UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA AIR CONDITIONING FOR CALIFORNIA HOMES BALDWIN M.WOODS AND BENEDICT K RABER BULLETIN 589 MARCH, 1935 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction ... 3 Test residences for study of air conditioning 4 Scope and purpose of this discussion ■ 4 Principles of comfort cooling and heating 5 Relief for hay-fever sufferers 6 Laboratory investigations of comfort conditions 7 The comfort zone 7 Common aspects of heating and cooling 9 Important distinction between heating and cooling for comfort .... 9 Weather zones 11 Weather conditions in California 11 The question of economy 13 Principles followed 13 Air conditioning, a prospective necessity rather than a luxury .... 14 Sample houses 14 Insulation 19 Principal problems in cooling 19 Effect of insulation applied to the sample cottage 19 Insulation of construction other than houses 22 Temperature delay due to insulation 22 Mechanical equipment 23 Types of mechanical equipment 23 Application of equipment to the sample cottage 25 Attic ventilation with night air circulation 25 Complete air-conditioning equipment 27 Room-unit conditioners with ice-melting tank 30 Central condenser equipment with room-unit conditioners 31 Combinations of equipment 31 Initial and operating costs of typical cooling systems 33 Initial costs 33 Operating costs 36 Factors affecting the selection and operation of air-conditioning systems . . 37 1. The building and its structural features 37 2. The portion of the building which is to be air conditioned 39 3. Outside air conditions to be encountered 40 4. Inside air conditions to be maintained 41 5. The allowable cost of air-conditioning equipment 42 Acknowledgments 43 Suggestions for additional reading 44 Periodicals 44 Books 44 Pamphlets 44 AIR CONDITIONING FOR CALIFORNIA HOMES 2 BALDWIN M. WOODS 3 and BENEDICT F. KABER 4 INTRODUCTION The cooling of homes in summer has recently made rapid progress. Before long, equipment to provide air conditioning as an all-year proc- ess will probably become commonplace. Interest in this development is widespread; many houseowners wish to know the meaning of air con- ditioning, the results that can be reasonably expected from different methods of providing it, and the cost of such service. This bulletin rep- resents an effort to provide useful information to the houseowner. Whether applied to heating a house in winter or to cooling it in sum- mer, the word "condition" means to control the temperature, the hu- midity or moisture content, and the purity of the air, and to regulate its movement. The most rapid progress has been made in appliances to be employed in industry. In these cases, either the conditions for the fabrication of a product or the need for maintenance of operating efficiency has stimu- lated the development, and resulting economies pay the cost. Of course, summer cooling has appeared to a considerable extent in hotels and res- taurants, small shops, railway trains, and theaters, where the added comfort attracts customers. The development has run from manufactur- ing to service industries and is on its way to the home. Since the largest potential field of application is the home, one may wonder why this was not the first place of use. It appears, however, that many useful mechanical devices have entered the home only after suc- cessful pioneering in business. On the farm one sometimes observes side by side a barn for the livestock, specially designed to provide adequate shelter and ample natural ventilation, and the farmer's house with little i Beceived for publication January 11, 1935. 2 This publication is the thirteenth of a series reporting results of investigations conducted by the California Agricultural Experiment Station in cooperation with the California Committee on the Belation of Electricity to Agriculture. This study was made by the Department of Mechanical Engineering of the University of California. 3 Professor of Mechanical Engineering. *■ Professor of Mechanical Engineering. [3] 4 University op California — Experiment Station or no provision for attic air change, and ready to overheat the family in the summer. The occupants of the home are now asking consideration of their comfort. It is to an understanding of air conditioning in the home that this bulletin is devoted. The group investigating the subject is unanimous in the belief that insulation is of primary importance in solving the problem, either for heating in winter or cooling in summer. Therefore, insulation has been given more extended treatment than the size of the bulletin would other- wise justify. This discussion has also been made as practical as possible. Test Residences for Study of Air Conditioning. — During the last two or three years, the need for rapid progress has led to the construction and operation of several test residences. Of these, three well-known ones are (1) at the University of Illinois, (2) at Schenectady, under the auspices of the General Electric Company, and (3) at Mansfield, Ohio, under the auspices of the Westinghouse Electric and Manufacturing Company. Much is being learned from the test houses concerning the best meth- ods of operation and the best systems of control. The equipment em- ployed to accomplish these purposes has been undergoing rapid changes. Engineers are endeavoring to perfect heating and cooling appliances which will condition air to a desired state. Scope and Purpose of This Discussion. — In this analysis, equipment for industrial use will be discussed only as it contributes to better under- standing of available methods. Attention will be devoted especially to rural homes and their problems. Since rural homes present on the aver- age more varied conditions than city homes, the study of their problems may call for a more complete listing of methods and results than would otherwise be justified. The problems of heating and cooling will be separated. Much greater progress has been made in the standardization of heating equipment than in that of cooling equipment. It will be wise, in the interest of brev- ity and clearness, to emphasize the