01Start with input power and time
kW is power; kWh is energy over time. An average input of 24kW for five hours uses 120kWh. A meter reading is a better basis for costing than the temperature setpoint alone.
A preliminary estimate is E = Σ(Paverage × t). Mark any assumed average input clearly. A controller display of 40% output does not necessarily mean 40% of rated input power, particularly with phase-angle control, staged loads or current limiting.
02A shift divided into operating periods
| Period or load | Illustrative assumption | Energy |
|---|---|---|
| Startup | 60kW for 0.5 hours | 30kWh |
| Steady operation | Heater average input 24kW for 7.5 hours | 180kWh |
| Circulation pump | Assumed measured average electrical input 2kW for 8 hours | 16kWh |
| Total | Other auxiliaries excluded | 226kWh |
03Apply the tariff to those periods
At an assumed energy rate of $0.12/kWh, the example costs 226 × 0.12 = $27.12 for energy alone. This is an arithmetic example, not a current local tariff or a quoted equipment cost.
For time-of-use pricing, calculate each tariff period separately. Demand charges, capacity charges, taxes and other items follow the applicable contract. Simultaneous starts may affect billing demand. Cutting operating hours does not necessarily reduce demand charges in the same proportion.
04Compare equipment at the same process duty
The material still needs heat to reach the same target from the same inlet condition at the same throughput. Differences between resistance-heating systems may involve insulation losses, overshoot, standby time, flow and control behavior. A change of element material alone does not justify a fixed energy-saving claim.
Record throughput or batch size, inlet/outlet temperatures, operating times and metered energy. Use kWh/batch for batch work or kWh/tonne or kWh/m³ for continuous production, with the material and temperature conditions stated. Bills from two different production schedules are not a controlled efficiency comparison.
05Keep a short operating log
Record the date, batch or throughput, startup duration, steady-run duration, temperatures, flow, heater energy, auxiliary energy and tariff period. Submeter the heater and auxiliaries where practical; if a shared meter is used, identify its other loads.
Find where the energy is being used before evaluating reduced standby, repaired insulation or a different startup schedule. That gives the comparison a defined basis instead of attributing a change in the total bill to one control adjustment.
↗Sources and scope
References support the design principles discussed here. Product-specific limits must come from the selected equipment and fluid documentation. Illustrative values are not purchase specifications.