Room Side Low-E coatings?

Douglas Flandro

Sustainability Design Leader, Exhibit Designer, Associate

CambridgeSeven

LEEDuser Premium Member

9 thumbs up

August 2, 2023

With the current push for improved window performance to meet energy codes and Passive House, room side low-e coatings can significantly improve window U-values. However, back in 2018 Payette did this excellent study that showed that while room side low-e coatings improved window U-value and increased the interior radiant temperature, the surface temperature of the glass decreased. This created a measurable increase in downdrafts at the glazing, and seems like it could create potential for condensation in extreme conditions, though not mentioned in the report.

A lot has developed regarding low-e coatings in the past 5 years. Being able to use a double pane IGU would have a significant benefit for embodied carbon and cost if we can still achieve our performance requirements. Of course, those cost and embodied carbon costs go out the window (pun not intended) if we then have to add perimeter heating. I’m curious if any of the Green Gurus group has updates on the current effects of room side low-e coatings and if this is still a concern or if solutions have been found.

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Mike Manzi

Bora Architects

LEEDuser Basic Member

0 thumbs up

Wed, 08/02/2023 - 16:26

Our preferred way to reduce glazing assembly U-values is to use lower conducting frames, especially commercial fiberglass windows. This is a solution for most applications except multi-story requiring curtain wall (there are wood options for curtain wall, but they can be expensive). U-values for dual pane glazing are similar to triple pane aluminum-framed systems (though thermal breaks in aluminum systems are improving, too). On a recent project, the contractor proposed an aluminum system as VE to our specified fiberglass system. While the aluminum system has a robust thermal break, they included a room side low-e coating to bring the assembly closer to the performance of our fiberglass system. We decided against the room side coating because we didn't want it holding heat in during the cooling period (mixed climate - Portland, OR, internal load dominated project). We also convinced the client to stick with fiberglass at areas with large portions of glass for better thermal comfort and only accepted the VE at smaller punched openings. Mike Manzi He/Him Bora Architecture & Interiors Main: 503 226 1575 Direct: 503 802 5007