The Complete Handbook of Evaporative Coolers

Chapter 1: Understanding Evaporative Coolers

Every cooling technology has a defining principle. For evaporative cooling, that principle is the absorption of heat during the phase change from liquid water to water vapor. When water evaporates, it extracts a significant amount of thermal energy from its immediate surroundings. This phenomenon, known as the latent heat of vaporization, is the engine that powers every evaporative cooler on the market, from a small portable unit on a workbench to a large industrial system on a factory floor.

The practical application of this is straightforward. A cooler pulls warm, dry air from the outside, passes it through a saturated pad or medium, and uses the heat in that air to evaporate the water on the pad. The air loses heat and gains moisture, and that cooler, more humid air is then blown into the space you want to condition. The energy that is "lost" from the air is not lost at all; it has been transferred into the water molecules, changing them from a liquid to a gas. The result is a measurable drop in the air temperature.

Consider a concrete example. On a hot afternoon in Phoenix, Arizona, the ambient temperature might be 38°C (100°F) with a relative humidity of 20 percent. A well-designed evaporative cooler can bring that air down to approximately 24°C-26°C (75°F-78°F) as it enters the living space. That is a very real, very usable temperature drop. But the same cooler operating in Houston, Texas, where the temperature might be