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504 Chapter 26 1945 Guide' Fronfconsideration'oLthe factors' whidrinclude'the cooling rangeland design wet-bulb temperature, the quantity of water required can be calculated from the amount of heat to be dissipated. The normal amounts of heat to be removed from various processes of the cooling equipment are: Compressor Refrigeration:. 220 to 270 Btu per minute per ton. Usual practice is to assume: 250 Btu per minute per ton which is equivalent to 30 gal per degree Fahrenheit per minute per ton. Steam Turbine Condensers: 950 to 980 Btu per pound of steam. Usual practice is to assume 970 Btu per pound of steam. Steam Jet Refrigerating Condensers: 1030 to 1150 Btu per pound of steam. Exact value depends upon initial steam conditions. . ' Diesel Engine Jackets: 2500 to. 4000 Btu per BHP per hour. Usual practice is to assume 3500 Btu per BHP per hour. Natural Gas or Gasoline Engines: 4500 to 6000 Btu per BHP per hour. Usual practice is to assume 5000 Btu per BHP per hour. Cooling Ponds A. natural pond is often used as a source of condensing water. The hot water should be discharged close to the surface at the shore line. Natural air movement over the surface of the water will cause evaporation and carry away- heat. Because increased density due to .the loss of heat causes the cooled water to sink to the botto.m of the pond, the suction connection for intake water should be placed as far below the surface as possible, and at as great a-distance from the discharge as practicable. Spray Cooling Ponds The spray pond consists of a basin, above which nozzles are located to spray water up into the air. Properly designed spray nozzles break up the water into small drops, but not into a mist because the individual drops must be heavy enough to fall back into the basin and not drift away with the air movement. The water surface exposed to the air for cooling is the combined area of all the small drops. Since the rate of heat removal by atmospheric water cooling is a function of the area of water exposed to the air, the difference in temperature between the water and the wetbulb temperature of the air, the relative velocity of air and water, and the duration of contact of the air with the water, a much larger quantity of heat may be dissipated in a given area with the spray pond than-with the cooling pond, because of (1) the speed with which the drops travel as they are propelled into the air and fall back into the water basin, (2) the increased wind velocity at a point above the surrounding structures or terrain, (3) the increased volume of air used, and (4) the vastly increased area of contact between air and water*. Spray pond effectiveness is increased by (1) elevating the nozzles to a higher point above the surface of the water in the basin, (2) increasing the spacing between nozzles of any one capacity, (3) using smaller capacity nozzles to decrease the concentration of Water per unit area, and (4) using smaller nozzles and increasing the pressure to maintain the same concentration of water per unit area. Usual practice is to locate the nozzles from 5 to 7 ft above the edge of the basin, to supply from 5 to 12 lb pressure at the nozzles, using nozzles spraying from 20 gpm to 60 gpm each and spacing them so the average water delivered to the surface of the pond is from 0.5 to 0.7 gpm per square foot. Best results are obtained by placing the nozzles in a long relatively narrow area located broadside to the wind. *A.S.H.V.E. Research Paper--Design of Spray Cooling Ponds, by S. Hori. U. A. Patchett and L. M. K. Boelter (A.S.H.V.E. Journal Section, Healing, Piping and Air Conditioning, October, 1942, p. 624). Spray Equipment 505 Spraypondsmaybelocatedom the ^oundr or they may be 'placed on roofs. To prevent excessive drift loss, or the carrying of entrained water beyond the edge of the pond by the air on the leeward side, louver fences are required for roof locations and for those ground locations where space is so restricted that the outer nozzles cannot be located at least 20 ft to 25 ft from the edge of the basin. Such fences usually are con structed of horizontal louvers overlapping so the air is forced to turn a corner in passing through the fence, and the heavier drops of water are thrown back, owing to their inertia. The louvers also restrict the flow of air, particularly at the higher wind velocities, and thus further reduce the possibility of water being carried off. The height of an effective fence should be equal to the height of the spray cloud. Louver boards are preferably of red gulf cypress or California redwood supported on castiron, steel or wood posts.. Where building ordinances forbid the use of combustible materials, sheet metal is customarily used. Algae growths, during warm weather, in cooling towers and spray ponds may be eliminated while the plant is in operation by the use of potassium permanganate. This chemical can be dissolved at the rate of 1 - lb in 1M to \l/l j*al of hot water. About 10 parts of permanganate should be used per million parts of cooling water. Enough of the permanganate solution should be added periodically to cause the water to have a pink color for a period of from 15 to 20 min. The best results are obtained when sufficient quantities are added periodically at intervals of several weeks, the time intervals being dependent upon local operating conditions. The chemical is non-poisonous and non-corrosive when used as directed. Natural Draft Spray Type Towers Where not more than 30,000 Btu per minute are to be dissipated, the natural draft spray type tower is a satisfactory apparatus. The word lower in this connection is somewhat of a misnomer as the apparatus is essentially a narrow spray pond with a high louver fence. As usually built, the nozzles spray down from the top of the structure and the distance from the center of the nozzle system to the fence on either side is not more than half the distance that the nozzles are elevated above the water basin. Heights range from 6 ft to 15 ft and the total width of a structure is not usually greater than its height. Spray towers occupy less space on small jobs than spray ponds of equivalent capacities because the towers have a capacity of from 0.6 gpm to 1.5 gpm per square foot of tower area. The louvers are continually wet, and so' add to the surface of water exposed to the cooling air. Natural -Draft Deck Type Towers In past years much of- the atmospheric water cooling on refrigeration work has been done with natural draft deck type towers, which are also referred to as wind or atmospheric towers. These towers consist of heavy ' wooden or steel framework from 20 to 40 ft high and from 10 to 20 ft wide, having open horizontal lattice-work platforms or decks at regular intervals from top to bottom, and a catch basin at the foot. The hot water is distributed over the upper part of the structure by means of troughs, splash heads, or nozzles, and it drips from deck to deck down to the basin. The object of the decks is to arrest the fall of the water so as to present efficient cooling surfaces to the air, whiqh passes through the tower parallel to the decks. The decks add to the area of water surface ' exposed to the air both by causing it to splash into fine droplets and' to