Why be energy efficient?
Optimising motor systems has the potential to save more electricity than in any other electricity end-use. Investing in motor efficiency also makes sense given the total cost of supplying electricity to a motor can overtake the motor purchase price in just two weeks. Effective management of electric motors will also improve their reliability, minimise the risk of lost production time and minimise life-cycle costs.
For information on the benefits of a whole of system approach, see Technology Background – Motors and Motor Systems.
There are numerous initiatives which can help improve the energy efficiency of motors. An effective strategy relies on an integrated approach which considers the energy efficiency of the ‘core motor system’ as well as additional opportunities in the ‘total motor system’ to enable larger energy efficiency improvements to be achieved.
For information on the benefits of a whole of system approach, see Technology background – Motors and Motor Systems. Also see other Technologies pages on the EEX website, including Pumps and Fans and Compressed Air.
Reduce demand for motive power
For any motor system, it is first important to ask what service the system provides and whether the need for this service can be reduced or eliminated. Opportunities to reduce demand include:
- Rearranging production machine layout to eliminate a materials handling task
- Changing production processes or chemicals used to eliminate a ventilation requirement
- Heat water where it is used, rather than remotely, to reduce heat losses and possible eliminate a pumping requirement.
- Altering the way work is done to enable substitution of a large motor for a smaller motor ie A factory using a large blower with 60 kW motor to move paper off-cuts might be able to substitute a small conveyor with a motor of 0.6 kW.
- Turn off steam supplied to inactive equipment.
Investigating the stretch goal of redesigning or eliminating the motor system is likely to uncover more possible saving methods than thinking about incremental efficiency gains.
If the need for a service cannot be eliminated, consider if it can be significantly reduced, or whether the task can be reconfigured, enabling a smaller motor to be used.
Install permanent metering
As energy is the largest cost of owning and operating a motor system, it is worth monitoring that cost by installing dedicated electricity metering for motors. This metering will provide useful data when conducting an energy audit, developing an energy mass balance or evaluating potential energy efficiency improvements to the motor and drive system. Energy metering can also provide indications of system problems such as excessive resistance.
Switch motors off when not required
Large and relatively easy savings can be made by determining which motors can be switched off when they are not required, e.g. outside normal production shifts. Some equipment may not need to operate continuously, even during working hours.
Savings can be achieved by implementing procedures such as:
- Develop standard shut-down lists so all staff know which machines to leave on and which to turn off.
- Develop standard start-up lists so plant is switched on only as early as required, e.g. if the factory is started at 10:00 p.m. on Sunday for a 7:00 a.m. start to the working week, not all equipment needs to be started at 10:00 p.m.
- Develop procedures to ensure that only the production equipment which is needed (e.g. for a particular product run) is turned on during hours of operation.
- Consider whether some equipment can be programmed to automatically switch off when it is not required using existing automation, i.e. Supervisory Control and Data Acquisition (SCADA) system or control system. In some cases, this automation can be achieved with the existing control equipment so only program changes are required.
Undertake maintenance on electric motors and motor systems
Regular maintenance of motors is a cost-effective way to improve energy performance. With good maintenance, many organisations can increase the operating efficiency of their equipment by 10–15 per cent.
There are a number of steps to ensure motor systems are well maintained, including:
- Cleaning motors of dirt and grease, particularly fans on fan-cooled motors.
- Checking for excessive vibration which may be a sign of motor misalignment.
- Checking connections or wires that might be loose or damaged.
- Keeping motors cool, by providing adequate ventilation, and keeping cooling fins and fan vents clear of dust, lint and fibres.
- Lubricating motors, bearings, gearboxes and chain drives according to the manufacturer’s recommended intervals and lubricant specifications.
- Ensuring belt drives are correctly tensioned, evenly matched and free of dirt and abrasives.
- Aligning motor drive shafts with the load.
- Surveying motors and bearing using an infra-red camera to identify motors which are running hot (and so consuming more energy than necessary).
- Checking that the load on the motor is not unnecessarily increased by avoidable inefficiencies in the driven system such as blocked air filters or liquid filters, closed dampers, partly closed valves etc.
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Developing a register of motors and drive systems will help facilitate:
- Planned, preventative maintenance
- The ability to replace a motor based on its actual load, rather than its nominal motor rating
- Identification of mission-critical motors and determining what would need to be done if a motor fails
- Re-assignment of motors within a factory according to actual load.
Upgrade or replace motor systems
There are opportunities for energy saving whenever upgrades are planned. Taking a whole of system approach to upgrading motor systems combined with implementing best practice motor management can potentially deliver energy savings of 30–60 per cent.
The most significant costs for most motors are the energy costs, followed by maintenance, then the initial purchase costs. Calculating the total life-cycle costs will allow an organisation to select the most cost-effective motor. In most cases, life-cycle analysis will show that the lowest cost solution is a high efficiency motor, drive and controls, even though the initial cost is not the cheapest of all the options.
Completing a life-cycle analysis for both new and replacement motor systems will help clearly communicate the business case for investing in such energy efficiency improvements.
Calculate required load and use the correct motor size
The efficiency of an electric motor decreases as the load on the motor decreases. Therefore, a motor which is oversized requires more input power to drive a load than a smaller, correctly sized motor.
The effect is more dramatic with older, standard efficiency motors which have lower part-load efficiency. Most motors operating in Australia are older, standard efficiency motors.
The actual motor power required should be calculated based on the service which is being provided by the equipment driven by the motor.
