Why is DOAS Fan Air Flow Rate inconsistent with design OA flow rate

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I set up a DOAS system with uncontrolled diffusers directly into each zone with exhaust from the zones exiting the outdoor air controller on the DOAS air loop. The air loop, supply and exhaust fans and the diffusers were autosized.

Each space type had a design specification outdoor air flow rate. Each zone had a fan coil unit.

The simulation showed a DOAS air flow about 6 times the design amount. I had to end up hard sizing the DOAS air loop, fans and diffusers.

Why would this be the case?

As the model was built in SketchUp 2019, I used OpenStudio Version 1-1-0 (EnergyPlus Ver 9-4)

Thank you.