This paper is concerned with developing a discretized analytical model to investigate the effect of backfills on the performance of a vertical U-tube ground heat exchanger. This work builds on the previous development of (1) an approximate analytical solution for a cylindrical heat source in a nonhomogeneous medium, (2) an equivalent-diameter expression for vertical U-tubes, and (3) a fully implicit finite difference technique for the temperature distribution within a U-tube ground heat exchanger. A small-scale U-tube test facility was set up to experimentally validate the system model of the U-tube heat exchanger buried in a nonhomogeneous medium. Two types of backfill materials, bentonite/masonry sand and bentonite/copper powder, were used in the setup. The predictions in the water temperature drop across the U-tube were within 0.5 °C (0.9 °F) of the experimental data for both tests.

Units: Dual