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indoor bacterial communities and create communities that are
more similar to outdoor-associated bacteria than air delivered
through a centralised HVAC system. In some buildings, this
can be accomplished through distributed HVAC units, such as
packaged terminal air-conditioners (PTAC) frequently found in
hotels, motels, senior housing facilities, condominium units and
apartments or through perimeter passive ventilation strategies
such as perimeter dampered vents. However, for most buildings,
the easiest way to deliver outside air directly across the building
envelope is to open a window. Window ventilation not only
bypasses ductwork but increases outside air fraction and likely
increases total air change rate as well. Administrators and building
operators should discuss a plan for increasing perimeter, and
specifically window, ventilation when outdoor temperatures are
adequate for this practice without substantial comfort or energy
implications.
Light is another mitigation strategy for controlling the
viability of some infectious agents indoors. Daylight, a
ubiquitous and defining element in architecture, has been
shown in microcosm studies to shape indoor bacterial
communities in household dust to be less human associated
than in dark spaces. Moreover, daylight in these microcosm
spaces reduced the viability of bacteria compared to dark
controls. Further research is needed to understand the impact
of natural light on SARS-CoV-2 indoors; however, daylight
exists as a free, widely available resource to building occupants.
Some electric lighting is already implemented as engineering
controls for disinfection indoors. Ultraviolet light in the region
of shorter wavelengths (254nm UV-C) is particularly germicidal
and fixtures tuned to this part of the light spectrum are
effectively employed in clinical settings to inactivate infectious
aerosols. However, ultraviolet germicidal irradiation (UVGI)
has potential safety concerns if the high-energy light exposure
occurs to room occupants. For this reason, UVGI is safely
installed in mechanical ventilation paths or in upper-room
applications to indirectly treat air through convective air
movement. More recently, far-UVC light in the 207-222nm
range has been demonstrated to effectively inactivate
airborne aerosolized viruses. While preliminary findings from
in vivo rodent models and in vitro 3D human skin models
appear favourable to not cause damage to human skin and
eyes, further research must be conducted to verify the margin of
safety before implementation. If implemented safely, UVC light
offers a range of potential disinfectant strategies for buildings.
Administrators and building operators should encourage blinds
and shades to be opened when they are not needed to actively
manage glare, privacy or other occupant comfort factors to
admit abundant daylight and sunlight.
Implementing targeted UVGI treatment may be prudent
in spaces where individuals that tested positive for COVID-19
All photos by IMD
were known occupants, but routine treatment may have
unintended consequences and should be implemented with
appropriate precaution. Spatial configuration of buildings
can encourage or discourage social interactions. In recent
years, Western society has valued design that emphasizes
visual transparency and a feeling of “spaciousness” indoors,
whether at home through the use of open plan concepts or
at workplaces that harness open office concepts with spatial
layouts that intentionally direct occupants to nodes of “chance
encounters,” thought to enhance collaboration and innovation
among employees. While these spatial configurations are
culturally important, they may inadvertently enhance or
reduce opportunities for transmission of viruses through
human interaction. For example, large, densely populated
open office spaces may increase connectivity while private
offices may decrease connectivity. Space syntax analysis
demonstrates a relationship between spatial disposition and
degrees of connectivity and has been shown to correlate with
the abundance and diversity of microbes within a given space.
Understanding these spatial concepts could be part of the
decision-making process of whether to implement socialdistancing
measures, to what extent to limit occupant density,
and for how long to implement the measures.
Increasing
evidence
indicates that
humidity can
play a role in
the survival of
membranebound
viruses.
www.hvacronline.co.za RACA Journal I August 2020 11