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This paper presents the analysis, simulation and performance study of heat transfer in a single U-tube borehole heat exchanger (BHE). Unsteady heat transfer method was used to analyze the heat transfer process of both inside and outside the borehole. Implicit numerical method applied on heat transfer equations obtained from energy balance (accompanied with thermal resistance model) was used to obtain the solution. The variation of mean fluid temperature, average borehole wall, grout and nearby ground temperature as well as borehole loading with borehole depth and time were investigated. Dynamic simulation was also performed to assess the influence of important parameters. The effect of two parameters, fluid mass flowrate and thermal conductivity of grout, on mean fluid temperature, borehole wall, grout and ground temperature as well as on borehole loading and borehole thermal effectiveness were investigated. The outcome of this study can substantially reduce the time devoted for research and to quickly determine the impact of various parameters on performance of vertical single U-tube borehole heat exchanger. Furthermore, the obtained result can be utilized as a reference for the design and optimization of heating and cooling system integrated with ground coupled heat pump system. • Transient heat transfer analysis for both inside and outside the single U-tube BHE was performed. • Modeling equations that govern heat transfer process inside and outside the BHE has been developed. • Variation of borehole loading and effectiveness of BHE with depth and time was examined. • Effect of mass flow rate and grout conductivity on performance of BHE was investigated. • Impact of heat carrier fluids on performance of single U-tube BHE was assessed. [ABSTRACT FROM AUTHOR]

Thermal performance of vertical U-pipe borehole heat exchanger (BHE) is an important research subject for the design and application of ground-coupled heat pump system (GCHPs). This paper presents an improved evaluation method for thermal performance of BHE based on analytical solution model, which is validated by comparing with duct storage system (DST) model and field experiment. Using the evaluation method, impacts of inlet fluid temperature, fluid flow rate and borehole depth on thermal performance of two types of U-pipe BHEs are studied. The study provides a good alternative of the experimental method for thermal performance test (TPT) and a useful thermal performance evaluation tool for BHEs in GCHPs. [ABSTRACT FROM AUTHOR]