Evaporative Cooler Efficiency

If you feel that you are having a problem with your evaporative cooler because the air coming out is not very cool, you may not have a problem other than you have an evaporative cooler. 

I am not trying to be sarcastic, but there is an equation called “The Wet Bulb Depression” that calculates the outside air temperature plus the humidity present in the air that determines the discharge temperature of your cooler.

For example, the present temperature in Tucson is 96 degrees F and the relative humidity is 25%, using the WBD formula, if the cooler is working properly, the discharge temperature should be around 75 degrees F. However, this afternoon when the temperature has risen to 105F and the RH is 40%, the discharge temperature at best will be 88F. Not too comfortable especially because of the increased humidity.

If you want to find out if your cooler is doing the best it can do, here is the formula:

(Outdoor Dry Bulb minus Outdoor Wet Bulb) X .2 + Outdoor Wet Bulb = EXPECTED COOLER DISCHARGE TEMPERATURE

You can use a wet bulb calculator from the internet to determine the wet bulb temperature by inputting the temperature and relative humidity from a weather service page.