There are two main types of GSHPs, closed-loop systems and open systems. Closed-loop systems circulate an antifreeze fluid through underground loops of pipe. The loops, installed either vertically in borings or horizontally in trenches or ponds, exchange heat with the ground.
Open systems use groundwater from a supply well, which passes through the heat pump and into a discharge area. In both systems, the steady cool temperatures of the subsurface can offset the seasonal temperature variations by serving as a reservoir of heat in the winter and as a drain of heat in the summer. However, the open loop system required much more maintenance and care of the water system.