Document wDonKKn6ZB1JLga0V7kKGvEK3

730 CHAPTER 54 1959 Guide Table 5 .... Equivalent Full Load Operating Hours of Refrigeration Equipment Used for Summer Cooling May 15 to Oct. 15," Application Hr Open for Atlanta Chicago Detroit Lot New New PfcJo- Oklaho Orleans York driphic ma City St. 0. c Barber Shops.......................... 12S0 1010 650 720 720 680 1080 830 860 1020 890 940 Department Stores................. 940 840 560 610 610 580 890 700 720 840 750 780 Drug Stores............................. 2100 1630 950 1060 1060 980 1790 1280 1330 1650 1420 1530 Funeral Parlors...................... 600 440. 300 330 330 310 470 370 380 440 400 410 Offices........................................ 940 870 560 620 620 580 900 710 740 880 770 810 Restaurant (Short Hour)___ Restaurant (Long Hour).... Speciality Shops (5 & 10)___ Theaters--Continuous........... Theaters--Neighborhood.... 1290 2100 1090 1500 900 970 1510 800 1010 640 535 820 530 700 420 620 930 590 750 450 620 570 1060 760 800 980 830 930 850 1690 1170 1210 1530 1300 590 560 860 670 690 810 720 750 720 1080 850 870 1020 910 450 430 650 500 520 650 550 * Modtr* Air Condilimtint, ffcarin# and VmtHaliaf, bjr W. H. Carrier, R. E. Cherne, ead W. A. Grant (Pitmu Publishing Carp., 1M0, p. 73). 880 1400 750 950 580 cost considered as maintenance. These costs vary con-, siderably with factors such as the type of system and the proficiency of the installing and servicing organization. Therefore, any forecast of maintenance costs should include consideration of the equipment as a part of the engineering study. The charges should be based upon the entire period under study rather than the early years of operation when, repairs may be expected to be at a minimum. Various estimates of maintenance costs vary from 5 to 10 percent of the installation cost. Table 4 is based upon an average of 7Vi percent for about a 75-ton installation. This probably would apply to most installations using highquality equipment. The maintenance cost must be modified for size of job and quality of equipment. With lower-cost equipment, higher maintenance costs can be expected. The accounting practices of the owner and the rules of the Bureau of Internal Revenue affect the charges for major overhauling or complete replacement which may restore, the capital value of certain equipment items. In these cases the expenditure may not necessarily be charged as maintenance but will become a fixed charge spread over the remaining years of equipment life. Table 4 gives some approximate costs for maintaining large air-conditioning installations using high-quality equipment. LABOR FOR OPERATION In some cases wth the installation, of automatic equip ment, operating labor may be non-existent, but where such labor is required, the cost is readily calculated. Where opera tors are required, the expense is often considered main tenance, but since they may have other functions'that are not properly charged to operation of the air-conditioning, heating, or ventilating installations, the charges should be properly allocated. This cost of experienced and competent operators is well justified in medium' and larger plants by economies that can be achieved in maintenance and energy costs. ENERGY AND WATER COSTS Energy costs include the costs for power, water, steam, coal, oil, etc., consumed to operate the system. From the selected equipment and type of installation, it is possible to segregate the relatively constant power loads and the total brake horsepower. Annual power cost can then be figured from the following formula: annua,l power cost --0-.-7--4-6--(-b--h--p)--t-f-R-v (l) - where bhp = brake horsepower. H TM annual operating hours. R power rate, dollars per kwhr. 9 ~ motor efficiency (decimal). In using Equation 1 it must be pointed out that the electric rate, R, must reflect the proper combination of energy and demand rates. These vary widely between the utility companies, and sometimes the rate structure is such that it is largely the demand charge which determines the proper value of R to use in Equation 1. Operating Refrigerating Equipment In an air-conditioning system the refrigerating equipment is usually the largest power consuming item to be considered. Also, the prediction of operating cost is more difficult be cause the power required for summer cooling is affected by many factors of a variable nature. Table 5 gives the equivalent full-load operating hours of refrigerating equipment used for summer cooling for the period of May 15th to October 15th. This table was cal culated from the following equation: H, -- m(6 + cf) (2) where H. = equivalent full load operating hours of refrigeration equipment used for summer cooling during period May 15 to October 15. m -- total hours during period May 15 to October 15 that the establishment is open for business. b " fraction of maximum load from internal heat under average operating conditions, c = fraction of maximum load that is due to external sources at maximum design conditions. / " ratio of the number of hours for a particular city, when the outdoor wet-bulb exceeds 65 F, during the period Juoe 1 to October 1 to the total number of hours Owning and Operaring Costs during that rntmt 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. It should be pointed out that certain southern cities may have seasons longer than the 5-month period indicated in Table 5. If it is desired to consider a longer season of opera tion, the ratio of full-load operating hours to hours open for . busines is smaller; in other words, the refrigeration load factor is lower. This is true because the extra increment of days added will be a relatively light load, since the table already includes the more severe part of the season. The season electrical power cost for refrigerating equip ment is then given by the following equation: season power costs 0--.-7-4--6(---bh--p)-,-7--7--f-.-R- 0) where (bhp) i *= 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 = maximum refrigeration design load, tons. R, -- equivalent full load refrigeration operating time, hours (from Table 5). R * power cost, including demand and energy charges, dollars per kwhr. 9 = motor efficiency at average load (decimal). 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. "7'~ If the refrigeration compressor is steam-turbine driven, the same general method can be followed, taking into ac count average water rate per brake horsepower-hour and the cost of steam. Condenser Wafer 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 temperature) constant;and in such case the entering water temperature becomes the major variable. The gallons per minute per ton nan readily be calculated for any water temperature rise. The following equation for cost of condenser water is useful: . 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 maximum 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, because they vary through the season. Maximum water main tempera tures are given in Chapter 41, but should always be verified locally. In lieu of this tedious work, the average gallons per (minute) (ton) may be taken as 80 percent of design gallons per (minute) (ton) with reasonable accuracy, for the condition of variable temperature of entering water obtained from rivers and lakes. Cooling towers and evaporative condensers virtually eliminate condensing water charges since the windage and evaporation losses are seldom over two or three percent of the water circulated. The savings in water consumed often will not in itself justify the installation of water-economizing equipment since the cost for pumping and the fixed or ownership charges may be in excess of the annual cost for once-through con densing operation. If operating costs are to* be the basis for selection, then fixed charges should be determined when studying application of this equipment which usually has a shorter life than the other components. Usually the primary factors influencing the installation of water conservation equipment are the lack of an adequate water supply or local regulations intended to conserve an existing water supply. Another factor influencing the installation, of such equip ment is the increasing trend toward the enactment of and service charges for condensing water wasted into city sewers. Certain municipalities will remit the sewer taxes where B - 0.060 a T H, C (4) B -- cost of water for refrigeration during period, dollars. o * average gallons per (minute) (ton). T = tons of refrigeration at maximum design load. ff. equivalent full load refrigeration operating hours (Table 5). C - water cost, dollars per 1000 gal. Vahmi given or* representative of dkMorodifluororuettiano {tafrigaroitt 12) reciprocating machinal of about 25 Tan* capacity m air-cond?- applications. Requirements of smaller machine! ara otxraliy higher, and for larger madunes may be lower. Vofuet drawn ore for liquid re frigerant at condenser temperafare (no subcooling). Subcoo/rng of fbe liquid may decrease these values approximately 0.3 percent to 0.5 per cent for each Fahrenheit degree the liquid temperature is lowered. Fig. 1 .... Typical Brake Horsepower Requirements for Refrigeration*