ASHRAE Journal - July 2022 - 14

TECHNICAL FEATURE
modeled for the airplane environment,
but only the cough was modeled
for the ICS.
In general, aerosols were tracked
within each environment. Airborne
particles were removed from the
environments by deposition onto
surfaces or exiting through return
air grilles. The mass of particles that
entered the breathing zone of occupants
was monitored, and the nonvolatile
mass of particles (in other
words, the mass of droplet nuclei)
inhaled by each occupant, except
the index individual, was calculated
following the methodology in Davis
and Zee, et al.11 The results demonstrated
the difference in exposure
between an aircraft and ICS, the
difference in exposure between a
cough and breathing-generated
aerosols, and validated the model
through comparison to experimental
U.S. Transportation Command
(TRANSCOM)12 data.
Particle Release
A cough was simulated, as
described in Davis and Zee, et al.11
A total of 106 million particles were
released over 0.4 seconds using a
time-dependent flow rate and a particle
size distribution including sizes
down to 0.1 μm (Figure 2, page 12).
Tidal breathing was modeled using
the methodology of Gupta, et al.13
Breathing was performed through
the nose with a nostril area of
0.11 in.2 (0.71 cm2). For each breathing
passenger, the tidal breathing
curve was calculated as:
Vtidal(t) = A sin (Bt + C)
Random values of A (amplitude)
and C (phase shift) were generated
for all occupants, with A ranging
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from 0.72 cfm to 0.89 cfm (0.34 L/s
to 0.42 L/s) and C ranging from 0
seconds to 5.8 seconds. As a consequence
of the random phase shift,
passengers were out of phase in
their breathing activities. The same
sinusoidal period with B = 0.45 π s-1
was used for all passengers.
Breathing passengers exhaled 88°F
(31°C) air at 100% relative humidity,13
and inhalation was modeled
to disrupt airflow. Particles were
released by the index passenger
only. Exhaled particles were 0.4 μm,
0.75 μm and 3 μm in diameter, with
367, 92, and 66 particles, respectively
per breath.13 Each index passenger's
exhalation released 9.7 ×
10-5 μg of nonvolatile mass over 2.22
seconds, followed by 2.22 seconds of
inhalation.
Aircraft Simulations
Within an aircraft cabin, a five-row
section of a single-aisle cabin was
modeled with periodic front and
back interfaces, as shown in Figure 1.
Air distribution nozzles were located
above each row on either side of the
aisle, and return air grilles were
located at every window seat position
below the window near the
floor. Breathing zones were defined
in front of the face of each occupant
with an air volume of 0.8 ft3
(0.02 m3) (Figure 3). All 30 seats
within the cabin were occupied, as
shown in Figure 4 (left), and susceptible
passengers were simulated
without the use of masks.
Exposure to particles from a single
cough in an aircraft cabin was modeled
following the methods found in
Davis and Zee, et al.11
For the aircraft, exposure to particles
from breathing by a single
infected passenger was modeled
J U LY 2022
FIGURE 3 Occupant breathing zone marked in yellow,
0.8 ft3 in volume.
at cruise conditions following the
methods described in Davis and Zee,
et al.,11 except as follows. Six simulations
were performed, including
three different index positions with
and without all passengers breathing
to disrupt airflow.
Respiration was simulated for
eight minutes, with 0.05 second
time steps. The nonvolatile mass of
particles that entered an occupant's
breathing zone between minute
three and eight were used to calculate
individual exposure at steady
state. The total mass inhaled over
five minutes was then scaled to eight
hours of exposure to represent the
longest regularly scheduled 737
flight.
Commercial Building Simulations
The ICS was selected for its
similarities to an aircraft cabin-a
relatively confined space with all
occupants in seated positions, a ceiling
air inlet and a ground level air
outlet. The dimensions of the ICS
shown in the middle and right panes
of Figure 4 were 25 ft × 20.5 ft × by
10 ft (7.6 m × 6.2 m × 3 m). An air outlet
with dimensions of 2 in. × 36 in.
(51 mm × 914 mm) was placed in the
corner of the room behind Seat 1 to
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ASHRAE Journal - July 2022

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