Although we are beyond the height of the COVID-19 pandemic, we continue to apply valuable lessons learned about airborne viruses, including the SARS-CoV-2 virus. While the pandemic has subsided, the importance of understanding how viruses spread through the air remains crucial for minimizing risks in healthcare settings, workplaces, and other indoor environments. This awareness isn’t just relevant for COVID-19; it informs our approach to combating all kinds of airborne diseases, including influenza and RSV. One of the key questions: how can HVAC systems reduce infection risk indoors?

Virus Transmission: Droplets and Aerosols

Scientists have confirmed that many respiratory viruses, including COVID-19, can spread through the air via droplets and aerosolized particles produced when people talk, cough, or sneeze. Droplets are larger particles that typically fall to the ground relatively quickly, while aerosols are smaller and can remain suspended in the air for longer periods, posing a lingering risk of transmission.

Current guidelines distinguish droplets from aerosols based on particle size: droplets are larger than 5 microns (μm), while aerosols are smaller than 5 μm. For reference, the SARS-CoV-2 virus itself is approximately 0.1 μm in diameter. This ability to become aerosolized means that, under the right conditions, viruses can remain in the air for extended periods, especially in poorly ventilated or crowded spaces.

How Do Airborne Particles Behave?

Both large and small droplets can be expelled during normal activities such as talking or breathing, and most particles, even those larger than 30 μm, can remain airborne in certain conditions. As large droplets dry, they shrink into smaller "droplet nuclei," which can remain suspended in the air. This process allows viral particles to disperse over long distances, potentially infecting people who were never in direct contact with the original carrier.
Humidity, temperature, and air circulation play significant roles in how long these particles remain in the air. For example, drier conditions can cause droplets to evaporate more quickly, increasing the potential for smaller, aerosolized particles to linger.

The Role of HVAC in Mitigating Airborne Viruses

Improving indoor air quality is one of the most effective ways to reduce the transmission of airborne viruses, and HVAC systems play a key role. Proper ventilation, humidity control, and filtration can drastically reduce the presence of virus-laden particles indoors, not only preventing COVID-19 but also mitigating future outbreaks of other airborne pathogens.
Here are some key considerations for optimizing your HVAC system to reduce airborne infection risks:

• Ventilation: Increasing the intake of outside air and enhancing the flow of air within indoor spaces is essential. Improved ventilation dilutes viral particles and helps remove them from enclosed spaces, particularly in areas with high occupancy.

• Humidity Control: The survival of many viruses is affected by humidity. Research suggests that viruses like SARS-CoV-2 survive longer in low-humidity environments. Maintaining indoor humidity levels between 40-60% can reduce viral transmission.

• Filtration: High-efficiency filters (e.g., MERV 13 or higher) can trap virus particles. However, not all HVAC systems are designed to handle these higher-efficiency filters. In such cases, a system upgrade or professional assessment may be necessary to improve air quality without overloading the system.

Working with Professionals to Optimize HVAC Systems

It's important to remember that HVAC systems are complex and interconnected. Ventilation, humidity control, and filtration all influence one another and require careful calibration to work effectively. Engaging a professional Testing, Adjusting, and Balancing (TAB) firm to assess and optimize your HVAC system can ensure that it is performing efficiently to minimize the risk of airborne viral transmission.

In a post-COVID world, where respiratory viruses continue to pose a threat, staying vigilant about indoor air quality remains a critical strategy for protecting public health. Properly managed HVAC systems, in conjunction with other public health measures, will help reduce the risk of airborne infection in all indoor environments, from hospitals to offices to homes.