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Heat Exchanger Brumation Chamber - Plans with link to pics

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Posted by Brian Macker on February 21, 2002 at 22:08:22:

Thought you might like to check out the brumation chamber I made. It's an old refrigerator with a homemade heat exchanger. The resulting chamber will maintain proper temperature, air circulation, and will not be overly humid. Plus you will save on energy costs.

A counter current heat exchanger is an extremely efficient means of preventing heat loss. This is a concept often used in nature. For instance, the arteries and veins of ducks legs lie next to each other to allow the body to stay warm while the feet are cold. In this case we wish to pump fresh air into the fridge without warming it. The heat exchanger consists of two long copper tubes that are taped together. One is for ingoing warm air and one for the outflow of the cold air. The exchanger is so efficient because there is small differential in temperature along the entire length of the tubes allowing heat to pass from the warm to the cold air. In fact when in operation if you feel the exposed ends of the exiting cold air it is nearly at room temperature. If you feel both copper tubes at once it is next to impossible to tell which is the ingoing and which the outgoing air.

Both tubes MUST have a separate air pump attached to them. If you just blow air in the warm air tube then it will just go out the crack in the door. Likewise if you just suck air from the cold air tube warm air will seep in through the door. Only if two identical pumps are used will their be a balance of air flow that will not lead to air leakage through the door.

I took a old double air aquarium pump and opened it up. I then figured out a way to make one pump suck air while the other I left alone. DO NOT USE aquarium air tubing as it WILL collapse and your snakes will suffocate. Use the stiff plastic tubing you can get from Home Depot. Every pump is different so the way I rigged mine may not work for you. Do this job first as it is most difficult to get right. If you cannot get the pump working all the other work is in vain. I made sure that the final intake and output tubes where far enough away from each other that I didnít just re-circulate stale air. You can see some extra extension tube running down the fridge those are double intakes that join inside via a T connector. Donít be confused that could have just been one intake tube instead but I just forked it so it would have an easier time with air flow.

I would have opened it up to take a picture but it is in use right now.

The heat exchanger was made from two 50 foot ľ copper refrigeration tubes. These are bought as double spiral coils with two layers. You will need two coils. The hard part is to wind them so they lay next to each other while still coiled. You have to fish the end of one through the center of one layer of the other coil but not through both layers. Then you spin the one coil till half of it has run through the other and lays against it. An interesting puzzle to say the least. First time I did it wrong and had to unwind the mess. Once you have them properly align you must tape them. Tape them tight together with electrical tape. Spiral the tape around and round overlapping on each turn. You will need two to three large rolls of tape. Patience. Then you slide on Ĺ inch pipe insulation. Start at one end and work a piece to the middle. Do one half first then switch and slide tubes of insulation on from the other end. I then pushed each piece up against itís neighbor and taped. Add ľ inch pressure fittings at the end so you can attach to stiff ľ plastic tubing on both sides. Four pieces of plastic tube in all.

To run the tubes into the fridge I drilled two ľ inch holes from the inside out. Put them an inch from the top of the cold section (not the freezer). They were Ĺ inch apart. Then I cut a hole in the outside metal skin of the refrigerator that encompassed both the smaller holes. I traced around a piece of insulation with a pencil to mark the size of the hole. I used a RotoZip to cut the hole. Which left me with a giant two hole metal button which I threw out. It was big enough to take the entire diameter of the insulation. I then cut two plastic tube at an angle to make a point and ran each one out through one of the holes in the plastic interior, through the insulation, and out the big hole. I then cut the tubes again so they had flat ends and attached them to the copper pipes. I slid the insulation down so it fed right into the metal skin and into the insulation lining the fridge walls. No heat can escape from the plastic tubes this way. On the interior I left the cold air out tube so it was short The warm air tube I ran into the lettuce crisper at the bottom of the fridge so that any condensation would gather their. Notice how the coil is on itís side. That is to allow condensation to run down hill the whole way. If you make a straight cylinder coil it will be too high so I made spiral out and up like a snail then in and up, then out and up, then in and up. There should be a gentle downward slope so the moisture can be pushed out. The warm air should run from top to bottom the cold from bottom to top. DO NOT SET THE COIL ON ITS SIDE as it fill with moisture and stop working. No aquarium air pump is strong enough to push the water through. Why? This is because each coil acts as a separate vertical water column pushing back against the pump. With thirty coils at one foot high your pump would be pushing up against the equivalent of a thirty-foot water column. I donít think these pumps were made for more than three feet of water. Donít stress the pump.

Look at how I jury-rigged the thermostat. I used a min-max thermometer (look it up) to find the lowest safe setting that was guaranteed not to go below 40 degrees. Be careful since on cold days some fridges will get colder inside due to poor thermostats. I then drilled holes and set screws so the setting could not go below this minimum. I kept the refrigerant fully charged.

Some people let refrigerant out of the system so that the system cannot produce freezing temps but I think this is dangerous. Why? Because, releasing freon will restrict the temperature to some minimum below room temperature. It is not restricted to an absolute temperature minimum. Well, if you set the thermostat to freezing by accident the pump will run all the time, which is expensive. But then if your house gets cold the refrigerator will be able to reach colder minimum temperature. Which may well be below freezing. As an example, if your house is normally 72 and the freon depleted fridge can only reach a minimum of 40 when running continuously then if the house temp lowers to 60 then your snakes will be at 28 degrees. Which is cold enough to freeze them solid.

Remember donít use too old a fridge or too old a pump otherwise you might have been penny wise and pound-foolish when you end up with frozen or suffocated snakes. Test the thing before you use it. I kept a stash of live earthworms in there for three months before I would trust it to work.

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