September 2020

30 n ENERGY EFFICIENCY Using a systems approach to maximise pump savings E uropean efforts to reduce energy consumption have focussed on components covered by the Energy Related Products Directive. The European Commission has already implemented legislation to ensure that products with poor efficiencies are phased out gradually across Europe. Although this is a significant step, new energy-efficient components may still have to operate within an inefficient system, impacting hugely on any possible efficiency gains. To evaluate pumping system efficiencies takes time, knowledge, and the will by both an energy auditor and the pump operator to make a determined change. But the rewards are definitely worth the effort. If the necessary changes are made to inefficient pumping systems, the potential savings across Europe are estimated to total 40-50TWh. Definition First, let us make clear what we mean by a system. A pumping system is defined as one or more pumps and those interacting or interrelating elements that together accomplish the task of moving a liquid. Such systems generally include pump(s), drives, distribution piping, valves, controls, instrumentation, and end-use equipment such as heat exchangers. Using the systems approach involves comparing the need or demand to the supply. It is important to understand how the different components in a system interact and influence each other. A change to one component might affect other components positively or negatively. For example, if you replace an old inefficient motor used to drive a pump, with a modern high-efficiency motor, the new machine will have less slip and will run faster than the old motor. When the pump is running faster, it will consume more energy and this increase in energy usage can be bigger than the savings achieved by the more efficient motor. To reap optimum savings from the change, the pump impeller might need to be trimmed. A system approach starts with defining the ultimate goal of the system. This includes determining the flow rates that the system must be able to deliver, whether there are variations in flow, and what kind of control is needed. These requirements will influence the control methods, the sizes of the pump, motor and piping – and so on. Figure 1 shows how the pump and system performance curves can be used to determine pump operating conditions and to evaluate methods of flow control. To determine the efficiency of a system, the minimum energy to achieve the process demand is compared with the actual energy used. Fig 2 illustrates the difference between looking at components and at systems. When looking from the component perspective, we can compare the input power to the motor from the MCC (motor control centre), to the liquid output from the motor and the pump (shown in Fig 2 by the purple box). This analysis could indeed yield an excellent result. If we broaden the view to include the elements in the green box, we can see a re-circulating line going back to the first tank. The flow rate coming out of the purple box in greater than the green area, but the power input is the same. Finally, we take a complete system view (red box), including the losses in the recirculation line as well as the losses in the regulating valve on the line to the second tank. What might have looked like a reasonably good system when measuring the components in the purple box can now be viewed as an extremely poor efficiency system when viewed at the system level Systems approach We need to define the system demand – the minimum pressure, flow rate and subsequent energy needed for the pumping system to work. To understand the knowledge and tools required to assess the system, the pump industry developed the international standard ISO 14414, which covers the assessment of pump system energy. To achieve the full electrical energy savings for pump systems, a stronger emphasis on the systems approach is needed, as well as a commitment to make this happen both from the pump industry and from the end-users who will ultimately benefit from lower energy bills. n For further information on the work undertaken by Europump, please visit www.europump.org or contact its Secretary General, Pierre Lucas, via email at pierre.lucas@orgalim.eu. Steve Schofield, chief executive of the British Pump Manufacturers' Association, who is also in charge of Europump's marketing commission, explains how adopting a systems approach can help to maximise energy savings in pump systems. Fig. 2 (right): A simple system for pumping a liquid from one tank to another. The efficiency of the pump measured on a component basis (purple box) is based on the ratio between the pump’s input and output. The system view (green box) includes a re-circulation line, while the red box shows the complete pumping system using a total system approach. Fig. 1 (left): Pump and system performance curves can be used to determine pump operating conditions and to evaluate methods of flow control. September 2020 www.drivesncontrols.com Fig. 1 Fig. 2