For Non-Residential fenestration system that are designed to be field glazed or field assembled units for compliance with ASHRAE 90.1-2010, the supplier provides a certificate according to NFRC procedures. The NFRC ratings is based on individual product simulated and have outside dimensions measuring 2000 mm x 2000 mm (NFRC Size for Glazed Wall/Sloped Glazing). For calculating the building envelope performance for the proposed building according to Appendix G, 90-1 2007, should the energy model use NRFC ratings (U-Factor, SHGC, Tvis) using standard NFRC size, regardless of actual size of the fenestration systems?

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Thu, 08/20/2015 - 16:23

It depends. There is usually more than on way to model the windows and frames. You can model the whole assembly values or you can separate the frames and the glazing. We will typically do the later as it tends to be more accurate. This will take size into account. Using a single NFRC value for all windows may be reasonably accurate if the window sizes to not vary to a significant degree. If they do vary significantly I would not use that method.

Curtis Clark

Director of Sustainability Services

GSBS Architects

LEEDuser Basic Member

3 thumbs up

Sat, 08/22/2015 - 14:58

Perhaps this warrants a formal interpretation. When you specify and purchase fenestrations, you use the rated NRFC fenestration values that is tested and simulated at NRFC standard sizes. For code compliance with 90.1-2010, you use the rated fenestration values in Comcheck. It would only make sense to use rated fenestration values when you rate buildings to Appendix G. For design of mechanical systems, you should make the adjustment for fenestration size.

Cansin Manyas

LEEDuser Basic Member

0 thumbs up

Mon, 08/24/2015 - 07:53

Hi, Glass manufacturers submit test reports in accordance with EN410 and EN673 for glass. And the S/Cs submit test reports for glass and frame. To the best of my understanding from your comments and after reading ASRAE 90.1-2007 since the values we have received are tested in compliance with EN410 and EN673 I should ask for values calculated and tested as per NFRC. I just wanted to make sure. Thanks and regards.

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 08/25/2015 - 13:59

Not all windows are NFRC rated for the whole assembly (curtainwall for example). International projects do not use windows that are required to be NFRC rated. As I said there are appropriate situations where using the NFRC data is appropriate but there are situations where it is not IMO. The LEED reviewers will accept several different methodologies for the determination of the window performance values. NFRC is just one way, but not the only way.

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