Field Test of Two-layered Straight and Slinky-coil Horizontal Ground Heat Exchangers

Abstract

Horizontal Ground Heat Exchangers (GHEs) for geothermal heat pump systems are not well distributed in Japan due to the requirement of large land space for installing the heat exchange pipes in the shallow ground. For reducing the land space to bury the GHEs, two-layered horizontal GHE systems, which install the loops at -1.0 m and -2.0 m, are proposed in this research. For evaluating the heat exchange performance of the GHEs, long-term cooling and heating tests and forced heat rejection tests were carried out in a field test site located in Itoshima City, Fukuoka, Japan. The results of field tests showed that the application of two-layered GHEs remarkably improve the heat exchange capacity of GHEs per unit area, which enable the significant reduction of the land space requirement. The field tests also showed that Slinky-coil horizontal GHEs have higher heat exchange capacity than conventional straight type horizontal GHEs in case the cost of pipes for the two types of GHEs is equalized.