In the wake of COVID-19, there’s never been a greater emphasis on indoor air quality (IAQ). Whereas it might not have been the most glamorous topic pre-pandemic—perish the thought!—interest in how air quality can improve building health seems to have increased in direct proportion to the public’s understanding of how airborne infectious diseases are spread.
Is this the moment mechanical engineers have been waiting for, a chance for their discipline to put on a cape and become a superhero? According to two of SHP’s mechanical engineers, Jacob Faiola and Steve Tossey, the answer is a resounding YES! (Actually, Jacob and Steve love what they do so much, they are always having a superhero moment!)
But really, yes. COVID-19 has ushered in IAQ’s 15 minutes of fame. People are looking to HVAC systems to help limit the spread of viruses. And rightly so.
That’s not to suggest there isn’t still misinformation “floating” around. (Pun intended.) There is. So, we turned to Jacob and Steve to shed some UV-grade light and bust a few myths on the topic. We’re so glad they are on the case.
Myth: Filtration is a Good Way to Prevent the Spread of Viruses
Fact: This one is sort of half-true. Filtration is the baseline for catching dirt, particulate matter, larger microbes and bacteria; if it wasn’t, air filters wouldn’t be an essential component of our HVAC systems. However, the ability of filters to catch everything in the air is limited.
Low-efficiency filters, used in warehouses and the like, catch large particles, like pollen, dust and small children. High-efficiency filters—ike the industrial-strength versions found in hospital and other healthcare settings—can catch much, much smaller particles, such as viruses.
But what we’ve found is that your average filters cannot reasonably or feasibly filter tiny airborne viral particles. So, in that sense, no, filters are not effective at slowing the spread of disease.
Myth: UV Lights Stop the Spread of Disease
Fact: Okay. This one is true… or perhaps we should say, true-ish. Because the kind of UV light you’re probably thinking of—the kind that comes from the sun? It won’t do diddly to stop a virus in its tracks.
You see, the kind of ultraviolet light that can disinfect surfaces, UVC light, has been in use for over 100 years and is extremely effective. But its applications are usually limited to use in unoccupied spaces, like recently vacated hospital rooms, buses and subway trains when parked overnight, circulating paper money (we’re not making this up…) and the cooling coils of air handling units.
Why? Because UVC is extremely dangerous. In order to work, the UVC light must shine directly on a virus for several seconds or at a very high intensity. In addition to killing bacteria and viruses, these strong UV rays damage the cells of other living things, like skin and eye lenses, which is why protective gear is always required for safe and proper UVC light operation.
And this only applies to viruses living on hard surfaces. Industry research is still trying to find a way to safely and reliably use UVC in air handling systems. In other words, UV light doesn’t have any effect on viruses sailing through the air on their flying trap-sneeze.
Myth: Recirculating Indoor Air Spreads Disease
Fact: Viruses cannot walk, swim, or fly on their own. When at rest they remain at rest; when in motion, they remain in motion. They only move when an outside force—someone or something—moves them. And once virus molecules drop to the floor, they are unable to overcome their own inertia and get moving again.
In buildings with large central air handling systems, viruses tend not to float all the way back to return vents and their air handler fan. There’s just too much space for them to cover. Smaller, room-sized HVAC systems, like unit ventilators or window air conditioners, will pick up viruses and blow them back into the room… spreading them.
In any case, what every building has in common is… people!
Our bodies are a far more significant force affecting the airborne transfer of viruses than a typical air handler. Typical human exhaled breath is 5-6 percent water vapor—that’s the vehicle viruses hitch a ride on. Consider that human breath travels at about 10 mph, a cough moves at about 50 mph and the velocity of a sneeze is about 100 mph… sufficient momentum for effective germ-spreading. Given the fact that we provide both the vehicle and velocity viruses need to survive in the air, the relevant question is, “What can be done to reduce the likelihood that moving viruses will make it all the way to another person?
To that end, Jacob and Steve recommend three strategies for improving infectious disease control through IAQ. There are plenty of “solutions” being offered to help flatten the coronavirus curve, many with limited usefulness and capability. But with the right mechanical systems in place, IAQ really can have its superhero moment—and stop COVID-19 in its tracks.