Due in part to recent pandemics, ultraviolet light is making a revival in the area of disinfecting air and surfaces in HVAC applications. Using UV-C light as a disinfectant is hardly a new concept. As early as 1878 Arthur Downes and Thomas P. Blunt, published a paper describing the sterilization of bacteria exposed to short-wavelength light. Later, the Westinghouse corporation followed with a commercialized germicidal lamp as early as the 1930’s. Since then, worldwide use of UV light to kill microorganisms has been implemented in: drinking and wastewater, indoor air quality, food safety, horticulture, healthcare and consumer products.
How UV-C light works
The sun emits different spectrums of UV light, but none is visible with the human eye. The wave lengths ranging from 10 to 400 nm, and include UV-A, UV-B, UV-C and UV-V. The earth’s ozone layer diminishes and prevents the shorter wavelengths of (UV-V, UV-C, and most of UV-B) from the sun to reach the earth’s surface. When pathogens like viruses, molds and bacteria absorb UV-C light it prevents the microorganisms from replicating their DNA and they quickly deteriorate. Once deactivated, these microorganisms are no longer able to reproduce and grow on surfaces. With this in mind, UV-C light emitters can now be added inside HVAC units or installed inside the duct. This enables HVAC units to be on the front lines of combating dangerous microbes that beget global illnesses.
For mold and bacteria, doses of UV-C energy may not cause immediate cell death but the microbe could be deactivated; while some biological activity may still exist, cell replication is impossible. The microbe is no longer able to spread. In order to maximize the effect of UV lights, it is best to pair them with an electrostatically charged filter. This allows them to capture and hold the microorganism for a long enough period of time for the UV light to deactivate its ability to reproduce. Finally, a DOAS (dedicated outdoor air system) can also be used to bring fresh air into the space. In this way, we create a system that greatly reduces harmful microbes.
Conclusion
Unfortunately, there is no guarantee that UV-C light will kill 100% of all microorganisms. Instead, recommendations are to take a multi-pronged approach to cleaning including filtration, air purifiers and disinfection of evaporator coils. With the proper filter, UV-C can kill and/or degrade what the filter has caught. Thus, for a given microbe, the filters effect can be an integral part of the resulting concentration in a space.