Synthetic Weather
optimum of comfort. A logical conclusion of these considerations is that the problem cannot be solved comprehensively by the control of temperature alone. Fortunately no one of the five senses is affected directly by humidity. This can therefore be varied between rather wide limits without unpleasant psychological response. Furthermore, the natural cooling system of the human body is adapted to function in any environment of sufficiently low relative humidity t o evaporate water a t a reasonable rate and each normal individual’s control mechanism of his personal cooling system is well adjusted to his personal needs. These facts permit the selection of some optimum humidity corresponding to each temperature within the comfort zone range which will result in an environment of comfort for the vast majority of people. Many investigators have determined this relationship of humidity to temperature and its limits, which as a diagram is called the comfort zone chart (Figure 1). Minor differences of opinion have naturally developed from these various investigations but the agreement is sufficiently close so that a practical set of data is available.
J
Despite the adverse economic factors of the depression, air-conditioning is rapidly assuming the proportions of a major industry. Chemistry plays an important part in its operation, but air-conditioning is far from being a chemical industry. Like other consumer goods industries it is complex, composed of psychology, physiology, physics, chemistry, applied engineering, architecture, economicsl and salesmanship. This complexity of the problem has produced a diverse series of solutions (similar to the automobile in its early years) which are confusing to anyone seeking definite trends. Competition and public acceptance alone will eventually make the proper selection. In the meantime we are justified only in stating the problem as it appears and in describing the solutions that have been proposed.
TABLEI. DESIRABLE INSIDE CONDITIONS (IN O F.) VARYINGOUTSIDE TEMPERATURES Outside Temp. 105 100 95 90 a5 80 75
Inside Conditions Dry-bulb Wet-bulb temp. temp. Dew point Average Occupancy, 15 Minutes a4 83
io
WITH
-
Relative humidity
63 62.5 61 60 57.5 55.5 55.5
50 50 50 50 50 50 52
68 60 67.5 60 67 60 66.3 58 63.5 56 63 55.5 62.5 55.5 Average Occupancy, 2 Hours or More
46 47 50 50 50
ai
so
77 75 74
69.5 68 67 64.5 63 62.5
Average Occupancy, 1 Hour
THOMAS MIDG LEY, JR.
105 100 95 90 a5
Ethyl Gasoline Corporation,
so
Detroit. llich.
,a
IR-CONDITIONING implies the creation of an atmospheric environment which is comfortable; comfort, in turn, implies a psychological condition closely associated with physiology. This environment is referred to as the comfort zone which has been aptly described as being not too hot, not too cold, not too dry, and not too damp. Add to this a pleasing motion of the air and the absence of dust, dirt, pollen, disease organisms, and unpleasant odors, and the definition is about complete. Note that this is a negative type of definition, it deals exclusively with the elimination of discomfort, assuming that comfort will logically follow. To a large extent this is true in the present case but not completely so. Like many other synthetic materials, synthetic weather is still inferior to the best that nature has to offer. No one yet has synthesized the weather of a perfect spring day or of a glamorous subtropical moonlit evening. The subtle factors are not even understood; until they are and can be introduced as positive factors in air-conditioning, we will continue to have movable windows in our dwellings. The limits of the comfort zone are affected by psychological factors. Unpleasant early experiences associated with the extremes of weather may cause some individuals to prefer higher or lower temperatures than would seem normal, and temperatures which are not unpleasant a t noon become insufferable a t midnight. Add to these the physiological factors of the variations of basal metabolism between individuals, acclimations to the various seasons and latitudes, variations of body heat generation with varying degrees of activity, and it becomes a t once evident that no single temperature may be selected as an
83 a2 80 78 76 75 74
51 52
A
1005
An examination of these data leads to the conclusion that any apparatus that is adapted to set up any of the optimum relationships and maintain them within reasonable limits would be quite satisfactory for establishing comfort. Unfortunately this is not quite true. The nature of the adjacent environment must be taken into account. The artificial environment must be so adjusted to the communicating environment that no great discomfort nor any health hazard shall occur as a result of passing from one to the other. This is accomplished by temperature adjustment and control according to Table I. Thus the temperature requirement for sound air-conditioning is a variable dependent on the outside temperature and the humidity requirement, in turn, becomes dependent on this. The only independent variable is, as it has always been, the outside weather.
