. — For heating work standard weight cast iron screwed fittings are used up to 6 or 8 inches in diameter. Above that it is usual to use flange fittings. When screwed fittings are used, flanges must be placed in the piping to provide for disconnecting in case of repairs. In screwing pipes into fittings the pipe grease should always be placed on the pipe threads so that the excess will not be left in the fit- tings. In describing a tee always give the dimensions of the "run" first and of the side outlet last. A bullhead tee is one in which the side outlet is larger than the outlets in the "run." It is better practice to use reducing elbows or re- ducing tees than to use standard tee or elbows and reduce them by means of bushings. Valves. — Valves 2 inches and under are made of all brass wnth removable discs. For radiators where the piping comes through the floor, angle valves are used. Where the piping comes over the floor ofifset or corner ofifset valves are used. Gate valves should be used in horizontal lines of piping which carry con- densation. Globe valves may be used in vertical pipes but not in horizontal pipes, as they dam up the water passing in the pipe. Where check valves are used they should be of the swinging check pattern. Valves above 2 inches are usually used with iron bod- ies and brass mountings and should have renewable disc seats. 317 CHAPTER XIV. AUXILIARY DEVICES FOR HEATING SYSTEM. A temperature regulator is an automatic device which will open and close the valve of the radiator so as to keep the room at a constant temperature. The temperature regulator in general consists of three parts. First, a thermostat which is so constructed that its parts will move with a change of temperature in the surrounding air and the motion of these parts will directly or indirectly open the dampers or valves which control the heat supply. Second, there must be some means of transmitting the motion from the parts of the thermostat to the valves or dampers con- trolling the heat supply. Third, some form of me- chanism for opening the valves or dampers. In most temperature regulating systems the thermostat mere- ly furnishes power enough to close or open an air valve or electric switch and thus start or stop the operation of the valves or dampers. The form most used at the present time uses com- pressed air to operate the valves and dampers. In the Johnson thermostat a small air valve is opened by the expansion of a curved strip composed of two materials having different rates of expansion. The bending of this strip due to change of temperature allows the air to escape and a small diaphragm to move back, thus opening a second valve allowing the air to come from the compressor or source of air supply and close the valve or damper on the radiator. When the room becomes cool the contrac- 218 Notes o n Heating and Ventilation tion of this strip closes the first small valve forcing out the diaphragm and closing off the compressed air supply to the valve or damper and releasing the air already in the valve or damper. Another form of thermostat extensively used is operated by means of a liquid confined in a thin metal vessel, the liquid Fig. 82. haxing a very high degree of expansion. As the liquid expands or contracts it controls the system of valves controlling the heat supply to the room. Temperature regulation is a desirable thing in all large heating systems, particularly for public Inijlcl- 210 Notes on Heating and Ventilation ings. The systems are quite expensive, but the ex- pense of construction is more than offset by the sav- ing in fuel bills. The saving in fuel bills in most cases is not less than 15 per cent and often as high as 20 per cent. In general the operation of these systems has been entirely satisfactory even after they have been in use some time without any attendance. The control of the temperature of the room should be regulated within 3 degrees. With proper care these systems should con- trol the temperature of the room within 2 degrees. Temperature regulating apparatus is particularly de- sirable in school rooms ; this places the temperature of the room outside the control of the instructor and it is then free from his own personal ideas in the matter, thus adding much to the health and comfort of the occupants of the room. With the fan system it is difficult to get satisfactory operation without tempera- ture regulation. The application of temperature regula- tion to the fan system is shown in Fig. 83. Air Piping System. The discharge of air from the air valves and radiators often produces a very disagree- able odor and in addition it is very difficult to obtain an air valve which will not at times discharge a certain amount of steam or water. This difficulty may be overcome by using an air valve so designed that the discharge connection to the valve can be fastened to a piping system. The pipes and air valves are carried to the basement, collected into a larger pipe and discharged to a sewer or suitable vessel. A system of air piping is very desirable, particularly in large buildings, such as hotels and office buildings, where it saves materially in the attendance necessary 230 Notes on Heating and Ventilation to keep the plant in operation. It is also desirable in nice residences where any discharge of water or steam might injure the furnishings. In case it is desirable to install a vacuum system of heating this system could be connected directly to a vacuum pump insuring more rapid circulation in the radiation. Damper Regulators. It is always desirable in a steam or hot water heating plant, particularly steam, to Install some form of damper regulator on the boiler. In some heating plants it consists of an ordi- nary rubber diaphragm enclosed in a metal case. The stearn is allowed to come in contact with one side of the diaphragm, pushes a leyer attached to the other side of the diaphragm. This lever operates a damper controlling the air supply to the fire and sometimes also operates the check valve in the breeching. This is a very desirable arrangement, as it reduces the at- tendance necessary to keep the pressure in the boiler at the point desired. Humidity Regulation. — The humidity of the atmos- phere is a very important consideration in any heating system. When the air is very dry it is necessary for a room to have a mucli higher temperature in order that it may feel comfortable than when the air is moist. It is, therefore, important that we keep the humidity