Different results for same inputs
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Eric Shadd
Apr 29, 2016, 3:15:45 PM4/29/16
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I am using "Convert EPW" with the Title 24 2013 climate zone EPW files. If I run SPOT with various climate zones then go back to climate zones I've already run, the results are different. I have changed nothing else besides the converted EPW files.
As a clarifying example: I create all the geometry, lights, etc. I convert CZ01.epw in SPOT and run SPOT. I look at the results in annual_day.ill. I then do the same with CZ02.epw, CZ03.epw, etc. When I go back and rerun with the converted CZ01 data, I get a different annual_day.ill results than the first run.
I do have two SPOT spreadsheet templates in the directory. One has different windows than the other. But, the runs I spoke of above are only done with one of the spreadsheets without opening the other spreadsheet. I don't open or touch the other spreadsheet with the different windows.
As a clarifying example: I create all the geometry, lights, etc. I convert CZ01.epw in SPOT and run SPOT. I look at the results in annual_day.ill. I then do the same with CZ02.epw, CZ03.epw, etc. When I go back and rerun with the converted CZ01 data, I get a different annual_day.ill results than the first run.
I do have two SPOT spreadsheet templates in the directory. One has different windows than the other. But, the runs I spoke of above are only done with one of the spreadsheets without opening the other spreadsheet. I don't open or touch the other spreadsheet with the different windows.
Zack Rogers
Apr 29, 2016, 4:09:24 PM4/29/16
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Hi Eric,
You should definitely get very similar results for two identical runs but they will never be exactly the same with Radiance as it utilizes several stochastic (or statistical models) where there is some randomness to the simulation. The higher the Radiance parameters the less variance you will see in the results of two identical runs.
If the differences you are seeing between your two different seem larger than just this stochastic randomness difference, there must be something else different with the simulation. Ensure the shade setting have been run the same and that the occupancy schedule is the same (this won't effect the design days but some of the other metrics). Changes in the months and times that you rget run will also have some impact on the overall result. The default of 3 months (equinox, summer and winter) works well but you would have a more accurate calculation if you select to run all 7 months and every single hour.
Hope this helps track down the differences you are seeing.
Cheers,
Zack
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Zack Rogers, P.E., LEED AP BD+C
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