Poor Man’s Peltier Air Conditioner


It’s summer in Germany, and [Valentin’s] room was getting hotter than he could handle. Tired of suffering through the heat, and with his always-on PC not helping matters any, he decided that he must do something to supplement his home’s air conditioner. The result of his labor is the single room poor man’s A/C unit you see above.

He had a spare Peltier cooler sitting around, so he put it to good use as the basis for his air conditioning unit. He sandwiched it between a pair of CPU heatsinks before cramming his makeshift heat pump into a shoe box. Warm air is drawn into the box and across the cold side of the Peltier before being blown back into the room. On the hot side of the box air is also pulled in by a fan, drawing heat away from the unit before being exhausted outdoors through his window.

While he hasn’t quantified the machine’s cooling power, he seems quite happy with the results. We have a spare Peltier kicking around here somewhere, perhaps we should try building one just for grins.

68 thoughts on “Poor Man’s Peltier Air Conditioner

  1. I’m no HVAC guy, but it is all about heat load and efficiency. Still, it’s interesting enough, and with some thermal sensors here and there, one could gather enough data to learn a bunch, and perhaps also have an excellent school project. And if it cools a fellow off a little bit more, great.

    1. Thermo-electric heat pumps are 85% inefficient. Meaning unless your power source is free! its a waste. An automobile engine that’s running anyway, solar, wind. Or in some places landlord supplied electricity.

      1. Does it matter how efficient a peltier is? Do you have any information about compressor system AC which can run below 100W and cost below $100? Thermoelectric cooler is the best answer of it, which can easily be run by 100W air or solar power module and can cool down yourself whether reading or sleeping, but don’t bother to cool all furnitures and fixtures in the room.

  2. More of a ‘fun project’ than anything useful- Peltiers are notoriously inefficient. Looks to be an 80W peltier, so he’d be lucky to be getting 8W of cooling ability.

    1. I have two 12706 side by side now, fitted on the window (removed a glass) and driven by a 200W solar panel. Who cares about efficiency! :D Even though the cooling is nothing much, it dehumidifies the air decently enough ( RH is around 70% here )

    2. Not even. If you add up all the losses and the fact that you are also pumping air from outside to compensate the pressure differential, you’ll find up you have a heater, not a cooler. It could feel nicer if it blows cooler air to your face, though. A fan does that better.

    1. This week we’re supposed to be hit with 38 to 40 Celsius! I also have a peltier kicking around, but I think it would be much better to draw cooling air in from outside, then vent it back.That way, you’re not sucking the hot outside air back into your house.

  3. @Wizzard: Peltiers aren’t THAT inefficient.

    Could be an 80W peltier like the TEC12709, in which case let’s see…

    80W electrical input, I’d approximate the temperature difference around 20 degrees between hot side and cold side, at which the peltier CoP is around 0.3 – 0.4. Therefore transferring about 24 – 32W of heat out of the air, and effectively 30-40% efficiency

  4. Down talk this guy down too much. This isn’t meant to cool the whole room its meant as a spot cooler. If he’s happy with the results, then I say more power to the guy.

    1. guys if you wanna make an air conditioner and maximize your peltier cooling effect just make the hot part cold enough so your peltier dont need to draw much heat and it will be colder enough..then it will now depend on your design…^^ have fun making this..nothings possible in this world only humans limit themselves but GOD created humans with limitless brains so make it happen…!!

      1. Your words inspired me to say, where does the ideas come from in our minds? I think He who created the brain pours down ideas in it? I have such an out of the box approach towards things that when ever the world say it is not possible I begin to think of possibilities, but knowledge is something that support ideas and it is pure power. One without knowledge is like an empty pot. Good luck heron

  5. @Dax,

    2nd’ed. From personal experience with these beasts, I can confirm, they take a whacking-great amount of oomph, to give cooling to a very localized area. Having worked with triple, and quad-staged cascade systems for my job, I can vouch for the amount of power they require to do anything aside from cooling small thermal loads.

  6. Using @Mike’s number of 32 Watts that comes out to 109.2 Btu’s. It takes aprox. 5000 Btu’s to cool a small room.
    Still a neat project, just not very useful.

  7. I did a similar trick with one 180w Pelt. I used my watercooling loop(external to my pc at the time) to cool the hot side, put the biggest CPU cooler I had at the time, It was like a desk cooler, the fan straight at me.

