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 
 
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 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 
 
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Bul. 589] Air Conditioning for Homes 17 
 
 TABLE 2 
 Brief Specifications of the Typical Cottage and Two-Story Houses* 
 
 (All lumber Douglas fir — "Oregon pine" — except as noted.) 
 
 Common Specifications — Both Houses 
 
 Foundation Concrete 
 
 Mudsills 2"X6" heart common redwood, bolted to concrete 
 
 Underpinning 2"X6" 
 
 Posts 4"X4" on 8"X8" redwood post caps 
 
 Floor joists 2"X10" and 2"X12", 16" on centers 
 
 Studding 2"X4", 16" on centers 
 
 Sills 2"X4" 
 
 Solid blocking Same as joists, over all bearings 
 
 Roof rafters 2"X4", 16" on centers, alternate rafters trussed to ceiling joists 
 
 withl"X6" 
 
 Sheathing 1"X6" or 1"X8", surface one side 
 
 Rough flooring 1"X6" or 1"X8", surface one side 
 
 Finish flooring Kitchen, 1"X4", No. 1 vertical grain, tongue and groove; baths, 
 
 tile; screen porch, composition; remainder, %"X1W plain 
 clear oak 
 Siding 1/X8" standard redwood rustic, pattern as selected 
 
 Note: Place 2-ply building paper between sheathing and 
 
 siding 
 
 Roofing No. 1 A split-cedar shingles, laid 43^" to the weather 
 
 Porch ceiling 1"X4" heart common redwood 
 
 Doors Front, 3'0"X6'8"X1M" thick 
 
 Interior, 2'8" and 2'4"X6'8"X W single-panel 
 
 Special Specifications — Cottage Only 
 
 Floor plates 2— 2"X6" 
 
 Ceiling joists 2"X4", 16" on centers 
 
 Doors Rear, 3'0"X6'8"X W glazed single-pane, 24-oz. glass 
 
 Sash Stock casement windows, single-pane, 24-oz. glass; bath and 
 
 kitchen stock double hung. Sizes as shown, 2'8" up. 
 
 Special Specifications — Two-story House Only 
 
 First-floor plates... 2— 2"X6" 
 
 Plates 2— 2"X4" 
 
 Ceiling joists 2"X6", 16" on centers 
 
 French doors 4'6"X6'8"X W single-pane 24-oz. glass 
 
 Doors Rear, 2'6"X6'8"X W, glazed single-pane, 24-oz. glass 
 
 Sash First floor — stock double-hung, single-pane, 24-oz. glass; sizes 
 
 as shown, 2 '2" up 
 Second floor — stock double-hung, single-pane, 24-oz. glass; 
 
 sizes as shown, 2'8" up 
 
 * Story heights are as follows: first-floor joists above ground, 2' 0" clear; cottage, ceiling 
 height, 8' 6" clear; two-story house, first floor, 9' 6" clear, second floor, 9' 0" clear. 
 
 Interior walls and ceilings are %" hard wall plaster on wood lath, except kitchens and baths, 
 which are cement. 
 
 Insulation is shredded redwood bark between studding, and on ceilings. 
 
18 
 
 University of California — Experiment Station 
 
 HEAT 
 
 GAIN 
 
 WITH 
 NO INSULATION 
 
 AND 
 
 SINGLE GLASS 
 
 UNSHADED 
 
 WINDOWS 
 
 WITH 
 WALLS AND 
 
 CEILING 
 
 INSULATED, 
 
 DOUBLE GLASS 
 
 SHADED 
 
 WINDOWS 
 
 WALLS 
 
 ■I 
 
 
 ;X SAVINGS V/ 
 % APPRO*;// 
 
 
 ROOF 
 
 11 
 
 
 ill 
 
 WALLS 
 
 GLASS 
 
 
 
 ROOF 
 
 SUN EFFECT 
 
 ON 
 
 GLASS 
 
 
 DOUBLE GLASS 
 SHADED 
 
 AIR CHANGE 
 
 AIR CHANGE 
 
 HEAT LOSS 
 
 WITH 
 NO INSULATION 
 
 AND 
 
 SINGLE GLASS 
 
 WINDOWS 
 
 O 
 
 o 
 
 1 
 
 ROOF 
 
 FLOOR 
 
 WALLS 
 
 GLASS 
 
 AIR CHANGE 
 
 WITH 
 WALLS AND 
 
 CEILING 
 
 INSULATED, 
 
 SINGLE GLASS 
 
 WINDOWS 
 
 ROOF 
 
 FLOOR 
 
 WALLS 
 
 GLASS 
 
 AIR CHANGE 
 
 WITH 
 WALLS AND 
 
 CEILING 
 INSULATED, 
 DOUBLE GLASS 
 WINDOWS 
 
 ROOF 
 
 FLOOR 
 
 WALLS 
 
 DOUBLE 
 GLASS 
 
 AIR CHANGE 
 
 B 
 
 Fig. 5. — A and B, Cemparison of heat gained during the cooling 
 season by the sample cottage: A, when not insulated or shaded; B, 
 when insulated and with windows shaded, showing approximate 
 savings in heat gain. C, D, and E, Comparison of heat lost during 
 heating season by the sample cottage: C, when not insulated; D, 
 when insulated, showing approximate savings in heat loss ; E, with 
 double glass and insulation, showing approximate savings in 
 heat loss. Total heat quantities in bars A and C are not equal. 
 
Bul. 589] Air Conditioning for Homes 19 
 
 When referred to as insulated houses, the above constructions are 
 considered not modified, except by the additions of insulation in the 
 spaces between the studding, and between the ceiling joists of the attic. 
 The insulating material chosen is shredded redwood bark, so applied 
 as to give a weight of approximately 1,500 pounds per 1,000 square feet 
 of wall or ceiling surface that is insulated. No shredded redwood bark 
 was considered applied below the lower floors, because of the assumption 
 that the basements would be closed and below earth grade, and, there- 
 fore, not subjected to the outside air temperatures that are effective on 
 the wooden walls of the structures. 
 
