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Can you cool an RV with solar power?

Updated: May 27, 2020

Before you read any further, let me tell you that this blog is about swamp coolers, not air conditioning. For those of you who don’t know what a swamp cooler is, it’s also called an evaporative cooler. They work on the time honored principal that converting liquid water to gaseous water absorbs a lot of energy. Swamp coolers can easily be powered by a few solar panels and small batteries.

Spoiler Aert! Here are the results of this swamp cooler experiment

1) Cooled entire 33' 5th Wheel trailer from 100F to 80F in 2 hours.

2) Used about 10 gallons of water.

3) Used only 250W of electricity (20AH out of a 12V battery) !

How do swamp coolers work? They trickle water through a filter, and blow a lot of air through the filter. As the air blows through, the water EVAPORATES and absorbs a LOT of heat from the air. So the air going out is MUCH cooler than the air coming in. In order for the water to evaporate, the outdoor relative humidity must be very low. Swamp coolers don’t actually work in a swamp, where the humidity is high. They don’t work in most of the southern states from Florida to Texas, because the humidity is high. But they work fantastic in the western states, where the humidity is low. A word of warning: too high of humidity inside an RV is a VERY BAD thing. Try to keep the humidity in your RV below 60% at all times.

Swamp Cooler mounted in window on RV

I’m currently living in my 5th wheel trailer in Grand Junction Colorado, which is also where our solar workshop is located. The average humidity in Grand Junction is around 10% in May, June and July. This is perfect humidity for cooling with a swamp cooler. Here is a picture of my swamp cooler conversion for my RV. Don’t laugh too much! I’m an electrical engineer and physicist, not a carpenter! The barrels are to provide a water source for the swamp cooler.

Here is a picture of the swamp cooler from the inside. It is mounted in the emergency exit window at the back of my RV. I cut a piece of styrofoam to get the swamper to fit the window opening. It needs a little more duct tape to seal it against bugs, but I’ll get to that later ;-)

For a swamp cooler to work, it has to move a LOT of air. Therefore, you have to open a window at the opposite end of the RV. Here is a picture of the open window in my bedroom at the front of the RV. If I opened the door or a roof vent, all the cool air would exit there, and I need the bedroom cool to sleep so that is the only window I open.

View of the bedroom window at front of RV

📷 The swamper pulled the hot air in the back of the RV, cooled it by evaporating a LOT of water, and then blew the cold air through the RV to exit out of the bedroom. This is a key part of a swamp cooler, it must have a LOT of air flow in and out of the RV. This is COMPLETELY different from an air conditioner, which must re-circulate the air in the RV.

After a recent fishing trip to Blue Mesa (see the Fishing Blog) I returned home to find my 5er at nearly 100 degrees inside. The outdoor temperature was about 97 all day, so apparently parking in the shade helped a lot, but 100 degrees is intolerable. So I decided to do quick experiment in swamp cooling. Here is what I did:

1) Filled the swamp cooler with water and turned it on.

2) Recorded the temperature in the main cabin and in the bedroom by taking pictures of the wall thermometers there.

3) Every so often, recorded the temperature again.

I have a nifty thermometer in both the main cabin and the bedroom that displays temperature, humidity and time. I changed the main cabin thermometer to Eastern time zone, and the bedroom thermometer is Mountain Time Zone, so we could easily tell which thermometer I was taking the picture of. Remember, I had just gotten back from a long fishing trip, and had a ton of stuff to do, so I only managed to take the pictures every so often. But at least they gave me a record of how fast the temperature came down and the humidity in the RV went up.

Here are a couple of the thermometer pictures. Remember, it was about 7:30PM at night, but the sun was still beating directly on my RV with great intensity.

Main Cabin Thermometer, it's actually 7:25PM

Here are the charted results with times, temperatures and humidity. Notice how much the humidity increased inside my RV.

Temperature in degrees F, humidity in %

Is that amazing or what? Here is the most amazing part, I run my swamp cooler off of nothing but my solar panels and batteries! A swamp cooler is a small water pump and a fan. Only draws about 90W on low and 125W on high. Compare that to a typical RV roof Air conditioner that draws 1500W. I had to refill the swamp cooler every 45 minutes or so with 3 gallons of water. I use two 55 gallon barrels and a pressure pump that does this automatically.

The amount of heat a swamp cooler can push out of an RV is directly proportional to the relative humidity and how much water you evaporate. The more heat you need to remove, the more water you need. This particular experiment required about 9 gallons of water, but I didn’t measure it precisely because I was busy cleaning and preparing the fish we just caught for dinner!

The best part of the day.

I could not survive in my RV in the Colorado summer without a swamp cooler. But what happens when the monsoon season hits in late July and August, and the humidity goes way up? We’ll do another blog then on how to manage that with air conditioning and dehumidifiers.

My swamp cooler install is more or less not portable. But I have found a great portable swamp cooler that I carry with me in my RV for those time when I'm traveling and need a breath of cool, humidified air.

Hope you enjoyed this blog. If you want to discuss the physics of evaporative cooling, please email me rather than try to do it in the comments. For more information, go to

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