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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 '20 at 8:57
  • $\begingroup$ This is an project I'm trying to implement for some other application. Also, aren't ACs more expensive? $\endgroup$ – Aman Agarwal Mar 3 '20 at 13:27
  • $\begingroup$ More expensive? For 30m3? Temperature change required? Time constraint? $\endgroup$ – Solar Mike Mar 3 '20 at 14:39
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    $\begingroup$ reddit.com/r/engineering/comments/fcr2zo/… $\endgroup$ – Aman Agarwal Mar 3 '20 at 17:24
  • $\begingroup$ It looks like the team over at /r/engineering have effectively answered this... tl;dr - not a good idea. $\endgroup$ – Jonathan R Swift Mar 3 '20 at 18:01
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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.

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  • $\begingroup$ 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 '20 at 14:50
  • $\begingroup$ Peltier modules are really cheap. $\endgroup$ – Aman Agarwal Mar 5 '20 at 14:13

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