It is important to think about filtration, ventilation and air cleaning in order to mitigate risk of COVID-19 transmission.

Let’s define some terms :

Droplets are propelled through the air, visible but fall to the ground after traveling 3-6 feet. Published research which has been replicated shows that droplets are only important when coughing and sneezing

Aerosols are much smaller than droplets (generally considered to be anywhere from 1 to 10 microns). They can be generated by talking, or by evaporation of droplets.

Aerosol (also referred to as “airborne”) transmission is similar to droplet transmission, except that the bits of fluid are so small that they can linger in the air for minutes up to 16 hours. Fears AC, Klimstra WB, Duprex P, et al. Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions. medRxiv 2020:2020.04.13.20063784. doi: 10.1101/2020.04.13.20063784

https://www.sciencedirect.com/science/article/abs/pii/S0360132320302183

Appropriate air filtration and ventilation ensures that adequate dilution is achieved where and when needed, avoiding the build-up of viral contamination

Ventilation is the replacement of stale or noxious air with fresh air to a space or building by natural or mechanical means (ISO, 2017). It controls how quickly room air is removed and replaced over a period of time. Ventilation plays a critical role in removing exhaled virus-laden air, thus lowering the overall concentration and therefore any subsequent dose inhaled by the occupants.

HEPA is a type of pleated mechanical air filter. It is an acronym for “high efficiency particulate air [filter]” (as officially defined by the U.S. Dept. of Energy). This type of air filter can remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm).

Public health messaging can be confusing. Scientists have issued a global statement through the World Health Organization stating that when it comes to COVID-19, the evidence overwhelmingly supports aerosol transmission.

With infectious diseases transmitted through aerosols, HVAC systems can have a major effect on the transmission from the primary host to secondary hosts. Decreasing exposure of secondary hosts is an important step in curtailing the spread of infectious diseases. HVAC systems impact the distribution and bio-burden of infectious aerosols.

https://www.ashrae.org/file%20library/about/position%20documents/pd_infectiousaerosols_2020.pdf

It is important to visualize the mechanism by which COVID-19 is transmitted, in order that individuals and institutions can understand how to protect themselves.

The closer you are to someone releasing virus-carrying aerosols, the more likely you are to breathe in larger amounts of virus. We know from detailed, rigorous studies that when individuals talk in close proximity, aerosols dominate transmission.

Superspreading events, where one person infects many, occur almost exclusively in indoor locations and are driving the pandemic. These observations are supported and explained by aerosols, and are very difficult or impossible to explain by droplets. https://www.medrxiv.org/content/10.1101/2020.02.28.20029272v2

Contact tracing shows that, when it comes to COVID-19, being outdoors is 20 times safer than being indoors, which argues that aerosol transmission is much more important than droplets. Outdoors, there’s plenty of air in which aerosols can become diluted; not so indoors.

As we move from warm weather outdoor activity season into autumn and winter indoor season, the Airscape HEPA.Tower provides an excellent ventilation solution to create fresh air indoors.

https://time.com/5883081/covid-19-transmitted-aerosols/

Since coronavirus is spread by breathing in respiratory aerosols from infected people, it stands to reason that avoiding breathing those aerosols is key to not getting COVID-19. One way to do that, according to a new study, is to keep humidity levels in indoor settings at 40 to 60 percent.

Researchers came to this conclusion after analyzing 10 international studies that were done between 2007 and 2020 looking at the rate of survival and infections of coronaviruses and influenza based on humidity levels in the air.

It was discovered that at higher humidity, the droplets grow faster, fall to the ground earlier and have less chance of inhalation by healthy people, meaning that viruses cannot spread as easily in humid conditions.

Although low humidity causes the droplets containing viruses to dry out more quickly, the survivability of the viruses still seems to remain high. Research concluded that other processes are more important for infection. If the relative humidity of indoor air is below 40 percent, the particles emitted by infected people absorb less water, remain lighter, fly further through the room and are more likely to be inhaled by healthy people. In addition, dry air also makes the mucous membranes in our noses dry and more permeable to viruses.

From the researchers’ point of view, more attention should be paid to indoor air to prevent future outbreaks of viral disease.

https://www.tropos.de/en/current-issues/press-releases/details/coronavirus-sars-cov-2-breitet-sich-bei-niedriger-luftfeuchtigkeit-in-innenraeumen-staerker-aus

HRV/ERV exhausts stale indoor air to the outside, and brings in fresh air from outside. This fresh air is then distributed throughout the home either by the HRV/ERV or by your furnace fan.

In the winter, the warm indoor air passes through the HRV/ERV core as its being exhausted and warms up the incoming fresh outside air. The the summer, the cycle is reversed and the cool indoor air cools down the hot outdoor air recovering the energy. The 2 airstreams never mix when passing through the HRV/ERV core.

https://www.ashrae.org/technical-resources/energy-recovery

During cold and inclement weather, high efficiency filter ventilation systems that recirculate some of the air are an excellent solution.

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