Concept reference

Specific Energy (kWh per m³)

C.1Plain-language definition

Specific energy lets stations and alternatives be compared without confusing a larger annual volume with worse performance. The hydraulic floor is set by head; wire energy is higher because pump, motor and drive efficiencies are below one. A single value is meaningful only with the duty and system boundary that produced it.

C.2Governing relation or decision logic

For steady duty, e = ρgH/(ηpηmηd) J/m³. Divide by 3.6×10⁶ J/kWh to obtain kWh/m³. Equivalently, measured specific energy is Ewire/Vdelivered. Density is kg/m³, g m/s² and head m.

C.3The failure to name

Using peak head and peak efficiency together may describe no real operating point. Comparing station meter energy with pump-only hydraulic calculations also shifts the boundary by ventilation, controls or ancillary loads.

C.4Field review checklist

• Define electrical and hydraulic measurement boundaries.
• Pair flow, head and efficiency at the same operating point.
• Weight variable duties by delivered volume or time as appropriate.
• Separate pumping, standby and ancillary loads when diagnosing performance.

C.5Where it fits in the course

§7.5 converts duty to specific and annual energy; §6.2 separates efficiencies.