The energy savings have been achieved by applying a combination of system pressure optimisation principles, matching air generation closely to demand, ensuring compressors are working at their optimum speed/efficiency, and operating compressors only when they are needed. The central element of control included in both sites is an EnergAir SX control unit, a specialised supervisory and control module designed to provide optimised pressure and sequence management of all the air compressors on each site.
EnergAir Regional Manager Nigel Clark comments: "The project began with an audit carried out on the two production areas that until recently used completely separate compressor houses and air ring mains. EnergAir carried out a comprehensive audit that measured system pressure, air usage and benchmarked a series of key performance indicators before the change and upgrade including; accurate metering of power consumption in kW/hours, air production volume in m3 and efficiency in kW/m3."
Analysis of the data led to a set of estimated results that predicted the energy savings achievable by fitting an EnergAir management control system and retrofit VSDs at each site. There are seven compressors in total, three 160kW units and four 200kW units - production runs 24hrs. Based on the overall cost of installing the system balanced against the reduction in energy that could be achieved, the payback period was estimated at 18 months for the entire project.
Based on these predictions, the Facility Co-ordinator at the time ordered the EnergAir system and retrofit VSDs. After seeing the potential this system had for achieving energy savings the customer was committed to installing it and getting the best results from it. Other plants with similar generating capacity have seen substantial recorded savings and so the project was quickly signed off. As predicted, the system did pay for itself after just eighteen months in operation.
Most large manufacturing companies are firmly committed to reducing energy usage and it is a responsibility carried by members of the facilities and production teams. Large plants such as this are continually changing, and the level of visibility and fine control provided by the EnergAir software has enabled the facilities team to continue making savings and improvements. For example, they have now connected the main air supply between both sites and use the EnergAir system to optimise overall system pressure and air generation in both compressor houses, but controlled and working as one.
The increases in efficiency are so pronounced, that they have been able to add another complete production line since the initial EnergAir install, without having to upgrade the compressed air generation facilities and have maintained the increased efficiency levels - generating efficiency is now at 97.18 per cent. The compressors are also being used to generate hot water for the site, something that they use a lot of on the production line. There are also plans to use hot air vented from the compressors through a heat exchange process for heating the building during the winter months.
Pressure sensors are fitted throughout the system and used to feed live data into EnergAir's EnerSoft - Analysis data management software that is hosted on an onsite PC, this collates and records all the data and makes it available to the EnergAir EnerSoft - Visual PC visualisation package. The complete compressed air system, from compressor, through to the dryers and out across the plant is represented visually on screen in a Windows environment, with key indicators such as system pressure and efficiency displayed clearly on screen as analogue style dials.
Through a series of SCADA style screens, the operators can drill down and check on the performance if individual compressors, set threshold alarms for performance variables, schedule servicing and maintenance tasks and crucially see the effect any changes made have on the system immediately. Using EnerSoft - Analysis data manager any of the Key Performance Indicators (KPIs) can be tracked over time and reported on at fixed intervals.
The data is updated every few seconds and the information seen on the screen is virtually live, making it far easier to accommodate changes to the plant and make positive changes to keep efficiency maximised, every time a change is made, the results are displayed instantly. Prior to having the EnergAir system the facilities team had to collate data over a period of time using much cruder indicators such as energy bills and it was a minimum of 10 days before we could see the results, in that time other factors could have cancelled out the improvement they made and they would never be completely sure how effective the change had been.
One thing in particular that has shown great savings and can be tweaked onsite is the overall system pressure, there are certain limits to how low it can go based on manufacturers recommended minimum operating pressures for machinery on the production line, some of which were set quite high.
After consulting the machinery manufacturers it was discovered there was a large overestimate made in some cases to offset the effects of the machinery being used in plants with little or no accurate secondary pressure sensing facilities. The team has been able to safely reduce the overall system pressure by over half a bar in increments. The savings achieved by that half a bar reduction are substantial bearing in mind the site uses over a Megawatt of generating capacity just for compressed air.
- EnergAir Solutions Ltd is based in Woking, Surrey, UK. www.energair.co.uk