Physics, Architecture, and Economics Ever since habitations have been built by man, efforts to approximate the comfort zone have affected their design. The degree of success attained has been limited by lack of knowledge, lack of materials, and economic balances. The application of the simple principles of physics by the heating and ventilating engineers in the recent past evidently has
INDUSTRIAL AND ENGINEERING CHEMISTRY
1Q06
50
60
70
80 Dry Bulb Temperature,?.
FIGURE 1. COMFORT ZONE CHART
resulted in establishing one of the limits of the comfort zone in actual practice, since there is no longer any excuse for an artificial environment to be too cold. The question of heat insulation has been intimately associated with this development. Economics enters at this point, since the justifiable cost of insulation is a function of the heating load and the fuel cost. In the northerly and colder climates, houses are heavily insulated with expensive materials while those in more temperate locations, close to sources of cheap fuel, are not. With the advent of cooling, insulation becomes increasingly valuable. The justifiable cost is a function of both the fuel cost of heating and energy cost of cooling. It is not too much to say that, in many instances, the saving in fuel bills resulting from insulation will go a long way toward paying the operating cost of the cooling required. Windows are a troublesome major factor in the general problem of insulation. Extreme proponents of air-conditioning have even advocated their complete elimination as a solution to the problem. Earlier in this paper it was indicated that such a procedure was not justified, considering the present state of the art. Movable windows will be with us for a long time to come. The problem which windows present must be met and solved, and not evaded. Simply stated it is this: Despite the most efficient insulation of walls and roof, tremendous heat losses (both in and out) occur through the windows. This fact not only adds to the otherwise ample power and fuel costs, but it is so great as to be a serious barrier to proper humidification during periods of extreme external cold, since ordinary windows then present a sufficiently cold surface to condense a large part of the moisture needed in the atmosphere to maintain the conditions of the comfort zone.
VOL. 27, NO. 9
The only p r a c t i c a l s o l u t i o n so far offered is t h e double-pane window. This solution alone is still unsatisfactory, for dust and moisture collect between the panes unless this space has been hermetically sealed. This sealing, in turn, is expensive and has not as yet been entirely p e r f e c t e d . Much improvement is needed. The problem of controlling radiant energy is closely related to insulation. Structures in the far south have for centuries employed surfaces designed t o reject a g r e a t p o r t i o n of t h e sun’s radiant energy. This principle can be employed and should be extended to further the economies of air-conditioning. Likewise t h e u s e of effective awnings o v e r windows exposed to direct radiation should be encouraged. Is it too much to expect t h a t f u t u r e s t a n d a r d s of living will include the a u t o m a t i c c o n t r o l of windows and awnings? In the development of the central heating plant, the direct system of hotair distribution has been improved to an excellent degree of efficiency. The same general principles may be employed for distributing conditioned air from a central cooling and dehumidifying plant, with one very i m p o r t a n t difference. Hot air rises, hence the outlets of ducts for heating should be placed in or near the floor, but cool air falls, requiring that duct outlets for cooling be placed in the ceiling to insure proper distribution. This is an important provision to include in any new structure for habitation even though it is not intended to air-condition it a t the present time, for it seems reasonably certain that long before the structure becomes obsolete from other causes it will be as out of date as a log cabin if air-conditioning cannot be installed.
Engineering From the definition of complete, year-round air-conditioning, it is obvious that seven essential functions must be performed. These are cooling, dehumidification, heating, humidification, cleaning, deodorizing, and circulating. Each of these functions may be accomplished in a variety of ways, and the resulting number of combinations is very large. Each of these combinations may be considered as fitting some given set of circumstances better than any other. It is t o be hoped that the elimination of the less desirable methods and combinations can soon be obtained in order that sound quantity production may follow with the consequent reductions in costs. The various methods in use and contemplated for performing the functions of air conditioning are as follows: (1) COOLINQ ( a ) Mechanical Refrigeration. A refrigerant is passed through the cycle of compression, condensation, and expansion-
evaporation, and recycled. Advantages: Can operate wherever pop-er is available; requires little attention. Disadvantages: Cost of power; must be built to be leakproof. ( b ) Absorption Refrigeration. A refrigerant is absorbed by weak chemical combination in some other material, is driven out by heat at a pressure that will condense it, is allowed to expand and evaporate, and then is reabsorbed.
IOOi
cooling air.
Advantages: Low cost; simple mechanism, consibting only R pump, B radiator, and ian. Disndrxmtagm: Ilrnit,ed to ecrtain :wens; not quite cool cnnugh for good dehumidification, hence roquirtas ndditional appmitus ior satisfactory air-conditioning; initial cost too high for mall instnllnbions. id) ICC. Air hlor\.n over icc is both cooled m d dehumidified. iirluoitlages: Very simple and inexpensive mechitnism. I>i.~ndullinlugui: Iligh operating cost (few proponents of icc lrave admitted thc Sui1 size of thr thermal load involvrd): difficoltiei of handling large quantities of ice and anticipating the rcquirements. ( e ) WCVatcr Xvrtporation. Air may he almost completely cldromidilicd by rheniicd means, such as passing over calcium
