KEVOS® MAKEOS · Power Transmission
Fan Duty, Fan Laws and Belt Drive
What power does this fan need, how fast must it run for more air, and what pulleys and motor does that take?
Fan drive sizing: air power and shaft power from flow, fan total pressure and efficiency; the fan speed, pressure and power for a new flow by the fan laws (as the affinity tool, on a system without static pressure); motor power with belt losses and margin and the next IEC rating; and the fan pulley diameter for the motor speed and motor pulley.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Present airflow | m³/s | Airflow the fan delivers now. |
| Fan total pressure | Pa | Total pressure rise across the fan at that flow. |
| Fan efficiency | % | Fan total efficiency at that point. |
| Present fan speed | rpm | Fan speed now. |
| Required airflow | m³/s | Airflow you need. |
| Belt drive efficiency | % | Efficiency of the belt drive. |
| Motor margin | % | Margin above the shaft power for the motor. |
| Motor speed | rpm | Motor full-load speed. |
| Motor pulley pitch diameter | mm | Pitch diameter of the motor pulley. |
Method and formulas
- Air power = Q p; shaft power = air power ÷ η.
- Fan laws: speed ∝ Q, pressure ∝ Q², power ∝ Q³ (same system, no static pressure).
- Motor = shaft power ÷ belt efficiency × (1 + margin), next IEC rating.
- Fan pulley = motor pulley × motor speed ÷ fan speed.
- Example: 6 m³/s needs the fan at 1,200 rpm, 9.8743 kW at the shaft and a 15 kW motor.
Limitations
- Fan laws assume the system curve passes through zero; systems with static pressure (filters, dampers held at pressure) need the fan curve.
- Check the fan’s maximum safe speed before speeding it up.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Find the fan speed and motor needed for more airflow
- Size pulleys to change a belt-driven fan’s speed
- Estimate the power saving from slowing a fan
Who it is for
- Plant engineers
- Maintenance engineers
- Process engineers
What you get
- Present air and shaft power
- Speed, pressure and power for the new flow
- Motor rating and fan pulley size
Interpreting the result
- Power rises with the cube of speed: 20% more air needs about 73% more power.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2487–2536. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
