Since we decided to settle in the San Diego area, Shelly and I have confronted a few issues related to RV living. The most serious may be dealing with the heat. We’re residing in the East Country area about 30-40 minutes from the Ocean, which pretty much kills any cooling effect from the water. Daytime highs will routinely hit 100°+ once July hits. With no cooling at all, the temperature inside the trailer will reach about 5° below the exterior temperature.
The problem stems from the design of RVs. It’s basically a giant solar cooker, and the on-board air conditioning system will only cool the interior temp about 10-15° below the exterior temperature. And it’s crazy expensive to run all the time.
I’ve had an interest in green building technologies for some time. This particular problem should be able to be easily solved with a little ingenuity. ‘ll get the opportunity to bust out my “layman engineering” skillz. I’m by no means an expert, but I do have a working knowledge of the very basic principles of heat transfer. So… what can be done to cool the trailer?
First, the guidelines. Any solution must meet the following criteria:
1. It has to be cheap. Money is tight, so I have a very limited budget. Besides, I find the “have to do it for close to free” limitation really flexes the creativity muscles.
2. It has to be fairly discreet. Since we’re in a campground, we can’t use anything that’s unsightly, noisy, or gives off offensive odors.
3. It has to be compact. We have around 350 square feet of living space. I can’t fill it with a huge contraption.
With this in mind, I brainstormed the following solutions:
- Swamp cooler. This evaporative cooling device is common in the Desert Southwest. At the most basic level, it’s a device that passes dry air through a material saturated with water. The water evaporates, which cools and humidifies the air.
- Shading. Any method of preventing the sun from directly hitting the outer surface of the RV will eliminate some of the radiant heat transfer from the rays of the sun.
- Radiant barriers. Using reflective devices on the exterior of the RV serves the same basic purpose of shading, but with a different application.
- Solar chimney. This is a device used to remove hot air from the interior of a structure using the “heat rises’ principle. Unfortunately, it requires a source of cooler air, which often comes from either underground tubes that act as heat exchangers (can’t dig in the campground) or a cooling tower. Besides, the campground would likely nix both ideas since the towers would have to be relatively tall.
- Air movement. This idea uses the principle of convection and buoyancy (hot air rises, cool air sinks.) Air moving across a surface will cool the surface faster.
There are a few other methods or ideas that could theoretically be utilized, but they would violate the three necessary rules from above.
So which of these methods can be used?
Step one: Control radiant heating. Shading and the use of radiant barriers are methods are easy to implement. We have a shade tree that provides shade early in the day, which helps. The next step is to block sunlight from entering the trailer windows. Based on positioning, most sunlight enters the three windows on the left side of the trailer. I’m not a fan of awnings, which are a pain in the ass if we decide to move again. Covering the interior of the window is a better solution. Solar shades, which block the sun but allow you to see, will cost about $150. I’ll opt for slightly less efficient light-blocking shades from a local department store. If I had a larger budget, I would install 4′ X 8′ sheets of foil-backed foam on the roof to reflect solar energy during the day. That may be a future consideration.
Step two: Build an evaporative cooler. The swamp cooler design will be based on this model because it’s compact and portable. I’ll make mine out of a garbage can. Instead of using a water pump to keep the water pad wet, I’ll use a soaker hose normally used for gardens. It will be connected directly to the water supply. I’ll set up the cooler outside the trailer (dry incoming air is a requirement, it cannot be recirculated) and vent the exhaust into a window at one end. This will allow cool, most air to be pumped into the trailer during the hottest part of the day.
Step three: Circulate air. Moving air will affect the perceived comfort level. More importantly, I have to vent the moisture from the swamp cooler. To accomplish this, I can use the solar chimney principle inside the trailer. The cool, moist air will be pumped in one end. At the other end, I’ll install a fan on the roof vent that will blow air out. Since the warmer air rises, it will continually eliminate the hottest air in the trailer. Ideally, the vent fan would be solar-powered same with the fan for the evaporative cooler.) Unfortunately they are outside the current budget constraints. Standard AC fans will be used instead.
It will take some time to build the entire setup, which I will document here. In the interim, I’ll take temperature measurements to serve as a baseline. Stay tuned for the results of the experimentation!