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

Mostapha Sadeghipour sadeghipour at gmail.com
Fri Jan 18 18:32:46 PST 2013


Dear All,

I added the weather data that I received from Weather Analytics in the 3rd
row, and the data from White Box Technologies (IWEC2) in the 4th.

Here is the graphs:
https://dl.dropbox.com/u/16228160/Sydney_Weather_Data_Comparision_II.jpg

And here is the graphs with normalized scales for row 3 and row 4:
https://dl.dropbox.com/u/16228160/Sydney_Weather_Data_Comparision_II_Normalized.jpg

The pattern of the radiation rose for both graphs are mostly similar to
IWEC graph, however the wind-rose for Weather Analytics file is slightly
skewed toward north-west. As a conclusion there should be an issue with the
RMY file.

I also did a comparison for average global and direct normal radiation
between the three weather files (IWEC, WeatherAnalytics, IWEC2). Average
global radiation in WeatherAnalytics data is 9.1% more then IWEC2. This
number is 20.7% more for direct normal radiation.
Here are the graphs for monthly and annual comparison:
https://dl.dropbox.com/u/16228160/radiationComparison_Charts.jpg

Unfortunately I don't have the measured data for comparison.

Excel spreadsheet is attached to this email.

Regards,
Mostapha


On Wed, Jan 16, 2013 at 11:03 AM, Joe Huang <
yjhuang at whiteboxtechnologies.com> wrote:

> **
> 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 94556yjhuang at whiteboxtechnologies.comwww.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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