Calculating Fan and Blower Power

Fans and blowers are critical components in process engineering for moving gases. Fan power is a function of the actual volumetric flow rate and the differential pressure across the unit. A widely used formula in Imperial units is:

P = 0.1175 × Q_cfm × ΔP_in / η

Where P is power consumption (Watts), Q_cfm is volume flow in cubic feet per minute, ΔP_in is pressure increase in inches of Water Gauge (WG), and η is fractional efficiency. For standard industrial use, if efficiency data isn’t provided by the vendor, it is safe to assume around 60%.

Fans vs. Blowers vs. Compressors

The distinction usually depends on the pressure ratio. Fans operate at low pressures (typically less than 0.1 bar or 1000 mmH₂O) and are used primarily for ventilation and HVAC. Blowers achieve higher pressures (up to ~1.5 bar) via centrifugal force. Compressors are utilized when the gas volume needs to be significantly compressed at high pressure ratios.

General Rules of Thumb

• Suction Velocity: Should generally be kept less than 10 m/s to prevent excessive frictional losses on the intake.
• Discharge Velocity: Should generally be kept less than 30 m/s to avoid excessive noise and vibration.

Take Your Skills Further

While calculating individual equipment power is necessary, evaluating how your blower interacts with piping networks, heat exchangers, and control valves requires an integrated approach. Learn how to simulate full plant models in our Aspen HYSYS Training Courses.