1. Scope

Keywords

Rationale

Glazed wall systems, such as curtain walls, are comprised of transparent and/or translucent materials as well as opaque areas known as spandrels. Studies have shown that the reported U-factors of these areas underpredicts their contribution to energy loss and that the standard modeling procedures are insufficient to reliability predict condensation resistance. While well-validated procedures like NFRC 100 exist for the many stand-alone fenestration products, there is limited guidance to practitioners for calculating the thermal performance of spandrel assemblies in glazed wall systems. While the focus of this Standard Practice is on the opaque portions of glazed wall systems, it is anticipated to additionally cover the three-dimensional thermal effects of the adjacent vision areas which have been shown to greatly impact the performance of these systems. This Standard Practice will be developed in conjunction with the Charles Pankow Foundation project: Thermal Performance of Spandrel Assemblies in Glazing Systems. The project includes physical “hot box” testing of representative variations of aluminum-framed glazed wall systems with various vision and spandrel assemblies to compare to two- and three-dimensional analytical models. The physical testing and modeling will be compared to refine modeling methodologies for optimal alignment with actual performance. Determination of spandrel assembly thermal performance must accurately reflect the actual performance of the assembly to allow for a better overall understanding of the energy dynamics of a building design. The Charles Pankow Foundation project's results and recommendations, as well as the new ASTM standard, are envisaged to inform changes to the model energy codes (e.g., IECC, ASHRAE 90.1). The proposed ASTM standard will establish a consistent calculation methodology for systematic product-based comparisons and building thermal performance for both vision and spandrel assemblies.