Document RaR4oByZzj7BJxN3xZYdRpban

814 , CHAPTER 44 - - - , o. 1948. Guide. The season electrical power cost for refrigerating equipment is then given by the following equation: 0.746 (bhpt) T He R Season power cost' u (3) where bhpt = Brake horsepower per ton (see Fig. 1) for 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, t) = Motor efficiency at average load (decimal)^ CONDENSER TEMPERATURE,FAHRENHCIT DEGREES Fig. 1. Typical Brake Horse Power Requirements for Refrigeration3 sValues 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 and the gpm per ton can readily be Calculated for any water' temperature rise.- The following equation for cost of condenser water is useful: Owning and Operating Costs 815 where B = 0.060 o r 7/e C B = Cost of water for refrigeration during period, dollars. ' a = Average gallons ger.minute (ton);.,, i. T = Tons of refrigeration at maximum design-load. ... He = equivalent full load refrigeration operating hours (Table 8). C - Water cost, dollars' per 1000 gal. . . .. (4) , . ., " The average gpm per ton must take into account the variable water temperature. When well water is used as a source, and entering and leaving temperatures are considered constant, the average . gpm-per ton obviously is equal to the design gpm per ton. : However,, when the source is river or lake water, its maximum seasonal temperature will generally be reached at the same time that, the refrigeration load factor is highest. Table 9. Representative Tons per 100 Sq Ft for Various Applications ....... Department Store (Main Floor) Department Store (Upper Floors)___ Dress Shop..................... Drugstore Lunch Room____________ _________ _ Office Bldgr....................... Restaurant............... ............. Shoe Shop____ ______ Theater (Tons per Seat). . . . Low o.so 0.29 0.29 0.33 0.83 0.21 0.58 0.29 0.064 Avg \ 0.58 . . 0.46 0.50 0.54 1.08 0.25 0.75 0.42 0.078 High 1 0.67 0.54 0.71 : 0.83 1.33 : ; 0.38 . 1.00 0.63 0.093 The average gpm per ton should be calculated from known or estimated water temperatures because they, vary through the season. Maximum water main temperatures, are given in Chapter 37 but should always be verified locally. In lieu of this tedious work, the average gpm per ton may be taken as. 80 per cent of design gpm per ton with reasonable accu racy,-for the condition of Variable temperature of entering water obtained from rivers and lakes. . i When cooling towers or evaporative condensers are used,, the windage and evaporation losses are usually;between 3 per cent and 5. per cent of;the water circulated. ,: ;: : . Heating The method of estimating fuel consumption to balance the building heat, loss is given in Chapter 20Y It is important to include the fuel required to heat ventilation'air as used in ventilating arid air conditioning systems. In estimating fuel consumption for ventilation air, the tendency of the conventional control systems to use less than the estimated quantity of outside air in cold weather should be considered in its effect in .lowering fuel consumption. In-addition, the heat required to accom plish winter humidifying.must hot.be neglected,-when this, feature is included in the equipment: . . . .. -, BIBLIOGRAPHY Modern Air Conditioning, Heating and Ventilating, by W. H. Carrier, R. E.Cherne, and W. A. Grant--Chapter IV (Pitman Publishing Corp., 1940). - = . Predicting Operating Hours of Refrigeration Equipment Used in Air Conditioning, By W. A. Grant (Refrigerating Engineering, July, 1941).' . : . Cost of Operation of Refrigeration .-Used for Air Conditioning, by . R. E. Cherne (Refrigerating Engineering, December, 1943). '