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.
This question is quite personal for us because we don’t have AC in our home. Friends and acquaintances shake their head at what they see as a pointless and even dangerous stubbornness toward maintaining a small environmental footprint, not to mention our avoidance of large electricity bills. Neither of us grew up with air conditioning, and even though we did buy and install units in homes we lived in as adults, we found we didn’t really like using them for reasons both economical and health-minded, and so when we decided to build our house we purposely found a location where the effects of sunlight in the summer were mitigated by surrounding vegetation and wind currents. There are, of course, designers who know exactly how to build structures that take advantage of local conditions to maximize cooling principles, and, unfortunately, we couldn’t afford such designers, but the one we did hire did the best they could. We live in a clearing in a forest on the top of a hill, and outdoor temperatures in summer are probably two to three degrees lower than surrounding areas in terms of the heat index. We have few rooms and lots of windows so as to maximize air flow throughout the house, though we’ve discovered that windows can exacerbate heat problems and thus resort to makeshift measures such as bamboo sudare to reduce the intensity of the sun’s rays. When the sunlight is particularly brutal, we even close the louvered amado (storm shutters). In addition, we have installed ceiling fans throughout the house and use small, portable circulators to help bring cool outdoor air into the rooms. This approach works most of the time. The problem, especially this summer, has been a lack of breezes, which means there is very little movement of air both within and without the house. It can get unpleasant.
But we have plenty of ventilation, and it should be noted that, traditionally, Japanese housing was designed with ventilation in mind. Though a lot of jokes are made about Japan’s cultural appropriation of four seasons, the fact remains that the winters can be terribly cold and the summers punishingly hot (and humid), and the old kominka design addressed these climactic realities ingeniously. The sleeping, dining, and socializing functions were in the core of the one-story house. This core was surrounded on one or more sides by a roka hallway, which acted as a kind of buffer zone between the living quarters and the outside. In the winter, the living quarters had an extra layer of protection from the outdoors, and thus heating countermeasures were more effective. In the summer, since all rooms within the house had sliding “fusuma” doors, the entire interior could be open to the outdoors, with the roka acting as a kind of breeze conduit. In addition, kominka were slightly elevated off the ground, adding another layer of cooling ventilation underneath the structure. By today’s technological standards, it sounds primitive — though Japanese people still get by nicely with coping mechanisms such as mosquito coils and uchiwa fans — but it did the trick and remains a kind of model for what is now known as the passive house. In any event, kominka definitely lowers the change of aerosol virus transmission, at least in the summer.
This type of thinking also went into the design of Japan’s first real mass-produced apartment blocks. The kodan structures built by the government housing authority in the 1950s, 60s, and 70s were also smart in terms of ventilation. It was not until the go-go 1980s that Japanese apartments would be designed for air conditioning, so until then they had to make do with good ventilation. Kodan apartments are typically entered from the “side” through a stairwell, thus leaving the two “ends” of the unit free to install windows. The whole apartment gets maximum cross ventilation as a result. The drawback, of course, is that such a design has no facility for elevators (thus they were limited to five floors), not to mention fire escapes, so when air conditioning became affordable to most people, apartment construction changed accordingly. Now, most apartment buildings have elevators that exit onto an outer open-air corridor from which individual apartments are entered. On this “end” of the unit, for security’s sake, windows are minimized, but in any case the interior layout is built to the landlord’s or the developer’s advantage rather than to the occupant’s, with lots of small rooms carved out of a large rectangle. Ventilation is not a priority, and no one really cares because they have air conditioning and verandas where they can dry their laundry.
Of course, this type of apartment is not just something you find in Japan. In some cities, especially Paris and some older part of New York, apartment buildings have light wells or even courtyards, central cavities that provide a means of generating cross ventilation in individual apartment units, but air conditioning has mostly obviated the need for cross ventilation in collective housing situations. With global warming a real threat now, AC has become a concern, since it adds to the heat island phenomenon in major cities. That’s even beyond the amount of energy needed to run AC systems. It’s become a vicious circle that seems endless. AC adds to global warming by boosting temperatures, thus making AC itself indispensable (the elderly are particularly susceptible to heat stroke, even indoors), and perpetuating the destructive cycle. So cross ventilation is not just a measure that can help mitigate the transmission of COVID-19. It is nature’s way of maintaining balance in a variety of ways that we may not even have thought of yet.