There are two main types of GSHPs:

• Closed-loop systems – these circulate an antifreeze fluid through underground loops of pipe. These pipes, installed either vertically in borings or horizontally in trenches or ponds, exchange heat with the ground. 
• Open systems – these systems use groundwater from a supply well which passes through the heat pump and into a discharge area.

In both systems, the steady cool temperature of the subsurface can offset the seasonal temperature variations. This serves as a reservoir of heat in the winter and as a heat sink in the summer.