One Room, Two People: The Openings That Give a Stated Number of Air Changes, and the Hour the Air Takes to Clear

A single room of 31.2 m³ holding a patient and a caregiver is ventilated only through openings. Under a light wind of 1.0 m/s, an opening of 0.1 m² gives 6.92 air changes per hour and an opening of 0.25 m² gives 17.31 air changes per hour. Under stack effect alone on a calm warm day, with a temperature difference of 2.0 K, reaching 6 air changes per hour requires 0.193 m² of opening and reaching 12 requires 0.387 m². After a source stops, air at 6 air changes per hour needs 30.0 minutes to fall to 5% of its starting concentration and 46.1 minutes to fall to 1%; at 1 air change per hour the same falls take 179.7 minutes and 276.3 minutes. Over a 2.0 hour visit with a constant source, the caregiver's time-integrated concentration is 56.8% of the unventilated value at 1 air change per hour, 27.8% at 3, 15.3% at 6, and 8.0% at 12. These are calculations from stated assumptions, not measurements.