RACA Journal November 2021 | Page 48

Technical

bacterium , causing mutations that prevent replication . This leads to the death of almost all bacteria and render these microbes non-infectious .

UV-C APPLICATIONS UV-C radiation wavelength is between 200nm and 280nm . Most UV-C lamps discharge optimally at 254nm . Far-UV-C lamps discharge at 207-222 nm . UV-C light applications include use in occupied and unoccupied spaces for airborne and surface disinfection , but are subject to stringent safety requirements , installation criteria , and limitations .

Various software programs calculate the effectiveness of surface disinfection , which is dependent on factors like the amount of UV-C light energy emitted , process time , the type of surface the light is disinfecting and desired cleanliness .

Table 1 : Summary of UVGI applications

Various upper-room UV-C devices generate a controlled UV-C field above the heads of occupants , and to minimise UV-C in the lower occupied area of the room . Upper-room UV-Cs are typically installed in fixtures suspended from a ceiling or mounted on a wall at 7ft or above .

Upper room UV-C placement is more suited for spaces where people congregate and where potentially infected persons may transmit the virus to others ( for example medical waiting rooms or homeless shelters ). Common corridors potentially used by unknown infected persons in a medical facility would also benefit from upper-room UVGI fixtures . Upper-room UV-C also covers situations where untreated re-circulated air might enter an occupied space .

The fixtures are typically shielded with louvers or baffles to block radiation below the horizontal plane of the fixtures , and should be appropriately spaced to accommodate the area , shape , and height of the space in which air is to be disinfected .

Clients interested in a UV-C system should consider cost of ownership and operating expenses when selecting a system . Major costs include the initial equipment and installation costs , maintenance costs ( primarily lamp replacement ), and energy costs ( increased direct cost of lamp operation plus increase in heating and cooling energy consumption ).

Air treatment systems and room surface disinfection systems have the objective of improving the safety , health , and productivity of building occupants through reduced incidence of infectious disease and sick building complaints . Although many studies exist to support claims of UV-C ’ s effectiveness in these applications , it is difficult to express the resulting benefits in economic terms . A conservative approach to economic evaluation is to compare the costs of alternative approaches such as dilution ventilation and particulate filtration that have the same effectiveness .

Other things to note are that the UV-C energy can be detrimental to most organic materials . UV rays in general will degrade paint , may damage plants , cause plastics to change colour , and degrade air filters based on their composition .

UPPER ROOM UVGI Upper-room UV-C ’ s primary objective is to interrupt the transmission of airborne infectious pathogens within the indoor environment .

RACA Journal I November 2021

Figure 2a : Sectional view of upper room louvered UV-C fixturesix

Disinfection effectiveness of upper-room UVGI devices improve when air in the upper and lower zone is mixed . Clean irradiated air in the upper room zone is replaced by infected air from the lower room zone .

Visual Lighting , an upper-room computer-based software , can calculate the average fluence ( the radiant exposure ) in the upper room ^x . Additionally , computational fluid dynamics ( CFD ) is being used to understand the interaction between airflow and upperroom UV-C ^xi .

" Clients interested in a UV-C system should consider cost of ownership and operating expenses when selecting a system ."

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