In the heating mode, the refrigerant enters the earth loops as a cold liquid (blue in the graphic) and comes out as a cool vapour (green in the graphic). When a refrigerant evaporates it absorbs a large quantity of heat from any surrounding material. Therefore as the refrigerant flows through the loops, it absorbs heat from the earth and stores it in vapour form for later release. The cool (green) vapour that is heat-charged after leaving the earth loops then enters the compressor where its temperature is raised from about 40^o F to about 160^o F. During this compression stage, the temperature of the vapour increases because of the intense compression and the vapour leaves the compressor (red in the graphic) hotter than the air in the building being heated.

Because the vapour leaving the compressor and entering the condenser is hotter than the inside air, heat flows into the air flow from the vapour as the air passes the blower. This warms your home.

As the heat is removed while the hot vapour passes through the condenser, the vapour condenses more and more until it exits the condenser as a liquid. This warm liquid (yellow in the graphic) enters the flow control unit, which monitors the amount of vapour arriving at the liquid flow control (LFC), and meters liquid only through the device for its return to the earth loop field.