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 some state energy codes and in Energy & Atmosphere (EA) prerequisite and credits in LEED 2009 for determining whole building energy performance. (The current version of the building rating system is set to be updated to LEED v4 in October 2016.) 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 (He credits their work in this field to his colleagues, Patrick Roppel, M.A.Sc., P.Eng., and Neil Norris, M.A.Sc., EIT.)
The Morison Hershfield team applied a European method to streamline the assessments of various assemblies by looking at the assemblies’ heat flow with the thermal bridge versus without it for a linear transmittance measurement. The researchers took the advice of the ORNL and began to account for several construction details previously not considered in earlier energy modeling 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 Canadian utility BC Hydro published Building Envelope Thermal Bridging Guide: Analysis, Applications, and Insights, which serves as a resource for designers and specifiers as they confront mitigation of thermal bridging and reducing energy consumption in buildings. It 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 makes it easier for the industry to comprehensively consider thermal bridging in building codes and bylaws, design, and whole building energy analysis;
- examining costs 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.
Fluid-applied thermal
break coatings
Due to new products and baseline energy performance data, construction details are now available for insulating steel and concrete penetrations. These coating products help give project teams new freedom for creative design for net-zero-energy buildings that can also address condensation resistance and energy efficiency when they are applied to structural building elements bypassing the insulated portions of the building envelope (Many of the insulation coatings have been tested with a variety of different primers and topcoats, so there is a system for most substrates and environments. Some manufacturers have tested their coatings with different intumescent and cementitious fireproofing products to ensure they have be approved for use in fire-resistive assemblies.)
Insulated coatings have been infused with fillers to produce a low-conductivity material that can be applied while in its fluid form. Fillers can be ceramic
or glass spheres, which can provide thermal conductivity in the 70 to
100 mW/mK range. Or, newer fillers like aerogel particles can help provide
a thermal conductivity as low as
35 mW/mK. In other words, an acrylic coating can stop the process of heat convection via a steel beam; once this is combined with an aerogel coating,
it also reduces convective heat loss (Aerogels are synthetic porous ultralight materials with low density and thermal conductivity. Essentially, they are gels where the liquid component has been replaced with a gas.)
Often, the beneficial attributes of a product developed for one use can also be repurposed to serve another role. This was the case for fluid-applied thermal break coatings, which were initially developed in 2010 to provide ‘bump protection’ (i.e. safe-to-touch applications) to protect skin-to-hot-pipe contact within certain workplace environments such as along steam pipelines and also in boiler rooms. A proprietary product first developed for deep-sea pipelines was introduced into acrylic coatings for this purpose, and testing proved its beneficial thermal performance on extremely hot surfaces.
According to Greg Pope, co-author of Aerogel Fluid-applied Coatings Solution for Thermal Bridging for Design Community, interest for architectural use grew quickly after the thermal performance test results were discovered.
“The low thermal conductivity of 12 mW/mK make aerogel 50 percent more efficient than still air,” he explained. “Once incorporated into a coating at very low film thickness, the aerogel coating at [1520 to 3800 µm] 60 to 150 mils reduced heat transfer by 47 to 51 percent.”
In order to put this in context, a person could touch a 150-C (300-F) metal pipe for approximately 10 seconds, without any burns, if it had been insulated with a fluid-applied thermal break coating. The aerogel-infused coating insulates the pipe, lowing the surface temperature of the coating to approximately 38 C (100 F).
