Re: [EnergyPlus_Support] Daylighting obstructions

[Rob Hitchcock <RJHitchcock@xxxxxxx>]

Regarding daylight (visible light) interreflections within a zone, the 
Detailed method uses a split-flux method, whereas DElight uses a 
modified radiosity method.  The split-flux method divides transmitted 
daylight into "downward-going" and "upward-going" fluxes and evenly 
distributes a portion of these fluxes as reflected light based on an 
area-weighted average surface reflectance for the zone. See the 
Engineering Documentation page 116 (PDF page 148) for more detail.  This 
method does not accurately account for interior obstructions in the 
interreflection calculation.  The radiosity method more accurately 
accounts for interreflection between interior surfaces by discretizing 
each surface into nodal patch areas and accounting for the reflective 
exchange of visible light between the patch areas.

Regarding direct daylight distribution (i.e., exterior light directly 
reaching reference points and interior surfaces through apertures), the 
Detailed method does account for the obstruction, by the interior face 
of zone surfaces, of direct daylight on reference points (but not on 
interior surfaces), while the DElight method currently does not, 
assuming zones are convex, as Mike describes below for solar gains.

Rob Hitchcock
==========
Michael J. Witte wrote:

> Well, I see that the daylighting section of the Input Output Reference is
> inconsistent on these subjects. (On the list to fix now.)
>
> Referring to p. 290 of the I/O Reference (pdf p. 327), internal 
> obstructions
> accounted for in daylighting. This is not mentioned in the list of 
> differences
> for DElight, so I assume that DElight also accounts for internal 
> obstructions.
> I cannot say that I have verified this for either of the daylighting 
> models.
>
> For solar gains, interior obstructions are not accounted for. The 
> FullInterior
> solar distribution options require a "convex" zone. From p. 12 (pdf p. 
> 49) "A
> formal definition of convex is that any straight line passing through
> the zone intercepts at most two surfaces.)"
>
> Mike
>
> On 8 Sep 2006 at 11:04, Andy Tindale wrote:
>
> > Mike,
> >
> > Is it possible to use EnergyPlus to model large internal obstructions to
> > solar and daylighting penetration within a zone using surfaces or other
> > objects?.
> >
> > Clearly this would require the full exterior and interior solar 
> distribution
> > option, but I just wondered whether the presence of any internal 
> obstruction
> > surfaces would be accounted for in the calculation of daylight 
> factors and
> > solar distribution about the space. Are Daylighting:Detailed and
> > Daylighting:DELight the same in this respect.
> >
> > Thanks,
> >
> > Andy
> >
> > Andy Tindale
> > DesignBuilder Software Limited
> > Email: andy@xxxxxxxxxxxxxxxxxxx <mailto:andy%40designbuilder.co.uk>
> > website: http://www.designbuilder.co.uk <http://www.designbuilder.co.uk>
> >
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> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com>
>
>  




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