The rise of COVID-19 in 2020 raised a lot of new questions about how we live and work. Among these questions, the health and safety of indoor air naturally became an essential issue to employers and employees alike.
Because of these concerns, air disinfection technologies, including bipolar ionization and ultraviolet germicidal irradiation, became popular options for lowering the risk of COVID-19 in buildings. While these technologies may seem similar on the surface, there are some notable differences to consider when deciding to invest in one or the other.
How Do UVGI and BPI Work?
The main points of comparison between ultraviolet germicidal irradiation and bipolar ionization arise from how the respective technologies work and their applications, so let’s first quickly cover the basics of how they work.
Ultraviolet germicidal irradiation (UVGI)
Ultraviolet germicidal irradiation, or UVGI, uses ultraviolet light to kill or inactivate microorganisms. As UV light from a UV lamp comes into contact with cells, the UV light breaks down the organism’s DNA, disallowing it from replicating.
UVGI generally comes in four varieties: in-room, upper-room, HVAC surface disinfection, and HVAC cross-sectional disinfection. In-room UVGI is far less common, as UV light is dangerous to humans, and in-room UVGI is only implemented when there are no building occupants, or when all occupants are utilizing the appropriate protective gear.
Upper-room UVGI is more common, especially in medical and school settings. Instead of irradiating the entire room, only the room’s topmost portion is exposed to UV light. As the air’s vertical movement pushes air from the breathing zone upwards, the entire room’s air is disinfected.
Another common application of UVGI takes place in the HVAC system, either through the disinfection of the air handling unit and air filters or through the cross-sectional disinfection of air as it passes through the ducts.
Bipolar ionization (BPI)
Bipolar ionization is quite different from UVGI, despite accomplishing a similar purpose. BPI units are typically located within the HVAC system, where they use an electrical current to create negatively and positively charged ions.
As these ions disseminate through the HVAC system and rooms, the ions attach to airborne microorganisms, interfering with proteins on the surface of cells or viral capsids. These ions also help break down and settle inorganic particles, where surface disinfection or air filtration can take care of them.
BPI vs UVGI: How Do These Technologies Compare?
Ultraviolet germicidal irradiation and bipolar ionization have similar use cases; both help eliminate biological contaminants from the air and are especially useful for dealing with COVID-19. However, there are some key differences to be aware of, which can impact which technology you implement in your project.
Bipolar ionization is one of these air cleaning processes. As negative ions interact with the air, oxygen molecules (O2) can split and reform into ozone (O3), which is a significant threat to building occupant health and safety. As the technology has matured over the years, the amount of ozone produced by BPI has decreased substantially, and some BPI products have even been certified as ozone-free by UL. If you decide to invest in BPI, it’s crucial to inspect manufacturer reports carefully. Monitoring indoor ozone is also a good choice, as you can make sure that ozone does not become a health hazard.
UVGI, if it uses an appropriate wavelength of UV light, generally does not produce ozone. Some wavelengths of UV-C light can create or destroy ozone, but the wavelength employed by some UVGI devices, approximately 254 nm, is safe. Like BPI, you should inspect ozone production data from the manufacturer before investing in this technology.
BPI units are usually self-enclosed, and depending on the manufacturer and type of bipolar ionization technology used, have far less maintenance than UVGI systems. UV lamps will need to be replaced, which can incur some maintenance costs.
Evidence for eliminating viruses
UVGI has a long history, especially when compared to BPI. The first studies of UVGI systems in public spaces occurred as far back as the 1930s, and the rise of infectious diseases like measles and tuberculosis during the 1980s and 1990s contributed to a resurgence in the implementation and research of UVGI. In the present day, there is a large backing of scientific study about UVGI, including the conditions where it is most applicable, that supports UVGI as an effective method for eliminating viruses in the air.
Bipolar ionization is a newer technology, originating in the 1970s, and does not have as much evidence backing as ultraviolet germicidal irradiation has. Information offered by the manufacturers of certain BPI products supports that BPI can be helpful in eliminating COVID-19, but there are not as many scientific studies about the efficacy of BPI when compared to UVGI. ASHRAE still considers BPI an emerging technology, but this status may change as we gather more data from the COVID-19 pandemic and organizations like ASHRAE continue their review process.
While UVGI is a reliable method for eliminating biological contaminants like mold, bacteria, and viruses, it is ineffective against other air pollutants, like particulate matter and volatile organic compounds (VOCs). To ensure good indoor air quality, additional air-cleaning measures, like air filtration and adsorbent purification, may be necessary.
Bipolar ionization has the advantage in this case, as ions can help break down odors and VOCs alongside biological threats. As ions cluster around larger airborne particles, the particles will begin to accumulate, making them settle or get picked up through air filtration.
As we can see from the above comparison, bipolar ionization and ultraviolet germicidal irradiation both have their pluses and minuses. While UVGI has a deeper scientific backing for inactivating viruses and does not produce ozone, BPI has broader applications for improving indoor air quality and generally has lower maintenance costs. Before choosing one or the other, carefully consider project goals and requirements to ensure that you pick the best technology to fit your project.
For a more in-depth discussion of BPI and COVID-19, check out our article: Can Bipolar Ionization Technology Help Eliminate COVID-19?