| Abstract |
Ground Source Heat Pump (GSHP) systems using vertical Ground Heat Exchangers (GHEs) are costly to install in Japan due to complex geological conditions. As a cost-effective alternative, Horizontal GHEs (HGHEs) can be installed at shallow depths using Horizontal Directional Drilling (HDD). However, HGHEs require large land areas, which limits their feasibility in land-scarce regions. HDD offers a viable solution for installing HGHEs in space-constrained environments. Nevertheless, thermal interference between adjacent GHEs can reduce system performance, making its investigation important for optimal design. In this study, field experiments were conducted in Saga City, Japan, to examine thermal interference between HDD-installed HGHEs spaced at 1 m, 2 m, and 4 m intervals. Thermal Response Tests (TRTs) were performed for each spacing scenario, confirming that greater distance between GHEs reduced thermal interference and improved heat exchange performance. A numerical model was then developed using FEFLOW based on geological conditions and was validated using measured temperatures at the turning and outlet points of the GHEs. The validated model was used to conduct long-term cooling simulations at GHE distances of 1 m, 2 m, and 4 m, respectively. As a result, thermal interference was observed on the 12th and 40th day after the start of the simulation at 1 m and 2 m spacing. Additionally, the predicted temperature difference between 1 m and 4 m spacing was only 0.6°C after 4 months, indicating that in GSHP systems with two HGHEs, the influence of thermal interference on overall energy efficiency is relatively small. |