Document Xzz4KOnpbymRMO9oDzb50rnpg

r i HEATINC VENTILATING AIR CONDITIONING CUIDE 1940 . 496 Fig. 4. A pproximate Well Water emperatures at Depths of 30 to 0 F tT CHAPTER 26. SPRAY EQUIPMENT 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 quantity 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 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 quantity of water being circulated, and the refrigerating tonnage being produced. A condenser having a large surface per ton of refrigeration may be designed to operate satisfactorily with the leaving hot water temperature within 3 or 4 F of the ammonia temperature corresponding 497