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.
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.
VSD as the optimal solution
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
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?
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.
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