How Effective are Evaporative Coolers?

February 26, 2014 5:57 pm

Most people will remember the sensation of climbing out of the swimming pool on a hot day, and feeling the chill as the water evaporates off of their soaked body. Or how many times have you climbed out of a hot Jacuzzi in colder temperatures and thought that your swimsuit was going to freeze onto your body; even though it was just in hot water? This is what happens when water evaporates; when it’s combined with a breeze or movement of air, it gets cold! This is also the same principal that is used to cool buildings on hot, dry summer days using an evaporative cooler, more commonly known as a “swamp” cooler.

Evaporative coolers have roots that can be traced all the way back to the ancient Egyptians. They would hang wet blankets in the windows and doorways of their abodes, allowing the air to pass through them, cooling the breeze to a comfortable temperature. The wealthy citizens would employ servants to use large fans to create a breeze for that “extra” chill.

A typical air conditioner uses vapor-compression or absorption refrigeration to produce cool air. While these methods are a godsend on hot days, the mechanisms can be complicated and difficult to understand. The swamp cooler is a very simple device, usually mounted on the top of a home, providing cool air into the ducts and throughout the building. However, the swamp cooler is not limited to outdoor placement; there are coolers that can be utilized indoors as well, as long as there is a source to pull in the dry air. It is relatively inexpensive and doesn’t use near the energy that other forms of air conditioning use. According to the National Association of Home Builders (NAHB), the monthly operating cost of the swamp cooler is only about one third that of a standard air conditioner.

How it Works

The mechanics of a swamp cool are simple, and quite easy to understand. As an example, let’s take a look at a rooftop model. There are only a few components. The first component is the shell, or box, which is not unlike the shell of a regular air conditioner. It sits atop the roof, positioned over a vent opening that goes into the home and connects with the central ductwork. The sides of the box are vented to allow easy passage of air into the box. Against each of the four vented sides there are fibrous pads (the second component). A small water pump (the third component) draws water from a water source running up to the cooler and distributes it to the top of each of the pads, allowing it to trickle down through them, keeping them moist. Inside the box is a blower fan (the fourth component) that pulls air into the box from the outside, forcing it through the saturated pads and cooling the air as it does. The cooled air is forced down into the ductwork, and is distributed throughout the home. What makes all of this possible is that the liquid evaporates by dispersing water molecules into the open air as it changes from a liquid to a gas. These suspended molecules absorb heat from the surrounding air, which cools down as the water and air find equilibrium.

Are Swamp Coolers the Same as Air Conditioners?

The standard air conditioner generates cold air by passing it over a series of coils that have a refrigerant (Freon) running through them. The coolant heats and cools as it compresses or expands, cooling the air that is distributed into the home or building, and expelling the hot air to the outside. It is then re-circulated and the process is continued as long as the air conditioner is turned on or until the desired temperature is reached. If a window or a door is left open, it allows cold air to escape to the outside, and warm air can enter into the home. This makes the air conditioner work extra hard to compensate for the temperature difference. In other words, the air conditioner is a closed system.

A swamp cooler is different, insomuch as there is a need to have a door or window open in order to allow the air being pushed in to circulate, creating a constant cool breeze throughout the home. It’s almost like blowing up a balloon. Air is being pushed into the home and once it is pressurized, there is no call for more, and the swamp cooler cannot force more air in. In other words, evaporative cooling is an open system.

Disadvantages of a Swamp Cooler

As great as swamp coolers are, there are a few downsides. First, the swamp cooler is only effective in a dry climate. If the air is already saturated with humidity, the water evaporation process won’t take place. Moisture cannot evaporate moisture. This means that if you live in a high humidity climate, the swamp cooler won’t work well for you.

Another caveat with regards to evaporative cooling is that it can create condensation in your home if the air becomes too saturated with moisture. According to the Environmental Protection Agency, if the humidity in your home becomes greater than 60%, it may be difficult to control mold and mildew. Hence, it doesn’t pay to run an evaporative cooler in your home during high humidity levels.

There is a degree of maintenance that must accompany a swamp cooler. The pads should be changed or cleaned regularly so you don’t get that “swampy” smell in your home. If the area you live in has a large amount of mineral content in the water, you will have to clean the cooler more often, de-scaling it as needed. Another thing to bear in mind is that swamp coolers require a constant flow of water when they are cooling. According to the NAHB, depending on the size of the unit, they can require from 3.5 – 10.5 gallons per hour.

If you have any questions about evaporative cooling verses standard air conditioning, don’t hesitate to call us at Hassell Air Conditioning and let us fill you in.

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