Optimising energy efficiency

Many pump manufacturers are offering higher efficiency pumps as they respond to the demands imposed on industry to reduce carbon emissions and from end-users seeking to keep down production costs. 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 to EFF2); IE2 high efficiency motors (comparable to EFF1); and IE3 premium efficiency motors. These classes are valid for two, four and six-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, energy efficient motors only make 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
KSB has identified five issues that need to be addressed in order to produce the most energy efficient pump installation. Firstly, 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, the end-user can be reluctant to consider 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. Secondly, 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 and is one of the greatest contributing factors to energy consumption.

Thirdly, the efficiency of the hydraulic parts has to be addressed and be matched exactly to the performance required. The impeller diameter is a specific example as oversized impellers waste energy. Trimming the outside of the impeller diameter to the exact flow rate required of the system can yield energy savings of up to 10%.

Controlling the pump speed is the fourth issue, offering by far the greatest saving potential, but matching the power input to the actual demand is still far from standard practice. A variable speed drive (VSD) provides dynamic pressure compensation, which will facilitate extra savings under low flow conditions. Using a throttling valve is another approach. However, VSDs can reduce power consumption by up to 60% and KSB’s motor-mounted Pump Drive, 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 increases motor efficiency and the EU required their use 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 VSD. In 2017 it is anticipated that motor efficiency IE4 (Super Premium Efficiency) will be introduced.

KSB is already offering an alternative solution to satisfying the IE3 level that will also address the proposed IE4 level. It will only be possible to attain this proposed level by using synchronous motors.

KSB sees using synchronous motor with a frequency converter as the way 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, the Supreme Motor, 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’. 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. With this product development, KSB is taking the long term approach and giving its customers the option to invest now for the arrival of IE4.