Installation Cost and Heat Extraction Performance Analysis of H-Shaped PC Pile Ground Heat Exchangers for Small Buildings

Abstract

Ground source heat pump systems are one of the renewable energy heat utilization technologies that can reduce the energy for HVAC and hot water supplies and consequently mitigate the progression of global warming. On the other hand, the development of ground heat exchangers that can be installed in small buildings with low installation costs is an important challenge for increasing the installation number of ground source heat pump systems in Japan. This study proposes H-shaped PC pile ground heat exchangers to reduce installation costs. The installation test and installation cost estimation of H-shaped PC pile ground heat exchangers showed that installation costs could be reduced to less than half compared to the conventional borehole double U-tube ground heat exchanger. The coefficient of heat extraction/injection of H-shaped PC pile ground heat exchangers was evaluated as 2.2–2.4 W/(m K) from the results of actual measurements during the heating and cooling operation of the GSHP system, and this was slightly high compared to the borehole single U-tube ground heat exchanger. In addition, the GSHP system with an 8 by 8 m long H-shaped PC pile ground heat exchanger could supply adequate heating output for the heating load of the residential house and operate with an SCOP of more than 3.0. Finally, the authors have confirmed that the GSHP system with H-shaped PC pile ground heat exchangers can reduce installation costs by 40% or more while maintaining the same running cost compared to conventional GSHP systems.