Compartmentalization and Ventilation System Impacts on Air and Contaminant Transport for a Multifamily Building

The proper provision of fresh air ventilation and avoidance of cross-contamination in multi-family apartment dwellings has never been more critical than during the global COVID-19 pandemic. The airtightness of interior partitions and the design of ventilation systems in multifamily buildings determines the flows across the exterior envelope and interior partitions. These flows change the total ventilation rate for the building and individual units, and also impact the mixing of air and contaminants between apartment units or with common spaces. These flow patterns can have important implications for HVAC energy use, indoor air quality (IAQ) and occupant health and comfort. This study examined the changes in air flow and contaminant transport in multifamily buildings using a combined CONTAM/EnergyPlus modeling approach. Key parameters were systematically varied, including weather, apartment airtightness, and type of mechanical ventilation system. Simulations were performed for a four-story, mid-rise building with an enclosed common corridor. Each case was simulated for a full year with three-minute time-steps that allowed for scheduling of occupancy-related contaminant releases and operation of ventilation systems. Contaminants simulated in the analysis were PM_2.5, formaldehyde and water vapor, together with CO₂ as an indicator of bioeffluents and other human-activity-related pollutants. The results of this work are intended to assist codes and standards bodies (e.g., ASHRAE 62.2) in setting appropriate air tightness limits and ventilation system design guidelines for multifamily buildings.