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Hardware Hacking Technology

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."
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Homebrew Air Conditioning for Under $25

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  • Why no pump? (Score:1, Interesting)

    by pirho666 ( 153073 ) on Monday June 13, 2005 @06:47PM (#12807347)
    Gets good points in my book, but it would be infinately cooler with a pump to circulate the water and then you could just add more ice from your freezer to get it cooler again.

    I know that the freezer will put out more heat than you will get from the ice but this is more likely to be used to keep a single room cool and not an entire house.

    Shouldnt be that much to add a small pump to the mix??
  • Re:Minor nit (Score:2, Interesting)

    by bhtooefr ( 649901 ) < minus punct> on Monday June 13, 2005 @06:55PM (#12807441) Homepage Journal
    Hmm... Gallon jugs of water in the freezer?

    Still uses energy, mind you, but that takes care of the ice water.

    Also, I thought that routing the water OUT was a bad idea. Why not catch the water in another bin, or in jugs, and freeze that? Makes SO much more sense...
  • by WillAffleckUW ( 858324 ) on Monday June 13, 2005 @06:59PM (#12807486) Homepage Journal
    is just to replace the standard incandescent lightbulbs in your house with compact flourescent bulbs.

    this will result in you using about 1/8 the electricity to get the same light, but drop the heat output from lighting - a major contributor to household heat - to virtually nil.

    I used to have a problem in my new house with having to get a fan until I realized it was mostly heat from lights that was making it hotter than a normal open window breeze could cool. Then I replaced my incandescent bulbs (well, most of them) with flourescent bulbs and suddenly it was cool enough I didn't even need a fan at all.

    Now, if the external temperature is above about 98 degrees Fahrenheit (30 C, I think), you may still need to do the water evaporator you describe, but the energy used by it will still be lowered by switching to compact flourescent bulbs for lighting.

    Oh, and get a flat panel LCD monitor - that will save a lot of energy usage and heat output as well.

    Save the fan to cool off your computer, not your room.
  • Re:To be pedantic... (Score:1, Interesting)

    by Anonymous Coward on Monday June 13, 2005 @07:00PM (#12807490)
    Did you bother checking where the link points to?

    This is Waterloo, Ontario, Canada. Normal RH is 60% or more in the summer.

    A swamp cooler simply won't work, period. They don't even sell them here because it's pointless. The air is so chock full of water it's just going to generate heat, if anything.

    Since he said it works, it must be moving the heat instead.
  • Re:Fan? (Score:3, Interesting)

    by Quikah ( 14419 ) on Monday June 13, 2005 @07:06PM (#12807540)
    Yes, but it would take a lot longer to occur. For example he could just point his fan at the bucket of cold water, however you have a limited surface area for the air to pass over. Running the water through the coiled tube increases the surface area, lowering the temperature much quicker.

    Probably some other factors as well, I had a bit of a dumb thermodynamics teacher (not to mention it was over 10 years ago and haven't used it since!).
  • by ciroknight ( 601098 ) on Monday June 13, 2005 @07:08PM (#12807554)
    A lot of people have ice makers in their home, which provides ice cheaply enough.. though one nit pick I had myself is that he wasn't adding any salt to the water!!! He could have dropped the water down at least another ten degrees, stretch out Newton's Law of Cooling the best you can.

    Had a similar idea, though closed circuit, and involving an old fuel pump from a car..
  • Bah! (Score:2, Interesting)

    by iminplaya ( 723125 ) on Monday June 13, 2005 @07:11PM (#12807587) Journal
    You call that innovative? This is how people cooled their buildings before in the invention of the room air conditioner. And, to be redundant, where is the cost of amking that ice water? You want innovative? THIS [] is innovative! And even it is old. And it will probably be cheap when it really catches on. More info [], in case you're interested.
  • Re:thermodynamics? (Score:2, Interesting)

    by Kumagoro ( 889194 ) on Monday June 13, 2005 @07:13PM (#12807604)
    Actually, this kid lives in residence on the University of Waterloo campus, the water from the taps in the res rooms is very cold (I am a student in Waterloo, with many friends in rez), just like getting it from a fridge except this water is cooled by the ground. So there is no heat generated by a fridge or freezer. If you had avoided the your ass umption that he had used a fridge for the water you would have been correct, but as it stands, you are the "retard".
  • Or: (Score:3, Interesting)

    by temojen ( 678985 ) on Monday June 13, 2005 @07:24PM (#12807696) Journal
    Put the bucket outside, in the wind, with a pump to cycle the water through the fan coil in the house, then back to the same bucket outside. Instant swamp cooler with the swamp outside and the cool inside.

