Long-Term Thermal Behavior of Energy Textile Constructed in Tunnel

As a new source of renewable energy, the geothermal energy from a tunnel structure can be extracted through a textile-type ground heat exchanger named "Energy Textile" that is fabricated between a shotcrete layer and a guided drainage geotexitle. Thermal performance of the energy textile is evaluated in this paper, which is installed in a test bed constructed in an abandoned railway tunnel located in Seocheon, South Korea. To observe the long-term thermal behavior of the energy textile, water with designed temperatures for simulating cooling/heating modes was circulated through each energy textile using a constant-temperature water bath. During the long-term monitoring, the temperatures of the inlet and outlet fluid of the energy textile were measured to estimate a daily heat exchange rate of the energy textile. Besides, the air temperature and the ground temperature were continuously monitored. Results from the tests show that the climatic condition in the tunnel can have a significant impact on the performance of the energy textile. In addition, a 3-D numerical analysis using FLUENT was adopted to simulate the operation of the energy textile as a ground heat exchanger with the consideration of the shotcrete and lining thermal conductivity and temperature variation of air in the tunnel. The numerical analysis shows a good agreement with results of the long-term monitoring.