RACA Journal November 2021 | Page 49

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Technical
Figure 3a : Typical elevation view of upper room UV-C applied in a hospital patient room xii
Figure 4 : Typical elevation view showing upper room UVGI fixture and UV intensity level xiii
Upper-room UV-C fixtures are selected based on the floor-toceiling height . Ceiling heights above 9.8ft ( 3m ) may allow for more open fixtures , which may be more efficient because they may allow for a larger vertical irradiation zone . In occupied spaces with lower ceilings ( less than 9.8ft ( 3m )), various louvered upper-room UV-C devices ( wall-mount , pendant , and corner-mount ) are available for use in combinations and are mounted with at least 6.9ft ( 2.1m ) from the floor to the bottom of the fixture .
The fixture should be mounted so that its UV energy is distributed parallel to the plane of the ceiling . Device construction , adjustment , and placement protect occupants from excessive ultraviolet energy . For example , in high-risk areas such as corridors of infectious disease wards , a maximum
UV irradiation of ( 1 μJ / s )/ 0.155 in 2 ( 0.4 μW / cm ²) at eye level is an acceptable level based on an engineering guide xiv . No longterm health effects of UV-C exposure at these levels in the lower occupied part of rooms are known .
Figure 4 shows a typical installation position and illustrates typical UV-C intensity level in a room . Many UVGI fixtures produce visible light to help indicate when the fixture is turned on . A UV-C installation that produces a maintained , uniform distribution of UV irradiance averaging between 30 and 50 μW / cm ² is effective in inactivating most airborne droplet nuclei containing mycobacteria and is presumably effective against viruses as well xv .
Beyond UV-C irradiance , effectiveness of upper-room UV-C is related to air mixing , relative humidity , and the specific characteristics of the pathogenic organisms being addressed xvi . Effectiveness can improve greatly with wellmixed air xvii , so ventilation systems that maximise air mixing receive the greatest benefit from upper-room UV-C .
Upper room UV-C is already proven 80 % effective against tuberculosis ( TB ) spread in two hospital-controlled studies xviii , xix .
Advantages
• Suitable for all climates and ventilation conditions
• Achieves high levels of equivalent air changes / hour ( equivalent ACH )
• A permanent built-in solution for room air disinfection
• Disinfects large volumes of room air when combined with forms of mechanical ventilation , natural ventilation , or hybrid types to mix the air ; and have a secondary benefit for surface decontamination
• Can be safely deployed and effectively used with proper installation , commissioning , operation , maintenance , and facility staff training
• Mitigates airborne spread of tuberculosis
• Available in a variety of open and louvered fixtures for different room geometries
Table 2 : Suggested UV-C Fixture Mounting Heightsi ( Note 1 )
Wall Mount Fixture
Ceiling Mounted Fixture
Corner Mount
Wall Mount
Pendant
Pendant With Fan
Beam Pattern
90 Degrees
180 Degrees
360 Degrees
360 Degrees
Minimum Ceiling Height
8ft ( 2.44m )
8ft ( 2.44m )
9.5ft ( 2.89m )
9.5ft ( 2.89m )
Fixture Mounted Height
6.9ft ( 2.1m )
6.9ft ( 2.1m )
7.9ft ( 2.4m )
7.9ft ( 2.4m )
Ideal Uv-C Intensity for Effective
Disinfection
> 10 μw / cm ²
> 10 μw / cm ²
> 10 μw / cm ²
> 10 μw / cm ²
1 Note that this table is a guidance only and additionally , manufacturer-specific advice on product operation and placement should be followed . Appropriately designed UV fixtures are available for all locations . Only the most commonly-used have been included in the table .

www . hvacronline . co . za RACA Journal I November 2021 47