ASHRAE Journal - July 2022 - 16

TECHNICAL FEATURE
FIGURE 4 (Left) Layout of aircraft cabin CFD model with inlets at ceiling above windows and return air grilles at floor level; (Center) layout of ICS CFD model; (Right) isometric
of ICS CFD model.
1A 1B 1C
2A 2B 2C
3A 3B 3C
4A 4B 4C
5A 5B 5C
1D 1E 1F
2D 2E 2F
3D 3E 3F
6
4D 4E 4F
5D 5E 5F
5
4
TABLE 1 Airflow and thermal boundary conditions used for CFD simulations
737 AIRCRAFT
COUGH
737 AIRCRAFT
BREATHING
SUPPLY FLOW RATE
(ACTUAL cfm)
RETURN FLOW RATE
(ACTUAL cfm)
AIR CHANGES PER HOUR
RELATIVE HUMIDITY (%)
OCCUPANT HEAT
GENERATION (W)
WALLS (°F)
CEILING, FLOOR,
STOWAGE BINS
FRONT AND BACK
INTERFACES
SUPPLY AIR
TEMPERATURE (°F)
ENVIRONMENT
AVERAGE TEMPERATURE (°F)
ALL OCCUPANTS INHALING/
EXHALING?
RECIRCULATION?
Yes for
simulations
with relative
humidity > 0%
Yes
Yes
No
represent a gap under a door or a return air grille. To
accurately model the relatively small but geometrically
complex ceiling air supply diffuser in the room and to
accelerate the simulation, a validated simplified method
by Mohammed15 was adopted for this study. Seven simulations
were performed, including three inlet airflow
rates, three index positions and two air inlet positions,
and the same cough as used in the aircraft simulation.
Simulations were performed with an air inlet placed
16
ASHRAE JOURNAL ashrae.o rg
J U LY 2022
Both
No
323 - 588
Same as
supply
24.7 - 44.9
0 - 20
70/person
55 - 65
Adiabatic
Periodic
62 - 67
75 - 77
588
Same as
supply
44.9
70/person
65
Adiabatic
Periodic
65
75
3
2
1
7
8
9
14
13
12 3 ft
-90°
11
6 ft
10
INDOOR
COMMERCIAL
SPACE
COUGH
171 - 683
Same as supply
2 - 8
50
70/person
Adiabatic
Adiabatic
Non-periodic
65
70 - 80
either in the center of the room, or above the head of
Seat 5 (Figure 4, circled in center pane). The air supplied
to the ICS was entirely outdoor air with no recirculation.
Exposure from particles released by a single cough
within an ICS followed the same methodology as in an
aircraft cabin,11 except the aircraft CFD models were
simulated until 1% or less of the particles remained in
the air, but ICS simulations were simulated for 15 minutes
regardless of airflow rate. Overall, mass remaining
airborne in the ICS simulations should lead to a slight
underestimation of the inhaled mass in the ICS when
compared to an aircraft.
A summary of boundary conditions used for the CFD
models are shown in Table 1.
Results
Comparisons Between Commercial Building and Aircraft
The total airborne particles within the airplane and
ICS environments were tracked throughout the simulations.
The set of simulation conditions presented
allow us to see the time-based performance of both the
aircraft and the ICS. The longer the period required to
lower the total number of particles, the more opportunity
for a susceptible person to breathe in those
particles.
Figure 5 shows the total number of airborne particles
versus time, displayed as a percent of particles released
during the simulation of a cough or breathing. It should
be noted that this is the percentage of total particles
present in the simulated release, not the percentage
in the breathing zone of susceptible persons in the
environment.
6.7 ft
44.5°
8.6 ft
10.9 ft
24.9°
55.8°
http://ashrae.org
ASHRAE Journal - July 2022

Table of Contents for the Digital Edition of ASHRAE Journal - July 2022
