[Radiance-general] gendaylit

[Jan Wienold]

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 
> <mailto: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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>>
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