Experimental study of thermal behaviour of energy tunnels at the entrance in cold regions

Energy tunnels in cold regions represent an innovative technology that integrates ground-source heat pump systems with tunnel linings. By harnessing geothermal energy, this method provides frost protection and warmth to the tunnel lining, enhancing both environmental sustainability and cost-effectiveness over traditional solutions. This study explores the heat exchange characteristics at the entrance section of energy tunnels in cold regions through indoor model tests. The analysis focused on how the flow rate of the heat exchange fluid and the inlet temperature affect the heat exchange performance. The results showed that, under the test conditions, the temperature of the tunnel’s inner wall could be increased by 5°C–6°C. However, the temperature of the surrounding rock, at a distance of 0.5 times the tunnel’s diameter, was largely unaffected by the ground heat exchangers. The heat transfer efficiency also increased with higher inlet temperatures and faster fluid flow rates. However, further increases were not recommended beyond a specific inlet temperature, as they did not significantly improve heat transfer efficiency. These findings offer valuable guidance for designing and implementing ground-source heat pump systems at the entrance sections of tunnels in cold regions.