Homebrew Air Conditioning for Under $25

inkey string writes "Summer has arrived, and I've been busy slowly overheating in my student house without central air. I decided to put my thermodynamics classes to work however, and produced this ~24$ homebrew air conditioner. It'll cool a room to a comfortable level in 15-20 mins, and will run for a few hours on a garbage pail full of water. It's cheap, environmentally friendly (just fire the waste water off to your garden), and makes a good one hour project for a quiet evening."

Comments

Minor nit

[Roadkills-R-Us]

Just great, assuming you have an infinite supply of free ice water. Add teh cost of the ice machine, and it costs a bit more than $24.

Re:Minor nit

[LurkerXXX]

Why you can get the ice out of the freezer/refrigerator in your kitchen. It just costs a little electricity to make. It makes it by using a condensing coil to use a gas medium to pump heat from the freezer are to coils on the back of the fridge which... then heats the room you are trying to cool. DOH!

Re:Minor nit

[LurkerXXX]

Yeah, that +5 must burn your ass. Tsk tsk.

The work has been shown multiple times in the various threads, but since you seem to be slow to catch on...

Starting state:

1) Room: temperature x (warm)
2) Water: temperature y (also ~room temp)

Net heat: x + y

Step 1:

Water gets put in fridge. Heat is pumped from water to room.

Result from Step 1:

Call the change of heat in the water z.

(Water gets colder. Room gets hotter. Even heat levels from that part.)

Inefficiency in the fridge adds net heat to room.

The inefficiency heat is i.

Net heat = (x + z) + (y - z) + i = x + z + i

Net Result: increased temperature from inefficiency.

Step 2:

Cold water from fridge is used to run through piping/fan to cool room. It's not done by swamp or other methods. The only thing going on is the warm air is blown past the tube of cool water, bringing the temperature of the room down, and the temperature of the water up. (The water doesn't go through any phase changes through the tubing or anything; it's simply equalizing the temperature)

Result from Step 2:

Heat n is transferred from the air to the water.

Room is warm and so is the water once again around room temp (going out the window now).

Heat m is added from the inefficiency of the fan.

(x + z - n) + (y - z + n ) + i + m

Net Result: (original heat)+ (excess heat)

x + y + i + m

We started with x + y. Now we have x + y + i + m.
Seeing the problem yet?

The water going through the tubing is *not* superheated. It's not warmer than the room air. At the very best it's the same temp as the room. That's if he gets complete transfer. No net heat is removed. It's added.

Water y gets dumped out the window. What are you left with? x ++

Please show your math for your strange theory that makes this perpetual motion machine work, and show how the water in the tube is well above room temperature in order to decrease the net temperature of the room.

And thanks for playing.

Re:Its going to be hot soon

[Anonymous Luddite]

>> I hope his server isn't in his room

It's actually a University of Waterloo server. I'm sure the sysadmin is gonna love this sudden DDOS.

Congrats on making your PH.d. pay for itself!

[jeffmeden]

But sadly this isnt that revolutionary, nor is it very 'green'. It takes a cold source of water to work, and if you have none in your area (tap water wont cut it unless you happen to get fed from a pipe running through a glacier) you have to get cold media from your local refridgerator/freezer. Why not instead rig a direct cycle through your cooling appliance of choice to offer a small, localized cooling effect? It also wouldn't waste water. Just remember, don't try to cool the room with the freezer in it.

Environmentally friendly?

[whoever57]

It's cheap, environmentally friendly (just fire the waste water off to your garden)

So, if it is environmentally friendly, just where did the "ice water" come from?

Unless you have a solar or wind-powered refrigerator, I suspect that the overall system is not actually all that environmentally friendly. What is the energy efficiency of the system?

hmmmm....

[MarcoAtWork]

#1 you can buy a bag of ice at the gas station/convenience store, not free but then neither is the electricity to run your freezer.

#2 even if you used the house freezer, you shut the door and basically you're pumping heat away from the bedroom into the kitchen, obviously you won't get huge temperature differentials, but 5-6C feels very noticeable when you're trying to fall asleep and it's too hot to do so.