Openstudio is providing different results for the same model

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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.

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?

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?

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.

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.