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Openstudio is providing different results for the same model

asked 2025-01-21 18:34:10 -0600

Draza's avatar

updated 2025-01-21 18:35:59 -0600

I am building an energy model in Openstudio to help calculate energy savings. I noticed something was off with the results I was getting with some measures. I went back and noticed that if I run the same model, I got three different results running the exact same model without making changes. The results I am specifically referring to are the annual gas and electric consumption as well as District cooling consumption. I know that this didn't used to be an issue with previous models. Is there a setting or something that i could have accidentally changed?

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What version of OS SDK are you using?

Julien Marrec's avatar Julien Marrec  ( 2025-01-24 10:11:35 -0600 )edit

OpenStudio SDK version 3.8.0

Draza's avatar Draza  ( 2025-02-07 16:02:28 -0600 )edit

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answered 2025-01-22 11:25:43 -0600

I suggest looking at the EnergyPlus IDF file that is produced for each run and then using a diffing tool (like WinMerge) to see what is different about the files. If two IDF files are the same, the simulation results will also be the same.

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Here is a link to the idf files that were created for 3 different runs. The biggest difference is that it is assigning different design specification outdoor air objects. Is there a reason for this? It is possible that i left something blank so it is autoassigning the object and choosing a different one each time? Any input would be greatly appreciated.

Draza's avatar Draza  ( 2025-01-22 12:12:13 -0600 )edit

Compare both "Controller Mechanical Ventilation 4" entries (in_1.idf vs in_2.idf), around line 6668. More specifically their respective "Design Specification Outdoor Air" objects. I suspect the intent was to refer to the (same) DesignSpecification:OutdoorAir:SpaceList "AHU-4 DSOA Space List". But instead, each refers to a different DesignSpecification:OutdoorAir object, hence the observed differences in results (I suspect). Something similar between in_2.idf vs in_3.idf. The same OSM file generated these different IDFs?

Denis Bourgeois's avatar Denis Bourgeois  ( 2025-01-22 14:07:31 -0600 )edit

OK, re-reading your follow-up comment. You're already aware that that the differences lie in the mech. ventilation controllers - my bad. Could you share the OSM as well? And are these different IDFs generated using the OpenStudio CLI or the Application?

Denis Bourgeois's avatar Denis Bourgeois  ( 2025-01-22 14:13:00 -0600 )edit

I uploaded the osm file to the same drive folder. I think I figured it out. There are multiple spaces with different space types assigned to a single zone. Each time I run it it seems to choose at random which outdoor air specification object to use. making a new zone for each space fixed the issue. Still unsure why it would choose a different object instead of the same one each time though?

Edit: to answer your question, yes the same osm generated these two different idfs without me making any changes to the osm itself.

Draza's avatar Draza  ( 2025-01-22 14:53:07 -0600 )edit
1

Can reproduce the (incorrect, I believe) forward translation. I think you're right, OS seems to pick one (out of maybe several related) spacetypes as a basis to set a zone's DSOA (instead of an area-weighted solution). You'll find some related (open) issues here. You could add a comment (to one of the issues) pointing to this UMH post ... or open a new issue.

Denis Bourgeois's avatar Denis Bourgeois  ( 2025-01-22 15:58:08 -0600 )edit
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answered 2025-01-27 16:15:35 -0600

sashadf1's avatar

updated 2025-01-27 16:18:41 -0600

Scott's answer is correct, and diffing IDFs/OSMs is a good idea. Diffing OSMs can get messy because of the handle strings for the objects, so diffing IDFs is probably preferrable. I would also add that if the two IDFs are identical and the simulation engine version of E+ is the same, the results will be identical. Comparing across versions of E+ is probably not your use case, though.

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Asked: 2025-01-21 18:34:10 -0600

Seen: 211 times

Last updated: Jan 27