U.S. Ground Temperature Map Regular air-source heat pumps exchange heat to and from the atmosphere, which varies a great deal throughout the year. Ground Source Heat Pumps (GSHP), on the other hand, exchange heat with the ground, which is relatively constant all year long. Cooler soil in the summer and warmer soil in the winter mean GSHPs operate more efficiently in all seasons. Although the ground piping means the initial cost of GSHP systems is higher, the lower operating expenses (less maintenance, lower electricity use, and much greater longevity of the system) make these systems very cost-competitive versus air source heat pump systems.
Please observe that the above-ground temperature map for the United States works for any landmass at the same latitude, north or south of the Equator – and approximate elevation. That means that other nations lacking ground-temperature data can benefit from all the research done in America, to easily duplicate the energy-efficiency results. Nations at other latitudes can similarly benefit from the research and practical experience of widespread GSHP usage in Iceland (cold), Japan (not so cold), and Indonesia (tropical).
Use of geothermal resources around the world is limited. A map at that link shows the western US, Mexico, Japan, Iceland, Indonesia, and central Europe are the only places where geothermal is in widespread use. “Geothermal” does not mean hot springs or easily accessible water heated underground and flowing to the surface. Geothermal energy is available everywhere: access is anywhere, within 10-2o feet from the surface. The greater the temperature difference between the average ground temperature and the ambient outside temperature, the higher the efficacy of ground source heat pumps: most notably, in very cold regions (Iceland) or very hot regions (Mexico).