Can Building Science Help Reduce the Risk of COVID-19?
Experts believe that the coronavirus is transmitted by person-to-person contact and by contact with virus-laden droplets expelled by an infected person’s coughing and sneezing. Coughs and sneezes certainly suggest “airborne” to most people, but such droplets travel only about 6 feet before falling out of the air and settling on surfaces.
Hefferman concludes that “as far as researchers know now, air is not the vector by which the virus spreads, and that air purifiers should not be considered protective.”
Is the virus airborne?
A recent study out of UCLA found that the virus can stay floating in the air. The author of the not-yet -released study tells NPR that “the virus can survive up to 72 hours on stainless steel and plastic surfaces and on cardboard up to 24 hours,” and also that “the virus can remain viable floating in the air for some number of hours. The experiments went out to three hours, and, you know, there were still viable viruses present.” So ventilation could become very important.
In an open letter to the W.H.O., 239 scientists in 32 countries have outlined the evidence showing that smaller particles can infect people, and are calling for the agency to revise its recommendations. The researchers plan to publish their letter in a scientific journal next week.
Another important point is that in a Passivhaus building, the interior air is not filtered and recirculated, as it is in normal homes; it is exhausted and replaced with fresh outside air through the Heat Recovery Ventilator. Because they are not recirculating the air, they do not need HEPA filters, which add a lot of flow restriction and would need more power. The filter on the HRV might clean the outside air of pollen and dust but not COVID-19 if someone happens to be coughing into your air intake. But if you live in a place with recirculated air, that HEPA filter might help.
Ventilation is crucial. Bringing in more filtered outdoor air in buildings heating/cooling systems (or opening windows in buildings that don’t) helps extract airborne contaminants from the building, making infection less likely.
For years, we have been doing the opposite: sealing our windows shut and recirculating air. Just look at the residential code requirements for ventilation. The result are homes, schools, and office buildings that are chronically under-ventilated. This not only gives a boost to disease transmission, including common scourges like the coronarovirus or the common flu, but can also significantly impair cognitive function.
If you don’t have mechanical ventilation in your home, make yourself a calendar reminder to open up the windows a few times per day for as long as you can. Obviously, depending on your climate this may prove difficult for thermal comfort or humidity introduction into your space, but still generally a good idea.
The real issue is the humidity
© Recommended humidity/ASHRAE
As the weather gets warmer this is less of a problem, but there is lots of research that keeping the humidity between 35% and 55% reduces transmission of viruses; as Peter Yost of Green Building Advisor notes, “The higher the RH the more quickly the virus falls to the floor.” Elrond Burrell points us to research by Doctor and Architect Stephanie H. Taylor that was written about flu transmission but is probably relevant:
Research continues to reveal that dry indoor air is connected to MORE infections in people. This helps explain why the flu season is in the winter, when cold outdoor air – already low in moisture, is brought inside and further dried out when warmed. The obvious solution is to provide indoor humidification to achieve a beneficial relative humidity (RH) level between 40 to 60%.
The non-recirculating air is really the best benefit. Direct exhaust from wet rooms & fresh supply to living spaces is probably going to become an essential feature of EVERY building.
© Stephanie H. Taylor