As the world’s students return to classrooms, a general unease remains over the dynamics of Covid transmission even as the omicron variant settles into a lull. A trio of researchers from Argonne National Laboratory and the University of Illinois at Urbana-Champaign used the most powerful supercomputer in the country to simulate how Covid particles might spread in a classroom and how different classroom policies might affect that spread.
The Argonne-led team studied this through large eddy simulations (LES) of aerosol particles ranging from 0.1 to 5 microns in a simulated 25-student classroom environment of around 500 cubic meters. Specifically, they were interested in how “canister ventilation” HVAC ducts (which are mounted high and blow air horizontally) could be mounted in this room to ensure optimal ventilation of these particles. The team simulated different locations for the HVAC ducts, as well as several scenarios using warmer and colder air.
The simulations were run on Summit, the IBM-built system at Oak Ridge National Laboratory (ORNL) that remains the United States’ top-ranked supercomputer at 148.6 Linpack petaflops. The team leveraged Summit’s immense power to run ensemble simulations, with the ability to run around 30 simulations simultaneously, each with slightly tweaked variables.
Typically, the HVAC ducts are found opposite the doorway of a classroom. This, the researchers said, creates “dead zones” where air does not effectively circulate.
“Imagine a scenario with a teacher facing the class with his back to the wall on which the HVAC duct is located. When the teacher starts speaking, the aerosol particles that are expelled tend to stay in the dead zone in which he is standing,” said Ramesh Balakrishnan, a computational scientist at Argonne, in an interview with ORNL’s Rachel McDowell. “If the teacher was infected, the aerosol particles that carry the SARS-CoV-2 pathogen are going to be in circulation in the room for a very long period of time, and the chance someone is going to be infected increases.”
However, they did find a solution.
“Through these simulations, we found that if we use the same air conditioning with the same blowing rate, the same velocity, and the same temperature gradient, but we put the door and HVAC inlet on the same wall, it reduces the formation of the dead zone significantly,” explained Balakrishnan.
In short: placing the duct on the same wall as the doorway ensured better airflow.
Introducing colder air, meanwhile, reduced the dead zones. “When cold air comes into the room, it sinks down because it’s heavier, and it creates a certain convective pattern,” Balakrishnan said. “So, the dead zone that existed in the previous study started disappearing with the lowering of the temperature. By the time we reached 20 degrees lower, the dead zone had completely disappeared.”
However, warmer air had the opposite effect, generating even larger dead zones.