The motor - introduction
Motor efficiency is determined by manufacture, selection, commissioning and operation.
Manufacture
The rated efficiency of a motor is a measure of the effectiveness of that motor in converting electrical power to mechanical power and is determined by its design and manufacture. Premium efficiency motors minimise losses through better winding designs, the use of high quality magnetic steel, better thermal design, improved fan system design, tight manufacturing tolerances and quality control. Older motors are generally less efficient than new motors due to factors such as poor maintenance, low quality rewinds and advances in technology.
The difference in rated efficiency between premium and standard efficiency motors varies depending on motor size. While larger motors consume more energy, there is a greater relative difference in efficiency between small premium and standard efficiency motors. With the introduction of Minimum Energy Performance Standards for electric motors in October 2001, all motors registered for supply in Australia will soon be listed on the motors database.
Selection
Selecting the right motor for your application can make a big difference to the energy efficiency of your system. Selecting the best motor and equipment involves considering a wide range of options before you buy, which can save you thousands of dollars. For more information, see motor selection.
Motor Solutions Online's free Motor Selector software has been produced to help simplify the process of selecting three-phase induction motors and to save you time and money. You can use Motor Selector to analyse the many factors involved in choosing a motor.
It is important to remember that the motor is one part of the system. Premium efficiency motors can be found operating in extremely inefficient systems, and standard efficiency motors can be found operating in relatively efficient systems. Focussing only on purchasing a premium efficiency motor may not necessarily result in value for money.
Commissioning and maintenance
Paying attention to detail when commissioning electric motors and motor driven equipment can result in a significant decrease in operating costs, through efficient operation, and a reduced risk of early motor or equipment failure. For more information, see commissioning.
Investigating the difference in efficiency between two fan systems in a biotechnology plant
This case study investigated the difference in energy efficiency between two fan systems that perform the same duty. The fan systems are part of an air-handling unit in a biotechnology plant. The investigation found that one fan system consumed 1.4kW less energy than the other. This difference was most likely due to the fact that a standard efficiency motor on one of the fan systems had been replaced by a premium efficiency motor.
This case study demonstrates that:
- significant savings can be achieved by analysing the life-cycle costs of motor replacement options using the Motor Selector software. The magnitude of savings depends on the electricity tariff, the range of motors available, and the application.
- strategic consideration of the operation of standby plant can also result in significant savings in both energy and greenhouse gas emissions.
The characteristics of the systems
The investigation considered two separate fan systems in an air-handling unit supplying bottle preparation and dispensing suites. One motor is always operating with the other on standby. The fans appear to be identical.
Fan 1 is driven by a 110kW premium efficiency motor, commissioned in 1996.
Fan 2 is driven by a 110kW standard efficiency motor, commissioned in 1993.
Both fans have pitch controllers to maintain conditions that are set and monitored by the Building Management System.
The premium efficiency motor was purchased to overcome harmonic distortions in an electrical system that were thought to have been caused by a faulty standard efficiency motor. The distortions were playing havoc with fast acting doors and other electronic equipment, and there was concern that if the situation was left unchecked, costly damage might be done to sensitive electronic equipment elsewhere in the plant. When the premium efficiency motor was installed, the harmonic distortions disappeared, but it is not certain that the two changes were directly linked.
This situation provides us with an excellent opportunity to analyse different operating and replacement options in order to reduce energy consumption, cut costs and reduce greenhouse gas emissions.
What was investigated?
The power consumption, current and power factor of the motors were logged over a six-day period in August 2000.
The following results from typical 48-hour snapshots taken during the logging exercise were:
- the standard efficiency motor powering Fan 2 consumed 4 148kWh of energy.
- the premium efficiency motor powering Fan 1 consumed 4 082kWh.
- the load for both motors remained relatively constant.
So the Fan 1 system consumed 66kWh more energy than the Fan 2 system over a 48-hour snapshot period - an average of 1.4kW extra per hour.
What were the causes of the differences in efficiency?
