With a hard winter upon us and warnings that generation capacity may not be enough, the interest in energy efficiency has never been greater. Designing for efficiency is not difficult - here are the top tips.
Energy efficiency is rising fast on industry's agenda. High energy prices and the government's tax incentives to adopt energy efficient technology means there has never been a better time for users to take a good hard look at energy costs. This means more demand for energy efficient design, often in applications where basic function and low initial cost used to be the top priorities.
One of the biggest users of electricity in industry is the electric motor. There are some ten million electric motors in UK industry, running virtually everything that moves. Motors left running when not required waste a significant amount of energy. For example, an 11kW motor which needs not run at weekends will waste almost £2,000 worth of energy per year if left running 24/7. Even under no load, motors can consume as much as 40% of full load power. Even if only running when needed, a poorly managed motor - one which is driving at full speed when the process can get by on a much lower speed - can waste thousands of pounds worth of electricity a year.
More precise control of motor speed is therefore essential, employing a technique that can run the motor at the speed demanded by the process. This means using ac variable speed drives. The control they bring to the speed of motors allows processes and machines to be run at exactly the right speed, saving electricity and cutting running costs. They can also ensure that the motor switches off when not needed, as well as match the motor speed to process variables, such as temperature or pressure.
One of the most effective ways to save energy is to target pump and fan applications, firstly because there are so many of them and secondly because the potential energy savings are so great. Because centrifugal fans or pumps are variable torque applications, power actually varies in proportion to the cube of the speed. Hence, by reducing the speed by a certain percentage, the power reduces by the cube of the speed change. So reducing the speed of a pump to 80% results in (0.8)3 = 51% power. In comparison with this, changing production volumes by mechanical means is very inefficient.
Replacing a single oversized fan with a smaller version equipped with speed control cut the energy consumption on one of the dryers at Salt Union's plant in Runcorn, Cheshire. The drive, installed for just £20,000, is now saving Salt Union over £100,000 a year. The old fan was replaced by a smaller version from Fan Systems of Halifax, equipped with a 132kW four-pole motor coupled to an ABB industrial drive. The resulting energy savings now average a staggering £9,000 a month, a reduction in the energy used by the plant's dryers of over 60%.
The previous fan sucked air through the dryer at a rate controlled by a damper in the pipeline. During normal operation, this damper was 95% closed so most of the fan's energy was being used to suck the air through the narrow constriction. An energy survey by ABB Drives Alliance member Central Electrical was carried out to determine what potential savings could be achieved. The original fan motor was rated at 337kW, but Central Electrical's calculations showed that 132kW should be enough to create the draft needed by the dryer. As the dryer is run for over 8,000 hours a year, the saving equates to over 1.6GWh per year.
A fully loaded motor will typically consume the same in electricity costs within its first 30 days of operation as its purchase price. An 11kW motor costing about £500 can consume over £50,000 worth of electricity over a ten year operating life. High efficiency motors are generally 3% better in efficiency than basic designs. A high efficiency motor can save tens of thousands of pounds over its operating life, compared to a standard efficiency motor. But the real savings arrive when high efficiency motors are used with consistency across the site. Because the motor driven applications are so numerous, massive savings can be made from implementing a motor management policy.
High efficiency motors are better in variable speed operation. All motors drop in efficiency when running at reduced speed, but high efficiency motors retain more of their efficiency. They are also more reliable than low efficiency versions because they waste less energy as heat, which degrades the motor windings. Windings are second only to bearings in terms of the number of motor breakdowns caused. Theoretically, a reduction of 10 -15 oC in the running temperature will double the life of the winding. The normal running temperature in high quality motors running at full load can be as low as 60-80oC while lower quality motors frequently run in excess of 90oC.
High-efficiency motors from ABB are saving a leading supplier of bakery products over £10,000 a year in energy costs and a further £5,000 in spare parts. Cereform is the only manufacturer of soya flour in the UK and produces around 12,000 tonnes a year at its site in Royston. It has some 120 motors on site and is gradually phasing out its older models in favour of high-efficiency alternatives.
ABB Motor Service Partner, Heasell Electromechanical Services, supplied eighteen 22kW high-efficiency ac motors to run nine flour mills. Site engineer Rory Perks estimates that the company was spending around £5,000 a year on replacement parts associated with the old motors. "Reliability is now excellent and the new motors are virtually maintenance free," he adds. Mr Perks also estimates that the 18 Eff-1 motors are saving over £10,000 a year in energy.
Taking action
Tips on how to save energy with motors and drives can be obtained from ABB's Six Step Energy Saving Plan. The company has launched an updated version of this award winning scheme, which helps end users with the practical steps to make substantial cuts in electricity use, reducing liability to the Climate Change Levy and helping companies under Climate Change Agreements meet their commitments. The plan shows users a route through six steps to achieving better energy efficiency and gives an understanding of the background to the legislation concerning climate change.
Details are available over the telephone (0800 783 7491) or online at www.abb.co.uk/energy. Financial help for those investing in energy efficiency projects is available from the Carbon Trust, which offers interest free loans to cover the initial investment in equipment.