Heat transfer analysis of double U-tube ground heat exchanger of closed loop ground source heat pump system during space cooling application for Indian climatic conditions

摘要

Use of ground source heat pump system (GSHP) for spce cooling application results in significantreduction in electricity consumption as the temperature of heat rejection (ground) is lower thanthe ambient.The main focus of the present research is to investigate the heat transfer andtemperature variation of heat transfer fluid in a double U-tube ground heat exchanger (GHE) of a5-ton GSHP system installed in IIT Roorkee, Roorkee in the northern region of India. Thermalproperties of the ground formation were obtained using thermal response test (TRT). An analyticalmodel has been developed using thermal resistance concept for the computation of temperatureand heat transer variation along the four legs of the GHE during space cooling operation. Resultsindicate 77% of heat is exchanged in the first U-tube and 23% in the second U-tube. Results arereported by assuming constant borehole temperature of 26°C. Comparison between theoreticalprediction and experimental results obtained for heat transfer through GHX indicates that thetheoretical model could predict the heat transfer rate through the GHX with 2 to 27% errordepending on the inlet temperature of heat transfer fluid in the borehole.