Re: [EnergyPlus_Support] Illuminance values - illuminance map

[Rob Hitchcock <RJHitchcock@xxxxxxx>]

One other factor contributing to the higher than expected values you are 
seeing "at the back of the room" might be the split-flux method used to 
calculate the daylight contribution to interreflected light at reference 
points.  This method "splits" the incoming daylight into "upward" and 
"downward" proportions and then evenly distributes the interreflected 
light based on area weighted average surface reflectances in these 
portions of the space.  The result is that the interreflected 
contribution is the same at all reference points, regardless of location 
in the space.  If this component is large relative to the direct 
contribution, as with highly reflective surfaces (white walls and 
ceilings) and no direct sunlight, this can skew the results.

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

> Check the coordinates for the illuminance map, noting that all 
> daylighting
> coordinates are relative to the zone origin (even if WorldCoordinates is
> specified for geometry.)
>
> EnergyPlus can model external reflectances, but this feature is off by 
> default.
> See BUILDING "Solar Distribution", and Shading Surface Reflectance.
>
> Mike
>
> On 1 Dec 2006 at 17:14, greici_ramos wrote:
>
> >
> > Dear all,
> >
> > I'm trying to work with the illuminance map, on a model with white
> > walls and ceiling. But the values are too high, even when there isn't
> > direct sunlight. For example, on the end of the day, at the back of
> > the room, which has 5m, there's values higher than 800lx.
> > - Weather file used: florianopolis.epw
> >
> > What could be the problem?
> >
> > And another doubt: Does the program consider external reflectances?
> > For example, the reflected light at a near building?
> >
> > Thanks,
> >
> > Greici Ramos
> >
> >
> >
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov <http://www.energyplus.gov>
> >
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/ 
> <http://groups.yahoo.com/group/EnergyPlus_Support/>
> >
> > Attachments are not allowed -- please post any files to the 
> appropriate folder
> > in the Files area of the Support Web Site.
> >
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.idf and 
> press the
> > "search" button.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com>
>
>  


-- 

Robert J. Hitchcock, Ph.D.
Lawrence Berkeley National Laboratory
1 Cyclotron Road, Mailstop 90-3111
Berkeley, CA  94720

RJHitchcock@xxxxxxx
530.295.9433 (telecommute office)



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