Sars-Cov-2 Filter Forensics in Large, Multi-Story, Residential Buildings: Modeling and Experimental Results

DAVID JARMA, Juan Pedro Maestre, Atila Novoselac, Kerry Kinney, University of Texas at Austin

     Abstract Number: 637
     Working Group: Health-Related Aerosols

Abstract
The COVID-19 pandemic has highlighted the critical role of adequate building ventilation and filtration in mitigating SARS-CoV-2 exposure indoors. The dust recovered from heating, ventilation and air conditioning (HVAC) filters is one promising method for capturing and monitoring SARS-CoV-2 signal indoors. Molecular signal for SARS-CoV-2 has been recovered from HVAC filters both in homes and in larger settings (Maestre 2021, Renninger 2021); However, it is not yet known if it is feasible to monitor the health of large, multi-story, residential buildings using dust samples recovered from the filter banks in centralized air handling units.

With knowledge of the HVAC system configuration and settings, a model was created to estimate the SARS-CoV-2 signal on the HVAC filters. This is important because enough dust mass must collect on the filter over time in order to provide a good sample; Sampling too frequently will not provide enough dust to see a signal, while too much time between sampling begins to defeat the purpose of a monitoring system. Using this model, an appropriate sampling schedule can be implemented, allowing an ample sample mass to be collected.

On three occasions, composite dust samples were collected from the HVAC filters in 8 AHUs. Additional dust samples were collected from the floor, return air grill, and other horizontal surfaces in a random selection of 25 residential units across three zones served by the previously sampled AHUs. Positive SARS-CoV-2 signal was consistently captured and detected in AHU HVAC filter dust. Across the three sampling events, detectable signal ranges in concentration from 102 to 106 copies N2 per gram of dust, comparable to those found in a COVID-19 home study (Maestre et al., 2021). It is important to note that a positive signal indicates that viral (RNA) material is present but does not provide any information about infectivity. The SARS-CoV-2 molecular signal can persist for up to one month in dust samples (Renninger 2021).

Results to date indicate that the SARS-CoV-2 molecular signal is readily detected in HVAC dust collected from AHUs in a multi-story, residential building. This data will be helpful for environmental monitoring of buildings as proactive COVID-19 testing within communities declines, and we need additional methods for identifying whether another outbreak may be imminent. These results indicate that the signal recovered from HVAC filters in AHUs is one potentially effective approach.