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How Air Source Heat Pumps Work

This page will explain how heat pumps operate and which homes are suitable for air source heating. Please click here for information on Heat Pump subsidies or find answers to our Heat Pump Frequenty Asked Questions.
 

Heat Pump Efficiency

Regardless of the outside temperature, a conventional boiler uses the same volume of fuel to produce a unit of heat – and even the newest models are not efficient enough to turn one unit of fuel into one unit of heat.

Heat pumps on the other hand use sensors to measure the outside temperature, and adjust their settings accordingly. The measure of a heat pump’s efficiency, averaged over a year, is called the seasonal coefficient of performance (SCOP).

Our heat pumps provide a SCOP of at least 3.2, meaning 1 unit of electricity is used to produce at least 3.2 units of heat.

Air source heat pumps offer significant savings for all properties off the gas grid, especially when replacing an LPG, or oil heating system.
 

Heat From Thin Air: The 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.
 

Heat Pumps Vapour Compression Cycle Diagram

Evaporation

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.
 

Compression

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

Condensation

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.
 

Expansion

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.
 

Which Heat Pump Do I Need

Correctly sizing a suitable air source heating system for your property requires a technical design process, whereby a series of measurements will need to be taken and heat loss calculations made.

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