The following terms apply to cooling-tower systems.
Cooling range is the number of degrees in Fahrenheit through which the water is cooled in the tower. It is the difference between the temperature of the hot water entering the tower and the temperature of the cold water leaving the tower.
Approach is the difference in degree Fahrenheit between the temperature of the cold water leaving the cooling tower and the wet-bulb temperature of the surrounding air.
Heat load is the amount of heat “thrown away” by the cooling tower in Btu per hour (or per minute). It is equal to the pounds of water circulated multiplied by the cooling range.
Cooling-tower pump head is the pressure required to lift the returning hot water from a point level with the base of the tower to the top of the tower and force it through the distribution system.
Drift is the small amount of water lost in the form of fine droplets retained by the circulating air. It is independent of, and in addition to, evaporation loss.
Bleed-off is the continuous or intermittent wasting of a small fraction of circulating water to prevent the build-up and concentration of scaleforming chemicals in the water.
Make-up is the water required to replace the water that is lost by evaporation, drift, and bleed-off.