How groundwater flow field change affects heat transfer in groundwater heat pumps based on physical experiments

Abstract

A groundwater heat pump (GWHP) is a form of ground-source heat pump that utilizes groundwater as its heat source and offers great efficiency, significant energy savings, and little pollution. As a GWHP system runs, thermal breakthrough is a crucial feature of system design that can result in a progressive shift in pumping water temperature and negatively impact GWHP performance. Variation in the groundwater flow field is crucial for heat transfer in terms of pumping and recharging well groups, especially when high porosity and permeability aquifers are taken into account, as this has a direct impact on the development of the groundwater temperature field. The primary goal of this study was to evaluate the impact of groundwater flow field variation due to groundwater velocity and recharge rate allocation changes on heat-transfer characteristics using laboratory physical experiments, to study the evolution trends of the groundwater flow field and groundwater temperature field, and to compare and determine various pumping and recharge well-group layout schemes to improve GWHP operation efficiency. The test results showed that the rise rate of pumping water temperature and the thermal breakthrough occurrence time increase with the increase of groundwater velocity, and when the groundwater velocity is the same, the thermal breakthrough occurrence time and the rise rate of pumping water temperature in the vertical well layout scheme are 0.48–0.76 times and 1.36–4.0 times that of the parallel well layout scheme, respectively. In addition, the recharge rate allocation has a greater impact on the parallel well layout scheme but a smaller impact on the vertical well layout scheme. The physical test results can provide a scientific basis for future research.