 INSULATION 
 
 Principal Problems in Cooling. — The problems in cooling may arbi- 
 trarily be divided into the reduction of heat entry and loss, commonly 
 referred to as insulation, and the processes employed for cooling, usually 
 requiring mechanical equipment. 
 
 Effect of Insulation Applied to the Sample Cottage. — Computations 
 for the sample houses show that in such a cottage, uninsulated, more 
 than 40 per cent of the heat enters through the roof. In figure 5 com- 
 parisons for the cottage have been made for the cooling season and for 
 the heating season. For the cooling season the heat which gains ad- 
 mission through the house is of primary interest. This is tabulated in 
 the two charts under the heading "Heat Gained." Two cases are shown. 
 With no insulation and single-glass, unshaded windows, the left bar, 
 figure 5 A, shows the proportions of heat gained from the walls, roof, 
 window glass, sun effect on the glass, and the air change required to pro- 
 vide fresh air for the occupants. Corresponding reduced amounts with 
 walls and ceilings insulated, double glass in the windows, outside shades, 
 such as awnings for the windows, are shown in the second bar, figure 5 B. 
 The saving possible by such insulation is striking. 
 
 Bars C, D, and E of figure 5 indicate the heat loss for the cottage under 
 different conditions of insulation during the heating season. Bar C 
 shows the loss from the uninsulated house, and the various components 
 of the total loss are indicated. Bar D, drawn to the same scale, shows the 
 total loss and the components if the house is insulated. The shaded por- 
 tion indicates the resulting percentage saving, based on the total loss 
 from the uninsulated house. Bar E is for the same conditions as D, ex- 
 cept that double glass was used in the windows. 
 
 The total heat lost from the uninsulated house in the heating season 
 (bar C) is not the same in amount as the total heat gained through the 
 uninsulated house in the cooling season (bar A). The basis of percent- 
 
20 University of California — Experiment Station 
 
 age in bars A and B is therefore different from that in bars C, B, and E, 
 and comparisons between the two groups as to total heat quantities are 
 not possible from the data given in figure 5. 
 
 In the cooling season reduction of the heat entry through the roof is 
 a primary problem. Trees to shade the roof and the windows would be 
 ideal, but even with exposed roofs one can improve the reflectivity and 
 provide insulation. 
 
 Most of the solar heat accompanies sunlight and can be reflected by 
 bright surfaces in the same manner as light. A white or bright metallic 
 surface reflects much more solar energy than black, green, or red sur- 
 faces. Consequently, covering an exposed roof with aluminum foil or 
 white plaster would be effective in reducing heat gain. Neither of these, 
 however, is a practical roofing surface. Hence, aluminum and white 
 paints may be used instead, and will reflect at least half of the sunshine 
 absorbed by ordinary untreated roofing materials. 
 
 A further step in excluding the heat is to provide false roofs with 
 adequate air circulation and, if feasible, a highly reflective surface, such 
 as aluminum foil, on the underside of the upper roof. With its high re- 
 flecting property this surface would make such a false roof practically 
 as good as tree shade. 
 
 The most inexpensive method of retarding heat flow from the roof 
 into the living quarters is to spread a bulk insulation, about 3% inches 
 deep, between the ceiling joists of the attic. Several materials are used 
 for this purpose and each has its advantages. The shredded redwood 
 bark, which is readily obtained in California, is an excellent insulator 
 which stays in place well and in bulk appears to be reasonably fire- 
 resisting. The shredded surface, however, in very dry weather is not 
 fireproof. Finely powdered materials, such as rice hull ash, must be 
 installed carefully to prevent blowing if the attic is open. All holes in 
 the ceiling must be plugged and a cover for bulk insulation between 
 ceiling joists must be supplied. 
 
 Although more expensive, probably the most effective arrangement 
 to keep the heat out in summer is to insulate the underside of the roof 
 itself with fill insulation and inside sheathing. The simplest method is 
 to apply a heat reflector, such as aluminum-foiled Kraft paper, across 
 the underside of the rafters. Such material has a very high reflecting 
 power and will return a large proportion of the radiant heat back to the 
 roofing. Heat transfer into the house by convection will also be reduced 
 if the air space between the roofing and the foiled paper is closed top 
 and bottom. This method may lower the temperature as much as 15° F in 
 a closed attic. 
 
Bul. 589] Air Conditioning for Homes 21 
 
 Any roof insulation restraining the entrance of heat will raise the 
 temperature of the outside roof surface. Therefore, in case of tar and 
 gravel roofs, ceiling insulation is preferable to roof insulation to avoid 
 increasing the flow of the tar. 
 
 The sun effect through the glass is shown in figure 5 A, in addition to 
 the normal inflow of heat due to temperature difference. The sun effect 
 itself could of course be prevented entirely by shading the windows with 
 screens or awnings. Where outside shading cannot be provided, simple 
 aluminum-foil screens can be placed inside the glass to reflect the sun- 
 light back with only a slight conversion to heat inside the room. Ordi- 
 nary window roller shades and drapes are less effective but useful, since 
 they concentrate the heat at the window and decrease the rate of heat 
 transfer into the occupied areas of the room. 
 
 Reduction of heat entering through the walls is next in importance. 
 The ordinary wood frame construction divides the stud space for each 
 wall height into two or three sections by headers at window frames and 
 by cross and diagonal bracing, and is closed top and bottom. This makes 
 it difficult to insert insulating material after a house is finished, although 
 means have been provided for blowing in powdered insulating material. 
 
 The most effective way of reducing the heat inflow through the walls 
 in a house already constructed and not shaded by trees is to cover the 
 walls with vines. This has two advantages : shading the walls and cool- 
 ing the air next to the wall surface by evaporation of moisture from the 
 living plants. Stucco walls often do not need repainting for a number 
 of years, and if necessary to repaint, the vines can be lifted from the 
 walls and replaced almost intact if considerable care is used in detach- 
 ing, preventing sharp bends, and protecting the vines against damage, 
 and by replacing on a netting or firm system of heavy strings. The in- 
 sulation of floors is not usually very important, from the point of view 
 of cooling systems. However, when heating systems are considered and 
 the temperature of the inside is raised materially above the temperature 
 under the house, floor insulation may become desirable. The shredded 
 redwood bark, or equivalent insulation, may be applied against the 
 underside of the floor by appropriate battens installed between the 
 floor joists. 
 
 Well-developed lawns and gardens surrounding a house contribute 
 materially to summer comfort. By providing cooled surfaces they pro- 
 duce an effect in marked contrast to the "baking" temperature of bare 
 soil. The relatively cool lawn will absorb heat reflected and radiated 
 from the walls of the house, whereas the reverse is likely to happen with 
 bare ground. These surfaces also reduce dust. The temperature of air 
 
22 University of California — Experiment Station 
 
 on the lee side of a field of ripened grain in one case was 112° F. 7 For a 
 nearby field of alfalfa it was 102° at the same time. One should have no 
 difficulty in judging from this the importance of heat-absorbing green 
 lawns around the house, in contrast to dry grass or bare ground. 
 
 In the new house, of course, the moderate amount required for insul- 
 ating ceilings and walls and for shading windows is a wise expenditure. 
 Even in an old house some of these may possibly be undertaken. In both 
 cases, but especially for houses already constructed, the development 
 of outside shade and cool surrounding surfaces is of definite value. 
 
 Insulation of Construction Other Than Houses. — Some of the same 
 materials now used for insulating houses will also prove valuable in 
 other construction. For example, the automobile top could be made to 
 exclude much more solar energy than it does if a reflecting surface like 
 aluminum foil were included in its composition, even though the surface 
 is under other surfaces. The aluminum-painted tops of many busses 
 and tank trucks now to be observed are evidence of the growing appre- 
 ciation of the possibilities of reflection. Also there is no reason why 
 similar methods should not be used in providing artificial shade out- 
 doors. Parasols could be covered with reflecting surfaces. 
 
 An example of such application to an ordinary bell tent is of interest. 
 During hot weather at Sandown, Isle of Wight, the inside surface of 
 the fabric was radiating heat equivalent to that given out by a black 
 body at 134° F. Under the same conditions, after an inner lining cov- 
 ered with aluminum foil had been provided, the surface radiation tem- 
 perature was 84° F; only a degree or two above the air temperature. 8 
 
 Temperature Delay Due to Insulation. — In some cases the mere appli- 
 cation of insulation to reduce heat entry will make such marked im- 
 provement that little more need be done. In some cases added circulation 
 of cool night air, plus insulation, will give desired results. Generally 
 speaking, the insulation means increased economy, in savings of fuel 
 or energy, as well as increased comfort. It has, however, other effects 
 than savings of fuel or energy. In particular it increases the length of 
 time elapsing between the maximum temperature outside and the maxi- 
 mum temperature inside. If, for example, the maximum temperature 
 of the outside air is reached at 3 p.m., and the lag between inside and 
 outside temperatures can be made 6 hours, the maximum temperature 
 inside (obviously not the same as that outside) will be experienced 6 
 
 7 Began, W. M., and G. A. Kichardson. Environmental temperature and the 
 dairy cow; the effect of green pastures. Abs. Papers Presented at the 29th Ann. 
 Meeting Amer. Dairy Sci. Assoc, p. 50. June, 1934. 
 
 8 Crowden, J. P. The use of bright metallic surfaces for increasing human com 
 fort in the tropics. Engineering 138(3587) :395. 1934. 
 
Bul. 589] 
 
 Air Conditioning for Homes 
 
 23 
 
 hours later. This effect is so marked and fits so nicely the temperature 
 variations throughout a 24-hour period that successful air conditioning 
 has been effected in some cases by building a well-insulated house, draw- 
 ing outside air through it during the night to cool it off, and recirculat- 
 ing this air inside the house during the daytime to keep it cool. The 
 results of such a system used in a residence in Rochester, New York, for 
 three hot days in September, 1931, 9 are shown in figure 6. The mere 
 
 £ 9C 
 o 
 
 IL 
 IS 
 
 
 
 
 
 Out doc 
 
 / 
 
 r~ 
 
 jr temp 
 
 r 
 
 eroture 
 
 
 
 
 
 
 
 
 
 
 
 /y/ 
 
 
 
 
 
 
 
 
 
 
 
 V 
 0) 
 
 L. 
 
 ■ 
 
 ■ 
 
 ^ 
 
 
 
 / 
 
 
 
 
 <•» •■' — 
 
 m \x 
 
 
 
 *• '""V.. 
 
 
 
 X 
 
 x x 
 
 / 1 
 
 5 , 
 
 
 . "x 
 
 
 
 X x 
 
 ^-— A- 
 
 * 
 * 
 
 \ 1 
 
 S 
 
 O 
 
 k. 
 91 
 
 a. 
 
 £70 
 
 
 
 7 lr 
 
 door t< 
 
 ^mperat 
 
 jre >x^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 No 
 - Sept. 
 
 on 
 1 1 - 
 
 
 No 
 
 sn 
 
 
 Noon 
 
 
 
 
 
 
 ~ 
 
 * 
 
 oept. 
 
 \<L 
 
 " 
 
 
 
 
 
 COOLIN6 A HOME BY AIR CIRCULATION 
 
 Fig. 6. — Cooling a home by air circulation : actual variations obtained from re- 
 cording instruments at a home in Eochester, New York, showing the decreased indoor 
 temperature realized by fan circulation of night air if the house is closed during the 
 day with no circulation. • 
 
 circulation of outside air in houses starting at sundown would, in a 
 great many cases, materially improve conditions for sleep. Sometimes 
 this is possible by merely opening the windows: usually, however, posi- 
 tive ventilation through the use of fans and ducts is required. 
 
