A novel analytical multilayer cylindrical heat source model for vertical ground heat exchangers installed in layered ground

Abstract

This paper presents a new analytical multilayer cylindrical heat source model for vertical ground heat exchangers (GHEs) installed in layered ground using the new integral-transform method. The analytical model was validated by model degradation, numerical simulation, and a laboratory-scale experiment. Results indicate that temperature profiles of vertical GHEs in layered ground are quite different from those in homogeneous ground, and that temperature differences increase with time. Thermal property differences between ground layers were found to result in additional vertical heat transfer across layer interfaces, which is not observed in homogeneous ground. Cross-layer thermal interaction was found to be stronger when thermal property differences are larger. The new cylindrical heat source model was also compared with the multilayer line heat source model, and it was found that differences between the two models decrease with time. Further, larger GHE thermal loads and smaller ground thermal conductivity values led to larger error of multilayer line heat source model. The new multilayer cylindrical heat source model was found to be suitable for quickly considering the effects of ground stratification on the design of vertical GHEs.