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Ambient temperature energy generation

  1. Jul 1, 2013 #1
    It is known that heat pumps create more energy than it consumes due to moving "heat" from one place to another. For example, if an air conditioner consumes 100 watts, the compressor will release 120 watts of heat since the heat in the room will be transferred to the compressor.

    Would it then be possible to extract the energy released from the compressor to generate electricity? This doesn't violate the conservation of energy since the energy is derived from the ambient temperature (The net temperature in the atmosphere will decrease to compensate for the energy we obtain).

    Is this logic flawed? Would such a device be possible and economically viable?
     
  2. jcsd
  3. Jul 1, 2013 #2

    mfb

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    2016 Award

    Staff: Mentor

    Not more than the compressor needs. The same advantage you have for heat pumps is a disadvantage for the opposite direction.

    It would reduce entropy, which is against the laws of physics, too.

    No, such a device is impossible. There is no loophole, it is pointless to ask "would it work if ...?".
     
  4. Jul 1, 2013 #3
    Why wouldn't it? A normal compressor would generate the same amount of energy as it would consume. Of course, we cannot extract as much energy as it needs since the generator or heat engine cannot be 100% efficient and some energy is loss as sound, EM radiation, vibrations, etc. However, the total energy released from the system must equal the energy we put into the compressor.

    Now if we used this compressor to move heat from the outside air into the machine, there would be more energy that it started with. Suppose the energy it release is 115% and is released as heat. Could we use the best technology we currently have to extracte 90% of the 115% of the energy it consume back as electricity? We would then have 3.5% energy left.

    Could anyone explain how this logic is flawed?
     
  5. Jul 1, 2013 #4

    russ_watters

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    Staff: Mentor

    The efficiency of heat engines and heat pumps are opposite functions of temperature difference: a greater temperature difference increases the efficiency of the heat engine, but decreases the efficiency of the heat pump.
    Logic explained above. For the numbers, rather than pulling them out of the air, you should plug them into the heat pump and heat engine efficiency equations. Then you'll see that you can't have a 115% COP coupled with a 90% efficiency.
     
  6. Jul 1, 2013 #5
    Alright thanks. I now realized how flawed this idea is. :smile:
     
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