I don’t get it. How is cold, even freezing air turned into heat? How is it less energy consuming than other heating systems?
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Heat pumps (at least refrigeration type heatpumps) work just like Air-conditioners in reverse.
They make use of 2 physical phenomena:
1. Latent Heat, which is the energy difference between a substance at the same temperature but two different states, so for example 100°C steam has a lot more energy than 100°C water, and this difference is the latent heat of vaporisation (you can actually see this difference in person when you boil water, it only takes a few minutes to bring a kettle or pot tona rolling boil, but takes a few dozen minutes to turn it all into steam). Another side effect of latent heat is that it makes it impossible for a gas to exist below its condensation point or a liquid above its boiling point in a stable state. Once a liquid reaches its boiling temperature, **all** of the energy you pour into it just makes it turn into a gas faster, it doesn’t make it hotter.
2. The change of a liquids boiling point depending on pressure. The higher the pressure, the hotter something has to get before it starts boiling (this is how pressure cookers work, by increasing the pressure you are able to heat water to more than 100°C without it boiling)
In a heat pump you take a refrigerant (a special gas) and you compress it to a really high pressure, in fact you compress it to such a high pressure that the boiling point of the substance becomes higher than the ambient temperature, so that when you then pump that gas into a radiator, it starts condensing into a liquid, and in that process it releases the latent heat that it had stored hy being a gas, making the radiator very hot. Once the gas has turned into a liquid you then pump it through a metering device that restricts it, and causes a much lower pressure on the other side. So low in fact, that the boiling temperature of the liquid shoots back down way below the ambient temperature. As you recall, a liquid can’t exist stably above its boiling point, so the refrigerant immediately starts boiling, and to boil it needs to absord the latent heat of vaporisation again, so it rapidly cools dowm to the boiling temperature because it’s turning its own internal heat into latent heat, and then starts absorbing more energy from the environment as you pump it through a second radiator. So long as the boiling temperature of the refrigerant is lower than that of the air, it will absorb all the latent heat from the surrounding air.
The refrigerant then enters back into the compressor to start the cycle anew.
Now all you have to do is put the hot radiator inside and the cold radiator outside, and you have a heat pump.
The Reason why the heatpump gives you more hest than it consumes in electrical energy is the aforementioned latent heat, which is abosrbed from the outside air and then transported inside.
So long as the temperature of the low pressure boiling refrigeratant is colder than the air, the refrigerant can absorb its energy, and work. Modern heatpumps can function down all the way to air temperatures of around less then -10°C
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