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CSIRO tests VSD compressors


Atlas Copco Compressors Australia commissioned the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to provide an unbiased test of the Atlas Copco Variable Speed Drive (VSD) and compare it to Slide Valve Control and traditional load/no load compressor controls for the same compressor power rating.

Comprehensive Testing

The control systems were tested across a typical air demand profile, which represents 85% of the most common industrial compressed air installations. This gave a most likely estimate of the electricity savings that could be obtained from each of the control options. The results showed that compared to the tested Slide Valve Control compressor, the VSD compressor was 29.8% more efficient. Compared to load/no load technology, the VSD was 38% more efficient. Thus proving that the Atlas Copco VSD technology will, in vast majority of compressed air installations, be significantly more efficient than both Slide Valve Control and the load/no load controls.

Test Specifics

Atlas Copco Australia - CSIRO VSD Testing

Test carried out by CSIRO

The test measured mass flow of air using mass flow meters, ambient temperature and humidity, air receiver pressure & temperature and most importantly, electrical power consumption  (current, voltage and power factor for each phase).  Each of the different new compressors with their own control philosophy were connected to produce air to the same air demand profile and the results were then recorded.
Summary of the test results are:

  • Start Up Current of 90kW Variable Speed Drive: 125A vs. 90kW Slide Valve Control: 425A 
    The Maximum Flow Rate of the Variable Speed Drive Compressor achieved the manufacturers published rating to within tolerance range of ISO1217. The tested Slide Valve Control
  • Compressor recorded 13.6% lower than the manufacturers published figure and outside the tolerance allowed in ISO 1217. 

  • The Variable Speed Drive Compressor could be slowed down to 10% of full speed (load).  The tested Slide Valve Control compressor could only turn down to 70% of full load, and thereafter operated as load/no load compressor and proved to be complicated to adjust even by manufacturer trained technician. 

  • Power Factor for Variable Speed Drive ranged between 0.8 & 0.9. The power factor for the Slide Valve Control ranged between 0.58 & 0.82, resulting in high kW/h usage for the slide valve compressors. 

  • The Variable Speed Drive saved 38% on power consumption where as the tested Slide Valve Control saved 8.2% of power consumption, when compared to the Load/no load control compressor.

As highlighted by this test, it is important to properly understand which technology is best to reduce power consumption depending on your application and associated air demand pattern. With greenhouse gas omissions on the rise, the world is looking at ways to decrease their carbon footprint. As the world leader in compressed air, it is Atlas Copco’s responsibility to provide energy efficient solutions and accurate information to the market. Recent contradicting simplified theoretical discussions regarding compressors controls now have data to prove the superior energy savings of the Atlas Copco Variable Speed Drive compressors, and it is not just based on incomplete theoretical assumptions.

VSD as the optimal solution

GA 90 VSD FF engery savings

GA90 VSD Full Featured Atlas Copco Compressor

Variable Speed Drive Compressors allow Atlas Copco as pioneers to patent and to offer a compressor which unlike traditional systems, follows the installation’s air demand profile.
Variable speed control involves using an inverter to slow down the speed of the compressor to reduce the amount of air compressed at part load. Any loss in efficiency associated with reduced rotor tip speed is more than compensated for by the efficiency gains obtained by operating the compressor more continuously without blowing off air to atmosphere and running unloaded without producing any air and in return consuming vast amount of electricity.
The latest generation of VSD compressors have been found to produce an average of 35% energy savings compared to load-no load compressors in most load profiles. No more myths about rotor tip speed. The efficiency of a rotary screw element is a combination of volumetric, dynamic and mechanical losses, and not only volumetric losses. Atlas Copco managed to design screw elements with a rather flat efficiency curve ideal for VSD control and do not take standard elements and add on a VSD drive. Apart from that the complete package design and control is adapted to suite the VSD control, and eliminate dynamic, mechanical losses and increase power factor at low load. 

The results of this test also showed that the simplified argument about rotor tip speed (volumetric losses) and inverter losses only, are significantly overstated. There is no comparison to losses associated with slide valve technology and total package control, design and power factor to name a few. With the presented results, we can confirm with great certainty that the VSD will offer superior efficiency across the entire compressor operating range. The reason for this lies in years of R&D in the design of the rotor profile, complete screw element design, valves, complete package and control of the complete compressor.

Importance of understanding your air demand profile


Take the guess work out of which technology best suits your application

Knowing your existing system’s air demand profile is a key step in determining an optimal solution. By analysing a week’s air demand profile, Atlas Copco, through an advance measurement system, can quantify not only the maximum and minimum air demand but the degree to which this demand fluctuate. With this information at hand, it is a matter of simulating several scenarios with advanced programs developed over years to find the optimal solution for the customer’s process.
Atlas Copco has addressed this issue with three key innovations: Advanced consulting services which accurately measure demand and then calculate the best technology for the application, Purposely designed and build (patented) Variable Speed Drive compressors which match air demand profiles and Energy Recovery solutions which recover heat loss in the production process. This will also take the guessing out of not only which technology best suits your application but also which size compressor you actually need, and total package providing you with the most efficient solution for your application.

How can Atlas Copco help?

Atlas Copco has been recognised for its sustainability work by a number of rating companies, e.g. Dow Jones Sustainability Index Top 100; FTSE4 Goods Global Index; Global 100 list by Corporate Knights Inc. and Amnesty Business Rating. The Group received it’s most recent recognition in January 2008.
As one of the top 100 world’s most sustainable companies, Atlas Copco takes energy efficiency very serious and has developed a range of compressors that utilise VSD technology.  To support our customers, Atlas Copco developed specific tools to enable the customers demand profile to be mapped and then simulated to compare different technologies, including VSD.  The result being that the customer can see how much energy saving can be achieved before deciding to purchase the equipment. In cases where VSD technology is not the best solution for the customer and a short payback is not evident, it is clearly stated and alternatives offered.


The results from the test prescribed conclusively prove that VSD technology significantly out performs the Slide Valve Technology in all critical areas associated with power consumption.
Although Atlas Copco always backed the results of our consultation tools 100% without reservation, we thought it important to commission a trusted organisation such as the CSIRO to verify these results and compare them to the results achieved with our consulting tools and give a true comparison against alternate technology of Slide Valve Control or Variable Output Control (VOC) as it is commonly known.

Test results are available for review by contacting Atlas Copco:
Phone: 02 9621 9600
Fax: 02 9622 3409

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