Performance of Textile Type Groud-Coupled Heat Exchangers in Tunnel

Textile-type ground-coupled heat exchangers, so called “energy textile”, were installed in an abandoned railroad tunnel located in South Korea. A test bed was then constructed to facilitate an evaluation of the in-situ thermal performance of the energy textile. To observe a long-term thermal behavior, the difference in the temperatures of the inlet and outlet fluid of the energy textile was monitored using a constant-temperature water bath (CWB) and a real simulation system for both cooling and heating operating. In the course of the experimental measurement, the inlet and outlet fluid temperatures of the energy textile, pumping rate, temperature distribution in the ground, and air temperature inside the tunnel were continuously recorded. From the long-term monitoring test, the heat exchange rate of each energy textile panel was in the range of 57.6~143.5 W per 1 unit for the heating cycle (average temperature difference between the inlet working fluid and air in the tunnel was recorded as 2.9 °C) and 362.3~558.4 W per 1 unit for the cooling cycle (average temperature difference between the inlet working fluid and air in the tunnel was recorded as 9.2 °C). These results show that heat exchange rate of the energy textile is sensitive to the fluctuation of air temperature in the tunnel. In addition, a series of CFD numerical analyses was performed to simulate the long-term monitoring results for the selected energy textiles with consideration of air temperature inside the tunnel. Then effect of drainage layer in energy textile was evaluated. For the given conditions, average decreasing of heat exchange in energy textile is about 8 % due to the drainage layer in energy textile (average amount of heat exchange with drainage layer is 445.6 W and that of heat exchange without drainage layer is 480.9 W). The CFD numerical analyses successfully simulated the field experiment, which shows the performance of energy textile in the tunnel can be indirectly estimated using the numerical model.