UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA AIR CONDITIONING FOR CALIFORNIA HOMES BALDWIN M.WOODS AND BENEDICT K RABER BULLETIN 589 MARCH, 1935 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction ... 3 Test residences for study of air conditioning 4 Scope and purpose of this discussion ■ 4 Principles of comfort cooling and heating 5 Relief for hay-fever sufferers 6 Laboratory investigations of comfort conditions 7 The comfort zone 7 Common aspects of heating and cooling 9 Important distinction between heating and cooling for comfort .... 9 Weather zones 11 Weather conditions in California 11 The question of economy 13 Principles followed 13 Air conditioning, a prospective necessity rather than a luxury .... 14 Sample houses 14 Insulation 19 Principal problems in cooling 19 Effect of insulation applied to the sample cottage 19 Insulation of construction other than houses 22 Temperature delay due to insulation 22 Mechanical equipment 23 Types of mechanical equipment 23 Application of equipment to the sample cottage 25 Attic ventilation with night air circulation 25 Complete air-conditioning equipment 27 Room-unit conditioners with ice-melting tank 30 Central condenser equipment with room-unit conditioners 31 Combinations of equipment 31 Initial and operating costs of typical cooling systems 33 Initial costs 33 Operating costs 36 Factors affecting the selection and operation of air-conditioning systems . . 37 1. The building and its structural features 37 2. The portion of the building which is to be air conditioned 39 3. Outside air conditions to be encountered 40 4. Inside air conditions to be maintained 41 5. The allowable cost of air-conditioning equipment 42 Acknowledgments 43 Suggestions for additional reading 44 Periodicals 44 Books 44 Pamphlets 44 AIR CONDITIONING FOR CALIFORNIA HOMES 2 BALDWIN M. WOODS 3 and BENEDICT F. KABER 4 INTRODUCTION The cooling of homes in summer has recently made rapid progress. Before long, equipment to provide air conditioning as an all-year proc- ess will probably become commonplace. Interest in this development is widespread; many houseowners wish to know the meaning of air con- ditioning, the results that can be reasonably expected from different methods of providing it, and the cost of such service. This bulletin rep- resents an effort to provide useful information to the houseowner. Whether applied to heating a house in winter or to cooling it in sum- mer, the word "condition" means to control the temperature, the hu- midity or moisture content, and the purity of the air, and to regulate its movement. The most rapid progress has been made in appliances to be employed in industry. In these cases, either the conditions for the fabrication of a product or the need for maintenance of operating efficiency has stimu- lated the development, and resulting economies pay the cost. Of course, summer cooling has appeared to a considerable extent in hotels and res- taurants, small shops, railway trains, and theaters, where the added comfort attracts customers. The development has run from manufactur- ing to service industries and is on its way to the home. Since the largest potential field of application is the home, one may wonder why this was not the first place of use. It appears, however, that many useful mechanical devices have entered the home only after suc- cessful pioneering in business. On the farm one sometimes observes side by side a barn for the livestock, specially designed to provide adequate shelter and ample natural ventilation, and the farmer's house with little i Beceived for publication January 11, 1935. 2 This publication is the thirteenth of a series reporting results of investigations conducted by the California Agricultural Experiment Station in cooperation with the California Committee on the Belation of Electricity to Agriculture. This study was made by the Department of Mechanical Engineering of the University of California. 3 Professor of Mechanical Engineering. *■ Professor of Mechanical Engineering. [3] 4 University op California — Experiment Station or no provision for attic air change, and ready to overheat the family in the summer. The occupants of the home are now asking consideration of their comfort. It is to an understanding of air conditioning in the home that this bulletin is devoted. The group investigating the subject is unanimous in the belief that insulation is of primary importance in solving the problem, either for heating in winter or cooling in summer. Therefore, insulation has been given more extended treatment than the size of the bulletin would other- wise justify. This discussion has also been made as practical as possible. Test Residences for Study of Air Conditioning. — During the last two or three years, the need for rapid progress has led to the construction and operation of several test residences. Of these, three well-known ones are (1) at the University of Illinois, (2) at Schenectady, under the auspices of the General Electric Company, and (3) at Mansfield, Ohio, under the auspices of the Westinghouse Electric and Manufacturing Company. Much is being learned from the test houses concerning the best meth- ods of operation and