What is the process of Evaporative Cooling? To begin, it is necessary to understand the properties of heat, air, and water vapor. The Direct type of Evaporative Cooler is the most common, in which hot outside air is cooled within the machine and forced into the building before being exhausted to the outside. Other types include indirect and air washers.
This excellent article discusses evaporative cooling.
What Exactly Is Heat?
The heat required to evaporate water into water vapor is referred to as the “Latent Heat of Evaporation.” For example, it is the heat given up by the hot pavement to evaporate the water after a summer rainstorm, or the heat is given up by the stove burner to evaporate the water in a boiling kettle. As liquid water condenses into vapor (which cannot be seen) it absorbs heat from its surroundings; the temperature does not change, but the amount of heat or energy absorbed is stored in the molecular structure of the vapor. Latent Heat is a natural phenomenon that allows for Evaporative Cooling.
Where Does Latent Heat Originate?
It is derived from the surrounding air and materials. When a substance transitions from solid to liquid (ice to water) or liquid to vapor (water to vapor or water to steam), it absorbs heat from its surroundings. That is, the surrounding air, solid objects, and liquids cool as they give up heat to the melting or evaporating process.
The sum of latent and sensible heat is known as total heat. It is the total amount of heat in a room, which includes both visible and invisible heat. Total heat is measured in kilojoules (kJ): 1000kJ equals 1000 BTUs. One liter of water absorbs approximately 2000kJ of heat energy during the evaporation process, which occurs without any external energy input. As a result, evaporative air conditioners require very little electrical power to operate. The only power required is to drive the fan and pump.
The Process Of Evaporative Air Cooling
The heat exchange process in Evaporative Air Cooling machines is enabled by a water pump that delivers water to cooling pads and a motor-driven fan that forces hot outside air through those media panels. These elements work together to speed up the natural heat exchange process.
When the water in the Evaporative Air Cooler is converted into water vapor, some of the sensible heat from the air (the heat you can feel) is converted into latent heat (the heat you can’t feel).
Because some of the hot air’s (sensible) heat has been used, the process of sensible heat converting to latent heat causes it to become colder. As a result, the air temperature drops. The cold air is then pumped into the structure and eventually exhausts from it. It is never recycled.
Evaporative Air Coolers will raise the humidity level inside the building slightly. However, we must keep in mind that the temperature has also dropped. Human comfort is created by the combination of temperature and humidity, and Evaporative Air Coolers are widely used around the world because they can create comfortable conditions. For example, 80 percent humidity and 30 degrees Celsius (86 degrees Fahrenheit) is extremely uncomfortable, whereas 80 percent humidity and 16 degrees Celsius (61 degrees Fahrenheit) are quite comfortable. Furthermore, increasing air velocity in hot conditions improves comfort, and Evaporative Air Coolers generate enough air movement to reduce the effects of humidity.