Foundation heat exchangers for residential ground source heat pump systems—Numerical modeling and experimental validation

Abstract

A new type of ground heat exchanger that utilizes the excavation often made for basements or foundations has been proposed as an alternative to conventional ground heat exchangers. This article describes a numerical model that can be used to size these foundation heat exchanger (FHX) systems. The numerical model is a two-dimensional finite-volume model that considers a wide variety of factors, such as soil freezing and evapotranspiration. The FHX numerical model is validated with one year of experimental data collected at an experimental house located near Oak Ridge, Tennessee. The model shows good agreement with the experimental data—heat pump entering fluid temperatures typically within 1°C (1.8°F)—with minor discrepancies due to approximations, such as constant moisture content throughout the year, uniform evapotranspiration over the seasons, and lack of ground shading in the model.

Acknowledgments

Lu Xing is Research Assistant. James R. Cullin Student Member ASHRAE, is Research Assistant. Jeffrey D. Spitler, PhD, PE, Fellow ASHRAE, is Regents Professor and C. M. Professor. Piljae Im, PhD, Associate Member ASHRAE, is R&D staff. Daniel E. Fisher, PhD, PE, Fellow ASHRAE, is E. Fisher Professor.