6.2 Fans
231
• 130 kW-fan characteristic curve: P fan = −1.0745Q
2
+ 60.885Q + 1613.2
• 150 kW-fan characteristic curve: P fan = −1.1906Q
2
+ 54.583Q + 2424.9
Determine the optimal series configuration of two equal fans which better meets
the system needs.
Solution
The system impedance curve, obtained from the table, is:
P sist = 2.277Q
2
The options of two units of 130 kW and of two units of 150 kW, in series, are
analysed.
(a) Coupling in series 2 units of 130 kW.
The characteristic curve of the fans and the system is:
P fan = −2.149Q
2
+ 121.77Q + 3226.3
P sist = 2.277Q
2
The common point is obtained by solving the system by equalization:
2.277Q
2
= −2.149Q
2
+ 121.77Q + 3226.3
Therefore:
Q = 44.06 m
3 s
−1
P = 4419.8 Pa
(b) Coupling in series 2 units of 150 kW.
The characteristic curve of the fans and the system is:
P fan = −2.3812Q
2
+ 109.166Q + 4849.8
P sist = 2.277Q
2
Equaling both expressions:
2.277Q
2
= −2.3812Q
2
+ 109.166Q + 4849.8
Therefore:
Q = 46.05 m
3 s
−1
P = 4827.56 Pa
The solution that best suits the needs is that of two fans of 150 kW arranged in series.
A comparative analysis of the different options is given in the following figure: