Seize control of energy savings

We are constantly being urged to fit inverter drives and save energy.However, Jeff Whiting, energy spokesman for Mitsubishi Electric's Energy Centre, says we should not overlook their sister technology - controls

Disciplines we learn in one field can sometimes be applied to others and yield useful results. Recently, for instance, I focused on the latest Machinery Directive to identify some of the design requirements of industrial equipment to minimise risk and make the equipment safe.

The standard process is well defined and I feel that some of the assessment approach could be modified and applied to minimising energy within our processes.

BS EN ISO 14121 (Risk Assessment) encourages a three-stage process to safety: Design out as many safety problems as possible; then those that can't be removed through mechanical and control design are brought under control with a safety solution light curtain, guard, etc. The final approach is through user information, such as instructions, limitations of use and training.

This process, in principle, could be applied to energy engineering. The assessment process would then become: to design out energy consumption where possible through the mechanical and control philosophy; to apply energy saving technologies such as inverter drives; and to provide information and training to minimise any other energy requirements that may require localised input.

More people are recognising the value of energy saving technologies, but what about designing out unnecessary losses in the first place? Many elements of a machine are left running for major parts of their duty cycle without any useful function taking place. In many cases it would be possible to switch them off when not operating; powering them up just before they are needed.Main culprits include lights, fans and pumps. To this you can add HMIs and other unmanned display/ control panels, possibly chillers or air conditioning, conveyors, and so on. It may feel like the energy savings will not warrant the effort required, but some rough calculations on the back of an envelope may well change your mind.

When designing a machine engineers primarily think functionally: what are we making, how can we do that, what processes are involved? Energy considerations, where they are considered, usually come low down the list. Yet it costs nothing to think about energy as a primary part of the project brief.

If heat is involved, can a smaller amount be applied more accurately; if cooling is required, can this be done intermittently rather than constantly; can the length of conveyor runs be cut; can conveyor speeds be slowed without impacting productivity; would reversing a plant's layout change lifting tasks to lowering ones; how many lights on a machine could be left off for long periods of time? Many of these questions could also be asked of existing machinery, but this brings up a universal problem. People would rather muddle on as they are, using the well known mantra, 'If it ain't broke… Don't fix it!' People come up with all sorts of reasons for not undertaking change. A good manager will work through these and properly assess the potential that change can unlock. The same observation is true with new build.

Design teams will generally have established ways of working and may not welcome the further dimension to the project of trying to 'sort out the energy before the machine is built'. Probably the most common objection to an energy saving initiative is that it will cost too much. This is often not the case.

Most machines have a relatively sophisticated control system that can be re-programmed to help minimise energy consumption. A few well-chosen sensors will say switch off empty conveyors, power down HMIs and lighting when there is nobody present, control temperatures to set levels, and so on.

Many control technologies have energy saving options readily available. SCADA and DCS software systems can easily integrate with operational and enterprise processes to provide energy data and control; PLCs can optimise the local processes and gain optimal energy requirements from management systems. In fact, usually the same control networks from the manufacturing cell through to complete factory can be used to monitor and control energy with little or no extra cabling requirements. Individual calculations would be needed, but extra equipment often pays back in energy saving in just a few months. Given that the life expectancy of automation equipment in the UK is 12 years+, substantial returns during the life of the machine can be expected.

Let's quantify savings we could reasonably expect.Many public buildings have been retrofitted with BMSs in recent years: a study of performance suggests that this leads to an average reduction in annual energy bills of 15 to 20%. In energy-hungry industrial processes, a 20% energy saving could be significant to the bottom line of the business.

It's reasonable to take this as a rule of thumb and say a plant/machine designed for energy efficiency will be one-fifth cheaper to own and run.Look at how car engine efficiencies have changed the market, when engineers got serious about energy performance.