(Bloomberg Opinion) -- Covid-19 has taught the world quite a few things. Not least, the value of fresh air. Indoors — in restaurants, church halls, nursing homes, meatpacking plants — the contagion spread easily, as virus particles exhaled by the infected hung in the air to be inhaled by new victims. Outside, flows of air dispersed those same aerosols enough to bring the spread of the disease almost to a stop. Schools, offices and other indoor spaces need better ventilation in order to minimize the harm from new coronaviruses, cold and flu viruses, and every other sort of airborne pathogen.
This calls for rethinking the way indoor air is controlled. New guidance on safer ventilation in schools is urgent, and currently under discussion. State and local building codes should also be revised. Economizing on buildings’ use of energy is vital in the fight against climate change — but the need for effective ventilation, which often requires more energy, can no longer be ignored.
Most big systems for heating, ventilation and air conditioning circulate air quite slowly, even when operating at their best. Fresh or filtered air is fanned in from the ceiling, mixes with air in the room, and eventually moves out through vents also in the ceiling. Typically, most of the air in a room changes about twice an hour, unevenly. That’s fine for maintaining comfortable temperature and humidity without wasting energy, but not for clearing exhaled virus particles from a room full of people. Such particles are heavier than gases, don’t mix well and can remain suspended for hours.
What’s needed is “displacement ventilation,” which sends cool air through vents low in the room and draws out warmer air through the ceiling. Some hospitals and other buildings (especially in Scandinavia) have these systems. They should be preferred in new construction — but what about existing offices, schools and other buildings that aren’t already equipped?
During the pandemic, the American Society of Heating, Refrigerating and Air-Conditioning Engineers recommended that buildings filter air more thoroughly (with portable high-efficiency systems, if necessary) and keep ventilation systems running for hours before and after people are present. This seems sensible, though more research is needed on using filtration and ultraviolet irradiation to minimize the risk of infection.
How well plug-in ionizers and other air “purifiers” clear virus particles is disputed. They certainly can’t be relied on to do the job themselves. Ionizers also release ozone, which can cause trouble for people with asthma. Too many schools have spent Covid relief funds on such devices while neglecting other measures (such as better filtration, or opening the windows). Most classrooms are still poorly ventilated. Stagnant air, thick with exhaled carbon dioxide, helps spread disease and hinders student performance.
It takes power to move and filter air adequately, but Covid has shown that regulators need to face this trade-off. As well as changing building codes, states should require building operators to tell occupants how well their air is being ventilated, so they can judge what’s safe and adjust their behavior when infectious diseases are spreading. The threat of contagion rises when people talk, laugh, sing, sneeze or cough — rendering it virtually impossible to make any room perfectly safe. Masks and social distancing help. Again, though, there’s a lot to learn about using placement and room-capacity limits to mitigate the risk.
Two years ago, not many policy makers had “quality of building ventilation” on their list of priorities. Score it as one more thing that, thanks to the pandemic, needs to change.
Editorials are written by the Bloomberg Opinion editorial board.
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