Air Disinfection Fan with UVC-light

There is an obvious possibility in applying UC-C technology for cleaning of SARS-CoV-2 and other bio contaminated air during a pandemic. Evidence shows that the Corona virus is airborne and that poorly ventilated buildings have higher risks of infectious disease transmission between people. Estimations suggest that inhaling about 1000 vira is enough for the Corona virus to take hold. Thus, it is clear that increasing air changes per hour with germ free air lowers the risk of inhaling sufficient Corona viruses to get infected.

Viruses are small making them more susceptible to UV-C than other organisms, leading to WHO to recommend UV-C radiation for inactivation of such organisms. One approach to minimize the risk of getting infected is regular opening of windows for ventilation, but such a strategy creates variating and unpredictable airflows and areas with little ventilation. Upper-air UV-C systems are well known for disinfection in hospital rooms and the effect highly increase with fans distributing the germ free air. High Volume Low Speed (HVLS) fans combined with UV-C delivers high rate of germ- free air in a low airspeed downwards manner, diluting virus numbers and lowers the infection risk.

Compared to general Upper-UV-C systems without fans improvement of 77 percent has been reported when adding the fans. The product combining a HVLS fan with UV-C integrated in the wings are patent-pending by Nordicco A/S and has been named Northern Light. Northern Light is showing an efficiency of 87,9% per air passage over the wings against SARS- CoV-2 by Comsol CFD analysis. No other known technology has paralleled efficiency for such high amounts of air evenly distributed in each recirculation passage.

The global health-threatening crisis from the COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2), highlights the scientific and engineering potentials of applying ultraviolet (UV-C) disinfection technologies for bio contaminated air as the major technology for removal of SARS-CoV-2 transmission. Various environmental public settings worldwide, from hospitals and health care facilities to shopping malls, airports and schools, are considering implementation of UV disinfection devices for disinfection of circulating air streams. (Milad, 2020)

Evidence shows that the virus is airborne in tiny droplets travelling for several hours. (Thorseth, A 2020. DTU.) (Ashrae, 2020). Authorities now generally recommend regular passive ventilation (opening windows) of indoor spaces to minimize impact of airborne viruses. New evidence of airborne spread cases is a daily event. 

In facilities where there are infectious patients, evidence shows that poorly ventilated buildings have higher risks of infectious disease transmission. (Li et al,2007) demonstrated the association between ventilation and air movements in buildings, and the transmission/spread of infectious diseases.

Coughing by a COVID-19 infected individual can produce about 3000 droplets in a wide size range (10−1 to 102 μm). Droplets larger than 100 μm deposit rapidly on surfaces. (Wang, J., 2020) (Garcia et al., 2020). Tiny droplets (0.1−5 μm) are capable of dissolving with the aerosol, remaining airborne, and traveling hundreds of meters. (Garcia et al., 2020) (Morawska, L., et al., 2020) Intermediate size range (5−100 μm) droplets also shrink to tiny sizes due to evaporation, (Garcia et al., 2020) and the peak concentration of droplets in bioaerosols are in two diameter ranges: 0.25−1.0μm and 2.5−10 μm. (Liu, Y,. et al., 2020)

The majority of larger emitted droplets are drawn by gravity to land on surfaces within about 1–2 m from the source (see Figure 2). General dilution ventilation and pressure differentials do not significantly influence short-range transmission. Conversely, dissemination of smaller infectious aerosols, including droplet nuclei resulting from desiccation, can be affected by airflow patterns in a space in general and airflow patterns surrounding the source in particular. Of special interest are small aerosols (<10 μm), which can stay airborne and infectious for extended periods (several minutes, hours, or days) and thus can travel longer distances and infect secondary hosts who had no contact with the primary host. (Ashrae, 2020) (Stadnytskyi,v. et al., 2020)

Disinfection using UV radiation has been a fast growing chemical-free technology over the past decades. UV radiation is highly efficient at controlling microbial growth in any medium, such as water and air, as well as on any type of surface. (Milad, 2020) (Thorseth, A 2020. DTU.)

UV-C radiation has a short wavelength and high energy, compared to other UV radiation, which enables
it to function the best in a direct line and at a short distance. Due to the high energy of the UV-C radiation, it is bound to the inverse square law where the propagation of light intensity decreases exponentially with

increasing distance from the light source. Studies developed by (Escombe et al., 2009) and (Casanova et al., 2010) provided that there is a sufficient circulation inside the room to mix the air, upper-room UV fixtures have shown to be an effective asset for use in infection control.

