Know the Limits: Constraints Drive Innovation to Meet Energy Codes

By Helen Sanders

Polyamide thermal barriers have been used to improve the thermal performance of aluminum fenestration for almost 50 years. Their size and complexity have developed from the early days with 10 mm (0.4 inches) wide barriers to ones that now extend beyond 100 mm (4 inches) in width. When used in combination with foam or complex legs, today’s barriers can reduce both conductive and convective heat transfer. Larger polyamide extruded profiles, such as pressure plates for curtainwall, and innovations such as shearless barriers, which prevent thermal bowing, also have increased the applications that can benefit from improved thermal performance.

For some fenestration systems, it is difficult to use wide thermal barriers because of frame depth limitations. For example, glazed door systems, particularly the sliding variety, need to maintain a slim sightline. This limitation makes it more challenging for these systems to meet today’s code requirements. Currently, the biggest challenge is in Canada, where the rate of increase in building energy code stringency is outpacing the U.S. The U-factor target for fenestration in the National Energy Code of Canada (NECB 2015) is 2 W/m2K (0.34 BTU/of.hr.ft2) for some regions. This can be a significant challenge for sliding doors.

New Options

Lower conductivity polyamide is a new material innovation that can help increase thermal performance without increasing barrier width and frame depth. The same barrier made with a lower conductivity polyamide, often referred to as “low lambda,” provides a lower (better) fenestration assembly U-factor.

While the lower conductivity polyamide material has lower mechanical strength than regular polyamide, it typically doesn’t impact the fenestration design. This is because the connection between the ends of the thermal barrier and the aluminum extrusion is often the limiting factor for structural performance. As a result, it may be possible to improve the performance of an existing design without changing extrusions, just by substituting the existing barrier with one made with lower conductivity polyamide.

Achieving Performance

Metra, for example, is using this technology in its new sliding door design to help meet the requirements of the NECB. Using low conductivity polyamide allows them to limit the depth of the frame, while also leaving enough room to incorporate an insect screen.

Fabricators need a variety of tools to deliver lower U-factors across many products. Low lambda polyamide is an option that provides designers with another option to deliver the needed improvements in thermal performance, while minimizing cost and manufacturing and supply chain complexity.

Helen Sanders is in strategic business development for Technoform North America Inc. in Twinsburg, Ohio. Read her blog each month at usglassmag.com/insights.

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