<p>Assessing and improving the safety of social settings is pivotal for the reopening of facilities and institutions during the pandemic. There is now evidence suggesting that the predominant medium of SARS-CoV-2 transmission is exposure to infectious respiratory droplets and aerosols. Airborne viral spread is particularly effective in indoor environments – which have been strongly implicated in high transmission rates and super-spreading events. This study focuses on employing computational fluid dynamics (CFD) models, using the commercial software ANSYS Fluent, to investigate the influence of room ventilation systems, settings, and geometry on airborne viral dispersion. In Fluent, ventilation models are developed to simulate the airflow patterns within a typical classroom in Cooper Union’s 41 Cooper Square academic building. Boundary conditions and simulation geometry are determined through surveys of the physical space and building management data. Model settings are based on HVAC industry practices. Several modeling choices, including – sub-modeling techniques and mesh coarsening, are made to reduce the computational costs of each simulation. A variety of convergence studies are conducted to show that optimized models remain in reasonable agreement with models consisting of high mesh refinement and ASHRAE standardized manufacturing data. Euler-Lagrange particle tracking is incorporated into the ventilation models to simulate the dispersal of viral-laden aerosols from infected individuals. Injected aerosols are modeled as tracers, perfectly following the flow continuum, to efficiently simulate the exhalation of particles due to breathing and speaking, a principal source of viral-laden aerosols. Preliminary results from transient simulations show that both aerosol concentration and residence time are related to an individual’s relative distance from a room’s exhaust. Additional particle models will consider a wider variety of droplet sizes and concomitant characteristics. These prospective models will supplant ideal tracers in modeling accuracy by including drag, ventilation, and buoyancy effects on injected droplets. Future transient simulations will be populated with several ventilation setting parameters, such as air change rates and humidity levels, to investigate their effect on particle concentration, distribution, and residence time. Efforts to validate CFD model data will include qualitative comparisons to similar studies conducted in recent literature. Further validation will include experiments analogous to simulated case study scenarios that utilize CO2 monitoring – CO2 being an accepted proxy for exhaled aerosols. Direct access to building ventilation controls will allow for simulation boundary conditions and HVAC parameters to be exactly replicated experimentally. Collectively, by characterizing the interaction between virus-laden particles and ventilation systems, this paper seeks to recommend HVAC adjustments to provide safer social spaces amid the ongoing pandemic.</p>

Computational Fluid Dynamics Modeling of the Efficacy of HVAC Adjustments on Mitigating Airborne Transmission of SARS-CoV-2

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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