6.2 Fans
229
Pressure
Airflow rate
Airflow rate
Power
Forward
Radial
Backward
Forward
Radial
Backward
Axial
a)
b)
Fig. 6.29 a Pressure and b power curves for different types of centrifugal fans
is not overloaded as long as the speed of rotation remains constant despite variations
in the resistance of the system.
6.2.12 Characteristic Curve for Series and Parallel
Connection of Fans
In a series arrangement of identical fans without mutual interference, the total pressure is equal to the sum of the individual total pressures provided by each one of
them (Fig. 6.30a, b). In this type of connection, if one of the fans is weaker than the
other is, it can act by slowing down the most powerful one (tandem effect).
25
10
20
Pressure
1 fan
2 fans
Airflow rate
a)
b)
25
20
10
25
Fig. 6.30 a Connection diagram of fans in series; b characteristic curves of the series connection
of two identical fans
Moreover, in a parallel system of fans, the total airflow rate is equal to the sum of
the individual flows provided by each of them (Fig. 6.31a, b).