Steady state heat transfer analysis of buried spirally coiled pipes

The heat transfer from a spirally coiled pipe buried underground, typically used in ground-source heat pumps, presents a significantly complex problem because of the complicated pipe geometry. Exact analytical solutions are not possible and grid generation around the coiled pipe, required for a numerical solution, becomes an intractable problem. The present work outlines the development of an approximate analytical technique, referred to here as the line source approximation (LSA). The LSA method is shown to be highly accurate when compared to known analytical results for a straight pipe and provides a reasonable representation of the thermal interference caused by the overlapping coils of the spiral geometry. The main focus of this research is to determine the effect of various geometric parameters on the heat transfer process. The physics is kept simple by considering a steady-state heat conduction problem in the soil around the pipe. A sensitivity analysis of the results, obtained via the LSA method, reveals the coil pitch to be the dominant geometric influence on the heat transfer from the spirally coiled pipe.