 MECHANICAL EQUIPMENT 
 
 Types of Mechanical Equipment. — To obtain a drop of 10°-20° F be- 
 tween the outside and inside air for comfort cooling of homes, there 
 are, broadly speaking, two general classifications of equipment. One 
 operates mainly by the cooling effect due either to circulation of air 
 which is cooler than the spaces through which it is to be circulated, or 
 to the use of water sprays either applied directly to the air as in 
 washers, or indirectly through heat exchangers. This classification is 
 usually characterized by low operating costs. Attention, however, should 
 
 9 Taylor, Frank C. Cooling a home by air circulation. Heating and Ventilating 
 Mag. 29(10): 79. October, 1932. 
 
24 
 
 University of California — Experiment Station 
 
 TABLE 3 
 
 Some Possible Combinations of Equipment Used to Condition Air 
 
 Some of the possible 
 equipment combinations 
 
 1 . Power fan and registers 
 
 2. Equilibrium air washer 
 with power fan 
 
 (no auxiliary cooling or 
 heating of the water) 
 
 3. Controlled air washer 
 with power fan 
 (auxiliary cooling of 
 the water) 
 
 4a. Dry surface coolers with 
 power fans and niters ; 
 surface cooled by 
 water (1) or refrigerant 
 vapor (2) 
 
 46. Dry surface heaters 
 with power fan and fil- 
 ter ; surface heated by 
 steam, water, electricity 
 or gas 
 
 5. Indirect evaporative 
 cooling unit with trans- 
 ferred effect, fans and 
 filter 
 
 6a. Warm air furnace 
 
 66. Warm air furnace, with 
 filter and equipment 2 
 
 6c. Warm air furnace with 
 equipment 3 
 
 6d. Warm air furnace with 
 equipment 4a 
 
 7a. Hot-water heating sys- 
 tem with ice tank, 
 water pump, and room 
 radiators 
 
 76. Hot- water heating sy s- ] 
 tem with ice tank, water | 
 pump, and room-unit | 
 conditioners having 
 filters and fans J 
 
 8. Steam heating system 
 with refrigerant com- 
 pressor and condenser 
 and equipment 4a as 
 room-unit coolers 
 
 Location 
 
 Central 
 
 Central 
 
 Central 
 
 Room units 
 
 or 
 central 
 
 Room units 
 
 or 
 central 
 
 Central 
 
 Central 
 
 Central 
 
 Central 
 
 Central with 
 room units 
 
 Central 
 with room 
 radiators 
 
 Central with 
 room units 
 
 Central with 
 radiators 
 and 
 room units 
 
 Principal effects 
 realized 
 
 Circulation 
 
 Ventilation 
 
 Cooling 
 
 Circulation 
 
 Ventilation 
 
 Washing 
 I Humidifying 
 [Cooling 
 
 Circulation 
 
 Ventilation 
 • Washing 
 
 Humidifying 
 (Cooling 
 
 [Circulation 
 Ventilation 
 { Filtering 
 jDehumidifying 
 (Cooling 
 
 [Circulation 
 I Ventilation 
 } Filtering 
 ( Heating 
 
 Circulation 
 Ventilation 
 Filtering 
 [Cooling 
 
 [Circulation 
 { Ventilation 
 [Heating 
 
 Circulation 
 Ventilation 
 Washing 
 Humidifying 
 Cooling or 
 heating 
 
 Circulation 
 Ventilation 
 Washing 
 Humidifying 
 Cooling or 
 heating 
 
 Circulation 
 Ventilation 
 Filtering 
 Dehumidifying 
 Cooling or 
 heating 
 
 /Cooling or 
 \ heating 
 
 [Circulation 
 
 Filtering 
 < Dehumidifying 
 
 Cooling or 
 [ heating J 
 
 Circulation 1 
 Filtering J 
 
 Dehumidifying } 
 Cooling or 
 heating 
 
 Air conditioning factors 
 affected 
 
 a 
 
 a 6 
 o . 
 
 £} M 
 
 7 
 
 +3 
 
 a 
 5 
 
 a 
 
 > 
 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 
 
 <t 
 
 ^ 900 
 
 O 800 
 
 Q 
 
 700 
 
 ^ 600 
 
 k 
 
 I/) soo 
 
 o 
 
 *° 400 
 
 300 
 
 ZOO 
 
 /OO 
 SO 
 
 II ! Ml 
 
 !■■■«■ Iff II III ill II I I 
 
 Hnlrim I It! I I #1 
 
 "ill n ii i n i i i ii i i i ii i i i ii i i i ii i i i i 
 
 TYPE 
 OF 
 SYS- 
 TEM 
 
 abed 
 
 Circulat- 
 ing Fan 
 
 For 
 Ventila- 
 tion Only 
 
 A 
 
 abed 
 
 Fan and 
 Simple 
 Equilibri- 
 um Air 
 Washer 
 
 B 
 
 abed 
 
 Extended 
 
 Surface. 
 
 With 
 
 Tower 
 
 Cooling 
 
 c 
 
 abed 
 
 Indirect 
 
 Eyap - 
 
 orative 
 
 Cooling 
 
 Unit 
 
 D 
 
 abed 
 
 Ice 
 
 Cooling 
 
 Using 
 
 Existing 
 
 Rad/ators 
 
 E 
 
 abed 
 
 Ice 
 Cooling 
 
 With 
 
 Air 
 Washer 
 
 F 
 
 abed 
 
 Mech- 
 anical 
 (Com- 
 pressor) 
 System 
 
 G 
 
 Fig. 12. — Comparison of costs for seven different cooling systems, A to G, 
 as applied to the two sample houses, (a) the cottage insulated, (b) the cot- 
 tage, not insulated, (c) the two-story house insulated, (d) the two-story house, 
 not insulated. 
 
Bul. 589] Air Conditioning for Homes 35 
 
 System A, figure 12, includes the installation of registers and fan as 
 outlined in figure 7 for the purpose of cooling the house by circulation 
 of air during the night, and counteracting the sun effect on the roof by 
 circulation of air through the attic during the day. This simplest of all 
 systems will evidently give best results in localities where night tem- 
 peratures are decidedly lower than those during the day. 
 
 System B includes the installation of a simple fan and air washer with 
 ducts and registers. This system gives best results in the dry regions of 
 zone I, where addition of moisture to the incoming air is desirable. If the 
 system is a recirculating one, excessive moisture addition may occur. 
 
