Homebrew Air Conditioning for Under $25 832
inkey string writes "Summer has arrived, and I've been busy slowly overheating in my student house without central air.
I decided to put my thermodynamics classes to work however, and produced this ~24$ 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."
At first, it looked like a great story... (Score:1, Insightful)
From who.int: "Billions without clean water": link [who.int]
The guy has no clue how lucky he is in his "student ghettos don't have gardens" home to have clean water to throw around.
Minor nit (Score:5, Insightful)
Re:Its going to be hot soon (Score:5, Insightful)
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! (Score:5, Insightful)
Environmentally friendly? (Score:5, Insightful)
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?
Re:Minor nit (Score:3, Insightful)
hmmmm.... (Score:5, Insightful)
#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.
Re:Minor nit (Score:5, Insightful)
Re:thermodynamics? (Score:3, Insightful)
While I agree that there are far more elegant ways to do this, You can still cool a room this way and not disobey the laws of Thermodynamics.
The heat generated by the Fridge stays in the Kitchen. Close the door and now you have effectively transfered heat from the cool room (bedroom or livingroom) to the kitchen. It is now far easier to relax.
Think it through before calling someone a moron.
Isn't this just a swamp cooler? (Score:2, Insightful)
Re:Minor nit (Score:1, Insightful)
In order for this to work you can't have your room as a closed system. If it is laws of thermodynamics say no matter what you do it will only get hotter. You have to dump the waste water out or bring cold water in to get any cooler.
If you had a freezer outside, then you could pump the water to a bucket outside, move that into the freezer and bring in a chilled bucket to continue cooling the room. But honestly, who has a working freezer sitting in their backyard?
Re:Minor nit (Score:3, Insightful)
Many people think that if you leave the refrigerator open, it will cool down the house. However, all a refrigerator does is take heat from its inside and move it to the outside. That's why those coils in the back are warm. Thus, if you open up the fridge to cool the house down, all you'll do is make the place warmer (since the efficiency isn't 100%). Also, you'll probably burn out the motor in your refrigerator.
I'll grant that in your particular comment, putting a fan in front of the freezer would work for a while, because it's already cold. But it wouldn't work for long.
Re:Environmentally friendly? (Score:3, Insightful)
Uhh yeah, except for the fact that he's using his freon-based refrigerator to make the ice, which then ventilates its heat exaust into the same room that he is attempting to cool off using his jerry rigged system.
Re:Minor nit (Score:3, Insightful)
I thought the guy had built up some swamp cooler or something like that, as that does really work - but this is just friggin lame/stupid in the long run to use. now... he could refine the idea quite a bit - use ground cooling to keep the water cool for example(just bury some copper pipes or some container a meter into the ground).
"hey i built a cooler. well, i just brought some ice water to my room!!!".
One minor issue (Score:3, Insightful)
costs (Score:4, Insightful)
The store needs to make a profit on top of the cost of the electricity to maintain the machine, and the ice...
...supplied by the ice company which bought the machine, maintains it, and freezes the ice, and trucks it to the store from their "plant"...and make a profit.
You do realize that 1kW/hr costs about 22 cents, whereas a 20lb bag of ice costs about $5, right?
You have to move 330J of energy to freeze one gram of water, basically. We'll assume a 50% efficiency here (pretty poor, I believe). A bag of ice, say, 20lb- would need about 3 million joules (watt-seconds), or 6 million watt-seconds of electricity. That's 1662 Watt-hours, roughly.
Or about 36 cents.
#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
Most refrigerators are virtually incapable of pumping that much heat (there's a reason they're insulated), and furthermore, are designed to work at a temperature range 60-90 degrees cooler than what you're asking of it. Ever noticed that a fridge takes forever to get from room temperature down to operating temperature?
This idea is so stupid, I can't believe I just wasted 5 minutes on this post. I want that 5 minutes of my life back.
Re:Air Conditioning for $1500/month (Score:3, Insightful)
And, yes, I work for a power company and know how the system works.
Re:Canada (Score:3, Insightful)
"That Fahrenheight 911 show was pretty good eh?"
"Fahrenheight? It's too damn hot in here for your jibberish. Go fill up the $24 AC with ice so we can get the temperature to a respectable level of Centrigadey goodness."
Make ice at night, cool room during day (Score:3, Insightful)
Re:Minor nit (Score:3, Insightful)
In order for this to work you can't have your room as a closed system.
His room is clearly not a closed system. For instance, there is an input of energy from his power lines.
If it is laws of thermodynamics say no matter what you do it will only get hotter.
That's not exactly what the laws say. Be more specific, and you'll see why you're wrong.
Re:Minor nit (Score:1, Insightful)
Re:Minor nit (Score:2, Insightful)
Hate to be a buzz kill, but I really take issue with using clean tap water as a resource for no more than its specific heat and the fact that it happens to be cool. And then dumping that tap water on the ground? That water is not free; your public services dam it, filter it, treat it and pipe it to you, sans cryptosporidium you know.
This is an unconscionable waste of resources. I'd be so impressed if you found a way to store the warm water to boil your pasta or at least wash your laundry.
Re:Minor nit (Score:3, Insightful)
Re:Minor nit (Score:5, Insightful)
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:Good show, but not a great idea... (Score:3, Insightful)
Very good point. Just where is the fridge located that produces the ice? Where is it putting the heat. The fridge is not included in the price of the project. Why not just take the door off the fridge and mount the fridge in the wall to expell the heat elswhere?
For those who don't know, fridges use a small compressor because they are cooling a small insulated enclosed space. They do not provide enough cooling to deal with the heat influx of a large room. It's BTU capacity is way undersized.
His fridge would not produce enough ice to keep his cooler supplied. The ice is a overnight creation cold storage medium to provide a short coling burst. This is not a cooling solution.
Air conditioning compressors displacement is designed to be effecient at expected cold side pressures and high (hot) side pressures. A fridge compressor is sized to work with lower suction pressures (larger displacement) for the creation of Ice in the freezer compartment. Running it with constantly elevated tempratures will overload the compressor causing ineffeciency.
When buying a compressor, they are sized for high temp use (air conditioning) and low temprature (freezers) The diffrence is the displacement is sized to the expected low side pressure.
High pressure moves more BTU/watt. Low pressure is for a large temprature differential.
Re:Its going to be hot soon (Score:3, Insightful)
Web pages for professors hardly get any news coverage, and these people are supposed to be at the top of the game. Surely research funding would leap to another quantum level if professors discussed on their websites how much impact or influence their research has, especially if those sites attracted page hits from large numbers of the public.
The adage of publish or perish seems to become perish and perish (i.e., lose, lose) when it comes to a little slashdotting.
Re:addressing all the flames/legitimate concerns.. (Score:1, Insightful)
here in australia i have a few mates that have set up sprinklers on top of the shed, can easily drop the temp inside by a few degrees which makes all the difference on a 40deg day
Obligatory Star Trek Reference (Score:3, Insightful)
Where he of course met Guinan and Data and was almost killed by time shifting aliens that were attempting to steal our souls. Wouldn't that be anyones worst season?