Feasibility of a medium-depth U-tube ground-source heat pump system in a severe cold zone in China

Abstract

ABSTRACT In China, residential buildings have a high-volume ratio and density, which limit the amount of buried U-tube space available, thereby hindering the application of traditional ground-source heat pump systems (GSHPs). Due to the imbalance in heat transfer, the operating efficiency of GSHPs decreases annually in severe cold zones. To alleviate these issues, we assessed the feasibility of medium-depth U-tube GSHPs. An experimental platform in Fuxin City, China, was established, and a simulation model was designed with TRNSYS software. The area affected by the heating load was analyzed, and the proposed system was compared with solar-soil and medium-depth casing pipe GSHPs. The proposed system was found to be stable and efficient for long-term operations, delivering not only the lowest equivalent annual cost but also a 4.61% improvement in heating (compared to solar-soil GSHPs), an 81.54% improvement in cooling, and a 23.08% improvement in emission reductions (compared to medium-depth casing pipe GSHPs).The application of a special U-shaped pipe elbow and a dual-temperature switching valve allowed heat exchange conversion between the heating and cooling conditions. The results of the simulation model demonstrated that dual-temperature operation resulted in greater cooling performance and cheaper operating costs than did the single-temperature system.