A two-region simulation model of vertical U-tube ground heat exchanger and its experimental verification

• Published in: Applied energy Vol. 86; no. 10; pp. 2005 - 2012
• Main Authors: Yang, Weibo, Shi, Mingheng, Liu, Guangyuan, Chen, Zhenqian
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2009; Elsevier
• Series: Applied Energy
• Subjects: Applied sciences; Devices using thermal energy; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Experimental validation; Ground coupled heat pump; Ground coupled heat pump Vertical U-tube Ground heat exchanger (GHE) Two-region simulation model Experimental validation; Ground heat exchanger (GHE); Heat exchangers (included heat transformers, condensers, cooling towers); Heat pumps; Heat transfer; Theoretical studies. Data and constants. Metering; Two-region simulation model; Vertical U-tube; Experimental validation; Ground coupled heat pump; Vertical U-tube; Two-region simulation model; Ground heat exchanger (GHE); Experimental test; Heat pump; Heat flow; U shaped pipe; Vertical tube; Underground heat exchanger; Simulation; Heat exchanger; Simulation model; Heat transfer
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2008.11.008

Heat transfer around vertical ground heat exchanger (GHE) is a common problem for the design and simulation of ground coupled heat pump (GCHP). In this paper, an updated two-region vertical U-tube GHE analytical model, which is fit for system dynamic simulation of GCHP, is proposed and developed. It divides the heat transfer region of GHE into two parts at the boundary of borehole wall, and the two regions are coupled by the temperature of borehole wall. Both steady and transient heat transfer method are used to analyze the heat transfer process inside and outside borehole, respectively. The transient borehole wall temperature is calculated for the soil region outside borehole by use of a variable heat flux cylindrical source model. As for the region inside borehole, considering the variation of fluid temperature along the borehole length and the heat interference between two adjacent legs of U-tube, a quasi-three dimensional steady-state heat transfer analytical model for the borehole is developed based on the element energy conservation. The implement process of the model used in the dynamic simulation of GCHPs is illuminated in detail and the application calculation example for it is also presented. The experimental validation on the model is performed in a solar-geothermal multifunctional heat pump experiment system with two vertical boreholes and each with a 30 m vertical 1 1/4 in nominal diameter HDPE single U-tube GHE, the results indicate that the calculated fluid outlet temperatures of GHE by the model are agreed well with the corresponding test data and the guess relative error is less than 6%.