the best systems of control. The equipment em- ployed to accomplish these purposes has been undergoing rapid changes. Engineers are endeavoring to perfect heating and cooling appliances which will condition air to a desired state. Scope and Purpose of This Discussion. — In this analysis, equipment for industrial use will be discussed only as it contributes to better under- standing of available methods. Attention will be devoted especially to rural homes and their problems. Since rural homes present on the aver- age more varied conditions than city homes, the study of their problems may call for a more complete listing of methods and results than would otherwise be justified. The problems of heating and cooling will be separated. Much greater progress has been made in the standardization of heating equipment than in that of cooling equipment. It will be wise, in the interest of brev- ity and clearness, to emphasize the cooling problem. To be sure, there is the chance in this of overlooking the joint heating-cooling equipment installation. The two problems should be considered simultaneously. Ultimately, the home should in many cases have its heating and cooling equipment combined. The ducts and piping will often serve both pur- poses. Some promising combined units are already announced. Addi- tional comparisons of heating and cooling problems will be considered later. The relative merit of different methods, applied under various condi- tions, will be discussed. An attempt will be made to supply the necessary Bul. 589] Air Conditioning for Homes 5 background for understanding the types of equipment available, their principles of operation, and the degree of effectiveness to be expected under certain conditions. Clearly, details of computation, problems of design, and the selection of equipment for a given home are technical problems of some complexity, the solution of which often requires an expert. Many otherwise good installations will probably give difficulty in practice because of errors in fitting the installation to the house. A section on initial costs and estimated operating costs of various types of equipment has been included as a general guide. These costs are based upon 1,000 hours of operation per summer. Of course, the amount of operation depends upon the climate, the special character- istics of a given season, the insulation of the house, and the inclination of the houseowner. Consequently, the cost should be adjusted to the actual time in prospect. For the Great Valley of California, and even for the inland regions of southern California, the cooling season appears to be from 75 to 150 days. Continuous cooling, of course, is not required throughout the entire period. PRINCIPLES OF COMFORT COOLING AND HEATING Definite knowledge of air conditions for human comfort is still limited and inexact. Of the four principal factors controlling air conditioning — namely, air temperature, movement, humidity, and purity — the first three have been shown by experimentation to combine to give the im- pression of warmth or cold which is experienced by the individual. A study of the physiological reaction to combinations of these factors is very interesting. For example, it is a matter of common knowledge that, within limits, one can endure a higher temperature with air of low hu- midity than with air of high humidity. Also air movement at ordinary temperatures generally produces a feeling of coolness, or at least of less heat, as shown by the universal attempt to find a breeze when the tem- perature is unpleasantly high. Throughout all extremes of climate the human body attempts to main- tain the same temperature. The body evidently has a thermostat, like a mechanical refrigerator or a heating system. The methods taken by the body to keep cool when the outside temperature is high and to keep warm when the outside temperature is low, may be described without, however, adequately explaining what controls the whole process. The location and construction of the "thermostat" has not been fully re- vealed, although physiologists believe there is a heat center in the brain. A nerve mechanism controls the surface capillaries through the "vaso dilators" and "constrictors." Whenever the body temperature is raised, 6 University op California — Experiment Station the dilators permit greater flow of blood in the capillaries, which, in turn, permits greater heat radiation. The opposite occurs when the body is chilled. One of the most interesting phenomena in connection with body cool- ing is the function of the sweat glands. Consider a person exposed to air of high temperature with fair movement. As the temperature increases above that of the body, if there should be no perspiration, the outside air would add heat to the body. This is due to the simple fact that heat flows from the hotter air to the cooler body. If, on the other hand, the sweat glands are functioning properly, the body is covered with a film of moisture, and the air flowing by, unless it is entirely saturated with moisture, absorbs additional moisture. The evaporation of the perspira- tion withdraws heat from the body and hence acts as a cooling process. Therefore, the body