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As @Molly Curtz points out in the comment above, the hard flow rate in the supply fan object (or any other component) is unknown to the system sizing calculations. The OA controller Maximum Outdoor Air Flow Rate autosizes to the design flow rate for the system. If you want to size components on an air loop to a specific system flow rate, use these Sizing:System object inputs.

Sizing:System,
VAV Sys 1,               !- AirLoop Name

Flow/System,             !- Cooling Supply Air Flow Rate Method
145.2,                   !- Cooling Supply Air Flow Rate {m3/s}
,                        !- Cooling Supply Air Flow Rate Per Floor Area {m3/s-m2}
,                        !- Cooling Fraction of Autosized Cooling Supply Air Flow Rate
,                        !- Cooling Supply Air Flow Rate Per Unit Cooling Capacity {m3/s-W}
Flow/System,             !- Heating Supply Air Flow Rate Method
145.2,                   !- Heating Supply Air Flow Rate {m3/s}
,                        !- Heating Supply Air Flow Rate Per Floor Area {m3/s-m2}
,                        !- Heating Fraction of Autosized Heating Supply Air Flow Rate
,                        !- Heating Fraction of Autosized Cooling Supply Air Flow Rate
,                        !- Heating Supply Air Flow Rate Per Unit Heating Capacity {m3/s-W}

Note that this flow rate will also be used to scale any autosized air terminal flow rates.