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I have an AirLoopHVAC with a fan constant volume, a DX cooling coil and a gas heating coil. Multiple zones are connected with ATUs of type AirTerminal:SingleDuct:Uncontrolled (autosized)

I want my loop to work at $X$ CFM of supply air constantly.

Here's what I've done:

• Specified $X$ for the AirLoopHVAC Design Supply Air Flow Rate
• Specified $X$ for the Fan:ConstantVolume Maximum Flow Rate
• Specified $X$ for the DX coil Rated Air Flow Rate

I was expecting the loop to run at this value, but it doesn't.

Even weirder, I had set the minimum and the maximum outdoor airflow rate of the Controller:OutdoorAir attached to the AirLoopHVAC:OutdoorAirSystem to a value $Y$, and the loop ends up running at a constant value that is even below this $Y$ value...

I've found that to have it run at $X$ CFM, I have to either:

• Modify the Sizing:System object attached to the AirLoopHVAC to have a Cooling/Heating Design Air Flow Method set to Flow/System and to enter $X$ for the Cooling/Heating Design Air Flow Method
• Hardsize the ATUs
• Set a different DesignSpecification:OutdoorAir (DSOA) for the zones

So it seems that E+ is just simple ignoring the Design Supply Air Flow Rate that I've entered for the AirLoopHVAC, and calculating another value that will meet the ATUs need (My Sizing:System is set to Type of Load to Size On at Sensible, though I've tried VentilationRequirement). Why is that? Is this the expected behavior?

For the record, I'm using OpenStudio 1.12.1, as I think this could be linked to the way OpenStudio uses and forward translates the Controller:MechanicalVentilation set to ZoneSum with all the DSOA for the zones served by the AirLoopHVAC