OPTIMISING ENERGY EFFICIENCY IN PUMP SYSTEMS

Phil Black - PII Editor 20/06/2011

196 7 minutes read

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Bryan Orchard interviews Daniel Gonterman of KSB AG, Germany

The majority of pump manufacturers claim to be offering higher efficiency pumps as they respond to the demands imposed on industry to reduce carbon emmissions and from end-users seeking to keep down production costs. In the EU, industrial plants account for almost half of all energy consumed and according to the German Electrical and Electronic Manufacturers; Association (ZVEI), more than two-thirds of this is used by pumps, compressors and fans. Pump systems account for around 30% of this demand.

There is no single solution or answer to improving the operating efficiency of a pump because any number of factors will influence its performance once it has been installed and commissioned. What the pump manufacturer can do is to develop a pumping system that utilises the optimum number of energy-saving devices and components and also assist the customer in the pump selection and specification process.

One aspect of energy efficiency that has attracted considerable attention in recent years is energy-efficient motors. According to IEC 60034-30 3008, standardised asynchronous motors fall into three energy efficiency classes, these being: IE1 standard efficiency motors (comparable toEFF2); IE2 high efficiency motors (comparable to EFF1); and IE3 premium efficiency motors. These classes are valid for 2, 4 and 6-pole asynchronous motors from 0.75 up to 375kW performance. IEC 60034-30 covers almost all motors, with the notable exceptions of motors made solely for converter operation and motors completely integrated into a machine (and which cannot be tested separately).

Using IE2 (EFF1) motors can improve energy consumption by an average of 3.5% in terms of overall efficiency. However, employing energy efficient motors only makes real sense if the other options to exploit savings potential have been implemented. If the pump is operating far off its best efficiency point, it is impossible for any energy efficient motor to achieve reasonable levels of energy consumption.

More than a motor
Daniel Gontermann at KSB AG has identified five issues that need to be addressed in order to produce the most energy efficient pump installation. Out the outset, he says that it is necessary for the pump manufacturer or supplier to have a comprehensive profile of the customer’s application before the pump is selected. Where pumps are being replaced, then an in-depth analysis of how the incumbent pump(s) have operated should be carried out.

Matching the pump to the application is all-important and analysing pump performance on existing applications is an essential part of the selection process. “Over many years, our discussions with customers about the load profile have revealed that many do not know exactly how the pumps are operating,” says Daniel Gonterman. “Many tell us that they have over-dimensioned their pumps so do not have accurate data.”

In many applications, particularly where a large number of smaller powered pumps may be required, carrying out such in-depth analysis can be impractical. Where the pumps may be up for replacement, there can often be reluctance from the end-user to consider looking at an alternative proposal. KSB has responded to this type of scenario by developing a monitoring device Pump Meter that will measure the suction pressure, discharge pressure, differential pressure and head and calculating the values will produce a pump curve illustrating the operating range and produce a load profile of the pump. From this, the pump supplier and the user will be able to deduce if the pump is operating efficiently or not and see at a single glance if the pump is providing efficient and cost-saving operation or if its availability is compromised. This monitoring unit replaces the pressure gauges upstream and downstream of the pump, plus the pressure transmitter normally required for the control functions and any additional monitoring equipment.

Moving on to the second issue, it is necessary to select the most appropriate pump material and pump size for the application. Over sizing pumps just to be safe is a common error made by many end-users and is one of the greatest contributing factors to energy consumption. Thirdly, the efficiency of the hydraulic parts has to be addressed as these have to be matched exactly to the performance required. The impeller diameter is a specific example of a hydraulic element that can influence performance. Oversized impellers waste energy, so trimming the outside of the impeller diameter to the exact flow rate required of the system can yield energy savings of up to 10% and in addition contribute to reduced maintenance costs and longer service life. At the same time the hydraulic efficiency of valves is important as pressure losses will affect pump performance.

The fourth issue relates to pump speed. Controlling the pump speed offers the by far the greatest saving potential, but matching the power input to the actual demand is still far from standard practice in many areas of industry. Solutions are available to control the speed of the pump exactly to the output that is needed. Using a variable speed drive provides dynamic pressure compensation, which will facilitate extra savings under low flow conditions. Using a throttling valve is another approach. However, variable speed drives can reduce power consumption by up to 60% and KSB’s motor-mounted PumpDrive, which also allows frequency converters to be added, can be retrofitted to existing equipment.

