Why Equivalent Clean Airflow Doesn't Have To Be Expensive

In May 2023, the U.S. Centers for Disease Control and Prevention (CDC) updated its ventilation guidance to reduce the airborne transmission of viruses that cause diseases like COVID-19 and recommended at least five air changes per hour (ach) of clean air in occupied spaces.1 ASHRAE recently issued the first pathogen standard, ASHRAE Standard 241, Control of Infectious Aerosols, which included minimum equivalent clean airflow (ECAi) in cubic feet per minute per person (cfm/person) for commercial, residential and health-care space types.2 Both the CDC and ASHRAE recognize that the recommended clean air targets can be reached using a combination of outdoor air and air cleaning. This column is a detailed review of simulation results that looked at the energy and carbon impacts of outdoor air ventilation versus hybrid strategies that combine outdoor air ventilation with air cleaning to meet the newly established CDC target (ach) and the Standard 241 ECAi.