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

[Graham Carter & Megan Lyall]

A quick and, but not definitive response.  There are known problems with the RMY files for Australian which I believe are left unresolved at this time as the government ran out of funding to correct the problems.  And yet we have them ratcheting up the energy provisions within our construction code and expecting sensible if not deliverable results from JV3 simulations (the equivalent of a 90.1 energy cost budget simulation)!

So today we still use Test Reference Year (TRY) Files that can be bought from ACADS-BSG in raw data form.  The BIN files on DOE-2.COM are built off of these TRYs.

Aside from that the radiation data itself is unsymmetric in Sydney.  I have not done a definitive analysis but we tend to see clearer mornings in the weather file leading to higher DNI and higher overall global horizontal in the morning half of the hemisphere than the afternoon half.  Over the course of the day our intense sun (10% more radiation or so in a southern hemisphere summer due to the elliptical orbit we have around the sun) leads to evaporation and cloud building up that lowers both DNI and global horizontal with all else equal.  I thought it was a weather file problem years ago but satisfied myself it wasn't in the end.  This wouldn't explain observing the sun rising earlier or later relative to the sunset if you are otherwise in the middle of the time zone...  

Sorry I can't provide more background on the Aussie RMY's but I need to get off to work.

G 
 
On 23/01/2013, at 2:06 AM, Mostapha Sadeghipour wrote:

> 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 94556
> yjhuang at whiteboxtechnologies.com
> www.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 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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