Document 3QwYBq2V0kMQVdRZQ5mprVRv6

Heating Ventilating Air Conditioning Guide 1939 and 4 or 5 times practically, as the work put in. There are a number of limitations, however, the most serious of which is the lack of ready availability of a practical source of heat. 1. Well water is the most desirable since its temperature is high even in the winter and thus a large amount of heat may be removed in relation to the weight of water handled. 2. Air may be used but its specific heat is low and its temperature uncertain. When the most heat is needed, the temperature of the air is lowest, thus resulting in the least favorable temperature combination. 3. It has been proposed to obtain heat by freezing water, but this is still in the theoretical stage. Some of the other factors which act as limitations are the large tem perature spread when using air as a source of heat and when attempting to cool with even moderately low outside temperatures, the frequent dis parity between the size of the cooling load and heating load requiring extra equipment for a complete heating load, and the relatively high initial cost of equipment at present available for the reverse cycle in comparison with that available for heating by conventional means. Because of these limitations, the present application of the system is largely limited to temperate climates, such as Florida and Southern California, or to heating only for intermediate seasons, or to other locali ties which have peculiar advantages as, for instance, the ready availa bility of well water. In these locations it is frequently possible to do all of .the heating necessary with the refrigeration equipment so that the extra cost is only that of reversing the functions of the condenser and evaporator. ICE SYSTEMS The use of ice for air conditioning is becoming more adaptable particu larly for the smaller commercial installations where first cost is paramount and where the operating period is limited to only a few hours per day. Restaurants serving only one or two meals per day, tea rooms, meeting halls and other comparable installations have found ice to be advan tageous in comparison with other methods. Local ite manufacturers will furnish complete data for this type of system. PROBLEMS IN PRACTICE .\ - 1 Electrically driven dichlorodifluoromethane condensing units are to be used in an air conditioning system, requiring 20 tons refrigerating capacity for conditions of maximum load.' An overall analysis of tile seasons operating conditions shows an average.load factor of 62.5 per cent, and allowing for varia ble time intervals.of operation of refrigeration units installed, three-quarters of the operating season, or 750 hr, would require operation of the equipment at one-half load, and one-quarter of the operating season or 250 hr full load capacity of the refrigeration equipment would be required. The increased first cost of 2-10 hp, 10 ton condensing units over 1-20 hp, 20 ton condensing unit is, $830.00 installed price, to the customer. The increased first cost of a 2-speed compressor motor of 20 hp size over a con stant speed 20 hp size motor including increased starter cost is $210.00. The 'efficiency of the 2-speed motor above is 83 per cent at full load speed, and 79 per cent for fuU load at 34 speed. At 34 speed, full load is 34 total bhp of full load speed. , 490 Chapter 23. Cooling and Dehumidification Methods Discuss the considerations involved in making a decision as to whether a single ,,it with a 20 hp motor of the 2 speed type would be used in preference to -10 hp constant speed units. The cost of 2-10 hp 10 ton units in excess of 1-20 hp, 20 ton unit with 2-speed motor, is 1830.00--$210.00 or $620.00, increased first cost. At 15 per cent fixed charges, this represents an increased annual cost of $93.00 for 2 compressors over one compressor. The advantage of 2 compressors instead of one compressor on an installation of this type, is in the breakdown service provided in the event one compressor is shut down for repairs the system could be operated at one-half capacity utilizing the duplicate machine. The motor efficiency of the constant speed unit would be higher at full load than would be the efficiency of the 2-speed motor at low speed. Offsetting this latter advantage however, is the fact that the condenser on the condensing unit would provide a lower refrigerant condensing temperature for 34 load operation with the same final condensing water temperature than would be the case with duplicate units each furnished with its own compressor and condenser. Operation at a lower condensing temperature would provide for a power saving compensating for the lower efficiency of the 2-speed motor when operated at slow speeds. It is, in a case of this kind, purely a question as to whether or not the purchaser would deem an investment of $620.00 more and an increased fixed charge of $93.00 a year, advisable to get breakdown service through the installation of duplicate units. In most cases, this increased first cost would not be warranted because of the fact that satisfactory' indoor conditions could not be obtained at full load if only one-half the refrigeration capacity were available. 2 For condensing purposes, an air conditioning system uses city water which has an average 70 F supply temperature. The following'table lists the number of hours per year during which definite wet-bulb temperatures and corre sponding refrigeration rates .pertain. Wet-Bulb Temperature F 80 79-75 74 - 70 69-65 64-60 59-55 54-50 No. of Hours per Year 6 100 277 330 277 158 52 Total 1200 hours Refrigera rion Required Tons 284 233 183 157 144 79 37 If the power requirements of a dichlorodifluoromethane refrigeration system are in accordance'with the following data on partial load operation, determine the seasonal power cost at 2 cents per kwhr: Tons of Refrigeration Kw per ton Seasonal power cost: 284 233 183 157 144 79 37 0.89 0.89 0.87 0.86 0.86 0.93 0.97 Wrr-BcLB Thmpibatubs F Ton-Hours Kwhr 80 79 - 75 74 - 70 69-65 64-60 59 - 55 54-50 Totals 6 X 284 = 1,704 100 X 233 = 23,300 277 X 183 = 50,700 330 X 157 = 51,800 277 X 144 = 39,900 158 X 79 '= 12,500 52 X .37 = 1,920 1,704 X 0.89 = 1,517 23,300 X 0.89 = 20,750 50,700 X 0.87 = 44,100 51,800 X 0.86 = 44,500 39;900 X 0.86 = 34,300 12,500 X 0.93 = 11,600 1,920 X 0.97 = 1,860 181,824 ton-hours 158,627 kwhr