Film and bag manufacturer Gelpack Industrial has made an annual saving of over 45 per cent on energy used to generate compressed air using a retro-fit variable speed drive package from EnergAir
A compressed air audit conducted at Gelpack revealed that a significant proportion of the input energy used to power the compressors was not productive, and that the system pressure was kept above what was required. This was due to the inefficient operation of two fixed-speed, 75kW compressors which were used on a rotating system to provide compressed air to the factory.
The audit highlighted the potential savings that could be made by retro-fitting a variable speed drive (VSD) package to reduce offload running and match air generation more closely to system demand.
In the current climate it is essential that all businesses reduce any energy use that is not essential. And one area that can use a lot of non-productive energy is compressed air generation. Many companies, says EnergAir, are still unwittingly operating systems very inefficiently through excessive compressors idling and unnecessarily over-pressurising systems. Careful management of a compressed air system can therefore lead to large savings on energy as well as reducing a company's overall carbon footprint.
Suspecting that this was the case with its own system, Gelpack commissioned an audit to test its compressed air system's efficiency. The audit lasted a total of 187.9 continuous hours, during which data was logged every five seconds. The site has two fixed-speed 75kW compressors, and the audit revealed that 40.18 per cent of the energy used to run the compressed air system was non-productive. Pressure in the system also fluctuated between 7.64 bar and 8.63 bar — the optimal system pressure for the site is 6.97.
Demand for compressed air on most sites will fluctuate. Fixed speed compressors will produce the same amount of compressed air regardless and regulate between a loaded (low-pressure set point) and unloaded (high-pressure set point) state; consequently a large amount of energy is wasted on unloaded running. A VSD connected to a control pressure feedback loop is able to measure the demand precisely, regulate compressed air generation and replace low and high pressure set points with a single 'target pressure' set point, so keeping the system at optimum pressure without generating excess air.
Halving the running costs
"We were aware that compressed air systems often run inefficiently so decided to examine the possible savings that could be made," said Gelpack's Paul Burns. "EnergAir was able to show how a variable speed drive, sensor feedback and a basic communication box could almost halve the cost of running the system. Recommending a retro-fit VSD package rather than a whole new compressor also made the costs far more manageable."
In order to improve the sites efficiency it was recommended that Gelpack retro-fit a VSD to one of the existing compressors. Gelpack opted to install an EnergAir VSD and control package that ensured the system synchronised perfectly between the two compressors. EnergAir's drives and controls package is able to maintain the mechanical integrity of the compressor and actually enhance electrical protection, thereby ensuring the upgrade would not adversely affect the compressor. Installing the VSD resulted in a substantially lower peak current draw and less non-productive energy usage.
Using the VSD to generate compressed air that matches demand has meant that Gelpack has seen massive savings since installation. The system now runs with over 92 per cent efficiency, at all times keeping within 0.21 bar of optimum system pressure. This increased efficiency has reduced annual energy costs by over 45 per cent, saving over £15,000 annually. With the savings that the EnergAir system has generated, the equipment had paid for itself within a matter of months, meaning that real saving were seen in the first year.
This installation has proved so successful that the group company Gelpack Excelsior Ltd has now completed a similar upgrade to its compressed air system.
