Hi Marija,
Although Optics5 is a great resource for glazing information. The radiance materials that get exported are perhaps too simplistic depending on how they are to be used. The three definitions that are output are 3 options to be chosen from, you do not use them all at the same time.
The glass definition (GlzSys_glass) really only represents the correct transmittance for the exported glazing system, the front and backside reflectance are equal and relatively low, ~7% (I do not remember for sure, so Greg will have to provide the authoritative answer on this one).
The two BRTDfunc definitions are really only useful for the selected condition (eg if you are inside or if you are outside). These two materials are dependent on the geometry being built with the surface normal pointing the correct way and uniformly for that class of geometry. A simpler way to combine these two materials into one definition is as follows:
void BRTDfunc GlzSys_front_and_back
10
if(Rdot, 0.134, 0.134) if(Rdot, 0.147, 0.147) if(Rdot, 0.147, 0.147)
0.740 0.803 0.779
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
In the case of your exported example, it looks like the front and backside reflectances are the same. Here is how to interpret this definition:
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
The "if" statement determines if the ray hits the front or back of the geometry, if it is positive then it takes the first value, if negative it takes the second value. You need to determine what front/back means though (eg front==exterior and back==interior).
NOTE that these BRTDfunc definitions do NOT account for angular dependencies of transmittance/reflectance of the material.
Another options is to take the transmittances and reflectances for the various surfaces (eg s1 through s4) and use them with the "glaze" script found in radiance. This creates a more sophisticated material representation for single and double pane type of glazing systems. To do this though you need to export radiance files from Optic5 not for the final assembly of the glazing system but for the individual sub layers.
Regards,
-Jack de Valpine
Marija Cvetkovic wrote:
···
Hi,
I am trying to use actual data for glazing materials, and I've found that
Optics5 has a good database. Since it has exporter to Radiance, single or
multi layer glazings can be easily converted to Radiance format.
Resulting file has a form like:
void glass GlzSys_glass
0
3 0.807 0.875 0.849
void BRTDfunc GlzSys_front
10
0.134 0.147 0.147
0.740 0.803 0.779
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
void BRTDfunc GlzSys_back
10
0.134 0.147 0.147
0.740 0.803 0.779
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
My question is how should I use these data in Radiance scene description.
I suppose that idea is to define window glass with 3 layers:
GlzSys_front GlzSys_glass GlzSys_back
Am I right?
One more question: does anyone know how this BRTD parameters are calculated from Optic5 data?
Thanks,
marija
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