cooling problem. To be sure, there is the chance in this of overlooking the joint heating-cooling equipment installation. The two problems should be considered simultaneously. Ultimately, the home should in many cases have its heating and cooling equipment combined. The ducts and piping will often serve both pur- poses. Some promising combined units are already announced. Addi- tional comparisons of heating and cooling problems will be considered later. The relative merit of different methods, applied under various condi- tions, will be discussed. An attempt will be made to supply the necessary Bul. 589] Air Conditioning for Homes 5 background for understanding the types of equipment available, their principles of operation, and the degree of effectiveness to be expected under certain conditions. Clearly, details of computation, problems of design, and the selection of equipment for a given home are technical problems of some complexity, the solution of which often requires an expert. Many otherwise good installations will probably give difficulty in practice because of errors in fitting the installation to the house. A section on initial costs and estimated operating costs of various types of equipment has been included as a general guide. These costs are based upon 1,000 hours of operation per summer. Of course, the amount of operation depends upon the climate, the special character- istics of a given season, the insulation of the house, and the inclination of the houseowner. Consequently, the cost should be adjusted to the actual time in prospect. For the Great Valley of California, and even for the inland regions of southern California, the cooling season appears to be from 75 to 150 days. Continuous cooling, of course, is not required throughout the entire period. PRINCIPLES OF COMFORT COOLING AND HEATING Definite knowledge of air conditions for human comfort is still limited and inexact. Of the four principal factors controlling air conditioning — namely, air temperature, movement, humidity, and purity — the first three have been shown by experimentation to combine to give the im- pression of warmth or cold which is experienced by the individual. A study of the physiological reaction to combinations of these factors is very interesting. For example, it is a matter of common knowledge that, within limits, one can endure a higher temperature with air of low hu- midity than with air of high humidity. Also air movement at ordinary temperatures generally produces a feeling of coolness, or at least of less heat, as shown by the universal attempt to find a breeze when the tem- perature is unpleasantly high. Throughout all extremes of climate the human body attempts to main- tain the same temperature. The body evidently has a thermostat, like a mechanical refrigerator or a heating system. The methods taken by the body to keep cool when the outside temperature is high and to keep warm when the outside temperature is low, may be described without, however, adequately explaining what controls the whole process. The location and construction of the "thermostat" has not been fully re- vealed, although physiologists believe there is a heat center in the brain. A nerve mechanism controls the surface capillaries through the "vaso dilators" and "constrictors." Whenever the body temperature is raised, 6 University op California — Experiment Station the dilators permit greater flow of blood in the capillaries, which, in turn, permits greater heat radiation. The opposite occurs when the body is chilled. One of the most interesting phenomena in connection with body cool- ing is the function of the sweat glands. Consider a person exposed to air of high temperature with fair movement. As the temperature increases above that of the body, if there should be no perspiration, the outside air would add heat to the body. This is due to the simple fact that heat flows from the hotter air to the cooler body. If, on the other hand, the sweat glands are functioning properly, the body is covered with a film of moisture, and the air flowing by, unless it is entirely saturated with moisture, absorbs additional moisture. The evaporation of the perspira- tion withdraws heat from the body and hence acts as a cooling process. Therefore, the body mechanism is constructed to provide liberal action of the sweat glands whenever the temperature rises. If the temperature becomes high, the wind velocity likewise high, and the humidity low, the perspiration may be evaporated so fast that the skin surface is maintained dry. In this case a moisture film does not protect the body and the hot air does transfer heat to the body. All of us, at one time or another, have experienced a dry hot wind, so hot and so dry that to be in the breeze was far less comfortable than to be out of it. At the other end of the scale is the condition of the man exposed to cold weather. As the surface of the body is chilled the flow of blood through the capillaries is reduced. This continues until all of the outer circulation of the body has been temporarily stopped and the blood is sent through the central system of large blood vessels at a rapid rate, maintaining the central portion at its standard temperature, as far as possible. When this equilibrium can no longer be maintained, death from chill is imminent. Relief for Hay-Fever Sufferers. — Dusts and pollens as breathed from the air are the cause of discomfort and even loss of health to many per- sons. Mock 5 in 1919 estimated that there were five million workers in the United States whose health was jeopardized by dusts alone. Conditions in the home are usually much better than in many industrial plants, but sufferers from ailments due to dusts or pollens become susceptible to smaller and smaller quantities of the irritant. To these persons the filter- ing of the air in home or workshop is a wonderful relief. Recently, a number of hospitals have equipped wards to care for these cases. The results are reported to be excellent. The general sense of physical well- s Mock, Harry E. Industrial medicine and surgery, p. 205. W. B. Saunders Com- pany, Philadelphia. 