Two Stage Evaporative Coolers

There is a semi-new type of air cooler on the market. These coolers are called two-stage evaporative coolers. Evaporative coolers cool air through the simple evaporation of water.

An evaporative cooler works the opposite of an air conditioner. Water is added to hot air to cool it down as opposed to moisture being removed as it is with an air conditioner. For this reason evaporative coolers are better suited for arid, dessert environments where additional humidity is a plus. Likewise, an air conditioner is a better choice for a humid environment where the removal of moisture is desired.

Direct Versus Indirect

In a direct or open circuit evaporative cooler a blower forces air over a water soaked pad. As the air makes contact with the pad, it is filtered, humidified and cooled.

An indirect or closed circuit evaporative cooler is similar to a direct cooler, except that the air never comes into direct contact with the pad. It is cooled by evaporation through a heat exchanger from the outside. A two-stage evaporative cooler combines the cooling effects of both the direct and the indirect processes.

Two stage direct/indirect coolers produce less humidity than direct or indirect. Air is passed through a heat exchanger which is cooled by evaporation on the outside. This pre-cooled air is then passed through a moist pad.

The pre-cooled air absorbs less moisture because of its already cooler temperature. This two-stage evaporative cooling process produces cool air with energy saving benefits and also cuts down on the humidity that is produced by a one-stage evaporative cooler.

Components of a Two-Stage Cooler

A fan blows hot, dry air over a rotating, moist pad cooling the air. The pad is kept moist by a tray of water fed by a tube. These cooling pads are made of wood wool or aspen wood fiber. They can also be made from plastic and melamine paper. This pad is contained in a plastic or metal box that is covered with vents that allow plenty of fresh outside air into the system. A fan or blower pushes the air through the box and into the room to be cooled.

Unlike air-conditioners which require all windows and vents to the outside be closed in order to keep the air cool, windows or ceiling vents need to be open when running an evaporative cooler. The large volume of outdoor air replaces the hot indoor air. This creates a fresh air environment as opposed to the stale air that you get with an air conditioner.

An evaporative cooler can be designed to be able to pump air through air conditioning vents or ducts and used to cool your entire house. They can be mounted on the roof, which produces a down draft or down flow. They can also be mounted on an exterior wall or window, which results in side draft or horizontal flow.


There are a great many benefits to using an evaporative cooler. They are comparably priced to air-conditioners of similar cooling capacity. They are less expensive to install than an air-conditioner. They are also cheaper to run.

They are very cheap to maintain. There are fewer parts to break and need fixed or replaced. They do not use any chemical refrigerants. This saves money. This also makes them a much more environmentally friendly way to cool your home.


There are also disadvantages to using an evaporative cooler. Although comparable in cost an evaporative cooler takes up about twice the area as an air conditioner. It requires a constant supply of water. This can be a problem in areas of extreme aridity and water shortage.

Although evaporative coolers eliminate the problem of stale, old air, the constant supply of fresh outside air can bring in odor and contaminants. They should be equipped with a filter if used in a home that houses people with asthma or severe allergies.

The following disadvantages are not an issue if you are using a two-stage evaporative cooler but are they are factors in direct cooling systems. High humidity decreases its ability to cool air, and humidity created by an evaporative cooler can increase corrosion and create condensation.