# Peltier Elements



## Casper10 (Mar 8, 2014)

Hi Evmetro, I have been using a Thermoelectric(peltier) system myself in my ute for a couple of years now and have no complaints, the efficiency thing is mainly in how the system is built and the quality of the modules. The common logic a couple of years ago was that a peltier system would not cool below approx 30 deg below ambient, but panasonic has now got commercially viable thermoelectric refrigerators on sale that have operating costs better than compressor fridges. The system I have is from topcool and heats as well as cools and some race teams are running them for the drivers cool suites, they are running them from a thermoelectric generator (teg modules) attatched to the exhaust manifold & any additional energy produced goes to the battery, that supposedly cuts the alternator load on the motor, a few free horses?. Go to *www.top-cool.en* and have a look. Regards Casper10


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## evmetro (Apr 9, 2012)

I checked out top cool, and it looks like they are on to something. I did not find pricing or where to buy their products, but I liked their stuff. I am considering getting a case of elements and building a system, but I have also searched this forum and the internet to see what the arguments are against using peltiers are, and there were plenty of warnings against doing this. On the other hand, I see that if you do not run full current through these things, they become more efficient, and they are indeed cheaper than they once were, so it is more realistic to be able to use more elements than needed, and to have an additional bank of them to recapture a portion of the waste heat that the main bank would produce. Perhaps a peltier radiator in the airflow up front to cool the hot water, a pair of water blocks sandwiching the main heating and cooling bank of peltiers, and a nice heat exchanger in the car to pull the cars heat out. It sounds like the peltiers will draw less current once the car is heated or cooled inside, kinda like the ceramic heaters do once they get up to temp, so maybe dump a whole lot of current into them to get to a reasonable temp, and then back the current off a little to maintain the temp at a more efficient level. I can see that their are diminishing returns on efficiency as the current goes up, so it would be a matter of finding the sweet spot for this particular car and having a large enough peltier bank to quickly achieve the desired temp and then be able to maintain at a more efficient level.


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## evmetro (Apr 9, 2012)

I would love to hear from some "devil's advocates"... Any engineers want to rough me up a little? I have found some general numbers on efficiency, but they do not seem quantitative... 15% + or - for peltiers, 70% + or - for freon/ compressor. The peltiers would not have any power losses from converting energy from one form to another, but the freon and compressor would. both sytems would need fans, the peltiers would need a pair of small electric water pumps. The peltiers would apparently be more efficient than the ceramics during winter, and less efficient for the summer. The efficiency numbers that I have found seem general, and seem to have a lot of variables...


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## Tesseract (Sep 27, 2008)

evmetro said:


> ...Any engineers want to rough me up a little? I have found some general numbers on efficiency, but they do not seem quantitative... 15% + or - for peltiers, 70% + or - for freon/ compressor....


The most useful metric for describing the efficiency of refrigeration systems is the "coefficient of performance" (COP or CP), which describes the ratio between the amount of heat removed vs. the amount of power required to remove it. Most thermoelectric systems have a COP of less than 1, which means they consume more Watts of power than they move Watts of heat.

Vapor-compression systems, on the other hand, have COPs of 2-5 (theoretical maximum of ~6), so move significantly more heat for a given input power than thermoelectrics, hence why you don't see thermoelectric systems used in cars, houses, etc. However, the COP of a vapor-compression refrigeration is somewhat proportional to size, so when you need to move a small amount of heat or cool a small space/object then thermoelectrics can actually be more efficient. Note that "small space" in this case would be around the size of a 12-pack cooler, and not, say, an automobile.

So you can certainly build an A/C system for a car with Peltier effect thermoelectric modules but it will probably take 2-3x more power on average for the same amount of cooling effect as the stock A/C.


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## evmetro (Apr 9, 2012)

Tess, Thanks for the info. If I divided the volume of mt car's interior space by the volume of a 12 pack cooler and then used that many or more peltiers, would the car's interior then be a small space? I am trying to figure out if the overkill and then maintain at a more efficient level approach has any merit.


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## Casper10 (Mar 8, 2014)

evmetro said:


> Tess, Thanks for the info. If I divided the volume of mt car's interior space by the volume of a 12 pack cooler and then used that many or more peltiers, would the car's interior then be a small space? I am trying to figure out if the overkill and then maintain at a more efficient level approach has any merit.


