Study of the sustainability of a ground source heat pump system by considering groundwater flow and intermittent operation strategies

In this study, the operation of a ground source heat pump system was investigated over a 25-year period with careful attention paid to the effects of groundwater flow and intermittent operation strategies. First, geological and hydrogeological investigations were conducted, after which ground thermal properties were determined by thermal response tests. In order to predict the heat transfer within borehole heat exchangers under a specific operating system, a numerical model was developed using finite element subsurface flow & transport simulation system (FEFLOW). The numerical model was validated with thermal response test measurements. Three operation conditions including continuous system operation without groundwater flow, continuous system operation with groundwater flow, and intermittent operation with groundwater flow were examined. Results indicate that ground temperature disturbance was effectively reduced during groundwater flow and the intermittent operation of the system. Compared with continuous system operation without groundwater flow, the borehole heat exchanger heat transfer rate increases by 10% with groundwater flow conditions and increases by 16% with further implementation of the intermittent operation strategy. Intermittent operation with groundwater flow is highly recommended for the sustainable operation of ground source heat pump system.