[Radiance-general] BRE Vertical Sky Component Calculations

[Bleicher, Thomas]

Nick.

I've done that a evaluation of that sort of calculation
a while ago.

If you use rtrace you will get a reference value from
the horizontal plane calculation. You don't need to create
a new model for that, just select a point higher than the
scene geometry. This reference value is your 100% VSC.
You have to normalise the results of your window calculations
to that value.

You can also specify a sky with a nice diffuse illumination
(say 10000 lux, gensky option '-B 55.866') and use the
results of the following rtrace calculations directly.

For the model setup:
a) use a 0% reflectance for the geometry in your scene
   no ground glow or a black ground plane

or b) use only one bounce (-ab 1) for the rtrace
   calculation (you need that one bounce because rtrace
   creates a virtual plane at the sample point and
   calculates the light falling on that plane)
   You still have to eliminate the ground glow.

Because you have a low '-ab' you can increase '-ad'
quite a bit to suit your geometry details. 

If you want to verify your methods, you can calculate
the geometric obstruction of a simple setup (like a
straight wall) according to established methods and
compare that to your Radiance calculations.

You still have to create an input file for rtrace
that contains all the centre points of the windows
(outside wall surface). Getting those will be the
most time consuming task.

HTH,
Thomas
   

> -----Original Message-----
> From: radiance-general-bounces at radiance-online.org 
> [mailto:radiance-general-bounces at radiance-online.org] On 
> Behalf Of Nick Doylend
> Sent: 22 September 2006 12:41
> To: 'radiance-general at radiance-online.org'
> Subject: [Radiance-general] BRE Vertical Sky Component Calculations
> 
> Hello,  I've been looking at VSC calculations using Ecotect 
> but have little confidence in the results.  I wonder if I can 
> get some guidance on using Radiance for this kind of 
> calculation.  I'm thinking perhaps I can set up a CIE 
> overcast sky and turn off the effect of all reflected light.  
> Then I could compare the amount of light falling first on an 
> unobstructed horizontal plane, then on an unobstructed 
> vertical surface, and finally on the centre points of all the 
> windows on the building, taking into account the shading 
> provided by the surrounding buildings.  Can anyone advise me 
> on the best way of doing this?
> 
> Thanks for your help,
> 
> Nick Doylend
> 
> 
> 
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