| Title | Field tests of horizontal ground heat exchangers under tidal influence |
|---|---|
| Authors | Satoko Taniguchi |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | Ground source heat pump, thermal response test, ground heat exchanger, groundwater |
| Abstract | In GSHP systems, Horizontal Ground Heat Exchangers (HGHEs) are widely used in areas with abundant land availability. However, the heat exchange rate per GHE length of the HGHEs is generally lower than that of vertical GHEs because the shallow ground to install HGHEs (1m – 2m) is usually unsaturated and has no groundwater flow. Hence, it is effective to install HGHEs deeper and also select locations where groundwater flow exists to improve the performance of GHEs by advection effect. In this research, preliminary tests were conducted at three sites in Saga Prefecture, western Japan and HGHEs were installed at the selected site. All of these sites are located near the coastline where a periodical groundwater flow is expected to occur in shallow ground due to tidal influence. First, we carried out heating cable-based Thermal Response Tests (TRTs) in 20m deep vertical wells at each site. The temperature measured in the well clearly showed a sinusoidal increase at Sites A and C, except at Site B. Next, we installed four HGHEs at Site C using horizontal directional drilling technology at 10m and 15m deep. The depths of the HGHEs were determined based on the TRT interpretation. The HGHEs were drilled along 2 lines, parallel to the coastline, spaced 15m apart. In the horizontal holes, double U-tubes of 25.6mm ID were inserted to be used as HGHEs. Long-term heating and cooling tests are scheduled to follow from 2026. |