two-stage evaporative cooler
In the first (indirect) stage, incoming warm air passes through a water-filled heat exchanger that cools without adding moisture. In the second (direct) stage, air passes through a water-soaked pad where the temperature drops more and the air picks up water, which increases the humidity. Because the air supply to the second stage evaporator is pre-cooled, less humidity is added to the air (because cooler air can't hold as much moisture as warmer air). The result is cool air with a relative humidity between 50 and 70%, depending on the climate, compared to a single-stage system that produces about 80% relative humidity air.
In most installations, air is delivered directly through the wall, or it can be ducted to one or two central locations. Air exits the home through vents to the attic, which cools the attic and further reduces heat gain.
An advanced two-stage evaporative cooler uses 100% filtered, outdoor air and a variable speed blower to circulate cool air. Two-stage evaporative coolers can reduce energy consumption by 60 to 75% over conventional air conditioning systems, according to the American Society of Heating and Engineers (ASHRAE). Yet this relative improvement depends on location and application. Evaporative coolers work best in very dry climates.
Related category• COOLING, REFRIGERATION, AND AIR CONDITIONING
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