When Swamp Coolers Stop Working

I received an email from a viewer about swamp coolers. Armando wants to know when it becomes too humid for the units to operate properly.

Well, Armando, I was first introduced to swamp coolers when I worked for a television station in Amarillo. I was amazed how they worked. I always enjoyed the humidity it brought to a dry home in a dry climate.

In El Paso, swamp coolers become inefficient when it becomes too humid. This begins to occur during the month of July when our monsoon kicks in. That’s when our humidity begins to shoot up along with our temperatures.
As most of you know, our evaporative coolers first cool the outside air and then blow it through our homes. The higher the outside air temperature the lower the humidity needs to be in order to drop our inside temperature the most. For example, if the outside temperature is 90 degrees or more (typical for the month of July and August here in town) and the relative humidity is 50 percent, then the swamp cooler can only cool our home to just about 80 degrees (about a 10 degree drop). If there is only about 10 percent humidity, the house will cool even more – to about 70 degrees (20-25 degree drop). So, as you can see, humidity makes a big difference. You’ll notice this yourself on a hot and humid day. The process of evaporation cools your body when you perspire. The more humidity there is, the less your body can cool itself.
Evaporative coolers operate great in the months of April, May and June. But once July, August and September arrive, those swamp coolers work about as good as a fan.