[Radiance-general] Annual simulations + BSDF

[Andrew McNeil]

Hi Greg,

Thanks for your reply.  Unfortunately I¹m not going to Boston.  Now I have
yet another reason to wish I was going.

I¹m glad you¹ve been able to further develop the 3-phase method.  I see
increasing demand for this type of analysis for complex façade shading
systems.  This is the fourth time I¹ve started down this route ­ the other
three times stopped abruptly for various reasons.  Twice before with
panelite products and once with an engineered scattering window film.  The
email I sent yesterday was a  partially complete left in my drafts folder
from two months ago - the last time this I was looking into this approach.

I don¹t have a hard deadline yet.  The goal for now is to develop a working
model and then focus on accuracy later.  Ideally I¹d have something that
works in the next 2 weeks.

Hopefully Panelite will have measured BTDF data in a few months that we slot
into the analysis.  If measured BTDF data doesn't become available then
we¹ll focus on improving the accuracy of the simulated BTDF.

So I guess my first step is approximating a BTDF with Radiance.  I was
thinking I could a uniform sky above the panelite model as input and a
hemisphere of points below as sensors.  With rtcontrib I could determine the
light output in a direction for each input direction.  The input directions
could be tregenza sky divisions (?).  The output could be phi/lambda
directions (?).  I imagine the key to a decent BTDF is lots of samples for
each output direction.  Maybe I create a grid of 1000(00?) points in a plane
just below the panelite and use a script to create a hemisphere of sensor
points centered at each grid point.

I know very little about BTDF¹s and even less about creating them so I could
use any tips, tricks, guidance, watch its, how are you going to account
for?s and examples that anyone is willing to offer.

Thanks,
Andy




On 10/15/09 1:37 PM, "Greg Ward" <gregoryjward at gmail.com> wrote:

> 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,
>>>  
>>>  I¹m 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.
>>>  
>>>  I¹m 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_tal
>>> k.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 don¹t have BSDF data from panelite, they are looking into
>>> having a sample measured but that won¹t 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 isn¹t 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 haven¹t discovered trolling through archives?
>>>  
>>>  Thanks,
>>>  Andy
>>> 
>>> 
>>> _______________________________________________
>>> Radiance-general mailing list
>>> Radiance-general at radiance-online.org
>>> http://www.radiance-online.org/mailman/listinfo/radiance-general

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