International News
CONDAIR COVID-19 REPORT
LOOKS AT BUILT ENVIRONMENT
CONSIDERATIONS:
By Condair
(PART 2*)
Indoor
humidification
is not common
in most HVAC
system designs.
With the increasing spread of severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2) that results in
coronavirus disease 19 (COVID-19), all citizens and building
owners and occupants have an opportunity to reduce the
potential for transmission through built environment (BE)
mediated pathways.
Building HVAC operational practices can also reduce the
potential for spread of SARS-CoV-2. Even though viral particles
are too small to be contained by even the best HEPA and
MERV filters, ventilation precautions can be taken to ensure
the minimisation of SARS-CoV-2 spread. Higher outside air
fractions and higher air exchange rates in buildings may help
to dilute the indoor contaminants from air that is breathed
within the BE. Higher outside air fractions may be possible by
increasing ventilation damper positions on air-handling units,
thus exhausting a higher ratio of indoor air and any airborne viral
particles present.
There are some cautions to consider relative to these building
operations parameters. First, increasing outside air fractions may
come with increased energy consumption. In the short term, this
is likely a worthwhile mitigation technique to support human
health but building operators are urged to revert to normal ratios
after the period of risk has passed. Second, not all air-handling
systems have the capacity to substantially increase outside air
ratios, and those that do may require a more frequent filter
maintenance protocol. Third, increasing air flow rates that simply
increase the delivery of recirculated indoor air, without increased
outside air fraction, could potentially increase the transmission
potential. Higher air flow rates could increase resuspension
from fomites and increase the potential for contamination
throughout the building by distributing indoor air more quickly,
at higher velocities and volumes, potentially resuspending
more ultrafine particles.
Administrators and building operators should collaborate to
determine if increased outside air fractions are possible, what
limitations or secondary implications must be considered, and
determine a plan around managing the outside air fraction and air
change rates.
Increasing evidence indicates that humidity can play a role
in the survival of membrane-bound viruses, such as SARS-
CoV-2. Previous research has found that relative humidity
above 40% is detrimental to the survival of many viruses,
including coronaviruses in general, and higher indoor relative
humidity has been shown to reduce infectious influenza virus
in simulated coughs. Maintaining a relative humidity between
40%-60% within the BE may help to limit the spread and
survival of SARS-CoV-2 within the BE, while minimising the
risk of mould growth, and maintaining hydrated and intact
mucosal barriers of human occupants.
Indoor humidification is not common in most HVAC system
designs, largely around maintenance concerns and the risk of over
humidification increasing the potential of mould growth. While
administrators and building operators should consider the costs,
merits, and risks of implementing central humidification, it may
be too time intensive to implement in response to a specific viral
outbreak or episode. Therefore, targeted in-room humidification
is another option to consider, and this may reduce the likelihood
of a maintenance oversight causing over-humidification.
Building ventilation source and distribution path length
can affect the composition of indoor microbial communities.
Ventilating a building by introducing air directly through the
perimeter of buildings into adjacent spaces is a strategy that
does not rely on the efficacy of whole building filtration to
prevent network distribution of microorganisms. Delivering
outside air directly through the envelope into an adjacent spatial
volume has been shown to increase the phylogenetic diversity of
10
RACA Journal I August 2020
www.hvacronline.co.za