at a point as high as consistent witli satisfactory operation. Cold air contains proportionately less moisture than warm air, and therefore when cold air is heated and brought into a building it should be moistened in order to keep a proper per cent of humidity. The average humidity is al)out 70 per cent, in the arid regions humidity may be as low as 30 per cent. Humidity as low as 30 per Notes o n Heating and Ventilation cent produces irritation of the lungs and smarting of the eyes. In cold weather, if the humidity of the out- side air is 70 per cent and this air is heated and brought into the room without moistening, its humid- TO a* PA Si DIfyiPBR Fig. 83. ity may be reduced as low as 30 or 35 per cent, mak- ing the air as dry as in the most arid regions. This produces a serious effect upon the inhabitants and also the furniture of the room. The decrease of hu- midity due to the action of the heating system occurs particularly in the indirect heating system. There has been placed on the market what is called a humid- Notes o n Heating and Ventilation ostat. This is similar to a thermostat except that it is arranged so that as the moisture decreases in the room the liiimidostat opens up a series of steam or water jets in the air supply so that the air in ])assin<^ Fig. 83. through the steam or water jet takes up moisture. When the moisture gets to a certain percentage, deter- mined by the setting of the humidostat, the apparatus closes ofT automatically the steam or water jets. Such devices are particularly desirable in connection with school and hospital heating plants. Air Washers. — In the large cities the smoke and dust in the air makes it undesirable to introduce thjs 933 Notes o n Heating and Ventilation air directly into the room for ventilating purposes. A great many schemes have been tried to remove the Z2i Notes on Heating and Ventilation dust from the air. The earliest form was to use bur- lap screens through which the air passes. These screens work fairly well, but the finer dust will always be carried through them. A better plan is to pass the air through a sheet or series of sheets of water. After passing through these sheets of water the air is passed through an apparatus which removes the excess of water. Fig. 84 shows the general arrangement of an air washing system. As you will notice from the figure, the air first passes through a tempering coil which raises the temperature from 60 to 70 degrees, then passes through the sprays or sheets of water, then through the eliminator, where the excess of water is removed, and then it passes to the heating coils to be heated. The water used for washing the air is circulated over and over again by means of a small centrifugal pump driven by a motor. In some cases it is desirable that the air should be cooled. This may be done by placing cooling coils in the tank where the water collects after having washed the air, and reduc- ing the temperature of this water to the desired point or by washing with cold w^ater. The washing of the air with water also increases the humidity of the air. In a plant installed by the author the humidity of the air has been kept at a point not lower than 70 per cent by means of this washer. Air washing devices are very effective in removing dirt ; the amount of dirt removed in some cases is very large. Vacuum Heating Systems. In the systems of steam heating that have been de- scribed the steam has been used at a pressure higher than that of the atmosphere. Plants are now installed 225 Notes on Heating and Ventilation in which the pressure in the radiator may be atmos- pheric pressure or lower. The advantages of such a system are : First. Where exhaust steam is used the heating w^ill not increase the back pressure on the engines, but may reduce the back pressure. Second. The air can be completely removed from the coils and radiators. Third. There is perfect drainage through the re- turns, preventing all possibility of water hammer. There are two distinctly different types of vacuum heating systems, one in which the air is drawn from the radiator by means of an air pump through the air valve, as shown in Fig. 75, and the other in which the radiator is fitted with a special form of return valve and vacuum is maintained on the return system by means of a pump or aspirator. The best example of the first type is the Paul sys- tem. In this system the air valves are all connected to a system of air mains. These mains extend to an air ejector. This injector may be operated by either steam or water. The advantage of this system de- pends principally on the quick removal of the air from the piping and radiators. This action is often strong enough to produce a pressure in the radiator lower than atmospheric pressure. The vacuum system of heating in which the air is drawn from the air valves is particularly desirable in hospitals and school buildings, as it does away with the objectionable odor from the air valves. This vac- uum system of heating does away very largely with the attendance required by air valves. The best example of the second type of vacuum 226 Notes on Heating and Ventilation system is the Warren Webster. Fhis consists of an automatic outlet valve on each coil and radiator con- nected to a return system in which vacuum is main- tained by means of a pump. Iliese automatic valves are traps which allow the water of condensation to pass l)ut close as soon as the water is removed. One of the advantages of this system is that it permits of the quantity of steam entering the radiator to be regulated without any possibility of water ham- mer. This system always requires two pipe radiator con- nections, but has the advantage that the return piping may be made smaller than in a gravity return system. The vacuum system has other advantages. It also permits of the radiator being placed lower than the level of the boiler and the condensation is raised from the lower level by means of the vacuum in the system. Oftentimes this enables the engineer to overcome seri- ous difficulties in the design of the heating plant. These systems can be profitably installed in old plants where the steam mains are overtaxed, owing to fre- quent additions to the plant. By additions of the vacuum system these old mains can be made to carry a larger weight of steam, the vacuum system permit- ting a higher velocity of steam in the system without increasing the back pressure. 227 1^ y )iill ^ One copy del. to Cat. Div. SEP s ISfl