A new study conducted by researchers from the Lawrence Berkeley National Laboratory explored some of the risks associated with poor ventilation.
“When everything’s well mixed, everybody’s exposed to the same conditions,” said researcher Woody Delp. “When it’s not well mixed, you can have, from a COVID perspective, potential hot spots. So, if there’s one infected individual in the room, instead of having their expelled breath fully dispersed and then properly diluted and removed by the HVAC system, another person sitting next to them or even across the room could get a high concentration of that infected person’s emitted viral aerosol.”
The risks of poor ventilation
The researchers conducted a study using nine test dummies in Berkeley’s FLEXLAB to understand how ventilation plays a role in infection risk. In one trial, the dummies were arranged classroom-style, and in another trial, they were seated in a circle. The dummies were programmed to release heat, much in the way humans would when talking, and the researchers manipulated the controls in the room to determine how ventilation came into play.
“With the FLEXLAB, we were able to control every aspect of the HVAC system, which is how we were able to iterate on so many different conditions for the two types of occupancy configurations,” said researcher Chelsea Preble. “We were also able to have temperature and air velocity measurements throughout the room in addition to our measurements of CO2. Those helped us verify and quantify the mixing problem.”
Ultimately, the researchers learned that when heat is forced into rooms, it can often create issues with contaminants if the air isn’t mixing properly around the space. When the air is cool or neutral, respiratory emissions aren’t as likely to travel around the room.
However, heat can become problematic, regardless of how far apart people are spaced out in the area. The researchers found that when there isn’t proper ventilation, forced heat can make people up to six times as likely to breathe in other respiratory droplets. This is concerning when thinking about the spread of infection.
“We know the chain of events that it takes to get a person exposed, and it’s complicated and extraordinarily variable,” said Delp. “An infected person talking and breathing expels droplets and aerosols of various sizes. But even when some of those are inhaled by someone else, they may or may not get infected.
“From others’ studies, we know that the quantity of viruses emitted by an individual infected person can vary widely,” he continued. “One person may expel millions more viruses than another infected person — and that varies over the course of an infection … And to top it off, the number of viruses that it takes to initiate an infection also likely varies between people and with the sizes of the aerosols that are inhaled. As indoor air quality scientists and engineers, our focus is on what can be done with ventilation, filtration, and air distribution to reduce risks even when all the details of the biology are not known.”