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

Mostapha Sadeghipour sadeghipour at gmail.com
Tue Jan 22 07:06:22 PST 2013


Hi Joe,

For or purpose of designing the mass of the building at the early
conceptual stage of the design, we are more concerned with the relative
magnitudes of solar radiation. This is not to say that we are entirely not
concerned with the solar radiation values, but that is less of an
importance at this stage.

Since the RMY file shows a skewed radiation-rose different from all the
other files we decided not to use that file for the studies. I also agree
with your point about the location of Sydney. I double checked and it is
near the center of UTC+10: (http://www.timeanddate.com/time/map/)

Regards,
Mostapha


On Fri, Jan 18, 2013 at 9:23 PM, Joe Huang <yjhuang at whiteboxtechnologies.com
> wrote:

> **
> Mostapha,
>
> So what was your conclusion about the hourly profile in the solar
> radiation, which was your original question?
> I contend that since Sydney is close to the standard meridian for its time
> zone (150 degrees east), the solar profile should be symmetrical around
> noon.
>
> On the total amounts of solar radiation, I have no basis to judge between
> the three.  Did you leave off the RMY for some reason?  Since these are all
> "typical year" weather files, they are likely to be different months from
> different years. Overall, it does seem that the WX is showing more solar
> than the IWEC or IWEC2, which are quite close.  The larger variation in
> direct normal is understandable, since all the models (as well as
> measurements) show that when total goes down, the fraction direct goes down
> even more.
>
> The only way to evaluate these weather files is to find some actual
> measurements, even if it's just of monthly or year totals. Otherwise, we
> can only say that there are differences.
>
> Joe
>
>
>
>
> 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 1/18/2013 6:32 PM, Mostapha Sadeghipour wrote:
>
> 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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