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PNNL latest Commercial models don't align with the ASHRAE 90.1-2019 code

asked 2024-02-22 10:14:15 -0600

Urvi Shah's avatar

updated 2024-02-22 11:37:34 -0600

I observed that the latest commercial prototypical buildings don't align with code ASHRAE 90.1-2019. (specially exterior walls). I tried to compare it with the older models which I had downloaded in 2023. I see that the latest medium office building has been assigned with three different wall U values which wasn't the case in older models. Has anyone faced this issue? What is the reason behind this change?

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(just guessing here - link to idf?)

90.1 has almost always had 4 above-grade wall categories/requirements (e.g. "mass", "steel-framed"). Depending on the climate zone, the steel- and wood-framed categories sometimes have the same U-factor requirements. This would boil down the actual number of wall requirements to 3 in some instances. So when I read "3" different wall U-factors, I assume all 3 requirements are likely being evaluated (e.g. GJ vs $). PNNL may have simply picked 1 (out of 3) in previous models, e.g. "steel-framed" for medium office? Hoping PNNL staff can chime in.

Denis Bourgeois's avatar Denis Bourgeois  ( 2024-02-22 14:55:39 -0600 )edit

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answered 2024-02-23 18:18:11 -0600

updated 2024-02-23 18:32:09 -0600

The prototypes were recently updated to address Addendum av, which characterizes the new thermal bridging requirements. The addendum contains data sets representing cases where thermal bridging is mitigated and un-mitigated. Since the 2022 prototypes represent mitigated thermal bridging (in climate zones 4 - 8, where required), the 2019 prototypes were updated to represent un-mitigated thermal bridging. Overall average de-rated u-values were determined on a floor-by-floor basis for multi-story prototypes, so that's why there are three different u-values for the ground, middle, and top floor of the medium and large office prototype.

The calculation of overall u-values that incorporate the thermal bridging assumptions will be detailed in a forthcoming Final Determination report.

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Ah! Good to know!

Denis Bourgeois's avatar Denis Bourgeois  ( 2024-02-24 05:12:43 -0600 )edit

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Asked: 2024-02-22 10:14:15 -0600

Seen: 206 times

Last updated: Feb 23