Takeaways for fenestration specification
Based on this study, below are some key takeaways and recommendations for fenestration specification to manage condensation risk:
- In addition to reinforcing the lack of correlation between U-factor and CR value, the results identify a lack of correlation between CR value and the extent of condensation. Condensation is driven by the combination of all window assembly components (the frame, the EOG, and the COG) and their material properties, rather than assembly U-factor or CR value.
- The window system’s individual components matter for condensation performance: CR value is not a predictor of the extent to which condensation covers fenestration surfaces, but rather this is determined by the thermal performance of the window system components: Frame, spacer, IGU configuration. Moreover, some windows with similar U-factors and CR values performed drastically different relative to condensation, exhibiting an 80 percent difference in the extent of condensation under identical conditions. This is attributed to differences in the material properties of their individual components, specifically the spacer in the IGUs.
- The weakest thermal link in the fenestration assembly drives condensation performance: The weakest thermal link is determined by the path of least resistance to heat flow, and is typically the frame, followed by the EOG. Recall that for window types with lowest performing frames, condensation occurred first along the interior surface of the frame. When frame thermal performance was improved, condensation occurred first at the EOG.
- First, improve the thermal performance of the frame, by adding wide and complex thermal barriers; then, improve the EOG, by adding a warm-edge spacer. In this study, condensation occurred along the EOG for window types with wide thermal barriers. The presence of a warm-edge spacer in place of an aluminum spacer significantly reduced this condensation. Further, in these simulations, for windows with a high-performance frame, warm-edge spacer, and triple-pane COG (CR >/= 67), condensation occurred only under extreme and highly unlikely conditions, if at all.
- Specify the performance of the individual fenestration components (frame, EOG, COG), in addition to specifying the fenestration assembly U-factor and CR value. Frame performance can be specified by defining a thermal barrier type and width (e.g. at least 25-mm [1-in.]), or by specifying one or more manufacturers’ frames which have the desired performance. Ideally, warm-edge spacer should be specified by type (e.g. PHSS) or by EOG effective conductivity (Keff), rather than generically as “warm-edge.” Generic “warm-edge” includes relatively high-conductance stainless-steel spacer. Neglecting to specify an IGU spacer typically results in the delivery of an aluminum spacer, which is a risk for condensation.’
Notes
1 S. Milosevic, A. Aksamija, A. Blakeslee, H. Sanders; Condensation Study of Windows: Thermal Analysis of Various Window Systems under Different Exterior Environmental Conditions; Façade Tectonics World Congress, October 2022; www.facadetectonics.org/papers/condensation-study-of-windows.
2 Dew point calculator www.dpcalc.com/.
Author
Part of Technoform’s team for nearly 10 years, Alexandra Blakeslee drives product innovation and technical collaborations with customers and industry and academic partners. She co-manages Technoform North America’s market team focused on edge bond solutions for insulating glass in windows, doors, and other fenestration systems. She earned a bachelor’s degree in mechanical engineering and music from the University of Akron and is pursuing a master’s in sustainable environmental systems from Pratt Institute. Blakeslee is an active member of the Facade Tectonics Institute (FTI), the Fenestration and Glazing Industry Alliance (FGIA), and other industry associations and events. She can be reached at alexandra.blakeslee@technoform.com.
Helen Sanders, PhD, is a general manager at Technoform North America. She has more than 25 years of experience in glass technology, market development, and manufacturing, especially in functional coatings, insulating glass, and thermal zone technology for fenestration. Sanders has a doctorate in surface science from the University of Cambridge, England. She is an active member of many industry organizations and in codes and standards development. She is the founding president of the FTI and is currently the immediate past president. She is a board member of the National Fenestration Rating Council (NFRC) and of the FGIA, co-chair of its Glass Products Council, and of its Innovation and Sustainability Steering Committees; and a technical liaison on the National Glass Association’s (NGA’s) Fabricating Committee. Sanders can be reached at helen.sanders@technoform.com.
