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Hydrology 2017, 4(2), 21; doi:10.3390/hydrology4020021

Field Analysis of Stepwise Effective Thermal Conductivity along a Borehole Heat Exchanger under Artificial Conditions of Groundwater Flow

1
Division of Human Environmental Systems, Faculty of Engineering, Hokkaido University
2
AquaGeoTechono Co., Ltd.
*
Author to whom correspondence should be addressed.
Academic Editor: Abdon Atangana
Received: 17 December 2016 / Revised: 22 March 2017 / Accepted: 27 March 2017 / Published: 29 March 2017
(This article belongs to the Special Issue Groundwater Flow)
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Abstract

Heat advection caused by groundwater flow can potentially improve the performance of a borehole heat exchanger. However, the required flow velocity is not achieved under most natural conditions. This study focuses on artificial groundwater flow generated by pumping and investigates the associated effect in a lowland area near the Toyohira River alluvial fan, Sapporo, Japan. Thermal response test results are compared under natural and artificial groundwater flow conditions. A pumping well is constructed one meter from the borehole. Temperature profiles are measured in the U-tube during testing, using a pair of optic fiber distributed temperature sensors. The effective thermal conductivity is calculated from the profiles obtained in each 10-m sub-layer; this thermal conductivity is termed the stepwise thermal conductivity. Additionally, the upward flow velocity in the pumping well is measured to estimate the mean groundwater flow velocity at the borehole. The results show that effective thermal conductivity increases at depths less than 50 m, where the pumping creates mean velocities greater than 0.1 m d−1 in each sub-layer (1.5 md−1 on average). Thus, a borehole length of 50 m is more reasonable at the test site for its efficiency in a ground source heat pump system coupled with the pumping well than that used. View Full-Text
Keywords: artificial groundwater flow; effective thermal conductivity; borehole heat exchanger; thermal response test; optic fiber distributed temperature sensor; groundwater flow velocity artificial groundwater flow; effective thermal conductivity; borehole heat exchanger; thermal response test; optic fiber distributed temperature sensor; groundwater flow velocity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Sakata, Y.; Katsura, T.; Nagano, K.; Ishizuka, M. Field Analysis of Stepwise Effective Thermal Conductivity along a Borehole Heat Exchanger under Artificial Conditions of Groundwater Flow. Hydrology 2017, 4, 21.

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