There are a few AHUs in the project for which I work. One AHU supplies less than 20% of the non-densely-occupied rooms with its air volume flow, but still has outdoor airflow measurement devices.

The mechanical engineer who designed our heating / cooling system placed the CO2 sensors for the gymnasium (with bleachers) in the return ducts.

The form for IEQc1 asks you to fill out table IEQc1-1 for all mechanical ventilation systems where 20% or more of the design supply airflow serves non-densely occupied spaces.