An Introduction to Swamp Coolers: What They are and How They Work

Swamp coolers—also known as evaporative air coolers, desert coolers, or wet air coolers—are an economically and environmentally friendly way to lower the temperature and add moisture to the air around you. They use the natural process of evaporation to cool your environment, providing more effective cooling than traditional fans without the financial and environmental costs of air conditioning systems.

Where do swamp coolers come from?

The concept of utilizing evaporation—the process through which liquid is turned to vapor—can be traced back to ancient Egyptian and Persian societies.  Persians, for example, used a form of evaporative cooling in which a structure called a windcatcher directed wind over a channel of water called a qanat, using the evaporation process to cool buildings. In more recent history, people sleeping on porches or inside with their windows open used to hang up wet linens and use fans to circulate cool, moistened air.

So, why are they called “swamp coolers”?

At this point, you might be wondering where the unique phrase “swamp cooler” comes from. In the initial days of mechanical evaporative coolers, Aspen pads were used to absorb water and utilize evaporation’s cooling powers. Unfortunately, this created a moldy, musty smell reminiscent of a swamp. But don’t worry—evaporative coolers have come a long way since the days of musty wooden cooling pads.

Exactly how do they work?

As previously mentioned, evaporative air coolers function by using the process of evaporation. Now, imagine you’re standing outside on a brutal July day, perspiring through your shirt and desperate for some refreshing reprieve. But then you step in front of a fan and the breeze running over you evaporates the sweat, dropping your body temperature.

How exactly is this possible? The process of evaporation produces a mixture of air and water molecules, a process that requires heat energy. The heat then dissipates, and you are left with cool, moist air. This is why evaporative cooling naturally occurs near waterfalls and lakes: Whenever dry air passes over water, some water is absorbed by the air, making it moist and cool.

To mimic this effect, evaporative coolers use a fan, a water tank, and a pump system to draw in dry air through a wet cooling medium that absorbs and retains water from the reservoir. These media, or cooling pads, are usually made of corrugated cellulose sheets that are glued together and chemically treated to prevent rotting (and that ol’ swampy smell). The fan draws warm air through the media, where evaporation converts water into water vapor and blows now-cooled air out the other side. Honeywell Evaporative Air Coolers use honeycomb cooling media, which allow for greater cooling efficiency because their increased surface area encourage more humidity to transfer into the passing air.

The extra moisture in the air then promotes evaporative cooling on your skin, which is more effective than experiencing airflow alone. And don’t worry about getting all wet from the extra moisture—it isn’t sprayed out like a mist but instead raises the general humidity level of the surrounding area. The temperature of the air emitted from the cooler depends on the temperature and humidity of the air entering the cooler. This means that in hotter, dryer climates, you will experience a greater drop in temperature than you would in a less warm, more humid climate.

When using indoors, you should always provide ventilation by opening a window or door when using an air cooler to allow warm air to exit the room while it is replaced by cool air. Ventilation also prevents indoor locations from feeling clammy due to oversaturation.