How to calculate the pump efficiency

[sowhatso]

I need to calculate the pump efficiency for an installed booster pump. I have a problem with calculating the output power of the motor (the brake horse power BHP) , I can calculate the input power for the motor by using the data I can get from the VFD , and I can calculate the output power of the pump by using the measurements I can get from the pressure gauge and the flow meter , But I can’t calculate the BHP as I don't have capability to measure the torque and the rpm values for the shaft , can I use the motor efficiency I got from the manufacturer datasheets and consider it as a constant value ???? Or do you have any other way to calculate the BHP??

 

[SNORGY]

What has worked for me in the past is measuring the motor current draw with the pump in operation in conjunction with the pressure and flow that you are measuring. Assuming a motor efficiency of 95% (or whatever number the motor supplier claims) you should end up pretty close to the power delivered to the pump shaft.

P = ?·?3·V·I·cos? <-- last term being power factor

You know the power imparted to the fluid by the pump (assuming a centrifugal, for example):

Hydraulic power = [(lb/min)*H]/33000 with H in feet

One divided by the other will yield the pump efficiency.

Once thus derived, you could check it using:

P = [Q*H*SG]/[3960*e], Q in USGPM and H in feet


Regards,

SNORGY.

 

[Artisi]

I using VFD it seems to me you would be missing the motor efficiency and power factor which must be varied from that of a standard wired motor.

 

[BigInch]

Efficiency of the motor varies with the load to rated load ratio too, so you'll need the complete motor efficiency curve, especially if your vfd is controlling the pump to 50% rpm or less.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[dabluffrat]

For an Approx BHP...

Motor Input KW from VFD / 0.746 = Input HP to motor

Input HP to motor Multiplied by NEMA Nominal motor efficiency = BHP (motor output HP)

Pump efficiency = (Head X Flow X SG) / (3960 X BHP)

If you need to go into more detail for the reduced speed, then yes motor efficiency will be less for reduced speed. Also consider HP consumed in the thrust bearing




Did you know that 76.4% of all statistics are made up...

 

[sowhatso]

dabluffrat ,

why did you divide the Motor Input KW from VFD by / 0.746 to get the Input HP to motor

How did you get this number 0.746 ? and is it applicable for all the VFDs ?

 

[sowhatso]

Sorry dabluffrat ,

I just observed it was the multiplier to convert the unit from KW to hp.

Thanks,