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What Makes Building Ventilation Good Enough to Withstand a Pandemic?

Here’s what it takes to upgrade HVAC systems — and how to know if particular indoor spaces have done it. 


What Makes Building Ventilation Good Enough to Withstand a Pandemic?

Here’s what it takes to upgrade HVAC systems — and how to know if particular indoor spaces have done it. 

HVAC systems are taking center stage as more people contemplate a future return to indoor spaces. 

HVAC systems are taking center stage as more people contemplate a future return to indoor spaces. 

Photographer: Liyao Xie/Moment RF
HVAC systems are taking center stage as more people contemplate a future return to indoor spaces. 
Photographer: Liyao Xie/Moment RF

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.

David Sasse at the San Francisco-based building inspection firm Healthy Building Science says they’ve seen a bump in HVAC inspection requests related to Covid over the last few months. But not every building manager can afford the upgrades or wants to cover the expense — upfront costs can be in the thousands of dollars and increased energy use can add to the price tag. 

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. 

So what makes for good ventilation? And how do you know if you have it? 

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. 

Newell says that the CDC’s guidelines largely track with recommendations from his own firm, Building Equinox. But he says they’re not specific enough about the right levels of air flow for these variable building types and uses. “How can a patron, employee, teacher, or worshipper know if proper ventilation is occurring?” Newell says. 

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

Another option is to ask the manager of a building you enter regularly if they’re meeting standards set by ASHRAE, what kinds of filters are in use, or if they’ve made any HVAC upgrades recently. If you have to be in a small, airtight space, look for and stay near open windows. 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. But Steve Nadel, executive director of the American Council for an Energy-Efficient Economy, isn’t too concerned about new ventilation systems undoing progress on building efficiency — as long as building managers follow CDC guidelines and don’t pull in more fresh air than what’s really necessary.

One thing that would make it easier to ensure the quality of building safety is to improve building standards across the board. Newell has been calling for ventilation standards to be updated to prepare for potential future pandemics, starting with doubling the minimum requirement of 20 cfm per person to 40 cfm per person — which corresponds with a safer CO2 reading.

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.

Studies have shown better air also boosts students’ performance. In fact, the $900 billion Covid-19 stimulus bill signed into law last month included a $54.3 billion fund to help upgrade HVAC systems in K-12 schools, many of which harbor unhealthy learning environments.

Plus, “when you think about the expenses that might be required to improve ventilation everywhere, we're talking about jobs,” Newell adds. “All of that money goes to paying someone to drill holes, to put in sheet metal and to add filter systems, so it's very productive spending.”

(An earlier version of this story said the Covid-19 stimulus bill was worth $900 million, not $900 billion. )