Author(s): Yosuke Suzuki; Hiroaki Terasaki; Teruyuki Fukuhara; Akira Saida; Masahiro Kusama; Haruki Taniguchi; Masato Tanaka
Linked Author(s):
Keywords: Ground heat; Groundwater flow; Lining borehole ground heat exchanger; Thermal response test; Effective thermal conductivity
Abstract: Ground Source Heat Pump (GSHP) systems are a popular means to reduce energy consumption. However, in Japan, the spread of GSHP systems is hindered by drilling costs, which are much higher than those in western countries. Therefore, in order to reduce drilling costs, we previously developed a Lining Borehole Ground Heat Exchanger (LBHE). This study aims to determine the effect of groundwater flow on the heat exchange rate of an LBHE by constructing a heat transfer model of the LBHE under some assumptions and performing numerical simulation. First, a Thermal Response Test (TRT) was conducted to identify the effective thermal conductivity of the surrounding ground including the influence of groundwater flow. The accuracy of the model was confirmed by comparing the calculated outlet fluid temperature with that measured by the TRT. The results show that the calculated and measured temperatures are in good agreement. Finally, a numerical simulation was conducted under the condition that the inlet fluid temperature and the flow rate of the LBHE were constant. The results of the simulation predicted that the heat exchange rate per unit length would increase by 13 % when groundwater flow existed in the two gravel layers. This suggests that the effect of groundwater flow should be considered in order to precisely evaluate the thermal performance of LBHEs.
Year: 2020