Approach - The difference in temperature between the cooled-water temperature and the entering-air wet bulb temperature. Because wet cooling towers are based on the principle of evaporative cooling, the maximum cooling tower efficiency depends on the wet bulb temperature of the air.

Blowdown - The portion of the circulating water flow that is removed in order to maintain the amount of dissolved solids and other impurities at an acceptable level.

Web-Bulb Temperature - The lowest temperature that water will reach by evaporative cooling. The name “wet bulb” derives from the classic method of measuring this property — with a thermometer that has its bulb covered with a moistened piece of gauze or cloth, which is then placed into a flowing air stream or whipped around to speed up evaporation of the water in the bulb covering. Cooling towers are specified and designed to achieve an “approach to wet bulb” of a certain number of degrees while circulating a specified amount of cooling water.