ASHRAE Journal - April 2024 - 42

TECHNICAL FEATURE
increasing outdoor air ventilation in corridors.
The CO2 generation rate of each teacher was assumed
to be 0.45 L/min (0.016 cfm)16 to account for their
moderate activity level. The CO2 generation rate of each
student was assumed to be 0.27 L/min (0.0095 cfm)
while in the classroom to account for their sedentary
activity level during instruction, and assumed to be
0.72 L/min (0.025 cfm) while transitioning between
classes in the corridors to account for their increased
activity (e.g., walking, talking).
The annualized exposure to CO2 either in the
classroom or in the corridor over the course of a
school year during core hours (8 a.m. to 3:50 p.m.)
was calculated using CONTAM simulated CO2
concentrations. Three levels of outdoor air ventilation
rates were simulated for the corridors: (a) no
ventilation, meaning no outdoor air was directly
supplied to the corridors mechanically. Classroom
doors had undercuts to passively ventilate corridors,
and classroom doors were open at transition times;
(b) the Standard 62.1-2022 required rate for general
corridors (0.3 L/s·m2 [0.06 cfm/ft2]); and (c) double the
requirement (0.6 L/s·m2 [0.12 cfm/ft2]). The outdoor
CO2 concentration was held constant for all simulations
at a value of 412 ppmv.17 It should be noted there may
be an outdoor air ventilation rate less than 0.6 L/s·m2
(0.12 cfm/ft2) that would meet an objective of matching
the annualized CO2 exposure in the corridors to that of
the classrooms. Double the Standard 62.1-2022 required
rate was a conservative value to simulate here.
To demonstrate the impact of changing outdoor air
ventilation in the corridors, where constant sources of a
variety of contaminants would be present, a total volatile
organic compound (TVOC) emission rate was taken from
a study of 144 classrooms.18 Thus, an emission rate of
32 μg/(m3·h) was simulated in the classrooms. In the
corridors, the emission rate was assumed to be 30% of
the classroom emission rate based on floor area.
Simulation Results and Real-World Solutions
At 7 a.m., the outdoor air ventilation system turns
on and people start to occupy the building. At 8 a.m.,
classes are in session. Figure 2 shows the simulated
indoor minus outdoor CO2 concentration in the
Secondary School on a typical day during core hours
† In this work, CO2 concentrations are expressed in ppmv, which is
equivalent to μL/L.
42
ASHRAE JOURNAL ashrae.org A P R I L 2024
(8 a.m. to 3:50 p.m.). The cyclical nature of the CO2
concentrations during core hours was due to the
simulated one-hour blocks.
As expected, the CO2 concentration in the corridors
was higher than the concentration in the classrooms,
no matter the outdoor ventilation rate in the corridors.
Keep in mind that with CONTAM, as with all multizone
models, the concentration of any contaminant is
instantly dispersed throughout a zone at a given
timestep since the zone is represented by a single node.
This means that in Figure 2, the CO2 concentration
may be building up faster than it would under real
conditions. Nonetheless, the relatively high density
of students in schools and their thermal plumes may
enhance mixing in the corridor. When the corridors
were ventilated at double the required rate, indooroutdoor
CO2 concentrations in the corridors reduced
an average of 27%. The annual average indoor-outdoor
CO2 concentration in the classrooms reduced 2% with an
increase in ventilation in the corridors.
As stated in the " ASHRAE Position Document on Indoor
Carbon Dioxide, " CO2 concentrations should only be
used to assess and evaluate IAQ. Because the students
are only in the corridor 10 minutes out of every hour,
the authors used an annualized CO2 exposure to take
into account the CO2 concentration in the space as well
TABLE 1 Simulated annualized CO2 exposure (ppmv·h).
CORRIDOR NOT
VENTILATED
CORRIDOR VENTILATED
AT REQUIRED RATE
Classrooms
Corridors
8900
14 500
8700
10 300
CORRIDOR VENTILATED AT
DOUBLE THE REQUIRED RATE
8500
7500
Notes: Classrooms in all simulations were ventilated at the ASHRAE Standard 62.1-2022
minimum required rate. The CO2 concentration is impacted by many factors, including
the assumed CO2 generation rates of the occupants.
as the time spent in the space. Table 1 summarizes the
average annualized CO2 exposure in the classrooms
and corridors at three levels of corridor ventilation.
Simulation results showed that improvements to IAQ
could be made in the corridor by doubling the per floor
area outdoor air ventilation rate in the corridor. By
doubling the corridor ventilation, the annualized CO2
exposure in the corridors was about the same as that in
the classrooms.
The authors also noted that relying solely on classroom
ventilation to ventilate the corridors is not an effective
method for providing outdoor air to the corridors.
In Table 1, with no ventilation provided directly to the
http://www.ashrae.org
ASHRAE Journal - April 2024

Table of Contents for the Digital Edition of ASHRAE Journal - April 2024
