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Homebrew Air Conditioning for Under $25 832

Posted by timothy
from the ice-is-free-after-all dept.
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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  • DOA (Score:2, Informative)

    by AmigaAvenger (210519) on Monday June 13, 2005 @06:46PM (#12807338) Journal
    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,
  • Thinkcycle (Score:3, Informative)

    by bigattichouse (527527) on Monday June 13, 2005 @06:47PM (#12807345) Homepage
    You may want to post this on thinkcycle.org as additional information for some of their cooling projects
  • MirrorDot (Score:4, Informative)

    by eric434 (161022) on Monday June 13, 2005 @06:47PM (#12807354) Homepage
    Next up, a $24 watercooling rig for his web server.

    http://www.mirrordot.org/stories/5cb66a4a72a5269bc 29e9dd8f982b3da/index.html [mirrordot.org]

  • Coral Cache (Score:5, Informative)

    http://www.eng.uwaterloo.ca.nyud.net:8090/~gmilbur n/ac/ [nyud.net]

    Will someone edit the submission to replace the URL, please? Sheesh.
  • No, it isn't (Score:5, Informative)

    by Roadkills-R-Us (122219) on Monday June 13, 2005 @06:48PM (#12807373) Homepage
    A swamp cooler pulls the air through the actual water. It uses evaporation for the cooling effect. That's rather different than this, which is just a crude radiator. effect.
  • Re:To be pedantic... (Score:1, Informative)

    by Anonymous Coward on Monday June 13, 2005 @06:49PM (#12807378)
    Read the article.

    It's not an evaporative cooler. Ice water cools a heat exchanger made of copper tubing. Air is forced through the heat exchanger.

    Swamp coolers increase humidity. If anything, this is going to decrease humidity due to the slight amount of condensation caused.
  • Working Mirror (Score:1, Informative)

    by Anonymous Coward on Monday June 13, 2005 @06:50PM (#12807386)
    This mirror [lerfjhax.com] has the article text and the pictures that go along with it.
  • Congratulations (Score:5, Informative)

    by overshoot (39700) on Monday June 13, 2005 @06:50PM (#12807388)
    At first I thought you'd reinvented the swamp cooler [arizona.edu]. On RTFL, however, I find that you've actually reinvented the 18th-century icehouse cooler, which is notably less efficient (like, where does the heat from the icemaker go?)

    It didn't seem all that likely that most /.ers would care about evaporative cooling, since even in Arizona they only work part of the year (like now, although today the Phoenix dew point got up to 10C. I woke up just knowing it had gone up because the cooler was blowing full speed and it still wasn't all that cool.) Never mind next month when the monsoons start. AC time then for sure.

  • mirrordot (Score:5, Informative)

    by kryogen1x (838672) on Monday June 13, 2005 @06:51PM (#12807394)
    Thank you mirrordot. [mirrordot.org]
  • Re:Canada (Score:5, Informative)

    by RobinH (124750) on Monday June 13, 2005 @06:56PM (#12807448) Homepage
    Dude, I'm in Canada... was 92 fahrenheit here on the weekend. Plus humidex.
  • Re:Canada (Score:4, Informative)

    by Quasar1999 (520073) on Monday June 13, 2005 @06:59PM (#12807487) Journal
    It's currently 28 degrees outside... check for yourself (http://weather.uwaterloo.ca/ [uwaterloo.ca]), if you can make snow at that temperature, I'd be impressed.
  • by FoolishBluntman (880780) on Monday June 13, 2005 @07:07PM (#12807545)
    Kenmore 5150 BTU Single Room Air Conditioner $89.00 new http://www.sears.com/sr/javasr/product.do?BV_UseBV Cookie=Yes&vertical=APPL&pid=04274054000&subcat=Si ngle+Room+Units [sears.com] I know students are poor, but really. You can probably pick up something like this at a garage sale for $20.
  • Re:Canada (Score:4, Informative)

    by Anonymous Luddite (808273) on Monday June 13, 2005 @07:16PM (#12807626)
    >> 92 fahrenheit here on the weekend.

    weekend? Ontario's been a rotten b*stard for the last week - 30 Celsius + humidity every day.

    I'm sitting between two fans, beer in hand, AC cranked. My effing hydro bill is going to make me cry...
  • by benjamindees (441808) on Monday June 13, 2005 @07:18PM (#12807645) Homepage
    Other than the obvious ingenuity involved in the creation of this device, the reason things like this don't exist in the real world is that they're hardly efficient. And comparing the purchase price instead of the operating costs of such a device is a sure sign you're missing something.

    Air conditioners are unbelievably cheap and unbelievably efficient nowadays.

