Investigating the Impacts of Building HVAC Systems on Aerosol Composition and Concentration in Different Seasons
XINXIU TIAN, Benjamin A. Nault, Bryan Berman, Bryan Cummings, Shannon Capps, Michael Waring, Peter F. DeCarlo, Johns Hopkins University
Abstract Number: 392
Working Group: Indoor Aerosols
Abstract
This work investigates how aerosols change in concentrations and chemical composition as they move through heating, ventilating, and air-conditioning (HVAC) systems in different seasons. In indoor spaces lacking strong emissions, outdoor-originated aerosols are the main contributor to aerosols observed indoors. Upon transport to the indoor environment through building HVAC systems, outdoor aerosol concentrations and chemical composition are modified due to filtration and air temperature control (heating or cooling), especially when the indoor-outdoor temperature gradient is substantial. To investigate the impact of a modern HVAC systems on outdoor to indoor transport of aerosols, measurements were conducted in a new HVAC system on the Johns Hopkins University Campus in Baltimore, MD during November 2021 and July 2023. During both measurement periods, the instrumentation sampled air from a valve-switching system pulling from four zones inside of the HVAC system: 1) return air, 2) mixed air where outdoor air is mixed with returned indoor air, 3) post filter and heating coil, and 4) supply - post cooling coil. We measured the concentration and chemical composition of particulate matter, gases, temperature, and relative humidity using a variety of instruments including 1) high-resolution time-of-flight aerosol mass spectrometer (HR-Tof-AMS), 2) scanning mobility particle sizer (SMPS), 3) three PICARRO gas concentration analyzers measuring CH4, CO, CH2O, CO2, NH3, and 4) Quant-AQ MODULAIR. Results from this study demonstrate that the primary source of PM in the building originates outdoors. Positive Matrix Factorization on the organic component of the aerosol indicated 4 different sources in winter and 5 different sources in summer. The identified factors changed in relative concentration as they passed through the HVAC system. The results suggest that the filtration efficiency of the MERV filters in the HVAC varied for different species in different seasons, and the installed filters did not achieve the expected filtration levels in both seasons.