Evaluating Variability of Ground Thermal Conductivity within a Steep Site by History Matching Underground Distributed Temperatures from Thermal Response Tests

Yoshitaka Sakata, Takao Katsura, Ahmed A. Serageldin, Katsunori Nagano and Motoaki Ooe
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Yoshitaka Sakata: Department of Environmental Engineering, Faculty of Engineering, Hokkaido University, N13-W8, Sapporo 060-8628, Japan
Takao Katsura: Department of Environmental Engineering, Faculty of Engineering, Hokkaido University, N13-W8, Sapporo 060-8628, Japan
Ahmed A. Serageldin: Department of Environmental Engineering, Faculty of Engineering, Hokkaido University, N13-W8, Sapporo 060-8628, Japan
Katsunori Nagano: Department of Environmental Engineering, Faculty of Engineering, Hokkaido University, N13-W8, Sapporo 060-8628, Japan
Motoaki Ooe: Inoac Housing & Construction Materials, Daiho-4tyome, Nagoya 456-0062, Japan

Energies, 2021, vol. 14, issue 7, 1-17

Abstract: The variability of ground thermal conductivity, based on underground conditions, is often ignored during the design of ground-source heat pump systems. This study shows a field evidence of such site-scale variations through thermal response tests in eight borehole heat exchangers aligned at a site on a terrace along the foothills of mountains in northern Japan. Conventional analysis of the overall ground thermal conductivity along the total installation length finds that the value at one borehole heat exchanger is 2.5 times that at the other seven boreholes. History matching analysis of underground distributed temperature measurements generates vertical partial ground thermal conductivity data for four depth layers. Based on the moving line heat source theory, the partial values are generally within a narrow range expected for gravel deposits. Darcy velocities of groundwater are estimated to be 74–204 m/y at the borehole with high conductivity, increasing in the shallow layers above a depth of 41 m. In contrast, the velocities at the other seven boreholes are one-to-two orders of magnitude smaller with no trend. These high and low velocity values are considered for the topography and permeability. However, the relatively slow groundwater velocities might not apparently increase the partial conductivity.

Keywords: thermal response test; ground thermal conductivity; distributed temperature sensor; history matching; groundwater flow; moving line heat source theory (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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