    As others have said, this setup has all sorts of problems, from a reliance upon a source of ice that may very well be dumping more heat into the local environment than it saves, to wasting water.

    Though this system doesn't use a pump, a recirculating system with a small electric pump could end up creating more heat than it saves.

    If you're really bent upon saving energy in a cost-effective fashion, adding insulation is almost always efficient. Good blinds on the windows are also a great investment.
  • by matthewn (91381) on Monday June 13, 2005 @07:20PM (#12807655)
    Mark Twain once famously noted that the worst winter he ever spent was his summer in San Francisco.
    No. No he did not [snopes.com].
  • by inkey string (35594) on Monday June 13, 2005 @07:22PM (#12807678) Homepage
    number one, yes i realise that in a closed system freezing ice to cool yourself off is foolish. this is why i make ice in the kitchen, and cool my room off at night.

    which addresses the why no recirculation/you need an infinite supply of ice criticisms. this was designed to cool me off before bed, so i could fall asleep without wanting to kill myself. once the bucket runs out of water/ice, it just becomes a regular fan which is fine once the house cools off in the wee hours. plus i dont have to worry about knocking anything over in a morning daze.

    ive rigged it up to a slowly flowing garden hose which will keep things cool indefinitely, but i find it easier and a bit cooler to just pick up a big bag of ice and dump it in when it gets really hot.

    anyways, take it or leave it. and to the graduating chemmie that said he was ashamed to call me a student - come visit me at my office by the weef lab (e2-1311), im sure i can address any of your concerns to my satisfaction.
  • by Anonymous Coward on Monday June 13, 2005 @07:23PM (#12807681)
    I bought one of these. Not this exact model, but from the same company (Haier). The instruction manual is worthless because the engrish is so bad. The thermostat is too close to the condenser and therefore not too accurate. And their definition of ultra-quiet is something which is quite a bit louder than my computer with the case off. That said, the unit does actually work.

    Also, 5000 BTU/hr will cool a small room by about 10 degrees fahrenheit. So if it gets hotter than that then you might want a larger model.
  • by overshoot (39700) on Monday June 13, 2005 @07:30PM (#12807748)
    I'm using a MasterCool [adobeair.com] that's almost 10 years old and aside from having to change the pads every four years it's great.

    Around here you can get them from Home Depot and the installation kit runs about $650; labor is up to you but if you're replacing an old one it shouldn't be too tough to do yourself.

  • Mirror (Score:2, Informative)

    by kpdvx (546561) on Monday June 13, 2005 @07:32PM (#12807765)
    Mirror: www.138productions.com/ACMIRROR/ [138productions.com]
  • by anthony_dipierro (543308) on Monday June 13, 2005 @07:47PM (#12807923) Journal

    The water isn't really what's getting wasted, it's the energy to move the water around (out of the ground and into the water tower, for instance). The specifics really depend on where you live, but consider those people who have wells right in their backyard, and can then dump the water back in their backyard when they're done with it.

    Even this could be saved, at least for heating the upstairs, if you kept the water in some reservoir and used it later. In fact, if you could redirect it into your hot water heater you'd actually save energy as your hot water heater would only have to heat from room temperate as it empties out. On a smaller scale, if you don't want to repipe everything, you could leave buckets by the toilet and wouldn't need to use water whenever you flush. Now, granted, flushing the toilet a couple times a day isn't going to use up all that water, but if you've got enough storage you'd be able to flush all year without using any additional water.

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

    by emarkp (67813) <slashdot&roadq,com> on Monday June 13, 2005 @07:52PM (#12807983) Journal
    Um, that's the point. His setup is thermodynamically equivalent to opening up the fridge. Thus, he's not actually reducing the heat in the room, he's just moving it around.
  • by jbridges (70118) on Monday June 13, 2005 @07:58PM (#12808047)
    Spend another $26, and buy a real airconditioner for $50 at CostCo.

    It's $99.99 with an instant $50 off rebate at the register.

    Less work too.....
  • by ishmalius (153450) on Monday June 13, 2005 @08:03PM (#12808093)
    I don't know if this guy ever took shop class, but the simple old trick of filling the part of the copper tubing to be bent with sand will help prevent it from collapsing from a too-tight bend.
  • Re:Minor nit (Score:3, Informative)

    by RevAaron (125240) <revaaron@noSPAm.hotmail.com> on Monday June 13, 2005 @08:08PM (#12808140) Homepage
    nope, from the photos in the FA it looks like he lives off-campus in a rented house.
  • by mboos (700155) on Monday June 13, 2005 @08:16PM (#12808221) Homepage
    No wonder I can't even get to my own website (on the same server) today. As I recall, the web hosting policies for the Engineering faculty recommend that if you're going to get a lot of page hits, to move your site elsewhere.
  • Re:Minor nit (Score:5, Informative)

    by racermd (314140) on Monday June 13, 2005 @08:25PM (#12808302)
    I hit this through the mirrordot link from above...

