An improved ground source heat pump system wherein the subterranean piping installation comprises modular heat exchange units. Each modular heat exchange unit comprises a plurality of parallel secondary or branch conduits. The use of multiple parallel secondary conduits significantly increases the heat exchange capacity of the system. Because of the increased efficiency of such a system, less piping is required, which in turn reduces the cost of labor and materials to install such a system and the area of land mass required to contain it. Moreover, because the heat exchange units are modular, they can be prefabricated at a remote site and then conveniently transported to construction site and installed much more quickly than the extended lengths of conventional piping.