 System C consists in the installation of fin-type cooling surfaces, with 
 cooling tower, a fan, and ducts with registers. This type of system will 
 give best results where humidity is low enough to allow a cooling tower 
 to show a reasonable drop in temperature. Fin-type cooling surfaces 
 allow recirculation of air in the house without cumulative increase in 
 humidity, whereas a simple air washer tends to build up the inside 
 humidity to intolerably high values with recirculation of the room air 
 through the washer. 
 
 System D includes the installation of an indirect evaporative cooling 
 equipment. Although this is based on a simple air washer for the refrig- 
 erating effect, the machine can nevertheless realize the economic ad- 
 vantages of recirculation without cumulative increase of room humidity 
 to very high values. This is accomplished by transferring the refriger- 
 ating effect, only, from the washed air stream to the room air stream. 
 The machine is illustrated diagrammatically in figure 9, and explained 
 in connection with the complete air-conditioning system using a simple 
 air washer. 
 
 System E of figure 12 includes the installation of an underground ice 
 tank for cooling water circulated in the room radiators of a combined 
 cooling and hot-water radiator heating system, the radiators and their 
 connecting piping and water heater not being included in the costs as 
 indicated. This cooling equipment is shown by items A, F, D, and G of 
 figure 10. When the number of days during which cooling is needed in a 
 given season is small, the ice system is a good one to consider. It gives 
 high cooling capacity without high installation cost. A number of suc- 
 cessful installations have been made. However, difficulty may be experi- 
 enced in this case with the formation of a stratum of cold air near the 
 floor, unless means of agitation, such as floor fans, are provided. The 
 trouble is due, of course, to the radiators. It may be remedied by sub- 
 stituting unit coolers with integral fans. 
 
 System F includes the installation of an air washer, and an ice tank 
 
36 University of California — Experiment Station 
 
 for cooling the spray water of the washer, and requisite registers and 
 ducts. This combination may be useful when high humidities and high 
 temperature prevail, as in zones II and III, because the cold-water spray 
 in the washer tends to reduce humidity in the rooms. 
 
 System G consists in the installation of a compressor and condenser 
 refrigerating unit, a central fin-type air-cooling coil, blowers, niters and 
 humidifier, and the necessary registers and ducts. Thermostatic control 
 is included in the cost estimates for this equipment. The mechanical 
 systems, based upon the use of refrigerating fluids and the employment 
 of compressors and evaporators, are well known, and present the great 
 advantage of being independent of the outside atmospheric conditions. 
 Much ingenuity is now being shown in the design of mechanical refrig- 
 eration systems to make them economically applicable to homes. In a 
 number of cases, they give results which justify the present cost. 
 
 Operating Costs. — The estimated operating costs to be expected dur- 
 ing a cooling season requiring 1,000 hours of actual operation are shown 
 by the broad black bars for each of the systems B to G inclusive, and 
 for each of the four house conditions. System A, using fans for cooling 
 at night, is estimated on the basis of 2,000 hours, because this system 
 requires both night and day operation for its fundamental effects, 
 whereas the other systems do not. For the purpose of these estimates, 
 the cost of electric power was taken at 3 cents a kilowatt hour, water at 
 50 cents per thousand cubic feet, and ice at $4.50 a ton. 
 
 The combined charges for interest at 6 per cent and depreciation at 
 5 per cent are shown for each case by the white bars, superimposed upon 
 the operating-cost bars. These amounts as shown are for one year. There- 
 fore, the total of operating interest, and depreciation charges is indi- 
 cated by the top of the white bars. 
 
 Cooling systems are commonly installed to reduce the temperature of 
 only a part of the house at a time — for example, a two-story house may 
 be provided with such a system as would cool the downstairs rooms 
 during the day, and the upper rooms during the night. Under certain 
 circumstances small families have been content with a single room 
 cooled and with the relief thus afforded. Accordingly, and as recom- 
 mended by the firms supplying the cost estimates, the following condi- 
 tions pertain in the seven systems for which costs are given in figure 12. 
 
 System A : All rooms cooled, for the four house conditions, the extent 
 of cooling effect depending upon the temperature of the night air. 
 
 Systems B, C, and D: Same as A, except extent of cooling effect is 
 dependent upon the humidity of the outside air. 
 
 Systems E and F: For the insulated and uninsulated cottage, the 
 
Bul. 589] Air Conditioning for Homes 37 
 
 rooms selected for cooling were the living room, dining room, breakfast 
 nook, and kitchen, it being understood that at night the cooling effect 
 would be transferred to the sleeping rooms. For the insulated and un- 
 insulated two-story house, the rooms selected for cooling were the living 
 room, dining room, kitchen, and maid's room, with transfer of this cool- 
 ing effect to second-floor sleeping rooms at night. 
 
 System G: For both of the insulated houses, the bidding companies 
 elected to cool all rooms. For the uninsulated cottage, the living room, 
 dining room, breakfast nook and kitchen, and bath were selected, and 
 for the uninsulated two-story house, the entire downstairs and one bed- 
 room (room 12 in fig. 4) . 
 
 Generally, for systems A, B, C, and D, it will be noted that the cooling 
 effect is dependent upon uncontrollable atmospheric conditions; for 
 systems E and F, the cooling effect is dependent upon the amount of ice 
 used, and for system G, the cooling effect is dependent upon the amount 
 of electrical energy and of cooling water used. 
 
 FACTORS AFFECTING THE SELECTION AND OPERATION OF 
 AIR-CONDITIONING SYSTEMS 
 
 A house owner, or prospective owner, who decides to investigate and 
 buy an air-conditioning system, may find the factors influencing a choice 
 to be so numerous and complicated that he will incline immediately 
 toward engaging technical help. Indeed, if truly competent and un- 
 biased assistance in such a problem is available, the prospective pur- 
 chaser will be wise if he enlists such aid, at least before making his final 
 commitments. But he may wish first to put in order in his own mind 
 some of the fundamentals that should be considered. Accordingly, the 
 following headings and remarks may aid in listing for attention the 
 items that may apply to a particular house and its air-conditioning 
 problem. 
 
