Too Poor for AC? Try this

June 15, 200521 yr

HOMEBREW AC

I'm a student, with limited funds and a cheap house without air conditioning. To avoid dying this summer, I've built a primitive air conditioner. It's a basic heat pump, using water as the medium. You'll probably need to fiddle a bit with the dimensions of the supplies based on your resources and preferences.

Materials:

Salvage from around the house a:

* large fan

* garbage can

Grab from Home Depot:

* 25 feet of 1/8 inch outer diameter (OD) copper tubing (~ $14)

* 20 feet of 1/8 inch inner diameter (ID) vinyl tubing (~ $6)

* a package of zipties (~ $3)

* 2 small hose clamps (~ $1)

Here's the basic setup. The garbage can is filled with ice water, which is then fed by gravity (a siphon) through the copper tubing coiled along the back of the fan. The hot air passing through the tubing warms the cold water, cooling the air. Waste warm water is then pumped outside.

The system will cool an average room to a comfortable level in approximately 15-20 minutes. Depending on flow rate, a full bucket of water will last approximately 1-3 hours.

It doesn't rip quite as hard as central air, but for less than $30 CAD I'm not complaining.

The main factor affecting the performance is the temperature of incoming water. Cool water will work, but ice water will result in a cooler room, quicker.

Here's what the fan looks like from the back. The biggest issue in construction was uncoiling 25 feet of copper tubing in a 15 by 20 room. Just be patient and don't attempt to bend the copper too severly, it'll fold over on itself and you've effectively chopped your nice copper tubing in two.

When coiling the copper into a spiral on the back of the fan, I started in the middle and put zipties every 15-30 cm (6-12 inches). Use your discretion, you want to preserve the spiral shape and keep the tubing as close to the metal mesh as you can. If you're a bit crazy, sand the paint off the back to improve heat transfer from the metal mesh.

It doesn't really matter how it looks as long as it's reasonably spaced out and consistent. A hint for construction: prebend your zipties into a J shape. Then you can hook them easily in and back out of the metal mesh on the back of the fan. I'd suggest cutting off any extra plastic once you've got them on.

If you look closely, you can see the condensation from the incoming icewater, but no condensation on the tubing leading out. This is perfect, as it means that heat is being transferred from the room to the water.

Once you've got the copper tubing coiled, the rest is easy. Cut your vinyl tubing into 2 pieces, with one about twice the length of the other (one piece 6-7 feet, other piece 13-14 feet).

Attach the shorter piece to the incoming side of the copper tubing. It should slide relatively easily over the copper, but be snug. Attach the hose clamp and tighten. Following a similar procedure, attach the longer piece to the outgoing side of the copper tubing. (I don't believe it really matters whether you feed cold water from the inside or the outside. It's up to you to run some numbers.)

Submerge the shorter end of the vinyl tubing in the garbage can (washed and clean). I suggest weighing down the end of the tube, to avoid it drawing in air and stopping the system. I used twist-ties to attach a thin rock to the end. If you have fishing weights, I would suggest using those.

Next, hang the longer tubing out your window. For the gravity pump to work, the end of the tubing must be below the water level of your garbage can, plus an allowance for head loss in the pipe. Just to be safe, get it as low as you can. I'd suggest arranging it so the waste water will feed into a garden, but student ghettos don't have gardens so in this picture it's being fed into a drain by the basement.

I had to poke a small hole in my screen for this to work.

To get the system started, make sure the vinyl tubing in the ice water is completely submerged. Then, bring the waste water tubing as low as you can and start sucking on the tube. If you've ever siphoned gas you know the drill.

Basically, suck as much as you can. Then plug the end of the tubing with you thumb, and repeat. You're done when you start tasting water. Just let go, and it should continue to flow normally.

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