Document wg7M1rR1Exvqe0nrpg8DBernB

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 Table 1. Average Maximum Water Main Temperatures3 (Concluded) State Cut Trap. F State Cur Temp. F Okla........... Oklahoma City____ Tulsa. _____ I Ore.............. Eugene....................... Portland ... Pa................ Altoona Erie....... Johnstown............... .. McKeesport--........... Philadelphia Pittsburgh............ ..... R. I..._______ Providence................ S. C............ Charleston................. Greenville- ............... Spartanburg. 5. Dak....... Rapid City Tenn........... Chattanooga............. Knoxville........ _........ Memphis.................... Nashville Texas. ........ Austin._...................... Beaumont... ........... Dallas........................ Fort Worth............... Galveston.................. Houston................ Port Arthur . San Antonio.............. Wichita Falls 82 85 60 64 74 75 74 82 83 81 68 80 81 78 55 84 89 70 90 65 90 86 86 84 90 84 83 76 85 Salt Lake City. Va Wash Seattle-- .................... W: Va........ Wis. Madison................... 44 60 73 58 62 51 57 85 78 78 54 58 70 68 Province Alta.. B. C............ Ont............. P. E. I....... Charlottetown:......... Que--......... Montreal................... Quebec..................... 64 60 50 63 48 78 68 These averages taken from various city water main locations, with some actual values slightly higher and some lower than values shown. As the heat content of the air increases, its wet-bulb temperature rises. (See Chapter 1.) Because it is impractical to leave the air in contact with water for a long enough time to permit the wet-bulb temperature of the air and the temperature of the water to reach equilibrium, atmos pheric water cooling equipment aims to circulate only enough air to cool the water to the desired temperature with the least possible expenditure of power. In an air washer, humidifier or dehumiclifier, the air is first conditioned by water to change its.moisture and temperature, and it is then sent to the place where it is to be used. In water cooling equipment the tem perature of the water is reduced by air, and the cooled water is carried to its point of usage. In the air washer, an excess of water is used to con dition a fixed quantity of air, while in water cooling equipment, an excess of air is used to cool a fixed quantity of water.- Both types of equipment have a common basis of design, however, in that the size of the equipment is determined by the quantity of air that must be handled. With the air washer, the size of the equipment is fixed by the quantity of air to be conditioned, and the amount of conditioning is controlled by the quantity and temperature of the water supplied and . its method of application. With water cooling apparatus, its size and the 540 CHAPTER 27. SPRAY EQUIPMENT quantity of air required bear no direct relation to the quantity of water being cooled, but vary through a wide range for different services and conditions. Sizes of Equipment Assuming a definite quantity of water to be cooled, the size and design of atmospheric cooling equipment are affected by the following factors: 1. Temperature range through which the water must be cooled. 2. Number of degrees above the wet-bulb temperature of the entering air to which the water temperature must be reduced. 3. Temperature of the atmospheric wet-bulb at which the required cooling must be performed. 4. Time of contact of the air with the water. (This involves height or length of the apparatus and velocity of air.) 5. Surface of water exposed to each unit quantity of air. 6. Relative velocity of air and water. Items 1, 2, and 3 are established by the type of service and geographical location, while items 4, 5, and 6 depend upon the design of the equipment. The establishment of a proper cooling range depends upon: 1. Type of service (refrigerating, internal combustion engine and steam condensing). 2. Wet-bulb temperature at which the equipment must operate satisfactorily. 3. Type of condenser or heat-exchanger used. Because the design of an entire plant is usually affected by the quantity . and temperature of the cooling water supply, plants should be designed for cooling water conditions which can be most efficiently attained. The first consideration is usually the limiting temperature of the plant. For example, if an ammonia compressor refrigerating plant is to be designed for 185 lb head pressure as a normal maximum, the limiting temperature of the ammonia in the condenser is 96 F. Should the ammonia tempera ture go above this figure the head pressure will exceed 185 lb and power consumption increases. To obtain this head pressure, the temperature of the circulating water leaving the condenser must always be less than 96 F by an amount depending upon the size and design of the condenser, the Table 2. Condenser Design 'Data Gab Maximum Pressure Condenser Gas Temperature Leaving Hot Water Temperature Deg F Dec F , Best Condenser Design Average Condenser Design Steam.... ......... 28 in. vacuum____ Steam__________ 27 in. vacuum........ Steam__________ 26 in. vacuum........ Ammonia______ 185 lb gage . head pressure...... Carbon dioxide.. 1030 lb gage head pressure...... Methyl 102 lb gage chloride....... head pressure...... Dichlorodi- 1171b gage fluoromethane head pressure----- 101.2 . 115.1 125.9 96.0 86.0 100.0 100.0 97. 110 120 92. 83 96 . 96 93 105 114 . 88 81 92 93 541