Development of energy textile to use geothermal energy in tunnels

A novel textile-type ground heat exchanger, a so-called "energy textile", is introduced in this paper. The energy textile to be assembled in a tunnel lining is devised to function as a ground-coupled heat exchanger (GHE) to operate a ground source heat pump (GSHP) system in tunnels. A test bed of six pilot energy textile modules with various configurations was constructed in an abandoned railroad tunnel in South Korea. Long-term field monitoring was performed to measure the heat exchange capacity of each energy textile module by applying artificial heating and cooling loads on it. In the course of monitoring, the inlet and outlet fluid temperatures of the energy textile, the pumping rate, the ground temperature, and the air temperature inside the tunnel were measured continuously. Each type of energy textile modules was compared in terms of its heat exchange efficiency, which appears to be sensitive to fluctuation of air temperature in the tunnel. In addition, three-dimensional computational fluid dynamic (CFD) analyses were carried out, employing FLUENT, to simulate the field test for each energy textile module. After verification of the numerical model with the field measurement, the influence of a drainage layer on the performance of the energy textile was parametrically examined. A conventional design procedure for horizontal GHEs was used in a preliminary design of an energy textile module, taking into consideration the air temperature variation inside the tunnel over the course of one year.