Ventilation Rate (62.1)
ASHRAE 62.1 sets outdoor air as two components added together: one per person for the occupants, one per square metre for the building itself. A room with nobody in it still needs the area component. Dividing by the distribution effectiveness Ez accounts for supply air that never reaches the breathing zone.
Rates are the ASHRAE 62.1 Table 6-1 values in SI — confirm the current edition and your local code, which may adopt a different version or add requirements. Lowering Ez raises the air you must supply but not the air that arrives, so the CO₂ estimate is taken from the breathing-zone rate and deliberately does not improve when distribution gets worse. It assumes a sedentary adult generating about 0.0052 L/s into a fully mixed room at steady state; CO₂ is a proxy for outdoor air per person, not a contaminant limit.
Design-stage estimates. A real project needs a full load calculation to the ASHRAE/CIBSE procedure, and ventilation rates are code-mandated — check the standard and jurisdiction that apply to your building. A helper, not a substitute for engineering judgment.