[bldg-sim] App G 2004 question (self-shading)

David S Eldridge DSE at grummanbutkus.com
Mon Jan 23 14:21:18 PST 2006


I'll throw out one take on this subject.  Disclaimer, I'm not on any
90.1 related committee and cannot give you an interpretation, official
or unofficial.  (Nor did I stay at a Holiday Inn Express (tm) last
night!)

Your modeling program may be able to turn self-shading on and off.  You
would still use your actual geometry, and all exterior surfaces that
would otherwise be in the sunlight would be subject to solar radiation
even if in reality they were blocked by another wing of your building.

Two ways to look at it:

1)  This item can give you a benefit for having a proposed building that
does shade itself.  If you can't turn self-shading off in your baseline,
and you can't rearrange the geometry so that it is thermally equivalent
but without the self-shading, then you won't fully realize your
potential savings.  I don't think your model would be "rejected" if it
turns out that you can't meet this requirement.  The intention seems to
be to help you find savings.

2)  Since you are now modeling the baseline in four orientations, it
won't penalize you when the baseline shades itself but your proposed
building doesn't.  Again, depending on your building you might be
penalizing yourself slightly, probably your model will be accepted even
if you can't implement.

You'd have to contact your AHJ I guess to get a variance on that
requirement, and/or someone on the ASHRAE committee or your USGBC
contact.  Or use different software.

My take on this topic assumes that there is more benefit for being
shaded at your location, maybe in some places it should be the opposite.

David





> -----Original Message-----
> From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf 
> Of Rohini Brahme
> Sent: Monday, January 23, 2006 3:13 PM
> To: bldg-sim at gard.com
> Subject: [bldg-sim] App G 2004 question
> 
> I have a question about the Appendix G in 90.1, 2004.
> In Table G3.1 the baseline building is to be simulated as follows: 
> " Orientation. The baseline building performance shall be 
> generated by simulating the building with its actual 
> orientation and again after rotating the entire building 90, 
> 180, 270 degrees, then averaging the results. The building 
> shall be modeled so that it does not shade itself." 
> What does --- the building shall be modeled so that it does 
> not shade itself ---- mean? 
> Does it mean that if there is, for example, an L shaped 
> building (which self shades), it has to be modeled as square? 
> rectangle?
> Any thoughts on this appreciated.

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