Document ga5vozDjE55V59kZNLBZvKDOa

American Socibtt of Heating and Ventilating Engineers Guide, 1937 Dichlorodifluoromethane System: Power requirements, Cooling tower fan Cooling tower pump 17.8 bhp 30.2 Total 48.0 bhp Power for cooling tower system = ^-0 X 0.746 X 1200 hr 0.80 motor efficiency 53,700 kwhr. The water cooler in a dichlorodifluoromethane system of the surface type requires no additional pumping head other than the friction drop through the cooler, which in this problem is estimated to be 10 ft. The total pumping head is, therefore, 75 + 10 = 85 ft. Power required for the chilled water system will be. 1200 gpm X 8.34 lb per gallon X 85 ft head 33,000 ft lb X 0.75 pump efficiency = 34.3 bhp. 34,3 bhp X 0.746 X 1200 hr ----- r0r.-8K0jr--m---o-t-o--r--e-f-fi-c--ie--n--c--y------ = 38,300 kwhr. Thus, the total power required by the auxiliary equipment will be 53,700 + 38,300 = 92,000 kwhr. The 92,000 kwhr at 2 cents per kwhr will cost The power cost of refrigeration, from Question 7, is *1,840 2,931 The total annual power cost, using a dichlorodifluoromethane system, is Steam Ejector System: *4,771 Power requirements, Cooling tower fan Cooling tower pump 35.6 bhp 47.8 Total 83.4 bhp Power for cooling tower systems = 83.4 bhp X 0-746 X 1200 hr 0.80 motor efficiency = 93,300 kwhr. In the flash tank or water cooler of the steam ejector system, the water is at a pressure corresponding to the chilled water temperature required. In this case it is at 46 F, which corresponds to an absolute pressure of 0.1532 lb per sq in. or 0.3118 in. Hg. This increases the pumping head on the chilled water circulating pump by 14.7 -- 0.15 = 14.55 lb per square inch, or 33.5 ft. The total pumping head is, therefore, 75.0 + 33.5 = 108.5 ft. 1200 gpm X 8.34 lb per gallon X 108.5 ft head 33,000 ft-lb X 0.75 pump'efficiency ~ 44,7 b p' 43.7 bhp X 0.746 X 1200 hr 0;80 motor efficiency The total power required by the auxiliary equipment is 93,300 + 48,800 = 142,100 kwhr. The 142,100 kwhr at 2 cents per kwhr will cost The cost of the steam, from Question 8, is 82,842 1,929 The total annual power cost, using a steam ejector system, is $4,771 These calculations indicate that for the assumptions made, both the dichlorodifluoro methane system and the steam ejector system would cost 2.6 cents per ton-hour to operate. In order to obtain a complete analysis it would be necessary to compare the fixed charges which include interest, depreciation, obsolescence, and .maintenance.. These are customarily computed at 15 per cent of the initial cost per annum. To this cost must be added the cost of refrigerant make-up per year. In the steam system this cost is negligible, while in the dichlorodifluoromethane system it may be approximated at about 10 per cent of the refrigerant charge per year. 216 Chapter 12 HUMIDIFICATION, dehumidification and WATER COOLING EQUIPMENT Air Washers, Apparatus for Direct Industrial Humidification, Spray Generation and Distribution, Self-Contained Humidifiers, Atmospheric Water Cooling Equipment, Design Wet-Bulb Tem peratures, Cooling Ponds, Spray Cooling Totcers, Natural Draft Deck Type Towers, Mechanical Draft Towers, Winter Freezing THE several available types of spray equipment are discussed in this chapter which are used for properly humidifying and dehumidifying the air circulated in a comfort or industrial air conditioning system or for cooling the condensing water of a refrigeration system. AIR WASHERS An air washer is essentially a chamber in which air is brought into' intimate contact with water to (a) regulate the moisture content of the air, and (b) to wash dust and dirt particles out of the air. The air comes in contact with the water by passing it through a spray of water broken up into a fine mist or by passing-it over surfaces wetted by a continuous flow of water; hence the classification: spray, scrubber, and combination spray'and scrubber type washers. (See Figs. 1 and 2.) A washer chamber may be constructed of wood, or stone, but it is most often constructed of sheet metal. The lower portion .of it is specially designed as a tank to receive the water dropping through the chamber and to serve as a reservoir from which the water may be recirculated. It is desirable that air leaving a washer contain no water in suspension, and for this reason eliminators are provided at the washer outlet. These may be in the form of plates or baffles upon which the free moisture is deposited as the air is deflected through several changes from its original direction of flow. In some washers, units of either steel wool or special glass fiber sections serve as eliminators. However, specially designed sheet metal plates are more generally used because they offer the least resistance to the flow of air, while performing effectively the function of moisture eliminationT They also have the advantage of acting as scrubber surfaces when flooded. When the air has a high sulphur content tending tojorm a weak acid, the eliminators have been constructed of ribbed, wire glass plates set in a cypress frame so that frequent renewal will not be necessary. It is essential to uniform performance in a washer, that air enter evenly- 217 -. /