Document jBpEk7zjwdJyJ4ywrp854647Q

HEATING VENTILATING AIR CONDITIONING GUIDE 1942 of hours per year during which definite wet-bulb temperatures and corresponding refrigeration rates pertain. Wet-Bulb Temfebetebe F 80 79 - 75 74 - 70 69 - 65 64-60 59 - 55 54-50 No. or Hobbs feb Year 6 100 277 330 277 158 52 Total 1200 hours Refbiqebation Requibbd 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 284 233 183 157 144 79 37 0.89 0.89 0.87 0.86 0.86 0.93 0.97 Solution. Seasonal power cost: Wet Bulb FTemtbbatukb 80 79 - 75 74 - 70 69 - 65 64-60 59 - 55 54-50 Totals Ton-Hours Kwhr 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 = 1,920 181,824 ton-hours 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 = 1,860 158,627 kwhr The 158,627 kwhr at 2 cents per kwhr will cost $3,173. ' ---- ,, , 158,627 kwhr ,,, The average consumption will be gg4 ton hours = 0.873 kw per ton. Example S. Using the data from Example 2, if city water costs 20 cents per thousand gallons, and if 1.25 gal are used per minute per ton, estimate the annual water cost. Solution. 0 X 1.25 = 75 gal per ton-hour. 81,824 ton-hours X 75 = 13,620,000 gal per year. 3,620,000 X 80.20 = g2 ?24 the yearly cooling water cost. 1000 508 '53=' Chapter 26 HEAT TRANSFER SURFACE COILS Coil Applications, Construction and Arrangement, Steam Coils, Water Coils, Direct-Expansion Coils, Flow Arrange ments, Applications, Calculation of Heat Transfer, Air Flow Resistance, Coil Performance, Selection THE coils described in this chapter are used in air conditioning sys tems for heating or cooling an air stream under forced convection. The surface coil equipment may be made up of a number of banks assembled in the field, or the entire assembly may be factory constructed. The applications of each type of coil are limited to the field within which it is rated. Other limitations are imposed by code regulations, by proper choice of materials for the refrigerants used and the condition of the air handled, or by an economic analysis of the possible alternates on each installation. For heating service, these coils are used as preheaters, reheaters or booster heaters, (see Chapters 21 and 22). The function of the coils is air heating only, but the apparatus assembly may include means for humidi fication and air cleaning. Steam or hot water are the usual heating media, although others are used in special cases, such as reheating by means of discharge gas from a refrigerating system. Coils are used for air cooling with or without accompanying dehumidi fication. Examples of cooling applications without dehumidification are precooling coils using well water or other relatively high temperature water to reduce the load on the refrigerating machinery, or water cooled coils to remove sensible heat in connection with chemical moistureabsorption apparatus. By proper coil selection it is possible to handle both sensible cooling and dehumidification together as further explained later. The apparatus assembly usually includes an air cleaning means to protect the coil from accumulation of dirt and to keep dust and foreign matter but of the conditioned space. Although cooling and dehumidi fication are the usual functions, there are cases of cooling coils purposely wetted as an aid to air cleaning and odor absorption. The usual cooling media used in surface coils are cold water and volatile refrigerants such as dichlorodifluoromethane and methyl chloride, but others are used in special cases. Brines are seldom required for the range of applications covered by this chapter, although there are cases where low entering air temperatures with large latent heat loads require a refrigerant temperature so low that water becomes impractical. Some- 509