Open or shut?
UNC Charlotte researchers discover whether it’s better to leave windows open or shut on public transit to minimize the spread of viruses like COVID-19.
Open or shut?
UNC Charlotte researchers discover whether it’s better to leave windows open or shut on public transit to minimize the spread of viruses like COVID-19.
By John Tibbetts
To many people, it makes sense to keep transit bus windows wide open, drawing in cross-ventilating air for passengers seeking safety from the COVID-19 virus. But opening windows might not be the best way to protect transit riders from viral particles. Instead, to reduce exposure to infection, bus operators might close all windows and operate air-filtration systems at top performance, according to Mesbah Uddin, director of the North Carolina Motorsports and Automotive Research Center at the University of North Carolina at Charlotte.
“When a bus’s air-filtering system is working at 100% effectiveness, it captures many viral particles and prevents their dispersal,” said Uddin, professor of mechanical engineering and engineering science. “It turns out that air filtration performs a better job of improving passenger safety than open windows in cross-ventilating the bus interior.”
Uddin’s research team began studying air safety for public transportation by precisely measuring a standard Charlotte Area Transit System bus, assisted by CATS staff. The team entered the measurements into a computer-aided design (CAD) model of the bus interior. The model was embedded in a computational fluid dynamics (CFD) model, which is commonly used in aeronautics, auto design and other fields to illuminate how gases or liquids move in space and across and around surfaces.
Productive Partnership
The UNC Charlotte researchers’ partner, Corvid Technologies of Mooresville, North Carolina, allowed the team to explore various options for protecting passenger health by providing hundreds of training hours on its proprietary RavenCFD program.
Specifically, the team modeled injections of three characteristic respiratory particle size distributions — from speaking, sneezing and coughing — into the driver’s area of the cabin, then analyzed simulations of airflow and airborne particles along the cabin’s length.
The model was configured with various passenger seating arrangements, seat-barriers placements, windows-open alternatives and heating-and-air-conditioning system (HVAC) settings. Simulations tested how particles in airflow were dispersed, diluted, concentrated or filtered out while the bus was in motion. More than 7 million hours of computing time were dedicated to this project over a tight timeline of two months.
As the researchers expected, airflow through the cabin was redirected by passengers and other large objects. “When airflow reaches one of these large objects, it can create eddies much like a stream current does when it encounters rocks,” said Greg McGowan, an aerospace engineer with Corvid Technologies.
When this happens, airflow stagnates and particles remain in place, recirculating in one spot, possibly to the detriment of passenger health.
“We want transportation systems to have the best standards for the health of the passengers,” said Vincent Lee, a Ph.D. candidate in mechanical engineering and one of three graduate students on the research team. The others, Will Timms and Muhammad Usman Zafar, completed master’s degrees in mechanical engineering in May.
Assessing the threat of surface-transmitted viral particles
A team of researchers from UNC Charlotte’s Department of Bioinformatics and Genomics — curious about how SARS-CoV-2 RNA, the virus that causes COVID-19 spreads and accumulates on surfaces — collected samples from Niner Transit, the campus bus system, to learn more about the possible presence and transmission of the virus from high-touch surfaces. Lauren Roppolo Brazell, a doctoral candidate in bioinformatics, talks about what they discovered and what they hope yet to learn.
A Win-Win
Joint efforts such as the one between UNC Charlotte and Corvid Technologies demonstrate the value and impact of academia-industry partnerships. “We were able to collaborate on a highly computational project in a timely and cost-effective manner,” said Elizabeth Coakley, director of corporate development, Corvid Technologies. “We came up with great results in a matter of months. You just can’t do that unless you work together.”
In addition, the opportunity to contribute to a discovery with potentially far-reaching applications makes a difference for graduate researchers as they launch their careers.
“During this project, we learned to analyze simulation data for different conditions and look for interesting patterns and trends,” said Lee, who is participating in a summer internship with NASA. “It is this kind of experience that has helped me explore and develop my career with its concentration in motorsports and specifically focusing on aerodynamics and turbulence modeling.”
McGowan concurred. “It’s been exciting for us to be involved in ‘bleeding edge’ research,” he said. “We’re always looking for grad students who have these skill sets. Giving them this experience is beneficial for all involved.”
Mesbah Uddin, director of the North Carolina Motorsports and Automotive Research Center at UNC Charlotte
New questions to explore
The study is generating new questions, such as what might be learned from additional research that examines airflow and particle behavior in instances when HVAC efficiency is reduced. “We started out assuming that air filters on a high setting would be very effective in eliminating foreign particles,” said Uddin. “But what if high-efficiency HVAC systems, which prove better for reducing particle transmission, are not widely available in transit buses in the real world?”
A second question involves the relative health dangers from different or new viral concentrations in particles. “We don’t know what concentration of particles would create a higher risk of infection,” said Uddin. “To incorporate that information, we will need a slightly different methodology.”
Uddin notes that the data and methods developed by the research team could lead to understanding airflow and particles in other closed spaces such as aircraft or ships, or in certain urban environments. “These tools could help track the spread of a future virus or any foreign agent, such as the weapons used in chemical or biological warfare,” he said. “It’s entirely possible to develop warning systems to prepare our population for the safest ways to reduce our exposure to a virus or a foreign agent.”
John Tibbetts is a freelance science and technology writer based in Charleston, South Carolina.