    It should be quite a bit more efficient than this guy's system.
  • Re:Minor nit (Score:2, Interesting)

    by pcmanjon ( 735165 ) on Monday June 13, 2005 @07:34PM (#12807781)
    "Still uses energy, mind you, but that takes care of the ice water.

    Also, I thought that routing the water OUT was a bad idea. Why not catch the water in another bin, or in jugs, and freeze that? Makes SO much more sense..."

    Actually, I've made a system EXACTLY like the one he has, but better. I used salt in my bin, which helps coolong another 15 degrees or so.

    I also have outside my window a collection bin, and a cheap "sump pump" type of pump, so after the water gets to a certain level (top of the bin) it pumps the water back in to my room.

    I also took and dismantled an old mini-fridge, straightened the coils out and put the "freezer plate" part of the fridge in the water, and the heating coils outside of the window.

    It works EXCELLENT, and the cold air the fan blows is ice cold.

    It's almost as good as a real air conditioner, it's just not all contained and of course (when it rains) I have to bring the parts in.

    I run it nearly all the time. It works great. Just a few pointers for people who wish to really try this.
  • Re:Minor nit (Score:2, Interesting)

    by Anonymous Coward on Monday June 13, 2005 @07:39PM (#12807836)
    I live in a student apartment where I don't pay the utilities, so it's not my problem if the landlord has to pay because I'm working the refrigerator extra hard.
  • by kfg ( 145172 ) on Monday June 13, 2005 @07:40PM (#12807848)
    San Francisco, Paris, whatever. :)

    Ah well, if you aren't lucky you learn something new every day.

    I'll make two notes though, Twain was a public speaker, and just because this particular witticism can't be found in his writtings is not actually an indication that he didn't say, and even orginate, the quote, it simply means it can be proven from the written record. There is such a thing as oral history. Many things I have orginated and said are not recorded in print, despite my post count, and the printed version of not a few things has been lost even to myself.

    The second note though is my observation (and I believe that of others before me) that sooner or later every American will attribute every witticism to Twain, especially as he often used the witticisms of others, often without direct attribution since the people of his time were well aware of their actual origin.

  • Swamp Coolers... (Score:4, Interesting)

    by GI Jones ( 21552 ) on Monday June 13, 2005 @07:56PM (#12808020) Homepage
    I had never heard of a swamp (evaporative) cooler until I moved to AZ. At first, I didn't like the idea of adding a ton of humidity to the air in order to cool some space, but when I bought my first house, I learned that I LOVE swamp coolers.

    Newer homes never have them, but the older house that I bought (built in 1979) had a monster one installed on it. During the early parts of summer (when the humidity is low) I can keep my house at 72 degrees when the outside temp is about 100 and my electricity bill is $65/mo.

    If I ran my AC unit and kept the house equally as cool with it, I would be looking at no less then a $150 in early summer and $200+ as the temp gets into the range of 110+.

    At this point, what I would love is a thermostat that runs both my swamp cooler and AC unit and can determine when to use one versus the other and switch automatically between them. Anybody know of such a device?

  • by MoralHazard ( 447833 ) on Monday June 13, 2005 @07:57PM (#12808031)
    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)

    It's currently 7:51pm in New York City, and the temperature outside is about 85F. The high today was 94 in Brooklyn (my hood).

    The tap water temp, though, is still a blissful 61F (after letting it run for about 15 seconds). That's practically icewater, compared to the outside temp.

    Since very few residential customers in the city get billed for water usage, this would be a PERFECT solution. That 25-35F temperature delta takes the edge off things, and since the buildings tend to be insulated to high heaven (on account of the cold winters), it's more effective than you would think.

    Last summer, I kept setting off the temperature alarms on my RAID servers at home, everytime the daytime high got over 90F outside. My GF was always bitching about how much A/C was costing us on our electric bill, so I moved the RAID arrays to the linen closet near the bathroom and set up a water-cooling rig similar to the one described in this article (I cheated and used an aquarium pump).

    I left the A/C off when we were at work, for the rest of the summer, and the disk temps never got above 70F. Put that in your pipe and smoke it!
  • Re:Canada (Score:1, Interesting)

    by Anonymous Coward on Monday June 13, 2005 @08:00PM (#12808062)
    Re:Canada (Score:1)
    by minus_273 (174041) on Monday June 13, @06:41PM (#12807861)
    Basic sceince. 28 degrees is below freezing of course you can get snow at that temperature.

