The plant
A plant runs 40 centrifugal pumps, each driven by an 11 kW 4-pole motor working at about 75 % load for 6,000 hours a year. The proposal: replace the IE2 motors with IE3.
Step 1 · The simple calculation
EMPD tested values at 75 % load: IE2 EM2-160M-4-11 91.0 %; IE3 EM3-160M-4-11 92.8 %.
Step 2 · The slip effect
An IE3 motor has lower losses, so it slips less: 1,475 rpm against 1,465 rpm for the IE2. A centrifugal pump's power rises with the cube of speed.
The pump now delivers about 0.7 % more flow and head than the process needs, and the extra is throttled away in the valve. The efficiency gain is spent on pumping water the plant does not use.
Step 3 · Unlocking the saving
Bring the pump back to its duty point. By the affinity laws, trimming the impeller in proportion to the speed increase does it:
Where pumps run on variable-speed drives, the controller does this automatically. With the duty point restored, each motor saves the full 1,055 kWh a year.
Step 4 · Power factor
The IE3 motor's power factor at 75 % load is 0.75 against 0.78 for the IE2. Across 40 motors the plant's reactive demand rises slightly; check the capacitor bank setting at commissioning.
Result
The IE3 retrofit saves about 42,200 kWh and 30 t of CO₂ a year, but only if the pumps are trimmed or speed-controlled. EMPD's application engineers run this check on every pump and fan retrofit enquiry. Try your own numbers in the energy savings tool.
Application study: an engineering example worked by EMPD with catalogue data. Your application is confirmed by our engineers before quotation. Send us your duty.
