[Radiance-general] Modeling reflective glazing and glazing with ceramic frit

[Rob Guglielmetti]

On Dec 27, 2006, at 9:11 AM, Arvinder Dang wrote:

> Hello Everyone,
> Its after a long time that I am posting a message on this list as I  
> haven’t been using Radiance much, so in a way I’m starting from  
> scratch and seeking help for some hopefully simple questions.

Hi Arvinder,

Welcome back to the Radiance world!

>
> I have read through the archives and have understood the following  
> from it. Please correct me if I have misinterpreted any information
>
> Convert glazing data from Optics 5 to Radiance.  However since this  
> does not account for transmittance/reflectance dependence of  
> incident angle use the BRTD definition and glazing.cal file to  
> define the angular dependence of transmittance/reflectance values.  
> (Since I have been using Radiance from within Ecotect, I really  
> don’t know how I should be doing this).

> Radiance material file from optics looks like this
>
>
> # FileName= HMHPR18.SWT
> # Product Name= Heat Mirror™ HPR 18 Suspended Film
> # NFRC ID= 1507
> # Manufacturer Name= Southwall Technologies, Inc.
> # Glazing Type= Coated
> # Coated Side= Front
> # Transmittance= 0.189
> # Front Reflectance= 0.649
> # Back Reflectance= 0.116
> # Thickness(mm)= 0.076
> # Appearance= Reflective
> #
>
>
> void  glass       HMHPR18_glass
> 0
> 0
> 3     0.143     0.215     0.371
>
> void  BRTDfunc    HMHPR18_front
> 10
>       0.745     0.636     0.400
>       0.131     0.197     0.341
>       0 0 0
>       .
> 0
> 9 0 0 0 0 0 0 0 0 0
>
> void  BRTDfunc    HMHPR18_back
> 10
>       0.163     0.100     0.092
>       0.131     0.197     0.341
>       0 0 0
>       .
> 0
> 9 0 0 0 0 0 0 0 0 0
>
> Can someone walk me step by step as to how I can convert this and  
> define my final material file which I should be using. I have to  
> try a couple of options for glass types so will have to do this  
> time and again, so I am interested in the process and not the final  
> outcome only. I know it should be fairly simple but somehow not  
> having worked in linux doesn’t make it seem simple.

The output from Optics5 is essentially "two in one", both a simple  
glass description of the material and the more accurate BRTDfunc  
description.  Honestly, I don't know which one of the BRTDfuncs would  
be the correct one to use in your lightshelf application.  You could  
try the glass description instead...

If all of these descriptions are in a single materials file (let's  
call it materials.rad) you can then call them and apply them to your  
lightshelf polygons.  You just have to make sure you define a  
material before it's applied to a piece of geometry.  When working on  
a project I typically have one file with all my materials definitions  
in it, and then I just make sure that that file gets listed first in  
any oconv command, to ensure that materials I have assigned will  
already "exist" when the actual scene files get fed to oconv.

>
> Also for modeling the ceramic frit coating I read I need to use the  
> glaze.csh script. How can I model a glass which is a sandwiched  
> panel with the ceramic coating on the inside.


The glaze script will give you a definition of a material that mimics  
the overall transmittance change resulting from the frit, but not the  
appearance of the frit.  As I recall, the script has a library of  
materials you can select from, but it's not extensive. You could also  
simulate this with a trans material; most glazing manufacturers  
publish the clear glass transmittance resulting from the application  
of various frit densities, you could use that as part of your trans  
material definition.

In both of these responses I realize I have suggested a gross  
simplification for the simulation of these materials.  But sometimes  
this is the best medicine, especially starting out.  I'm sure some  
folks on the list can offer more info on using the more fanciful  
material primitives, but my experience doesn't really go beyond trans  
just yet.

Good  luck, keep asking questions and post results as well.  And  
happy holidays, everyone!

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