mechanism is constructed to provide liberal action of the sweat glands whenever the temperature rises. If the temperature becomes high, the wind velocity likewise high, and the humidity low, the perspiration may be evaporated so fast that the skin surface is maintained dry. In this case a moisture film does not protect the body and the hot air does transfer heat to the body. All of us, at one time or another, have experienced a dry hot wind, so hot and so dry that to be in the breeze was far less comfortable than to be out of it. At the other end of the scale is the condition of the man exposed to cold weather. As the surface of the body is chilled the flow of blood through the capillaries is reduced. This continues until all of the outer circulation of the body has been temporarily stopped and the blood is sent through the central system of large blood vessels at a rapid rate, maintaining the central portion at its standard temperature, as far as possible. When this equilibrium can no longer be maintained, death from chill is imminent. Relief for Hay-Fever Sufferers. — Dusts and pollens as breathed from the air are the cause of discomfort and even loss of health to many per- sons. Mock 5 in 1919 estimated that there were five million workers in the United States whose health was jeopardized by dusts alone. Conditions in the home are usually much better than in many industrial plants, but sufferers from ailments due to dusts or pollens become susceptible to smaller and smaller quantities of the irritant. To these persons the filter- ing of the air in home or workshop is a wonderful relief. Recently, a number of hospitals have equipped wards to care for these cases. The results are reported to be excellent. The general sense of physical well- s Mock, Harry E. Industrial medicine and surgery, p. 205. W. B. Saunders Com- pany, Philadelphia. 1919. Bul. 589] Air Conditioning for Homes 7 being experienced on a clear day after a rain is a strong testimonial to the merits of clean air. A further result of filtering, of interest to the housekeeper, is the trapping of the dust before it settles in the house. Dusting of furniture and cleaning of curtains and drapes is needed considerably less often. Laboratory Investigations of Comfort Conditions. — The purpose of air conditioning in homes is to produce conditions conducive to human comfort. As stated above, knowledge of what constitutes comfort is at present limited. Comfort appears to be in part a matter of physiological response to stimuli and in part psychological response. It is much to be hoped that investigations will be made and the results translated into terms usable by engineers. There are definite indications of relations between the heart rate, the respiration rate, and the condition of the skin, as physiological factors, and the sensation of comfort as a psychological factor. Engineers in charge of operation of air-conditioning installations located in buildings occupied by both men and women believe that on the average, the com- fort temperature for women is likely to be about 2° F higher than for men, owing probably to considerable differences in clothing. It is found also that not every one is comfortable under a given set of conditions and further that the state of a given person varies from time to time. Undoubtedly also, the weight of clothing worn and the activities of the persons in air-conditioned buildings have much to do with comfort. The Comfort Zone. — Until more complete determinations have been made, the laboratory studies of the American Society of Heating and Ventilating Engineers will probably serve as the standard guide to com- fort conditions. This society has determined the combinations of tem- perature and humidity, which, for given air velocities, will be found comfortable by many persons. 6 These combinations have been shown in the comfort zones, presented in figure 1. For the purpose of this chart, the subjects were asked to vote "com- fortable" or "uncomfortable" for each condition experienced. Some of the tests conducted in summer showed comfort at higher temperatures than in winter, doubtless owing to the adjustment of the body to the seasons. Thus, 98 per cent of the subjects felt comfortable in the summer at a temperature of 75° F and a relative humidity of 60 per cent. In winter, this condition was a little warm for many, and only 50 per cent were comfortable. At any time there may be some who desire excep- tional conditions. 6 Houghten, F. C, and C. P. Yagloglou. Determining lines of equal comfort. Amer. Soc. Heating and Ventilating Engin. Trans. 29:361. 1923. Yaglou, C. P., et al. How to use the effective temperature index and comfort charts. Amer. Soc. Heating and Ventilating Engin. Trans. 38:410. 1932. 8 University of California — Experiment Station 90 80 70 60 r- 50 Z UJ o UJ 40 30 5 2° D X UJ > < _l LU a: 70 60 50 40 30 20 98% '•/Summer Comfort Zone 07. 507. 981 507, 07. \\ 1 , fc ^ \ \ \ \ \ \ \ \ 0% 60% 98% 50% 0% > 1 1 j i j j 97% <\. '^Winter Comfort Zonef<£ 6 4? 07. 507. 