I am wondering about the OA Minimum Limit Type in OS:Controller:OutdoorAir vis-a-vis ASHRAE 62.1 in a run-of-the-mill VAV system. The Ventilation Rate Procedure in OpenStudio/EnergyPlus calculates my minimum OA air flow rates, and I can follow all steps of that calculation. Unless the occupant count changes, those should be the minimum OA flow rates at all times, except when unoccupied.
As such, I am tempted to use the FixedMinimum for said Minimum Limit Type. Of course, when using the ProportionalMinimum, my EUI is reduced compared to FixedMinimum, which is desirable. However, if I understood the manual correctly, then for ProportionalMinimum, the OA flow rate is reduced proportionally to the ratio of supply air flow rate to design supply air flow rate, which could easily drop below the ASHRAE 62.1 minimum OA flow rate. Therefore my question: Is the ProportionalMinimum in violation of ASHRAE 62.1 and must I not therefore always use FixedMinimum if I want to follow ASHRAE 62.1?
Also, is the Minimum Limit Type applicable regardless of whether I run an economizer, or does it only apply when I run an economizer?
Furthermore - and loosely associated with my primary question above - even if I do not use Demand Controlled Ventilation (DCV), ASHRAE 62.1 includes a component that varies with occupant count. As the occupancy count may change throughout the day, should not the ASHRAE 62.1 minimum OA flow rate change throughout the day also? Or is the ASHRAE 62.1 minimum OA flow rate calculation done only once during sizing, and thus a changing occupant count cannot be accounted for "dynamically" (unless one uses DCV, of course)?
