Beschreibung:
Ground-source heat pump (GSHP) systems are helpful for reducing building-sector heating and cooling energy consumption. As the core part of the GSHP system, the underground heat exchanger has a large influence on the heat transfer performance (HTP) of the system. The ground temperature variation characteristics of a new efficient coaxial casing heat exchanger (ECCHE) for heat extraction or rejection were investigated. The study was based on dynamic analysis of linear thermostatics used in the thermal response test and the HTP of the ECCHE. Influences of drilling borehole depth, circulation flow rate, and exchanger structure were considered. Results show that the HTP of the ECCHE is 1.61 (1.46) times that of doublet U-pipe heat exchangers during heat extraction (heat rejection), and the radius thermal influence distance of the ECCHE is >10 m. The spiral ribs of the ECCHE extend the heat transfer time between the fluid and surrounding rock, and the heat transfer in upper part of the borehole is greater than that near the deeper part, so it is easy to produce continuous heat or cold accumulation near the borehole tops. Due to gneiss with higher thermal conductivity, the recovery rate of the ground temperature after heat extraction is faster