[Radiance-general] Re: Determining Specularity Values - Spandrel Panels: Marble vs Fritted Glass

[Greg Ward]

Hello Nastassja,

> Marble – Originally white, but panels have become grey with dirt  
> over time, not polished, dull finish
>
> Type:                Plastic
>
> Colour:             (0.91, 0.91, 0.83)
>
> Specularity:       ?????? (I think this may be low because it is  
> not polished marble)
>
> Roughness:      0.05 (???)
>

I concur with the others that this reflectance is too high for any  
surface that has been exposed to the exterior for a period of time.   
My experience is that dirt & grime reduce reflectance values by a  
significant amount.  I would suggest a reflectance of 50-60% for  
white marble.  The specularity is probably around 0.01 and a  
roughness of 0.08 for an unpolished surface is a reasonable guess.
> Glass Frit – Composed of: Clear glass, 60% coverage white frit,  
> clear glass, 100% coverage white frit. From Window 6, I estimate  
> the solar reflectance of the system to be around 25-35%.
>
>  Typle:               Metal ??? (Does the frit have specular and  
> diffuse reflection of light?)
>
> Colour:             (1.0,1.0, 1.0)
>
> Specularity:       ????? (Clean polished glass)
>
> Roughness:      0.00
>
I would start using the "glaze" script, entering the above  
parameters.  This should give you good results.  Attached is what I  
used for your 60% fritted glass and the output produced.

Best,
-Greg

% glaze
Enter the number of panes in the system: 1

Window normal faces interior

   | |
   | |
   | |
   | |-->
   | |
   | |
   | |
  s1 s2

Supported surface types are:
    1 - clear glass
    2 - VE1-2M low-E coating
    3 - PVB laminated
    4 - V-175 white frit
    5 - V-933 warm gray frit

What is the type of s1? 1
What is the type of s2? 4
Enter fraction coverage for s2 (0-1): .6

############################################
# Glazing produced by Radiance glaze script
# $Revision: 2.7 $
# Material surface normal points to interior
# Number of panes in system: 1
# Exterior surface s1 type: clear glass
# Interior surface s2 type: V-175 white frit
# s2 coating coverage: .6
# Exterior normal hemispherical reflectance: 0.228534
# Interior normal hemispherical reflectance: 0.384534
# Normal hemispherical transmittance: 0.478928
#
void BRTDfunc glaze1_unnamed
10
         sr_frit_r sr_frit_g sr_frit_b
         st_frit_r st_frit_g st_frit_b
         0 0 0
         glaze1.cal
0
11
0.354
0.354
0.354
0.1536
0.1518
0.1506
0.126
0.126
0.126
         -1      .6

---------
P.S.  Apologies if these answers are redundant with others, as I am  
composing this on a plane w/o internet access.