Superposition of the single point source solution to generate temperature response factors for geothermal piles

Geothermal piles are a very promising technique to exploit the low enthalpy resource for ground coupled heat pumps. In fact, they are heat exchangers integrated in the foundation structures of the buildings, with reduced need in term of ground surface availability and diminished drilling costs. Unfortunately, to evaluate the ground thermal response to their presence it is not possible to use classical analytical solutions due to their low aspect ratio and to the relevant effect of the heat capacity of the inner cylindrical volume. In addition, different shapes of the pipe arrangement are possible: helix around the foundation pile or a series of vertical pipes connected through U bends at top and bottom of the cylindrical volume.