Calculation sequence
Step-by-step method
- Define the equipment and metering boundary.
- Confirm representative power, runtime, and load factor.
- Multiply power by runtime and load factor.
MechanicalBeginnerEnergy
Fan Energy-Use Calculator
Calculate fan electrical energy from input power, runtime, and average load factor.
Why it matters: Fan energy depends on both power and operating duration.
Calculated result
Engineering evaluation
Fan electrical energy (E)30,000 kWh
- Entered input power (P)
- 20 kW
- Runtime (t)
- 2,000 h
- Average load factor (LF)
- 75 %
Engineering interpretation
Estimated fan electrical energy is 30000 kWh for the entered interval. This is a screening estimate, not an acceptance result.
Important limitations
- A single load factor is a screening approximation. Interval power data and tariff analysis provide better results.
Motor-driven equipment
Estimate electrical demand and energy use
Use nameplate information and an operating schedule to screen motor input power, current, annual energy, and operating cost. Results update automatically.
Choose the motor nameplate output-power convention.
Rated shaft output, not electrical input.
Used to estimate current; it does not change the hp-based energy result.
Use efficiency at the evaluated load point when available.
Use measured or defensible operating load rather than motor nameplate size alone.
Used only for the estimated current calculation.
Assumes all selected motors operate concurrently at the entered load.
Replace the profile with the actual occupied, process, or control schedule.
$/kWh
Use the applicable marginal utility energy charge; demand charges are not included.Estimated result
Total motor input power (Pin,total)6.21 kW
- Current per motor (I)
- 9.18 A
- Total coincident current (Itotal)
- 9.18 A
- Daily energy (Ed)
- 50 kWh/day
- Annual operating hours (Hy)
- 2,080 h/year
- Annual energy (Ey)
- 12,925 kWh/year
- Annual energy cost (Cy)
- $1,551/year
Equations and assumptions
Nameplate-based screening method
Horsepower is converted using 1 hp = 0.7457 kW. This estimate assumes steady average load and the entered operating-point efficiency. Voltage and power factor affect estimated current, but hp, load, efficiency, quantity, and schedule establish the energy estimate. VFD speed profiles, cycling, standby power, demand charges, and process variation require separate evaluation.
Technical basis: U.S. Department of Energy — Determining Electric Motor Load and EfficiencyEngineering knowledge center
Understand the calculation—not just the answer
Governing relationships
E = P·t·LF/100
Current substitution
E = 20×2000×75/100 = 30000 kWh.
Equation legend
Inputs and calculated quantities
- P
- Fan electrical input — kW
- t
- Runtime — h
- LF
- Average load factor — %
- E
- Fan electrical energy — kWh
- P
- Entered input power — kW
- t
- Runtime — h
- LF
- Average load factor — %
Applications
How this calculation is used
Building design
Screen fan operating energy.
Construction
Check power-meter and status-point boundaries.
Commissioning
Calculate trend-period energy from representative power and runtime.
Quality controls
Assumptions and limitations
Assumptions
- Entered data describe one stable operating condition and use consistent measurement boundaries.
- Time, energy, and performance values are representative of the stated interval.
Limitations
- This is a preliminary evaluation and commissioning-support tool, not an automatic acceptance determination.
- Project sequences, manufacturer data, tariffs, codes, and professional review remain controlling.
Field use
Verification procedure
- Confirm the operating mode, test boundary, and instrument calibration.
- Collect simultaneous readings or a documented trend interval.
- Compare the result with the approved sequence, submittal, and project criteria.
Common engineering mistakes
- Combining measurements from different operating modes or time intervals.
- Ignoring sensor uncertainty, trend sampling, or the defined equipment boundary.
Technical basis
References and source standards
- U.S. Department of Energy—Better Buildings Solution CenterFederal HVAC energy-management and equipment-performance guidance.
- ASHRAE Handbook—HVAC Systems and EquipmentHVAC equipment, central-plant, air-system, and control-performance context; verify the licensed current edition during professional review.
- NIST Measurement and Calibration ResourcesFederal measurement, calibration, timing, and unit-system context.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement