The use of the ground as an energy source, sink or storage element for coupling to a heat pump has attracted renewed interest in recent years. Several system options have been developed, some of which use additional solar-derived energy. In applying ground coupling in a given situation, three major decisions must be made. First, it must be decided whether to use solar energy in the ground-coupled system, and if so, whether to design for long- or short-term energy storage. Second, the type of in-ground

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heat exchange device must be selected. These include the horizontal coil, the vertical heat exchanger, the buried water tank, and the buried flat plate. Third, the heat-exchange device must be sized relative to the heat pump, the load, and the solar components, if any. The ways in which these decisions have been approached in a variety of countries and climates have been analyzed as a base for assessing the outlook for ground-coupling applications in terms of economic, energy supply, and technology development scenarios which could work for or against ground coupling. These include availability and cost of the various forms of energy, in particular gas versus coal; availability of capital and interest rates; utility load profiles; and technical developments in air-to-air heat pumps, g s furnaces, and gas-fired heat pumps. The paper concludes with a discussion of research and development needs for ground coupling.

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