    This is exactly how a good thermal heat-pump operates. However, a few "upgrades" would make this perfectly viable for a home of 1500+ sq. feet.

    1: Make it a closed-loop system, or even a dual-loop system.
    2: Use a good radiator and heat-block. Think of a water-cooling rig on a PC, but in reverse and a much larger scale.
    3: Use the earth, itself, as both the source and destination of heat.

    Most people that have done this for their homes use the earth as a natural heat sink. If it's new construction, they typically dig shallow, but wide. In a retro-fit, they'll drill deep and narrow. Either way, the earth holds a pretty steady temperature below 6-8 feet or so. All that's needed is a way to put heat into it when you want to cool off and a way to get heat out of it when you want to warm up.

    This way, all that you spend money on is the electricity to pump the heat-carrying fluid/gas/whatever into and out of the tubes in the ground. If that isn't enough, a small furnace and/or A/C unit can supplement, if need be. Either way, the energy consumed from the utility companies is a fraction of "normal".

    I have plans to build a new home in the next 3-5 years, and I'm looking at all sorts of alternatives to just about everything that consumes energy in a home.

    1: Geothermal heat pump(s) for climate-control.
    2: On-Demand, CNG water heater (i.e.: no tank to keep warm)
    3: Solar-powered radiant heat (suplements forced-air from #1)
    4: On-Demand lighting (sensors that detect room occupancy)

    I'm missing a number of other things I could do, but the goal is to have a home with all sorts of modern conveniences while trying to reduce the energy usage associated with most of them. It's tempting to add a water-cooling loop to the climate-control system for the comptuers. They're already producing heat, so why not just send it directly to it's destination and avoid that pesky conversion to heated air?

    Getting back on-topic, this guy hasn't done anything new. In fact, it's rather wasteful to just use a coil of copper tubing tied to the back of a fan. The fact that he's using ice water (as mentioned in other posts) does nothing to save energy costs. After all, he's got to power a freezer to make the ice to begin with, which offsets most of the savings. Never mind that the heat from the water (plus the heat from the machine, itself) went into the living space that he's trying to cool.

    And that he's a student, and *probably* not paying for much, if any, of his utility costs. But I digress...
  • by malfunct (120790) on Monday June 13, 2005 @09:18PM (#12808720) Homepage
    He would be much better off just aiming the fan over the top of the barrel of ice water and getting the evaporative cooling going along with the cooling from the ice. In fact I can't remember but its something like 5 or 10 degree temp drop by just putting ice water in front of your fan as opposed to the fan alone. But his rig is rather a waste in comparison. He should look into evaporative cooling if his climate isn't too humid to start out with.
  • Capacity (Score:3, Informative)

    by ColaMan (37550) on Monday June 13, 2005 @09:39PM (#12808880) Homepage Journal
    This is all very well and good, but he's missing one thing - capacity.

    Air-conditioning systems are sometimes rated in "tons". That's "how many tons of ice required to melt in a 24hr period to get the same cooling effect."

    Surprisingly, in AC terms, a ton is not a very large unit. A typical car air-conditioner is about 2-2.5 tons. This size AC is capable of cooling about half a house. So, a 5kg bag of ice? Forget it. Go buy a real air-conditioner. Scrounge around - 30 bucks can buy a decent old second-hand unit.
  • Re:Minor nit (Score:3, Informative)

    by poopdeville (841677) on Monday June 13, 2005 @10:01PM (#12808994)
    Since he claims that his contraption cools his room, some step in your analysis must fail. Can you please show me evidence that he kept the refridgerator in his room? Because it looks to me like he was living in a house. And most houses keep their refridgerators in the kitchen.
  • by One Childish N00b (780549) on Monday June 13, 2005 @11:12PM (#12809531) Homepage
    Spend another $26, and buy a real airconditioner for $50 at CostCo. It's $99.99 with an instant $50 off rebate at the register. Less work too.....

    Yeah, and if Linus Torvalds had dropped some cash for UNIX, he wouldn't have had to write his own. Less work there, too.

    I have to ask if you've ever built anything yourself, because there's a real pride to be enjoyed in knowing that what's working for you was built by you that seems to have passed you by - I'm writing this message on a computer I built myself on a desk I made and listening to music on media player software that I wrote - sure I could have saved time and effort buying an off-the-shelf eMachine, a desk from Office World and a copy of WinAMP5, but I didn't want to - I wanted to build it for myself because solving problems is what we geeks like to do.

