# car A/C using peltier devices, is it feasable'

In a couple of forums where we are working on kit cars with VW air cooled engines and therefore little room for conventional air con compressors etc we are looking at electronic means of getting cooled air into the interior and peltier devices have been mentioned. There is the advantage that we have small two seat cabins, about 2,5 cubic meters so not a lot needed but with ambient external summer temperatures of 30c to 42C and a large, almost horizontal windscreen, internal temps can get as high as 60c+.

I have looked at a few kits and assemblies and I can see where we could use and even utilize these but how COLD if one could expect from say a 6.5A to 10A unit using something like a CPU cooler heat sink and fan.

Alternative idea is to cool the fluid with Peltier devices in an insulated container (like a cool box) and then use that to construct a pumped cooled fluid system passing the pipes through the cooled fluid and a matrix in the car with a fan as normal and again use the heated side when needed for warming the car, when not needed the heat would be vented away or the whole thing just switched off. A/C using peltier devices, is it feasible'

Any brain storming ideas would be very welcome as I can get my head around the engineering side but electronics are limited to 12vDC car systems.

My Mercedes air con delivers as low as 5c at the vents but that is too cold and it is a much larger area.

• peltiers are very inefficient and need lots of current to run, as well as decent heatsinks and probably fans. For anything bigger and less insulated than a simple cooling box a compressor based heat pump will be much more effective. – PlasmaHH Apr 29 '15 at 10:01
• No. Compressor systems deliver about 4x as much cooling for the same power input. And they start pretty small and low power - search for Danfoss BD35 for one example. – Brian Drummond Apr 29 '15 at 10:40
• You'd have to keep the hot side relatively cool and even then it wouldn't work very well. Practical EV A/C systems such as this one generally use DC motor-driven compressors- because of efficiency. – Spehro Pefhany Apr 29 '15 at 12:46
• Excellent summary at this site. Basically, only electric vehicles have electric compressors, because of the power involved. They run at about 2 kW, 40 A @ 48 V. At 12 V that's 200 A, which is just too much current. Now consider that a Peltier is several times less efficient! – tomnexus Apr 29 '15 at 16:47

May be possible, but not viable.

Have a look at the Datasheet of a TEC1-12714S from Thermonamic Module. This is a 62x62x4.9mm³ PE, maximum current 14A, maximum voltage 17.2V. It is one of the most powerful devices on the marked.

The first problem a PE has is that it also conducts heat from the warm to the cold side, and this linearly depends on the temperature difference. While the heat pumping power is about constant, this means that the effective heat pumping power has it's maximum when there is no temperature difference. As soon as the difference rises, heat is also conducted backwards, and at some point, this "back-flow" equals the pumping power. So, the first diagram shows a linear dependency between temperature difference DT and effective pumping power Qc:

However, as long as it's really hot inside the car, the full pumping capacity will be available.

Note also that the maximum pumping power is about 140W for 14A and DT=0. If you have a look at the second diagramm, this current occurs at about 12V. So the PE consumes 12V*14A=168W of electrical power, already more than what it pumps. If there is a temperature difference, effective pumping power decreases while power consumption increases due to higher voltage. So, if t's really hot outside (40°C) and you want 20°C in your car, this PE will only have an effective pumping power of 100W.

Also, you have to dissipate pumping power plus consumed power at the outside, so 268W for the last example.

Up to now, we did not say much about how much power you need. A hair dryer typically has about/above 1000W, which heats your bath room only slowly. 100W may me much for a solder iron, but it's quite negligible for heating a room. The sun heats your car about 1000W/m².

I did not find numbers about car ACs, but is well-known that an AC takes some kilowatts from your engine. You may not notice it on most cars, but I do. I've only about 50kW, and on the highway with a slight slope, I sometimes call the AC switch my "inverse turbo boost". For sure, the AC takes about 2-5kW. As the pumping power can be higher than the consumed power (see this discussion, though not answered yet), you can estimate the pumping power to at least 3kW.

3kW, that's 30*100W, so 30 peltier elements each consuming 168W, being 5040W or 420A at 12V. Furthermore, you have to dissipate 30*268W=8040W of heat somehow.

I think, the numbers of my last paragraph show that it would be better to think of a compressor-based AC solution...

• I'd considered a peltier bank once for "green" residential cooling. Turned out to use WAY too much power; it's just impractical for anything bigger than a lunchbox. – rdtsc Apr 29 '15 at 12:52
• the bigget problem is that it's very easy to find around all needed components to build a peltier cooler; but try finding components for a 12V compressor-based cooler! – jumpjack Dec 27 '18 at 18:33

As mentioned in sweber's answer, a peltier device doesn't meet your minimum needs for cooling. An alternative to the peltier device are the compressors found in the trucking industry for No-Idle Heavy Duty Trucking Air-Conditioning. Masterflux is one such supplier.

http://www.masterflux.com/products/

Another alternative is an electrically-driven rotary compressor. The first one I found on Google is a 12V model that takes 840W and pushes 3412BTU. It functions exactly like a belt-driven unit, except its power source is electrical instead of mechanical.

The idea is sound. I have built a home air / heater with Thermoelectric devices

For all the non believers please read this: https://www.researchgate.net/publication/280775058_REVIEW_PAPER_ON_THERMOELECTRIC_AIR-CONDITIONER_USING_PELTIER_MODULES

• Welcome to EE.SE, we love to see what you built, but this is a Q&A form and you need to follow the format and answer the users questions, since this question doesn't really have questions in it, it is an oddity but please answer the questions in the future. – Voltage Spike Aug 2 '16 at 21:37
• "For all the non believers ...". This isn't a quack site so it's not a question of "belief". Please summarise actual facts and numbers from the article and address the OP's questions. e.g., How much cooling could they expect from 10 A at 12 V? – Transistor Aug 2 '16 at 22:11
• From your abstract: Using these refrigerants can get maximum output but one of the major disadvantages is harmful gas emission and global warming. You do know there are refrigerants that don't contribute to "harmful gas emission and global warming", and they're legally required to be used in all new systems, right? Basically, a fundamental basis for your thesis appears to be completely invalid. – Connor Wolf Sep 6 '16 at 1:03