1. The variable-frequency drive (VFD) itself consumes 3% of the power. Motor efficiency drops significantly when operating away from rated power and speed, and the optimal oil-air mixture ratio in a screw air compressor is disrupted when the rotor speed deviates from the rated speed, also leading to a marked decrease in efficiency.
Therefore, while using a variable-frequency screw air compressor allows air output to continuously match the pipeline network's consumption, the power consumed to produce each cubic meter of compressed air actually increases. In other words, under continuous loading conditions, a variable-frequency screw air compressor does not save energy.
2. In most screw air compressor applications, pipeline air consumption fluctuates constantly, making it impossible for the compressor's output to remain exactly equal to the network's consumption. When the network pressure reaches the setpoint, the compressor enters an unload (idle) state. During idling, the compressor consumes 30%–40% of the motor's rated power, resulting in very low efficiency. Reducing idle time or preventing the compressor from entering the idle state yields energy savings.
3. Variable-frequency screw air compressors can effectively reduce idle time or prevent the compressor from entering the idle state; consequently, they offer energy-saving benefits when the compressor's rated output capacity exceeds the pipeline network's air consumption.
4. Variable-frequency screw air compressors are highly effective at stabilizing pipeline network pressure, maintaining it within a range of ±0.01 MPa—a level of stability difficult to achieve with other flow control methods.