[Radiance-general] Annual simulations + BSDF

[Greg Ward]

Hi Andrew,

With funding from Southern California Edison through the Heschong- 
Mahone Group and separate funding from LBNL, I've been working on the  
3-phase method described.  We have a few tools in the HEAD version of  
Radiance now, which I'll be talking about next week at the Radiance  
workshop.  Unfortunately, I haven't prepared any presentation  
materials yet, but if you make it to Boston, I will have something by  
then and we can have a nice conversation.

The lack of BTDF data is a serious issue, and could be addressed with  
appropriate modeling.  I don't know how well rtcontrib would work for  
this, as I've never tried it, but it's an interesting suggestion.  The  
folks in the Windows group at LBNL have been using TracePro to  
generate their BTDFs when they aren't taking measurements.

It's an ambitious project you have, and not something you're going to  
sort out in an afternoon.  What's your deadline?

Cheers,
-Greg

> From: Andrew McNeil <andrew.mcneil at arup.com>
> Date: October 15, 2009 12:17:02 PM PDT
>
> Hi Everyone,
>
> I’m trying to figure out how to incorporate clearshade from panelite  
> ( http://www.e-panelite.com/downloads/Panelite_IGU_Oct08.pdf ) into  
> an annual daylight simulation.
>
> I’m considering the three-phase method Greg described on slide 11 of  
> in his workshop #6 talk:
> http://www.radiance-online.org/radiance-workshop6/GregWard/WardUsingBTDF_talk.pdf
>
> Which in theory seems pretty straight forward:
> 1 – determine daylight coefficients incident on the glazing
> 2 – use a BSDF to define the relationship between incident light  
> directions and exiting light distribution for the glazing.
> 3 – determine the relationship between exiting light directions and  
> illuminance in the space.
> 4 – multiply results by many other results to produce an annual  
> illuminance profile.
>
> However I face a couple of challenges for which I seek advice:
>
> Challenge 1 – I don’t have BSDF data from panelite, they are looking  
> into having a sample measured but that won’t help me right now.  I  
> was thinking that I could build a radiance model of panelite and use  
> rtconrib to generate a BSDF of sorts.  Is this a terrible idea?
>
> Challenge 2 – Writing a rtcontrib expression to separate  
> contributions according to exiting direction from the portal.  Can I  
> use directions from treganza.cal?  Is there some reason that this  
> isn’t a good idea?  Klems directions has been mentioned.  I have no  
> knowledge of klems directions.  Is that a better alternative?
>
> And I guess the overall questions:  Are there more challenges I have  
> yet to discover?  Is anyone who has done this willing to share  
> experiences?  Would I be better off creating a model with thousands  
> of cylinders between glass panes and using rtcontrib + brute force?   
> Is there an even better method that I haven’t discovered trolling  
> through archives?
>
> Thanks,
> Andy
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