Document bO52D2m4pNq1q0bB4VgO2DzOy

438 Chapter 23 1945 Guide 2. Water temperature is too high for practical sensible heat removal (above1 65 F). 3. Cold water (below 55 F) is available.in adequate quantities so that it can be directly used, for both sensible and latent heat removal, or can be further chilled cheaply, by mechanical refrigeration. . .4. Electricity is low in cost compared with gas or steam. - No single unfavorable item listed will necessarily disqualify a method, but generally there will be several offsetting favorable factors required to'make it`the choice on a purely economic basis. When analyzed with respect to the broadening scope of applications for air conditioning, it is now evident that direct or chemical dehumidification can be used, within its legitimate economic limits, for human comfort, commercial drying or storage of food products requiring low humidities, anIdtinpdrouvsitdreiasl parnocaedssdiintigonaanld cdhroyiicneg.as to the type of equipment best suited to meet the requirements of special applications and conditions. Particular attention is called to those industrial and drying applications in which the dried air can be used at effluent temperature without further treatment. references Direct Evaporative Cooling for Homes in the Southwest, by A. J. Rummel (A.CSh.Hem.Vi.cEa.l TDreahnusmacidtiifoicnast,ioVnol.A4g6e,n1t9s,40b,yp.F3.81R).. Bichowsky (A.S.H.V.E. JovsumSection, Heating, Piping and Air Conditioning, October, 1940, p. 627). CHAPTER 24 l9e` ation Mechanical Refrigeration, Characteristics of . Compression System, Absorption. Systems, Expansion Valves, Condensers, Evaporators and CoolersRefrigerant Pipe Sizes, Ice Systems, . Storage Systems, Equipment Selection, Reverse Cycle. GOOLING and dehumidification in air. conditioning work usually require refrigeration equipment. The localities where cold water, from a natural source is at a sufficiently low temperature for-comfort air conditioning are rare, and evaporative cooling is generally restricted to sections of the country where humidities are naturally low. The important difference between the refrigeration equipment used for comfort air conditioning and that used for commercial refrigeration is the use of a relatively higher evaporator temperature. This temperature is usually above freezing in air conditioning refrigeration equipment. The higher evaporator temperature (that is high suction- pressure) affects the design of the system used, and makes possible the use of systems that are not always practical for commercial refrigeration. MECHANICAL REFRIGERATION The fundamentals of mechanical refrigeration systems are similar, although they differ in the methods used for compression of the refri gerant vapor. Refrigerant vapor, usually saturated or slightly superheated, is drawn into the compressor as diagrammed in Fig. 1. It is then compressed and discharged at a higher pressure to a condenser. The vapor is condensed as it contacts a heat transfer surface over which is flowing a cooling medium such as water, air or a combination of the two. The liquid refrigerant flows.to the evaporator through an expansion valve which reduces its pressure .and regulates its flow. In the evaporator, the refri gerant absorbs heat from the medium which.is to be cooled. When this medium is water or brine, the evaporator is known as a'water or brine cooler and the refrigeration system, if used for air cooling, is known as an indirect system. When the medium cooled is ait, the evaporator is known as a direct expansion cooler and the system is known as a direct expansion system. Fundamentally, the function of the system is to absorb heat at one temperature and, pump it to a. higher temperature, where it may.be removed .by . an available cooling medium. In-order to conserve refri gerant, virtually all refrigeration systems are completely closed and the same refrigerant is recirculated. The fundamental heat equations (disregarding losses) which should be kept in mind are: (1) the heat absorbed in the evaporator plus the heat added to the-refrigerant during compression equals the heat rejected by the condenser; ,(2).the heat added to the refrigerant during compression 's equal to the input to the compressor shaft less the heat dissipated from the compressor to the surroundings. In the case where the compressor is driven by an electric motor, the heat due to compression is equal to the motor input less the electrical