I know that heat flow from higher temperature to lower temperature, but theoretically, is it possible to build heat pump that can move energy from ocean which are at ~295 kelvin to a small boiler which could be at ~500 kelvin.

I am asking out of curiosity that If its at least theoretically possible or not ? i.e. if I put, say, 5 kw in to the heat pump, can energy of 15 kw be transfer from ocean to boiler ?

  • $\begingroup$ Actually, if you think about it, what you're describing is actually equivalent to what you'd get if you turned a freezer inside-out, dropped it into the ocean, and turned it on. $\endgroup$ Apr 6, 2014 at 12:48
  • $\begingroup$ so freezer will be heated more than the energy I put in its heat pump ? by what amount ? $\endgroup$
    – iamgopal
    Apr 7, 2014 at 8:20
  • $\begingroup$ Yup, that's the interesting thing about heat pumps and refrigerators: you can, for example, move 2400J of heat energy into a reservoir while only spending 1000J of electricity (if the COP is 2.4, as Mirc pointed out). This may seem like it violates conservation of energy, but it actually doesn't. Most courses on thermodynamics will discuss this topic when they talk about heat pumps/refrigerators/engines, so you can also learn more from there. $\endgroup$ Apr 7, 2014 at 11:58
  • $\begingroup$ I get it that entropy being constant or increasing as "good" electricity energy is used, and bad ( heat of the atmosphere or ocean ) is being transfer. But the obvious next question is, than why not all the boiler in the world run by using ocean energy ? do heat pump with its cold end at 50 degree can move energy to 500 degree reservoir ? $\endgroup$
    – iamgopal
    Apr 8, 2014 at 12:39

1 Answer 1


Yes that's possible. For a Carnot heat pump the coefficient of power is

$COP= \frac {T_{hot}}{T_{hot}-T_{cold}}$ so about 2.4 in your case. Which means you would get 2.4 times more heat out than work in.
In reality the COP is smaller than that due to non-reversibilities.


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