Increase Efficiency with Adjustable Speed Drives

This comprehensive tip sheet from the U.S. Department of Energy explores how Adjustable Speed Drives (ASDs), particularly Variable Frequency Drives (VFDs), enhance motor-driven system efficiency. It includes performance data, energy-saving calculations, and recommendations for implementation, helping engineers and facility managers reduce energy use in variable torque applications.

Key Points

  • Efficient Speed Control: ASDs enable motors to match speed with load requirements, leading to substantial energy savings in variable torque systems.
  • Performance Metrics Provided: Table 1 offers representative part-load efficiency values for Pulse Width Modulated (PWM) drives across various horsepower ratings.
  • System Efficiency Formula: The overall system efficiency is the product of the ASD, motor, and equipment efficiencies.
  • Resource Access: Recommendations include using the DOE’s MotorMaster+ tool to obtain motor efficiency data.
  • Power Consumption Reductions: For centrifugal fans and pumps, reducing motor speed by 20% can cut power requirements by approximately 50%.
  • Load Factor Consideration: Calculating energy savings requires understanding the motor’s load factor and the drive’s efficiency at partial loads.
  • Real-World Example: Demonstrates that even with low efficiency at part-load, the overall energy savings can be substantial.
  • Practical Implementation Tips: Encourages collaboration with equipment suppliers to determine accurate part-load performance values.