All cooling towers operate on the principle of removing heat from water by evaporating a small portion of the water that is recirculated through the unit. The heat that is removed is called the latent heat of vaporization. Each one pound of water that is evaporated removes approximately 1,050BTU’s in the form of latent heat. The amount of heat lost by the water depends on the temperature rise of the ambient air before it leaves the tower. This means that both the dry bulb and wet bulb temperatures of the air are important. When WBT = DBT, this condition corresponds to 100% relative humidity (RH) that implies the air is fully saturated. The air will no longer accept water and the lack of evaporation do not allow the wetted bulb to reject heat into the air by evaporation.
