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Re: [EnergyPlus_Support] TMY3 Weather files


The DOE-2 weather file records only the total global and the direct normal.  The total diffuse is calculated by DOE-2 as the
         total global - direct normal * solar angle
If you want to determine the cause of this discrepancy in diffuse radiation , you should compare the diffuse solar calculated by DOE-2 (using hourly reports) to the diffuse solar in the converted EPW file as well as that in the original TMY3 file.

BTW, you did mention again the wind direction discrepancy.  How significant was that?  Wind direction in DOE-2 is reported in octets from 0 to 15. so if the discrepancy is minor it would be round-off errors but if it's large it would suggest a conversion problem.


Joe Huang
White Box Technologies, Inc.
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On 10/19/2012 10:33 AM, Mehry Yazdanian wrote:

I am aware of different units. The Direct solar matches very well, it is the diffuse. The difference I see in the diffuse solar varies between locations. For some it is about 25% difference so I don't think it is a truncation issue. What I don't understand is that even if the .bin file does include the diffuse, the weather converter somehow calculates it. Could it be a problem in the converter program?

On Fri, Oct 19, 2012 at 10:14 AM, Linda Lawrie <linda@xxxxxxxxxxxxxx> wrote:

One simple note is that the .bin files have solar radiation in IP units (BTUH) vs EPW files in Wh/m2). So there is a translation.
Plus, the .bin files have Total Solar/Global and Direct.  But no diffuse.  So, another translation.

oh, and you need to unpack the .bin to FMT which may truncate some of the values -- depending on the precision used.

Wind direction should be a direct copy unless how the original TMY3 was converted differed.

 At 11:04 AM 10/19/2012, mehry1205 wrote:
I am making some DOE2 and EnergyPlus comparison runs, I want to make sure I use the comparable set of weather files for both. Here is what I did:
1) I downloaded the TMY3 DOE2 Weather files (.BIN) from the site ( http://www.whiteboxtechnologies.com/weather_data.html)

2) I Then used EnergyPlus weather converter to get epw from the .BIN file (I first created the .fmt and then ran weather converter on the .fmt).
3) When I made the comparison runs, I see that the diffuse Horizontal solar is different between the two programs.
4) I compared the translated EPW file to the EPW file that I get from EnergyPlus Website. I see that the diffuse Horizontal solar is also different between the translated EPW and the distributed EPW.
5) I also see some differences in wind direction between the two EPW files.
I need to understand why there is a difference and how to make sure I use the comparable weather files (BIN and EPW).


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