
efficiency was doubled, and the mean age of air was maintained despite a
reduction of the ventilation rate – and of energy use – by a factor two.
Mapping the age of the air in rooms
This chapter demonstrates how to assess the age of air at some location and
on the average in a room. It may nevertheless be interesting to map this
quantity in a room, in order to check, for example, if the occupants have
the best possible air, or to look for dead zones. Davidson and Olsson (1987)
have already generated such maps using computer codes, and some
qualitative representations have been drawn from measurements (Valton,
1989). Since the measurement of the age of the air at a given location is not
Hall
Air inlets
Added air inlet
Exhaust grilles
Added exhaust grille
Added door
Office
Conference
room
Figure 3.7 Arrangement of the conference room after improvement
Source: Roulet et al., 1998.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0
100
200
300
400
500
600
700
800
900
1000
Initial values After improvement
Air change efficiency
Age and time constant [s]
Mean age of air
Nominal time constant
Air change efficiency
Figure 3.8 Room ventilation characteristics be fore and after improvement
Source: Roulet et al., 1998.
Age of Air and Ventilation Efficiency 49
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