Definition of Evaporative Cooling

Evaporative cooling is becoming increasingly relevant as energy costs continue to skyrocket, because it can be up to 80 percent more efficient than classic refrigeration or absorption air conditioning. Evaporative cooling is simply cooling of air or anything else by the evaporation of water or other liquids.
It is easy to illustrate by merely pointing out the effectiveness of perspiration cooling, the human body's own built-in evaporative cooling system. Evaporative cooling works best in warm, dry climates such as is found in the Southwestern United States.

Latent Heat

Whether from a boiling pot or a wet towel, water takes about the same amount of heat to vaporize, or turn from a liquid, a lower energy state, into a gaseous form, a higher energy state. This is called the latent heat of vaporization, and the heat source is any material or space from which or in which the vaporization takes place.

Preferential Environments

Dry air has a particular affinity for moisture because water has such a low partial pressure due to water, and it is relatively easy for molecules of water that are moving rapidly to be absorbed by the dry air and assumed in a gaseous form. This is why the visible spires of water vapor rising off a hot cup of coffee disappear only several inches above the cup. Therefore, evaporative cooling is far more effective in dry locales, such as deserts and prairies, as opposed to tropical and subtropical climate zones, such as Florida.

Perspiration

There is nothing quite like a brisk breeze on a hot day, because more strident air movement presents perspiring skin with a much higher volume of air with an affinity for water. Ceiling fans provide even and steady air movement, which is often just enough to keep diners or sleepers in tropical climes cool and comfortable. Dogs pant on a hot day because they only perspire through their tongues, and the panting or rapid breathing instinctively increases the amount of air passing over the tongue, which absorbs the water that causes the evaporative cooling.

Nature's Cooling

Trees evaporate enormous amounts of water into the air through their leaves, which is why many vacationers prefer a cool stroll through a dense, tall forest on a hot sunny day to a walk on a beach.

Direct-Indirect Cooling

The only downside to evaporative cooling is that the air becomes more humid as it is cooled, which can be a tradeoff on a hot, muggy day. For this reason, indirect systems evaporate water outside of recirculating air ducting, so that a portion of the heat absorbed comes from the living quarters, without the added humidity, which is subsequently exhausted outside.

References

• Consumerenergycenter.org
• Colorado.edu
• Evapcooling.org

Resources

• About.com