    In short, dude, we're geeks, we like to flex our geek thought-muscles and build things ourselves - 'less work'? the work is fun. This guy isn't stupid, if he wanted to go out and buy an air conditioner, he would have done. He just felt like, in the traditional geek spirit, building his own.
    Anyone want to stop the flames now, please?
  • Re:Swamp Coolers... (Score:4, Informative)

    by Tsu Dho Nimh (663417) <abacaxi.hotmail@com> on Monday June 13, 2005 @11:24PM (#12809608)

    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? Nope, and you won't find one. It's a fast way to kill your AC.

    I had a tenant who manually switched between AC and evap every day, when we were in one of those "not quite dry enough for evap" months. Her theory was that in the PM, when the RH was low, she could use the evap, then use the AC the rest of the time. Then she called me because the AC was not working.

    The first day or so of an AC switchover from evap is when the AC has to remove all that moisture left by the evap. The tenant had been switching often enough that the humidity removed made a sheet of ice on the coils and the AC died. Because it wasn't cooling rapidly enough, she cranked the T-stat down as low as possible, which made the icing worse. Fortunately, there was no permanent damage ot the AC, but she had to swelter with no cooling until the ice caking the coils melted. She wasn't willing to pay the AC guy his hourly to stand there with a blow dryer and melt yhe ice.

  • by gerardrj (207690) on Monday June 13, 2005 @11:59PM (#12809784) Journal
    Your roof is only one part of the issue, probably a minor one if your have an attic.

    During the daytime the sun warms the roof and walls of a house. The surfaces most perpendicular to the Suns rays will get hotter, faster.

    In the morning the sun is low in the sky and the light rays are mostly perpendicular to the house walls. Since the air is still relatively cool from the night period, the heat imparted to the walls is mostly released back to the atmosphere.

    For the mid-day the walls are washed in light mostly parallel to the walls, but the roof is heated quite a bit. With an attic and proper insulation and ventilation, most of this heat will be released back to the atmosphere.

    In the afternoon/evening the sun is again low in the sky an the rays are again perpendicular to the house wall, causing them to heat up. Now, though, the atmosphere around the walls is also warm so less of this heat is released back to the atmosphere outside the house and instead finds it in to the home . Heat is conducted to the interior walls and then to the air in the house. Additionally heat is radiated from the interior wall surfaces to the occupants causing people to feel warmer than the thermostat reading would imply.

    The radiation portion of that scenario is why opening the windows does not alleviate your warm feeling and cooling the roof does not help much.

    If you were to run water down the west walls instead of the roof during the afternoon you could remove the accumulating heat. Better yet shade those walls, you would go a long way to keeping cooler. Another option is to more heavily insulate the western walls, building up their thickness if necessary.
    Shade is the most efficient way of keeping cool, you remove the heat before it gets to the home and either release the heat to the atmosphere, or let plants convert it to food.

  • by kernelfoobar (569784) on Tuesday June 14, 2005 @01:08AM (#12810105)
    actually, ever heard of Maple [maplesoft.com]? UWaterloo started it [maplesoft.com].
  • Re:Minor nit (Score:3, Informative)

    by evilviper (135110) on Tuesday June 14, 2005 @01:27AM (#12810209) Journal
    2: On-Demand, CNG water heater (i.e.: no tank to keep warm)

    Unless they've improved drastically in the past few years, these systems are terrible, and they only sell because they trick the "green" crowd into believing they're wonderful, and because of cheapo construction companies who buy this cheap junk instead of a more expensive tank-based water heater.

    Basically, when you turn on the hot water, you can expect the first gallon to be scalding hot, and the rest will be barely warmed above room tempurature...

    If you want to be environmentally friendly, use a normal hot water heater, leave it set low, and put lots and lots of extra layers of insulation around it.
  • by k98sven (324383) on Tuesday June 14, 2005 @02:22AM (#12810387) Journal
    >>Put salt in the water. The ice and chilled water mixture gets colder with salt.

    >Errggh.... no it doesn't :}

    Errgh.. yes it does.

    Salt in the water just allows it to be a liquid at a lower temp.

    Which means what? It means that you've shifted the equillibrium between ice and water to a lower temperature. Which will lead to the ice melting faster until the depressed freezing-point is reached. (after which the melting will actually proceed slower than before since the whole solution is colder)

    The reason you use ice in an icecream maker is to allow better thermal conduction to the container with the ice cream.

    I assume you mean 'salt in an icecream maker'. And that is wrong too.

    But if you don't take my word for it (although you should; I've got a degree in physical chemistry), then perhaps you should go look at this [frostburg.edu] entry in the General Chemistry Online FAQ, which adresses exactly this.

    Perhaps you should read the whole thing before you start correcting people on basic chemistry.

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