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Re: [EnergyPlus_Support] Re: AMY-weather files for North Europe

David,

You have to be careful about GHI vs. CC (i) because of the cloud 
enhancement effect under partly cloudy conditions and high sun, and (ii) 
because CC can be high but only due to thin (cirrus) clouds that have a 
high transmittance (i.e., the opaque cloud cover is small).
Normally, the GHI and CC data in the TMY3 files are self consistent 
since the latter is used to derive the former.

Chris


-- 
Chris A. Gueymard, PhD
Solar Consulting Services
P.O. Box 392
Colebrook, NH 03576, USA
Florida's Office:
Tel. (386) 402-8949
http://www.SolarConsultingServices.com




> I've played around a bit with using the ZH model to generate solar for 
> custom annual weather files.
>
> The approach I used was to develop "site specific" ZH model 
> coefficients from the observations listed in TMY3 files.  You can't 
> let all the coefficients vary (at least using the least-squares solver 
> I used), but developing new coefficients for 2-3 of the more 
> influential variables helped quite a bit in fitting the model to the 
> data (as might be expected, CC was most important, have to look back a 
> notes to remember the others I settled on).   Up until this thread, I 
> was not aware of the Koeppen Climate Classification coeffs, but would 
> like to look at those now to see how they might apply to my location 
> (Pacific NW).
>
> One of the biggest issues with this approach was hourly cloud cover 
> data in the TMY3 files didn't always appear to jive with the solar 
> radiation data (ex. CC = 8-10 when the GHorz was close to expected 
> clear sky value).  Haven't had enough time to investigate further, and 
> I assume there maybe a serious flaw in this approach if the TMY3 data 
> values aren't expected to jive with eachother, but in any case, this 
> was just my first pass at trying to use the model for my application.  
> Now, that custom weather files are readily available from a few 
> vendors, it has been hard for me to justify spending a lot of time on 
> it...
>
> - David



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