Document NGBxnV06EkEvJB4gBNKZygN1w

820 CHAPTER 44 1946 Guide Owning and Operating Costs 821 ' The season electrical power cost for refrigerating equipment is then given bythe following equation: Season power cost 0.746 (bhpt) THeR - - t) ' (3) where . bhpt = Brake horsepower per ton (see Fig. 1) lor average load during period, (Due allowance should be made for poorer compressor efficiency at light load). T -- Tons of refrigeration at maximum design load. He = Equivalent full load refrigeration operating hours (Table 8). R = Power cost, dollars per kwhr, including demand and energy charges, i) = Motor efficiency at average load.(decimal). `M o d e m A ir C o n d itio n in g , H e a tin g arid V e n tila tin g ,1b y ,,W . H . C arrier, R . E. Cherne and W . A. G ra n t (P itm a n P ublishing Corp. 1940, p. 73). Fig. 1. Typical Brake Horse Power Requirements for Refrigeration aValues..given are'representative of *`F-12" reciprocating machines of about 25 tons capacity in air conditioning applications. Requirements of smaller machines are usually higher, and for larger machines may be lower. Values shown are for liquid refrigerant at condenser temperature (no subcooling). Sub* cooling of -the liquid may decrease these values approximately 0.3 per cent to 0,5 per cent for each Fahren heit degree the liquid temperature is lowered. Table 9 will be useful in estimating the design load in the absence of detailed load estimates. . In considering refrigeration power consumption, it should be noted that the use of weather records for a specific year may lead to large, inaccuracies in estimating operating costs, since there may be wide; variations from year to year, and therefore, average yearly weather records should be used rather than those for any individual year. If the refrigeration compressor-is steam turbine driven, the same general method can be followed, taking into account average water rate; per bhp-hr and the cost of steam. Condenser Water Condenser water cost estimates can also be based on equivalent full load operating hours of the refrigeration equipment. The varying, temperature of the water at its source, as well as the temperature of the discarded water, must however be taken into account. In general, when water is purchased, control is provided to hold the leaving water tem perature-(or condensing temperature) constant; and in such case' the; entering water temperature becomes the. major- variable arid the gpm per ton can readily be calculated for any water, temperature risev- The following equation for cost of condenser water is useful: .