Evaporative Coolers

By Kenton Shepard

Direct Evaporative Coolers

Source: Kenton Shepard

In an evaporative cooler, a small motor (top) drives a large fan (center) which blows air out the bottom and into your home. The fan sucks air in through the louvers around the box, which are covered with a water-saturated, absorbent material kept wet by a circulating pump. This is an older cooler and maintenace by a specialist would typically be rocommended.

In low-humidity areas, evaporating water into the air provides a natural and energy-efficient means of cooling. Evaporative coolers, also called swamp coolers, rely on this principal, cooling outdoor air by passing it over water-saturated pads, causing the water to evaporate into it. The 15°–40°F-cooler air is then directed into the home, and pushes warmer air out through the windows.

When operating an evaporative cooler, windows are opened part way to allow warm indoor air to escape as it is replaced by cooled air. Unlike central air conditioning systems that recirculate the same air, evaporative coolers provide a steady stream of fresh air into the house.

Evaporative coolers cost about half as much to install as central air conditioners and use about one-quarter as much energy. However, they require more frequent maintenance than conventional air-conditioners and they’re more suitable for areas with low humidity.

Indirect (2-stage) Evaporative Coolers

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’s 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 ...

• Blower assembly and motor bearings need lubrication.
• Fan belts should have the proper tension, movement should be approximately 1 inch maximum.
• The 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.
• The water tray should be free of debris.
• Cooler pads should be in good condition. 
• Water lines should be disconnected and blown free for the winter in cold climates.