Variations In HVAC System Fresh Air Exchange Among Child Care Centers
HEREK L. CLACK, Khalil Chedid, Andrew Hashikawa, Krista Wigginton, Adam Lauring, Linsey Marr, Emily Martin,
University of Michigan Abstract Number: 761
Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation
AbstractMITIGATE FLU is a multi-site project that seeks improved understanding of influenza transmission through integrated laboratory, animal, and human studies. The human study arm seeks to correlate incidence of influenza infection in child care attendees to influenza concentrations found in the environment (surfaces and air) of child care centers in our local region. Child care centers vary greatly in their design and operation, making it difficult to develop comprehensive guidance for reducing the risk of airborne transmission of influenza and other infectious diseases. During the early stages of the COVID-19 pandemic, general guidance from public health agencies suggested maximizing HVAC system fans to increase the number of air changes per hour (ACHs) and thereby more rapidly flush airborne pathogens from indoor spaces. However, within child care centers enrolled in the MITIGATE FLU project, HVAC system layout varied substantially; notably, several centers were designed with adjacent classrooms sharing a thermostat and an HVAC unit. To explore the implications of these varied HVAC configurations, we used CO2 tracer decay in adjacent classrooms at several child care centers to experimentally measure actual ACHs. The results revealed that adjacent classrooms that share a thermostat and HVAC unit experience varying degrees of air recirculation, greater than 70% to less than 25%. For cases where air recirculation is high, operating HVAC systems more intensively has the potential to facilitate greater airborne pathogen transmission between classrooms, depending on the quality of HVAC filter installed. Our results underscore the need for a nuanced approach to reducing airborne disease spread in child care centers. An effective strategy likely requires detailed consideration of the center layout, HVAC system operation, and filtration strategy that is tailored to each site, rather than generalized guidance based on a simplified geometry and assumptions.