977. ; 50% 0% y l\ \ I \ n V \ \ \ \ 0% 50% 97% 50% o% 60 70 80 AIR TEMPERATURE (Deg. Fahr.) 90 Fig. 1. — Comfort zone in terms of relative humidity and air tem- perature, as determined by the American Society of Heating and Ventilating Engineers. Under the conditions of the test, the sub- jects were at rest and exposed for 3 hours or more, and the air move- ment was 15 to 25 feet per minute. The upper chart is for summer, the lower for winter. Each line shows the various combinations of temperature and humidity at which a given percentage of subjects expressed themselves as comfortable. Bxil. 589] Air Conditioning for Homes 9 An interesting measure of the effect of humidity is the slope of the lines in the diagram. For the temperatures here shown a decrease in humidity always accompanies an increase in the temperature for com- fort. This means that at higher temperatures relatively drier air is pre- ferred. In general, the addition of moisture to warm air, that is to say, air above 70° or 80° F, makes it less comfortable; the air feels much hotter. Also, there is a point, somewhere between 45° and 50°, below which the addition of moisture to air makes it feel colder. This may explain the reputation for cold weather of certain seaports where the winter tem- perature runs between 30° and 45° and there is much wind from the ocean. Additional charts become important to the engineer to show the re- sultant state of moist air after its temperature has been changed and after a certain amount of moisture has been added or subtracted. Such charts are called "psychrometric" charts. The comfort zone is an ele- mentary diagram of this kind. For a detailed account of psychrometric charts the interested reader may consult textbooks on refrigeration and air conditioning, and the Guide of the American Society of Heating and Ventilating Engineers (see the books listed under "Suggestions for Additional Reading," p. 44) . Common Aspects of Heating and Cooling. — Heating and cooling are, as have been noted, merely two aspects of the same thing. In due time, as has already been intimated, equipment may commonly be designed to serve both purposes. The average home has a heating system. If on the unit plan, that is, with units located in various parts of the house, it may employ oil stoves, coal stoves, wood stoves, fireplaces, gas heaters, electric heaters, gas-steam radiators, circulating heaters, or others. If it has a central heating system, it may circulate the heat through air ducts, as in the case of most hot-air systems, or through steam or hot- water radiators. Other systems also are in use. Equipping the home for heating in the winter and for cooling in the summer are two parts of the same job. They present economic problems. If some or a large part of the equipment can be used for both purposes, then capital cost is reduced. Furthermore, if in a home already built, a heating system which has been installed can serve in part for the cooling system later desired, particularly as an aid in distribution, adding the cooling system becomes less difficult and less expensive. Important Distinction Between Heating and Cooling for Comfort. — There is one distinction, however, between the problems of heating and of cooling which should be brought forcibly to the attention of every one. 10 University op California— Experiment Station For heating, there is a minimum temperature in the neighborhood of 70° F, below which the average person, unless active, is uncomfortably cool. It does not matter whether the outside temperature is zero or 30° or 40°, this comfort temperature remains approximately at 70°. There are in- dications from operators that it is probably nearer 72° or 74° than 70°. With summer cooling, however, as the outside temperature rises, many, if not the majority of people, remain comfortable until a temper- ature of 80° F or, in the case of relatively dry air, 85°, is reached, or a lower temperature in the case of moist air. Moreover, this is not a fixed condition of comfort, but is dependent upon outside temperatures. This means that comfort cooling depends upon providing a temperature a reasonable number of degrees below the outside temperature of the air. Where persons are to remain continuously in the conditioned air, the reduction of temperature for an optimum condition will probably be greater than for short exposure. Homes, however, are rarely occupied continuously. Hotels, restaurants, and theaters have discovered that a drop of 10°-20° below the outside temperature is all that the majority of patrons desire. The same discovery has been made by railways under- taking air conditioning for the comfort of their passengers, especially for short hauls. This distinction is of considerable economic consequence. In the case of heating systems, the house must be warmed to 70° F on the coldest possible day. Actually, in laying out systems, some concession is made in the design to infrequent very cold weather. In cooling systems, however, it appears sufficient to provide a band of cooling maintained at 10°-20° F — in exceptional cases more — below the outside temperature. An approximate working rule is to seek a re- duction of temperature equal to one-half the difference between the outside temperature and 72°. Briefly, then, the difference between the design of heating and cool- ing systems is this : heating systems must produce an indoor temperature of at least 70° F, regardless of the outside temperature; cooling systems should produce a drop in temperature of 10°-20°, and in a few cases, somewhat more. As air conditioning progresses, consideration will have to be given to the effect that the transition from a comfortable cooled house to the hotter outdoors will have on the individual. This is not known at present, but the general belief is that the difference between the indoor and out- door temperatures should, as stated above, be kept moderate. Bul. 589] Air Conditioning for Homes 11 WEATHER ZONES Weather Conditions in California. — In air conditioning, whether for heating or for cooling, the fundamental information needed by the de- signer always includes the kind of air available on the outside and the kind to be provided in the house. The designer will ask "What are the initial temperature, humidity, and degree of purity of the atmosphere ; what final values of these same data are to be provided; and what air movement is desired or is permissible ?" The type of equipment suitable for any home is really affected as much by the weather of the region in question as by any other single factor. Analysis of weather reports from stations scattered throughout Cali- fornia shows that there is a very considerable region over the whole of which the maximum daily temperature for July is above 90° F. July is, in general, the hottest month of the year in California, and 90° is an average maximum above which comfort cooling is strongly indicated as desirable. A study of these weather reports and of the map of the state suggests the delineation of zones in which conditions appear to be similar. The region above referred to, over which the average daily maximum tem- perature for July is above 90° F, has been indicated on the smaller, or pilot chart, of figure 2 as zone I. This region includes practically all of the area of the interior valleys of California, together with a consider- able portion of the interior mountainous region of southern California. Comparison with the larger relief map shown on the same figure will afford a picture of the relations of the zones to the mountain ranges and the coastal regions. The entire coastal and most of the delta area lies outside of zone I. Analysis with reference to the humidity encountered, as well as the temperature, indicates the desirability of dividing the coastal region into two zones. That portion north of Santa Barbara is strongly affected by the cool waters of the Japan current off-shore. It is labeled zone III. The portion from Santa Barbara south, has high relative humidity, but it has higher temperatures. The southern coastal region is labeled zone II. Since these assignments of zones are made arbitrarily from average conditions for the region, exceptions are to be expected. It appears that the area around Stockton, because of higher humidity than is found in most of the Great Valley, and the area around San Diego, may require separate consideration. Stockton is placed in zone I but has a high hu- midity in contrast with the rest of its zone; and on the other hand, 12 University op California — Experiment Station Mojave and Chico have weather characterized by extremely low humid- ity. San Diego city has conditions similar to those of zone III, although located in zone II. The northern Sierras, as a whole, require shade for ttW* *% Fig. 2. — Zones of temperature and humidity conditions for California, in the small map at the upper right, as compared with the physical features of the state, shown in the large relief map. Zone I has high summer temperatures usually with low humidities ; zone II has moderate summer temperatures usually with higher humidities ; zone III has lower summer temperatures with moderate humidities. (By permission of H. A. Sedelmeyer, copyright owner.) comfort in summer. If note is taken of these exceptions, the zoning shown will furnish a fair guide to conditions to be expected. Average daily summer temperatures at Davis, California, which falls in zone I and is near Sacramento, are given in table 1. This table is par- ticularly significant in exhibiting the relatively low night temperatures, Bul. 589] Air Conditioning for Homes 13 lasting for at least 6 hours, in the summer months, especially in many parts of zone I. Considerable amelioration can be obtained from a cooling system which will pump night air into the house and will prevent rapid warming during the day by proper use of insulation. Steady heating for longer periods is thus counteracted by forced short-time cooling. Further TABLE 1 Average Daily Temperatures, Davis, California, October, 1929-September, 1934 Month Maximum Minimum Night temperature not exceeded for 6 hours Mav op 80.5* 88.7 97.1 953 88.2 81.7 o p 47.1 52 54 3 53.1 49 5 43.9 op 52.7 June 57 5 July 60.7 August September 60.2 56.9 October 513 * Average of the 155 daily maximum temperatures occurring in the months of May during the 5-year period. Similarly for other months and for the minimum temperatures. reference to this will be made in the discussion of different types of equipment for cooling. The high variability of weather