Cooling Tower Terms and Definitions
Some useful terms, commonly used in the cooling tower industry:
1. BTU (British thermal unit) – BTU is the heat energy required to raise the temperature of one pound of water one degree Fahrenheit in the range from 32° F to 212° F.
2. Cooling Range – The difference in temperature between the hot water entering the tower and the cold water leaving the tower is the cooling range.
3. Approach – The difference between the temperature of the cold water leaving the tower and the wet- bulb temperature of the air is known as the approach. Establishment of the approach fixes the operating temperature of the tower and is a most important parameter in determining both tower size and cost.
4. Drift – Water droplets that are carried out of the cooling tower with the exhaust air. Drift loss does not include water lost by evaporation. Proper tower design can minimize drift loss. The drift rate is typically reduced by employing baffle-like devices, called drift eliminators, through which the air must travel after leaving the fill and spray zones of the tower.
5. Heat Load – The amount of heat to be removed from the circulating water within the tower. Heat load is equal to water circulation rate (gpm) times the cooling range times 500 and is expressed in BTU/hr. Heat load is also an important parameter in determining tower size and cost.
6. Ton – An evaporative cooling ton is 15,000 BTU’s per hour. The refrigeration ton is 12000 BTU’s per hour.
7. Wet Bulb Temperature (WBT) – The lowest temperature that water theoretically can reach by evaporation. Wet-Bulb temperature is an extremely important parameter in tower selection and design and should be measured by a psychrometer.
8. Dry-Bulb Temperature – The temperature of the entering or ambient air adjacent to the cooling tower as measured with a dry-bulb thermometer.
9. Pumping Head – The pressure required to pump the water from the tower basin, through the entire system and return to the top of the tower
10. Makeup – The amount of water required to replace normal losses caused by bleed off, drift, and evaporation.
11. Bleed off – The portion of the circulating water flow that is removed in order to maintain the number of dissolved solids and other impurities at an acceptable level. As a result of evaporation, dissolved solids concentration will continually increase unless reduced by bleed off