Using Thermal Modeling of Fenestration in the Design Process

December 21, 2017
Publication: Journal of the National Institute of Building Sciences
Author(s): David Artigas

Designers typically have two concerns about thermal performance when it comes to fenestration: energy performance and condensation potential. Thermal modeling standards provide ways to assess the performance of different assemblies and products for achieving a comfortable, energy-efficient building without condensation issues. However, some designers use early modeling to specify fenestration performance requirements without considering design parameters such as frame geometry, glass size, mullion spacing, occupancy loads, humidification, etc. Due to the variability of fenestration and design options, this “let’s model first” approach can slow the design process because the modeling does not represent a project-specific design approach. Alternatively, designers may wait until the design is nearing completion to perform modeling to verify that their design “works,” only to find it has high condensation potential or does not meet their assumed energy performance, which can result in having to hurriedly redesign the fenestration or leaving it to the contractor to figure out as “delegated design” during construction.