The technology used in evaporative coolers (or swamp coolers) is a versatile and energy efficient alternative to compressor-based cooling. In favorable climates (most of the western United States and other dry climates worldwide), evaporative air coolers can meet most, or all, of a building's cooling needs, and they only use one-fourth the energy of conventional equipment. They can also be cost-effectively integrated with conventional chiller systems.
How exactly do evaporative coolers work?
They work by adding moisture to hot, dry air. As the moisture evaporates - changing from a liquid to a gas - the heat dissipates, leaving cooler air behind. This air is then spread into the building by a fan. The lower the relative humidity of the air, the greater cooling effect possible when moisture is added.
What is the internal structure like?
The basic components are a water tank, a water pump, a fan, and one or more cooling pads. The pump circulates water to saturate the pads. As hot outside air enters the cooler and passes over the water-saturated pads, evaporation occurs - using the heat in the air as energy. From there, the cooler air (15-40 degrees lower) is directed into the home, pushing the warmer air out through windows. Since this process also humidifies the air, evaporative coolers are best used in areas with low, summertime humidity.
What do I need to know when buying an evaporative air cooler?
Most importantly, consider the surrounding climate. For instance, if you live in a very dry, arid climate like Albuquerque, New Mexico, or Tucson, Arizona, a direct evaporative cooling system would be the perfect solution. However, if you live in a humid area like Boston, Massachusetts, or Miami, Florida, an evaporative system will be fine for the dry weather, but it would need to be supplemented by a compressor-based cooling system during the humid season.
The following chart shows some examples of temperatures relating to wet bulb (accounts for moisture in the air) and dry bulb (standard thermometer's temperature) conditions in various cities in the United States during the month of July. The cities where the wet bulb range is well below the dry bulb range are top candidates for swamp coolers.
Evaporative air coolers are rated by the cubic feet per minute (CFM) of air delivered to a building. Most models range from 3,000 to 25,000 CFM. Manufacturers recommend providing enough air-moving capacity for 20 to 40 air changes per hour, depending on climate.
What types of evaporative coolers are there to choose from?
Direct evaporative coolers add moisture to the air while increasing the relative humidity. Direct systems require a building's exhaust system to match the rate at which the conditioned air is introduced to the space without circulating the same air. (Central air conditioning systems sometimes work similarly to direct systems.)
Indirect evaporative coolers lower the temperature without adding moisture to the air. However, this type is more expensive than the direct type. Keep in mind that indirect systems provide the same energy efficient alternative as a direct cooler, in situations where the direct type may not be practical or useful.
Direct Evaporative Cooling System
Indirect Evaporative Cooling System
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