1919. Bul. 589] Air Conditioning for Homes 7 being experienced on a clear day after a rain is a strong testimonial to the merits of clean air. A further result of filtering, of interest to the housekeeper, is the trapping of the dust before it settles in the house. Dusting of furniture and cleaning of curtains and drapes is needed considerably less often. Laboratory Investigations of Comfort Conditions. — The purpose of air conditioning in homes is to produce conditions conducive to human comfort. As stated above, knowledge of what constitutes comfort is at present limited. Comfort appears to be in part a matter of physiological response to stimuli and in part psychological response. It is much to be hoped that investigations will be made and the results translated into terms usable by engineers. There are definite indications of relations between the heart rate, the respiration rate, and the condition of the skin, as physiological factors, and the sensation of comfort as a psychological factor. Engineers in charge of operation of air-conditioning installations located in buildings occupied by both men and women believe that on the average, the com- fort temperature for women is likely to be about 2° F higher than for men, owing probably to considerable differences in clothing. It is found also that not every one is comfortable under a given set of conditions and further that the state of a given person varies from time to time. Undoubtedly also, the weight of clothing worn and the activities of the persons in air-conditioned buildings have much to do with comfort. The Comfort Zone. — Until more complete determinations have been made, the laboratory studies of the American Society of Heating and Ventilating Engineers will probably serve as the standard guide to com- fort conditions. This society has determined the combinations of tem- perature and humidity, which, for given air velocities, will be found comfortable by many persons. 6 These combinations have been shown in the comfort zones, presented in figure 1. For the purpose of this chart, the subjects were asked to vote "com- fortable" or "uncomfortable" for each condition experienced. Some of the tests conducted in summer showed comfort at higher temperatures than in winter, doubtless owing to the adjustment of the body to the seasons. Thus, 98 per cent of the subjects felt comfortable in the summer at a temperature of 75° F and a relative humidity of 60 per cent. In winter, this condition was a little warm for many, and only 50 per cent were comfortable. At any time there may be some who desire excep- tional conditions. 6 Houghten, F. C, and C. P. Yagloglou. Determining lines of equal comfort. Amer. Soc. Heating and Ventilating Engin. Trans. 29:361. 1923. Yaglou, C. P., et al. How to use the effective temperature index and comfort charts. Amer. Soc. Heating and Ventilating Engin. Trans. 38:410. 1932. 8 University of California — Experiment Station 90 80 70 60 r- 50 Z UJ o UJ 40 30 5 2° D X UJ > < _l LU a: 70 60 50 40 30 20 98% '•/Summer Comfort Zone 07. 507. 981 507, 07. \\ 1 , fc ^ \ \ \ \ \ \ \ \ 0% 60% 98% 50% 0% > 1 1 j i j j 97% <\. '^Winter Comfort Zonef<£ 6 4? 07. 507. 977. ; 50% 0% y l\ \ I \ n V \ \ \ \ 0% 50% 97% 50% o% 60 70 80 AIR TEMPERATURE (Deg. Fahr.) 90 Fig. 1. — Comfort zone in terms of relative humidity and air tem- perature, as determined by the American Society of Heating and Ventilating Engineers. Under the conditions of the test, the sub- jects were at rest and exposed for 3 hours or more, and the air move- ment was 15 to 25 feet per minute. The upper chart is for summer, the lower for winter. Each line shows the various combinations of temperature and humidity at which a given percentage of subjects expressed themselves as comfortable. Bxil. 589] Air Conditioning for Homes 9 An interesting measure of the effect of humidity is the slope of the lines in the diagram. For the temperatures here shown a decrease in humidity always accompanies an increase in the temperature for com- fort. This means that at higher temperatures relatively drier air is pre- ferred. In general, the addition of moisture to warm air, that is to say, air above 70° or 80° F, makes it less comfortable; the air feels much hotter. Also, there is a point, somewhere between 45° and 50°, below which the addition of moisture to air makes it feel colder. This may explain the reputation for cold weather of certain seaports where the winter tem- perature runs between 30° and 45° and there is much wind from the ocean. Additional charts become important to the engineer to show the re- sultant state of moist air after its temperature has been changed and after a certain amount of moisture has been added or subtracted. Such charts are called "psychrometric" charts. The comfort zone is an ele- mentary diagram of this kind. For a detailed account of psychrometric charts the interested reader may consult textbooks on refrigeration and air conditioning, and the Guide of the American Society of Heating and Ventilating Engineers (see the books listed under "Suggestions for Additional Reading," p. 44) . Common Aspects of Heating and Cooling. — Heating and cooling are, as have been noted, merely two aspects of the same thing. In due time, as has already been intimated, equipment may commonly be designed to serve both purposes. The average home has a heating system. If on the unit plan, that is, with units located in various parts of the house, it may employ oil stoves, coal stoves, wood stoves, fireplaces, gas heaters, electric heaters, gas-steam radiators, circulating heaters, or others. If it has a central heating system, it may circulate the heat through air ducts, as in the case of most hot-air systems, or through steam or hot- water radiators. Other systems also are in use. Equipping the home for heating in the winter and for cooling in the summer are two parts of the same job. They present economic problems. If some or a large part of the equipment can be used for both purposes, then capital cost is reduced. Furthermore, if in a home already built, a heating system which has been installed can serve