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562 CHAPTER 38 1959 Guide Centrifugal compressors are used for large installations, and usually where the.indirect system is required. The driving mechanism can be a steam turbine or electric motor. The steam-jet system is used where steam is available and cooling water can be had in large quantities. It will be noted by referring to Fig. 16 that all systems using compressors have a common characteristic, namely, that the capacity varies with the evaporating temperature. Not only can the equipment be selected to produce a given result, but the performance can be predicted under varying load conditions by the simple expedient of using the vari able of evaporating temperature as the abscissa, and the load or capacity as the ordinate in a series of curves. Manufacturers of compressors and cooling coils furnish performance data for apparatus that can be plotted in the form of curves wmilar to those shown in Fig. 18. The per formance of a compressor is plotted as a series of curves, each curve being drawn for a given condensing pressure. The performance of a direct-expansion coil at two different air velocities is plotted on the same graph. The operating point will be, of course, where the two curves cross. Data given in Table 9 illustrate two types of conditioned enclosures having the same total load of 148,000 Btu per hour, but with two different ratios of sensible to total heat. In the case of the office with a ratio of 82 percent sensible to total heat, the operating point A in Fig. 18 is found to be 42.2 F evaporating temperature, with a face velocity of 500 fpm. In the case of the restaurant, with a ratio of 695 percent sensible to total heat, the air velocity is lowered to 300 fpm, and the evaporating temperature is towered to 34.4 F as shown in point B of Fig. 18. In order to obtain the same capacity, a larger condensing unit is used. This illustration assumes zero pressure drop through the suction line. The pressure drop can be tklfon into account by shifting the compressor performance curves by the amount of pressure drop expressed in Fahrenheit degrees. REFERENCES 1 P. C. Scofield: Air cycle refrigeration (Refrigerating En gineering, Vol. 57, June 1949, p. 558). * A. R. Mumford and A. A. Markson: Application and econ omy- of steam jet refrigeration to air conditioning (ASHVE Transactions, Vol. 44, 1938, p. 33). * A. A. Berestoeff: A new development io absorption re frigeration (Refrigerating Engineering, Vol. 57, June 1949, p. BIBLIOGRAPHY Refrigerating Data Book, Vol. 1 (American Society of Re frigerating Engineers). H. J. Macintire: Refrigeration Engineering (John Wilev A Sons, New York, 1937). N. R. Sparks: Theory of Mechanical Refrigeration (McGrawHill Book Co., New York). B. F. Raber and F.'W. Hutchinson: Refrigeration and Air Conditioning Engineering (John Wiley A Sons, New York, 1945). J. A. Moyer and R. 13. Fitts: Refrigeration (McGraw-Hill ' Book Co., New York). W. R. Haiosworth: Refrigerants and absorbents (Refrig erating Engineering, August, September 1944). B. H. Jennings and S. R. Lewis: Air Conditioning and Refrig eration (International'Textbook Company, Scranton, 1944). Jordan and Priester: Refrigeration and Air Conditioning (Prentice-Hall, Inc., New York, 1948). CHAPTER 39 THE HEAT PUMP History and Development; Basic Circuits; fundamentals; Types; Heat Sources and Sinks; Performance Characteristics; Tem perature Levels; System Balance; Seasonal Performance; Annual Operating Cost; Components; Applica tion; Criteria for Feasibility; Design and Selection; Systems for Larger Buildings; Sensible, Latent, and Low-Side Heat Storage THE term heat pump as applied to a year-rcund air- History in the United States conditioning system, commonly which refrigeration equipment is heat is taken from a heat source and ditioned space when heating service denotes a system in used in such manner given up to the con is wanted, and is re thatStaPtieosnewearsincgowndourckteodn heat-pump development through the early 1930's in the United mainly under sponsorship of a few investor-owned electric utility com panies, with the objective of promoting wider use for their moved from the space and discharged to a heat sink when cooling and dehumidification are desired. The thermal cycle' is identical with that of ordinary refrigeration, but the ap service. The character of electric load from sum mer air conditioning, after a record of steady growth, was then already making evident its likelihood of creating new plication is concerned alike with the cooling effect produced peak on utility systems. This prompted the in at the evaporator and with the heating effect produced at vestigation of methods whereby such load could be made the condenser. In some applications, both the heating and the cooling effects obtained in the cycle are employed simul taneously. more favorable both to the customer and to the electric company. The first major installation in the United States was made The heat-pump principle is also applied for purposes other than air conditioning, such as: supply of domestic hot water in residences and commercial buildings, recovery of lowtemperature heat as a useful byproduct in industrial opera tions, and disposal of heat from processes involving evapo ration of water or other fluids at depressed temperature and pressure. Defrosting of evaporator coils in refrigerating systems by intermittently admitting hot gas directly from the compressor is another application of the heat-pump method. Descriptions and diagrams of various beat-pump systems and criteria for feasibility are given later in this chapter. about 1931, for a new 3,800,000 cu ft office building of Southern California Edison Company in Los Angeles. Re frigeration equipment of the already existing air-condition ing system was modified to permit heat-pump operation with outdoor air in a conventional cooling tower serving as heat source. An installation made in Salem, New Jersey4 in 1934 was the first commercial heat pump in this country designed for complete heating and cooling. A number of buildings occupied by subsidiaries of American Gas and Electric Company in Ohio, West Virginia, Virginia, and Kentucky were equipped during the middle and late 1930's. The home office of Louisiana Power and Light Company at HISTORY AND DEVELOPMENT Over a century ago, William Thomson (Lord Kelvin)1 sug gested the use of a compressor as a warming engine to beat buildings, as an alternate for combustion of fuels. Somewhat prior to 1910 Dr. S. Z. Ferranti, Prof. J. Perry and Mr. T. V. Morley, in England, strongly advocated the undertaking of development in the design and application of heat.pumps, but the economic outlook, then unfavorable, deferred fur ther investigation. It was not until a paper on the principles and economics of heat pumps, prepared in October 1928 by T. G. N. Haldane, was presented before the British Institute of Electrical Engineers in December 1929,* that develop ment was started in the United States. Haldane reported the trial results from early installations made in Scotland. Ap plication for water heating was then as prominent abroad as use for space heating. Dr. A. R. Stevenson, Jr. was an early advocate in this country, having first presented the possibility to the Re frigeration and Gas Committee of the American Gas Asso ciation in April 1926, and later to the Franklin Institute.1 Algiers, Louisiana was equipped in 1936, using purchased city water as source of heat. An office building* of United Illuminating Company at'New Haven, Connecticut, erected in 1939, was equipped with a water-source heat pump. It utilized as a standby beating system a large water storage tank equipped with immersion electric heating elements. Throughout this early period all installations were custom built, employing standard equipment components modified where necessary to suit the dual-purpose functions. After World War II the use of heat pumps increased, particularly with the introduction of unitary equipment, in which the re frigeration system, fans, pumps, and the necessary automatic controls were assembled within a single housing. In recognition of the status attained by heat pumps and their growing engineering importance, the American So ciety of Heating and Ventilating Engineers appointed a Technical Advisory Committee on the Heat Pump in 1947. An independent group from the electric utility industry, known as Joint AEIC-EEI Heat Pump Committee, was founded in February 1947. This body has worked closely The concept held in this country today, that heat pumps with equipment manufacturers, giving advice on matters re for the large majority of space-heating applications should lated to suitability of equipment types and control methods, be regarded essentially as year-round air-conditioning de to experience resulting from trial installations, and espe vices, did not become generally accepted until about 1950. cially to the characteristics of electric loads. It has also under- 563