ASHRAE Journal - August 2021 - 30

COLUMN IEQ APPLICATIONS
3. Verify outdoor air quantity and recommission outdoor
air tracking; install a dedicated minimum outdoor
air duct in some air handlers.
4. Increase outdoor airflow, even as high as double the
code-required minimum, with the precaution that overall
capacity and humidity control need to be addressed.
5. Recommission equipment, control sequences and
settings to improve control of ventilation, thermal comfort
and humidity.
In focusing on ventilation actions, we did not cover
other issues of building operation outside our areas of
expertise, including cleaning, social distancing, maskwearing
policies, signage, etc. Of course, much occupant
and visitor behavior is beyond the control of anyone
except the individuals involved.
Upper-Room UVGI
In-duct UVGI and the recommendations above depend
on clean or disinfected air distributed from a central air
handler. The benefits of all these are inherently limited
by the quantity of air distribution to the room. An option
that interrupts the transmission path within the room is
upper-room UVGI, which the owner may wish to consider
in high-risk occupancies.
The 2019 ASHRAE Handbook-HVAC Applications
(Reference 1, page 62.5) describes spaces appropriate
for upper-room UVGI as " ...congregate spaces, where
unknown and potentially infected persons may share
the same space with uninfected persons (e.g., a medical
waiting room or a homeless shelter). " One might reasonably
extend the application to spaces such as prisons,
extended care facilities and waiting rooms for any public
services.
In this application, UV fixtures are placed high in the
room, typically 7 ft (2 m) above the floor, where they
will not harm occupants, yet will irradiate and deactivate
respiratory aerosols brought there by air currents,
either natural or induced. The 2019 ASHRAE Handbook
lists research from the 1930s to recent years demonstrating
the benefits of this technique. The benefit of
upper-room UVGI is offset by installation cost, which is
reported to be greater than in-duct.
Summary
Installation and operating costs of in-duct UVGI in this
case study were higher than those in the 2019 ASHRAE
Handbook by factors of five to nine and by two to four,
respectively. When rules of thumb are used for proposing
UVGI installations, detailed submittals should be
provided showing lamp layout, air handler and duct
geometry and resulting irradiance time to demonstrate
that the kill rate will be achieved. Prior to installing
UVGI, the full benefit of basic ventilation and filtration
should be verified by recommissioning of systems.
Acknowledgments
The author would like to thank William Bahnfleth,
Ph.D., P.E., Presidential Member/Fellow ASHRAE, for
his assistance in using the deactivation rate equation
and estimating k values for coronaviruses; and Andrew
Persily, Ph.D., Fellow/Life Member ASHRAE, for his
review and comment on earlier drafts.
References
1. 2019 ASHRAE Handbook-HVAC Applications, Chap. 62 " Ultraviolet
Air and Surface Treatment. "
2. ANSI/ASHRAE Standard 185.2-2020, Method of Testing Ultraviolet
Lamps for Use in HVAC&R Units or Air Ducts to Inactivate Microorganisms on
Irradiated Surfaces.
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ASHRAE Journal - August 2021

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