Fritted Glass

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

Zack:

Thanks for the follow-up.I understand your glazing
definitions. I also know a variety of ways to
generate a pattern whether dots or lines, this gets at
the appearance of the frit when viewed close up.

Based on the data that I have seen available from
manufacturers of glazing sytems, the measured
performance data are for the composite glazing system
(with the frit applied). What are your assumptions
about the fritting material itself? How do you go
about determining the frit definition as a trans? Can
you walk through your process in greater detail for
the trans material?

Best Regards,

-Jack de Valpine

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

_______________________________________________
Radiance-general mailing list
[email protected]

http://www.radiance-online.org/mailman/listinfo/radiance-general

···

---- [email protected] wrote:

John de Valpine wrote:

Based on the data that I have seen available from
manufacturers of glazing sytems, the measured
performance data are for the composite glazing system
(with the frit applied). What are your assumptions
about the fritting material itself? How do you go
about determining the frit definition as a trans? Can
you walk through your process in greater detail for
the trans material?

...

> 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

...

The trans model can be fitted to BRTF data of the material (rarely
available from manufacturers, but quite easily measured:
http://www.ise.fhg.de/radiance/gonio-photometer\), resulting in a
validated trans model with known error bounds. If trans is not a
suitable fit, use BRTDfunc with you own model: Functions which
empirically model the underlying physics of the material (e.g. extruded)
and steered with few variables (2-6 approx.) fit best (german
description found at http://www.pab-opto.de/apian/phd/phd.html\).

-Peter

···

--
pab-opto, Freiburg, Germany, www.pab-opto.de