Evaluation of groundwater pumping impact on the thermal conductivity of neighboring ground source heat exchangers

This study evaluates the correlation between groundwater velocity and the thermal conductivity and heat exchange performance of the ground source heat exchangers. The groundwater was extracted from un-grouted water well, which is located beside the drilled ground source heat exchangers (GHEs), to make artificial groundwater velocity in the region. The thermal response tests were carried out for three GHEs, which were drilled around the water well at different distances at the test site in Yamagata City, Northern Japan. During the tests, the pumping rate varied from 0 (no pumping) to 200 L/min in three steps and at two days intervals. The hydrothermal parameters of the ground around the GHEs were estimated for the GHEs and each step of pumping rate using a script in MATLAB software and with the help of the moving line source (MLS) method. This method can estimate the groundwater velocity and the effective thermal conductivity of the soil for different pumping rates to study the effect of the pumping on the neighboring GHEs. As a result, the thermal conductivity was improved by pumping groundwater in all GHEs. The rate of pumping had a direct relation with the improvement level and higher rate of pumping caused higher amount of thermal conductivity improvement. Moreover, this study showed that the location of the GHE around the pumping point does not effect on the level of thermal conductivity increment. Therefore, there was no correlation between the distance of the GHE and pumping well and the closest GHE was not necessarily experienced highest impact.