You may have heard people mention swamp coolers; there are different types of these units on the market.
This article is focused on the basic concept of evaporative cooling. Evaporative coolers help to cool you for two reasons:
One is that they ventilate your room. If heat accumulates in your room (which usually happens when there is a lack of ventilation), then ventilation will literally blow it outside. The other reason is that they literally cool the air via evaporation.
They operate by using a fan to draw air from outside, and then pass it through a cooling pad, which is a pad soaked with water. As the air passes through the pad, the heat in the air causes the water to slowly vapourize. During vapourization, the water expands into water vapour. While it expands, it absorbs heat from the air passing through it.
The cooled air then enters the room and pushes out the stagnant warm air in the process. This ventilation/cooling process requires that another window is open so that the stagnant air can exit, otherwise, if the window is closed, the room’s humidity will increase very quickly until the air in the room is saturated with water vapour.
In simpler terms: At that point, the evaporative cooler ceases to function completely. If the humidity of your geographic region is high, evaporative coolers will not be effective, as evaporation decreases as humidity increases, and evaporative coolers consume water.
If your geographic location has a low average humidity, an evaporative/swap cooler can work wonders for you, and without damaging the ozone layer with HCFC refrigerants. Their high efficiency is attributable to the fact that they normally only use a fan and a water pump.
If you would like to experiment with the concept of evaporative cooling yourself (for fun), you can spray a scouring pad or other highly porous sponge with water and pass air through it (i’ve done that before).