A geothermal heating system doesn't use combustible materials to heat your home like a gas or propane furnace does. Instead, it uses refrigerant to carry heat from one system component to the next. The compressor within the heat pump moves the refrigerant throughout the entire system.
In winter, the earth’s heat is absorbed by the ground loop and carried to the coaxial coil. The inner coil contains the water from the ground loop, and the outer tube of the coil houses cold refrigerant. Through the walls of the coil, the heat from the ground loop’s water is passed to the refrigerant. Then, the refrigerant moves the heat to the compressor where it is pressurized. The pressure makes the refrigerant extremely hot.
Once the refrigerant is good and hot, it’s pumped through the air coil’s pipes and fins. When air is forced across the now-hot coil, heat is transferred into that air. A blower then moves the heated air through your duct system and into your home to heat the space.
Next, the refrigerant is moved to the expansion valve, where the pressure is low. The low pressure cools the refrigerant so it’s ready to move back to the coaxial coil. Once refrigerant returns to the coaxial coil, it is again ready to absorb the heat from water carried through the ground loop.
For cooling your home, the ground source heat pump simply works in reverse. Refrigerant will flow in the opposite direction and excess heat will be pulled from inside your home to be deposited back into the ground. This excess heat can also be used to heat water for your home.