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I Seebeck generator from placing water heater next to freezer

  1. Apr 3, 2017 #1

    DWT

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    Water heater is set at 130 degree f freezer is 5 degrees f.

    Is it possible for a thermoelectric generator to collect energy from these placed side by side?

    Would the extra energy used by the heater and freezer due to the presence of the generator cancel out and then some any energy that could be collected?
     
  2. jcsd
  3. Apr 3, 2017 #2

    fresh_42

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    2017 Award

    Staff: Mentor

    If I read your question correctly, the answer is:
    There cannot be a perpetuum mobile (PMM) in our universe. (Reason: laws of thermodynamics)
     
  4. Apr 3, 2017 #3

    DWT

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    I am not suggesting a perpetuum mobile, i am asking more about conservation of energy. Since one thing is allready hot the other cold couldnt we conserve some of that energy and give it back to grid?
     
  5. Apr 3, 2017 #4
    Short answer is "no." A freezer pumps heat from the inside chamber and exhausts it externally in its refrigeration cycle. The outside of the freezer gets warm.

    It would be better to have the watersupply going into a water heater jacket where the incoming water is cold, and put your peltier device inbetween the jacket and water tank.

    The reality is, its not cost effective.
     
  6. Apr 3, 2017 #5

    russ_watters

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    The water heater and freezer are both insulated to prevent heat transfer. That's the opposite of what an energy harvesting device needs. So there really is almost no energy available to be captured and at an extremely low delta-T (because of the insulation), you get an extremely low efficiency.

    Broader; the laws of thermodynamics do indeed forbid such a device from being useful, even if it isn't obvious how. The energy required to create your temperature difference must always be greater than the energy gained by harnessing it. In this case, it is particularly bad because most electric water heaters don't even use a heat pump (COP: 4:1), they use resistors (efficiency: 100%/COP: 1:1)
     
  7. Sep 6, 2018 #6

    LURCH

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    Or maybe just set up a heat exchanger between the two, so that heat from the compressed refrigerant fluid gets put into the cold water entering the tank? This would perform some of the work of heating the water and cooling the refrigerant, practically for free. Wouldn’t that reduce the amount of energy needed to do both jobs? Would probably work best when the water is in motion, so I don’t know how much of a savings it would be. Just a thought.
     
  8. Sep 6, 2018 #7

    russ_watters

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    In fact, this product already exists: it's called a heat recovery chiller. It makes process hot and cold water at the same time, instead of rejecting the condenser heat to nowhere useful.

    https://www.carrier.com/commercial/en/us/products/chillers-components/heat-recovery/

    Really, it's just different in function from a normal water cooled chiller.

    It isn't done on a scale as small as a residential refrigerator that I know of though.
     
  9. Sep 6, 2018 #8
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