There are two broad types of evaporative coolers available on the market, direct and indirect, both commonly known as two-stage.
In a direct evaporative cooler, a blower forces air through a permeable and water-soaked pad. As the air is passing through the pad, it is filtered and cooled as well as humidified. On the other hand, an indirect type evaporative cooler carries a secondary heat exchanger that prevents humidity levels from being increased in the airstream that enters the home.
Evaporative coolers can be employed as a compact and often the sole cooling system in a home. They can also be used in combination with a regular air conditioner system. However, one should avoid simultaneously operating conventional air conditioners along with direct evaporative coolers. This is because air conditioners dehumidify, whereas evaporative coolers humidify. As a result, the two systems will tend to work in opposition.
Evaporative coolers capacity is based on its airflow measured in cubic feet per minute (cfm). Improperly sized evaporative cooler will cause wastage of precious resources like water and energy. It may also cause excess humidity.