The challenge of the ground heat Exchangers: A review of heat transfer efficiency

With its ability to accomplish heat transfer, the ground heat exchanger (GHE) is a crucial component of a ground source heat pump system. Numerous research on various kinds of GHEs have been conducted recently, which has substantially increased their ability to transmit heat. This study aims to present an extensive overview of current research on the newest advancements in GHE technology. A brief description of the various forms of GHEs is given, along with a tally of the actual sizes of Helical coil type and u-type GHEs installed in recent years. The impact on the heat transfer effect of many novel forms of GHEs with optimized structures is discussed. It has been demonstrated that the structure-optimized GHE significantly improves heat transmission. The idea is to improve the GHE's thermal performance by expanding the heat transfer area while keeping the traditional drilling depth. The use of backfill materials, including controlled low strength materials (CLSM), graphite, and bentonite, is examined, and a brief overview of the most current developments in backfill materials is provided. The impact of altering the ratios and adding new materials to the backfill on the heat transmission of buried pipes is examined. Furthermore, different modes of operation of GHEs are investigated and assessed, and the employment of various types of novel refrigerants in the cooling and heating cycles of ground source heat pumps is discussed. Lastly, future prospects, ideas, and recommendations for GHE research are discussed.