In 2019, Americans prepared for another long, hot summer by purchasing 5.4 million air-conditioning units.
But a year on, with forecasters predicting blisteringly hot summer weather for much of America, some experts are saying it isn't the best idea to blast them too furiously. They cited two studies which found that coronavirus particles could be blown further afield by heating, ventilation, and air-conditioning systems.
Most humans spend 90% of their lives in built environments like buildings, cars, and public transport, breathing in shared indoor air, and touching potentially contaminated surfaces.
"Air conditioners will take air and re-circulate it through the room, and it's through that mechanism that these coronavirus droplets can be transmitted," said Qingyan Chen, a mechanical engineering professor at Purdue University.
Chen pointed to what happened on the Diamond Princess cruise shop, where 700 out of 3,000 passengers got sick. "After quarantine, many people still got sick on the ship and I suspect that the air conditioning system could played a role there."
Other experts are skeptical. Epidemiologist Meghan May, a professor at the University of New England College of Osteopathic Medicine, said that keeping physical distances is a far more important consideration than worrying about air-conditioning. "I'm not yet convinced it is a concern," May told Business Insider. "But if it is, I would say air-conditioning is the least of your worries in mass transit or apartments."
Here's what you need to know about home AC units and viral spread:
Air-conditioning blew coronavirus droplets around a restaurant, infecting 9 people
The main study that has raised concerns about air-conditioning during the pandemic was one published April 2 about a restaurant in China.
In a research letter for the journal Emerging Infectious Diseases, researchers linked nine coronavirus infections in Guangzhou to one 63-year-old woman. Most hadn't had any direct contact with her, but sat on neighboring tables at a restaurant. It seems the eatery's ventilation blew viral particles around.
It is alarming because it implies that air-conditioning can help spread disease, but heartening because the droplets didn't seem to blow far: In a restaurant with 83 people, only 10 got sick. It may also hold important lessons for restaurants looking to open up for the summer.
Turn off the AC and open a window if someone in your home has COVID-19, or has been exposed to the virus
A central air-conditioning system uses a fan to draw warm air from the room towards a return vent, blowing it past coils that absorb heat and cool the air. The fresh air is then forced out into the home, and the heat is blown into the outside world.
In the typical American home with a central air-conditioning system, there is no option to use outside air. In homes where everyone is healthy, this is fine, but in homes where someone has the novel coronavirus or has been exposed to the virus, this can be dangerous.
A recent study by the University of Oregon and the University of California, Davis, found the best way to ventilate a remove to limit viral spread is to open a window.
"Some experts will recommend that you should turn off air conditioning systems, and I don't think that's a good approach," said Chen. "If you don't get enough fresh air, especially in the interior of a building, that will just create incubators of infection."
In a house with a sick person, Chen recommends turning off the air and opening a window instead, because the AC system might handily re-circulate coronavirus droplets from one room in the home to another.
Opening a window is crucial. "When you open a window, you get a lot more outside air, which will lower the possible concentration of coronavirus [droplets] inside of the room," said Chen.
If you have air-conditioning on, and a sick person in the house, it's a good idea to limit the flow through your home
But turning off the AC to the whole home is not always a realistic option, for example if it's 90-degree weather, or if someone in your home has asthma or seasonal allergies, and can't be in a room with open windows.
In that case, the most important thing to do is keep sick people away from air vents.
"If central air disperses infectious virus, being close to the exhaust point is a risk factor," said epidemiologist Meghan May, of the University of New England College of Osteopathic Medicine. "If a person has a sick relative and central air, therefore, keep the sick person distant from the intake point."
You can use duct tape to seal the return vents in the room of someone in self-isolation.
Don't let it get too cold
Having proper ventilation is a crucial part of preventing infection. "We actually recommend air conditioning, as a means to prevent [viral spread]," said Ana Rule, assistant professor at the department of Environmental Health and Engineering at the Johns Hopkins Bloomberg School of Public Health.
Rule's research on COVID-19 found, that after social distancing, ventilation was the second most significant part of preventing infection spread, because air conditioning prevents infection by removing air from a room where there are virus droplets.
After people staying home, eliminating the virus from streets and public spaces, removing contaminated air from a space is key," said Rule. "A well designed and well maintained ventilation system should never contribute to spreading."
That said, it's imperative that you maintain a warmer temperature than you normally would to help prevent the virus from lasting for long lengths of time on surfaces like tables or laptops.
"The virus loses infectivity with increasing temperature," said Rule, "so keep your home less cold than you usually like it in the summer."
Rule recommended keeping the thermostat between 70-75 degrees, and not being overzealous in changing air conditioning filters, because those actually get more effective over time, as dust particles accumulate. She also said people should consider buying a humidifier or an air purifier, which uses a filter to capture 99% of particles.
"I think we have to assume, at least in the United States, that spaces are reasonably well-ventilated and well-air conditioned," said Rule.
Source: Business Insider