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Re: [EnergyPlus_Support] Re: weather file radiation




NREL is currently updating their solar model as part of creating
a new 30-year (1971-2000) data set for the US of 230+ locations.
We (EnergyPlus development team) are monitoring that work.  If
it appears to solve many of the problems we've run into with solar,
we may add solar calculation to the weather converter.  Right now
none of the solar calculation algorithms do a good job once you're
below the tropic lines....

If you would like a copy of the IWEC report--which describes the
evaluation of various solar models against measured solar, let
me know.  It's too large to send through the Yahoo_group.

Dru



                                                                                                          
                      "Hector Huerta                                                                      
                      <edhugar@xxxxxxxx        To:       EnergyPlus_Support@xxxxxxxxxxxxxxx               
                      m>" <edhugar             cc:                                                        
                                               Subject:  [EnergyPlus_Support] Re: weather file radiation  
                      02/06/2003 12:50                                                                    
                      PM                                                                                  
                      Please respond to                                                                   
                      EnergyPlus_Suppor                                                                   
                      t                                                                                   
                                                                                                          
                                                                                                          




hello Ned

yeah you're right, the excel program doesn't account for cloud cover
corrections, something I'll have to figure out...seems like I could
get sky clearness factors (1-10, 10 full covered), do you think I
should aply those directly as a percentage of the global radiation(
ed. 8/10, 9/10). or should that affect only either the duffuse or
direct components?...

but .. yes.. that could still be a mere approximation as you well
point out

as for the model used itself I searched and found this url
http://www.nrel.gov/docs/legosti/old/761.pdf as referenced by the
author of the excel file.

best regards

hector huerta
edhugar@xxxxxxxxx
A00603447@xxxxxxxx


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Edward Lyon"
<eglyon@s...> wrote:
> The problem with these calculations for energy modeling is that
they give you a perfect clear day solar value for any time period
you calculate.  If you had additional sky weather data for cloud
cover, you could try to apply some cloud cover corrections.
However, correcting the solar data with a cloud cover algorithm is
still not as good as measured solar data, it can be as much as 50%
off.  I know these cloud algorithms have been applied to some of the
canned weather files we use that do not have direct solar
measurements, but I have not seen the source equations yet.
>
> Ned Lyon
>
> Senior Staff Engineer
> Simpson Gumpertz & Heger Inc.
>
> 41 Seyon Street
> Building #1, Suite 500
> Waltham, MA  02453
>
> Phone:  781-907-9000
> Fax:  781-907-9009
>
>
> >>> edhugar@y... 02/06/03 11:28AM >>>


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