TMY weather data as input for Gensky

Dear group,

I would like to use the direct solar and diffuse irradiance data from TMY weather files for setting the direct and diffuse values in Radiance's Gensky program. Gensky expects values for the visible component only, however I'm assuming the TMY data is for the full spectrum of light and, as such, must have an appropriate luminous efficacy factor applied to it to. Is this correct?

Also, I gather that the Gendaylit program will take the weather data as input, however I've been unable to find an active link to the program for downloading. Does anyone have a link for this? Thanks in advance for any help.

Chris Humann

Here is the link you need:
http://radsite.lbl.gov/radiance/pub/generators/gendaylit.tar.Z

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De : [email protected] [mailto:[email protected]] De la part de Christian Humann
Envoyé : mardi, 17. juillet 2007 01:43
À : Radiance general discussion
Objet : Re: [Radiance-general] TMY weather data as input for Gensky

Dear group,

I would like to use the direct solar and diffuse irradiance data from
TMY weather files for setting the direct and diffuse values in
Radiance's Gensky program. Gensky expects values for the visible
component only, however I'm assuming the TMY data is for the full
spectrum of light and, as such, must have an appropriate luminous
efficacy factor applied to it to. Is this correct?

Also, I gather that the Gendaylit program will take the weather data as
input, however I've been unable to find an active link to the program
for downloading. Does anyone have a link for this? Thanks in advance
for any help.

Chris Humann

Chris,

Be wary that gendaylit can produce skies with massive distortions (e.g. huge -ve luminance cusps at low altitude) for certain combinations of direct, diffuse and solar altitude. The absolute values for these tend to be uninteresting for daylight provision (i.e. on the low side), but they could foul-up an automated procedure and/or bias output if they are not picked up. The distortion occurred in routine application of UK climate datasets, and I believe it has been noted with use of other climate files. Note that, when it occurs, the normalisation to diffuse horizontal is still correct -- so you can't test for it by comparing predicted diffuse horizontal with the corresponding value from the climate file. However, predictions for vertical illuminances (or light through a window) could be way out. The only safe way to test is to send out a hemisphere of rays to the sky and check for any returned -ve luminances (replace these instances with CIE overcast).

-John

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-----------------------------------------------
Dr. John Mardaljevic
Senior Research Fellow
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972
+44 (0) 116 257 7981 (fax)

[email protected]
http://www.iesd.dmu.ac.uk/~jm