Hi Christoph,
I think that there are a lot of things that need to be considered here. Based on some work that Greg has consulted with us on, the basic radiance material definitions output from Optics 5 are perhaps too simplistic to fully account for a variety of glazing related behaviors. Nevertheless let me make a couple of points that may be obvious to many:
1. There are many types of glazing that will have front and back side
reflectances that are different and the "glass" material type is
probably not suitable for these materials.
2. If you want, it is possible to combine the front and back side
definitions to one material definition and thus surface geometry
(one polygon) with uniform normal orientation into our out of the
space as follows
void BRTDfunc TestSystem_front_and_back
10
if(Rdot, 0.230, 0.289) if(Rdot, 0.263, 0.336) if(Rdot,
0.326, 0.371)
0.585 0.594 0.521
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
The "if(Rdot, ReflFront, ReflBack)" will apply the relevant
reflectance depend upon which side of the polygon is being
evaluated. This may be suitable depending on the needs (and
information available) at hand. However this material does not
suitably account for angular dependencies that may impact
reflectance and transmittance.
Note also that if you were to use two pieces of geometry, then you
would need to be very careful of what you think you are applying
material wise. For example if you developed an insulating glass in
Optics 5 made up of 2 glass layers and export this then this needs
to be applied to "one" polygon not "two."
There is a shell script called "glaze" that is in the current release of Radiance (probably need to get the latest HEAD release for some updates). This script works by enabling the user to specify the makeup of the glazing (currently allowing for single and double pane glazing as well as frit coverage). The makeup is based on a small database that includes front and back reflectances as well as transmittances for a few glass materials. Some of these have been taken directly from the Radiance output provided by Optics 5. We have also added a feature recently that allows a separate file to be specified with additional glazing types (eg build your own). The material definitions (BRTDfunc) that the script outputs have a more robust model for single and double pane glazing systems. Probably, the best thing to do is try it out to see how it works.
One last note/thought. I think that as far as things go, Optics 5, is an excellent resource. The issue is really how to effectively use the data in a useful Radiance material definition.
Regards,
-Jack de Valpine
Reinhart, Christoph wrote:
···
Dear colleagues,
I know, I know. The topic of modeling glazings in Radiance using Optics 5 data has been extensively discussed in January 2004. I just reread the emails with great interest in the archives. BUT I am still undecided whether to go with Optics 5 is worth the effort.
in January, everybody agreed that creating a specific glazing in Optics 5 creates an output as follows:
#
# header info
void glass TestSystem_glass
0
3 0.638 0.647 0.568
void BRTDfunc TestSystem_front
10
0.230 0.263 0.326
0.585 0.594 0.521
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
void BRTDfunc TestSystem_back
10
0.289 0.336 0.371
0.585 0.594 0.521
0 0 0
.
0
9 0 0 0 0 0 0 0 0 0
Philip mentioned that to use this material description, one would need "two glass polygons for each window, one for the front and one for the back". I assume this means:
TestSystem_front polygon FrontOfWindow
0 0
12 0 0 0
1 0 0
1 1 0
0 1 0
TestSystem_back polygon BackOfWindow
0 0
12 0 0 -0.01
0 1 -0.01
1 1 -0.01
1 0 -0.01
Is this correct? How does the glazing know its transmittance, i.e. how does TestSystem_glass come into play? Also, does anybody have any references or experience how much more accurate a simulation gets if one uses the full optics 5 file instead of a stripped down version such as:
void glass TestSystem_glass
0
3 0.638 0.647 0.568
Any thoughts are elcome,
Christoph
Christoph Reinhart, Ph.D. tel: (613) 993-9703
Research Officer fax: (613) 954-3733
Institute for Research in Construction e-mail: [email protected]
National Research Council Canada 1200 Montreal Road M-24, Ottawa
Ontario K1A 0R6 Canada
Daylighting Analysis Software:
The Lightswitch Wizard (initial design) www.buildwiz.com <http://www.buildwiz.com/lightswitch/index.cfm>
DAYSIM (expert software) www.daysim.com <outbind://26/www.daysim.com>
IEA Task 31 http://www.iea-shc.org/task31/
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