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Air Source Heat Pump Vapour Compression Cycle

In the same way that a fridge extracts warm air from inside to stay cold, air source heat pumps extract the warmth from the air from outside, using the Vapour Compression Cycle.


Air source heat pumps extract air from the outside, this air is then passed over a (low pressure) refrigerant liquid, turning the liquid into a vapour. HOW? The outside air will always be warm enough to turn this refrigerant liquid into a gas, even when the outside temperature is below freezing, because (at a low pressure) the refrigerant gas has a very low boiling point. (All of the heat pump calculations we undertake use -3 degrees as an average for the outside temperature).

Air from the outside is sucked into the side of the heat pump and passed over a refrigerant liquid. The warmth in the air turns this refrigerant into a gas, which is then passed through a compressor, further increasing it’s temperature, before it is transferred to the heating system through a heat exchanger.


The heat pump compresses the refrigerant vapour, raising it’s temperature.


The compressed vapour is then moved to a condenser. The process of condensation turns the refrigerant vapour back into a liquid, and in doing so, releases the heat. This heat is passed through to the water via a heat exchanger.


The (pressured) liquid refrigerant is allowed to expand, lowering the pressure. As the liquid is now at a low pressure, it naturally draws-in heat energy (evaporation)… and the process begins again.

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