    Shoe boxes work too, the AC unit in my old office had four “panels” of peltiers with huge heat-piping(commercial design) this cooled a 20×30′ office with 28 PCs. The panels had to have thousands of watts. But the whole unit fit in the 10ft wall, no more than 3 inch deep.about 4ft wide.

  8. I was looking at designing something like this to market. Would have been great if it could work. Only 2 moving parts. After doing the research I found that it would require far more power than a conventional unit to cool even a very small room. I figured there had to be a reason it hasn’t been made already. The only way i can see this being useful is as a supplement to a phase change system.

  9. Peltier exchange, something most of the industry are too smart to realize the potential of.

    My friend works for a company who currently has the most efficient method in full manufacturing(using serial-wired iron pellet grids). We beat the best energy star fridge rating using 40 usd in parts one night…I still use it to keep food in the garage 2 years later..

    It’s a heavily underrated method, it can replace even industrial ammonia-gas systems at 1/5 the cost and consumption…

    HINT: If you can get the pellets, hot-glue is perfect for doing the grid method. It’s hard to do decent peltier coolers homebrew cause of the iron material resources and sizing.

  10. I’d like to see people getting into actually making homebrew manufacturing for these, the most efficient way to date is publicly documented by companies making them.

    It’s electric cooling and freezing..

  11. @xorpunk: Why don’t you start us off by doing a small write up on it (something fun rather than dry industry papers)? The hacking community is a force to be reckoned with, we just need a nudge in the right direction to get started.

  12. I AM an HVAC guy, and points for concept, but none for scale, and minus several for moisture control. most people don’t realize the First function of your AC unit is to dehumidify the air, it can be 110 degrees but if the air is dry, your sweat will keep your body temperature stable. The first thing this will do is try to remove the moisture from the air, he probably noticed it pooling in the bottom of the box. if he doesn’t have a drain, it will probably start to play host to all sorts of bacteria. of course he could have just gotten a dc electric cooler off ebay for $40 and added fans to it, works on the same concept.

  13. A standard A/C will have a COP that is about 10 times better than that of a peltier.

    It would make more sense to put the peltier directly on the forehead or something like that.

  14. Going by the photo of the DMM, and the stated 18V supply voltage, less than 75 W is being consumed. I can’t see how that would be that noticeable especially if the mini AC is only cooling air already cooled by a home AC, as Mile Nathan suggests in his post. However I didn’t see a mention a home AC on Valentin’s blog detailing the build. In reading the spec sheets for TEC there is a recommended amount of force that should be used to make the “sandwich” to get the best performance I doubt the method use here meets that. And BTW a heat sink equipped with a fan is not a passive cooler. Anyway it is what it is, if Valentin had fun building it, and is satisfied with the results is all that matters, no one is required to duplicate it

  15. He could have gotten 300 Watts of “cooling” by just exhausting the heat of his PC to the outside. But wait- thats to simple and doesn’t have Peltiers and LEDs.

  16. I’d like to see a wrist version of this for cooling your blood by contact with the veins in your inner wrist. Much more effective way to cool off your body.

    1. Not a bad idea, but the SF 49ers research has found that it works better by placing the cooler across the palm of your hand. Want to learn more? Google info on the “cooling glove”: after an initial workout and a few minutes of one hand in the cooling glove, athletes performed BETTER in the immediate follow-up to the glove, than they did in their original workout.

      1. Very good, but if anyone tried that they really need to use a precise temperature controller, maybe one of those industrial standard PID controllers, to regulate how cold your hand gets. Too cold and the blood vessels constrict reducing blood flow and pretty much halting any further heat transfer. The stanford researchers are looking for a marketable item, but are they able to compromise by not using a vacuum to swell the blood vessels? Trying to include a peltier module into a ‘cooling glove’ is not necessarily the right approach here. Maybe a glove designed to be worn while driving a race car, with thermally conducting metallic wire with a high ability to flex a lot without breaking, sewn around very thin passages that air or water is run through? But what I really want is a car seat skin that can be installed into any car with this sort of thing. And it really should be air cooling because there’s also a humidity control factor I want to address concerning my backside regions.

  17. This was probably done for kicks. I’ve played with them some. Tried to make a beer cooler one time. Just WAY too much power consumed for what you get.

