During the coronavirus pandemic, building owners and developers need to make sure they have the best air-cleaning technologies for their HVAC systems, given there is evidence that airborne transmission of the virus is possible.
Two of those air-cleaning technologies that can mitigate risk include Ultraviolet Germicidal Irradiation (UVGI) and Bipolar Ionization (BPI). These can help reduce airborne exposure and may reduce disease transmission, though neither should be considered a silver bullet that can protect tenants perfectly.
What are the pros and cons of each? Let’s take a look at both.
Ultraviolet light has been used for disinfection for more than a century, with the first HVAC system application taking place in 1940. It is a thoroughly vetted technology that has a proven track record. Typical commercial products use the UV-C band wavelength of 253.7 nm, which is a near optimal wavelength for degrading organic material and inactivating microorganisms and pathogens. Use of the UV-C band energy to inactivate microorganisms is often referred to as UV Germicidal Irradiation.
UV exposure is hazardous to humans, so it is typically used in one of four configurations:
- In-Room Disinfection: High intensity UV-C lamps located within the occupied space that are activated for brief periods only when the room is unoccupied. Typically used in health care applications for disinfection of operating rooms between patients.
- Upper-Room Disinfection: Standard UV-C lamps installed so that all UV energy is directed above the occupied zone. Typically used in health care and school applications where continuous operation is helpful.
- In-AHU Surface Disinfection: Standard intensity UV-C lamps located in the Air Handling Unit (AHU) at the cooling coil used to irradiate the coil, filter, condensate drain pan, and other wetted surfaces. Controls microorganism growth and reduces biofilm in order to reduce maintenance, reduce coil air pressure drop, and improve coil heat transfer effectiveness.
- In-AHU Airstream Disinfection: Similar to surface disinfection described above, but higher intensity and a greater quantity of UV-C lamps are used. The UVGI efficacy is a function of time times intensity, so a higher UV output can be used to inactivate microorganisms “on-the-fly” in the airstream, in addition to the surface disinfection described above.
Bipolar ionization or non-thermal plasma technology (BPI) is a relatively newer technology used in HVAC systems. Different products use different technologies, but they all generally work by using electric voltage to generate ions and supply them to the occupied space. The ions work in two main ways in the space:
- Ions cluster around airborne particles such mold, viruses, bacteria and Volatile Organic Compounds (VOCs) and break them down to inactivate them.
- Charged ions bond with and agglomerate airborne contaminants into a larger mass that can either drop out of the air or be more effectively filtered at the AHU.
Bipolar ionization systems are typically installed in AHUs to distribute the ions through the ductwork system and into the occupied space. There are also packaged self-contained systems that can be mounted within critical high traffic spaces for local filtration. If installing BPI systems, further review on a case-by-case basis can help determine the appropriate BPI technology and approach for the specific building and application.
UVGI is a proven technology that can be effective at mitigating airborne infectious disease transmission. It is specifically recommended by ASHRAE in its COVID-19 response guidance.
BPI can provide many of the same benefits as UVGI, with the added benefits of odor control and VOC reduction. BPI may also kill pathogens in the air and on surfaces in the space, not just at the AHU.
However, some BPI products generate harmful ozone and there is a lack of scientific data and testing protocols with which to evaluate and compare technologies. These risks must be evaluated but can be mitigated to some extent. If BPI is used, proper specification with ozone free UL listings is critical. Field performance testing and validation is recommended to confirm the efficacy of the installed product.
Both UVGI and BPI may be appropriate for new construction and retrofit applications to improve indoor air quality and mitigate airborne infectious diseases. Careful consideration can help determine which technology is best for the application, evaluated on a case-by-case basis.