Fenestration Focus October 2021

October 8th, 2021 by Nathan Hobbs

Energy Star 7.0: Four Ways to Meet the Proposed Northern Zone Criteria

By Doug Hauck

I recently wrote a post for the [DWM] Shop Talk blog covering the state of the proposed Energy Star Version 7.0 requirements. It included industry reactions and some high-level thoughts on how manufacturers might go about meeting the proposed northern zone U-factor and solar heat gain coefficient (SHGC) requirements. (If you haven’t read, just visit dwmmag.com and look for “Shop Talk.”) I believe this is an important topic because many manufacturers could find these requirements very challenging.

At the moment, the specification is expected to be finalized in January 2022 and likely will go into effect in 2023 but may be delayed. If—or when—that happens, what are your options? Below I present my findings with a caveat that these are preliminary findings of potential methods and should not be taken as gospel.

A Look at the Options

Out of the 50 or so double-pane configurations I modeled, only four met the northern zone requirements. None of them made the base values of 0.22 U-factor and 0.17 SHGC, passing instead via one of the SHGC equivalencies. All required premium low-E coatings on surfaces two and four, a true warm-edge spacer system, argon gas filling and an ultra-premium, foam-filled vinyl frame. So yes, it is possible to meet northern zone requirements with doubles, but it will be difficult.

The next question might be whether these requirements can be achieved using a triple-pane IG in the same frame that is used for doubles. In my modeling, triples were more likely to meet the base 0.22 U-factor requirement, but less likely (because they were darker) to meet one of the SHGC equivalencies. However, in this scenario, you’ll be looking at narrower air spaces to fit into a 7/8-inch to 1-inch overall frame thickness, which can pose problems for getting to the 0.22 U-factor. One option is to move to a more expensive Krypton gas fill. Another is to stay with Argon and invest in top-shelf spacers, foamed vinyl frames and specialty low-E. Even so, you might still have issues with carrying the weight of all that extra glass in a traditional frame. Long term, the better option might be to switch to a platform designed to accept triples.

Another possible means for meeting the new requirements is to replace a pane of glass in your double with VIG, a technology that can improve thermal performance dramatically while reducing the size and weight of the overall unit, compared to a triple of similar performance. VIG is available but is considered emerging because of the relative cost to produce. One school of thought is that if the industry can get more time, there will be time for VIG to come down in cost.

Lastly, we’ve talked a lot about thin-glass triples in prior articles, but Version 7 might be the catalyst for a more widespread adoption, because they make it possible to improve U-factors using Argon rather than Krypton. A thinner center lite allows manufacturers to maintain wider air spaces in a frame for doubles.

What these findings tell me is that meeting the proposed requirements will take a lot of planning, investment and forethought. Manufacturers might be faced with decisions about the future of their product designs—and whether continuing to participate in the Energy Star program is worth it.

Doug Hauck is a technical services engineer for Quanex Building Products.
douglas.hauck@quanex.com

To view the laid-in version of this article in our digital edition, CLICK HERE.

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