The intent is to ensure that while the building is operating your ventilation schedule should assist in removing bioburden during, pre-, and post- occupancy of the building. Flush the building for a duration sufficient to reduce concentration of airborne infectious particles by 95% . For a well-mixed space, this would require 3 air changes of outside air (or 3 equivalent air changes including the effect of filtration and air cleaners) as detailed in the calculation methodology.
In lieu of calculating the air change rate, pre- and post-occupancy flushing periods of 2 hours (for a total of 4 hours) may be used since this should be sufficient for most systems meeting minimum ventilation standards.
So for each mode, the control would be as follows:
- Occupied: bring in the most outside air that the systems can accommodate as described above
- Pre- and Post-: The general method is to operate the systems in Occupied Mode for 2 hours prior to, and after, daily occupancy. To determine actual time required for 3 complete air changes for your facility consult your professional mechanical engineer