I am thinking of building a indirect Peltier AC to cool a room of approx size 30m3. Single/multiple Peltier modules will be used to cool a insulated box with water inside. The box will be kept outside the room. A pump will circulate the cold water of the box in a pipe which will go inside the room. Inside the room, The pipe will be connected to something similar to a radiator, but rather than throwing heat into the air, it will throw cool air. Also, I want to achieve maximum efficiency, by correctly balancing the current, voltage and temp difference. Pumping heat out of the Peltiers will most probably not be a problem as they will be water cooled. Is this practically possible?

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    $\begingroup$ Possible yes, but would AC be more efficient? $\endgroup$
    – Solar Mike
    Mar 3, 2020 at 8:57
  • $\begingroup$ This is an project I'm trying to implement for some other application. Also, aren't ACs more expensive? $\endgroup$ Mar 3, 2020 at 13:27
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    $\begingroup$ reddit.com/r/engineering/comments/fcr2zo/… $\endgroup$ Mar 3, 2020 at 17:24
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    $\begingroup$ It looks like the team over at /r/engineering have effectively answered this... tl;dr - not a good idea. $\endgroup$ Mar 3, 2020 at 18:01
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    $\begingroup$ A conventional AC will be cheaper and probably more efficient. $\endgroup$
    – Eric S
    Mar 4, 2020 at 4:01

2 Answers 2


Peltier thermoelectric cooling modules can be used to cool anything you like. It will not be economical compared to a standard off the shelf air-conditioner (R-134A compressor cycle). If you source the modules, pumps, heat sinks and fans cheap and ignore your labor cost you may be able to come out at roughly the same manufactured cost a regular air conditioner. The cost of operation however will be considerably more expensive as the efficiency of themoelectric modules is much less.

So a thermoelectric cooler would not be "practical" for everyone, but if you had other constraints, it may make it a good solution.

  1. Such a device could be made to run silent (as long as the fans and
    pumps were very quiet)
  2. Can run off of variable amounts of power (for example variable power output from a solar array)
  3. If the system is properly designed they can last much much longer than a compressor (no moving parts)

Here are some notes on the efficiency. Here is a clip from the Thermoelectric Cooling Wiki:

In refrigeration applications, thermoelectric junctions have about 1/4 the efficiency compared to conventional means (they offer around 10–15% efficiency of the ideal Carnot cycle refrigerator, compared with 40–60% achieved by conventional compression-cycle systems

The Carnot efficiency can be improved by lowering the temperature of sink (location you are discharging the heat). There are some options here since the design permits storing heat in water. Running the cooler at night when the air temp is colder permits the cooler (and a compressor unit) to run more efficiently. Similarly you could put water storage on the hot side of the modules as well, allowing that water to circulate at night and provide a cooler sink than the air would during the day.

And just because themoelectric modules are not comparatively efficient today, does not mean it will always be the case. Material science is always pushing the limits. Solid state devices will only get better and better as new materials and techniques are developed.

  • $\begingroup$ Great answer, except I’m guessing even the part cost will be much higher than a conventional AC since peltiers are expensive and there won’t be any volume discounts. $\endgroup$
    – Eric S
    Mar 4, 2020 at 14:50
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    $\begingroup$ Peltier modules are really cheap. $\endgroup$ Mar 5, 2020 at 14:13
  • $\begingroup$ @AmanAgarwal: Peltiers that I found are at 2-3 usd for 16cm^2, or some 1500 usd / m^2. Not in my definition of really cheap. Especially that you want the bigger area possible to maximize efficiency. $\endgroup$ Apr 19, 2021 at 10:29
  • $\begingroup$ @AdrianMaire Yes, I have given up on this idea long ago lol. It is more like trying to heat a cold room with a light bulb. $\endgroup$ Apr 20, 2021 at 16:34

The simple answer: YES, a compressor will still be slightly more effective (2022) and noisier, but yes it can work well if well designed.

It will draw more power compared to a compressor but will be almost silent and super compact.

Proof of concept.

Built one out of an old plastic container, 4 old pc fans (low speed) an old PSU and some cabling, separate the box into 2 compartments: Hot and Cold.

Peltiers are super cheap now days, just add some ventilation ducts and ... voila your own portable AC, it's too bad power prices today make it more costly in the long run than a compressor design, but in summer it's sure a blessing to have.


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