Understanding the required load will avoid replacing like-with-like, when the original motor may have been oversized. The original motor may be the incorrect size because it:
- may have been selected for a different load
- may have been a forced choice because the correctly sized motor was not available
- was reused from another application
- was selected very conservatively expecting that the load may grow in the future.
Some loads need to run at a constant speed, but some loads may vary, e.g. conveyors in mines, metal stamping presses and escalators. In these instances, one possible approach is to use a load sensing optimiser. This is a motor controller which can sense the load on the system and automatically adjust the power supply (current and voltage) to the motor to maintain speed with the minimum energy required.
Install the highest efficiency motor available
The efficiency of electric motors varies. The Energy Rating website has an extensive list of electric motors available in Australia.
Minimum Energy Performance Standards (MEPS) for electric motors manufactured or imported into Australia were introduced in October 2001 (MEPS1) and updated in April 2006 (MEPS2). This means that new motors on sale today are likely to be more efficient than most motors currently being used in industry.
For more information on MEPS requirements for motors, see the Motors content on the Energy Rating website.
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Replace before forced replacement
The initial purchase price of a motor can be less than 1% of the cost of owning and operating the motor, so keeping an old inefficient motor will not save money; it will cost money.
It makes financial sense to calculate the potential energy and financial savings available by replacing an existing, low efficiency, oversized motor and belt drive with a modern, high efficiency, correctly sized motor with speed matched to the load’s required speed.
Use variable speed drives
An electronic variable speed drive (VSD) varies the frequency of the alternating current electricity supplied to an induction motor in order to reduce its speed. The most common applications of VSDs are with fans and pumps.
Motors need to be sized to satisfy the maximum load, but the motor speed can be varied using a variable speed drive to match the load and save energy. Varying loads include:
- Pumping, where the volume to be pumped varies
- Cooling, which requires higher airflow during warmer weather
- Ventilation for dilution, which needs to be higher in response to higher occupancy or more vehicle movements.
The volume of air flowing through a fan or liquid flowing through a centrifugal pump is proportional to the speed of the pump, but the electrical power required is proportional to the cube of the speed of the pump.
Other advantages of VSDs include:
- Fewer motor starts (less motor heating and longer service life)
- Softer motor starting
- More accurate level control
- Less stress on the electrical supply and downstream plumbing components
- Lower electrical demand
A VSD also has the potential to result in a higher power factor, providing this is specified when ordering the VSD (VSDs do not always have a high power factor).
Consider using smart motors or multi-speed motors
A smart motor is an electric motor and electronic VSD in an integrated package. The advantages of smart motors include:
- The motor and VSD are matched by the manufacturer
- They require less on-site wiring and space.
The purchase of a new smart motor may also provide the opportunity to replace a standard efficiency motor with a high efficiency motor.
Some induction motors can be switched to one or two (or even three or four) speeds. In some situations this can provide some of the savings of a VSD at a lower cost. This strategy is often used in carpark exhaust systems, where the fan and motor are sized according to the maximum ventilation requirement which occurs during two daily peaks, but is switched to low speed for all other times.
Replace belt drives
Belt drives are used to transmit power from an electric motor to a driven load. They allow speed to be selected by choosing pulley sizes and allow the use of a small high speed motor and belt slip to reduce motor strain when starting.
Their main disadvantages are inefficiency, caused by energy absorbed by the drive belts, lower reliability, space requirements and associated maintenance costs.
The energy losses arise from slip and heating, the force required to bend the belt every time the belt goes around each pulley and the energy required to compress the belt into the V-notch of the pulleys.
V-belts can be replaced with:
- Synchronous belts, e.g. toothed or cogged belts
- Modern flat belts
- Direct drive, i.e. a shaft which will usually require a new, lower speed motor.
Note that changing the type of belt will also require changes to pulleys.
Select energy efficient components for the motor system
Motor systems are made up of a range of components centred on a motor-driven device such as a compressor, pump or fan. To ensure the overall efficiency of the system, it is important to consider components for the system which are energy efficient, as well as how they interact.
- Energy Rating Website
- Equipment Energy Efficiency (E3) Program
The Energy Rating Website provides information on the energy performance of a range of residential, office and industrial equipment which is communicated via energy rating labels.
The website also includes information on mandatory minimum energy performance standards (MEPS) which apply to a large range of equipment, appliances and lighting products including refrigerators, clothes washers, televisions, compact fluorescent lamps and industrial motors.
- Motors, Pump and Fan Efficiency - More Drive, Less Work 2010 (Opens in a new window)
- Queensland Government
- PDF 247 KB
This resource developed by the Queensland Government outlines eco-efficiency opportunities for manufacturers in relation to motors, pumps and fans. It includes information on high efficiency motors, using the correct motor, power correction factors and pump and fan efficiency.
- Motors and drives technology overview 2011 (Opens in a new window)
- UK Carbon Trust
This resource looks at some of the simple actions that can be taken to save energy, cut costs and increase profit margins around motors and drives. Note, there is a cost for downloading the PDF.
In addition to the overview, UK Carbon Trust also provides more specific guidance about motors and drives in PDFs which are free to download.
- Industrial Efficiency Technology Database 2012
- Institute for Industrial Productivity
The Industrial Efficiency Technology Database (IETD) provides information to help decision-makers in industry assess the cost-effectiveness of energy efficiency investment options. The information includes descriptions of technologies and processes, key data, benchmarks, energy savings, CO2 reductions and costs. The IETD currently covers the cement, iron, steel and pulp and paper sectors, as well as electrical motor-driven systems.