
concentration C (C
i
indoors and C
o
outdoors) by:
Q
e
¼
S
C
i
C
o
ð1:22Þ
where S is the CO
2
source strength, i.e. about 20 l/h. The equivalent outdoor
airflow rate per person can then be assessed during the periods of time when
steady state can re asonably be assumed, that is when the CO
2
concentration
is constant.
Example of application
CO
2
concentration was recorded every five minutes during several winter days
in an office room occupied by one person.
The evolution of CO
2
concentration is shown in Figure 1.1. A base outdoor
concentration of about 600 ppm was determined from the minimum values at
the end of long decay periods (weekends). This base concentration is deducted
from the CO
2
concentration to get the increase resulting from indoor sources.
On 19 November, a CO
2
concentration of about 1500 ppm is observed. This
corresponds to an equivalent outdoor airflow rate at 22 m
3
/(h person), obtained
by natural ventilation. Decay periods are selected in the record (rectangles in
Figure 1.1).They correspond to night or weekend periods, without occupancy,
when windows and doors are closed and the air change rate results from
infiltration only. The average nominal time constant from these five decays is
found to be 10 2 hours.
Application to buildings, multi-zone
Most buildings include several interconnected zones. In order to measure not
only the airflow between internal and external environments but also inter-
zone flows, either several tracer gases should be used simultaneously (injecting
each of them in a different zone), or several experiments should be conducted
successively, injecting the tracer successively in the different zones, and
assuming that the measurement conditions, in particular the airflow pattern,
Figure 1.1 Records of CO
2
concentration in an office room
Source: Roulet and Foradini, 2002.
6 Ventilation and Airflow in Buildings
Comentarios a estos manuales