QIYUE FAN / BUYER ECONOMICS
Annual Fan Energy Cost: Compare the Duty Cycle, Not Motor kW
Two quotations can meet the same peak duty yet consume different amounts of electricity over the year. Compare the time spent at each operating case before calling one option more economical.
Compare energy costs only after both fan selections meet the required airflow, pressure and operating conditions.
Start with one common power boundary
Use electrical input power at the same defined boundary for both offers, including the drive/controller where applicable. Fan shaft power, motor mechanical output and motor nameplate rated output are not interchangeable with that input.
If a supplier provides only shaft power, ask for the applicable motor and transmission/controller assumptions needed to establish comparable electrical input. Identify estimates separately from measured results. The fan power calculation guide explains these boundaries.
A worked example with three operating cases
The annual schedule below contains 6,000 non-overlapping operating hours. “Low,” “normal” and “peak” are case labels, not guaranteed speed or airflow percentages. In a real comparison each row needs its own verified flow, pressure, gas condition and control basis.
Scroll the table horizontally on a narrow screen to compare all columns.
| Operating case | Hours/year | A input kW | A kWh/year | B input kW | B kWh/year |
|---|---|---|---|---|---|
| Low duty | 1,000 | 8 | 8,000 | 10 | 10,000 |
| Normal duty | 4,000 | 18 | 72,000 | 16 | 64,000 |
| Peak duty | 1,000 | 30 | 30,000 | 28 | 28,000 |
| Total | 6,000 | Not summed | 110,000 | Not summed | 102,000 |
Annual energy for the example above; both bars use the same scale.
Check the arithmetic before comparing the price
Annual energy = sum of (electrical input kW × hours at that case).
A: (8 × 1,000) + (18 × 4,000) + (30 × 1,000) = 110,000 kWh.
B: (10 × 1,000) + (16 × 4,000) + (28 × 1,000) = 102,000 kWh.
For an assumed flat energy-only tariff of USD 0.10/kWh, the example gives A = USD 11,000/year and B = USD 10,200/year: an USD 800/year energy-charge difference. Replace the assumed tariff with your site’s energy rate.
A uses less power in the low-duty row, but B uses less annual energy under this schedule. A different operating schedule can change the comparison. Do not use one favorable point as proof of the annual result.
What this example deliberately leaves out
- Time-dependent tariffs and demand charges: apply the actual billing structure. A blended kWh price alone may not reproduce the bill.
- Non-running consumption: include relevant standby, control, cooling or auxiliary loads at the defined boundary. Do not silently set them to zero in a real project.
- Lifecycle costs: keep purchase, installation, maintenance, downtime and other agreed costs separate from the energy calculation.
- Uncertain production hours: show the base schedule and a credible alternative schedule. Do not present estimated production as measured history.
Ask for a comparable energy submission
Give both suppliers the same operating-case schedule. Ask them to return each case’s airflow and pressure basis, gas condition, speed/control method, electrical input boundary, supporting curve or calculation reference, and any exclusions. Keep assumptions and revisions visible.
The DOE/AMCA sourcebook’s Fan System Economics chapter emphasizes representative operating data and load-duty cycles; it also distinguishes energy charges from more complex tariff and lifecycle considerations. A single snapshot is not enough for a widely varying load.
Continue with the quotation scope comparison and performance evidence review. For a project enquiry, send the duty schedule and comparison basis.
Official reference
DOE/AMCA: Improving Fan System Performance, A Sourcebook for Industry, Fan System Economics, printed pages 55–58.