In late December, the U.S. Center for Disease Control published an official guide of ventilation recommendations to mitigate the spread of COVID-19 in interior spaces. This is the first comprehensive guide published by the government organization, and was heavily influenced by the recommendations made by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

The guidelines are drafted from standards outlined by ASHRAE. Source: CDCThe guidelines are drafted from standards outlined by ASHRAE. Source: CDCMany of the strategies laid out have been tactics used since the pandemic's beginning, such as increasing outdoor ventilation to all interior spaces and supplementing with window fans, preferably blowing outwards. Or ensuring all HVAC systems are operating to specification, and components are not cracked or malfunctioning to permit airflow bypass or create recirculation.

Other recommendations include changing operating parameters to common equipment, such as opening outdoor air dampers during beyond minimum settings in mild weather to reduce or eliminate HVAC air recirculation. Or encouraging interior ambient airflow to flow in one direction by re-evaluating the positioning of supply and exhaust air diffusers and dampers.

Finally, it offers more specific recommendations for favorable technologies. Portable high-efficiency particulate air (HEPA) systems are recommended for all HVAC systems, and especially those servicing high risk zones. The use of ultraviolet germicidal irradiation (UVGI) in-duct systems can kill COVID-19 viral particles inside central ventilation systems. Upper-room UVGI systems can provide more localized, portable air cleaning.

The full list of recommendations is available from the CDC website. In addition, the CDC notes that a layered approach to COVID-19 ventilation, with multiple strategies enacted, will be most effective. However, no number of mitigation techniques will completely eliminate the risk of contracting COVID-19 in public spaces.

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