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NC-2009 EAp2:Minimum Energy Performance

Appropriate Fenestration U-value for Baseline Model

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PATRICK CORRIGAN
MECHANICAL ENGINEER, PE, LEED AP
ARCHITECTURAL EXPRESSIONS, LLP
LEEDuser Basic Member
7 thumbs up

I can not tell, from either ASHRAE 90.1-2007 or from the LEED User's Manual, what U-value I am supposed to use for the baseline vertical glazing. Each referenced standard states "...match appropriate requirements in Tables 5.5-1 through 5.5-8." In that table there list 4 types of vertical glazing. Let's say I have a building with 40% glass. In the proposed design there is a room with an perimeter wall, but no glass. In the baseline model, I am to arbitrarily add 40% glass to this wall, but I do not know what the appropriate U-value of the glass should be. Am I missing something here? To be more specific, I am in climate zone 5A.

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Mon, 08/29/2011 - 17:23

For 90.1-2007, the windows for both baseline and proposed are modeled in the same place if the window area is less than 40% of the total wall area for the building. This is usually the case. 90.1-2004 required bands of windows to be placed around the baseline building. This put windows in places on the baseline building where there were none on the proposed. As far as the U-values, use the same category of window as the proposed building. Notes b and c under the table on page 23 (90-1 2007) help clarify. Hope this helps.

Thu, 09/01/2011 - 19:40

"As far as the U-values, use the same category of window as the proposed building" THANK YOU THOMAS, THIS IS WHAT IS MISSED IN EVERY EXPLANATION!!!

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