As can be seen from the figure above, when the fan Rotational Speed (S) is the same, the Outlet Air Velocity (V) of a forward-curved fan will be much higher than that of a backward-curved fan. Therefore, to generate the same Airflow Volume and Pressure, a backward-curved fan requires a higher Rotational Speed or an increased fan Dimension.
Because of this, a smaller Dimension, lower Rotational Speed, and lower Noise are the Advantages of a forward-curved fan compared to a backward-curved fan. However, the Efficiency of a backward-curved fan is much higher than that of a forward-curved fan, offering better energy savings.
The formula for the fan to generate Pressure is:
$P_t = \rho \left[ \frac{C_2^2 – C_1^2}{2} + \frac{U_2^2 – U_1^2}{2} + \frac{W_2^2 – W_1^2}{2} \right]$
Benefiting from the fact that it is easier to obtain higher Pressure at the same Rotational Speed, forward-curved fans are also used in applications with extremely small Airflow Volume and ultra-high Pressure (where Efficiency is extremely low), in cases where Efficiency can be ignored.
Overall, backward-curved fans are suitable for conditions with relatively high Pressure, low Flow Rate, and high Power. In contrast, forward-curved fans are suitable for Operating Conditions with large Airflow Volume, low Pressure, and low Power, or ultra-low Airflow Volume and high Pressure.