in part for the cooling system later desired, particularly as an aid in distribution, adding the cooling system becomes less difficult and less expensive. Important Distinction Between Heating and Cooling for Comfort. — There is one distinction, however, between the problems of heating and of cooling which should be brought forcibly to the attention of every one. 10 University op California— Experiment Station For heating, there is a minimum temperature in the neighborhood of 70° F, below which the average person, unless active, is uncomfortably cool. It does not matter whether the outside temperature is zero or 30° or 40°, this comfort temperature remains approximately at 70°. There are in- dications from operators that it is probably nearer 72° or 74° than 70°. With summer cooling, however, as the outside temperature rises, many, if not the majority of people, remain comfortable until a temper- ature of 80° F or, in the case of relatively dry air, 85°, is reached, or a lower temperature in the case of moist air. Moreover, this is not a fixed condition of comfort, but is dependent upon outside temperatures. This means that comfort cooling depends upon providing a temperature a reasonable number of degrees below the outside temperature of the air. Where persons are to remain continuously in the conditioned air, the reduction of temperature for an optimum condition will probably be greater than for short exposure. Homes, however, are rarely occupied continuously. Hotels, restaurants, and theaters have discovered that a drop of 10°-20° below the outside temperature is all that the majority of patrons desire. The same discovery has been made by railways under- taking air conditioning for the comfort of their passengers, especially for short hauls. This distinction is of considerable economic consequence. In the case of heating systems, the house must be warmed to 70° F on the coldest possible day. Actually, in laying out systems, some concession is made in the design to infrequent very cold weather. In cooling systems, however, it appears sufficient to provide a band of cooling maintained at 10°-20° F — in exceptional cases more — below the outside temperature. An approximate working rule is to seek a re- duction of temperature equal to one-half the difference between the outside temperature and 72°. Briefly, then, the difference between the design of heating and cool- ing systems is this : heating systems must produce an indoor temperature of at least 70° F, regardless of the outside temperature; cooling systems should produce a drop in temperature of 10°-20°, and in a few cases, somewhat more. As air conditioning progresses, consideration will have to be given to the effect that the transition from a comfortable cooled house to the hotter outdoors will have on the individual. This is not known at present, but the general belief is that the difference between the indoor and out- door temperatures should, as stated above, be kept moderate. Bul. 589] Air Conditioning for Homes 11 WEATHER ZONES Weather Conditions in California. — In air conditioning, whether for heating or for cooling, the fundamental information needed by the de- signer always includes the kind of air available on the outside and the kind to be provided in the house. The designer will ask "What are the initial temperature, humidity, and degree of purity of the atmosphere ; what final values of these same data are to be provided; and what air movement is desired or is permissible ?" The type of equipment suitable for any home is really affected as much by the weather of the region in question as by any other single factor. Analysis of weather reports from stations scattered throughout Cali- fornia shows that there is a very considerable region over the whole of which the maximum daily temperature for July is above 90° F. July is, in general, the hottest month of the year in California, and 90° is an average maximum above which comfort cooling is strongly indicated as desirable. A study of these weather reports and of the map of the state suggests the delineation of zones in which conditions appear to be similar. The region above referred to, over which the average daily maximum tem- perature for July is above 90° F, has been indicated on the smaller, or pilot chart, of figure 2 as zone I. This region includes practically all of the area of the interior valleys of California, together with a consider- able portion of the interior mountainous region of southern California. Comparison with the larger relief map shown on the same figure will afford a picture of the relations of the zones to the mountain ranges and the coastal regions. The entire coastal and most of the delta area lies outside of zone I. Analysis with reference to the humidity encountered, as well as the temperature, indicates the desirability of dividing the coastal region into two zones. That portion north of Santa Barbara is strongly affected by the cool waters of the Japan current off-shore. It is labeled zone III. The portion from Santa Barbara south, has high relative humidity, but it has higher temperatures. The southern coastal region is labeled zone II. Since these assignments of zones are made arbitrarily from average conditions for the region, exceptions are to be expected. It appears that the area around Stockton, because of higher humidity than is found in most of the Great Valley, and the area around San Diego, may require separate consideration. Stockton is placed in zone I but has a high hu- midity in contrast with the rest of its zone; and on the other hand, 12 University op California — Experiment Station Mojave and Chico have weather characterized by extremely low humid- ity. San Diego city has conditions similar to those of zone III, although located in zone II. The northern Sierras, as a whole, require shade for ttW* *% Fig. 2. — Zones of temperature and humidity conditions for California, in the small map at the upper right, as compared with the physical features of the state, shown in the large relief map. Zone I has high summer temperatures usually with low humidities ; zone II has moderate