In last year’s carbon budget, UK Government committed to reducing the country’s emissions to half the level of 1995 by 2027. Mark Proctor, managing director at European Automation, explains how engineering designers can help UK Plc take a big step towards reaching these environmental targets by using variable speed drives.

While the publicity surrounding the launch of the third carbon budget suggested that specific energy saving recommendations to help fulfil it would be made in early 2012, no announcement has yet been forthcoming. As a result, it falls to British industry to educate itself about energy saving technology.

While senior managers in UK engineering are aware of the environmental consequences of excessive carbon emissions, there is limited understanding of how electricity usage and the inherent costs can be effectively reduced at the design stage.

For instance, variable speed drives (VSDs) are one of the most cost effective ways to reduce carbon emissions in electric motor applications. While there’s no question that this technology could help Britain meet its carbon reduction commitments in the allocated timeframe, only 10% of relevant electric motor applications currently use a VSD.

VSD benefits

VSDs regulate the speed and rotational force (or torque) of an electric motor and in doing so can reduce its speed in line with the requirements of the application. Providing the motor has a variable load, this will in turn reduce the amount of electricity used and thus the amount of carbon emitted.

With millions of motors in use in Britain and 65% of all industrial electrical energy accounted for by these devices, it is evident why the implementation of VSDs could make a huge difference. Electric motors can be found anywhere – from sewage and irrigation pumps, lifts and conveyors, and paper machines, to power-plant fans, HVAC systems and process applications.

As 90% of the lifetime cost of a motor comes from its energy consumption, even a small reduction in speed can give significant savings. For example, a centrifugal pump or fan running at 80% speed tends to consume only half of the energy of one running at full capacity, due to the pressure difference across the impeller in the pump. Thus, when less pressure is produced, less acceleration of air or fluid across the impeller is required.

Energy use in motors is governed by ‘power cubed’ law, which means that the energy reduction is equal to the speed reduction cubed – hence, a relatively small speed change produces a large fall in the carbon emitted. For example, a speed decrease of 10% in a motor produces an average energy saving of about 27.1%. Similarly, an application functioning at 80% capacity will only use 48% of the power it would have needed at 100%.

An additional benefit of VSDs is that the motor will require less frequent maintenance work because it is no longer running constantly at full speed.

In many industries, motors are frequently over specified so they can cope with worst case scenarios where high energy levels may be required at some point. Installing a VSD wouldn’t remove this ability to manage extreme situations, but it would reduce the cost of running the motor on a day to day basis.

The 2027 target

Some of you might recall the plot of the movie 2012 in which, due to pollution and global warming, the planet is almost destroyed in a series of outrageously unrealistic disasters. While 2027 is very unlikely to witness the absurdist events of the 2012 movie, if the Government does not make the right recommendations next year, 2027 may well see us miss our climate improvement targets. Given the circumstances, there ought to be a sense of urgency amongst Government officials when preparing recommendations to promote the installation of energy saving equipment such as VSDs.

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