Motor HP for Given CFM

Pressure rise multiplied by volumetric flowrate divided by efficiency. It will get to the right order-of-magnitude.

Use Kruger software for the same.

Use following equation to get the BHP.

BHP = {[capacity in cfm X pressure in inches ] \ 6356 }* 0.75

This BHP is at duty point .

Now , Motor hp = 1.15 * BHP.

From motor selection data select next available motor. Also, don`t select the motor on borderline, cause fan is fabricated one and it is an art. So some allowance should be considered.

The fan can be tested by IS method or simply by anemometer method. Current consumption at different damper opening gives you suitability check for the motor you selected.

Make sure these are intersecting values or pressure and airflow on pressure airflow curve in the normal operating conditions,and are not the maximum pressure and maximum airflow, Otherwise your all calculations may go wrong, and you may end up with much bigger unit than of required.

Following formula can be used to calculate motor power:

Air Power (kW) = Pressure rise (Pa) x Flow rate (Cu.m/s)

If pressure is static it is 'static air power' and for total pressure it is 'total air power'.

Break kW = Air Power (kW) x Efficiency

Use 'static efficiency' or 'total efficiency' (~0.75) depending on air power.

Motor kW = 1.15 x Break kW

Motor HP = Motor KW/ 0.75