When will indoor environments be safe? This question will seem counterintuitive to the many who have remained sequestered at home, away from public spaces, to avoid transmission of COVID-19. Yet new findings that the coronavirus spreads effectively via aerosols raise concerns about the dangers of indoor air. According to studies conducted in China and Japan, the risk of COVID-19 infection is between four and 19 times greater inside than outside.
Unlike in interior environments, microbes tend to disperse or get diluted in outdoor air and spaces. Lisa Brosseau, a researcher at the University of Minnesota Center for Infectious Disease Research and Policy, explained the difference to FiveThirtyEight using the analogy of food coloring. Outside, coronavirus transmission is akin to adding a few colored droplets to a river. Inside, it is like adding food coloring to a birdbath.
The two means of counteracting the spread of coronavirus indoors are ventilation and filtration. Fresh air delivery dilutes and replaces contaminated air, whereas appropriate filtration removes viruses altogether. Both strategies do more than just move the air. Many HVAC systems can be coaxed to increase airflow throughout a building—a strategy that may actually deliver virus-laden particles more effectively. Instead, architects and building owners should aim to improve fresh air circulation via operable apertures and effective HVAC system filtration. These goals should motivate us to look simultaneously to the past—and future—of architecture.
Before the proliferation of air conditioning, buildings were designed to encourage cross-ventilation. For example, early skyscrapers were supplied with operable windows and shallow floor plates to maximize air circulation as well as daylight. Sadly, such an approach today would be a radical departure from standard practice. With the exception of residential dwellings, fixed windows and deep floor plates are now default design characteristics for many buildings, given the assumption that air conditioning now satisfies climate requirements. Unfortunately, sick building syndrome (SBS) and now COVID-19 reveal that these structures actually serve as Petri dishes for illness.
Reversing this unhealthy paradigm in existing buildings is a daunting prospect that requires replacing exterior windows, re-engineering HVAC controls, and even punching holes in deep floor plates. That said, environmental retrofits, especially if they offer future cost savings by making buildings more energy efficient, can be a way to pursue these larger projects. Green building programs and industry references such as the LEED rating system, ASHRAE 62.1-2007, and the Carbon Trust Good Practices Guide 237 recommend operable windows as a means to improve natural ventilation and save energy. Although more expensive, operable windows are often less difficult to install in building retrofits than fixed apertures. “Typically, it is easier and often preferred to install operable windows when completing retrofit projects, because you can conceal the anchor fasteners between the sash and frame and often forgo the need for anchor clips,” says Steven Saffell, the technical director with the Fenestration and Glazing Industry Alliance.
HVAC systems also require upgrades for human health, as most are not equipped to reduce coronavirus transmission. In fact, the typical building HVAC system has recently been labeled a virus superspreader. In an example study in Guangzhou, China, 10 people from three families contracted COVID-19 from ducted air within a single restaurant. In addition to increasing the exchange rate to reduce recirculated air, these systems may be improved with better filtration technology. The current standard is High-Efficiency Particulate Air (HEPA) filtration, which removes particles 0.3 microns in size. However, a COVID-19 particle is approximately 0.1 microns, small enough to pass through a HEPA filter.
Researchers at the University of Houston have developed a new filter that effectively traps and destroys the coronavirus. Made of foamed nickel, the filter is porous enough to allow air passage. Unlike conventional filters, however, it is folded into a shape with multiple compartments that facilitate particle capture. Electrical wires deliver heat to the nickel foam, causing its temperature to rise to 250°C—sufficient to destroy the virus. In tests, this “catch and kill” filter eliminated 99.8% of COVID-19 particles in one pass.
Another air purification strategy involves the use of UVC light. Scientists at Columbia University Irving Medical Center have developed a far-UVC light (wavelength of 222 nm) that kills airborne SARS-CoV-2 viruses. While germicidal UVC light has been used for decades to disinfect spaces in hospitals, its typical wavelength of 245 nm is damaging to living cells. The far-UVC version is safe for human occupants yet still effective against 99.9% of viral particles. (Far-UVC light consists of radiation wavelengths of up to around 200 nm, and is not visible to the human eye.) “Because it’s safe to use in occupied spaces like hospitals, buses, planes, trains, train stations, schools, restaurants, offices, theaters, gyms, and anywhere that people gather indoors, far-UVC light could be used in combination with other measures, like wearing face masks and washing hands, to limit the transmission of SARS-CoV-2 and other viruses,” said biophysics professor David Brenner in a Columbia press release.
The newfound imperative to revisit airflow in architecture—by looking to the past and the future—reinforces the importance of invisible factors in buildings. This is an enlightening realization for a profession that prioritizes the visible. In his essay “Improving the Weather: On Architectural Comforts and Climates,” Andrew Cruse, AIA, writes that despite the critical role of the interior climate, “architects typically outsource its creation to mechanical engineers,” who target a narrow temperature and humidity band within hermetically controlled environments. Cruse, an architecture professor at the Knowlton School at The Ohio State University, advocates that architects embrace the alternative Adaptive Thermal Comfort model, arguing that “the formal, spatial, and material intelligence architects bring to the design process can further advance the goal of a more comfortable, less energy-intensive architecture.”
ATC is based on studies that show that a closer connection to the environment allows for a wider range of comfort preferences among users. Such an approach necessitates the use of operable windows as a means for building occupants to deliver fresh air and have more control over their health.
For climate-attuned design firms like Tokyo-based Tezuka Architects, operable apertures are also a fundamental design ingredient. “For many reasons, architects have used fixed windows,” says partner Takaharu Tezuka. “However, we always feel that to open a window has a stronger meaning, and makes better architecture. And so I think our projects are really dependent on the window. The window must be open.”