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

Mostapha Sadeghipour sadeghipour at gmail.com
Tue Jan 22 19:22:49 PST 2013


Sorry Joe! I didn't see your last email... Ignore the previous email.

On Tue, Jan 22, 2013 at 6:26 PM, Joe Huang <yjhuang at whiteboxtechnologies.com
> wrote:

> **
> My fault.  When I recalculated the IWEC2 solar using awk, I got the same
> numbers as Mostapha, rather than the higher number I got using Excel.  So
> now, it would seem that IWEC is right in the middle, ACADS and IWEC2 are
> low,  and WX is high.
>
> 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 1/22/2013 4:10 PM, Joe Huang wrote:
>
> Graham,
>
> Thanks for the information.  I downloaded the ACADS-BSG weather file and
> also ran some statistics on it.
> I also went on the web and within a few minutes found several sources for
> solar radiation in Sydney, which seems
> to average between 16-17 megajoules /m2  or 4444-4722 Watts/m2 per day.
> If anyone wants to devote a few
> hours to this, I'm sure one can get quite a good sense of the measured
> solar radiation in Sydney.
>
> I also recalculated the totals from ACADS, IWEC, and IWEC2, and think that
> Mostapha made a mistake on  the
> IWEC2 total horizontal,  because what I got was 4519 rather than the 4180
> reported by Mostapha :
>
>
> ACADS   IWEC   IWEC2    WX (as calculated by Mostapha)
>
>             (all in W/m2 per day)
>                                         Total Horizontal
> 4386     4526      4519    4940
>                                          DIrect Normal
> 4442    3979      3628    4802
>
> Based on what I've seen so far, I would say that the IWEC and IWEC2 solar
> are in the middle of the measured data, the ACADS is somewhat  low, and the
> WX seems somewhat high.
>
> 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 1/22/2013 11:47 AM, Graham Carter & Megan Lyall wrote:
>
> 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 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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