Document baorXqrN5856MeEMpz5ROGM8Z

904 CHAPTER 43 - 1950 Guide e " Fraction of maximum load which is due to external sources at maximum design conditions. jf -- Ratio of the number of hours for a particular city, when the outside wet-bulb> exceeds 65 F, during the period June 1 to October 1 to the total number of hours during that same period. . Total hours are assumed as 8 hr. per day period for barber shops, department stores, funeral parlors, offices, short' hour restaurants, and specialty shops, and 12 hr per day period for drug stores, long hour restaurants; and theaters. Table 8 was calculated from Equation 2. It should be pointed out that certain southern cities may have seasons longer than the 5-month period indicated in Table 8. If it is desired to consider a longer season of opera tion, the ratio of full load operating hours to hours open- for business is smaller; in other words, the refrigeration load fadtor is lower.. This is true Fig. 1. Typical Brake Hohsf. Poweb Requirements for Refbiqeration* * Values given are representative o! "F-IS" reciprocating machines of about 25 tons capacity in air con ditioning applications. Requirements of wmaiw machines are usually higher, and for larger manhinw may be lower. -Values shown are for liquid refrigerant at condenser temperature (no aubcooling).- Subcooling of the liquid may decrease these values approximately 0.3 pier cent to 0.5 per cent for each Fahrenheit degree the liquid temperature is lowered. ; because the extra increment of days added will be at relatively light load, since the table already includes the mores.severe part of. the Season. ' The season electrical power cost for refrigerating equipment is then given by the following equation^- ` ' 0.746 (bhpi) T H, R Season power cost v (3) where bhpi = 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. . H. ca Equivalent full load refrigeration operating hours (Table 8) .. ... R *= Power cost, dollars per kwhr, including demand and energy charges, v p hfqtor efficiency, at average load (deeimal). Owning and Operating Costs 905 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 genera method can be followed, taking into account average water rate per brake horse power-hour 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 temperature (or condensing Table 9. Representative Tons peb 100 Sq.Ft fob Vabioub Applications Department Store (Main Floor)---- Department Store (Upper Floors)-- Dress Shop__..__ --. Drug Store.___ Lunch Room___ - " . ' Office Bldg___ Restaurant__ Shoe Shop:__ Theater (Tons per Seat)---- ------------- Low . 0.50 0.29 0.29 0.33 0.83 0.21 0.58 0.29 0.064 Avc . .0.58 0.46 0.50 0.54 1.08 0.25 0.75 0.42 0.078 - High 0.67 0.54 . 0.71 0.83' 1.33 . 0.38 1.00 0.63 0.093 temperature) constant; and in such case the entering water temperature becomes the major variable, and the gallons per minute per ton can readily be calculated for any water temperature rise. The following equation for cost of condenser water is useful: B = 0.060 a TB.C (4) where B = Cost of water for refrigeration during period, dollars. a = Average gallons per minute (ton). T = Tons of refrigeration at maximum design load. //,, Equivalent full load refrigeration operating hours (Table 8). C = Water cost, dollars per 1000 gal. The average gallons per minute 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 gallons per minute per ton obviously are equal to the design gallons per minute per ton. However, when the source is river or lake water, its max imum seasonal temperature will generally be reached at the same time that the refrigeration load factor is highest. The average gallons per minute per ton should be calculated from known or estimated water temperatures, be cause they vary through the season. Maximum water main temperatures