Evaporative cooling has existed as long as the Earth has had water on its surface, whether as oceans, lakes, ponds or streams. It is no accident that prehistoric animals and primitive humans sought out water sources, especially in hot environments, because they needed it to survive.
But proximity to water provided a powerful benefit beyond hydration – natural cooling.
Ancient Egyptian frescoes dating to about 2500 BC provide the earliest evidence that people developed systems to leverage the natural power of evaporative cooling. In these plaster paintings on temple walls, slaves are shown fanning urns filled with water to cool Egyptian royalty.
Remember those classic movies about Cleopatra and Moses that showed lush spaces and people lounging near interior pools? The architecture was more than a set director’s vision of how ancient Egyptian royalty lived. We know they designed enclosed spaces with shaded water ponds, pools and narrow rills of water to cool the surrounding air.
da Vinci’s sketches show type of evaporative cooling
Common Egyptians as well as Romans hung wet mats over doors and windows to help cool their living spaces. Wealthy Romans maintained a cooler air temperature in their homes cooler with water circulated from the aqueducts through pipes in the walls.
Medieval Persia (now Iran) is credited with building the first evaporative cooling towers that trapped wind and funneled it past water at the base and into a building. No other than Leonardo da Vinci, the great Renaissance inventor, thinker and artist, sketched an early mechanical air cooler as part of his exploration of energy and water.
His sketches show a water wheel with flaps or paddles that directed air as it passed over the wheel.
Fast-forward a few centuries. Settlers in the American Southwest hung wet sheets on porches to create a cooler spot to sleep. Some even wrapped themselves in wet sheets with a fan pointed on them – they achieved short-term relief from brutal heat but often developed pneumonia. Many cases were fatal.
Electricity accelerates evaporative cooling advancement
The biggest change, though accompanied widespread use of electricity in the early 1900s. In the Southwest, notably Arizona and California, air coolers – both direct and indirect – used water to create cooler air.
Early designs forced air through wet cloth attached to a wooden frame. Adding sump pumps or recirculating pumps kept water moving and became the foundation for machines known by different names, from wet boxes to drip coolers and desert coolers to swamp coolers.
In them, a fan pulls air through thick, wet pads but mineral deposits in the water clog these membranes, which need regular cleaning and maintenance. This traditional approach to evaporative cooling is also demands significant amounts of electricity and water.