Field Test of Ungrouted Ground Heat Exchangers with In-Hole Vertical Ground Water Flow

Abstract

In ground source heat pump (GSHP) systems, vertical groundwater flow in the ground heat exchangers (GHEs) could improve the heat exchange performance of them. In this study, a GHE was drilled and completed without grouting in a location of Kuroishi City, Aomori, Japan, where a vertical groundwater flow is expected in the GHE, to investigate the thermal advection effects of the groundwater flow. The results of velocity logging of vertical groundwater flow in the GHE showed the existence of a vertical flow of 0.1-0.3 m/min. Series of thermal response tests (TRTs) were then carried out at the ungrouted GHE using two-types of heat load and number of U-tubes. The results of TRTs showed that a single U-tube GHE has a higher efficiency than a double U-tube GHE because the larger cross-sectional area of the water-filled space resulted in larger heat capacity of the groundwater flow.