Document G6GyOEk20NZoNewvjmgp1EEwv

540 CHAPTER 37 1959 Guide Comfort Healing (American Gas Association, 1838). W. M. Myler, Jr. and H. W. Nelson: Are automatic ^ shutters justified on a gas-fired conversion burnerT (AMivli, Transactions, Vol. 55, 1849, p. 111). * J. W. Tieman and F. L. Bagby: Efficiency of bituminous- coal-burning heater .(ASHVE Transactions, Vol. 57,1951, R A Sherman and R. C. Cross: Heat losses and efficiencies of fuels in residential beating (ASHVE Transactions, Vol. 43, 1937, p. 185). . '.Fuels and Burners (University of Illinois, Small Homes Council Circular G3J>, July 1949). "A. P. Krats and S. Konso: Investigation of Oil-fired Forced-air Furnace Systems in the Research Residence (Uni versity of Tiling Engineering Experiment Station Bulletin No. 318, November 7, 1939). u paul d. Close: Graphical method of calculating heat loaes (ASHVE Transactions, Vol. 49, 1943, p. 345). " House Heating (American Gas Association, Industrial Gas Series, 3rd ed.). ... "Report of commercial relations committee (National Dis trict Heating Association Proceedings, 1932). "Rutcher Skagerbere and J. E. Phifer: Fuel consumption analysis for multi-family housing projects (ASHVE Transac tions, Vol. 59, 1953, p. 113). "C. W. Signor: Heat requirements of buildings (ASHVE Transactions, Vol. 57; 1951, p. 517). "J. H. Walker and G. H. Tuttle: The heat requirements of buildings (ASHVE Transactions, Vol. 41, 1935, p. 171). CHAPTER 38 REFRIGERATION Refrigeration Theory- Definitions and Basic Concepts, Refrigerants, Vapor Compression Refrigeration Cycles, Suction and Discharge Pressure Effect, Complex Refrigeration Cycles, Air Cycle, Steam Jet, Absorption System; Basic Refrigeration Equipment: Compression Machines and Controls, Condensers, Evaporators and Coolers/ Refrigeration Control, Piping and Accessories; Equipment Characteristics and Selection ITH the increasing use of all-year comfort air-condi evaporator is then raised in pressure (by a compressor, or by W tioning installations, the importance of refrigeration the absorber-generator combination of the absorption sys to the air-conditioning engineer has been greatly magnifieted.m) until its new boiling temperature exceeds the tempera The details of equipment operation, maintenance, and de ture of the available cooling medium. Under these conditions, sign remain problems for the refrigeration engineer,.but the heat transfer is established from the refrigerant vapor to the air-conditioning engineer does retain a responsibility to the cooling medium with resultant condensation of the refriger customer which requires on his part some knowledge of the ant. When condensed, the high-pressure liquid refrigerant iB different refrigeration cycles and the relative merits of each. reduced in pressure and again allowed to bod in the evapo In order to assist in meeting this need, the present chapter rator. has been divided into four parts-, the first covering the funda In order to permit evaluation of the effectiveness with mental technical relationships which govern the selection and which any given cycle operates, some term' is desirable that analysis of an operating cycle, the next two presenting brief would be comparable to the term efficiency used for heat en discussions of basic refrigerating equipment and auxiliaries, gines. In. refrigeration the desired effect is heat extraction, and the last, information on selection criteria. and the cost of achieving this extraction is the amount of energy that must be supplied as shaft work. Thus the ratio REFRIGERATION THEORY of refrigerating effect to the heat equivalent of the compres sor work is used as a measure of effectiveness, and is defined Definitions and Basic Concepts . - as the coefficient of performance. If the desired effect is the rejection of heat through the The ton of refrigeration is a quantity unit which'originated ' condenser instead of heat extraction through the evaporator, m the days when harvested ice was the principal source of ' the refrigeration system is then termed a heat pump. In this summer cooling. By definition the ton is the cooling effect case'the coefficient of performance is the ratio of the heat re- realized when one ton of 32 F ice melts to water at 32.F. Since. ' jected from the condenser to the heat equivalent of the com the latent heat of fusion of ice is 144 Btu per pound, the ton pressor work. The coefficient of performance for the heat represents a unit cooling effect of 144 X 2,000 = 288,000 Btu. pump is greater -than that for a system operating as a re In common practice the ton is usually considered a rate frigerating machine, because all mechanical shaft work re (rather than quantity) unit, and is taken as 288,000 Btu per quired to operate the compressor is dissipated as useful heat day (24 hours), or 12,000 Btu per hour, or 200 Btu per min- - through the condenser. ute. Thus for air-conditioning calculations, the size of the The Carnot cycle, an ideal, thermodynamically reversible requisite refrigeration machine, expressed in tons, can be ob cycle consisting of an adiabatic expansion and an isothermal tained by dividing the heat gainof the structure, expressed expansion, followed by an adiabatic compression and an iso in Btu per hour, by 12,000. In equation form: thermal compression to form a closed cycle, may be shown to , Hi (Btu per hour heat gun) -s- 12,000 (1) be a measure of the maximum possible, conversion of heat energy into mechanical energy. In its reversed form it is a where measure of the maximum performance possible for any re H, -- load in tons. frigeration cycle operating either as a refrigerator or as a heat pump. Although it cannot be applied in an actual machine The xcorking substance, or refrigerant, is the fluid which because of the impossibility of obtaining complete reversi carries heat through the refrigeration cycle from the evapora bility, it is, nevertheless, extremely valuable as a criterion of tor, where heat enters the refrigerant, to the condenser where inherent limitations. The coefficient of performance (CP) of the heat is discharged to some cooling medium. The great ma a reversed Carnot cycle system operating as a refrigeration jority of modem refrigeration systems use a liquefiable vapor system is as the working substance. By altering the' pressure of the refrigerant its boiling temperature, is changed, allowing the material to bod in the evaporator at a temperature suffi con - -f. ciently lower than that of the conditioned space, to insure maintenance of an effective heat transfer rate from the space where (or in some cases from a secondary cooling fluid such as brine T, = evaporator temperature, Fahrenheit, absolute. or cold water) to the refrigerant. The vapor formed in the T, = condenser temperature, Fahrenheit, absolute.' 541