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Richard Green
As we change the rules of thermal performance for facades, we are changing the conditions the glass is subject to in shadow boxes and glazed spandrel panels. The occurrence of fritted spandrel glass failures in over 30 buildings in different thermal climates is indicative of a bigger problem; these failures are just ‘the canary in the coal mine.’ This paper describes when and why the golden rule of 'heat-strengthened glass is OK in spandrels' now needs a few caveats, including care in selection of the IGU spacer and opacifier.
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Edlyn Garcia La Torre • Ivan lee • Shahima Rahmatipour
Glazed wall systems, such as curtain walls and window walls, are one of the most commonly used façade systems in modern buildings in North America. These systems consist of transparent and opaque areas, which allow natural light, views, and solar gains through the transparent sections, as well as thermal resistance and concealing interior building components covered by the opaque sections. While the thermal and optical performance of the transparent areas is very well understood and evaluated through industry standards such as NFRC-100 and 200, the thermal performance of the opaque sections of glazed wall systems, also known as spandrel assemblies, is not.
The process of calculating heat loss through spandrel assemblies is complicated due to thermal bridging caused by highly conductive mullions and framing members. This makes it challenging to evaluate using traditional 1D or 2D calculations. While thermal bridging is also present in transparent sections, the additional heat loss near the center of the spandrel assembly is different. Using similar evaluation techniques can lead to misleading results. Studies reveal significant differences in the performance of current simulation methods for spandrel assemblies, which can diverge up to 20% compared to laboratory testing. This divergence has caused many designers to believe their systems perform better than they do, resulting in increased heating and cooling demand and condensation problems. This uncertainty also poses a risk for compliance with more stringent energy code requirements. As building codes in North America are reducing energy demand requirements to lower operational greenhouse gas emissions through lower facade U-factors, there is a need for more accurate methods to evaluate facade systems to reflect their actual thermal performance.
This paper compares various thermal simulation techniques for evaluating the thermal performance of spandrel assemblies in typical curtain wall systems with variations for glass types, insulation levels, and cladding, among others. These include 2D and 3D simulation methods:
This paper aims to highlight the differences in thermal simulation results for spandrel assemblies in terms of overall heat loss (U-factors) and surface temperatures to evaluate condensation risks. Results aid in identifying shortfalls of procedures to determine the right tools for the correct application.
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Faruk Cakir • Daniel Arztmann
The prevalence of fully glazed facades in modern office buildings has been steadily increasing, primarily driven by architects' focus on aesthetic appeal. While the desire for fully glazed designs with seamless transitions across buildings is evident, the shadow box, which consists of two layers of glass and an opaque back pan with an air cavity in between, stands out among other spandrel panel applications due to its unique visual effect on the facade. Architects frequently opt for the shadow box in designing the opaque sections of modern glass facades because these applications provide them with a high degree of design freedom. However, the shadow box is a complex system that requires precise design and manufacturing to prevent any negative impact on the overall building performance. It is susceptible to issues such as condensation, contamination, and overheating, which give rise to project-specific challenges for engineers and designers, adding complexity to detailing and real-life applications. This research constitutes the second phase of the study previously published for the ISCCGF – Zagreb 2023 Conference. Building upon the earlier work, this follow-up study employs a mock-up test approach to investigate the issue of overheating in shadow box systems.
The primary aim is to conduct extensive analysis of the underlying reasons for this problem. This will be achieved by utilizing the same test units while expanding both the dataset and the observation period. While the initial study mainly focused on type 3 shadow box behaviour, this current study addresses all shadow box types, drawing comparisons between them and re-examining the type 3 findings within a longer timeframe. The findings are expected to have considerable impact on future shadow box applications. Thus, the overall goal is to examine the behaviour of different shadow box settings and provide valuable information to the industry to overcome the potential problems faced in most projects. Moreover, the long-term goal is to contribute to the development of an enforceable consensus on shadow box applications in the industry, which currently does not exist.
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