Indoor air quality is significantly affected by outdoor pollution, but the extent depends on a building’s HVAC system, according to new research from the University of Utah. The study, published in Building and Environment, conducted on the Salt Lake City campus, revealed that wildfire smoke can infiltrate buildings with certain HVAC systems, while pollution from dust storms and winter inversions is largely kept out. The findings highlight the critical role of ventilation systems in maintaining healthy indoor environments.
The research team, led by chemical engineering professor Kerry Kelly, deployed low-cost sensors in 17 indoor and two outdoor locations to monitor air quality during different pollution events. They found that buildings equipped with air-side economizers, systems designed to improve energy efficiency by drawing in outdoor air, were more susceptible to infiltration of fine particulate matter (PM2.5) from wildfire smoke. In contrast, pollution from dust events and winter inversions had minimal impact on indoor air quality, regardless of the HVAC system.
Graduate student Tristalee Mangin explained that the team analyzed the ratio of indoor to outdoor PM2.5 levels. Wildfire smoke showed four to five times higher infiltration rates compared to other pollution sources. However, exceedances of international health guidelines were rare and limited to buildings with air-side economizers.
The study also uncovered why certain pollutants behave differently indoors. Dust particles, being larger and heavier, are effectively filtered out, while inversion-related particles, primarily ammonium nitrate, often transition to a gas phase indoors, reducing their detectable presence.
“Our buildings are big and complicated, but this is a very solvable problem. Even simple solutions like portable air filters do a great job,” said Kerry Kelly.
Sean Nielson, a co-author from Facilities Management, added, “Every building and system has unique features. We’ll need to evaluate them individually to find the best solutions.”
The ongoing research aims to help building managers optimize HVAC systems to balance energy efficiency and air quality, particularly during wildfire season. While the study underscores the challenges posed by diverse building systems, it also points to practical solutions, such as targeted adjustments and improved filtration. The team continues to monitor air quality to refine their recommendations.
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