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ASHRAE90.1-2010 - Energy Cost Budget Method - Fenestration Orientation

asked 2015-04-09 15:21:08 -0500

updated 2015-07-11 20:04:13 -0500

Hi fellow modelers,

I am working on a compliance energy model for which we are considering the ASHRAE 90.1-2010 Energy Cost Budget (chapter 11) method. Under the budget (baseline) building, section 5 in Table 11.3.1, the instructions refer to the section where the baseline model needs to comply with:

As>=Aw and As>=Ae

As= south oriented vertical fenestration area Aw= west oriented vertical fenestration area Ae= east oriented vertical fenestration area

Our building has As=0. The code says: "If the fenestration area facing west or east of the proposed building exceeds the area limit set in Section, the area shall be reduced proportionally until the area is the same as the area limit set in Section The area limit is the fenestration area facing south in the northern hemisphere or the fenestration area facing north in the southern hemisphere as defined in Section"

Has anyone dealt with this before? Does this mean that we should assume no windows for east and west sides on this building to comply with this section?

Any thoughts/interpretations would be appreciated.

@nfonner Yes, we did.

There are adjacent buildings on the south plus the scenic view on the north, east and west has probably mandated the glazing on those orientations not on the south.

We are considering the exception with 75% shaded fenestration areas as an alternative but are wondering what would one do if there was no escape from this rule? how should the area on the east and west be reduced PROPORTIONALLY to reach the southern fenestration area given that As=0?

The adjacent buildings to the south would not qualify the project for exception b (buildings that have an existing building or existing permanent infrastructure <20ft to the south... and half as tall as the proposed project.)

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Couple of questions:
Did you account for the 45 degree off of true N,S,E,W when computing As?
Why are there no windows on the South facade? This one may lead to an exception BTW.

Otherwise, hope to heck another exception applies. This one always throws designers for a loop when I tell them of this requirement.

nfonner gravatar image nfonner  ( 2015-04-09 15:34:19 -0500 )edit

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answered 2015-04-09 17:08:03 -0500

SDBBCER gravatar image

This requirement was changed in 2013. Unfortunately I don't recall the addendum letter that made the change. However, for 2013, the text states that if this condition exists, reduce the total area to the total building percent and rotate the building at 90° intervals to average the exposure (like Appendix G). It may be possible to ask the building official to allow the use of the addendum that affected this text as it is unlikely that the intent of the text in 2010 was to force the baseline building to have 0 glazing in this situation.

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wow that makes a lot more sense now, thanks @SDBBCER there a chance that you can share the exact wordings with me? I do not have access to the 2013 version at this time...

Amir Rezaei gravatar image Amir Rezaei  ( 2015-04-09 17:30:50 -0500 )edit

Addendum bb has the wording. It was primarily an envelope addendum so the ECB changes are pretty far down. The following link (to a pdf download) has many of the addenda to 2010 and the changes are marked:2010 Addenda

SDBBCER gravatar image SDBBCER  ( 2015-04-09 18:23:10 -0500 )edit

Addendum bw is where the changes impact ECB.

nfonner gravatar image nfonner  ( 2015-04-10 16:02:02 -0500 )edit

sorry about that. nfonner is correct, it's addendum bw.

SDBBCER gravatar image SDBBCER  ( 2015-04-10 17:11:40 -0500 )edit

answered 2015-04-09 16:43:58 -0500

nfonner gravatar image

updated 2015-04-09 16:44:18 -0500

This is somewhat hypothetical, but I would say the Aw, As and Ae for the budget model would all be 0.

The requirement is clearly too aggressive IMO given the lack of freedom concerning siting in most projects, not to mention the actual energy penalty of E/W glazing would not be nearly so severe in the real world, but it's black and white for 90.1-2010.

Might be time to bounce back to IECC-2012 if applicable in your area. Not that that is without a lot of conversation, but at least it would be a more sane comparison for this project.

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That's is exactly the problem we have, how aggressive this seems. It's good to hear a similar thought process from you. We are modeling for both 90.1-2010 and IECC-2012 routes to make sure we can comply...

Amir Rezaei gravatar image Amir Rezaei  ( 2015-04-09 17:27:31 -0500 )edit

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Asked: 2015-04-09 15:21:08 -0500

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Last updated: Apr 09 '15