368
8 Secondary Ventilation
From which we get the total pressure:
P T v = P T c + P
vv = 2913.564 Pa + 655.58 Pa = 3569.14 Pa
Fan selection
The operating point of the fan is, therefore:
P T v = 3553.4 Pa
Q v = 41.87 m
3 s
−1 [calculated in (f)].
If η = 0.83 (remember that η varies with P and Q and has to be obtained from
graphs) as given in the statements:
Pw =
P T v Q v
η
=
3569.14 Pa · 41.87
m
3
s
0.83
= 180048.06 W
Pw = 180 kW
If the fan performance curve was provided, we would interpolate the curves and
follow this scheme:
Total Pressure
Airflow rate
Airflow rate
Power
41.87 m
3 s
-1
3569.14 Pa
180 kW
Pitch angle
Pitch angle
It should be noted that the installation might require such a large power that it
cannot be supplied by a single fan. In this case, several fans are used in series. Another
aspect to consider is that the calculations have been made for the maximum length
of the gallery. However, during the advance, gallery length will be smaller than this
maximum. As a result, the airflow rate must be regulated using a variable frequency