[Equest-users] [Bldg-sim] LEED project - maximum limit allowed to simplified wall azimuth.

Thu Dec 15 10:17:39 PST 2016

Put another way:

If you have a perfectly circular floorplate, ASHRAE wants you to model an octagon, with respect to a minimum number of facets.

This specific query reminds me:  There was a pretty interesting thought-study presented at ASHRAE's energy conference in 2015 where someone tested this logic, by asking the question (paraphrasing) "how few facets can we get away with and still accurately represent a perfect circle?"  I don't recall exactly the answer but the results surprised me with how far you could go in simplifying the shape & still maintain relative accuracy.  I believe a 4 sided square (corrected geometrically for volume) in fact performed very closely to the baseline.

If you're sincerely & specifically interested in modeling an octagon as a square, I think you'll find that could actually be pretty accurate so long as you are correcting for conditioned volume / exposed area.  I'd seek out that actual paper/presentation while you're at it ;-).

~Nick

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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Leonard Sciarra via Bldg-sim
Sent: Thursday, December 15, 2016 12:05 PM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] LEED project - maximum limit allowed to simplified wall azimuth.

Julian -

The text is written to include 45 degrees.  So if they are 45 degrees, then you can make it a square, although the exception was intended for curved surfaces.

Hope this helps.

Leonard Sciarra, AIA, ASHRAE, LEED ap+
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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of via Bldg-sim
Sent: Thursday, December 15, 2016 11:17 AM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] LEED project - maximum limit allowed to simplified wall azimuth.

Hello,

Does anyone know how to interpret "no more than 45 degrees" of exception 5.b - table G3.1 (90.1-2007/2010/2013) ? :

5.  Building Envelope
All components of the building envelope in the proposed design shall be modeled as shown on architectural drawings or as built for existing building envelopes.

Exceptions:
b. Exterior surfaces whose azimuth orientation and tilt differ by no more than 45 degrees and are otherwise the same may be described as either a single surface or by using multipliers.

Because "no more than 45 degree" include 45 degree, does the exception still apply if the azimuth of two walls is exactly 45 degrees?
In other words, considering a LEED project, can a perfect octagonal building shape be modeled as a square building (as long as they have the same floor area and the 8 walls have a similar construction) ?

Thanks

Julien
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