The Effect of Groundwater Flow on the Thermal Performance of a Novel Borehole Heat Exchanger for Ground Source Heat Pump Systems: Small Scale Experiments and Numerical Simulation

Ahmed A. Serageldin, Ali Radwan, Yoshitaka Sakata, Takao Katsura and Katsunori Nagano
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Ahmed A. Serageldin: Environmental System Research Laboratory, Division of Human Environmental Systems, Hokkaido University, Sapporo 060-8628, Japan
Ali Radwan: Environmental System Research Laboratory, Division of Human Environmental Systems, Hokkaido University, Sapporo 060-8628, Japan
Yoshitaka Sakata: Environmental System Research Laboratory, Division of Human Environmental Systems, Hokkaido University, Sapporo 060-8628, Japan
Takao Katsura: Environmental System Research Laboratory, Division of Human Environmental Systems, Hokkaido University, Sapporo 060-8628, Japan
Katsunori Nagano: Environmental System Research Laboratory, Division of Human Environmental Systems, Hokkaido University, Sapporo 060-8628, Japan

Energies, 2020, vol. 13, issue 6, 1-26

Abstract: New small-scale experiments are carried out to study the effect of groundwater flow on the thermal performance of water ground heat exchangers for ground source heat pump systems. Four heat exchanger configurations are investigated; single U-tube with circular cross-section (SUC), single U-tube with an oval cross-section (SUO), single U-tube with circular cross-section and single spacer with circular cross-section (SUC + SSC) and single U-tube with an oval cross-section and single spacer with circular cross-section (SUO + SSC). The soil temperature distributions along the horizontal and vertical axis are measured and recorded simultaneously with measuring the electrical energy injected into the fluid, and the borehole wall temperature is measured as well; consequently, the borehole thermal resistance ( R b ) is calculated. Moreover, two dimensional and steady-state CFD simulations are validated against the experimental measurements at the groundwater velocity of 1000 m/year with an average error of 3%. Under saturated conditions without groundwater flow effect; using a spacer with SUC decreases the R b by 13% from 0.15 m·K/W to 0.13 m·K/W, also using a spacer with the SUO decreases the R b by 9% from 0.11 m·K/W to 0.1 m·K/W. In addition, the oval cross-section with spacer SUO + SSC decreases the R b by 33% compared with SUC. Under the effect of groundwater flow of 1000 m/year; R b of the SUC, SUO, SUC + SSC and SUO + SSC cases decrease by 15.5%, 12.3%, 6.1% and 4%, respectively, compared with the saturated condition.

Keywords: Ground source heat pump; oval cross-section; groundwater; borehole heat exchanger; CFD; Sandtank (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: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (6)

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