I don't know about cooling a 6 pack cooler,the top cool unit in my car gets that hot on full power you could not stay in the car and on cool cycle it is only margialy different than the ac it replaced, but it doesn't dry your eyes & throat on long trips like ac does. Top cool have been working on these things for a long time now and have improved the modules performance greatly. Read ther spec sheets and white papers Evmetro for their COP rates,they are also working with Renault etc putting these in new vehicles & Bmw has a teg system on one of their vehicles to generate power. I doubt if you would harvest much power from the heatexchanger though, most of the teg systems are run off exhaust(waste) heat.There is a town(village?) in Alaska or Canada that generates their electricity by burning wood to heat the modules.I think I read about it on one of TE's pages. Thermoelectrics has gained a lot of headway in the last couple of years any knowlledge older than 2 odd years is out of date as the efficiencies have been improved greatly.They have units that heat and cool your home and they come from Holland, gets plenty cold there.


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## Tesseract (Sep 27, 2008)

evmetro said:


> Tess, Thanks for the info. If I divided the volume of mt car's interior space by the volume of a 12 pack cooler and then used that many or more peltiers, would the car's interior then be a small space? I am trying to figure out if the overkill and then maintain at a more efficient level approach has any merit.


That will sort of give you the right number of modules & power consumption to achieve a similar temperature differential for the larger volume, but it doesn't change the efficiency of the modules. I only mentioned the 12-pack cooler example because it is a small enough application that a vapor-compression refrigeration system would end up at a lower overall COP than a thermoelectric one.

Additionally, keep in mind that a 12-pack "Igloo" cooler is rather well insulated compared to the typical car interior. Combine this with the fact that rate at which the sun dumps energy onto this planet is around 1kW/m² you can see that a Peltier system needs to be able to move at least 1kW, and perhaps as much as 4kW, to keep a small sedan comfortable.



Casper10 said:


> ...Top cool have been working on these things for a long time now and have improved the modules performance greatly. Read ther spec sheets and white papers Evmetro for their COP rates,they are also working with Renault etc putting these in new vehicles & Bmw...


Okay, I just downloaded the "Eco Clima-tec" datasheet and attached a screen capture from the page in it that shows the amount of heat moved versus the input power. In all cases the ratio between those two shows a COP of less than 1, just like I said it would be. [edit: in all cases of *cooling* the COP is less than 1; when the device is configured to warm the cabin the COP can go higher than 1 (which is better than a resistance heater, because the waste heat of the module is added to the heat it moves.)]

Again, I'm not saying it won't work, and doesn't have some advantages over vapor-compression systems, I'm just saying that "efficiency" isn't one of those advantages.


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## Caps18 (Jun 8, 2008)

I'm not sure they are powerful enough to effectively cool or heat a cabin. It might help if there was some spray foam insulation added inside the body panels, but I don't see it. I might be wrong though.

I would think a small dehumidifier would work better in the Summer, along with a vent fan that ran constantly when in a parking lot (Toyota stole my idea  ). I haven't looked into if they make a electric dehumidifier that would work though.

Maybe get two of these? And run the drain to spill on the ground.
http://www.amazon.com/Ivation-Dehum...d=1395589003&sr=8-7&keywords=car+dehumidifier

Then you have to figure out how to keep the dry air inside, but still cool down the solar loading by having a thermoelectric heat exchanger like you are talking about.

And in the winter, I don't know. I'm wondering if something like this would work.
http://www.amazon.com/Eco-heater-NA...615&sr=8-3&keywords=room+heater+electric+400W 

I would need to add some foam insulation to my truck though.


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## Casper10 (Mar 8, 2014)

The Top cool units work perfectly well,I have had one of their units in my car for around 4 years now and have no complaints,cools the car nearly as well as an AC,but doesn't dry you out and the heater gets that hot on full power that you couldn't stay in the car even on days that are 0 deg C it was only used at 75% power. Once the unit reaches the set temperature it just maintains and uses hardly any power I can see it on the amp meter kicking in and out. On our dyno the AC compressor used 8hp getting to temp and the same when it cycled on - off, roughly the same as a belt driven power steer pump,an electric DC Airco unit used between 0.25 and 1.00hp thru the alternator,which is just slightly more than an electric p/s pump,the thermoelectric unit used between 0.25 and 1.50hp when in use the high end when getting to temp and dropped right off when maintaining which is higher than the DC electric AC unit but still way better than the original unit & it is noticably cheaper when you fill up. all the electric driven units are more cost effective than the traditional belt driven items,I can't claim to know the reason for the vast difference,frictional losses etc, Im sure one of our electro minded persons would know the answer? The above results are in addition to the alternator base line hp drain which was 7hp on the vehicle used, but all ICE vehicles must run an alternator. 
PS: Tesseract, I wasn't disputing anything that you said, just quoting what the engineers at Hydrocool had written about thermoelectric modules. Casper10


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