[Radiance-general] gendaylit

[Greg Ward]

Hi Ehsan,

Could this be the difference between irradiance measured over the entire spectrum (as measured by a pyranometer) and the visible-spectrum irradiance as reported by rtrace?  I believe there is a conversion factor in gendaylit that converts one to the other, but Jan Wienold or Wendelin Sprenger would know better.

-Greg

> From: "Ehsan M.Vazifeh" <em.vazifeh at gmail.com>
> Subject: [Radiance-general] gendaylit
> Date: July 30, 2014 9:36:03 AM PDT
> 
> 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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