 1. The Building and Its Structural Features. — If a new house is to be 
 designed, many features of its general construction may be so modified 
 as to aid greatly, during both the heating and the cooling seasons, in the 
 economical operation of air-conditioning equipment, as well as in the 
 reduction of the initial cost of the equipment. 
 
 a) Tightness of construction : Windows and other openings should 
 be capable of such closure that air leakage is reduced to a minimum. The 
 attic should also be reasonably tight against gross air infiltration, with 
 even as simple a cooling installation as the attic fan equipment, shown in 
 figure 7; for during the night operation, the fan should draw the air 
 from the rooms, and not merely through leakage openings in the attic. 
 
38 University op California — Experiment Station 
 
 During a heating season, also, a tight attic is evidently desirable. Leak- 
 age of air into or out of a basement may add a considerable load to either 
 a heating or a cooling installation. Fireplaces should always be provided 
 with a damper, to close the chimney completely against heat loss when 
 the fireplace is not in use. Generally, attention to such features as will 
 avoid leakage will pay excellent dividends during both the heating and 
 the cooling season. If the house is already built, good returns may like- 
 wise accrue from the application of window stripping and other means 
 of sealing. 
 
 b) Insulation: As explained in earlier sections, the advantages of 
 house insulation are apparently more generally appreciated in the colder 
 areas than in states of moderate climate. However, the growing interest 
 in the reduction of heat gains during the cooling season and of heat 
 losses during the heating season is inevitably focusing more and more 
 attention upon the proper insulation of the house. Shredded redwood 
 bark insulation for the sample cottage, described and shown in figure 3 
 and table 2, is estimated to cost, in place, approximately $150, installed 
 while the house is being constructed. Of this, certainly not more than 
 half, or $75 is chargeable to cooling equipment, and $75 to heating equip- 
 ment. Similarly, the cost for the two-story house would be approximately 
 $235, the location in each case being the San Francisco Bay area. In 
 other locations these costs would be increased by the addition of trans- 
 portation charges. 
 
 Insulation of the walls of existing houses is somewhat more expensive, 
 since special materials suitable for blowing into the interstudding spaces 
 must be used. The insulating values of these materials and of shredded 
 redwood bark are approximately the same. With materials blown in, 
 the estimated costs of insulating the two houses as above, but already 
 built, are $275 for the cottage and $505 for the two-story structure. 
 Accordingly, the penalty incurred for not insulating during construc- 
 tion is roughly 85 per cent for the cottage, and 115 per cent for the two- 
 story house. 
 
 By reference to figure 12, some idea may be obtained as to the effect 
 of insulation in the reduction of initial costs of cooling systems. For the 
 cottage, it may be there noted that, for systems C, D, F, and G, the 
 decrease in initial equipment costs due to insulation is fully twice as 
 great as the cost of insulation chargeable to cooling; namely, for the 
 cottage, $75. But even greater gain from insulation results from the 
 reduction of power or ice, and fuel bills for the entire life of the home. 
 Insulation, if properly installed, occupies no useful space, it requires 
 no regulation, it functions automatically, it never fails to operate. 
 
Bul. 589] Air Conditioning for Homes 39 
 
 Noteworthy results may often be accomplished by insulating only 
 above the ceilings of rooms, especially when no attic floor is used. This is 
 particularly true of cottages, where the total area of ceiling may ap- 
 proach or exceed the total area of the wall surface. For instance, the 
 sample cottage assumed in this publication has exterior wall surface, ex- 
 cluding that of attic and basement, of 1,080 square feet; and total ceiling 
 surface of 1,120 square feet. Owners of cottages may, therefore, expect 
 excellent returns if merely the accessible upper surfaces of ceilings are 
 insulated, particularly since the heat transferred there may be greater 
 than through the walls. If complete insulation is not to be afforded, then 
 certainly, the ceiling surfaces should be given careful consideration for 
 such treatment. 
 
 c) Double, or storm windows, and awnings: Particularly effective in 
 the heating season are double windows, or storm windows, in reducing 
 heat losses. Also, during the cooling season any awnings which will 
 eliminate the sun effect on windows are likewise helpful. Both of these 
 items are excellent adjuncts to the use of insulation, for the general pur- 
 pose of reducing the load on air-conditioning equipment. 
 
 d) Generally, adequate provisions for duct work and a basement of 
 sufficient size to accommodate air-conditioning equipment readily will 
 tend toward reduced costs in the application of desirable systems. 
 
 2. The Portion of the Building Which Is to Be Air Conditioned. — For 
 the purpose of effecting economies not only in the first cost of equipment, 
 but also in its operating cost, common practice inclines toward air con- 
 ditioning of only a portion of a residence whenever conditions justify 
 this procedure. Some equipment systems are inherently of such nature 
 as to permit the shifting of the air-conditioning effect from one portion 
 of the house to another. Sleeping rooms may have the benefit during the 
 night from the same equipment that supplies the remainder of the house 
 during the day. This feature allows the installation of a machine of less 
 capacity and cost than would be required for simultaneously condition- 
 ing the entire building. Occasionally cooling equipment for a single room 
 is installed. The number of persons to be made comfortable, and their 
 personal desires, as well as the allowable expenditure, must dictate the 
 final decision. 
 
 Even insulation may be applied only to those walls receiving sun effect 
 and to the ceilings of special rooms, but such an installation possesses 
 no insulating effect during the heating season on the remaining walls and 
 ceilings, where heavy heat loss may be incurred, with the resulting high 
 cost of total fuel used. In some localities, of course, heating systems must 
 be so generally effective throughout the structure, even including the 
 
40 University of California — Experiment Station 
 
 basement, as to eliminate the possible freezing of plumbing at certain 
 times during the heating season. 
 
 Whatever the final decision may be regarding partial or total service, 
 it may be wise, in the case of new construction especially, to have a com- 
 plete system designed, even though only a portion may be immediately 
 installed. By such procedure one is assured that the various additions 
 and extensions will ultimately form a properly functioning whole. 
 
