ASHRAE Journal - September 2020 - 27

TECHNICAL FEATURE

transmission. Natural ventilation has not been evaluated
with respect to COVID-19.
Air Distribution. Studies suggest that how air is
discharged and circulates within a space could be an
important factor determining whether exposure is sufﬁcient to cause disease. For example, wall-mounted FCUs
can discharge air into the breathing zone, potentially
directing virus to other occupants. Relative pressurization can also contain or spread contamination. No ﬁeld
data were available showing the impact of air distribution on COVID-19 exposure.
Filtration. Recently reported results of surface
sampling inside recirculating HVAC systems provide
an indicator of ﬁlter efﬁciency. Data suggest that a
MERV 10 preﬁlter reduced the amount of deposited
SARS-CoV-2 by approximately 70% and that a MERV
15 ﬁnal ﬁlter may not have removed additional virus.
Insufﬁcient ﬁeld data are available to guide ﬁlter
selection for COVID-19. Filtration within the space
(i.e., portable HEPA units) could reduce virus exposure in localized areas with appropriate design and
placement.
UV Disinfection. Although UV light has the potential
to reduce virus exposure in some situations, there are
insufﬁcient data to support widespread application.
Humidity Control. It has been demonstrated that
coronaviruses survive longer and occupants are
more susceptible to respiratory infection in drier
conditions. Although COVID-19 initially spread in
areas with drier (i.e., winter) conditions, there was
also community spread in humid areas (i.e., tropical climates and southern hemisphere summer).
Continuing high rates of COVID-19 in the United
States this summer further suggest that humidity is
not an important factor. Available information does
not support humidiﬁcation when the RH is below 40%
as a control for COVID-19.
Sewage. SARS-CoV-2 has been found in feces and
urine, making sewer gas and sewage a potential source
of exposure. Studies are needed to develop effective
strategies to avoid infecting occupants.
Mechanical Hygiene. SARS-CoV-2 has been detected
on surfaces inside recirculating HVAC systems. It is not
known if this can contaminate the airstream.

Recommendations for Expedited Research
Research is urgently needed to identify and

implement cost-effective measures to operate buildings during the pandemic. While basic research can
take years, valuable data could be compiled much
faster using available epidemiology and by testing
buildings.
Environmental Epidemiology. Studies can suggest
the relative role played by the various routes of disease transmission and evaluate the efﬁcacy of control
measures. To accomplish this, engineers and health
scientists collaborate to compile exposure factors
(i.e., ventilation, airﬂow patterns, ﬁltration, occupant
density and spacing) to determine their relationship
with case location and timing. If outbreak investigations, contact tracing and evaluation of widespread
testing could include the collection of environmental
information, ﬁndings would help support the selection of HVAC response measures. Critical questions
that could be addressed by epidemiological studies
include:
* What do infection patterns suggest with respect to
the signiﬁcance of airborne and fecal transmission as
the cause of infection?
* How do ventilation, air distribution and humidity
affect infection rates?
* How effective are various ﬁltration and air disinfection measures in reducing exposure?
Field Studies. Valuable information can be produced
by sampling for contaminants in occupied buildings
for airborne and surface SARS-CoV-2 (both total RNA
copies and infectious virus). Comparison of data collected in buildings with varying systems, uses and
infection rates would provide valuable information to
guide response efforts. Field measurements of particular value include:
* Concentrations of SARS-CoV-2 in air with recirculating HVAC systems in spaces with and without infected
individuals;
* Both air and surface SARS-CoV-2 in ducts and air
units recirculating air from spaces with infected individuals;
* SARS-CoV-2 concentrations over time after removal
of infected occupants;
* SARS-CoV-2 in air over time in relation to opening
windows;
* SARS-CoV-2 concentration in air associated with
different ventilation rates and ﬁlter efﬁciencies;
* Pilot testing of space conditioning measures, such
SEPTEM BER 2020

ashrae.org

ASHRAE JOURNAL

https://www.ashrae.org/

ASHRAE Journal - September 2020

Table of Contents for the Digital Edition of ASHRAE Journal - September 2020