Three Strategies for Improving Infectious Disease Control through Indoor Air Quality
The benefits of a high-quality HVAC system have always been important, but historically, have largely flown under the radar… until there’s a problem. Consider your own daily routine: You likely notice when the temperature is uncomfortable, humidity is too high, something smells bad. Pre-coronavirus, so-called “bad air” wasn’t considered life-threatening in the short-term.
But since COVID-19 hit – and because Americans spend almost 90% of their lives indoors – it seems building owners, facility managers and even the general public have become more aware of how important mechanical systems are to the overall health of our buildings. As a result, SHP’s mechanical engineering team predicts there will be an even stronger emphasis on creating healthier indoor environments, driven by stronger indoor air quality (IAQ) components and more sophisticated and clean mechanical systems.
In fact, many of our clients are already looking to HVAC systems to help limit the spread of viruses, especially since the World Health Organization acknowledged that coronavirus can be airborne in crowded, poorly ventilated places. SHP engineers Jacob Faiola and Steve Tossey report an uptick in interest in the long-term consequences of investing in systems that can properly address the spread of infectious diseases. Here, they offer three options for cleaner air in the wake of the coronavirus.
First, Some Basic Science
There are two ways viruses spread: inhalation and ingestion. Although most any air movement can cause viruses to spread, according to the Centers for Disease Control, the main route of transmission of COVID-19 is through respiratory droplets generated when an infected person coughs or sneezes. The virus hitches a ride on a small water droplet and poof! It becomes airborne.
Any person who is in close contact with someone who has coronavirus infection is at risk of being exposed to respiratory droplets in the air. Droplets may also land on surfaces, where the virus could remain for several hours to days. This is why washing your hands before picking up your corn chips (or picking your nose) will stop the spread.
Second, Some Basic Best Practices
Keep in mind: The most important air cleaning methods – and slowing the spread of disease – are air exchange with the outdoors and particle filtration.
- Air exchange with the outdoors: The atmosphere is full of ions, created by sunlight, which break down the bonds of viral chemical structures… essentially rendering them neutral. Bringing that healthy outdoor air into the building is an important first step in slowing the spread.
- Particle filtration: Low efficiency filters catch large particles, like pollen and dust, while high efficiency filters can catch much, much smaller particles. Particle filters are an important air cleaning tool, however, their ability to catch everything you might inhale, including viruses, is limited.
So, what does work? To slow the spread of viruses through inhalation, Jacob and Steve recommend these three strategies.
Strategy #1: Displacement Ventilation
Most spaces use air mixing—that is, a combination of supply air and air that is already in a space—to provide air conditioning. Mixed airflow churns the air in a space, moving air and contaminants to all parts of the room.
Displacement ventilation gently delivers supply air through floor or baseboard vents. Heat from the people or equipment in the space causes the air to warm and then ascend, where it is removed from the room. Viruses or other airborne contaminants have more difficulty spreading from person to person.
Pros & Cons of Displacement Ventilation: Displacement ventilation is a great way to minimize swirling of air and random mixing of viruses. It also has the advantages of noise reduction, greater comfort via the elimination of drafts, and a decrease in overall energy use. But it’s also the kind of system that is best designed and installed at the beginning of a construction project. Existing HVAC systems are not easily (or inexpensively) converted to accommodate displacement ventilation.
Strategy #2: Relative Humidity
As previously noted, viruses travel on water vapor droplets. The second strategy for slowing viral spread, therefore, is maintaining proper relative humidity in a range of 40 to 60 percent.
The drier the air is, the faster water vapor evaporates; the faster water evaporates, the farther what’s left of the water vapor (and the virus) will travel before gravity pulls it to the ground. In other words, low relative humidity allows smaller and smaller particles to travel farther and farther distances through the air – and more deeply into our lungs. To make matters worse, low relative humidity also causes our respiratory tract to dry out, making our bodies less effective at catching water vapor droplets and other contaminants from the outset.
Pros & Cons of Relative Humidity: Adding humidity is a straightforward process, as humidifiers can be added to both new and existing HVAC systems or as stand-alone units in individual rooms. They have the additional benefits of increasing comfort and providing a better environment for wood floors, art and other objects that are sensitive to humidity.
Where humidifiers present a challenge, however, is the hassle of the ongoing maintenance. Humidifiers tend to be messy and leak water from time to time. Also, depending on water quality and configuration, they can create mineral deposits in the ductwork. In addition, larger central air systems require bigger ductwork and generally more complicated systems—which in turn require more plumbing, hardwired power supply and a steady stream of water. When added to the labor required to retrofit an existing system, humidification becomes a less attractive option.
Strategy #3: Bipolar Ionization
Like humidification, the third strategy for improved IAQ is very straightforward: turn the virus into something else.
A virus has a set of instructions for its reproduction. But it doesn’t contain any actual cell-building material. If the viruses can be broken up prior to merging with living cells, reproduction will not occur.
Ions, meanwhile, are atoms that are either missing an electron or have one electron too many. They crave stability, which they achieve by taking or giving an electron to a passing complex molecule… for example—you guessed it—a virus. The complex molecule’s atoms are transformed into simple atoms that are no longer bound together and can’t reproduce.
Enter bipolar ionization, which discharges ions into the airstream. These killer atoms are dispersed to all spaces, neutralizing particles and disrupting viruses. As a bonus, the ions also bond to dust and mold particles in the air, improving the efficiency and efficacy of filters to entrap smaller contaminants.
Pros & Cons of Bipolar Ionization: Bipolar ion generators are easy to add to the air handler or fan-coil unit of new or existing HVAC. In addition to requiring just about zero maintenance, bipolar ionization units prevent microbiological buildup on cooling coils. By keeping the cooling coils clean, heat transfer is improved, increasing overall energy efficiency and system costs. Bipolar ionization is also effective at reducing building odors—and who could complain about that?!
Good, Better, Best IAQ Solutions?
Displacement ventilation, relative humidity and bipolar ionization: are these good, better and best among current IAQ solutions for reducing COVID-19? It’s really difficult, maybe impossible, to say, though our engineering team continues to assess data daily from our manufacturing partners. Certainly, the pros and cons of each approach are factors, as are the age and health of your existing HVAC system, budget, maintenance capabilities, water and energy availability, and the all-important supply chain. (We’re already seeing a backlog of certain devices, with lead times pressing into September.)
For our money, though, bipolar ionization appears to be the most effective solution available on the market today. The technology has been around for years and has been proven at eliminating other airborne illnesses, such as SARS. Early lab results from coronavirus testing has demonstrated effectiveness at destroying 99 percent of the virus, among other potentially harmful organic matter.
It’s also worth noting that these three solutions aren’t mutually exclusive. According to Jacob and Steve, they work well with one another; some buildings our team is currently designing recommend all three systems.
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