[Radiance-general] glazing modelling

[Marija Cvetkovic]

Hi,
I have few questions about accurate modeling of different glazing. I've read 
all previous discussions on this list, and now I'll try to summarize my 
thoughts about this subject.
Suppose we want to simulate the behavior of some single or multiple layer 
glazing in Radiance, and the data of available glazings can be found in 
Optics5 database (actually IGDB).
These are few possible procedures how to define and use this material:

PROCEDURE1
1. convert glazing (all layers) data from Optics5 to Radiance.
2. use output glass material for glazing definition.

Problem:
*Glass reflectance is calculated implicitly, and values from Optic5 database 
don't have any effect.
This can be solved by using trans.cal functional file, and changing index of 
refraction to obtain appropriate reflectance.
*Dependence between light incident angle and transmittance/reflectance is 
implicit and it is calculated using the algorithm for common glass material.

PROCEDURE 2:
1. convert glazing (all layers) data from Optics5 to Radiance.
2. adjust BRTDfunc data, like Jack de Valpine suggested:
void BRTDfunc GlzSys_front_and_back
10
    if(Rdot, <r_front_refl>, <r_back_ref>l) if(Rdot, <g_front_refl>, 
<g_back_refl>) if(Rdot, <b_front_refl>, <b_back_refl>)
    <r_trans> <g_trans> <b_trans>
    0   0   0
    .
0
9 0 0 0 0 0 0 0 0 0
3.Use this BRTD definition for glazing.

Problem:
*No transmittance/reflectance dependence of incident angle is taken into 
account!

PROCEDURE 3:
1.convert glazing (all layers) data from Optics5 to Radiance.
2.Use BRTD definition and glazing.cal file to define angular dependence of 
transmittance/reflectance values.  Definition would look like:
mod BRTDfunc my_glazing
10     rrho grho brho
        rtau gtau btau
        0 0 0
        glazing.cal
0
18     0 0 0
        0 0 0
        0 0 0
        FRRHO FGRHO FBRHO
        BRRHO BGRHO BBRHO
        RTAU GTAU BTAU
where:
    FRRHO FGRHO FBRHO is front normal spectral reflectance
    BRRHO BGRHO BBRHO is back normal spectral reflectance
    RTAU GTAU BTAU is normal spectral transmittance

3.Use this definition for glazing material.

Problem:
*glazing.cal calculate these functions ONLY for coated and clear glass with 
the cut- off point transmittance=0.654. Below that value it is supposed that 
glass is coated, and above that it is clear.

PROCEDURE 4:
1.convert each layer of glazing  from Optics5 to Radiance.
2.Create input file for glaze.csh script (see question below)
3.Call glaze.csh script and define 1 or 2 panel glazing, and all its 
surfaces.
4.Use BRDTfunc created as output of the script, as glazing material.

Problem/question:
*Is it important what kind of glazing user defines? I know the main goal of 
this script is to define fritted glass, but is the calculation OK for user 
defined types of surface.


QUESTIONS:
1.Which of this procedures should be used in which real case? I suppose for 
single pane clear glass we could use only glass primitive. Can glazing.cal 
be used for all coated glazings, and glaze.csh for fritted ones?
2.What is the format of input file for glaze.csh script?
3.What if glazing have more than 2 layers?

Thanks,
Marija.