Monday, September 6, 2010

Camper refridgerator project

We own a pop-up camper that has an inside refrigerator. It can run on propane, 12v batteries, or 120v AC hook-up from the site. We've seen on multiple camper forums that one project/"mod" some people do is improve their fridge's efficiency. The main things people did were to add a fan and a better baffle (explained later). It wasn't too hard and the results were reportedly very good, so we tried it ourselves.

First, an explanation of refrigeration, the issues with the camper fridge, and the fixes.

Refrigeration is sort of a complex process that I don't fully understand. It involves the sequence of heating and cooling and pressurizing and depressurizing a coolant liquid so that it can be cooled (and re-cooled). One thing to remember if you're trying to learn the process is that, in physics, you don't "get cold," you lose heat/transfer heat/energy to something else. This is the idea of an important part of the refrigerator sequence, the cooling fins, which is what we dealt with and improved.

Cooling fins and fridge compartment with the working pieces (explained below).

The cooling fins are thin plates of metal attached to a tube. Heated liquid runs through this tube and gives it's heat to the air through the fins, effectively cooling down. Thin metal plates are used because they radiate heat easily because of their thickness. The heat would not as easily radiate out of the thick tube itself. Normally, new, colder air flows through the fins by convection, which is the principle that hot air rises and cold air sinks (the cooling fins are at the top of the fridge unit to catch all the moving air). But if you add a fan, you can blow or suck the air through the fins faster and more effectively. This is what we did with our camper.
As an analogy, this is similar to a car's radiator. To keep it from overheating, a car pumps coolant through its parts, mainly the engine. This fluid takes away the heat from the engine (remember, you don't "get cold," you lose heat). The coolant is now hot and must be cooled to be used again. It is piped to the radiator, which is at the front of the car. If you look through a car's front grill, you'll likely see all the thin plates of the radiator. This radiator has many more fins and is much bigger than a camper's cooling fins. There are also multiple tubes that share the fins (many smaller tubes radiate more heat than one big one). When you drive, flowing air blows through the radiator fins and take the heat from the fins and coolant. Some (most?) cars have fans that start to blow the air if the car has been sitting still for a while.

Another part of the fridge you can improve is the baffle. This is just a separator, a wall so to speak, that separates the incoming air from the used, "hot" air that has gone through the fins. If there was no baffle, especially when just using convection, the air could flow around and go through fins again, or not really go anywhere. Furthermore, a baffle helps to direct air only through the fins, instead going around them and out the camper (like the hot, used air). The previous baffle on our camper was a pitiful board that was too small to do anything whatsoever to section "in" from "out." There are multiple ways to make a new baffle (types of materials, shape, etc), but the idea is to make a successful seal.

Pictures of Modifications:
General picture of above area modification. We found some metal L-brackets to mount the fan (Radio Shack 12v) and stapled and taped some Refletix inside as a baffle. Refletix is a bubble-wrap-shiny-plastic material you can buy in rolls, mostly for insulation. For here, it's easy to shape to the area. The silver ducting tape is stiff and provides support for the bends.

Close-up on cooling fins and inside:

Lower area with added switch for fan. This taps into the 12v battery wires on the bottom left that powers the fridge. The other fridge controls are also here. Note the red and blue wires on the left going up to the fan.

Close-up on switch. Bought one from Radio Shack and made a box to hold it out of sheet metal/flashing. Crude but it works. Screwed it down and folded it up.

The baffle seems to have done the most work and the fan only really works on very hot days. Before the modifications the fridge kept itself at about the low 60s F. After, we can keep it at the 50 degree mark. Other people have reported different levels of efficiency on camping websites and forums. It depends on the model of fridge and how good of a job you do. We could have gone all out and made a perfect seal with the baffle by covering up the sides of the cooling fins too.

Hope that was interesting and possibly helpful for any other projects!

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