From the modest differential in energy consumption, it appears likely that the premium efficiency motor powering Fan 2 is delivering the energy savings. For a 110kW 4-pole motor, the minimum difference in efficiency between a standard motor and a premium efficiency motor is in the order of 1.5 per cent. At 75 per cent load, the expected savings would therefore be 62.2 kWh over 48 hours, very similar to those observed.
The fans were assumed to have identical performance characteristics and the flowrate of air provided by both fan systems during the logging period was assumed to be identical. The observed differential in energy performance is at the lower end of the range of expected savings (delivered by a premium efficiency motor over a standard efficiency motor) so these assumptions appear to be sound.
Opportunities for improvement
There are at least two options for improving the energy efficiency of the system: running the Fan 2 system continuously with the Fan 1 system on standby, and adopting life-cycle costing for the replacement of motors.
Option 1. Run Fan 2 system continuously with the Fan 1 system on standby
Savings could be achieved by changing the way in which the two fans are operated. It may be possible to run the Fan 2 system (incorporating the premium efficiency motor) all the time, rather than sharing the duty between the two motors.
Table 1 shows that this option would deliver annual savings to the company of around $680 and reduce their greenhouse gas emissions by 17 tonnes. Although these savings are not large, they are obtainable at zero capital cost and are therefore a good investment.
Industrial sites run large numbers of motor systems where standby systems are operated half the time. If the more efficient motor systems were operated all or most of the time, the energy and cost savings would quickly add up.
Table 1: Motor Selector analysis of running the Fan 2 system continuously
| Option 1 | Annual running cost* | Greenhouse gas emissions |
|---|---|---|
| Motor 1 shared duty 50% | $45 412 | 415t |
| Motor 2 shared duty 50% | $44 729 | 398t |
| Total | $90 140 | 813t |
| Motor 2 continuous duty | $89 457 | 796t |
| Premium or Saving | $683 | 17t |
*This analysis is based on an electricity tariff of 12c/kWh.
Option 2. Adopt life-cycle costing for the replacement of motors (using Motor Selector)
If the biotechnology company introduced life-cycle costing for the replacement of failed motors, significant savings would be made. For example, if the standard efficiency motor on the Fan 1 system failed tomorrow, it could be replaced with a premium efficiency motor of the same brand that is 2.8 per cent more efficient.
Motor prices vary considerably and depending on the client, suppliers may offer discounts of up to 50 per cent. Also depending on the motor stock available and potential for future custom, one supplier may offer a discount significantly larger than others. For a valid comparison between different motors to be made all prices need to be checked and updated prior to analysis. It is generally accepted that premium efficiency motors have a 10 to 15 per cent price premium over standard efficiency motors. For this analysis a 15 per cent premium has been assumed.
Motor Selector has been used to compare the motor replacement options and the results are shown in Table 2.
Table 2: Dollar and greenhouse savings through life-cycle costing
| Option 2 | Annual cost/saving* | Greenhouse Gas (t) | Motor price |
|---|---|---|---|
| Zero capital cost analysis premium | $5 745 | ||
| Motor 1 Standard efficiency | $56 009** | 415 | $4 650 |
| Motor 1 High efficiency option (15 per cent price premium) | $54 066** | 400 | $5 348 |
| Premium or saving | $1 943 | 15 | $698 |
*This analysis is based on an electricity tariff of 12c/kWh.
**These figures represent the equivalent annual cost of operating each option for 15 years at the electricity tariff above.
If the premium efficiency motor was purchased and then operated even half of the time, the company would save around $1 900 and 15 tonnes of CO2 every year. This is an excellent saving and would justify the 15 per cent price premium for the premium efficiency motor. Over the life of the motor (assumed to be 15 years) the company would save almost $10 000. The rate of return on the investment would be in excess of 200 per cent.
The zero capital cost analysis premium in Table 2 represents the additional capital cost that is economically justifiable for a motor that is 2.8 per cent more efficient with an equivalent life-cycle cost. In this case it illustrates that it would still be a good investment decision to purchase a premium efficiency motor even at twice the purchase price of the standard efficiency motor. This feature of Motor Selector enables the comparison of different motors before purchase prices are known.