The industry standard for effectively knocking out aerosols that carry pathogens, bacteria, and Covid Virus is 4 to 6 ACH.
According to ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), the minimum required total ACH that occurs in most households is 0.35 ACH of outdoor air, and schools should be designed for approximately 10 times higher rates, although most schools do not meet this in practice. The suggestion for increasing the target to 4 to 6 ACH is more consistent with rates set in hospitals, where the higher ACH requirements underscore the potential role of air change rates as an infection control strategy.
“Providing 5-6 ACH is recommended as it will replace about 99% of the volume of air in an indoor space with fresh filtered or outdoor air every 45 – 60 minutes.” (Selection and Use of Portable Air Cleaners to Protect Workers from Exposure to SARS-CoV-2, National Institute of Environmental Health Sciences.)