We are working on a YMCA with multiple single zone packaged rooftop units.  The engineer has designed every unit with CO2 based demand control ventilation to reduce energy use.  The units are constant volume, but the reference guide states in Step 5 Implement airflow monitoring  that any system with a "variable amount of supply or outdoor air" is a VAV system and that a direct outdoor airflow measurement device must measure the intake flow rate.

ASHRAE 62.1-2010 User's Manual appendix A has provided control logic for DCV for constant volume systems without airflow monitoring.  Would the combination of this control logic and a current or pressure transducer on the outside air supply fan satisfy the requirement for airflow monitoring for this type of system?  I assume this would not work for a multi-zone system and could only be applied to single-zone systems.

This would save the owner a significant amount of money if allowed.