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[EnergyPlus_Support] Re: creating 'real' weather files - Wind/solar data

Hi,

Thank you Chris and Ed, both your answers are helpful.

Chris, when i mentioned reservations i was referring to the previous post in the other topic, when you asked Linda about how this was calculated. 

Looking at the direct irradiance, i believe, although not directly stated that it is DNI, as the definition states it is measured by a pyrheliometer, which the wisdom of the internet tells me measures at normal incidence...which would fit with the direct being larger than the global.

So, as Linda has just said i can now use E+ to calculate diffuse irradiation, im not sure i know how, but will look into it and ask again if i cant.

Ed, thank you the graphical display was useful,and helped me to understand, if only i could have a graphical display like this for all the weather stations i need!

Thank you every one, your help has been invaluable.

Paul


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Chris <chris@...> wrote:
>
> Paul,
> 
> > Thank you for your advice, i had seen the previous post, but some was not relevant as i am in the UK. However since yesterday i have found more solar data, which reports global and direct radiation, but not diffuse, am i right in thinking that E+ will work with these two variables....but you have reservations about the method used...?
> >   
> 
> I have no reservation whenever you can obtain locally measured data of 
> at least two components (e.g., global and direct, or direct and diffuse) 
> and they are quality controlled. But this is rarely the case.
> I'm quite sure that E+ can derive diffuse from global and direct 
> transparently, but this would be a question for Linda. See also the next 
> question below.
> 
> > The other major point is that the data is approx 30km from the site, is this too far away? this is the closest with current data however...
> >
> >   
> 
> This is quite good, specially if the terrain is relatively flat with no 
> lake or coastal area around.
> 
> > I also have reservations about the data i have, from the definitions of the terms from where the data is from, it appears as i read it that global is the radiation from the whole sky, and direct is from the sun only, so if this is true i would expect global data to be larger than direct...as global would include the direct data, however in the data this is not true...sorry if i am making a basic error, but an explanation woudl be very useful.
> >   
> 
> You understood the definitions correctly. However, there are two ways of 
> reporting direct irradiance: either with reference to the horizontal 
> plane (in which case you should have global = direct + diffuse, as you 
> surmised), or wrt the normal plane to the sun. This is most often 
> referred to as 'direct normal irradiance' or DNI. In that case, the 
> relationship becomes Global = Direct*cosZ + Diffuse, where Z is the 
> sun's zenith angle. Depending on Z, DNI might be larger than Global.
> 
> Another reason why Direct could be larger than Global is that one of 
> them is not recorded correctly due to instrument failure, etc.
> 
> Chris
> 
> -- 
> Chris A. Gueymard, PhD
> Solar Consulting Services
> P.O. Box 392
> Colebrook, NH 03576, USA
> Tel. (603) 237-8550
> Fax  (603) 237-5314
> http://www.SolarConsultingServices.com
>




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