Better ventilation is a key component of the Biden administration’s plan to resume in-person learning at the majority of the nation’s K-8 schools by the end of April.
In an executive order issued on January 21, President Biden directed the departments of Education and Health and Human Services to issue guidance for schools to safely return to in-person learning “including by implementing mitigation measures such as cleaning, masking, proper ventilation, and testing.”
Dr. Joseph G. Allen, director of Harvard’s Healthy Buildings Program, is encouraged that the president is giving attention to ventilation. Allen is also chair of The Lancet’s Covid-19 Commission Task Force on Safe Work, Safe Schools, and Safe Travel. He says that along with other mitigation measures, such as universal masking, ventilation strategies are important because respiratory aerosols that escape masks can accumulate if they’re not diluted through ventilation or captured through filtration.
While many of the nation's schools have severely outdated ventilation systems, Allen and his team have developed inexpensive strategies for schools to quickly increase ventilation with strategic system upgrades, or something as simple as opening a window a few inches.
“In the guidance we released in June, we recommend that schools target four to six air changes per hour, through any combination of enhanced ventilation or filtration,” he says. “The recommendations we've made do not have to cost millions of dollars or take many months to implement.”
Maximize Your System
Schools with centralized heating and cooling should adjust those systems in a way that prioritizes bringing in outdoor air. “You want to be sure that any recirculated air is going through a higher-efficiency filter, specifically what's known as a Merv 13 filter,” Allen says. “Most mechanical systems have a Merve 8 filter. That captures about 20 percent of the particles we're interested in. A Merv 13 will get you above 80 percent.”
But there are limitations to what can be accomplished through this action. Many school systems are not designed to bring in large amounts of outdoor air, says Richard Loveland, vice president of BVH Integrated Services, a mechanical engineering company in Connecticut that installs HVAC systems for many schools. “Typical air handling rooftop equipment takes in about 20 percent outdoor air and the coils and the heating units within that unit are designed for that 20 percent,” Loveland says. If you bring in more outdoor air, you’re not going to be able to provide proper heating and cooling.
The same is true when it comes to filters.
“Most of these systems are designed for a certain range of filters in terms of how robust they are,” says Michael Tyre, principal at Amenta Emma Architects, whose company often works with Loveland’s. He adds that many schools want high-capacity filters but the systems just aren’t designed to have that kind of filters.
However, there are other ways to overcome your schools’ HVAC limitations.
Portable Air Cleaners
For schools with existing equipment that can’t get four to six changes per hour, Allen recommends the use of portable air cleaners with heavy filters. “These devices can cost $200 or $300,” he says. “They are a relatively inexpensive means of ensuring that sufficient air cleaning is happening in a classroom when they are sized correctly for the room.”
Look for a portable air cleaner with a HEPA filter. “You don't want any bells and whistles, you don't want or need UV ionization or any fancy sensor technology,” Allen says. “You do want to look for something that has a device that has a high clean-air delivery rate or CADR.”
Allen recommends a CADR of 300 for every 500 square feet in the space you are using the air cleaner. (More information on how to make these calculations is available here.)
Even Opening a Window Can Help
While it may sound like a low-tech solution, opening a window to let in some air can make a big difference, and can work in colder areas because the window does not have to be open so much that it will let out lots of heat. “Even two or three inches can greatly increase the amount of ventilation that a room gets,” Allen says. “When we've done experiments, we get anywhere from 2 to 14 air changes per hour in a classroom through opening windows.”
To test how much air flow your open window is getting, you can use a carbon dioxide monitor. Humans release carbon dioxide when they breathe, and therefore, by measuring how much accumulates in a room, you can calculate the number of air changes a room is experiencing. On Healthy Buildings’ website there is information for schools on how to calculate the carbon dioxide level a room should not exceed by putting in the size of a room, the number of people who will be in it, and the amount of air changes per hour you are targeting.
A New Way of Thinking About School Buildings
The pandemic-fueled focus on school ventilation is part of a larger conversation around designing schools that foster a more healthy environment that is better suited to education.
“We're talking about indoor air quality, but there's a host of other considerations that revolve around health and wellness that have become increasingly in demand for academic environments,” Tyre says.
In recent years, there has been more awareness about the way building design interacts with physical health. “Whether it's access to daylight, or good air ventilation, or noise levels that allow you to concentrate--all of these things have been studied and have been shown to have correlations between how active and engaged and joyful kids are when they're in school,” Tyre says.
“We've known for a long time that things such as higher ventilation rates are associated with better cognitive function and lower infectious disease transmission,” Allen says. “We see higher ventilation rates associated with higher math scores, higher reading scores, higher science scores.”
Solutions such as portable air cleaners are a stopgap measure to get through the next few months but longer-term planning is required. “We need to be making much larger investments in the buildings and the mechanical ventilation systems,” says Allen. “And when we do, we know from the scientific literature that this will provide years and years of benefits to both kids and adults.”