Energy Efficient Control of Pumps: Cyclic Control vs VFD

Energy Use in Motors and Pumps: Nearly 45% of global electricity is consumed by motors, many of which drive centrifugal pumps. Improving efficiency in these systems has major cost and environmental benefits Static vs Friction Head: The energy efficiency of a pumping system depends on its hydraulic design—whether it’s dominated by static head or friction losses Key Findings: Cyclic control proved more efficient than VFDs for medium to high static head applications; VFDs offer only marginal gains at very low static heads Bad Practice Warning: Using a VFD purely for on/off cyclic control is inefficient due to higher losses and cost compared to fixed-speed controllers

Flow Control Strategies: Pumping systems can be designed for real-time flow control (requiring VFDs) or time-averaged flow control (ideal for cyclic control using soft starters or DOL starters) Comparative Study: Simulations compared cyclic and VFD control under different static head ratios (5%, 25%, 50%, 75%) using real pump data, motor models, and VFD efficiency curves System Design Recommendations: For most systems, it’s best practice to design for cyclic control—reducing installation costs, avoiding harmonic issues, and minimizing wear and cavitation Publisher Information: The paper was published by Benshaw, Inc., a leader in applied motor controls, and includes contact details for their U.S. and Canadian operations