Providing opportunities with fluid-applied thermal break coatings

How heat is transferred within a building envelope was determined by Toronto-based engineering firm Morrison Hershfield in American Society of Heating, Refrigerating, and Air-conditioning Engineers’ (ASHRAE’s) Research Project 1365-RP, which initiated a catalog of thermal performance data for 40 common building details for mid-rise and high-rise construction.^* Published in 2011, the goals of the project were to:

• calculate thermal performance data for common building envelope details for mid-rise and high-rise construction;
• develop procedures and a catalog that allowed designers quick and straightforward access to information; and
• provide information to answer the fundamental questions of how overall geometry and materials affect overall thermal performance.

The team of engineers at Morrison Hershfield employed heat transfer software, with the resulting models calibrated and validated against measured and analytical solutions. International Organization for Standardization (ISO) standards for glazing were used, along with a guarded hot box test measurement. They assessed 40 construction details common to construction methods in North America; while there was some focus on glazing, the highest priority was on the details with thermal bridges in 3D.

The research project was initiated when ASHRAE 90.1-2007, Energy Standard for Buildings Except Low-rise Residential Buildings, was the most ubiquitous standard applied in U.S. energy codes and in the then-current LEED 2009 program’s Energy & Atmosphere (EA) prerequisite and credits for determining whole building energy performance. However, ASHRAE 90.1-2007 largely avoided the thermal bridging of outside assemblies, according to Mark Lawton, P.Eng., FEC, of Morison Hershfield’s Vancouver office. Crediting the work of his colleagues Patrick Roppel, M.A.Sc., P.Eng., and Neil Norris, M.A.Sc., EIT, Lawton says the standard did not address avoiding potential improvements to building envelope assemblies beyond its continuous insulation (ci) prescriptive compliance path.

The Morison Hershfield team applied a European method to streamline assessing various assemblies by looking at their heat flow with and without the thermal bridge for a linear transmittance measurement. In this respect, they were North American pioneers for taking into account construction details not previously considered in earlier energy modelling programs.

Since the ASHRAE project, more has been developed for industry professionals who have been tasked with designing energy efficient building envelopes—especially in situations where lateral heat flow is affecting thermal performance of the assembly via linear transmittance (or thermal bridging). In August 2014, Morrison Hershfield and BC Hydro published Building Envelope Thermal Bridging Guide: Analysis, Applications, and Insights, which serves as a guide for designers and specifiers as they confront mitigation of thermal bridging and reducing energy consumption in buildings.

The guide addresses several issues challenging project teams today and addresses those challenges by:

• cataloguing the thermal performance of common building envelope assemblies and interface details;
• providing data-driven guidance that will make it easier for the industry to comprehensively consider thermal bridging in building codes and bylaws, design, and whole building energy analysis;
• examining the cost associated with improving the thermal performance of opaque building envelope assemblies and interface details and forecasting the energy impact for several building types and climates; and
• evaluating cost-effectiveness of improving the building envelope through more thermally efficient assemblies, interface details, and varying insulation levels.

^*Visit morrisonhershfield.com/wp-content/uploads/2015/11/MH_1365RP_Final_-small.pdf.