New Correlations for Thermal Resistances of Vertical Single U-Shape Ground Heat Exchanger

The effective pipe-to-borehole and pipe-to-pipe thermal resistances of vertical single U-shape ground heat exchanger are numerically studied. The non-uniform temperature distributions along perimeter of both borehole and outside diameter of two pipes are taken into account to evaluate both the pipe-to-borehole and pipe-to-pipe thermal resistances. The best-fit correlations for these two thermal resistances are proposed and compared with the available equations in the literature. It is found that the present correlations of effective pipe-to-borehole and pipe-to-pipe thermal resistances are more accurate than those of available formulas.