Evaporative air conditioning works by evaporating water instead of using refrigeration systems like other types of air conditioners. The principal behind this type of air conditioner is that the evaporation of a liquid, such as water, cools and object or another liquid in contact with it. For an evaporative air conditioning system to function there must be a latent heat source present to induce the water’s evaporation. You first need to understand what wet-bulb temperatures and dry-bulb temperatures are.
Wet-bulb temperature is the lowest temperature that can be reached by evaporating water. Think of this reading as an indication of the amount of moisture or water in the air.
Dry-bulb temperature is the temperature of the air when not exposed to moisture. This is typically thought of as a traditional temperature reading.
So overall, web-bulb temperature can be thought of as the amount of moisture in the air and dry-bulb temperature can be considered the actual temperature of the air. When considering the potential for evaporative cooling, you need to compare the wet-bulb temperature to the dry-bulb temperature. The general correlation of the two is that the greater the variance between the wet-bulb temperature and the dry-bulb temperature, the greater the amount of evaporation and therefore cooling. When the temperatures are too similar, there is no evaporation and therefore no cooling.