[EnergyPlus_Support] Re: Daylighting obstructions - Does DELight account for external obstructions?

["Ralph_Evins" <ralphevins@xxxxxxxxx>]

There's an input in _DELight.in called BUILDING SHADES, however I get "N_BShades 0", even when the .idf specifies a variety of shading devices (Shading:Building, Shading:Building:Detailed, Shading:Zone:Detailed, Shading:Overhang...).

Any ideas?

Alternatively is there another way to calculate daylight factors across a zone (e.g. 10 by 10 grid of points) that does take account of external shading devices? 

Thanks,

Ralph.

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Rob Hitchcock <RJHitchcock@...> wrote:
>
> 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@... <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
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> [Non-text portions of this message have been removed]
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