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ESD and Morrison Hershfield co-host seminars: “Hidden underperformers – the real impact of thermal bridging through interface details in typical building envelopes.”

At the end of 2014, I co-presented a series of three seminars in Chicago along with Christian Cianfrone and Stephane Hoffman from Morrison Hershfield.

The seminars focused on the latest data and research in thermal bridging and the true thermal performance of modern opaque wall construction. During the first part of the presentation, Christian Cianfrone and Stephane Hoffman from Morrison Herhsfield presented on their Building Envelope Thermal Analysis (BETA) Guide and the results of the research associated with the guide.

The BETA guide provides a catalog of the thermal performance of common envelope assemblies and interface details directly relevant to construction in British Columbia and North America in general. The guide also provides information that makes it easier for the industry to comprehensively consider thermal bridging in building codes and bylaws, design, and whole building energy simulations.

During the second part of the presentation, I presented the results of ESD?s in-house research on a data set of 16 new-construction buildings in the Chicagoland and the Midwest area. We looked at the impact  of thinking about the building envelope from a 1D versus 3D perspective. The research as well as the data in the BETA guide reiterates the importance of accurate thermal performance assessment and the need for concept design energy modeling and integrative design approach.

The 1D opaque wall thermal performance analysis is widely used in the industry by architects and engineers, but disregards the effects of thermal bridging. The buildings in the study varied in size, shape, and type. The energy modeling research showed an overarching negative effect for buildings in heating predominant climates. The documented energy increase in the data set varied from 2% to 14% and was proportional to energy cost increase. We also noticed a strong correlation between the surface area to volume ratios, window to wall ratios and the energy cost increases, a trend presented in Figure 1. The optimum point for buildings in the data set where the energy increase penalty went beyond 4% was found to be for buildings with a surface area to volume ratio lower than 0.6 (thinner profiles) and for window to wall ratios lower than 45%.

We also noticed that the peak heating demand increase varied between 1% and 29%, while the peak cooling demand varied between 1% and 8%.

Figure 1. 1D vs 3D Assembly R-value: Energy Usage Comparison

Some buildings in the analysis saw more drastic penalties like the office building below. Because of its thinner profile and a lower window to wall ratio this project?s energy consumption penalty was 8%, peak cooling increase 7%, and peak heating increase 30%.

Figure 2. Case Study Infographics

I also spoke about the diminishing benefit of added back-pan insulation in curtain wall and window wall modules as well as ways of optimizing a spandrel design for the best cost-benefit ratio.

Figure 3. Curtain-wall vs window-wall thermal performance and the diminishing benefit of added insulation

ESD encourages building design professionals and building owners to pay close attention to how their walls really perform. We should work together early on to create bespoke design approaches to each building by considering the BETA guide, energy modeling, and our combined intelligences. We also stresses the need to continuously evolve our thinking about the building design!

Over 150 local architects, engineers, and industry professionals attended the seminars and participated in round-table discussions on the topic. The seminars were hosted by Cannon Design at the Building Enclosure Council Annual Chair Gala, by the AIA Chicago COTE committee at the Skidmore, Owings and Merrill offices, and by ESD at our offices.

We?d like to thank everyone for attending the seminars, participating in the discussions, and constantly pushing the boundaries of their respective trades for the sake of bettering our industry and innovating.