View Full Version : Need a new AC unit? Cant really afford one? LOOK NO FURTHER!

06-26-2006, 09:49 AM


Salvage from around the house a:

large fan
garbage can
Grab from Home Depot:

25 feet of 1/4 inch outer diameter (OD) copper tubing (~ $14)
20 feet of 1/4 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. I use a single bucket before bed on hot nights, which lets me get to sleep. Once the water runs out, the house has cooled off enough that the fan alone provides sufficient cooling.

It doesn't rip quite as hard as central air, but for less than $25 CAD I'm not complaining. (and, btw, that's my girlfriend's makeup mirror, not mine)


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.

Add salt to the water if you're adding a large volume of ice, as this will drop the freezing point of the water and increase the cooling effect of the fan.

You can attach the tubing to the front of the fan as well. This will increase performance, just make sure that your fan can handle the additional torque of tubing full of water attached to the front.


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.

Some have suggested using an old car radiator attached to the front of the fan instead of coiled copper tubing. Cost prevented me from trying this, but as long as the head loss from the radiator is low enough to allow the siphon to operate, this should increase the performance (better heat exchange). As well, make sure your fan can handle the weight of the radiator.


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.

I've also hooked this up to a garden hose as the cold water feed. Check out the "New and Improved Water Supply" section of this site for more details.


A closed circuit version of this is entirely possible. I've spoken with someone who is in the process of constructing a version of this using antifreeze as the fluid, dry ice to cool, and a small pump to keep the system moving.

I would also suggest constructing a geothermal heat pump. Dig a deep hole near the window, the soil at this depth will be quite cool. Bury a coil of copper tubing spaced well through the soil, this will act as your heat sink. Pumping water from the fan coil to the underground coil and back will exchange heat from the warm room to the cold soil. I'd love to implement this, but my landlord may not take well to large holes in his backyard.

I realise small air conditioners are quite cheap. But then you don't get to build anything!

06-26-2006, 10:56 AM
and the best thing is, nobody would call me a redneck if that was sitting in my living room.

Rain Man
06-26-2006, 11:16 AM
Let's see .... water .... electricity .... I'm out.

06-26-2006, 11:20 AM
Wow ...

And I thought I was a tight ass penny pincher.


06-26-2006, 11:44 AM
Thats a helluva idea! Its much better then ripping the neighbors out of their window which is what some people do. I wish I know about this when someone took mine during a hot Kansas summer.

Douche Baggins
06-26-2006, 11:48 AM

Mr. Flopnuts
06-26-2006, 12:34 PM

I agree, yet disagree. Definately has the look and feel of "ghetto". I just can't lump it in the ghetto catagory though because of the time, thought, and skill it took to design it and put it to work. Hmm. If he was on crank when he designed this, then yeah, ghetto.

Spicy McHaggis
06-26-2006, 01:04 PM
Wait. You're in college and spent this much time building something that has nothing to do with the dispensing or consuming of beer/other alchoholic beverages?

06-26-2006, 01:11 PM
Wait. You're in college and spent this much time building something that has nothing to do with the dispensing or consuming of beer/other alchoholic beverages?


I dont think that the guy who designed this was in college though..... it looks more like an rental home or something of that nature.

06-26-2006, 01:14 PM
that little heat exchanger may work in canada, but you'd need somethin a little bigger here

06-26-2006, 01:46 PM
I'd just spend the extra couple of hundred bucks and get a new a/c from Westco.