Keeping the inside cool

When it starts to get above ninety outside, the inside is going to need some help to provide a comfortable environment. I hear Wally Byam put a floor vent in his trailer so he could get ground air to flow up and out through the roof vents.

These days, the usual custom is Air Conditioning. 13,000 BTU/hr cooling is needed for smaller RV’s and 30,000 or more for the larger class A’s. These are usually roof mount heat pumps although there are other options. The problem is that this method needs a lot of electricity. A typical roof mount RV A/C will run $500 – $1000.

To run an A/C off grid you will need a genset. A 3 KW unit is minimum and many RV’s will have 5kw or larger gensets. These have to be able to handle the initial current surge required by the heat pump compressor when it starts up as well as the continuous operation at fairly heavy load.

Reducing energy consumption is why a lot of folks look at evaporative cooling (aka swamp collers). This a great method for cooling in dry climates but suffer a bit when the humidity goes up. Evaporative Cooling (they make fabric for clothing that cools) says “To evaporate one gallon of water requires almost 8,700 BTUs.” Water Cooling Secrets says 8100 (this company sells misters for desert patio cooling).

A first hand account of swamp cooling an RV describes the ‘made for RV’ Turbo Cool and a customized cooler from an alternative energy specialist. The big thing to note is that he is looking at adding another 100 gallon water tank to his RV. At 8100 BTU per gallon, the evaporative cooler is going to need to evaporate more than a gallon of water per hour to keep up with even a small Air Conditioner. To do that will also mean a good blower that will probably draw current similar to a forced air furnace (5 to 10 amps). The cost of the swamp cooler is also near the same as for a heat pump type A/C

Swamp coolers also become rather uncomfortable when the afternoon thunderstorms show up and the air gets humid.

side note: Online Conversion – Ton of air conditioning is a discussion about a ton of air conditioning. 12,000 BTU/hr is cooling enough to make a ton of ice per day. So the small RV needs a 1 ton cooling plant and the larger ones 3 or more. The same discussion notes that a one ton cooling rate requires about 1400 watts electricity.

The Wikipedia article also has some interesting information.

Bigger is not Better has some interesting issues to consider when thinking about how much you need. Also see Selecting Size / Cooling Capacity

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