Last week the Wall Street Journal ran a story about how proper ventilation of rooms can help prevent the spread of COVID-19 indoors. Japanese twitter responded in particularly derisive fashion by pointing out that in Japan proper ventilation was considered a pillar of the country’s anti-COVID measures as long ago as February as part of the government’s san-mitsu strategy, which told people to avoid “close” contact with others in “closed” rooms. Generally speaking, this strategy covered commercial, educational, or work spaces, since those were the most problemantic places in terms of keeping people safe from the spread of the virus. The operational logic then and now is that the virus doesn’t survive as long in the open, and so bringing the outdoors inside is a good way of keeping it at bay. For businesses, that means opening windows and/or optimizing ventilation systems to keep air moving through the space.

In Japan, however, greater attention is now being paid to transmission within homes, among family members. Coverage tends toward the inevitability of being infected by a loved one, since there is little you can do about your living situation. However, we would be very interested in seeing a study showing the relationship between intra-household infection rates and specific home layouts and other structural conditions. The first question that comes to mind is whether air conditioning systems help or hinder the spread of the virus. Generally speaking, the virus is in its best element in droplets of saliva expelled while talking or breathing, but scientists also talk about aerosol transmission, meaning the virus itself is carried on air currents. These particles can travel greater distances than droplets because they are much lighter and can still infect others by passing into their lungs when they inhale. Scientists are still debating the scale of infection due to aerosol transmission, but one thing that seems certain is that air currents in closed spaces are instrumental in propelling the virus and keeping it viable for longer periods of time than would happen outdoors or in indoor spaces with air flow passages that connect to the outdoors. Air conditioners are typically heat exchange mechanisms, and the public may misinterpret that to mean they exchange outside air for inside air, but that’s not really the case. Mainly they recirculate inside air and expel the ambient heat through outdoor fans. Consequently, there’s the possibility that if there are virulent particles in the inside air AC units may increase the possibility of causing those particles to enter into the bodies of humans in that space, and this is the main issue, especially in Japan where air conditioning, at least in residences, is a modular affair. Central air conditioning usually comes with filters that may be able to take out virulent particles (though viruses are really, really small). Apparently, some manufacturers have been touting anti-COVID features this summer, but one has to take such claims with a handful of salt. Daikin, to its credit, has been up front about air circulation and says that people should open their windows and use circulators and fans to facilitate ventilation. In other words, don’t count on their air conditioners. Because in the end the cooling efficacy of AC is dependent on how closed the room is and the efficiency of the insulation. That means all windows have to be closed tight and that there be no drafts in order to make full use of your AC. The entire home becomes a closed system, and the potential ventilation advantages of the AC unit-fan relationship is reduced by that much. The thing is, we just don’t really know now how this plays into viral infection rates. Read More