Clearing the air: HVAC systems and COVID-19 mitigation

December 17, 2020

Written by Stephen T. Triphahn

Few will disagree that the year 2020 has earned a special place in the history books – one of infamy. Not since the great influenza pandemic of 1918 has American society been so heavily impacted by a public health emergency. And as we enter a new year with hope of at least some return to normalcy, we must accept the realization that COVID-19 will likely continue to challenge businesses and institutions into 2021, making it imperative that we take steps to make public spaces safer for all of us.

As 2020 unfolded, we learned more about the coronavirus and how it is transmitted. While contact with surfaces was a primary concern in the early days of the pandemic, we now know that airborne transmission from person to person is by far the most common source of spread. This, of course, has raised concerns in the minds of the managers of office buildings, hospitals, apartment buildings and other congregate working and living arrangements sharing HVAC systems. And while the jury remains out on the issue of HVAC transmission, the concerns are real. Fortunately, there are effective solutions.

Aerosols generated by coughs, sneezes and even loud talking have been shown to carry transmissible viral particles, hence the emphasis on masks and social distancing. However, because aerosols can linger in the air for a measurable period depending on the rate of air circulation, the importance of good ventilation and air filtration is gaining increasing attention among facilities managers.

A growing range of ventilation and air filtration options are currently available or are coming online for incorporation into new construction and for retrofitting existing HVAC systems. 

Layered filter systems

As the Centers for Disease Control and Prevention (CDC) and others have reported, the best mask designs incorporate multi-layered materials to effectively screen ambient droplets and particles. The same is true for HVAC systems. Layered filter systems installed in building HVAC equipment are proven ways to remove particles from air streams. Both fabric and fibrous filters working in concert will greatly improve the ability to filter potentially infectious agents from circulating airflows.

Germicidal Ultraviolet Systems

Studies have shown that UVC radiation, the frequency of ultraviolet light with the shortest wavelength and hence stronger than UVA and UVB, can be highly effective in destroying the outer protein coating of the 2002 SARS coronavirus. While today’s SARS-CoV-2 virus, which causes COVID-19, is somewhat different from its earlier cousin, it is likely that UVC can inactivate this virus as well. UVC is already being used to disinfect vacant hospital rooms, hotel suites and other occupancies, and can be equally effective when installed in commercial HVAC systems.

Plasma Ionization Systems

Originally designed for use in hospitals, plasma ionization systems are highly effective in removing bacteria, viruses and other allergens from interior air and are gaining increasing application in office and commercial occupancies. A plasma purifier forms negative or positive ions as air circulates over the ionization tubes.

The units clear the air in three complementary ways. First, they reduce particles in the air by bonding with toxins, making them easier for filters to capture. They also sterilize bacteria and mold, disrupting their ability to multiply. Finally, they are adept at removing a wide variety of odors, both organic and chemical in nature.

Significantly, a recent University of San Diego report suggests that ionizers can reduce the presence of COVID-19 coronavirus by 99.4% in 30 minutes.

Amitigation case study

Recently, the WT Group worked with a local city government intent on retrofitting the HVAC systems on several municipal buildings, including city hall, public works and the police station.  The age of the air handling units (AHUs) on one of the buildings could not be determined but was estimated to be at least 30 years. Other buildings had AHUs in service for shorter durations, but which would still benefit from air quality and filtration upgrades.

In the case of the oldest units, WT Group engineers recommended bipolar ionization systems in all three AHUs. The upgrades consisted of linear arrays of ionization-producing elements incorporated in the coil sections of the units. The equipment will be easy to maintain and economical to operate, since the recommended solution does not include parts requiring regular replacement and only needs periodic cleaning of the elements. And the units have low amp draw, allowing them to be powered from any nearby 120-volt circuit.

For additional filtration efficiency, our team recommended portable filtration units to be installed in spaces with higher occupancies, such as conference rooms, open offices, assembly rooms, etc. The units incorporate HEPA filtration and can be equipped with UVC light sterilization or bipolar ionization. Our recommendation was to use the bipolar ionization option. The portable units plug into a standard 120-volt outlet and have casters for easy moving.

Building resilience for an uncertain future

The COVID-19 pandemic will be defeated, but it will not happen overnight. Businesses want to return employees safely to the workplace and all of us want to return to a semblance of pre-pandemic life, but in truth life may never be entirely the same again. Looking back on the Asian SARS epidemic of 2002, the Ebola outbreak of 2014 and now COVID-19, there is little doubt that society will face similar events in the future. By looking ahead and adapting our public spaces to make them safer for all, we will contribute to building society’s preparedness and resilience for whatever challenges the future may present.