Measure energy before predicting savings
An ejector system needs coolant flow for chip evacuation. Its energy use must be measured for the actual machine and cycle; a generic subsystem percentage or pump nameplate does not establish energy per accepted hole.
Define the measurement boundary
Meter the whole machine or clearly named subsystems. Include cutting, approach/withdrawal, loading, standby and auxiliary loads consistently. Count accepted holes over the same period.
1Cycle energy (kWh) = average measured input power (kW) × time (hours)
2Energy per accepted hole = total measured energy / number of accepted holes
A transparent calculation example
This is arithmetic with assumed values, not a machine benchmark:
| Input | Assumption |
|---|---|
| Average whole-machine input during a cycle | 45 kW |
| Cycle duration | 8 minutes |
| Accepted holes per cycle | 1 |
| Electricity price | $0.12/kWh |
Energy = 45 × 8 / 60 = 6 kWh. Electricity cost = 6 × 0.12 = $0.72. Replace all inputs with measured values; tool cost, labor and finishing are separate.
When pump affinity relationships apply
Centrifugal-pump similarity relationships concern corresponding operating points and assumptions about geometry and efficiency. Reducing speed also changes available head. Changing drill-head resistance is not automatically the same as moving between those corresponding points. Check the pump and system curves, required pressure, control method and efficiency. KSB technical reference.
A hydraulic estimate can use pressure rise × volume flow; electrical input additionally depends on pump and motor efficiency. Consistent units and a defined operating point are essential.
Evaluate a flow-saving design
The SPH paper reports a lower minimum stable flow for a particular experimental design. Verify the minimum needed for your chips and bore quality, then measure electrical input at the feasible new operating point. Do not cube the reported flow reduction and present that as measured machine savings.
Calculate payback from documented inputs
1Annual energy saving = (baseline kWh/accepted hole - trial kWh/accepted hole)
2 × annual accepted holes
3Annual net saving = energy saving × electricity price
4 + documented other savings - additional recurring costs
5Simple payback (years) = installed investment / positive annual net saving
Include installation, control changes, maintenance and production downtime. If quality or tool life changes, include that evidence before accepting the economic case.
Fluid-flow reduction and electrical energy are different quantities
The study comparison measures the minimum fluid flow at its defined stable-process endpoint. It does not turn the percentage change in flow into an identical percentage change in total electrical energy.
For an energy investigation, name the meter boundary and time interval. A pump-only measurement and a whole-cell measurement answer different questions. A reading while cutting and a charge covering loading, circulation and idle periods also use different boundaries. Keep accepted output with the selected interval before reporting energy per delivered hole.
An illustrative calculation shows the denominator issue without claiming a trial: if a defined interval consumes 12 kWh and yields 40 accepted holes, its assigned energy is 0.30 kWh per accepted hole. If only 30 holes are accepted, the same interval becomes 0.40 kWh per accepted hole. Neither example establishes a pump-efficiency curve or a coolant setting.
A process modification may be worth evaluating while the energy claim remains open. Record actual energy, time, tool configuration and inspected output rather than borrowing a fluid-flow percentage as the answer. Continue to parameter records and the accepted-hole cost tool for consistent comparison boundaries.
Revision note
October 8, 2026: revised the technical explanation and connected reading after source review. Original publication date and URL retained.
