Factors influencing the performance of shallow Borehole Heat Exchanger

Abstract

Borehole Heat Exchanger is one of the main elements of Ground-Coupled Heat Pump and its performance is directly related to the heat pump Coefficient of Performance. In this paper, a comprehensive numerical simulation model was built to evaluate the annual performance of the shallow Borehole Heat Exchanger installed in different soils subjected to land surface seasonal hydrothermal variations. It was found that the shallow Borehole Heat Exchanger installed in sand had a better performance of 8% than in clay. The same performance difference between sand and clay was observed in most of the investigated scenarios. The annual average heat pump performance presented a variation more than 27.2% with the meteorological condition, the grout thermal conductivity and the heat load level. The multi-pipe solution and the carrying fluid velocity also influenced the heat pump performance, ranging between 12.2 and 16.2%. Other factors such as the hydraulic condition, the groundwater flow, the grout volumetric heat capacity, the grout diameter, the shank spacing, the pipe inner diameter, the pipe thickness, the pipe thermal conductivity, the carrying fluid material and the heat load mode had less impact on the heat pump Coefficient of Performance, varying between 0 and 11.6%. These findings could be used as a guideline for the future studies of Borehole Heat Exchanger, especially for the applications installed in unsaturated soils.