Knowledge!Method for Calculating the Power of a Fan Motor

The selected motor power is calculated as follows: N = (Q/3600) * P/(1000*η) * K.

Where Q is the air volume in m3/h, P is the total pressure in Pa, N is the power in kW, η is the total pressure efficiency of the fan (according to relevant standards, the total pressure efficiency should not be lower than 0.7, though actual efficiency can be slightly lower and can go as low as 0.6. For small fans, take the lower value and for large fans, take the higher value), K is the motor capacity factor, as shown in the table below.

1. Centrifugal fan

Power,KW	General	Dust	High Temp
<0.5	1.5	1.2	1.3
0.5-1	1.4	1.2
1.3	2-5	1.2
>5	1.1-1.15

2. Axial fan：1.05-1.1，Take the higher value for small power and the lower value for large power.

The selected motor power is calculated as follows N=（Q/3600）*P/（1000*η）*K
Calculation of Fan Motor Power: The formula for calculating the power P (kW) of a fan is P = Q * p / (3600 * 1000 * η0 * η1).

Q – Air volume, m3/h;

p – Total pressure of the fan, Pa;
η0 – Internal efficiency of the fan, usually taken as 0.75 to 0.85, with lower value for small fans and higher value for large fans.

η1 – Mechanical efficiency:

1. Direct coupling between the fan and motor is taken as 1;

2. Coupling with a coupling device is taken as 0.95 to 0.98;

3. Triangle belt transmission is taken as 0.9 to 0.95;

4. Flat belt transmission is taken as 0.85.

How to calculate the current of the motor:

I = (Motor Power/Voltage) * c

Power unit: kW

Voltage unit: kV

c: 0.76 (product of power factor 0.85 and power efficiency 0.9)

Explanation of the formula for calculating fan shaft power: N = Q * P / 1000 * 3600 * 0.8 * 0.98

Q is the flow rate in m3/h, and P is the total pressure in Pa (N/m2).

Note: The basic unit of power is W. In dynamics, W = N.m/s.

QP has the unit of N.m/h = W * 3600.

Fan shaft power is generally represented in kW.

1000 is used to convert W to kW.

3600 is used to convert hours to seconds.

The above calculation obtains the output power of the fan itself. Fan shaft power refers to the input power of the fan, which is equal to the output power of the motor. Dividing the fan output power by the conversion efficiency gives the fan shaft power.

0.8 is an estimated value of the internal efficiency of the fan.

0.98 is an estimated value of the mechanical efficiency.

(Please note that these values are for reference and may vary depending on the specific fan being used.)