[Radiance-general] Re: Trans Oddities Part Deux

[Zack Rogers]

Hi Rob,

My two cents on the subject.

Have you tried raising -ab?  I typically use -ab 5 when doing rtrace 
calcs - and this just comes from case studies I've done and read, it 
seems to get the calc within a 1% for most cases.

Also, the -av setting, for such a low light level calc seems like it 
could have the impact you are seeing, as has been discussed.  Have you 
run this with a -av 0 0 0 setting yet?

Are the interior illuminances you are reporting an average using a grid 
of points or a single point?

Finally, the average workplane illuminance will only be linear (ie. half 
the Tvis = half the workplane illuminance) to the combined Transmittance 
of the skylight/shade system if the interior reflectance of the system 
is constant.  I only briefly looked at how you defined the shades and 
noticed the reflectance is slightly different (although it doesn't seem 
different enough to give an 100% error).  I also noticed the shades are 
mostly specularly transmissive.  If the skylight is not completely 
diffuse transmittance, then you are getting some sort of sun patch on 
your workplane.  If you are doing an average calc using a grid of 
points, a sun patch could cause the average workplane to seem off, 
although it may be off the same for each of your runs.

Also, perhaps a rendering of the room will reveal any oddities that are 
occuring.  Whenever I get unintuitive results, a rendering will often 
show me whats happening.

Hope this helps.
Zack

-- 
Zack Rogers
Staff Engineer
Architectural Energy Corporation
2540 Frontier Avenue, Suite 201
Boulder, CO 80301 USA

tel (303)444-4149 ext.235
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