summer temperatures usually with higher humidities ; zone III has lower summer temperatures with moderate humidities. (By permission of H. A. Sedelmeyer, copyright owner.) comfort in summer. If note is taken of these exceptions, the zoning shown will furnish a fair guide to conditions to be expected. Average daily summer temperatures at Davis, California, which falls in zone I and is near Sacramento, are given in table 1. This table is par- ticularly significant in exhibiting the relatively low night temperatures, Bul. 589] Air Conditioning for Homes 13 lasting for at least 6 hours, in the summer months, especially in many parts of zone I. Considerable amelioration can be obtained from a cooling system which will pump night air into the house and will prevent rapid warming during the day by proper use of insulation. Steady heating for longer periods is thus counteracted by forced short-time cooling. Further TABLE 1 Average Daily Temperatures, Davis, California, October, 1929-September, 1934 Month Maximum Minimum Night temperature not exceeded for 6 hours Mav op 80.5* 88.7 97.1 953 88.2 81.7 o p 47.1 52 54 3 53.1 49 5 43.9 op 52.7 June 57 5 July 60.7 August September 60.2 56.9 October 513 * Average of the 155 daily maximum temperatures occurring in the months of May during the 5-year period. Similarly for other months and for the minimum temperatures. reference to this will be made in the discussion of different types of equipment for cooling. The high variability of weather conditions throughout the state makes desirable a weather analysis for every locality, before general conclu- sions are reached regarding the merits of different types of equipment. THE QUESTION OF ECONOMY Principles Followed. — In this, as in all equipment problems, the ques- tion of cost must be kept constantly in the foreground. Where the need for summer cooling is not great, the justifiable expenditure for obtain- ing results may similarly be small. In certain communities, also, weather conditions and the availability of cheap cold water and low electric rates may make possible relatively inexpensive cooling systems. As a preliminary guide, the assumption has been made that "ulti- mately the homeowner may be willing to pay as much per year for cool- ing as he now pays for heating." In climates where the warm season lasts most of the year, the homeowner will probably be willing to pay more; in climates where the winter season is long and cold, the situation will be reversed. For the central valleys of California the rule may prove a fair one. A number of commercial installations in the valley climate of California have shown approximate equality between annual heating and cooling charges. A study of figure 12 (p. 34) indicates that the 14 University of California — Experiment Station initial cost of a cooling system, or perhaps of a combined system, is at present about that of the family automobile. Doubtless, with increased production and standardization of equipment, the initial cost can be reduced. Air Conditioning, a Prospective Necessity Rather Than a Luxury. — Although economy is an important consideration, as soon as the home- owner becomes thoroughly desirous of having equipment for this pur- pose, and as soon as he is convinced that the equipment is fairly priced and will do the work, he will be inclined to install it. Some years ago the cost of an automobile was commonly thought to be beyond the purchasing ability of the average family. Nevertheless when the desire became great enough, the automobile passed from the luxury to the necessity class. The situation is also similar to that which confronted the advocates of good highways some twenty years ago. In the beginning, short stretches of good highway gave a powerful demon- stration of their desirability by contrast with the rest of the road. Such is the case at this time with air-conditioning installations in our warmer localities. It appears that the hotels, theaters, restaurants, and occa- sional residences containing such installations, now stand out as did the isolated stretches of good pavement of fifteen or twenty years ago. Conservative and thoughtful men throughout the country are prophe- sying rapid development of air conditioning for residences. A number of authorities also believe that important changes in the design of homes are likely to take place. These changes, to their way of thinking, should make the home more serviceable than it now is, should suit its construc- tion to modern materials, and should reduce its cost. Those interested in the problem of air conditioning will wisely give consideration to these prospective changes and will attempt to incorporate flexibility into the equipment proposed for use. Those considering the construction of new homes should be even more thoughtful about the problem of air conditioning than those who desire to improve conditions in older homes. As will appear, arrangements, especially for insulation and air ducts, can be made in the beginning at little cost which later prove not merely expensive but difficult; and also no more significant factor exists in this subject of economy than in- sulation. SAMPLE HOUSES Two sample houses are used in this bulletin as the basis of discussions and comparisons of such items as the effect of insulation and the cost of the equipments for summer cooling. The assumed floor plan of the Bul. 589] Air Conditioning for Homes 15 first house, a typical five-room cottage, is shown in figure 3, the general external appearance in figures 7, 8, 10, and 11, and the brief specifica- tions in table 2. The second sample house is a two-story, eight-room home. The floor plans are given in figure 4. The general features of the assumed con- struction are shown in the form of brief specifications in table 2. *Oh.lH- t: Fig. 3. — Floor plan of the sample cottage used as the basis of comparisons of cost of cooling equipments and effect of insulation. Both houses are typical California homes. The usual frame of 2 x 4 inch wooden studding is assumed to be sealed outside by fir sheathing, building paper, and redwood siding, and inside by wood lath and plaster. The roof design in each case is a simple gable type with wooden rafters and roof sheathing and cedar shingles. The floors consist of the usual 1-inch pine subflooring and %-inch oak finish-flooring, with building paper between. Basements, adequate in size to contain the necessary equipments, are assumed under the houses. 