Here’s what it takes to upgrade HVAC systems — and how to know if particular indoor spaces have done it.
In October, students at the University of Illinois, Urbana-Champaign, held an intimate jazz concert at a bar downtown, with an audience of about 20 peers and faculty members — all of whom held digital passes indicating they’d recently tested negative for Covid-19. Two jazz ensembles performed, sometimes with masks and coverings for their instruments, and other times without. Behind the scenes, mechanical engineering professor Ty Newell tinkered with the airflow, turning the exhaust and recirculation fans on and off at different points during the night. His students monitored for changes in the air quality, using a special instrument to measure the concentrations of carbon dioxide and fine particulate matter, both key to determining if a building is well ventilated. The experiment sought to highlight the significance of proper ventilation, something that Newell said hadn’t been paid enough attention, until now. As evidence suggesting Covid-19 can spread through aerosol transmission continues to mount, health experts are focused less on sanitizing surfaces and more on improving indoor air quality. In December, the U.S. Centers for Disease Control and Prevention finally put out its ventilation recommendations to combat Covid-19, based on standards set by ASHRAE, or the American Society of Heating, Refrigerating and Air-Conditioning Engineers. Experts like Newell say the investment is worth it. It will be the key to a safe and healthy return to offices and schools, even with the rollout of Covid vaccines, he says. New disease outbreaks are expected to crop up in the future, and “apart from the pandemic, having an improved filter also gets other particulates out of the air that impact your health — these very fine particulates that easily go way down into your lung,” he says. “Only good things happen when you bring in more fresh air,” including a potential increase in productivity and academic performance.
Improving ventilation typically involves some combination of letting in more fresh air, upgrading air filtration systems and installing technologies like UV light to kill those pathogens.
The human nose may be able to smell the stagnant air of a very poorly ventilated room, but patrons or employees may not always know if a building is well-ventilated enough to affect tiny particles like the coronavirus. For a typical office building, current ASHRAE standards recommend 20 cubic feet of outdoor air per minute (cfm) per person, and experts like Sasse recommend that a room’s air should be replaced three to five times per hour. But the proper ventilation and air change rates vary depending on building size, occupancy and use.
One of the best ways to know is to measure the concentration of CO2 in each room or part of a building, he says, because it shows the amount of exhaled air that has built up in the room without enough fresh air to flush it out. C02 levels should register no more than 800 parts per million. “If you see [a place with] levels much above 800 ppm, don’t spend much time in there,” Newell advises.
But that measurement requires specific technology. Ideally, Newell would like everyone to carry a CO2 meter in their pockets, but those instruments can cost upwards of $100.
But it’s important to acknowledge that while ventilation helps mitigate your chances of contracting Covid-19, the risk is rarely zero.
For building managers implementing these upgrades, Sasse also advises clients to switch to higher-rated filters. Many HVAC systems in commercial and residential buildings use filters with MERV 8 ratings (for minimum efficiency reporting value), but the CDC recommends using MERV 13 filters, which can remove up to 90% of air particles, or a HEPA filter (for high efficiency particulate air) — what’s typically used by medical facilities. “A true HEPA filter is MERV 16, but not all systems can handle bigger filters because of the pressure they require,” Sasse says. More energy will be needed to heat and cool the additional amount of incoming air and to push existing air through denser filters. In some cases, HVAC systems may be too old to accommodate CDC-recommended changes, which would then require them to be replaced completely. “We’re sacrificing energy efficiency for health,” Sasse says. The payoff would be immediate, he says, pointing to a 2000 study from Harvard University looking at how air quality affected the use of sick leave among more than 3,000 employees across 40 buildings. The researchers found that office workers in moderately ventilated sections were 53% percent more likely than those in highly ventilated areas to take time off due to illness. Preventing those absences could save companies $480 per worker each year, according to the study, and as much as $22.8 billion nationally.