What is Evaporative Cooling?

Perspiration is the most common example of the term ‘evaporative cooling’. Evaporative cooling happens when heat is applied to water making it change its state from liquid to vapor. Evaporation takes place when the warm energy of the remaining hot liquid is taken by the vapor to the air . The result is a cooler liquid. The evaporation of sweat in perspiration results in the absorption of heat to cool the body.

The principle underlying evaporative cooling is the need for heat to change from liquid phase to vapor/air phase. Once heat is applied to water, some of the water changes its phase to vapor (evaporation) while the remaining liquid cools off because evaporation takes off its heat in the process.

Temperatures in evaporative cooling systems

Evaporative cooling systems function on the same principle. The evaporation of water results in a loss of energy from the air which causes a reduction in the temperature. When dealing with evaporative cooling systems, two temperatures are relevant:

Dry Bulb Temperature, commonly known as the air temperature and measured through an ordinary thermometer.

Wet Bulb Temperature measures the lowest temperature which can be reached only by water evaporation. This is used in measuring the water evaporating into the air.

When humidity becomes less than 100%, the air starts absorbing water and evaporation begins. A volume of air can hold only a certain amount of water vapor. The degree it can absorb depends on how much or how little it is holding. Relative Humidity is calculated with the use of dry and wet bulb temperature.

Humidity is used to describe the amount of water in the air in relation to the amount it is capable to hold. When it can’t hold anymore water, air becomes saturated. Taking the sponge as an example, if it can hold only half of its water, then its Relative Humidity is 50%.

Evaporative coolers and how they work

With the combination of water evaporation and an air-moving system, evaporative coolers are able to serve their purpose. These equipments pull fresh outside air then they cool them through evaporation and by circulating the cool temperature throughout the house by means of a blower. As it happens, the air temperature lowers by about 30 degrees.

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