 3. Outside Air Conditions to Be Encountered. — The capacity and type 
 of air-conditioning equipment selected are dependent to a considerable 
 degree upon the requirements imposed by the outside air. Its variations 
 and averages for any given locality should be known, and these may 
 usually be obtained from weather bureau records. Such information 
 is also the basis for the prediction of operating costs and number of days 
 in either the heating season or the cooling season. 
 
 a) Outside air temperature : Heating of residences is usually consid- 
 ered desirable at any temperature less than 68° F. Cooling equipment 
 is not often operated until the temperature approximates 85°. The 
 amount of moisture with the air will vary this range to some extent. If 
 a given locality, on the average, shows a large number of days of the year 
 within this 17° temperature range, then the sum of the heating and the 
 cooling-season days will be correspondingly small, and this usually will 
 be reflected in the extent of provisions for air conditioning. Conversely, 
 locations having only a small number of days within the 17° range will 
 have need for more extensive air conditioning. 
 
 The efficiency obtained from a given capacity of any one of the sys- 
 tems on figure 12 is only slightly dependent upon the outside tempera- 
 ture of air which each must condition, with the exception of system A. 
 The latter is very greatly dependent for its results upon the outside 
 temperature and particularly upon the differences between day and 
 night temperatures. 
 
 o ) Moisture in outside air, or humidity : The greater the ventilation 
 used in any given structure, that is, the amount of outside air which is 
 brought in and which must be conditioned, the greater the effect of 
 moisture in the air. In localities where humidity goes to high values, 
 considerable refrigeration, or its equivalent, is necessary to remove the 
 moisture, if drier indoor air is to be maintained. Some of the systems of 
 figure 12 have no inherent capacity to remove moisture, namely, systems 
 A, B, C, and D. On the other hand, systems E, F, and G may be arranged 
 to operate at temperatures which will condense out the moisture, reduc- 
 ing thereby the moisture content of the air that is conditioned. System 
 G has the greatest inherent capacity to accomplish this result. It may be 
 
Bul. 589] Am Conditioning for Homes 41 
 
 adjusted to remove varying amounts of moisture by varying the temper- 
 ature of the cooling surfaces. 
 
 c) Dust, including pollens, with outside air : The removal of dust and 
 pollens by air conditioning may constitute a very real advantage in some 
 localities, or for some owners. Definite reduction in the expense of clean- 
 ing interior decorations has been justly claimed, and the relief afforded 
 those with respiratory ailments has been established. For dust removal, 
 system A would have no value, unless the air brought into the room was 
 taken through an appropriate filter. The resistance to air flow so in- 
 serted, however, would necessitate a special fan, not ordinarily used in 
 this type of installation. The systems using washers would automatically 
 reduce dust and pollens, and the dry-surface central units are usually 
 equipped with filters. A simple radiator-type system, such as E, will 
 not remove dust, nor will system D, unless this is equipped with an air 
 filter for the cooled stream of air brought into the rooms. 
 
 4. Inside Air Conditions to Be Maintained. — Within the house, cer- 
 tain requirements may be specified, and these are usually temperature, 
 humidity, dust removal, movement of the air, and change of air, or 
 ventilation. A sixth item is sometimes also included, namely, sound fil- 
 tering. Any air-conditioning system which will control all six of these 
 items to any required degree, with exactness, and entirely independent 
 of outside conditions, is necessarily a very complicated and expensive 
 machine. Hence for residence work, certain modifications from these 
 most rigorous specifications are made. 
 
 a) Inside air temperature to be maintained : During the heating sea- 
 son, it is reasonable to expect this temperature to be maintained at 70° 
 to 74° F, with not more than 3° or 4° variation at the working zone. This 
 may be accomplished through the use of various automatic thermostat 
 controls at nominal cost. 
 
 During the cooling season, air-conditioning equipment should be 
 adjustable to maintain a reduction of outside temperature equal to ap- 
 proximately one-half of the difference between outside temperature and 
 72° F, but with minimum inside temperature at about 80° to 85°. The 
 reasons were given in earlier sections for not maintaining inside tem- 
 perature at 70°, independently of outside temperature during the cool- 
 ing season. In comparing the possible performances of the various sys- 
 tems in figure 12, it should be noted that system A has no inherent 
 capacity for varying the inside temperature independently of outside 
 variations, and that system G has the greatest capacity for independent 
 performance. Systems B, C, and D are limited in capacity to decrease 
 the air temperature by the amount of moisture carried in the outside air, 
 
42 University of California — Experiment Station 
 
 for at higher humidities their possible capacity is seriously impaired. 
 On the other hand, in locations where the atmospheric humidity during 
 the cooling season is fairly low, systems B, C, and D are often found to 
 give satisfaction. 
 
 b ) Moisture with inside air, or humidity control : The simultaneous 
 control of humidity and temperature each to fixed values is so involved 
 an undertaking that it is seldom specified in residence work. Instead, 
 humidity is allowed to vary to some extent, say, between 35 per cent and 
 50 per cent, or occasionally as high as 60. With respect to independent 
 humidity control of recirculated inside air, the general statements made 
 under 3b above will apply. 
 
 c) Sound-elimination filters: Some equipment is provided with filters 
 which effectively prevent noise transfer into the rooms from the equip- 
 ment itself or from the outside. This requirement is receiving greater 
 consideration than formerly, although great advances have been made 
 in the elimination of noise in fans and motors. None of the systems of 
 figure 12 includes a sonic filter. Special streamline registers are available 
 to aid in decreasing noise from registers due to air flow into the room, 
 but they have not been included in the comparisons. 
 
 5. The Allowable Cost of Air-Conditioning Equipment. — In attempt- 
 ing to determine an appropriate budget allowance for air conditioning, 
 the prospective purchaser should realize that the cost depends greatly 
 upon his requirements. It should be evident that many different degrees 
 of air conditioning can be realized, with the costs naturally increasing 
 as specifications become more rigorous. This is graphically demonstrated 
 in figure 12, where for the sample insulated cottage, the costs of present- 
 day actual cooling systems vary from $170 to $1,200, or, if half the cost 
 of insulation is considered chargeable to cooling equipment and half to 
 heating equipment, the range is $245 to $1,275. The accompanying vari- 
 ation in operating costs is likewise shown, and the discussions have 
 pointed out the extensive variations in the inherent capacities of these 
 machines, and the varying conditions under which they are particularly 
 advantageous. 
 
