How Humidity Effects Evaporative Cooling

Throughout the years, we’ve often heard the refrain that evaporative coolers will not work in humidity or in various areas of the world because of humidity levels. There is without a doubt a pervasive perception that evaporative coolers will not work in humid climates. While we agree that evaporative coolers achieve significant temperature drops in more arid climates and drier spaces, we know they CAN provide relief from the heat in any climate due to the advancements in evaporative cooling technology. Our customers from the south central (East Texas and Louisiana) to the southeast (Alabama to Florida), to the upper east coast (New York and New Jersey) are good representatives of the cooling relief Portacool portable evaporative coolers can provide regardless of the climate.

One of our customers in Florida said, “I’ll take a 13°F degree [temp] drop within an hour any day. The temperature in the shop in the middle of the day was 89°F with the Portacool coolers running, but until you’ve had to work in a 100°F shop, you don’t realize how great 89°F feels!”

So, let’s start with the basics behind how Portacool products work. Then we’ll discuss the science behind humidity and its effect on evaporative cooling efficiency.

How Evaporative Coolers Work

Evaporative cooling systems use water to cool air naturally. They should not, however, spray water or produce any mist or fog. In our Portacool products, the water used for evaporation is propelled up by a pump and distributed over our exclusively engineered Kuul™ evaporative media (often incorrectly referred to as “cooling pads”). Hot or warm air is pulled through the media and interacts with the water to complete the process of evaporation. As the water evaporates, the hot air is cooled. This chilled air is then distributed through the front of the evaporative cooler by a fan.

Now let’s tackle how humidity comes into play relative to achieving evaporative cooling efficiency.

Scientific facts on humidity

Regardless of what you might have heard, if the humidity level (wet bulb temperature) is below 100% there is room for SOME evaporation. The higher the ambient air temperature (dry bulb temperature) is, the faster evaporation can happen and the cooler the air will be. The more space between your wet bulb and dry bulb temperatures, the higher your evaporation efficiency will be.

In layman’s terms, the bottom line is this: as temperatures rise (it gets hotter), humidity levels go down (it gets dryer). That means on a typical day, humidity will be higher in the morning when it is cooler. That humidity will reduce as the mercury rises and it becomes hotter in the afternoon.

Put more scientifically, when the air temperature (dry bulb) goes up, humidity (wet bulb) will go down. Of course, rain is an exception to the rule.

Honestly, most of us are not good at judging how hot it is or what the humidity level is without measuring equipment, such as thermometers and hygrometers. Under natural conditions, it cannot be 100°F with 90% humidity even though we as humans will declare an oppressive outdoor climate, saying “It feels like it’s 110 degrees with 99% humidity.” We understand that it feels that oppressive, but scientifically, it cannot happen.

Portacool evaporative coolers CAN drop the air temperature up to 30°F when the air is very dry such as arid climates of the Southwest where relative humidity is typically 30% or less. That said, even in hot and humid areas such as Houston, you can still expect to achieve a 10°F-13°F drop in temperature.

Our own experience with humidity

We as a company know hot and humid conditions all too well. We are located in the small East Texas town of Center near the Louisiana border, and we are afflicted by this climate for a majority of the year. We use our own portable evaporative cooling products to keep our manufacturing employees safe and comfortable for more than half the year!

Example temperature & humidity graph

Here’s an overview example of the heat/humidity with expected temperature drops from evaporative cooling:

*The temperature drop provided only reflects the performance of Portacool’s Kuul Comfort™ evaporative media. The drop does not factor in the velocity or volume of the air provided by our high-performance fans (wind chill). The “real-feel” or perceived temperature will be cooler. Results will vary based on your current conditions.

**The examples shown represent average July conditions of the listed cities.

Evaporative Cooling is a Practical Solution

Portacool portable evaporative coolers are a reasonable option for creating a more comfortable environment where air conditioning is not practical. From the manufacturing facility, automotive garage, barn, porch, shed, dugout or football sidelines a portable evaporative cooler helps you better enjoy outdoor activities and spaces on hot days.