Context? eg house vs open-plan office? automated vs manual? For small-scale residential (or similar), I have found BEopt's EMS solution to be the most practical, given the uncertainties one needs to deal with (eg occupant perception + forecasting, subsequent actions). You can look up the EMS entries in a BEopt-generated IDF (and adapt to suit your needs/hypotheses). In a nutshell (this may have been revised in recent years):

• at each timestep, BEopt evaluates house/space thermal conditions
• BEopt evaluates free cooling potential from balanced ventilation + air infiltration alone (eg off-season)
• if insufficient, infiltration ACH is overridden (eg 1, 2 or 3 ACH), a proxy for opening windows

Revised ACH are notoriously tough to pin down:

• climate dependent (e.g. hot/humid? windy?)
• microclimate dependent (e.g. wooded area? urban canyon?)
• design dependent (single-sided ventilation vs cross-ventilation, number/location of windows)
• static pressure distribution, discharge coefficients of openings (e.g. awning vs casement)
• occupant dependent (eg presence/absence, night cooling)

A lot of uncertainties (regardless of the calculation method), uncertainties, but at least one can simulate/evaluate a range of likely outcomes. Hope this helps.