The Wet bulb temperature (WBT) is a site condition measured by placing a thin film of water on the bulb of a thermometer. A non-wetted thermometer reading provides ‘dry bulb’ temperature (DBT) reading. A comparison of wet and dry bulb readings allows the relative humidity to be determined from a psychometric chart or the air properties table. The wet bulb temperature is always lower than the dry bulb value except when the air is fully saturated with water – a condition known as 100% relative humidity. This is when the wet and dry bulb temperatures are the same. A tower cannot cool the hot process water to a temperature any lower than the wet bulb temperature of the entering air.
