This study investigates thermal performance and characteristics of spiral-tube ground heat exchanger (GHE) for ground source heat pump in laminar and turbulent flows. The thermal performances are evaluated by numerical method using a CFD code. Various models of spiral-tube GHEs installed in a borehole and backfilled with silica-sand were simulated. In comparison with the conventional U-tube GHE, the performance of spiral-tube GHE increases by 62.7 % in the laminar flow and by 33.5 % in the turbulent flow. Due to the interest in applying the GHE in concrete foundation piles, the spiral-tube GHE installed in a concrete pile is also simulated. Its performance shows a slight better performance of 5 % in the laminar flow and 6 % in the turbulent flow compared with that of a borehole backfilled with silica sand. Furthermore, the performance of spiral-tube GHEs with outlet pipe installed inside and outside the spiral tube in the borehole, and varying spiral pitches of p = 0.05 m; 0.1 m and 0.2 m are investigated. The effects of outlet pipe positions on the performances are shown. The spiral-tube with outlet pipe installed outside gives a better performance, of 2 % in the laminar flow and 10 % in the turbulent flow, than that of the outlet pipe installed inside. Water temperature distributions of the both spiral-tube GHEs are presented. Varying the spiral pitch significantly affects the performance of the spiral-tube GHEs. Increasing the spiral pitch reduces the number of spirals per meter borehole depth.
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