Humidity Perceptions and Evaporative Cooling Efficiency


When it comes to how we humans feel temperature, it can be difficult to separate fact from perception. Humidity throws an extra wrench in things. When we check the weather and see a high humidity percentage, we know we’re in for frizzy hair, clammy skin, and the temperature feeling warmer than it actually is. But how does humidity affect the efficiency of evaporative cooling? To determine that, we’re going to dive into the science behind humidity.

In a Portacool evaporative cooler, water is pumped over the Kuul Comfort™ evaporative media from a built-in reservoir. When air is pulled through the media, the interaction between water and air causes the water to evaporate and heat to be removed from the air. The result is fresh, cool air from the front of the evaporative cooler.

The humidity we usually hear about in weather forecasts is relative humidity. According to How Stuff Works, relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity, which depends on the current air temperature. In simpler terms, it’s a measure of the amount of water vapor in the air relative to how much the air can hold. As air warms, it can hold more moisture. As the air cools down, its ability to hold moisture decreases. A Forbes article makes a comparison using a sponge. Warmer air is like a larger sponge that can hold more water. Colder air is like a smaller sponge that can hold less water. If both sponges are half-filled to capacity with water vapor (half = 50%), the warmer air holds much more moisture. However, in both cases, we say the relative humidity is 50%.

How does humidity affect evaporation?

Assuming standard atmospheric pressure, water will evaporate anywhere between solid and gas forms. In this space, the amount of cooling you can expect has to do with the distance between your wet bulb and dry bulb temperatures. If the humidity level, or wet bulb temperature, is below 100% there is room for some evaporation. The higher the air temperature, or dry bulb temperature, the faster evaporation can happen, and the cooler the air will be. So, the more space there is between the humidity level and the air temperature, the higher your evaporation efficiency will be. Put simply, this is why evaporative cooling can achieve nearly 30-degree temperature drops in hot and arid climates like that of Arizona.

Portacool customers on the East coast have found Portacool evaporative coolers to provide much-needed relief. Although the temperature drop may not be as substantial as it is in arid climates, those that work in the humidity agree that even a 10-degree drop can make a huge difference when it’s 100° F outside.  We often hear from happy business owners from New Jersey to Florida who rely on this cooling method to achieve cooling that keeps their workers comfortably productive when the heat is unbearable.

While evaporative coolers do utilize water to provide cooling, it is important to note they do not spit, mist, or spray water. Additionally, if operated correctly and used with adequate ventilation, Portacool portable evaporative coolers should not produce any noticeable added humidity or moisture to your environment. If you believe your evaporative cooler is adding too much humidity to your space, be sure to introduce more ambient air by opening an additional door or window – or use the water adjustment valve to reduce the amount of water flow over the evaporative media.

Please note, however, that by reducing the amount of water flowing over the evaporative media you are also reducing evaporative efficiency. That said, sometimes it is worthwhile to sacrifice a bit of efficiency to reduce humidity levels. In the past, evaporative cooling companies, including us, have advised having a few dry streaks on the evaporative media was optimal. That is simply not true. When possible, the evaporative media on the back of your evaporative cooler should be totally saturated. Any dry streak that appears is an avenue for warm air to enter the stream, affecting your cooling efficiency.

Overall, humidity may have some effect on the efficiency of evaporative cooling in terms of significant temperature drops, but Portacool coolers can provide a degree of perceived cooling relief in any environment – arid and humid.