The history of swamp coolers may go back as far as 6000 years and stretch to the opposite side of the Earth. That’s because this technology is incredibly intuitive, effective, and efficient. Wherever people are looking to cool themselves efficiently, this technology comes up, sometimes passed down directly, and other times developed independently because it just makes sense.
Swamp cooler is a common synonym for an evaporative cooler. Swamp coolers are also sometimes called desert coolers or wet air coolers. An evaporative cooler cools air by using it to evaporate water. Water can absorb a tremendous amount of energy before it evaporates. When it is evaporating in the open air, it takes that energy from the air, cooling it.
Evaporative coolers use basically the same mechanism as sweating. In fact, it is the same cooling mechanism used by almost all terrestrial plants and animals, although we all do it slightly differently.
Plants use a form of evaporative cooling we call transpiration. On plants’ leaves are tiny pores that let water move to the surface of the leaf. When this water evaporates, it cools the plant. Plants even have mechanisms to increase this effect, such as expanding their leaves and stretching themselves up higher from the ground – until, of course, they lose too much water, and the loss causes them to sag (wilt).
When dogs pant, they are cooling themselves evaporatively. Water from the lining of their nose, throat, and lungs evaporates, cooling their bodies. Dogs even have distinct blood vessels that work as heat exchangers between their nose and their brain, helping to keep the brain cooler than the rest of the body.
Cats also use a similar mechanism to keep cool. While the primary purpose of licking their fur is for grooming, it also provides importation temperature regulation functions. The moisture on a cat’s fur when it grooms itself evaporates, cooling its body.
Pigs and other animals that wallow are using evaporative cooling. They coat themselves in mud, then let the water from the mud evaporate, cooling their bodies.
It’s hard to know exactly when humans started using evaporative cooling. From very early human history, people began adding fountains to their architecture. This is a passive way to utilize evaporative cooling. As air passes over the fountain, some of the water evaporates, cooling the air. Bubbling or spraying water increases surface exposure for the water, increasing evaporation. Though this is more like a mister than an evaporative cooler, the two are closely related.
We know that ancient Egyptians used to hang wet blankets or reeds across their doorways. This would cool the air entering their homes.
A more definitive form of evaporative cooling began in very ancient times. People living in the deserts of Iraq and Egypt tried to cool their homes with special chimneys designed to catch the wind. These structures would direct cool air into the home, which would push out warm air. These structures may have been in use as early as 4000 BC. We don’t know exactly when, but by the 5th century, it seems that people were adding pools of water to these wind towers so that the air entering buildings would be further cooled upon entry. This, arguably, was the first of what we would recognize as a swamp cooler, with forced air deliberately being used to evaporate water for cooling.
These structures were highly effective, even by today’s standards. They could drop the temperature of the interior spaces by up to 18° F without using any electricity or motors whatsoever.
Swamp coolers were also used on a smaller scale. For example, ancient Egyptians would cool water for drinking by placing it in a porous jug. Water passed through the pores and evaporated, cooling the remaining water. Wrapping the jug in a coarse cloth would increase the area of exposure between the water and the air, increasing the power of cooling.
Although these are all good examples of swamp coolers, it wasn’t until the 20th century that we would get what we currently think of as a swamp cooler. Then, several people patented forms of swamp coolers for use in homes, businesses, and food storage facilities.
These swamp coolers generally used an evaporative medium, such as wood wool. An evaporative medium works like the cloth around the water jug: it increases the surface area for contact between water and air. This increases the ability of the water to evaporate, which improves the cooling effect. The evaporative medium sits in a pool of water, whose level is controlled by a float valve. A fan forces air over the evaporative medium. This further encourages the evaporation of water, leading to more cooling.
One interesting application of swamp coolers in the early 20th century was car coolers. These were basically tubes that attached to the outside of cars. They were filled with water and had an evaporative medium in them. As the car drove, it forced air into the tubes. This evaporated water and cooled the air. Cooled air was then directed into the interior of the vehicle. These remained in common use from the 1930s to the 1960s when efficient compressors allowed air conditioning to be placed in cars, although these had (and sometimes continue to have) a noticeable power drain on the car.
At Portacool, we have mixed feelings about the term “swamp cooler.” On the one hand, there is a primitive connotation and unclean odor to the term that is hard to reconcile with the very clean and advanced machinery that we produce at our Center, Texas manufacturing facility. In particular, our latest development, the Portacool 510, is so advanced it seems to defy association with a label like “swamp cooler.”
On the other hand, if the term links us to the long, proud tradition of evaporative cooling, we’ll let you use it, although we would say it’s not a swamp cooler, it’s a Portacool.