Document 8Vqq028Mm0524yBGxQEkKbaxm

American Society of Heating and Ventilating Engineers Guide,19jj^ mentioned. Cooling by evaporation is satisfactory only when the aird be cooled is very dry; air motion as a means of producing cooling effecty never entirely adequate in the range of high temperatures. Of the t<5 evaporative cooling, or adiabatic saturation of the air, is a much iw dependable method which will make more reduction in. the effect^ temperature than will an increasing air motion within permissible' limits As an example of this, consider an outdoor condition of 96 F dry-b^ and 80 F wet-bulb. The effective temperature is 85.7 F and, if thestjj air is moved with a velocity of 300 fpm, the effective temperature will b? reduced only 2.0 F while saturation at the wet-bulb temperature would reduce the effective temperature 5.7 F. At 300 fpm velocity this sati; rated.airwould[reduce theeffective temperature to 75.6 F, thus makings total improvement of 10.1 F. '. : " T ? Evaporative Cooling Evaporative cooling is accomplished by passing air through a wattf spray in which the water is being continually recirculated. The aijj entering in an.unsaturated condition, evaporates a part of the water attbf expense of the sensible heat. As this is an adiabatic transfer, the tod heat content of the air remains constant, while the dew point rises and tl* dry-bulb falls until the air is saturated! A system1 of ducts and a propd! ling fan are used to distribute the air in a proper manner. ... | It will be seen that the* reduction in dry-bulb temperature-is,a direct function of the wet-bulb depression of the air entering the dehumidifia arid that the resulting air temperature is governed entirely by the enterW wet-bulb temperature of the outside air. ....................... 1 Dehumidification ..Dehumidification may be accomplished in three ways: 1. By cooling the air beiow the dew point and causing a part of the' moisture contaiid to precipitate. 2. By extracting all or part of the moisture by absorption. . . . 3. By extracting all or part of the moisture by adsorption. As used in this discussion, the term adsorptionpertains to the action| a substance in condensing a gas or vapor arid holding the condensate * its surface without any change in the chemical or physical structure of fk substance and with the release of sensible heat. The term, absorptift implies a change in the chemical or physical structure of a substance inti* process of dehydrating air. Adsorbers include silica gel and lamisilr1 absorbers include sulphuric acid. Dehumidification by Refrigeration Air conditioning imposes requirements on refrigeration equipment j usually found in general cooling work, so that specially designed appara is often needed to replace that normally used for industrial coo^t Standard equipment can be adapted to meet air conditioning req merits but- extreme care must be taken to determine the-limits or applicability! 'See Air Washer Performance-in Chapter 11; also Theory of Atmospheric Cooling in same ctaP 166 Chapter 10--Cooling Methods - ; dustrial or process cooling systems the load is fairly constant, noise ln ,njon is not of paramount importance, space is available or re- fa oper condenser water is not a source of worry, and the cooling latlVm is to a great extent separate and independent of other mechanical ^ment. By contrast, air conditioning, especially as used for space e(P?P an(j comfort work in office buildings, theaters, and places where 000 le eather requires special consideration of all these factors. Space in P6??- buildings is limited and condenser water is expensive. Noise P^rferes with the occupants, and the cooling equipment must dovetail ffi the Other air-handling apparatus. Most important, the load fluctu- ^tes tremendously and is seasonal. Heat of Compression Added to Gas " 77 r -.wv.wv.w.. w* uiwiuyuj iiaiuii. piuuicuid U1 ICLIl^CrdUUH is given in the Refrigerating'Data Book2, 1934, so only a brief description of the cycle will be given here before the problems peculiar to air con ditioning are considered. The. refrigeration system consists of three main parts, the evaporator the coridenser, and the compressor. Fig. 1 shows a diagram of the cycle. Hat is absorbed in the evaporator and released in the condenser. The compressor changes the level of the heat by taking it from a lower to a mgher plane. There are also many valves, accessories, and special devices nfcess?.T *or proper operation, which vary somewhat with different types systems and different refrigerants. rpfrLr s`mpte, 'Uustrative cycle of a refrigeration system, the liquid rwbSJ?!?1 P. er pressure has both its pressure and temperature conlpr'1*'' /"!nS expanded through a suitable valve into an evaporator or allhwcb; u" l , evaPorator the low temperature of the refrigerant the evar^ a,bS0rbJleat from substance to be cooled, which surrounds _ 'Prator- This absorption of heat increases the pressure of. the by American Society of Refrigerating Engineers.