ASHRAE Journal - July 2020 - 6

INDUSTRY NEWS

Epidemic Task Force Chair
Talks Best Practices, FAQs
ATLANTAÑSince being established in March, ASHRAE's

Epidemic Task Force has developed guidance on mitigating potential health risks in light of the COVID-19
pandemic. From best practices when reopening
buildings to ﬁltration and disinfection strategies, the
guidance covers various building types. The wideranging guidance has helped built environment
professionals navigate the pandemic.
To better help ASHRAE members navigate the guidance, ASHRAE Journal staff talked with the task force's
chair, William Bahnfleth, Ph.D., P.E., Presidential
Member/Fellow ASHRAE.
What are the biggest misunderstandings that exist
regarding the role of HVAC systems in the transmission of airborne diseases?
Bahnﬂeth: The biggest misunderstanding is that
air conditioning inherently increases the risk of airborne disease transmission and that we are safer with
air-conditioning systems off than on. Air conditioning includes heating and cooling, humidiﬁcation
and dehumidiﬁcation, ventilation and air cleaning
and air movement. The main risk factor that may
be associated with air conditioning is the spreading
of infectious aerosols within a space. This may have
been a factor in some of the COVID-19 superspreader
incidents; however, inadequate ventilation may have
been an even more important contributor.
Ventilation with outside air and particulate ﬁltration both reduce infectious aerosol concentrations
in the air and reduce risk of infection. Controlling
humidity to within a moderate range from about 40%
to 60% relative humidity also seems to be protective.
So, on balance, a properly designed, maintained and
operated system is likely to reduce risk.
What are a few easy operating strategies building
owners and facility managers can implement to
help reduce the likelihood of transmission of airborne diseases?
Bahnﬂeth: Best strategies depend to some extent on
what type of systems the owner has. The objectives of
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infection risk management are to
lower concentrations of infectious
aerosols by diluting them with
outdoor air, capturing them with
ﬁlters, disinfecting, and containing them using pressurization.
For recirculating systems such
as VAV systems, there should be
William Bahnﬂeth, Ph.D., P.E.,
some ability to increase outdoor Presidential Member/Fellow ASHRAE
airﬂow within the limits of control of the system, so that acceptable temperature
and humidity are maintained. Temporarily disabling
demand controlled ventilation will also increase the
average outside air supply. For once-through ventilation systems such as dedicated outdoor air systems
(DOAS), increasing outdoor air may not be an option.
Filter upgrades to central systems is another option
that may be easy for some systems.
Systems designed to minimum ventilation standards like ANSI/ASHRAE Standard 62.1-2019,
Ventilation for Acceptable Indoor Air Quality, and ANSI/
ASHRAE Standard 62.2-2019, Ventilation and Acceptable
Indoor Air Quality in Residential Buildings, will have
MERV-8 or MERV-6 ﬁlters, respectively. These do not
effectively remove particulate matter of the size produced by respiratory aerosols. Upgrading to at least
MERV-13, if possible, will capture a large fraction in
this size range.
Owners may also consider adding air disinfection
using ultraviolet germicidal irradiation. However,
systems must be evaluated to determine their ability to accommodate filters that may be somewhat
higher in flow resistance than the filters for which
the system was designed. Flushing buildings with
outside air for a period of time preoccupancy will
also reduce risk from any residual infectious aerosol
that may have been left after the previous occupied
period.
As buildings start reopening, what are the top
tasks engineers should pay attention to?

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ASHRAE Journal - July 2020

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