Estimation of groundwater flow from temperature monitoring in a borehole heat exchanger during a thermal response test |
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| Authors: | Mayumi Yoshioka Shinichi Takakura Youhei Uchida |
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| Institution: | 1.National Institute of Advanced Industrial Science and Technology (AIST), Geological Survey of Japan,Tsukuba,Japan;2.National Institute of Advanced Industrial Science and Technology (AIST), Renewable Energy Research Center,Koriyama,Japan |
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| Abstract: | To estimate the groundwater flow around a borehole heat exchanger (BHE), thermal properties of geological core samples were measured and a thermal response test (TRT) was performed in the Tsukuba upland, Japan. The thermal properties were measured at 57 points along a 50-m-long geological core, consisting predominantly of sand, silt, and clay, drilled near the BHE. In this TRT, the vertical temperature in the BHE was also monitored during and after the test. Results for the thermal properties of the core samples and from the monitoring indicated that groundwater flow enhanced thermal transfers, especially at shallow depths. The groundwater velocities around the BHE were estimated using a two-dimensional numerical model with monitoring data on temperature changes. According to the results, the estimated groundwater velocity was generally consistent with hydrogeological data from previous studies, except for the data collected at shallow depths consisting of a clay layer. The reasons for this discrepancy at shallow depths were predicted to be preferential flow and the occurrence of vertical flow through the BHE grout, induced by the hydrogeological conditions. |
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