[Radiance-general] Re: Fritted Glass
Zack Rogers
[email protected]
Fri, 21 Jun 2002 11:58:59 -0600
Hello,
I just recently tackled fritted glass for a project with a huge central
atrium covered by a huge glass spire roof. I used the perforate function to
combine the glass material and the frit material as follows (the perforate
function creates a pattern of dots or holes, a different function would be
needed for fritted lines);
1).....Definition of glass material from optics 5;
void glass SGP_VE1-2M_glass
0
0
3 0.661 0.759 0.670
void BRTDfunc SGP_VE1-2M_front
10
0.104 0.105 0.107
0.607 0.696 0.615
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
void BRTDfunc SGP_VE1-2M_back
10
0.095 0.110 0.102
0.607 0.696 0.615
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
notice this definition can be simplified to an identical definition as
follows (as seen in the glazing.cal file);
void BRTDfunc CLEAR_6_2_glass
10 rrho grho brho
rtau gtau btau
0 0 0
glazing.cal
0
18 0 0 0
0 0 0
0 0 0
0.104 0.105 0.107
0.095 0.110 0.102
0.607 0.696 0.615
2)....Definition of Frit material;
void trans blackfrit
0
0
7 0.091 0.091 0.091 0.010 0.150 0.556 0.000
3).....Using mixfunc and perforate.cal to combine glass and frit materials;
void mixfunc frit-b40
6 SGP_VE1-2M_glass blackfrit z_hole perforate.cal -s .5
0
1 .357
or in general
void mixfunc name
6 foreground_material background_material (z_hole,x_hole or y_hole)
perforate.cal -s 1
0
1 (radius-to-spacing fraction)
where;
x,y,z_hole signifies the direction of the dots or holes
the spacing of the holes is determined by the scale -s command (one-to-one
relationship. ie. -s 1 = 1 unit spacing)
the radius/spacing fraction tells how large the radius is compared to the
spacing. (ie. with a value of .5 the dots will touch, a value of 1 is
completely dots, a value of 0 is no dots)
Hope this helps!
Zack
> Hello:
>
> I am interested in people's comments on how best to simulate frit
> glazing systems from a performance and appearance standpoint. We are
> interested in comparing the appearance based on available performance
> data of a variety of fritted glazing systems on the exterior of a
> building system under daylight conditions. The fundamental challenge it
> seems to me is how to use the data that is readily available (from
> software such as LBL's Optics5 as well as from manufacturers themselves)
> to make an appropriate material in Radiance and whether the readily
> available data is in fact sufficient to describe the material behavior.
>
> All the frit systems that we are looking at use the same basic
> insulating glass with the following makeup:
>
> * (exterior) 6mm clear glass with low-e coating on the second surface
> * (airspace) 13.2mm
> * (interior) 6mm clear glass
>
> A Radiance material description (brtdfunc) for this makeup can be
> generated by the LBL Optics5 program. Note that Optics5 outputs material
> descriptions for the glass primitive as well as interior and exterior
> descriptions based on the BRTDfunc. In this case I believe that the
> "front" version of the BRTDfunc represents the exterior and is the
> appropriate description to use for this study.
>
> void glass ve1-2m_glass
> 0
> 0
> 3 0.712 0.791 0.719
>
> void BRTDfunc ve1-2m_front
> 10
> 0.111 0.114 0.116
> 0.653 0.726 0.659
> 0 0 0
> .
> 0
> 9 0 0 0 0 0 0 0 0 0
>
> void BRTDfunc ve1-2m_back
> 10
> 0.112 0.125 0.122
> 0.653 0.726 0.659
> 0 0 0
> .
> 0
> 9 0 0 0 0 0 0 0 0 0
>
> The information that we do know is as follows:
>
> * measured photopic transmittance, and exterior and interior
> reflectance of base insulating glass system (70%, 11% and 12%)
> * radiance material description of base insulating glass system
> * measured photopic transmittance, and exterior and interior
> reflectance of selected composite frit glass systems (ie the
> composition of the frit silkscreen [white] onto the 2nd or 3rd
> surface of the base insulating glass system, for example 45%,
> 22%, and 24% based on a 50% frit on the 2nd surface) , note that
> as far as I can tell it is not possible to build up such as system
> in a program like Optics5 (unless additional baseline measured
> data can be obtained from the manufacturer)
>
> Is it sufficient to figure out the percentage variations for the
> transmittance and reflectance values between the original glass and the
> composite frit glass and then modify the brtdfunc material description
> accordingly? I know that this will not completely account for the change
> in color of the glass due to the white silkscreen on the 2nd or 3rd
> surface. But is this a reasonable approximation to start with.
>
> Another thing to consider is the 'modeling' of the actual frit pattern
> on the glass. My thinking is that this is only important for cases where
> the glass is very close to the viewer. Typically a lot of the frit
> patterns (such as dot and lines) tend to disappear the the farther away
> from the building you are. Now in the cases where the view is close to
> the glass, what is a good way to build a composite material in Radiance
> (a mixfunc is probably a good starting point)? We know the data for the
> base insulating glass but what is a good way to figure out the
> reflectance of the frit silkscreen as seen through the glass?
>
> I will look forward to your suggestions and comments.
>
> Regards,
>
> -Jack de Valpine
--
Celebrating 20 Years of Improving Building Energy Performance
Zack Rogers
Daylighting Designer/Engineer
Architectural Energy Corporation
2540 Frontier Avenue, Suite 201
Boulder, CO 80301 USA
tel (303)444-4149 ext.235
fax (303)444-4304
www.archenergy.com