Document OzMXD3vQLjXonMq56b2K3kdyp

American Society of Heating and Ventilating Engineers Guide, 1937 i / 4 Discuss the difference in results obtained in cooling and dehumidifying jj, ` an air washer from those obtained in a surface cooling coil. ! Air leaves a dehumidifying air washer in a saturated condition at a dew point tempera. > ture which can be easily maintained at a constant level by controlling the spray water temperature. This saturated air may then be reheated to proper delivery temperature i by reheating coils or by mixing with by-passed air. .'1 , For a set air velocity and a set mean refrigerant temperature, a given cooling coil is capable of absorbing a definite amount of heat. Whether the air leaving the coil is saturated or not depends then on the entering dry- and wet-bulb temperatures. From practical operating standpoint, the easiest way to control the output of the cooling coii is by means of the dry-bulb temperature of the conditioned space. This means then that the final dew point will vary somewhat depending on entering air conditions. \j * - 1 -j Summarizing then, the air washers permit close control over both final dry-bulb and final dew point temperatures, while the surface coolers permit close control over the final dry-bulb only. * ' 1 1 <: 5 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 Refrigeration Required Tons 284 233 183 157 144 79 37 Total 1200 hours 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 Seasonal power cost: m 3E Wet-Bulb FTemperature Ton-Hours Kwhr 80 79 - 75 74 - 70 69 - 65 64 - 60 59 - 55 54 - 50 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 Totals 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 $3,173. , 158,627 kwhr _. The average consumption will be igfg24 ton-hours = -878 kw Per ton- 214 Chapter Using the data from Question 5, if city water costs 20 cents per thousand 6 jjJns, and if 1.25 gallons are used per minute per ton, estimate the annual gauw"'-i wa-t-e---r-nst. gg x 1.2-5- = 75 --ga'l per ton-hour. 181,824 ton-hours X 75 = 13,620,000 gal per year. 1--3-,-6--2-0--,0jq0q0qX----$--0-.2--0 = $2,724, txhl e year.ly co.olin.g w.ate.r cost. 7 ( Using the data of Question 5, if a cooling tower were installed for re-using the condensing water, estimate the annual operating cost ofa dichlorodifluoro- methane refrigeration system if the final temperatures of the water leaving the cooling tower and the kilowatt input per ton are the following: Tons 228844 233 183 157 114444 79 37 Temperature of water leaving tower, F Kw input per ton 86.7 1.10 81.8 0.94 76.5 0.85 72.1 0.80 66.4 0.74 80 79 -75 74 - 70 69-65 64-60 59 - 55 54-50 L Vlaiu 1,704 23,300 50,700 51,800 39,900 12,500 1,920 X0 X X X X X _______181,824 top-hours 1.10 0.94 0.85 0.80 0.74 0.59 0.62 1,875 21,900 43,300 41,400 29,500 7,370 1,200 146,545 kwhr The 146,545 kwhr at 2 cents per kwhr will cost $2,931. . ... , 146,545 kwhr 0.805 kw per ton. Tihnee advvecriag6ev c---onsumption will be t1-8.t1.-,S8o24.--t-o--n--;h--ou--rs - 8con0dIitfioansintegasmysetejemctoorf Qsyusetesmtiown e5r,ecuosmepduttoe stheceuarennthuealresftreiagmeracotiostniffostretahme aisir sold for 53 cents per thousand pounds and if there is an average steam con sumption of 20 ib of steam per hour per ton when used with a cooling tower s1y8s1t,8e2m4.tons X 20 lb of steam per ton 3,636,480 lb of steam. The 3.636,480 lb at 53 cents per thousand pounds will cost $1,929. 9 From the data given in the following table covering auxiliary equipment, make a comparison between the operating costs of the complete dichlorodi fluoromethane system of Question 7 and the complete steam ejector cooling system of Question 8. A cooling tower is used for condenser water recovery. Plant Operation Dichlorodifluoromethane System Hours of operation______ Cooling tower fan, bhp.......... Cooling tower pump, bhp--- Chilled water, gpm..................................I Discharge head on chilled water system, ft ...............................................' Pump efficiency, per cent........... Motor efficiency, per cent.......... Chilled water temperature, F,, 1200 17.8 30.2 1200 75 75 80 46 nti n i Steam Ejector System 1200 35.6 47.8 1200 75. 75 80 46. 215