How a ground source heat pump works

1) Heat transfer fluid enters system.
The heat pump collects stored solar energy. It contains a heat transfer fluid which is a solution of water and glycol. This antifreeze mixture collects the heat from the earth and is fed into the evaporator. The temperature is on average around 3-5ºC.

2) Evaporator.
In the evaporator, the heat transfer fluid meets the refrigerant. At this stage, the refrigerant is in a fluid state and is at approximately -10ºC. When the refrigerant meets the heat transfer fluid it starts to boil. It then forms a vapour, which is fed into the compressor. The temperature of the vapour is around 0ºC.

3) Compressor.
The pressure of the refrigerant increases in the compressor and the vapour temperature rises from 0ºC to approximately +150ºC. The hot gas is then forced into the condenser.

4) Heat transferred to heating system.
The condenser transfers the heat to the heating system (underfloor heating or perhaps radiators) and the hot water system. The vapour is cooled in the condenser and becomes liquid. The pressure in the refrigerant is still high when it reaches the expansion valve.

5) Expansion valve.
The refrigerant pressure is lowered in the expansion valve. At the same time, the temperature also drops to approximately -10ºC. When the refrigerant passes the valve and the evaporator it changes to vapour again. There is also a valve for regulating refrigerant flow.

6) Transfer fluid returns to ground.
The heat transfer fluid is led out from the heat pump to the ground loop to collect new stored solar energy. The temperature of the fluid is approximately 3ºC cooler than the flow in.