How do heat pumps work and why are the energy efficient?
Edit: the question is sufficiently answered. Thanks guys!
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A thermodynamic heat pump is something that moves thermal energy from one place to another. Moving energy does not necessarily have any relationship to how much energy you are moving. For example, if I carry a gallon of oil from one place to another, I moved a tremendous amount of energy, but I didn’t have to expend a particularly large amount of energy to do so.
So, thermodynamic heat pumps, which include both cooling and heating systems, can move much more energy around than the electrical energy you are using to power the system. The only real limit are the laws of thermodynamics – you aren’t allowed to create such a large difference in temperatures that you could use it to eventually extract more work than you put in, or where you would decrease the entropy of the overall pump+room+environment system.
[The wiki](https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits) has some numbers – given temperature differences found in the real world, you can expect to be able to move around 2-10x as much thermal energy as the electrical energy you’re expending on doing so, with the average of practically build able systems really being around 2-5.
The colloquial term “heat pump” refers to the product that is used to heat your home. This is a special instance of a thermodynamic heat pump, which also includes AC systems, fridges – anything used to make one place hotter and another colder. It is more efficient than a normal electric heater because a normal electric heater that is using 1000 watts heating your room is only ever putting 1000 watts into your room. A heat pump can use those 1000 watts to make a flow of several thousands of watts from the outside into your room. It almost looks like cheating, since you get over 100% efficiency – but of course the place we’re getting that energy is completely different, so conservation of energy is always respected.
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