[Radiance-general] gendaylit

[Ehsan M.Vazifeh]

Dear Jan,

Thanks again for this useful information. Actually, at the moment, my work
is comparison of different sky models with measurements from sky scanner.
And as I am working with the radiance and irradiance values there should be
no problem with using -O 1 option.

Bests, Ehsan


On Thu, Jul 31, 2014 at 10:34 AM, Jan Wienold <jan.wienold at epfl.ch> wrote:

>  Dear Ehsan,
>
> just one more comment - if you use the -O 1 option, the simulation is
> performed in the solar spectrum, so you can't calculate the visible range
> with it (because you don't use the in-built luminance efficacy model). For
> solar spetrum calculations, you also need reflectance/transmission values
> for the solar range. For spectral sensitive materials/coatings, the
> difference can be huge. (e.g. for glazing).
> So for daylight simulations, you should use the default option of
> gendaylit, then the luminance efficacy is calculated for the sky/sun
> condition according to the Perez efficacy model.
>
> Cheers,
>
> Jan
>
>
> Am 7/31/14, 9:31 AM, schrieb Ehsan Vazifeh:
>
> Dear Jan and Greg,
>
>  Thank you all. using -O option solved the problem. I didn't think about
> the spectrum other than visible.
>
>  Cheers, Ehsan
>
>  On 30 Jul 2014, at 18:49, Jan Wienold <jan.wienold at epfl.ch> wrote:
>
>  if you want to have solar raditaion output in W/m2, then you have to use
> the -O 1 option for gendaylit (see manpage).
> in your case, you get then 246 W/m2 calculated...
>
> cheers,
> Jan
>
> Am 7/30/14, 6:36 PM, schrieb Ehsan M.Vazifeh:
>
>  Dear All,
>
>  I am using Perez sky model (gendaylit) in Radiance. When I calculate the
> horizontal irradiance and compare it with global irradiance sensor I get
> systematic error (rtrace gives around 70% lower values). I checked
> everything in between so far nothing was wrong in the code, Here is one
> sample:
>
>  gendaylit -ang 22.11 -64.30 -W 370.67 108.20 > genday_03_22_07_20.rad
>
> then I add the sky description in the rad file:
>
> skyfunc glow skyglow
> 0
> 0
> 4 1 1 1 0
> skyglow source sky
> 0
> 0
> 4 0 0 1 180
>
> void glow groundglow
> 0
> 0
> 4 1 1 1 0
> groundglow source ground
> 0
> 0
> 4 0 0 -1 180
>
> then I create an octree file:
>
> oconv genday_03_22_07_20.rad > genday_03_22_07_20.oct
>
> after that using rtrace I calculated the horizontal irradiance which is:
> 150.718 w/m^2
>
> echo '0 0 0 0 0 1' | rtrace -w -ab 7 -ad 4096 -ar 512 -aa 0.1 -as 64 -I -h
> genday_03_22_07_20.oct | rcalc -e '$1=$1*0.265+$2*0.67+$3*0.065'
>
> 150.718
>
> but the measured global horizontal irradiance
> (Pyranometer)
> is 252.2 w/m^
> 2
>
>   I calculated this output for the whole year but still the Perez is
> significantly underestimating the horizontal irradiance. I should add that
> I used gensky to generate the same output and results showed gensky
> horizontal irradiance fit well with Pyranometer irradiance. Does anyone
> have any idea what is wrong here?
>
>   Thank you all, Ehsan
>
>
>
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