20 September 2011
In Japan, the usual geothermal air-conditioning system comprises a borehole and U-tubes that are normally made of cross-linked polyethylene pipe but, due to the very high cost of the excavation involved, this system is not widespread. We therefore constructed an
economical geothermal air-conditioning system using cross-linked polyethylene pipes buried horizontally at the bottom of the building frame, instead of the usual borehole system. Usually, the ground temperature rises in summer because the air-conditioning load of buildings is radiated into the ground. Likewise, the ground temperature drops in winter because a geothermal air-conditioning system draws thermal energy from the ground. In our proposed system, the ground temperature is restored to its original level (recovers) at night. We evaluated the performance of this system after it was installed in an actual building.
The heat exchange capability of this system was nearly equal to the heat exchange capability of the usual borehole system. However, the construction cost of the ground heat
exchanger of this geothermal air-conditioning system, using heat pipes buried horizontally at the bottom of the building frame, was about 1/3 that of a borehole system.