    Anyone else find it funny that a user whose login name is absolute zero in Celsius thinks in Fahrenheit? And apparently assumes that the rest of the world does as well?

  • by foxtrot ( 14140 ) on Monday June 13, 2005 @08:08PM (#12808142) cool a room, as has been noted repeatedly, a few refinements that can be done easily and cheaply:

    1) Get a second trash can. Drain to trash can number 2. This will allow you to save water, plus:

    2) Put salt in the water. The ice and chilled water mixture gets colder with salt.

    You probably don't want to drain salt water to the yard. :)

    You can run from one trash can to the other, then when it's done draining, swap one can for the other and ice down the other can. If you've got some freezer space to dedicate to the project, the bottles of ice are probably an excellent idea-- have a set in the freezer and one in the heat pump.

  • by shawb ( 16347 ) on Monday June 13, 2005 @08:40PM (#12808434)
    still gotta pay for the water bill.

    Nah... at most rental properties water is included.

    Reminds me of me el-cheapo humidifier I once made... put a bucket of water on the ground. Drape a slightly damp towel over the back of a fan down to the bucket and let a process similar to evapotranspiration in trees turn liquid water into humidity. Drops temperature a tiny bit, which is unfortunate as I'd use this in the winter when it's dry indoors. But it is a quick way to dump a couple gallons of water in the air overnight.

    Just make sure that you have something like a towel of plastic sheet on the ground in front of the fan, as a small amount of water is atomized in the process rather than evaporated. This factor really makes sure that this is a short term solution rather than long term. That and you eventually have to wash the towel, as salts from the water build up and leave it kinda nasty.
  • Here's the flaw (Score:2, Interesting)

    by everphilski ( 877346 ) on Monday June 13, 2005 @08:48PM (#12808497) Journal
    Not only is ice not free, but the refrigerator (being a non-ideal, non-reversible thermodynamic entity) is putting off MORE HEAT than what it is cooling (the same is true of an A/C unit... that's why they are located outside). Since he is in a dorm room, the freezer is located in his room, the constant cooling of additional water in addition to his normal "load" will actually cause his room to head up more. If he gets the ice from a common machine down the hall then yes, the bucket itself is pretty efficient, but the machine as a whole (which must include the production of ice) sucks it bigtime compared to a commercial air conditioner.

    Moral of the story: "The laws of science be a harsh mistress" -Bender, Futurama

  • Homebrew swampcooler (Score:3, Interesting)

    by gessel ( 310103 ) on Monday June 13, 2005 @09:14PM (#12808697) Homepage
    Years ago, during a heatwave in Oakland, I built a homebrew swamp cooler with some muffin fans and a mist nozzle from McMaster (like 32215K11).

    From thermodynamics, the say you have 1kg of water to work with:

    Changing it from ice to water: 334kJ
    Raising it from 0C to 25C: 104kJ
    Converting from liquid to vapor: 2,260kJ

    Compared with vaporizing water, melting ice is trivial.

    For swamp coolers to work, the humidity has to be low--if it's high the ice bucket trick is a good one. But for those in dry hot climates, a swamp cooler works well.

    I connected mine to a hose spigot with 1/8" tubing, which supplied a continuous flow of water to the mist nozzle, which was mixed with a good flow of hot dry air from the fans, and resulted in a good flow of cool slightly damp air.

  • Re:Minor nit (Score:3, Interesting)

    by Fortunato_NC ( 736786 ) <> on Monday June 13, 2005 @11:17PM (#12809567) Homepage Journal
    Just barely off-topic, but there are apartment units in New York that don't have windows in the bedrooms, however if I remember correctly, residents technically aren't allowed to be called these rooms "bedrooms". These apartments are usually in converted office buildings where what was large, open, "bullpen" areas are walled into relatively narrow apartments with windows along only one end. The areas with windows are used for living rooms, while the non-bedroom "bedrooms" are closer to the center of the building, and thus have no windows. Kinda like having your own cave.
  • by nbritton ( 823086 ) on Tuesday June 14, 2005 @05:07AM (#12810834)
    If you have a fan only setting on your thermostat then go down into the basement and bypass the air return ducks so that it's sucking in cold air from the basement. think of your concrete foundation has a big ass heat sink.

Don't tell me how hard you work. Tell me how much you get done. -- James J. Ling