Finite Cylinder-source Model for Pile/Borehole Heat Exchangers in Multilayered Medium

Analytical and simulation models of ground heat exchangers (GHE) are necessary for proper sizing piles with smaller depth to radius ratio than boreholes. Most existing methods of design ignore the transient thermal processes within the piles or boreholes: some software programs are based on the classical “hollow” cylindrical surface source or line-source models. In order to take into account thermal capacity of large diameter piles, an integral mean temperature approach is applied to the response induced by “solid” cylinder-source of heat (Man et.al, 2010). The average temperature response to a constant heat rate is reduced to a single integral only by integrating the exact solution over the depth of a finite cylindrical source of heat embedded in ground on a distance D from its surface. Anisotropy effect of the multilayered ground is examined using the mean solution at the center and at the edge of a single GHE. Simple form of the obtained solution is suitable for analysis and thermal design.