Thermal Analysis of Complex Glazing

Design Optimization Using a Transient Systems Simulation Program and Bidirectional Scattering Distribution Function Window Definition



Photo of Adrian Turcato

Adrian Turcato

Transsolar KlimaEngineering

Photo of Chris Stutzki

Chris Stutzki


Stutzki Engineering

Photo of Erik Olsen

Erik Olsen

Managing Partner

Transsolar KlimaEngineering



The use of bidirectional scattering distribution function incorporated in a transient systems simulation program, allows engineers to accurately determine glazing surface temperatures for complex glazing assemblies in architecturally ambitious projects. Understanding the thermal behavior of complex glazing assemblies is increasingly critical to high-performance facades - for structural, condensation and occupant comfort considerations. Bidirectional scattering distribution functions account for the way that radiation with different angles of incidence are transmitted through and reflected from glazing. To date these functions have been more widely applied in daylight analysis and not in thermal analysis, partially due to a lack of thermal analysis tools utilizing these functions. Newly included bidirectional scattering distribution function features in a transient systems simulation software allow a more precise accounting for heat flow through glazing assemblies, including air gap temperatures and glass surface temperatures. This newly extended capability was used to investigate the thermal stress in glazing assemblies for two projects: Grace Farms in New Canaan, Connecticut (built and occupied) and the new Little Caesars’ corporate headquarters in Detroit, Michigan (under construction), both located in humid continental climates. These projects, both using glazing innovatively, required additional structural analysis of the glass due to differential thermal loading (Grace Farms with ~3000 linear feet of 12-14 feet tall curved double-glazed insulated glass units and the Little Caesars’ headquarters with a highly-articulated curtain wall facade). In the case of Little Caesars’ project, the calculation allowed for designers to identify dangerous levels of thermally induced stress in the assembly design. These case studies represent two of the first real-world examples of this methodology.


The two projects discussed in this paper are Grace Farm, located in Connecticut and designed by Japanese architect SAANA, and the new Little Caesars’ corporate headquarters, located in Michigan and

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BSDF are used frequently for modeling daylight in complex fenestration and shading. As originally described by Heckbert in 2001, BSDF calculations take account of the scattering effects of light as

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The BSDF calculations were completed using a detailed heat transfer model run by TRNSYS 18. The model accounts for all heat transfer effects according to the International Standards Organization (ISO)

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Due to space constraints, results will be shared primarily for the novel BSDF calculations. The data of primary importance are the temperature profiles across the IGUs. Typically, this is the

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For Grace Farms, it was originally anticipated that the glazing would experience issues around the edges, where the glass is sitting in the sill channel. It was expected that during

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Conclusion and Future Work

In both the case of Grace Farms and Little Caesars the failure of an IGU represented a significant risk to the building owner. For these innovative and complex facades glass

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Rights and Permissions

Hiller, M., Schöttl, P. 2014. Modeling Complex Fenestration Systems in TRNSYS. BauSim 2014, September 22-24, Aachen.

ISO. 2013. Thermal performance of windows, doors and shading devices. ISO 15099:2013.

ABAQUS UNIFIED FEA. Dassault Systemes.

McDowell, T., Bradley, D., Hiller, M. Lam, J., Merk, J., Keilholz, W. 2017. TRNSYS 18: The Continued Evolution of the Software. Building Simulation 2017, August 7-9, San Francisco.

Mitchell, R., Kohler, C., Klems, J., Rubin, M., and Arasteh, D. 2006. Window 6.1 / Therm 6.1 Research Version User Manual – For Analyzing Window Thermal Performance. Lawrence Berkeley National Laboratory.

Schöttl, P. Integration komplexer Verglasungsysteme mit Bidirectional Scattering Distribution Function in TRNSYS. PhD thesis, Technical University of Munich.

Stutzki, C. Kuba, M., Knowles, J., and Fischer, C. 2013. Studies of Effect of Temperature Changes on Insulated and Laminated Glass. GPD Glass Performance Days Finland 2013, Tampere Finland.

Sonntag, A., Stutzki, C., and Kuba, M. 2014. Structural Insulated Glass. GlassCon Global 2014, Philadelphia.