    I had a hard enough time making a smaller insulated cooler. So I can’t see using something like this even for a “spot cooler.”

    I’m sure anything this maker is feeling, is probably just the feel good from playing with these things and not actual cooling.

  18. Dax’s noting about how the PSU could generate more heat than the peltier would offset probably holds water, I have a couple of 100watt peltiers I’ve yet to properly impliment into something and have hesitated because a 60watt 12v PSU brick I use for something else can get quite hot and I dread to think what heat a 100watt brick would put out.

    Currently to help keep sane in hot weather I have a set of 9 12cm computer fans stuck together and blowing air around the room, using a Picaxe 08m I can control the speed easily through PWM and have them almost silent whilst still blowing air.
    As for PSU heat problems there is none, they’re being powered from an old car battery charged from a 30w solar panel :)

  19. @sneakypoo: The actual design has to be done with magnification and super-fine soldering, using bulky size drastically decreases the efficiency. Also the materials(bismuth telluride is most efficient) is kind of hard to form into millimeter blocks at home..

    @ztraph: All solutions including newer non-ammonia gas systems in consumer appliances have that problem. It’s commonly reused for cooling where it vaporizes externally..

    In camping coolers that use this tech it’s also used to cool, it actually takes care of itself in those applications without pumping though by simply using ventilation.

    This ‘hack’ is just a manufactured unit poorly implemented. The tech is super useful though.

  20. @Flame 500

    I’m assuming you’re deliberately trolling. However, in the case that you’re not, BTUs and Watts are not the same thing – BTUs measure energy, Watts measure power (rate of change of energy). It’s really important that units are correctly used and understood – so often on Hackaday I find well-meaning comments that serve to confuse and misdirect.

    32W is, in fact, 109.2 BTU/hr. Notice the rate of change factor here. With this in mind, where does your 5000 BTU figure come from?

  21. This is exactly how those tiny car refrigerators work – for suitably small amounts of “work”. Peltiers are quite inefficient even for such small volumes of air, let alone cooling rooms. Whatever effect he thinks he’s feeling in this room from this contraption, he’s fooling himself.

  22. @Stefan
    I was simply attempting to provide some useful metrics to help people analyze this project. You are correct, I neglected to include the /hr suffix. That was semi-intentional because I wanted to compare this project to the way consumer window AC’s are rated. They are marketed based on a cooling capacity in BTU’s. I believe this is actually BTUs/hr and was attempting to avoid unnecessarily complicating the matter.
    To answer your question, 5000 BTU/hr is the smallest window air conditioner you can buy and that size is only supposed to be capable of cooling a 150 sq. ft room.

  23. @Flame 500

    Thanks for clarifying. Re-reading my post, it probably came across more aggressively than I intended. It’s good to learn a bit about AC from someone who clearly knows more than I do about it – I’ve only ever seen BTUs used to rate the contents of flammable gas canisters.

  24. i like the ingenuity, but wouldn’t he be better to use a cooling coil that runs through an ice chest and then a fan blow through something like a heater core from an automobile? lots of retrofitting, but that’s what we like on HAD right?

  25. looks like you are using a power supply for a printer.

    you are probably going to burn that power supply.

    you will need a power supply that can supply more than 10 amp.

  26. I have some years of experience with a commercial print system that used peltiers to cool the recycled ink, and I can tell you that these things will kill *themselves* with internal condensation. The condensation on the cold plate will corrode the solder & eventually eat the copper between the blocks. If you want the unit to last, you have to seal that internal airspace.

  27. When I was 12 made an “AC” unit out of a fishtank pump a heater core and blower and a tub of water.

    I put the pump in a tub of water outside and put the heater core inside with the blower. It worked ok then I got the idea of burying the radiator and that worked much better. Me and my best friend spent two days and managed to get it about 6 feet in the ground.

    It was decently effective at making a “cool” flow of air, better than nothing when it’s 99 degrees F. humid and still.

    Germany’s ground temp should be even cooler than Southern Indiana.

  28. @ joe pittsburgh
    i have done almost the same thing.
    i used the watercooling loop of my server (wich has the radiator dangling out the window) to cool the hot side of a peltier module. i used a shoebox as a seal between the hot and cold side. et voila a nice cooler that cools your legs/head/arms. its even better if you place it hanging above you ^^.

