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

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: [email protected]
[mailto:[email protected]] On
Behalf Of Nick Doylend
Sent: 22 September 2006 12:41
To: '[email protected]'
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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