A new algorithm has been developed as part of ASHRAE research project RP-1016 for approximating the performance of vertical bore heat exchangers installed in a stratified geological regime. The new algorithm, named the multi-layer borefield design algorithm (MLBDA), uses the analytical solution for a cylindrical heat source in an infinite region. It is shown that the new algorithm accounts for differing thermal properties in each stratum within the geological regime and the effect of various borehole completion techniques. No valid field data were available for comparison, so the algorithm was tested using a hypothetical three-layer geological regime in which the thermal conductivity of the middle layer approached that of a perfect insulator. It is shown that the multilayer model effectively isolated the middle layer from the global heat transfer process. The result of this test qualitatively validated the algorithm.

Units: Dual