Recent years have seen an increased use of insulated glazing units in spandrel applications to visually blend the appearance between the vision and spandrel glass. There has been several instances of glass breakage for this type of design due to thermal stress, despite the spandrels being vented. Anecdotal information and some research are available to support the theory that the glass is breaking due to inadequate heat strengthened ceramic opacified glass in relation to thermal stress. However, the real benefit of providing venting to control thermal stresses is not well quantified, and if venting is not an effective solution to reduce thermal stress and the associated need for higher strength glass, then it is desirable not to vent to avoid dirt buildup on the inside glass surface as it cannot be cleaned.
Simulations with 3-D thermal and computational fluid dynamics (CFD) were implemented to investigate and expand on a recent study (Schwartz et al. 2017) that explored the impact of venting glazing spandrel sections to control heat buildup and moisture. The field monitoring included spandrels with a combination of single- and double-glazing, three different venting scenarios, and clear- and opacified-glass scenarios. The field monitoring data was cross-validated using computer simulations that also provided insight into the impact of discrete parameters that are part of the experimental data. Preliminary simulations results show good agreement with the field monitoring data and highlight the need to utilize explicit 3-D thermal and CFD versus traditional modeling approaches that rely on correlations to model the spandrel air cavity. The full 3-D thermal and CFD model is currently being created and results are pending. The simulations will broaden the relevance of the findings of the field study through the investigation of other conditions including different spandrel designs, venting scenarios, and climates, allowing designers to better predict the impact of thermal stresses and the potential for breakage.
Insulated glazing units are increasingly being used in spandrel assemblies either in shadow box installations or with an opacifier on the 4th surface to provide some depth in appearance. There
The previous study to test the effectiveness of venting spandrel sections to control heat build-up is summarized here. An experimental setup was designed such that three different spandrel installation configurations
In order to test the experimental setup and validate to real world conditions, the modeling of the glazed spandrel sections involves capturing the effects of the mockup characteristics:3-D geometry with
This section provides a summary of the field monitoring results and analysis as discussed in a previous contribution by Schwartz et al. (2017) that was used in calibrating the computer
All simulation results were obtained using 3-D finite element analysis proprietary software from Siemens called NX. The 3-D thermal and CFD simulations were calibrated using data from the field monitoring.
The initial findings from the field monitoring demonstrate that double-glazed spandrel assemblies perform differently from traditional single-glazed spandrels. Double-glazed assemblies can be exposed to significantly higher temperatures that can approach
We gratefully acknowledge the financial support of BC Housing as part of the Building Excellence Research & Education Grants Program, and Starline Windows Ltd. for providing the mockup and glazing assemblies.
AGGA Glass and Glazing Association of Australia 2011. Technical Fact Sheet: Thermal Stress Glass Breakage.
Arztmann, D. 2016. “Shadow Box Re-Engineered”, Proceedings of Facade Tectonics 2016 World Congress, Volume 2.
European Window Film Association, www.ewfa.org, 2012. Accessed October 11, 2017 via https://www.glassonweb.com/article/thermal-stress-film-glass-compatibility.
Haldimann, M., A. Luible, and M. Overend. 2008. Structural Engineering Document 10: Structural use of glass. Zürich, Zürich, Switserland: IABSE / ETH.
Maniatis, I., and M. Elstner, 2016. Investigations on the mechanical strength of enamelled glass. Glass Struct. Eng., 1: 277-288. DOI: 10.1007/s40940-016-0025-2
Mitchell, R., Kohler, C., Curcija, D., Zhu, L., Vidanovic, S., Czarnecki, S., Huizenga, C. (Rev 2013). THERM 6.3/WINDOW 6.3 NFRC Simulation Manual. Lawrence Berkeley National Laboratory, Berkeley, California, USA.
Morrison Hershfield Limited., 2016. “Building Envelope Thermal Bridging Guide”, Version 1.1.
PPG 2008. Glass Technical Document TD-109: Thermal Stress Update. Revision 6.
Saint-Gobain, 2013. Tech Bulletin: Laminated Glass and Thermal Stress.
Schwartz, J., Roppel, P., Hoffman, S., Norris, N., 2017. “Quantifying the Benefit of Venting Glazed Spandrels to Reduce Glass Breakage and Control Moisture”, 15thCanadian Conference on Building Science and Technology Proceedings.
Vockler, K., Krytenberg, T., Norville, H., Blanchet, S., Swanson, J., Barry, C., Carbary, L., Hoffman, S., Torok, G., and Fronsoe1, C., 2017. “Silicone Based Opacifiers: Maintaining Original Glass Strength in High Performance Spandrels”, Glass Performance Days 2017 Proceedings.