16 University of California — Experiment Station N ? o o • rH 00 •IH OO -*- s cr o> be - "o o o x^ No - Sept. on 1 1 - No sn Noon ~ * oept. \ o a V >> '§ PL, Absolute humidity 1 <^ | Temperature No No V V V V V V V \ V V V V V V No V V V No V 9 V No No V V V V V V V V V 8 V V V V No No No V V' v 7 V V 10 V \ V V 11 to >. a . Otfl U o B F C (1) G (2) D E Bul. 589] Air Conditioning for Homes 25 be paid to the amount of water, if it is used, since this may constitute a considerable fraction of the operating expense. Also, one should make certain that the resultant air is of acceptable temperature and humidity. In the second classification, mechanical power is applied to a refrig- erating fluid with the aid of compressors and evaporators to provide a refrigerating system. An equivalent effect may be realized by a com- bination of the first system with ice, obtaining approximately the same results, but with less accurate control. At the present time ingenious developments are taking place in both classifications. Table 3 lists some of the many possible combinations of equipment used to condition air. When the installation is commonly in the base- ment or attic, the combination is indicated as being central, although some combinations, in slightly varying form and size, are also suitable as room units as indicated. In applying these different equipments cer- tain effects are obtained. These are seven in number, and are circulation, ventilation, filtering, washing, humidifying or dehumidifying, cooling, and heating. In the third column of the table are listed those effects which each combination realizes in its normal operation. The four principal factors in conditioning — movement, purity, absolute humid- ity, and temperature — are also included in table 3. Whether a given combination of equipment uses any or all of these factors while adjust- ing the room air condition is also indicated. The figure numbers which illustrate a few of the combinations are given, as well as the references, by letters, to those sections of figure 12 which indicate approximate costs of the cooling systems. Application of Equipment to the' Sample Cottage. — Figures 7, 8, 10, and 11 illustrate four typical systems that might be installed in the cottage, floor plans of which are given in figure 3 (p. 15). The systems shown are illustrative of available equipment. They show only a few of the many possible combinations. They do not show every detail or the limit of equipment for any particular system. Attic Ventilation with Night Air Circulation. — The major pieces of apparatus for this equipment and their installation in the sample cot- tage are shown in figure 7. Operation : During the day, ceiling registers, C, are closed and "air inlets," B, are open, so that with the fan running, air is drawn in at one side of the attic, and forced out at the opposite side by the fan. This air stream removes the heat coming in through the roof. The attic tem- perature is thus maintained near that of the outside air temperature, and the flow of heat into the living quarters greatly reduced. As soon as the outside air temperature drops below the inside tern- 26 University of California — Experiment Station perature, manual controls are operated so as to close B and open the ceiling registers C. Air is then drawn into the living rooms, through whichever windows have been opened, through the ceiling registers into the attic, and forced out by the fan. The night air quickly cools the air in the rooms to a comfortable temperature, and, during the course of ATTIC VENTILATION DURING DAY HINGED WINDOW OPEN FOR DAY CONDITIONS AND CLOSED FOR NIGHT ATTIC FLOOR •WINDOW OPERATING CORD FOR CLOSING DURING NIGHT (AND WINTER SEASON) \\wiNDOW FOR CLOSING \DURING - WINTER SEASON ROOM REGISTERS CLOSED FOR DAY CONDITIONS AND OPENED FOR NIGHT CONDITIONS ROOM VENTILATION DURING NIGHT Fig. 7. — Equipment for attic ventilation with night air circulation. A, Control panel in living quarters ; B, air inlets in attic with cord pulls for operating ; C, ceiling registers with cord pulls for operating ; D, attic fan and motor to circulate air. the night, continued operation cools the furnishings and interior of the house to approximately the outside temperature. The next day, as soon as the attic air temperature exceeds the outside air temperature, the controls are operated to close C and open B and the day operation is resumed. The cool interior of the house will increase in temperature slowly while absorbing the heat entering during the day and will not reach as high a temperature as an unventilated house. Bitl. 589] Air Conditioning for Homes 27 Complete Air -Conditioning Equipment. — The major pieces of ap- paratus and their arrangement in the sample cottage are shown in figure 8. Fig. 8. — Equipment for all-year air conditioning. A, Inlet ducts for air supply to rooms; B, controls for motors and furnace; C, return air duct to conditioning equip- ment; B, condensing unit (motor, compressor, liquid receiver and condenser) for furnishing refrigeration when needed; E, cooling tank, containing evaporator coils of refrigeration system for cooling washer spray water ; F, motor and drive for cir- culating fan ; G, air-washer unit, containing sprays, eliminators, and filter elements, and circulating fan, H, oil-fired or gas hot-air furnace, usually automatically con- trolled; I, refrigerant lines from condensing unit to evaporator in cooling tank; J, oil burner and control or gas line and control valves or automatic stoker ; K, control wiring to compressor motor ; L, pump and motor furnishing water to washer sprays. Operation: In winter the furnace H furnishes heat when needed. The best plan is to have the fan driven by motor F run continuously when the furnace is going. As an alternative, it