Thermal Performance of Wall Systems Utilizing Radiant Barriers

Abstract

Typical brick veneer wall assemblies contain an air space to provide drainage inside the wall. This air cavity results in heat transfer through the wall via conduction, convection, and radiation, with radiation typically being the dominant heat transfer mechanism across the air space. Due to the significance of radiative heat transfer, any modification to the surface properties of the wall facing the air space can result in significant energy savings if the radiation heat transfer can be reduced. Radiation heat transfer can be minimized by installing a radiant barrier in the brick veneer wall. A radiant barrier is a thin metallic foil whose surface has an average emissivity of around 0.05. In this research study, first several commercially available radiant barriers were characterized using a heat flow meter apparatus. The thermal emissivity was estimated indirectly by measuring the thermal resistance of a known air space. Second, small-scale hot box testing was carried out to determine if the radiant barriers performed as expected in a more complex wall assembly. Third, full-scale hot box testing was carried out using one of the commercial radiant barriers. Finally, finite element models were verified against experimental results to allow for predicting the performance of radiant barriers in other wall systems. It was found that installing a radiant barrier in a typical residential brick veneer wall resulted in an increase in the R-value of the system and a significant increase in the dynamic thermal performance of the wall.