ASHRAE Journal - July 2023 - 62
TECHNICAL FEATURE
FIGURE 12 Susceptible individuals infected as a function of the time all persons spend in the common spaces.
FIGURE 13 Susceptible individuals infected as a function of air renewal and of the fraction of air extracted from
the common spaces.
It is interesting to observe that, in
the case illustrated in Figure 7, the
reproduction index R* reaches a
maximum as the air recircculation
rate increases to 75 m3 h-1
person-1 (44 cfm/person) and then
decreases at higher recirculation
rates. This result, also evident in
Figure 9 for removal/inactivation
efficiencies less than 80%, is due
to the double, contrasting effect
of increasing air recirculation
when air purification devices are
present in the supply ducts. On
one hand, air recirculation spreads
the virus to the rooms occupied by
the susceptible individuals; on the
other hand, the device in the airhandling
system remove/inactivate
the virus content in all the rooms.
Note that the same results on
the risk of infection are obtained
with the installation of the viral
filtration/inactivation device on
the recirculated air fraction only,
with a smaller flow rate than the
total supply flow rate, given the
assumption of no virus in the
outdoor fresh air.
Common Spaces Ventilation
Management
By suitable adaptation of
Equations 3, 4 and 5, it is possible
case of double-occupancy rooms, the effect of virus
removal/inactivation on all exposed subjects. As
seen in the plot labels in Figures 6, 7, 8 and 9 and Online
Figure 2, the case refers to two people in room 1 (one
infected and one susceptible person) of volume
2V1, while the other NS − 2 people are segregated in
the other rooms; each individual again has at his
disposal a volume V1 = 50 m3 (1800 ft3). Therefore the
number of potentially infected individuals includes
one susceptible individual in room 1 and NS − 2
susceptible individuals in the remaining rooms;
because of the presence of the infector's roommate,
R* cannot reach 0 even for rc = 0.
62
ASHRAE JOURNAL ashrae.o rg
J U LY 2023
to extend the segregated model to specific realworld
applications and to consider common spaces
and a likely scheduling for room occupation as well.
Figure 10 shows the situation where, in addition to NS
single-occupancy offices, there are common spaces
(corridor, service rooms) with a volume amounting
to 20% of the total volume of the offices served by
the primary air HVAC plant. It must be noted that
this is not an all-air plant, but a ventilation/primary
air system. The infected individual is in room 1 and,
along with his workmates, spends a fraction of the
working time (8 h per day) in the common areas. In
addition, all the occupants leave the building for a 1 h
http://ashrae.org
ASHRAE Journal - July 2023
Table of Contents for the Digital Edition of ASHRAE Journal - July 2023
Contents
ASHRAE Journal - July 2023 - Intro
ASHRAE Journal - July 2023 - BB1
ASHRAE Journal - July 2023 - BB2
ASHRAE Journal - July 2023 - Cover1
ASHRAE Journal - July 2023 - Cover2
ASHRAE Journal - July 2023 - 1
ASHRAE Journal - July 2023 - Contents
ASHRAE Journal - July 2023 - 3
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