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Driving down the cost of compressed air

01 January 2009

Energy costs arising from the operation of a 90kW rotary compressor installed at the site of one of the UK’s prominent automotive Tier 1 suppliers, have fallen by £14,000 per year following the installation of a variable speed drive

Glaston Compressor Services has been responsible for supplying and maintaining energy efficient HPC compressors at Tier 1 automotive supplier, Albion Automotive’s site since 1996 and, on the basis of its experience elsewhere, the company knew that fitting a variable speed drive would yield substantial energy saving for its customer. The choice came down to Vacon’s NSX drive; this replaces an existing single-speed starter, and works in conjunction with a compressor management system to ensure that the compressor output always matches the instantaneous demand. Glaston managing director, Michael Douglas takes up the story:

“We’ve been using Vacon drives for some time to upgrade fixed-speed compressor systems, and we’ve found them to be robust, reliable and easy to work with. We’ve also found that we can always rely on superb support from Vacon, with direct access to the company’s top people.”

In order to quantify the savings that would be made possible by fitting the Vacon drive, and to make a compelling business case for Albion Automotive to invest in the upgrade, a free detailed energy survey was carried out at the site. The findings initially indicated that the new drive would provide savings of £7,000 per year, against a total cost for the project of around £12,000.

With the prospect of payback in less than two years, Albion Automotive decided to proceed. The installation went smoothly, with minimal disruption to compressor operation, as Albion’s maintenance facilitator, Tony Stableford explains.

“Glaston did a lot of preparatory work so that all that remained to be done on site was a small amount of wiring. Once this wiring had been completed, the compressor was up and running in less than half an hour. The Glaston engineers then spent another couple of hours using the full range of facilities offered by the Vacon drive to fine tune the installation so that it would maximise our energy savings.”

In addition to the anticipated energy savings, it also proved possible to make further savings by reducing the nominal operating pressure of the installation. The minimum acceptable delivery pressure at Albion’s site is 6bar. In the past, the installation has been operated at a nominal pressure of 7.0 to 7.5bar to ensure that, even under conditions of maximum peak demand, the delivery pressure never fell below the required minimum.

With the much more precise and responsive control achieved by the Vacon drive system, the nominal delivery pressure can now be reduced to just 6.05bar, with total confidence that the actual pressure in the installation will never fall below the 6bar limit. As a result of this reduction, and a number of other minor energy saving adaptations made by Glaston, the total cost savings increased from the forecast £7,000 to £14,000 per year.

“Payback in 14 months is within the company’s set financial hurdles,” says Mr Stableford. “Our only regret is that we didn’t make the change to variable speed operation for the compressor sooner. From our point of view, the project was completed smoothly and quickly with almost no disruption to our operations, and now it’s not only contributing to cost savings, it’s also helping us to reduce the environmental impact of our operations. However you look at it, that’s a great result!”


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