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VSD explained

Learn how a VSD air compressor saves energy and cuts cost by matching compressed air flow to demand

In most industrial operations, the demand for compressed air fluctuates. An Atlas Copco air compressor with Variable Speed Drive (VSD) automatically adjusts the compressor’s operating speed to match air production to demand in real time, saving significant amounts of energy. How does it work?

VSD compressor - energy

The motor

VSD adjusts the compressor’s speed (RPM) by means of an inverter. Instead of all the power going directly into a traditional AC motor that runs only at full capacity, the inverter provides the VSD compressor with the specific voltage required to meet demand, saving energy.
roatry screw

The element

VSD technology works best with rotary screw compressors. A rotary screw compressor’s flow rate and power consumption are virtually proportional to speed. As the motor adapts its speed to reflect demand, the rotary screw elements adapt in sync so the amount of compressed air delivered matches demand. (Atlas Copco rotary screw compressors, both VSD and fixed-speed, are available in oil-injected and oil-free versions, and in a wide range of sizes to suit practically any application.)
elektronikon touch

The brain

The motor speed of an Atlas Copco VSD compressor is controlled by a frequency inverter and the on-board controller called the Elektronikon®. Sensors continually measure system pressure and the system adjusts the motor speed to meet the actual air demand.

When a VSD compressor makes sense

For operations where the demand for compressed air fluctuates, a VSD air compressor automatically adjusts motor speed to match air demand, providing significant energy savings. In contrast, a traditional fixed-speed air compressor can operate only at full capacity. If less than full air flow is required for pneumatic processes, a lot of energy is consumed and wasted.

When a VSD compressor may not make sense

A VSD compressor is not designed for continuous operation at full speed. Switching losses of the inverter result in lower energy efficiency at full speed than an otherwise identical fixed-speed compressor.

Does a VSD compressor makes sense for you?

A professional air audit is the best way to identify the most appropriate compressor and controls for your specific application. These audits are available from companies, including Atlas Copco, that specialize in the implementation of compressed air equipment.

Comparing 2 variable speed machines

  • Comparing FAD's for VSD's make less sense. It's a matter of speed. Most of the comparison can be done on a graph of specific energy consumption in function of the FAD. It is possible that the unit with the lowest energy consumption is depending on the customer profile.
    • Unit 1: Most air consumption >150l/s
    • Unit 2: Most air consumption <150l/s
  • In case the consumer profile is varying much, also cycle losses becomes important (and unload power in case of unloading cycle). A bigger turn down ratio can be important to decrease the amount of cycle losses.

Watch this video to learn more about VSD

Ask an air system professional about your best solution for energy-efficient compressed air production.