How Air Source Heat Pumps Work
An air source heat pump is similar in operation to any fridge, which uses a vapour compression cycle. The main parts of heat pump are the compressor, an expansion valve and two heat exchangers.
The Heat Exchanger
Heat is collected by a fan forcing air over a heat exchanger (simply a copper coil factory-filled with refrigerant) to extract heat from the outside air.
The Evaporator takes heat from the heat exchanger and boils a refrigerant (which boils at approximately -10°C), this boiling turns the refrigerant into a vapour which is moved into the Compressor.
The Compressor compresses the vapour in volume and as its volume is reduced its temperature is increased. Temperatures of between 75°C and 125°C are possible as the gas is fed through a heat exchanger.
The Condenser/Heat Exchanger
Forcing the hot gas across the cold water from the central heating system condenses the ozone-friendly refrigerant turning it back into a liquid. As it condenses its heat is passed into the heat exchanger which heats your hot water cylinder and central heating system.
The Expansion Valve
The refrigerant flows within a factory sealed closed circuit in the heat pump, the only thing necessary in operation is to reduce the pressure of the condensed liquid which is done via an Expansion Valve.