When water evaporates into the atmosphere, it reduces the air temperature in the area where evaporation is taking place. This phenomenon is termed evaporative cooling. Based on this phenomenon, devices called evaporative coolers are available, to cool the house on a hot day. These devices are also known by names such as air coolers, desert coolers, or swamp coolers. Evaporative coolers are available in two main categories i.e. direct and indirect coolers.
The most common coolers are the direct evaporative coolers wherein the air enters the cooler, passes through a pad soaked with water and is released back outside. The water soaked pads are known as cooler pads and as the air passes through them, it undergoes filtration, is cooled, and has moisture added to it. This means that when the air re-enters the atmosphere, it is humidified.
Another type of cooler is the indirect evaporative cooler. This cooler has two stages in its functioning. The air first passes through a heat exchanger, for cooling purposes. From the heat exchanger, the cooled air flows through the cooler pad, where it undergoes moisturization. The difference between this system and the direct cooler is in the humidity levels. Cold air absorbs less moisture than warm air. Consequently, air that is cooled before being humidified has a moisture content of around 60 %. In comparison, air that passes through the direct evaporative cooler has 80 % humidity.
Evaporative coolers provide cooling solutions and they are similar to air conditioners. Evaporative coolers have many benefits. To begin with, they are cheaper to purchase than air conditioners. They provide energy savings because they require considerably less electricity to function and consequently, they are cheaper to run.
Air conditioners typically make use of refrigerants like chlorofluorocarbons (CFCs), which when released into the atmosphere, cause damage to the ozone layer. This allows the sun's ultraviolet rays to penetrate through the ozone layer. On the other hand, evaporative coolers do not use any refrigerants and hence, do not damage the environment in any way.
Since evaporative coolers add moisture to the air, they are an ideal choice for homes in desert areas and those places with a naturally low water content in the air (mountain regions for example). Thus, evaporative coolers can serve a dual purpose of being cooler and humidifier.
Evaporative coolers are useful as a stand-alone cooling system or in combination with an air conditioner. However, the two cooling systems should never be used simultaneously. This is because both systems work on opposite principles. Coolers add moisture to the air while air conditioners dehumidify it.
When an evaporative cooler is running, it is necessary for windows to remain open. This ensures a steady supply of fresh air for the cooler. Coolers also require a fairly large amount of water, to hydrate the cooler pads. This does increase a home's water consumption by around 19,000 gallons per year but the overall cooling and cost benefits make up for this gain.