Document YjjvpNg35wrBaO1mXJnX16QgN

Heatino Ventilating Air Conditioning Guide 1939 The 158,627 kwhr at 2 cents per kwhr will cost 83,173. ... . 158,627 kwhr The average consumption will be 181i824 ton-hours 0.873 kw per ton. 3 Using the data from Question 2, if city water costs 20 cents per thousand gallons, and if 1.25 gallons are used per minute per ton, estimate the annual water cost. 60 X 1.25 = 75 gal per ton-hour. 181,824 ton-hours X 75 = 13,620,000 gal per year. 13,620.000^X 80.20 = $2 724 the yearly cooUng water cost 4 Using the data of Question 2, if a cooling tower were installed for re-using the condensing water, estimate the annual compressor power cost of a dichloro! difluoromethane refrigeration system if the final temperatures of the Water leaving the cooling tower and the kilowatt input per ton are the following. Tons Temperature of water leaving tower, F Kw input per ton 284 233 183 157 144 79 37 86.7 81.8 76.5 72.1 66.4 61.3 55.6 1.10 0.94 0.85 0.80 0.74 0.59 0.62 Wet-Bulb Tbupsbatubb p 80 79 - 75 74 - 70 69 - 65 64-60 59 - 55 54-50 Ton-Hours 1,704 23,300 50,700 51,800 39,900' 12,500 1,920 Kw feb Ton Kwbr X 1.10 X 0.94 X 0.85 X 0.80 X 0.74 X 0.59 X 0.62 = 1,875 21.900 43,300 41.400 29,500 7,370 1,200 Totals 181,824 ton-hours____________________ 146;545 kwhr The 146,545 kwhr at 2 cents per kwhr will cost $2,931. ... , 146,545 kwhr _ orir , The average consumption will be 24 ton hours = ton* 5 If a steam ejector system were used to secure the refrigeration for the air conditioning system of Question 2, compute the annual steam cost if steam is sold for 53 cents per thousand pounds and if there is an average steam consumption of 20 lb of steam per hour per ton when used with a cooling tower ; system. 181,824 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. 6 Discuss the difference in results obtained in cooling and dehumidifying in ' 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 - by reheating coils or by mixing with by-passed air. ' 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 coil is by means of the dry-buib temperature of the conditioned space. This means then that * the final dew-point will vary somewhat depending on entering air conditions. * Summarizing then, the air washers permit close control over both final dry-bulb and c final dew-point temperatures, while the surface coolers permit close control over the } final dry-bulb only. I \ 492 Chapter 24 HEAT TRANSFER SURFACE COILS Coil Applications, Construction and Arrangement, Steam Coils, Water Coils, Direct-Expansion Coils, Flow Arrange ments, Applications, Calculation o 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 out 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- 493