conditions throughout the state makes desirable a weather analysis for every locality, before general conclu- sions are reached regarding the merits of different types of equipment. THE QUESTION OF ECONOMY Principles Followed. — In this, as in all equipment problems, the ques- tion of cost must be kept constantly in the foreground. Where the need for summer cooling is not great, the justifiable expenditure for obtain- ing results may similarly be small. In certain communities, also, weather conditions and the availability of cheap cold water and low electric rates may make possible relatively inexpensive cooling systems. As a preliminary guide, the assumption has been made that "ulti- mately the homeowner may be willing to pay as much per year for cool- ing as he now pays for heating." In climates where the warm season lasts most of the year, the homeowner will probably be willing to pay more; in climates where the winter season is long and cold, the situation will be reversed. For the central valleys of California the rule may prove a fair one. A number of commercial installations in the valley climate of California have shown approximate equality between annual heating and cooling charges. A study of figure 12 (p. 34) indicates that the 14 University of California — Experiment Station initial cost of a cooling system, or perhaps of a combined system, is at present about that of the family automobile. Doubtless, with increased production and standardization of equipment, the initial cost can be reduced. Air Conditioning, a Prospective Necessity Rather Than a Luxury. — Although economy is an important consideration, as soon as the home- owner becomes thoroughly desirous of having equipment for this pur- pose, and as soon as he is convinced that the equipment is fairly priced and will do the work, he will be inclined to install it. Some years ago the cost of an automobile was commonly thought to be beyond the purchasing ability of the average family. Nevertheless when the desire became great enough, the automobile passed from the luxury to the necessity class. The situation is also similar to that which confronted the advocates of good highways some twenty years ago. In the beginning, short stretches of good highway gave a powerful demon- stration of their desirability by contrast with the rest of the road. Such is the case at this time with air-conditioning installations in our warmer localities. It appears that the hotels, theaters, restaurants, and occa- sional residences containing such installations, now stand out as did the isolated stretches of good pavement of fifteen or twenty years ago. Conservative and thoughtful men throughout the country are prophe- sying rapid development of air conditioning for residences. A number of authorities also believe that important changes in the design of homes are likely to take place. These changes, to their way of thinking, should make the home more serviceable than it now is, should suit its construc- tion to modern materials, and should reduce its cost. Those interested in the problem of air conditioning will wisely give consideration to these prospective changes and will attempt to incorporate flexibility into the equipment proposed for use. Those considering the construction of new homes should be even more thoughtful about the problem of air conditioning than those who desire to improve conditions in older homes. As will appear, arrangements, especially for insulation and air ducts, can be made in the beginning at little cost which later prove not merely expensive but difficult; and also no more significant factor exists in this subject of economy than in- sulation. SAMPLE HOUSES Two sample houses are used in this bulletin as the basis of discussions and comparisons of such items as the effect of insulation and the cost of the equipments for summer cooling. The assumed floor plan of the Bul. 589] Air Conditioning for Homes 15 first house, a typical five-room cottage, is shown in figure 3, the general external appearance in figures 7, 8, 10, and 11, and the brief specifica- tions in table 2. The second sample house is a two-story, eight-room home. The floor plans are given in figure 4. The general features of the assumed con- struction are shown in the form of brief specifications in table 2. *Oh.lH- t: Fig. 3. — Floor plan of the sample cottage used as the basis of comparisons of cost of cooling equipments and effect of insulation. Both houses are typical California homes. The usual frame of 2 x 4 inch wooden studding is assumed to be sealed outside by fir sheathing, building paper, and redwood siding, and inside by wood lath and plaster. The roof design in each case is a simple gable type with wooden rafters and roof sheathing and cedar shingles. The floors consist of the usual 1-inch pine subflooring and %-inch oak finish-flooring, with building paper between. Basements, adequate in size to contain the necessary equipments, are assumed under the houses. 16 University of California — Experiment Station N ? o o • rH 00 •IH OO -*- s cr o> be - "o o o <H O 00 o O oo 00 C3 00 00 o o o 'E. 00 (I) -+- «H O 00 C 03 "ft O O \K bJD •rH 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