ASHRAE Journal - July 2020 - 23

TECHNICAL FEATURE

The method can be the basis of future collaborative
works of HVAC engineers, virologists and other specialists in studying and improving protective qualities of
air-handling systems. Wide-ranging experiments would
further substantiate the system-induced virus transmission concept and advance the method with a knowledge
database related to individual contamination.
Site measurements of SARS-CoV-2 virus concentrations and emission rates from the patients in hospitals
and buildings in quarantine should be undertaken to
determine vulnerable buildings and systems and provide an empirical base of the actual system's contamination containment efﬁciencies.
Overlaying the infected room and ductwork layouts in
buildings that have already been in quarantine would
allow conﬁrmation of the concept on a statistical level.
The unfortunate infection spread on the Diamond
Princess cruise ship in January 2020 would be an appropriate case study. The suggested experiments would take
a long time, while the current pandemic dictates quick
actions. The proposed method allows an engineer to
identify and implement the following measures:
* Mixed air systems serving educational, recreational
and other facilities with air ﬁlters rated below MERV-9
should be examined for virus containment efﬁciency.
For the systems with low efﬁciency, an emergency control sequence increasing the minimum outdoor air ratio
to an amount predicted by the method should be implemented. The amount must correlate with the capacity of
the system to condition a greater volume of outdoor air.
The sequence will monitor the outdoor air conditions
and interact with existing safety controls. The demand
control and free-cooling sequences will be overridden if
they conﬂict with the emergency sequence.
* Typical air-handling systems in hospitals with
MERV-13 ﬁlters, for example the systems that serve
emergency areas and patient wards, are efﬁcient to
control inﬂuenza A or similar size viruses. However, a
pilot CCE analysis in this article suggests that the systems
may not be efﬁcient enough for controlling SARS-CoV-2
or other viruses of smaller size. If further works conﬁrm
the suggestion, the systems should be upgraded with
UVC germicidal lights in the common return air duct in
addition to the emergency outdoor air control sequence
that is described above. The upgrade will reduce the
virus count in recipient spaces and minimize the probability of infection.

* Houses heated by a 100% recirculating air furnace
with a low-grade ﬁlter and ﬂoor-mounted air outlets
exhibit the lowest protection from virus spread through
the ductwork. This is particularly an issue if one member of the household has become infected. Development
of protective measures in air-heated residences remains
an open question, subject for further studies.

Acknowledgments

The author would like to express his special gratitude to
Anton Neschadim, Ph.D., chief scientist, ImmunoBioChem
Corporation, who provided valuable insights in interpretation and use of the virus-related characteristics and existing methods of viral infection evaluation.

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ASHRAE Journal - July 2020

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