Indirect Evaporative Cooling

Indirect Evaporative Cooling (closed circuit) is similar to direct evaporative cooling, but uses some type of heat exchanger. The cooled moist air never comes in direct contact with the conditioned environment.
Traditional evaporative coolers use only a fraction of the energy of conventional air-conditioning systems. Unfortunately, except for in very dry climates, they may increase humidity to a level that makes occupants uncomfortable. Two-stage (indirect) evaporative coolers do not produce humidity levels as high as that produced by traditional single-stage evaporative coolers.
The difference between a conventional evaporative cooler and an Indirect evaporative cooler is that the indirect evaporative cooler cools the air in two operations before it is blown into the home to avoid adding moisture to the cool air. Although both operations use water for cooling, only the second operation adds moisture to supply air.
According to manufacturers, the difference is cool air with a relative humidity between 50 and 70 percent, depending on the climate, compared to a traditional system that produces about 80 percent relative humidity air.

MAINTENANCE
Evaporative coolers require maintenance. Here are some of the items that should be checked ...

lBlower assembly and motor bearings need lubrication.

lFan belts should have the proper tension, movement should be approximately 1 inch maximum.
lThe water level should be a little below the top of the tray, with the top of the overflow pipe sticking out of the water. If the water is not at the proper level the float arm may need adjustment.
lThe water tray should be free of debris.
lCooler pads should be in good condition. 
lWater lines should be disconnected and blown free for the winter in cold climates.