Optimization of the Global Largest Ground Source Heat Pump System

Abstract

Large-scale ground source heat pump systems (GSHPs) are increasingly used for space heating and cooling. In comparison to small-scale GSHPs, large GSHPs are often coupled with hundreds of borehole heat exchangers (BHE), which are more susceptible to significant ground temperature changes due to the intense thermal interactions between the BHE. In this study, we developed a new model to optimize the operation of large-scale GSHPs to mitigate the underground heat/cold accumulation. The Daxing Airport GSHP system, containing 10497 BHE, making it the largest GSHP system in the world, was selected as the target for performance optimization. Four key parameters were optimized, including the cooling/heating starting sequence, operation continuity, thermal load variability, and partition mode. Our results revealed that extreme cold accumulation mainly exists between the BHE arrays, rather than inside a single array. We recommend that spacing of adjacent BHE arrays should be greater. Meanwhile, an operational sequence of cooling, with intermittent operation and constant thermal load, is also suggested. In comparison, the partition mode only lowers the thermal anomaly inside the BHE array. Our findings imply that for large-scale GSHPs, the distance between BHE arrays is the most critical factor impacting performance, which differs from small-scale GSHPs.