[Bldg-sim] EPW Weather Data (Local Time vs Solar Time)

[Joe Huang]

I took a look at an old atlas and Sydney's near the middle of its time zone. Please keep 
in mind that the solar data in the vast majority of weather files is modeled, i.e., 
calculated from other parameters or satellite imagery, so they're quite dependent on the 
solar angle calculations.  I know that's the case with the IWEC, not positively sure about 
the RMYs, though.

I'm attaching a scratch version of the weather file for Sydney I created for the ASHRAE 
IWEC2 set (file sent in separate e-mail to just Mostapha,  I think I'm allowed to do 
that).  Please look at that for a comparison, and let me (and others) know what you find.  
The file is in text, and the columns are clearly identified.

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 1/16/2013 8:12 AM, Mostapha Sadeghipour wrote:
> All,
>
> We were looking at weather data files for Sydney Australia, (Sydney.Airport.947670), and 
> we found that there is a of about an hour for some of the data in 
> AUS_NSW.Mascot-Sydney.Airport.947670_RMY versus AUS_NSW.Sydney.947670_IWEC.
>
> Please see the attached jpg. Looking at the direct normal radiation and radiation-rose 
> you can see that sun-rise and sun-set in RMY file happening earlier. When combined with 
> solar position calculations based location and time this makes the sky to appear to be 
> skewed, with more radiation  from the east. We found a similar pattern in 
> AUS_NSW.Sydney.947680_RMY weather file.
>
> Which weather file is the one that you suggest us to use for the analysis?
>
> Is there a known difference between the RMY and IEWC standard that would account for this?
>
> Is it because Sydney is near the eastern edge of its time zone, and the RMY standard is 
> defined in terms of actual local time rather than ‘solar time’ and the IEWC standard 
> were defined in terms of solar time rather than local time?
>
> Regards,
>
> Mostapha
>
> PS: I uploaded the jpeg file here because the list does not allow sending me the email 
> with the attachments (>200k): 
> (https://dl.dropbox.com/u/16228160/Sydney_Weather_Data_Comparision.jpg)
>
>
>
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