 Perhapes the time-honored and practical method of writing specifica- 
 tions, and calling for competitive bids thereon with complete statements 
 of the performance guaranteed, is the best plan to obtain accurate and 
 competitive cost data for the solution of a given air-conditioning prob- 
 lem. If costs are stated by divisions, such as for insulation, for heating 
 system, for combined heating and cooling system, with the right re- 
 served to accept any one, or any group, or all of the separate bids, the 
 greatest flexibility results. Those sections may be selected which come 
 
Bul. 589] Air Conditioning for Homes 43 
 
 within the budgeted amount. If only the insulation and a heating system 
 are first realized, then the possibility remains of obtaining harmonious 
 additions later. 
 
 The question will inevitably arise as to whether or not the lowest of 
 competitive bids on perhaps the poorest equipment should be accepted, 
 or whether a better quality of product should be selected at higher price. 
 Some formal specifications state that the bid accepted shall be that of 
 the lowest responsible bidder. In this regard, it may be difficult to 'frame 
 any better statement of a general nature than the often-quoted observa- 
 tion of Ruskin, who said, "There is hardly anything in the world that 
 some man cannot make a little worse and sell a little cheaper, and the 
 people who consider price only, are this man's lawful prey." 
 
 ACKNOWLEDGMENTS 
 
 The authors desire to acknowledge valuable service rendered by repre- 
 sentatives of the industry who have at considerable expense of time and 
 labor supplied cost estimates and data; to Mr. D. 0. Rusk and Mr. A. 0. 
 White, who served successively as secretaries to the group studying the 
 problem at the University of California; to Dr. F. A. Brooks, of the 
 Division of Agricultural Engineering, and to members of the engineer- 
 ing professional organizations of the San Francisco Bay region, who 
 have maintained continuous interest in the progress of the work. 
 
44 University of California — Experiment Station. 
 
 SUGGESTIONS FOR ADDITIONAL READING 
 
 Periodicals 
 
 The Aerologist. Aerologist Publishing Co., 121 N. Clark St., Chicago, III. 
 
 Domestic Engineering. Engineering Publications, Inc., 1900 Prairie Ave., Chicago, 
 111. 
 
 Heating, Piping and Air Conditioning. Keeney Publishing Co., 1900 Prairie Ave., 
 Chicago, 111. 
 
 Heating and Ventilating. The Industrial Press, 140-148 Lafayette St., New York 
 City. 
 
 Books 
 
 American Society of Heating and Ventilating Engineers Publishing Com- 
 mittee. 
 1935. Guide. 1008 p. Amer. Soc. Heating and Ventilating Engin., 51 Madison 
 Ave., New York City. (Yearly editions.) 
 
 Harding, L. A., and A. C. Willard. 
 
 1932. Heating, ventilating and air conditioning. 963 p. John Wiley and Sons, New 
 York City. 
 
 Hill, E. V. 
 
 1931-32. Air conditioning engineers' handbook. (Looseleaf.) Aerologist Pub- 
 lishing Co., 121 N. Clark St., Chicago, 111. 
 
 Hill, E. V. 
 
 1930-32. Aerology for amateurs and others. (Looseleaf.) Aerologist Publishing 
 Co./ 121 N. Clark St., Chicago, 111. 
 
 Lewis, S. E. 
 
 1932. Air conditioning for comfort. 244 p. Keeney Publishing Co., 1900 Prairie 
 Ave., Chicago, 111. 
 
 Mellish, A. J. 
 
 1933. First steps in air conditioning. 85 p. E. A. Scott Publishing Co., 45 West 
 45th St., New York City. 
 
 Moyer, J. A., and E. U. Fittz. 
 
 1933. Air conditioning. 390 p.. McGraw-Hill Book Co., New York City. 
 
 Pamphlets 
 *Backstrom, Eussel E. 
 
 1931. House insulation — its economies and application. U. S. Dept. Com. Natl. 
 Comm. on Wood Utilization Eept. 19: i-vi, 1-52. (10 cents.) 
 
 *Backstrom, Eussel E. 
 
 1933. Insulation on the farm. 49 p. U. S. Dept. Com. Natl. Comm. on Wood 
 Utilization. (10 cents.) 
 
 Kratz, Alanzo P. 
 
 1931. Humidification for residences. Illinois Engin. Exp. Sta. Bui. 230:1-30. 
 (Obtainable from the Engineering Experiment Station, Urbana, 111., for 
 20 cents.) 
 
 * The publications starred may be obtained from the Superintendent of Documents, Washing- 
 ton, D. C, for the amounts indicated in parentheses at the end of each item. Cash, not stamps, 
 should accompany all orders. 
 
Bul. 589] Air Conditioning for Homes 45 
 
 Mallory, G. D. 
 
 1932. Insulation of new and old homes. 73 p. Canada Dept. Int. Dominion Fuel 
 Board, Ottawa, Canada. 
 
 *Perkins, Nelson S. 
 
 1931. How to judge a house. U. S. Dept. Com. Natl. Comm. on Wood Utilization 
 Eept. 17: i-iv, 1-85. (10 cents.) 
 *United States Department of Commerce Building Code Committee. 
 
 1923. Eecommended minimum requirements for small dwelling construction. U. S. 
 Dept. Com. Bur. Standards Bldg. and Housing Pub. 18: i—viii, 1-107. (15 
 cents.) 
 
 * United States Federal Board for Vocational Education in Cooperation with 
 the United States Department of Commerce National Committee on Wood 
 Utilization. 
 1931. Light frame house construction; technical information for the use of ap- 
 prentice and journeyman carpenters. U. S. Fed. Bd. Vocat. Ed. Bui. 145: 
 i-xii, 1-216. (40 cents.) 
 
 * The publications starred may be obtained from the Superintendent of Documents, Washing- 
 ton, D. C, for the amounts indicated in parentheses at the end of each item. Cash, not stamps, 
 should accompany all orders. 
 
 18m-3,'35