An Experimental Study of the Effect of Groundwater Flow on the Thermal Performance of Borehole Heat Exchangers

Abstract

Ground source heat pumps (GSHPs) have been used increasingly for renewable energy buildings in recent years. The performance of GSHPs depends strongly on the heat transfer between the soil and borehole heat exchangers (BHEs). In the present work, a thermal performance experiment of a BHE under groundwater flow was conducted in Baoding, China. The results show that, due to the strong groundwater advection, the thermal performance of the BHE was enhanced. The enhanced effect depends to a great extent on the distribution and thickness percentage of the ground layer with the greatest groundwater flow. Compared with the case without the groundwater flow, the heat injection and heat extraction of the BHE were enhanced on average by 9.8% and 12.9%, respectively, under a typical operating fluid temperature ranging from 28°C to 30°C in summer and from 6°C to 8°C in winter, when the total thickness of coarse sand and gravel layer as a percentage of the borehole depth was 10.64%. The enhanced effect is favorable for reducing the possible imbalance between heat injection and extraction from and to the ground, which is helpful for the long-term operation of GSHP systems.