I am hearing about this as a low carbon method to heat or cool buildings but I can’t find a good article or video to see how it works. The closest I can figure is like a fridge in reverse… the pump or refrigerant gets hot and you use that heat. Cold climate systems supposedly extract heat down to -25c. How?
In: Physics
That is exactly it. Like a fridge. The laws of thermodynamics say that you cannot have cold without heat. Even at -25c there is heat above absolute zero that can be extracted from the air. As long as molecules are moving there is ‘heat’ in any given item/system, and this happens at all times above absolute zero. Heat pumps will run in reverse to pull heat from the outside air, and bring it inside, this causes condensation on the outdoor unit since it is getting colder than the air. When the condensation reaches a point where the system won’t correctly draw heat from the outdoor air due to ice buildup, the system will automatically go into a defrost cycle where it acts as a normal a/c pulling heat from indoors and using the outdoor air to dissipate it. This causes the metal coil to heat up melting any ice buildup. Then it switches back to running as a heat pump. Once the outdoor air reaches a temperature that ices the coil up immediately, the system becomes redundant. That is usually at about -20 to -40c depending on the system design parameters.
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