re FAN EFFICIENCY FORMULA DERIVATION

Dear XXXX,

Simply, Fan Process Power = Flow in M3/s*Fan total pressure in pa

and Shaft power is given by supplier at that particular RPM, so this process power / Shaft power = Fan's efficiency and the motor rated power is given by supplier @ 0.85 % to 0.9 %.

or Shaft power = Torque*rpm/9550

where , Torque(NM )=  Moment of Inertia * Angular acceleration / acceleration due to gravity

and Moment of Inertia = Mass of Fan * ( R2+r2) / 2  in Kg-M2

similarly for moment of inertia of motor

add both moment of inertias .

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re FAN EFFICIENCY FORMULA DERIVATION

Hello Sidhant,

Your example;-

 1mmwc = 9.8 Pa

so put 1Pa = 0.102 mmwc

efficiency = m3/s X 0.102 mmwc *100/( motor kw x motoe eff.)

is incorrect, because you need to divide a value expressed in mmwc by 0.102, to convert to Pascals, not multiply !

The fan efficiency formula is in SI units. ie.  Air Flow must be in m3/s, Pressure must be in Pascals, and Power must be in Watts.   So, to use mmwc in the formula,  you need to convert the mmwc into Pascals by dividing by 0.102.  So, it should be;-

1mmwc = 9.8 Pa    or  1Pa = 0.102 mmwc

Lets call the pressure measured in mmwc, Pmmwc. So, dividing Pmmwc by 0.102 to get Pascals we get, (Pmmwc/0.102)  Pa.  Now, using this value in the efficiency formula gives us;-

% efficiency =  m3/s *  Pmmwc / 0.102 * 100 / ( motor W * motor eff.)

Or;-

% efficiency = ( m3/s *  Pmmwc  * 100) /( motor W * motor eff. * 0.102)

Now, expressing power in kilowatts instead of watts we get;-

% efficiency = (m3/s * Pmmwc * 100) / ( motor KW * 1000 * motor eff. * 0.102)

And, simplifying we have;-

% efficiency = (m3/s * Pmmwc * 100) / ( motor KW * motor eff. * 102)

Hope this makes it clear for you, Sidhant.

Also thank you Chari for your worked example.

Regards,

Ted.

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re FAN EFFICIENCY FORMULA DERIVATION

DEAR CHARI & TED,

THANKS A LOT FOR THE CLARIFICATIONS BUT

WATT = M3/S x Pa

NOW 

1MMWC = 9.8Pa

SO Pa= 1/9.8MMWC

PUTTING

WATT = M3/S x MMWC/9.8 

NOW 

1000xWATT = 1000 x M3/S x MMWC/9.8

KW = 102 x M3/S x MMWC 

NOW TELL BE WHERE IS THE MISTAKE.

REGARDS

SIDHANT

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re FAN EFFICIENCY FORMULA DERIVATION

Dear XXXX,

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