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OpenStudio/Radiance insensitive to blind's slat angle

asked 2016-05-09 14:51:32 -0500

Determinant gravatar image

updated 2016-05-09 15:36:05 -0500

In OpenStudio I have varied the slat angle in the material definition for blinds from almost completely closed to nearly horizontal but the Radiance results are almost identical. Looking at the annual illumination map, the hot spots and levels look the same and if I do some overall statistics they are very very close.

I would've expected the nearly horizontal case to have light bouncing off the top surface of the blinds, then to the ceiling, then back down, but that doesn't seem to be the case.

I also would've expected the nearly closed case to not have any hot spots but the hot spots look the same as the horizontal slat angle case.

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answered 2016-05-10 12:31:19 -0500

Yes, the Radiance implementation of shading devices is simplified somewhat. Radiance will use one of four standard BSDF files to model the effect of blinds/shades/EC glazing/daylight redirection devices. As such, any changes to e.g. the blind slat configuration will not have any effect on the simulation. In the case of blinds, the "standard BSDF" is of a venetian blind with its slats set to block all direct sun.

See this UH Post and this page in the docs for more info.

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Thanks. Hoping this will change soon though or that at least we'll be able to enter our own BDSFs...also blocking all direct sun is a function of lat, long and orientation so it's hard to imagine, apart from being fully closed, that there could be a single slat angle that could do it for all lat, long and orientation.

Determinant gravatar imageDeterminant ( 2016-05-10 14:57:32 -0500 )edit

I don't expect this will change anytime soon, as there is no funding to work on this. At least from the application side. As for the slats, I should have said "most of the year, on the south, mid-latitudes". =)

rpg777 gravatar imagerpg777 ( 2016-05-10 15:14:21 -0500 )edit

Thanks for clarifying..and for orig answer. Reminder to self, don't mis-spell BSDF like I did above and search on internet.

Determinant gravatar imageDeterminant ( 2016-05-10 17:25:03 -0500 )edit

Since it's "Open"Studio, I'm hoping to track down how I can edit the code for some work-around to use my own BSDFs. So far it looks like the key file is blinds.xml (for blinds). Everything else seems either the same or is generated from blinds.xml. The problem I see though is that blinds.xml is generated anew each time. Am I on the right track?

...rob, in my digging saw what rpg stands for. This is Eric Shadd, former energy modeler at AEC San Francisco.

Determinant gravatar imageDeterminant ( 2016-05-17 16:53:35 -0500 )edit

Yep @Determinant (Eric! Hi!!), the whole Radiance model including the BSDF file system is created each time the Radiance measure is run. It actually happens when the model is translated from OpenStudio to Radiance format. You'd need to write a little script (measure) to add your own custom BSDFs. Ideally, we would add some option to the Radiance measure so you could specify alternate BSDFs, and that will be easy to do when version 2.0 of PAT is released later this year. Meanwhile you'd need to make your own version of the Radiance measure.

rpg777 gravatar imagerpg777 ( 2016-05-18 09:54:18 -0500 )edit

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Asked: 2016-05-09 14:51:32 -0500

Seen: 130 times

Last updated: May 10 '16