Effect of pumping well operation on borehole heat exchangers

Abstract

The heat exchange efficiency of borehole heat exchangers can be enhanced by the groundwater flow. In this study, we evaluated the effect of pumping well operations on the performance of a borehole heat exchanger by performing heating operation tests and numerical simulations. The heating test was conducted using a ground source heat pump system installed near existing pumping wells in Akita City, Japan. The coefficient of performance of the ground source heat pump system increased during operation of the pumping wells, although the level of groundwater notably dropped. Next, a numerical model of the pumping well, borehole heat exchanger, and surrounding ground was developed using FEFLOW software ver.7.1 and validated through history matching using the water level and temperature measured during the heating operation test. Case studies were also conducted to evaluate the effect of the pumping well on the borehole heat exchanger. The case studies showed that the pumping well significantly enhanced the performance of the borehole heat exchanger during intensive pumping. Additionally, a high pumping rate improved the heat exchange capacity of borehole heat exchanger. Finally, installation of a borehole heat exchanger upstream to a pumping well in the ground with natural groundwater flow enhanced the performance of the borehole heat exchanger. Therefore, installation of a borehole heat exchanger within a radius of 80 m from the pumping well with a pumping rate of 250 L/min or more was estimated to improve the system.