DEVELOPMENT OF A GROUND SOURCE HEAT PUMP SYSTEM WITH GROUND HEAT EXCHANGER UTILIZING THE CAST-IN-PLACE CONCRETE PILE FOUNDATIONS OF BUILDINGS

Ground-source heat pump (GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump (ASHP) systems because the ground, which functions as the heat source or sink, is at a higher temperature in winter and lower in summer than the air temperature (Kavanaugh 1992; Kavanaugh et al 1997). In addition, there will likely be some mitigation against the effects of the heat island phenomena, as this system does not emit exhaust heat into the atmosphere during air conditioning. However, GSHP systems are not popular except as experimental versions in Japan. This is primarily due to the high cost of boring to run piping underground. For example, such boring costs average about ¥3,000/m (approx. US$30/m) in the USA, whereas the same work is about ¥10,000/m (US$100/m) in Japan. Thus, even if the heat pump performance in GSHP systems is more effective than that of the more common ASHP systems, the GSHP systems are unable to recoup the initial piping costs within their lifecycles. Recently, GSHP system employs the foundation piles of buildings as heat exchanger (so called “energy pile system”) is introduced into some buildings in order to reduce the initial boring cost (Hamada et al 1997; Arup Geotechnics 2002; Presetschnik et al 2005). However the effective and low cost design method for energy pile systems has not been developed yet. In addition, almost energy pile systems have used the precast prestressed concrete pile or the steel pipe pile. Recently, in Japan