may be under control of a separate thermostat in the hot-air outlet so as to run only when the 28 University of California — Experiment Station air is above a predetermined temperature. The pump and motor L are operated whenever the humidity in the room falls below the desired per- centage, the spray water increasing the humidity of the returned air before it enters the furnace. This humidification is controlled by a humidistat and solonoid valve. In summer, the fan, F, in washer unit G usually runs continuously, the sprays being operated by starting the pump unit L whenever the room air temperature, which operates a controlling thermostat, is above that desired. The humidity may be controlled automatically by a room humidistat acting to start the compressor D whenever the humidity rises above the point for which the controls are set. Various automatic control hook-ups are possible, but the general prin- ciple is always that the fan circulates the air which has been cooled and dehumidified by the cold spray water in the washer, thus producing the desired degree of comfort in the occupied quarters. Registers with louvers are generally provided, so that in extreme hot weather certain rooms only of the house may be conditioned at a time, thus reducing the size and consequent cost of the equipment required. When a simple air washer is used in a system that recirculates the air of the cooled rooms repeatedly, the tendency is toward a cumulative and undesirable increase in humidity. But recirculation has definite eco- nomic advantages, since thereby the cooling of an air stream all taken from the outside is avoided. Therefore, equipments have been designed which will realize a refrigerating effect by a simple air-washer action and yet allow recirculation without cumulative moisture increase in the rooms. Figure 9 shows a diagram of the component parts which may be included in such a special evaporative air-cooling unit to realize indirect cooling of the room air by transferred effect. The machine includes one motor to drive two fans, one of which moves the air from and to the rooms, while the other draws a separate air stream through the simple air washer. Both streams move through the plate-type heat-transfer surface wherein the warmer air of the rooms transfers its heat to the cooler stream of the air washer. The two streams do not mix, for the heat-transfer surface is arranged as parallel narrow and alternating ducts. All the even-numbered ducts may pass room air and all the odd-numbered ducts the washed, humid, and cooler air. The separation between any odd-numbered duct and an adjacent even-num- bered duct is a thin plate of metal, from which the name "plate-type transfer surface" is derived. This surface may be made so efficient in actual machines as to effect a reduction in the room air of three-fourths or more of the drop in tern- Bul. 589] Air Conditioning for Homes 29 perature realized by a simple air washer. Since the latter may drop the wet air temperature as much as 30° F, the transferred effect in the room WET AIR INTAKE 3k. -VS — <\\ t / , COOLING \ "\ \ Fig. 9. — Indirect evaporative air cooling unit with transferred effect, to realize in the rooms supplied by air stream No. 1 the cooling effect of washed air stream No. 2 without introducing into the rooms the high humidity of No. 2. air stream may actually maintain a drop of 22° to 25° F below outside air temperature. The waste, moisture-laden air stream may be vented to attic, or to basement, where it may aid in reducing high temperatures. 30 University of California — Experiment Station It will be noted that in this indirect evaporative air-cooling unit no special refrigerating fluid is used, no compression machine is required; only circulation, evaporation, and transfer are involved. The system •ROOM UNIT- WITH COIL FOR HEATING OR COOLING -FILTERS -FAN MAIN FLOOR FILTERS FAN Hj-± =G£ 3?S O THREE-WAY VALVES ICE-MELTING TANK igr V R PUMP kjjQLj WATER HEATER B SUPPLY CONNECTION ^RETURN 'CONNECTION BASEMENT FLOOR Fig. 10. — Equipment for all-year air conditioning using hot-water heating system and iee-melting tank for cooling. A, Steel ice-melting tank in redwood box packed with insulation; B, water heater; C, water- circulating pump and motor; D, three-way valve, manually operated in conjunction with valve in boiler return and tank spray lines, to change over from heating to cooling; E, room-unit conditioners containing heat-transfer surface, fan and motor, filter, and drip pan; F, ice-loading hatch on ice tank ; G, controls and room thermostat ; R, return line to pump from conditioners ; S, supply line (hot or cold water) to conditioners from pump. Note: B and S should be insulated where exposed. can be used to advantage in localities where the atmosphere on hot days is sufficiently dry, as in most of the zone I, and some portions of zone II. Room-Unit Conditioners with Ice-Melting Tank. — The major pieces of apparatus for this equipment and their arrangement in the sample cottage are shown in figure 10. Bul. 589] Air Conditioning for Homes 31 Operation : In winter the boiler B is regulated to maintain a prede- termined water temperature. The valves D are manipulated to connect the boiler outlet to the pump supply, and the return to the boiler. This is a manual, not an automatic adjustment. When the room thermostat G makes contact for heat, the pump C is started, circulating the hot water until the conditions for which the thermostat is set are obtained. Then the thermostat will stop the pump C. The fan in E may be started manually and should then control the system. In summer, the valves D are adjusted manually to connect the return to sprays in the ice tank, and the suction of pump C to the bottom of the ice tank. When the room thermostat G makes contact for cooling, the pump C is started and cold water from the ice tank is circulated through the conditioners, the return spraying over the ice and melting it to sup- ply the required refrigeration. When the lower thermostat setting is reached, the pump is stopped. The fans in the conditioners may run continuously, under