Engineered transition zone systems for enhanced heat transfer in thermo-active foundations

Abstract

Results are presented from both field and laboratory studies on the thermal properties Piedmont residual soils, as well as a numerical model and a laboratory scale physical model, to demonstrate the potential for improvement in thermal performance of shallow thermo-active foundations resulting from a novel concept termed the Engineered Transition Zone (ETZ). An ETZ provides a means to introduce a thermally optimized zone between the foundation and the surrounding geomaterials to reduce thermal resistance. It also allows decoupling of the structural portion of the foundation from the thermal portion, such that the length of each component can be selected individually to meet the specific structural and thermal needs. Additionally, it allows for various novel circulation pipe configurations to be used to further enhance heat transfer due to increased pipe surface area available for heat transfer. Both the numerical and physical models show that there is a potential for significant improvement in thermal performance. Such improvements can make shallow thermo-active foundations a more feasible renewable and sustainable energy alternative for heating and cooling of buildings (provided that the ground energy balance can be equilibrated; that is, there is balance between heat extracted for heating and heat re-injected for cooling), particularly in areas where poor subsurface thermal properties might otherwise preclude their use. Public policy considerations for shallow thermo-active foundations are also discussed, and recommendations for future research are presented.