[Radiance-general] Re: Fritted Glass
John de Valpine
[email protected]
Fri, 21 Jun 2002 15:25:29 -0700 (PST)
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
---- [email protected] wrote:
> 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
>
>
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