Energy-Saving Methods for Pumps and Fans

Pumps and fans are widely used in manufacturing, power generation, cement plants and building HVAC. Matching their output to actual demand can reduce energy use and operating costs.

Project examples include ABB ACS310, ACS550 and ACH550 drives. These model references reflect the equipment discussed at publication; selection and availability must be confirmed for a new project.

How speed affects flow and power

For suitable centrifugal pump or fan conditions, the affinity relationships provide a useful approximation:

• Flow is proportional to rotational speed: Q ∝ n.
• Torque varies approximately with speed squared: T ∝ n².
• Shaft power varies approximately with speed cubed: P ∝ n³.

At 80% speed, the theoretical power ratio is 0.8³ = 0.512, or about 51% of the original value. This illustrates potential savings; it is not a prediction of electricity savings for every installation.

Why actual consumption differs

Motor, drive, pump and fan efficiency, static head, pipe or duct resistance and operating constraints all affect results. Fixed and variable losses must be considered, including losses across throttling valves or dampers.

See ABB’s discussion of variable-speed pump control for the engineering context.

Throttling versus variable speed

In a conventional arrangement, a valve or damper restricts flow while the motor continues at its normal speed. A variable-speed drive can instead adjust the source of flow by changing motor speed, reducing avoidable throttling losses in suitable systems.

Existing valves or dampers may still be needed for isolation, balancing, minimum-flow protection or process safety. Their position and control logic must be decided through system design, not by universally removing them or opening every valve fully.

Assessing a project

1. Measure the flow, pressure, power and operating hours across the real duty cycle.
2. Review equipment curves and process limits.
3. Compare the existing control method with a suitable variable-speed arrangement.
4. Calculate expected energy savings, capital cost and maintenance effects.
5. Commission the controls and verify performance against the baseline.

The example illustrates nearly 50% theoretical power reduction at 20% lower flow, and more than 40% against a particular throttling comparison. Actual savings must be calculated for the specific system.

Other potential benefits

Appropriate speed control can also reduce unnecessary mechanical stress and wear. These benefits depend on correct equipment selection, control settings and operating practice.