A detailed numerical simulation tool was used to carry out this research. The problem of heat transfer was solved with an equivalent electrical circuit of thermal resistances and capacitances. This simulation tool was also used on a double U-tube heat exchanger in order to include axial heat conduction in the ground and the borehole.
The two borehole heat exchangers were analyzed over both long- and short-term periods; the thermal properties of the ground, energy loads and the axial effects of weather conditions were also taken into account. Finally, a reduction in the borehole length for the helical-shaped pipe was also assessed and compared with the performance of the double U-tube.