Finally, optimum energy efficiency depends on the type of motor used. The use of IE2 (EFF1) motors will increase motor efficiency and the EU will require their utilisation from June 2011. However, from January 2015 motors with a rated output of 7.7 – 375kW should be no less efficient that the IE3 Premium level, or match the IE2 level and be equipped with a variable speed drive. In 2017 it is anticipated that motor efficiency IE4 (Super Premium Efficiency) will be introduced.

Motor efficiency
“In the pump industry almost every manufacturer is already offering IE2 (EFF1) asynchronous motors as standard,” continues Daniel Gonterman. “Much before 2015 the IE3 level will be expected by customers, even though it is not mandatory. Already there is strong competition within the pump industry to meet this standard well in advance of the deadline. At KSB, however, we have reservations about the incoming IE3 regulation because it does not state what the nominal efficiency of the pump should be. To be effective for asynchronous motors, the IEC regulation needs to state what the nominal efficiency point should be. From our point of view this regulation for asynchronous motors is flawed because it does not take into account the nature of the application and how it can affect motor efficiency.”

KSB says that it is already offering an alternative solution to satisfying the IE3 level that will also address the proposed IE4 level. According to Daniel Gonterman, it will only be possible to attain this proposed level by using synchronous motors. The synchronous motor has a big advantage over asynchronous motors in that it is easier to control with a frequency converter and does not exhibit the power loss resulting from the slip that is necessary to magnetise the rotor in the asynchronous motor. The synchronous motor has a constant efficiency over the load, a high nominal efficiency point and high efficiency when combined with a frequency converter.

The only reason synchronous motors are not more widely used for pumping applications under existing regulations is that they are more expensive than asynchronous motors. Also, the asynchronous motor is robust, requires little maintenance and does not need a frequency converter as it reacts to the operation itself. If the load increases, so does the slip and in turn the torque is raised and the operation point is maintained.

KSB sees its future as going down the route of using synchronous motor with a frequency converter in order to satisfy the incoming IE3 and proposed IE4 motor efficiency regulations. The main advantage of this concept is that this solution provides high efficiency over the whole load range which matches the load profile of the pump. The company has already developed such a motor, which is called Suprememotor and this gives 15% less losses than the IE3 level standardised under IEC 60034-30 3008. An additional feature of this motor is that it does not use permanent magnets; it is described by KSB as a ‘synchronous reluctance motor’.

Frequency converters are now very much established within the pump industry and their take up is continuing to grow. However there are applications where frequency converters are not required, for instance where there is a fixed operating point and for this the IE3 level asynchronous motor will continue to be the most cost-effective solution. There are a growing number of applications requiring speed control and where these are encountered it is simple to switch to a synchronous motor. Anywhere that speed control operation is needed, the synchronous motor with frequency converter will give the highest level of efficiency and reduced loss even when running on 50% load.

It has to be stated that this solution represents a higher initial investment cost but this is paid back over the long term through reduced energy costs. When IE3 level motor regulations come into effect, customers currently using IE2 asynchronous motors will have to pay an additional price because the motors will be larger. It does, therefore, appear to make sense to consider the synchronous motor with frequency inverter where speed control is required. KSB is not the only pump manufacturer going down this route and many others are now either recommending synchronous motors with permanent magnets or seeking ways of modifying their pumps to operate more efficiently with asynchronous motors. It is a complex issue and there will be different approaches from manufacturers to meet IE3 regulation. KSB is taking the long term approach and giving its customers the option to invest now for the arrival of IE4.

Summary
Energy efficient motors are an issue that all pump users are going to have to address sooner or later. It is clear that simply fitting an energy efficient motor is not sufficient on its own to reduce a pump’s energy consumption
Whether motivated by saving energy to increase profits, reduce production costs or to comply with incoming IEC regulations, pump users can examine any number of ways to make their systems run more efficiently. Following the five principles set out by Daniel Gonterman would appear to make good sense as they provide a sound foundation from where to start.

KSB Aktiengesellschaft
Johann-Klein Strasse 9
D-67227 Frankenthal
Germany

Can be contacted on:

Tel: +49 6233 86-3702
E-mail: Daniel.Gonterman@ksb.com
Web: www.ksb.com