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Worldwide use of geothermal heat-pump (GHP) has extensively grown in recent two decades. In this century, the energy use of GHP increased 3.6 times in five years, reaching to 87,503 TJ/year in 2005 (Lund, 2005). GHP may achieve higher coefficient of performance (COP, thermal output / power input) than conventional air-source heat pumps that may contribute to energy savings and environmental protection. Intensive use of GHP system may: (a) Save energy and reduce CO2 gas emission (b) Reduce urban heat-island (UHI) phenomenon (c) Normalize electricity consumption through a day Among these three effects, (a) is common for anywhere. Replacing fossil fuels for heating to GHP may drastically reduce CO2 emission. Replacing conventional air-conditioner to GHP may save electricity by its high COP and also reduce CO2 emission if the energy source of electricity is fossil fuel. Several authors show high COP of around 5 for both heating and cooling by GHP systems, which means GHP can produce heat energy 5 times higher than electricity input. By combination with the effect of (b), total electricity saving for space cooling in central Tokyo may amount to 10 % with the maximum installation of GHP in the area (Genchi, 2001). Effect of (b) is peculiar in urban areas. UHI phenomenon, an endless bad-circulation of air temperature increase, is a common severe problem in densely populated cities in east Asia. Human activities with energy consumption raise atmospheric temperature, which induces more intentional use of air conditioner, resulting in even higher outside air temperature. Use of GHP may reduce UHI by releasing heat into underground but not to the atmosphere. Genchi (2001) estimated that full installation of GHP in the central part of Tokyo may reduce the daily maximum atmospheric temperature in Groundwater Temperature Survey for Geothermal Heat Pump Application in Tropical Asia