HVAC Strategies to Reduce Airborne Pathogens like COVID-19

By Nate Echtenkamp and Emily Waldenmeyer, Professional Engineers at The Beck Group

SARS-CoV-2, the virus that causes COVID-19, became a global pandemic overnight, changing almost every aspect of our lives, including how we design and build.

Through insight provided by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE), we know that ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the concentration of airborne pathogens and thus the risk of transmission through the air.

Evaluating HVAC systems as a preventative measure in spreading the virus is now a priority for building owners, operators, and occupants. When evaluating your system, we recommend considering five ASHRAE-backed strategies.

Upgrade your mechanical filters to MERV-13 or higher

MECHANICAL FILTERS

• Replacing standard MERV-8 filters with higher rated ones is a simple, yet effective way to reduce the concentration of airborne transmitted illnesses.
• MERV stands for “Minimum Efficiency Reporting Value.” A higher MERV rating indicates a higher filter efficiency. A 95 percent-efficient MERV-13 filter is roughly the equivalent of N95 masks worn by healthcare workers.
• We recommend a mechanical engineer assess HVAC supply and return fans because most high-efficiency filters create a large pressure drop. Increases in fan power requirements also translate to increased energy consumption.
• No filter is 100 percent effective, and even HEPA filters, which are 99 percent efficient, may still allow airborne pathogens to pass through.

ELECTRONIC AIR FILTERS

• Consider transitioning to electronic air filters if your system cannot take on the additional pressure drop created by a high-efficiency mechanical filter.
• These filters combine passive filtration with electrostatic attraction. A DC voltage creates an electrostatic field inside the filter, attracting particles to the media, resulting in high-performance contaminant removal, low-pressure drop, and a longer maintenance cycle.
• A mechanical engineer must select and size electronic air filters. Compared to mechanical filters, the cost for these filters is higher, but they require less maintenance over time while also using less fan energy.

Use Bi-Polar Ionization to eliminate airborne pathogens in the air and space

• Bi-polar ionization creates charged ions in the air that attract and inactivate airborne contaminants, including viruses, bacteria, mold, fungi, and VOCs.
• The devices can be centrally located in the air handling unit or the supply duct with little impact on the design and operation of the HVAC system.
• We recommend careful consideration of the manufacturer data, as peer-reviewed academic studies are not available on this emerging technology concerning its impact on viruses.
• Some bi-polar ionization products produce ozone. If you consider this type of product, it must carry the UL 2998 listing for non-ozone-producing performance.

Consider Ultraviolet Germicidal Irradiation to inactivate airborne viruses

• A narrow portion of the ultraviolet spectrum has proven effective at disrupting and breaking down the DNA of microbiological organisms. Viruses are susceptible because UV-C radiation inactivates a virus’s ability to replicate, making it non-infectious.
• Installing UV-C lamps downstream from cooling coils helps disinfect the coil and drain pan, where many biological contaminants flourish. There are also opportunities to mount lamps in supply air ducts.
• UV lamps do not substantially increase power consumption, nor do they negatively affect the performance of air handling equipment.
• UV-C radiation can irritate skin and eyes, so proper safety cutout switches and PPE are necessary. Some products may produce ozone, so it is essential to choose one with the UL 2998 listing for non-ozone-producing performance.

Improve ventilation with higher flow rates of fresh air to dilute pathogens

• One of the most straightforward strategies to consider implementing is increasing the amount of fresh air in a facility. Research shows that increasing ventilation rates of outside air can help dilute internally generated contaminants like VOCs, pathogens, and allergens.
• This approach may result in increased HVAC heating and cooling loads and increased annual energy consumption. A mechanical engineer can help to evaluate this strategy.

Maintain at least 40 percent relative humidity to minimize the time pathogens are airborne

• The optimal range for relative humidity should remain between 40 and 60 percent in the occupied space. The following may contribute to increased transmissibility at a low relative humidity (<40 percent):
• Faster evaporation of airborne droplets containing viral agents results in smaller particles, which are more easily airborne.
• A drier space condition may desiccate the mucus membranes of the sinus and lungs, making a person more susceptible to respiratory virus infections.
• A humidifier is critical in maintaining relative humidity levels, especially in colder months. Humidifiers are installed in air handling units or supply air ducts and consume additional water and energy.

The strategies in this list differ in cost and complexity. For more information and to begin implementing, please contact:

Nate Echtenkamp P.E. | 815-621-3130