Ground Heat Exchanger (GHX) 20101

Ground Heat Exchanger (GHX)

A ground heat exchanger is simply a heat exchanger placed in the ground. Heat transfer fluid, usually water and an antifreeze solution, is circulated through the GHX to transfer energy to and from the ground.

Energy transfer can take place when the heat transfer fluid is either cooler or warmer than the ground around the pipe. The fluid is typically cooled by a heat pump located in the building. When the building requires heat, a heat pump extracts heat from the fluid much like a refrigerator extracts heat from milk in a refrigerator. The heat is used to warm water or air that is distributed throughout the building as needed. When heating the building, the ground around the pipe is cooled by the chilled fluid circulating through the pipes.

Most heat pumps are also designed to cool a building when needed. When cooling the building the heat pump cools water or air that is distributed through the building. The energy taken from the building warms the heat transfer fluid, that in turn warms the ground around the pipe.

A GHX can be built in many different configurations. Pipe can be placed in vertical boreholes from 15 to 300 m in depth, or it can be laid horizontally in excavated trenches or horizontally bored holes. Pipe or metallic heat exchangers can also be placed in ponds, lakes or even the ocean. Where ground water is available, it can be circulated directly through a heat pump. For some projects it may be useful to connect more than one building to a common GHX to take advantage of energy transfer opportunities.