Take control when it comes to energy saving options

21st February 2013

We are constantly being urged to fit inverter drives and save energy. But Jeff Whiting says we should not overlook their sister technology - controls.

Disciplines we learn in one field can sometimes be applied in other areas and yield really useful results. In recent weeks, for instance, I have been focused on the latest Machinery Directive to identify some of the design requirement 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 outlined could be modified and apply to minimising energy within our processes.

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

This process is very sensible and 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. Secondly to apply energy saving technologies such as inverter drives.

Finally, to provide user information and training to minimise any other energy requirements that may require localised input.

More and more people are recognising the value of energy saving technologies, stage two in my analogy, but what about designing out unnecessary losses in the first place?

When you think about it, many elements of a machine are left running for major parts of their duty cycle without any useful function taking place.

In a lot of cases it would be possible to switch them off when they are not actually operating; powering them up just before they are actually needed.

The main culprits for running unnecessarily include lights, fans and pumps. To this you can add HMIs and other unmanned display/control panels, possibly chillers or air conditioning, conveyors, etc. At first it may feel like the level of energy savings will not warrant the effort required. But some rough calculations on the back of an old envelope make well change your mind rather quickly.

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 somewhere low down the list of goals.

But it costs nothing to think about energy as an 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 reduced; can conveyor speeds be slowed without impacting overall productivity; would reversing a plant's layout change lifting operations into lowering ones; how many lights on the 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 generally don't like change. They would rather muddle on as they are, using the well known mantra, "If it ain't broke ... Don't fix it!"

Creative efforts are often reserved for things perceived as new and exciting. People easily come up with also sorts of reasons for not undertaking change. But a good manager will make the effort to 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 in trying to 'sort out the energy before the machine is built'.

Rationally they know it can be done and that it should be done, but it may be a new trick too far for some old dogs.

Probably the most common objection to an energy saving initiative is that it will cost too much. However, 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, etc.

The good news is that 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 needed often pays back in energy saving in just a few months. Given that the life expectancy of automation equipment in the UK is over 12 years, substantial returns during the life of the machine can be expected.

In our increasingly carbon-conscious world, it will soon become a common requirement in a client's brief that defined energy targets are met. Until then there is a window of opportunity for a few years in which a competitive edge can be generated by designers offering an energy dimension as part of their proposal.

And finally, let's quantify savings we could reasonably expect. Many public buildings have been retrofitted with Building Management Systems (BMSs) in recent years: a comprehensive study of their performance suggests that this leads to an average reduction in annual energy bills of around 15-20 per cent.

In energy hungry industrial processes, a 20 per cent energy saving could be very significant to the overall bottom line of the entire business.

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

Jeff Whiting is energy spokesman for Mitsubishi Electric's Energy Centre, Hatfield, Herts, UK.




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