  29. This “air conditioner” suffers from a defect common to many of the “portable air conditioners” that I have seen in that it fails to consider the source of make up air to replace the air exhausted outside will be more warm air. In order for this device to work, the warm side of the thermal interface should be outside of the building envelope and both the supply and return (basically a heat sink with a fan) should be there. The other side of the thermocouple should be inside the building envelope, where it can both draw its supply air and exhaust cool air without creating suction from outside. This will also improve air quality and make the device’s parts that have the potential to make people ill, (if they were to accumulate potential mold food which would get and stay wet from condensation.) more cleanable and accessible.

    There should be no air communication between the outdoors and indoors parts.

    The same principles apply to any cooling device.


    1. I like that approach, cut a board(insulating foam panel?) to fit tightly in a window, mount the peltier device in the middle of the board through a hole in the board, use a fan on both sides, mount the PSU on the outside of the board(maybe use the PSU exhaust as the peltier hotside cooling?), mount a sun/weather shielding box(rest of the foam panel?) on the outside, mount an aluminum flex hose on the inside to aim the cool air to where you want it. Maybe run a plastic flex hose right to your chair and connect it to one of those air-conditioned shirts from japan?

  30. Design matters, integrated with proper cooling [hotside], peltiers are good and efficient than all you people think. and it can cool more efficient than current compressor type air conditioners, with less power. Use PC PSU s for powering peltiers, they are much efficient and outputs much less heat.

  31. I was thinking about doing something like this with a solar panel I live in florida plenty of sun! Im sure its not that efficient but lets say like this setup I get a output of 32W thats 109.2 btu an hour if I have a pretty sealed small room and not much in the way of heat generation in it wouldn’t it keep the room cooler throughout the day?

    1. Not noticably. I have a 40W peltier mini-fridge. It can’t even cool a can of pop on a warm spring day. And that’s just cooling a square foot of insulated box!

      If you only have a solar panel you need some other method. Maybe pumping cool water round, or spraying it somehow. An indoor fountain might cool the place, maybe put a few drops of bleach in the water, to keep horrible things from growing.

      Peltiers really are no use for cooling anything much bigger than they are. And of course, in a closed room, they generate more heat than they take away. You’d have to window-mount it, but again, just opening the window would do much more cooling.

      1. Very true. In my experience only thing you can do is water cool the hot side, which an A/C unit would be more efficient than a pump and fan and pelt. I’ve done the water cooling route with a already water cooled computer and it can make for a 1C difference in a closed case

  32. I have seen a few 6 60 watt peltier devices that are water cooled … On my boat I have a limitless source of water in the low to mid 70 degree range. I wonder how many btu’s it can gobble up. My generator on the boat provides only 900 watts . Not enough to kick off the compressor on a 5k btu AC unit. I just want something to take the edge off and peltiers seem like the ideal solution for my boat. The aft cabin is the size of a queen size mattress and half of it is like 4 feet tall the other half just over 6 feet. 6 60 watt peltier modules should be about 1200 btu’s if I read some of these posts right my generator could probably supply two or so of these things . At night that would be around 2400 btu . That might just cut it. What do you think.

    1. Some sort of evaporative cooler might help. The air in a boat is always going to be humid. And you wouldn’t want, for example, canal water squirting into your breathing air, you wouldn’t live long enough to switch it back off again. Maybe some sort of heat exchanger? Maybe a system where there’s a radiator by your feet with cold water run through it? You could stick your feet on it to cool down, and it should take heat out of the room.

      As David says, Peltiers are only useful for cooling small areas very inefficiently. Like the top of a computer’s CPU, but they don’t even use them for that much any more, CPUs started generating more heat than a Peltier could carry away.

  33. Air room temperature which will be eventually cools. Is been sucked to cool the heat side of the peltier. So. therefore, the air room cool temperature will never be cool. Examine a conventional a/c the room side is never suck to cool the condenser. Only the outside air cools the condenser. And the evaporator gets the cool air and recycle back to the air room cool temperature. Nothing is wasted.

  34. I’d like to try to convert an old fridge/freezer to run as an AC. This old Fridge would sit in the basement, and I’d have to pipe down the room air to circulate it through the fridge, and back up to the room. It would warm the basement, unless one manages to do something with the heat emitted from the back of the fridge, such as domestic water heating.

    I’m not sure what sort of trouble one might run into, such as ice build up from condensation, etc.

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