[Radiance-general] Current practice for LEED sky modelling?

[Galen Burrell]

In our office, we use gensky clear sky model (with sun) but explicitly define the diffuse and direct radiance component using the IESNA methodology, in lieu of the gensky defaults (which I recall Greg saying were not correct).

Zack's python script would be pretty handy for this!


Galen Burrell
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Message: 3
Date: Tue, 19 Jun 2012 11:33:09 -0600
From: "Guglielmetti, Robert" <Robert.Guglielmetti at nrel.gov>
To: Radiance general discussion <radiance-general at radiance-online.org>
Subject: Re: [Radiance-general] Current practice for LEED sky
	modelling?
Message-ID: <CC0612D0.11881%robert.guglielmetti at nrel.gov>
Content-Type: text/plain; charset="us-ascii"

On 6/19/12 11:23 AM, "Zack Rogers" <zrogers at daylightinginnovations.com<mailto:zrogers at daylightinginnovations.com>> wrote:

Hi Lars, Rob,

>From what I understand, gensky produces accurate CIE sky descriptions according to the older definitions of 3 different sky types (clear, partly cloudy, and cloudy) - but does not include definitions for the newer CIE standard that has 15 different sky types derived from 5 different parameters (A-E).  For the older CIE sky types, I am not clear on what gensky uses to predict the magnitude (zenith luminance, Lz) but from what I have seen it does not match the methodology that the IESNA lays out for predicting Lz.  With gensky alone I might get around 70,000 lux on a sunny summer day where as the IESNA guidelines would predict around 100,000lux.  This is the reason I wrote a IES_gensky.py python script, it produces the same CIE sky distribution functions (adopted by IESNA) but also uses IESNA guidelines to determine Lz based on some lookup tables.  I recall some babbling from me on this topic around when I developed this:

http://www.radiance-online.org/pipermail/radiance-general/2003-October/001074.html
http://www.radiance-online.org/pipermail/radiance-general/2003-October/001090.html


Hi Zack,

It's my understanding that gensky produces sky type 1, which is the standard overcast sky, and sky type 12 for the clear sky from the 15 in the CIE table from 2003. I'm not sure which one it uses for the intermediate sky, nor do I know if it's using the 5 parameter method or something else.

- Rob

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