Abstract: The performance of three kinds of heat transfers,which were single U-tube heat exchanger,double U-tube heat exchanger and tube-in-tube heat exchange,was studied when a source-ground heat pump system was operated as an unsteady heat rejection mode.After experimental data were arranged,the variations of the temperature of soil,outlet water as well as the heat exchange capability with time were gained.Comparison of the performance between three heat exchangers shows that the double U-tube is the be...

Key words: buried heat exchanger； unsteady performance of heat transfer； flow resistance；