UV-C systems inactivates microorganisms by damaging the structure of nucleic acids and proteins at the molecular level, making them incapable of reproducing. The most important of these is DNA, which is responsible for cell replication (Harm 1980). Absorbed UV photons can damage DNA in a variety of ways, but the most significant damage event is the creation of pyrimidine dimers, where two adjacent thymine or cytosine bases bond with each other, instead of across the double helix as usual (Diffey 1991). In general, the DNA molecule with pyrimidine dimers is unable to function properly, resulting in the organism’s inability to replicate or even its death (Diffey 1991; Miller et al. 1999; Setlow 1997; Setlow and Setlow 1962). An organism that cannot reproduce is no longer capable of causing disease.

Based on systematic literature reviews the World Health Organization (WHO) recommended use of bacteria disinfecting UV-C radiation in upper room use as a means of prevention and control of tuberculosis infection (WHO, 2019). (Ko et al., 2000; Peccia et al., 2001). Escombe et al. (2009) studied bactericidal UV radiation in the upper part of rooms in a hospital in Lima without air-conditioning, and found a marked reduction in the risk of transmission of airborne tuberculosis despite the high relative humidity of 77%. (Thorseth, A 2020. DTU.)

Centers for Disease Control and Prevention (CDC) has approved UV as an adjunct to filtration for reduction of tuberculosis risk and has published a guideline on its application (CDC 2005, 2009). (Evidence Level A).

Personalized ventilation systems that provide local exhaust source control and/or supply 100% outdoor, highly filtered, or UV-disinfected air directly to the occupant’s breathing zone (Cermak et al. 2006; Bolashikov et al., 2009; Pantelic et al. 2009, 2015; Licina et al. 2015a,2015b) offer protection against exposure to contaminated air.

Ultraviolet radiation has been explored to reduce the spread of airborne infections at least since the 1930s. Ultraviolet radiation can disinfect surfaces, room air (called upper air systems), and air in ducts. To inactivate an organism (such as a virus), the ultraviolet radiation must strike the organism. Upper air (room) systems rely on air circulation in the room to carry microorganisms to the upper air zone where sufficient ultraviolet light shine on them. (Mphaphlele, 2015; Escombe et al., 2009; DHHS, 2009)

UV-C irradiation is highly effective in inactivating and inhibiting SARS CoV-2 replication (Bianco, et al., 2020)

At a virus density comparable to that observed in SARS-CoV-2 infection, an UV-C dose of just 3.7 mJ/cm2 was sufficient to achieve a 3-log inactivation, and complete inhibition of all viral concentrations was observed with 16.9 mJ/cm2. UV-C effect on viruses has been intensely studied by several authors (As an example; Rauth, A.M., 1965)

These results are important for the development of novel sterilizing methods to contain SARS- CoV-2 infection.

The primary objective of upper-air UV-C placement and use is to interrupt the transmission of airborne infectious pathogens within the indoor environment.

In a room ventilated by an HVLS overhead fan, the air layers are well mixed so the supplied disinfected fresh air can reach the occupant level.

In naturally or HVAC (Heating, Ventilation and Air Conditioning) ventilated spaces, fresh air is uneven distributed throughout the space, so localized areas may have stagnant pockets, resulting in poor air quality and buildup of pollutants including bacteria and virus. Fans disperse these pockets and increase the circulation of fresh disinfected air, evenly distributing it throughout the space, diluting virus number per volume and improving indoor air quality. (C.Canada, 2020)

The use of UV technologies in the HVAC industry is well established and understood. The technology has been paired with HVAC equipment use since the early 1940s and the benefits they provide reduce occupant exposure to contagions by disinfecting indoor air near specially designed UV devices. (C.Canada, 2020)

Increasing of the rate of air circulation between the upper and lower air zones, can improve the performance of upper-room ultraviolet germicidal irradiation (UVGI) systems by up to 77 per cent (C.Canada, 2020).

Conclusion

It has been shown by simulation that an 87.9% inactivation of SARS-CoV-2 can be achieved with the Northern Light fan per passage of recirculating ventilation air. The degree of inactivation has been calculated from the modelled dose distribution using a UV sensitivity reported in the literature (k-value of 1.87 cm2/mJ (Bianco et al., 2020)). The effect is expected to effectively reduce likelihood of inhaling the around 1000 SARS-CoV-2 that leads to Covid19 disease in treated areas.