The Effects of Humidity on Evaporative Coolers

Function

• Evaporative coolers are one of the simplest types of air conditioning in use in the desert southwest. The coolers use absorbent pads, water pumps and electric motors to pull air through the pads and send it into buildings using the existing ducts, a window or an opening in a wall or ceiling. As the cooler draws air through the pads, the temperature of the air drops, which blows through the building. These coolers depend on vents or open windows to equalize the pressure inside the building; if they didn't, too much back pressure would be created and the units would not work effectively.

Considerations

• Unlike air conditioners, evaporative coolers are completely dependent on weather conditions, including temperature and humidity, whose relationship is called the dew point. When the dew point reaches 55 degrees F or higher, the coolers do not work nearly as well. As a rule, the months when they cool effectively are April, May, most of June and September. In July and August, the humidity levels increase in the desert southwest, and the dew points go well over 55 degrees.

Costs

• The coolers use substantially less electricity than air conditioners, but they use a fair amount of water, depending on the size of the cooler and the humidity levels when water does not evaporate as readily as when the humidity levels are low. In areas where water is expensive, running an evaporative cooler may not result in substantial savings on utility bills. Swamp coolers are mechanically simpler than air conditioners, and many people who use them maintain them on their own, saving money on labor costs. The replacement parts are also relatively inexpensive.

Warnings

• As the humidity climbs in the summer, the coolers blow warmer, more humid air into homes and buildings, which contributes to higher humidity levels. The levels can support the growth of mold and mildew, creating a health hazard. The increased humidity in buildings also decreases the comfort factor, particularly when the outdoor temperatures soar over 100 degrees F. People who suffer from allergies may find that evaporative coolers increase their discomfort because the coolers require a constant flow of fresh air from outdoors to work, bringing in a constant stream of pollen.