[Radiance-general] gendaylit

[Martin Moeck]

Dear Radiance experts:
 
try this with gendaylit:
 
gendaylit 4 13 7 -a 40.3 -o 79.4 -m 75 -W 20.5 200.5 
 
This is for Pittsburgh. The weather station data are 20.5 W/m^2 diffuse horizontal and 200.5 W/m^2 for the "beam" component (towards the sun). Both irradiance data are in the visible range only. 
 
I expect 46.8 W/m^2 from the sun, measured on the horizontal plane, since the sine of the sun altitude angle multiplied by 200.5 gives 46.8
 
What I get is 21 W/m^2. Does the gendaylit -W option require W/m^2 measured over the full spectrum? The gendaylit man page says it uses data based on the visible spectrum. 
 
I asked someone who used gendaylit previously and this is what he wrote:
 
------------------------------------------------------------------------
"Martin,

> try this with gendaylit:
> 
> gendaylit 4 13 7 -a 40.3 -o 79.4 -m 75 -W 20.5 200.5

I did.  Here's what I got -

gendaylit 4 13 7 -a 40.3 -o 79.4 -m 75 -W 20.5 200.5
# gendaylit 4 13 7 -a 40.3 -o 79.4 -m 75 -W 20.5 200.5
sky clearness or sky brightness out of range 1.029410    0.620136

Hmmm...  It appears we are using different versions.
Are you using, as I am, UNIX or some PC version?

The header for my gendaylit.c is:

/*        Copyright (c) 1994    *Fraunhofer Institut for Solar Energy Systems
 *                              Oltmannstr 5, D-79100 Freiburg, Germany
 *                              *Agence de l'Environnement et de la Maitrise de
l'Energie
 *                              Centre de Valbonne, 500 route des Lucioles,
06565 Sophia Antipolis Cedex, France
 *                              *BOUYGUES
 *                              1 Avenue Eugene Freyssinet,
Saint-Quentin-Yvelines, France
*/


And for the cal file:

{ SCCSid "@(#)perezlum.cal 2.5 15/02/94 ISE" }

I haven't used gendaylit for ages, I tend to stick with the sky
blends described in the thesis chapter.  I'm still a little concerned
that Perez can give unexpected distortions.
"

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This makes things even more confusing. Any suggestions? I am using Redhat 7.2. 
 
Martin
 
Dr.-Ing Martin Moeck, Assistant Professor
Pennsylvania State University
Department of Architectural Engineering
USA - University Park, PA 16802
e-mail mm12@psu.edu
http://www.engr.psu.edu/ae