control of a hand switch on each cabinet, and may control the system, or they may operate in conjunction with the room thermostat. Humidity control may also be provided if desired. Central Condenser Equipment with Room-Unit Conditioners. — Fig- ure 11 shows the major pieces of apparatus used in this equipment and their arrangement in the sample cottage. Operation : The unit conditioners in the rooms contain separate heat- ing and cooling surfaces, a fan and motor, a filter, a drip pan, and usually some form of humidifier, in an ornamental cabinet. In winter, the unit operates as a steam-radiator system under control of the room thermostat E. The thermostat control circuit is commonly arranged to be incomplete until fans are running, thus assuring ventila- tion preceding the heat application. In summer, the condensing unit A furnishes refrigeration, the heat being absorbed by the cooling (evaporator) surfaces in the units D. The room thermostat may either control the compressor directly, the fans running continuously, 'or it may control the fans, the compressor being controlled by means of an automatic pressure switch in the suction line. The latter gives better control of the humidity in the room in summer but generally requires a separate thermostat for each room conditioned. Control of the humidifier in the winter may be either manual or by means of a humidistat incorporated in the control panel E. Combinations of Equipment. — As mentioned above, various combina- tions and extensions of these equipments may be used. In particular, attic ventilation, figure 7, may be used with any of the other equipments 32 University of California — Experiment Station with a resulting decrease in operating cost. The advisability of such combination depends upon the extent to which air temperatures at night are lower than during the day, as often occurs in zone I. Also the ice Z~jf$t :-----•;- |f-3S — filters !! il ( .1 I ! I FAM -ROOM UNIT- WITH CONDENSING COIL FOR HEATING AND EVAPORATOR COIL FOR COOLING FILTERS- FAN MAIN FLOOR FAN \ " ? ' ' .II il 7 % =£3 1£ REFRIGERANT CONNECTIONS REFRIGERANT COMPRESSOR CONDENSER AND RECEIVER IE ZZ LOW PRESSURE STEAM BOILER B N STEAM CONNECTIONS BASEMENT FLOOR Fig. 11. — Equipment for all-year air conditioning, using steam for heating and a refrigerant compressor and condenser unit for cooling. A, Condensing unit, com- prising compressor, motor, condenser, and liquid receiver for furnishing refriger- ation; B, steam boiler (one-pipe system shown) ; C, steam line to heating surface in conditioners in rooms ; B, unit conditioners in rooms ; E x thermostat in living quar- ters; F, oil burner and controls or gas-burner control valves or automatic stoker; L, liquid line from liquid receiver to evaporator or cooling surface in conditioners; S, suction line returning refrigerant from room conditioners to compressor. tank and pump of figure 10 may be substituted for the condensing units of figures 8 and 11 and vice versa. If well water or other water supply is amply available at 60° or 65° F in temperature, this cooling medium may be used instead of ice, if the cost of the water is not excessive. Further, the heating and cooling equipments may be entirely separate, and any form of heating system — steam vapor, hot water, or hot air — Bjtl. 589] Air Conditioning for Homes 33 may be used either in conjunction with, or combined with, any of the cooling systems illustrated. Again, a heat-transfer surface may be sub- stituted for the washer G of figure 8 for containing the cooling medium, and a heat-transfer surface, using steam or hot water, may be used for heating in place of the hot-air furnace H of figure 8. The combinations may thus be seen to be numerous. INITIAL AND OPERATING COSTS OF TYPICAL COOLING SYSTEMS The costs of systems of equipment completely installed and connected, ready for operation, will vary with differences in time, location, labor costs, installing conditions, and quality, capacity, and type of equip- ment. Installing conditions include type of construction, insulation, available space, and many other variables. Therefore, any general state- ment as to approximate costs of typical equipment should always be considered subject to adjustment for a specific set of conditions. Never- theless, a statement of approximate costs is valuable in making com- parisons of installations and in giving an idea of budgeting provisions. Initial Costs. — The bar chart, figure 12, indicates initial costs for the year 1934, as given by California firms, without freight or transporta- tion inclusions from San Francisco, for seven different typical summer cooling systems, as recommended by these firms, for the cottage and for the two-story house, previously referred to in this bulletin. For each system, the first long bar shows bid cost installed and connected in the cottage, when insulated, the second long bar the same for the cottage uninsulated, the third long bar for the two-story house insulated, and the fourth long bar for the two-story house uninsulated. The firms were asked to select no larger capacity of their equipments than would be necessary to guarantee a maximum drop of 17° F from outside air temperature to that inside of the spaces to be cooled. Of course, such guarantee was not possible with system A because its results depend upon night air temperatures, nor with systems B, C, or D because these depend upon both temperature and humidity of the outside air for the final results. Only with systems E, F, and G was it possible to guarantee the specified drop of 17° F under any and all of those outside air conditions requiring cooling that are encountered in California. Whenever the system or bid required, uniform allowances for piping, wiring, registers, and duct work were added, respectively, of $15, $20, $35, and $50 for the cottage; and $15, $20, $50, and $75, respectively, for the two-story house. All costs are for nonautomatic, or manual con- trol, except for system G, where complete automatic thermostat control was included. 34 University of California — Experiment Station 1700 1600 1500 1400 1300 1200 1 100 lf)/OO0