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designing a peltier air conditioning system

Discussion in 'General Electronics Discussion' started by evil_lies, Jan 9, 2011.

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  1. evil_lies

    evil_lies

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    Jan 9, 2011
    Hopefully someone here can help me out with designing an air conditioning system for a vw bug using peltier modules. I think that using a traditional air conditioner will rob too much power from the small engine, and the a/c kits are expensive. I think I can piece a diy system together much cheaper. Anyway, i've always been interested in electronics but don't have much knowledge about it, so I have some basic questions. I am looking at using something like this

    http://cgi.ebay.com/168Watt-Peltier...318?pt=LH_DefaultDomain_0&hash=item483e5419be
    or
    http://cgi.ebay.com/Gigantic-62mm-5...996?pt=LH_DefaultDomain_0&hash=item483622e5ac

    How many modules would you think I will need to cool the interior of a vw bug? It doesn't have to be freezing, but would like to cool down the texas heat build up inside. Also, what size heatsink and fan should I use?
    My idea so far is to house everything in an ammo can attached under the dash and then run ducting to 2 individual air outlets, and put temperature & fan controls on the outside the box. Or I may try to incorporate it into the vw heating system but add a system to cool rather than heat, but I think it will be easier to have a seperate system... so any ideas?
    Thanks,
    Brandon
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,489
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    Jan 21, 2010
    I think you're barking up the wrong tree.

    A typical peltier device that I looked up can remove 80W of heat energy for the expenditure of 136W of energy.

    In contrast a traditional refrigerated unit rated at 136W would typically be able to remove more than 400W of heat.

    So, a Peltier-based air conditioner would require almost 5 times the amount of energy to do the same cooling job.

    And unless you're planning to carry a heap of batteries and charge them at home, that energy can only come from one place...
     
  3. evil_lies

    evil_lies

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    Jan 9, 2011
    i've heard they weren't extremely energy efficient, but i'll have to investigate more then. I was thinking about possibly putting a roof rack on it with a solar panel on top. I don't know if it would produce enough energy to power the a/c or not. Anyway, thanks for your input!
    Brandon
     
  4. davessi

    davessi

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    Dec 24, 2010
    Yeah, Steve is right to achieve any substantial heat-pump effect (delta-T) using thermoelectric peltier devices is hard to do. You end up expending large amounts of energy for little gain. I designed thermoelectric fridge/freezers for NASA back in the 90's and although our applications were simple and extremely successful...we didn't have any illusions that the cabin of the next shuttle would be cooled by a thermoelectric engine.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It *IS* rocket science!!!! :D
     
  6. davessi

    davessi

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    Dec 24, 2010
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,489
    2,830
    Jan 21, 2010
    That is just so cool! And welcome to Electronics Point.

    My formal paid work is related to HLA research and testing, so I can relate to the uses your little sample freezer was put to.

    Let's relate the approximate power consumed, delta T and volume of the device. It would be interesting for evil_lies to imagine that scaled up (and the delta-t scaled down) to cool the interior of a car -- and let's just ignore the presumably good thermal insulation you would have used.

    That device has a delta-T of around 40 degrees (I assume), consumes 140 Watts, and has a capacity of around 1 litre.

    If we assume that a delta-T of 20C would require 70W, and the thermal mass of the car cabin is 1000 times greater, then you could achieve that with about 70kW of energy going to a (series of) peltier devices.

    OK, a ballpark figure of AT LEAST several tens of kW of power would be required.
     
  8. part_time

    part_time

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    Jan 18, 2011
    Add a second alternator and use a inverter to power a small window AC unit

    I'm not trying to be a smart... but it has been done by others

    Also VW had a evap cooler that mounted it the passenger side window you could put dry ice in
     
  9. davessi

    davessi

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    Dec 24, 2010
    hi guys, guess I am a year off from my last post. But, yes the delta-t was actually more around 70 degrees...we used a dual heat pump with large heatsink/fans to cool the hot side of the pump. There were obvious losses due to inefficiencies of the devices and heat transfer, but we accomplished what we wanted to with around 196 watts of power consumption....at 28VDC.
     
  10. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    I got a couple of these out of curiosity a year or so ago: http://www.mindsetsonline.co.uk/product_info.php?cPath=16_445&products_id=1009613

    Theyre not particularly remarkable. In order to achieve any useful amount of cooling, you need pretty good heat transfer from the hot side (usually involving fans which consume more power). The only real use for these things if for cooling ICs or other hot running / temperature critical components that are in direct contact with the cold side.

    They'd probably be more efficient when used as heaters :p
     
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