UVC for indoor air quality


Ultravioleta germicidal irradiation (UVGI) uses short-wave ultraviolet (UVC) energy to inactivate viral, bacterial, and fungal organisms so they are unable to replicate and potentially cause disease. UVC energy disrupts the deoxyribonucleic acid (DNA) of a wide range of microorganisms, rendering them harmless (Brickner et al. 2003; CIE 2003). Early work established that the most effective UV wavelength range for inactivation of microorganisms is between 220 and 280 nm, with peak effectiveness near 265 nm. The standard source of UVC in commercial systems is low-pressure mercury vapor lamps, which emit mainly near-optimal 253.7 nm UVC. Use of germicidal ultraviolet (UV) lamps and lamp systems to disinfect room air and air streams dates to about 1900 (Reed 2010). Riley (1988) and Shechmeister (1991) wrote extensive reviews of UVC disinfection. Application of UVC is becoming increasingly frequent as concerns about indoor air quality increase. UVC is now used as an engineering control to interrupt the transmission of pathogenic organisms, such as Mycobacterium tuberculosis(TB), influenza viruses, mold, and potential bioterrorism agents (Brickner et al. 2003; CDC 2002, 2005; GSA 2010; McDeVitt et al. 2008; Rudnick et al. 2009).
UVC lamp devices and systems are placed in air-handling systems  and in room settings for the purpose of air and surface disinfection. Control of bioaerosols using UVC can improve indoor air quality (IAQ) and thus enhance occupant health, comfort,
and productivity (ASHRAE 2009; Menzies et al. 2003). Detailed descriptions of UVGI components and systems are given in Chapter 17 of the 2016 ASHRAE  Handbook—HVAC Systems and Equipment. Upper-air (also commonly called upper-room) devices are installed in occupied spaces to control bioaerosols (e.g., suspended viruses, bacteria, fungi contained in droplet nuclei) in the space. In-duct systems  are installed in air-handling units to control bioaerosols in recirculated air that may be collected from many spaces, and to control microbial growth on cooling coils and other surfaces. Keeping the coils free of biofilm buildup can help reduce pressure drop across the coils and improve heat exchanger efficiency (therefore lowering the energy required to move and condition the air), and eliminates one potential air contamination source that could degrade indoor air
quality. UVC is typically combined with conventional air quality control methods, including dilution ventilation and particulate filtration,
to optimize cost and energy use (Ko et al. 2001)

The primary objective of upper-air UVC placement and use is to interrupt the transmission of airborne infectious pathogens within the indoor environment. The source of these infectious organisms may be infected humans, animals, or bioaerosols introduced for terrorism purposes. Humans are the predominant sources of airborne agents that infect people (ACGIH 1999). The measles and influenza viruses and the tuberculosis bacterium are three important infectious organisms known to be transmitted indoors by means of air shared, by any means, between infected and susceptible persons. Studies of person-to-person outbreaks indicate at least two transmission patterns: within-room exposure such as in a congregate space, and transmission beyond a room through corridors and by entrainment in ventilation ductwork, through which air is then recirculated throughout the building. ASHRAE also provides guidance on protecting buildings from extraordinary incidents in which a bioterror agent is aerosolized into a building (ASHRAE 2003).