Behind the scenes, sanitary, heating and air-conditioning technicians are increasingly in demand as advisers to energy commissioners, because the legislator has intensified its search for inefficient energy users – particularly in companies that do not fall into the small and medium-sized business category (non-SMEs). These businesses are frequently targeted by energy audits or alternatively subjected to the mandatory implementation of an energy management system. Cross-sectional technologies such as pump systems are usually first in line to be audited. If the audit identifies energy-wasting devices, the next question is: Which new pump is the most cost-effective one for the job?
Efficiency labels such as IE5 specify a highly efficient pump motor, but fail to give the specialist technician any truly reliable answer by themselves. The crucial element is rather the combined efficiency of the electric motor, pump hydraulics and electronic controls of the pump that has been adapted to the demand at partial load, applicable over the majority of a year.
Old and robust, but inefficient
According to some estimates, approximately ten per cent of global energy consumption can be attributed to the operation of pumps. This figure illustrates the extraordinarily high number of installed units. It comes as no surprise then, that the legislator has, against the backdrop of the climate goals adopted by the European Union and the German energy revolution, moved its focus to pumps as energy consumers. Non-SMEs are, for example, obliged to analyse their energy consumption in order to instigate efficiency measures. Energy-intensive cross-sectional technologies are usually the first ones to attract attention. This includes the primary company-wide system used for the supply of heating and cooling or water and steam - all of these being distribution systems that rely on pumps. And, as a matter of fact, often very reliable pumps, even after many years of operation, thanks to their robust design. However, their outdated technology causes them to consume extremely high amounts of energy. Inefficient pumps have nowhere to hide in an energy audit and are swiftly identified by energy management systems. A replacement almost always pays off if the new pump is highly efficient and has been set up specifically for the respective system. The decision on which pump to install is usually left to a sanitary, heating and air-conditioning technician, being the expert in his field. It is therefore important to have some general knowledge about the efficiency indicators of pumps and how to successfully identify the best-suited pump for a particular application.
Pump efficiency does not equal motor efficiency
Efficiency specifications have become common place for devices consuming electricity. The EU Eco-Design Directive, also called the ErP Directive, sets the standards for both consumer and industrial goods. Its objective is to make products comparable in terms of their energy efficiency by way of easy to understand labels. The comparability of pumps is however hampered by different physical events. A motor converts electricity into mechanical energy and in turn into hydraulic energy via an impeller. The efficiency of each of those processes must be calculated, but each will be represented by a separate indicator. Only an overall perspective will ultimately provide reliable information about the actual efficiency of a pump. Moreover, the load profile of the distribution system and the pump controls are crucial factors in achieving maximum energy savings. Sanitary, heating and air-conditioning technicians have to consider three different energy efficiency indexes:
• IE (International Efficiency): This efficiency index refers to the efficiency of the electric motor. It considers the conversion of electricity into mechanical energy. The calculation base for the classification of electric motors is IEC 60034-30-2, which has already been revised. Until recently, the scale went from IE1 (worst value) to IE4 (best value). The standard was updated because electric motors exceeding the IE4 benchmarks have been on the market for a few years. Electric motors can now be labelled IE5. The Eco-Design Directive specifies a timeline that specifies from what date electric motors of certain energy efficiency classes are no longer permitted to be sold (see box).
• MEI (Minimum Efficiency Index): This index refers to the hydraulic efficiency of water pumps (for fluid temperatures between -10 °C and +120 °C). The efficiency of different types of pumps is assessed at their respective best efficiency point, at partial load and at overload, using a formula prescribed by the EU Directive No. 547/2012. The MEI puts the measured results of the respective pump in relation to the most energy efficient product on the market (as of 2010). An MEI of 0.7 marks the best reference value available at that time and MEI of 0.1 marks the poorest. For example: MEI = 0.4 means that 40 percent of other pumps on the market have an inferior hydraulic efficiency. MEI ≥ 0.7 means that 70 percent of the other available pumps of the same type have an inferior efficiency. The Eco-Design Directive specifies a timeline that specifies from what date pumps with a certain MEI are no longer permitted to be sold (see box).
• EEI (Energy Efficiency Index): This index is the most realistic one for assessing the efficiency of a pump, but is currently only used for glandless circulators. It determines the power consumption in relation to the hydraulic output. The variable demands at partial load are also taken into account when calculating the EEI. Similar to the MEI, the EEI represents a ratio and is not an accurate measure as such. To determine the EEI, the directive draws on the reference values of available pumps. An EEI of 0.27 is the minimum efficiency value while an EEI of 0.20 represents the best available value at that time. For example: A pump with an EEI of 0.27 will consume 27 percent of the reference electrical power consumption assessed by the EU and less than 20 percent in the case of an EEI ≤ 0.20. The Eco-Design Directive specifies a timeline that specifies from what date pumps with a certain EEI are no longer permitted to be sold (see box).
The different energy efficiency labels illustrate the difficulty faced by sanitary, heating and air-conditioning technicians when tasked with identifying the most efficient solution for exchanging a pump in a specific application setting. This applies in particular to glanded pumps as the EU is yet to enact a directive for the assessment of an EEI for these types of pumps.
“Such an assessment is however quite possible, because the procedure to define the overall efficiency for glandless pumps can be adapted for use with glanded pumps. The process is currently being dealt with in the committees,” Wilo Project Manager Jörg Keller explains. “If the project is merely concerned with the replacement of an old pump with a high-efficiency pump – which is the easiest and most economical initial response for many supply networks – the specialist technician can also research the right pump with just a couple of mouse clicks.” Keller points to the comprehensive online tool available from Wilo for the configuration and selection of pumps - Wilo-Select 4 online.
Life cycle costs the crucial factor
The free Wilo online tool - wilo-select.com - offers specialist technicians two convenient ways to identify the most efficient solution. The first one is to simply enter the type designation of the existing pump into the database. Wilo has stored the characteristic values of the most popular pumps of other manufacturers. One click and the database displays a selection of suitable high-efficiency glanded and glandless pumps that match the hydraulic parameters and construction type of the existing pump.
The comparison of glanded pumps in particular should not exclusively rely on designations such as IE5 or MEI ≥ 0.7 alone: “The really crucial factor for making an economic choice, is to look at the life cycle costs of glanded pumps,” according to Jörg Keller. “The lower power consumption of an IE5 motor is of course an important aspect – but it is only one among many. The algorithm of the comparison database takes into account all cost and efficiency values required for an economic efficiency calculation pursuant to the LCC procedure or VDI 2067.”
If the pump type cannot be determined, the “Wilo-Select” database offers the option of entering the hydraulic data in order to determine a suitable and efficient replacement pump. The operating costs over a service life of 15 years are displayed for all suggested replacement pumps. Energy commissioners can make a comparison of characteristics of the new pump compared to those of the existing pump. It enables them to perform a precise evaluation of the investment, in particular with regard to the standardised energy management system ISO EN DIN 50001.
Characteristics of high-efficiency pumps
The constant effort to increase efficiency has changed pump technology profoundly. Knowledge about the most important characteristics of high-efficiency pumps assists specialist technicians in evaluating the solutions offered by different manufacturers in terms of installation procedures and the potential for optimised operations. This is made abundantly clear when looking at the “Wilo-Stratos GIGA” glanded pump.
The “Wilo-Stratos GIGA” has been developed for pumping heating water - in accordance with VDI 2035 - cold water and water-glycol mixture without abrasive substances in heating, cold water and cooling systems. Its hydraulic output reaches delivery heads up to a water column pressure of 51 metres or a volume flow of up to 120 m3/h.
With regard to its efficiency characteristics, Jörg Keller says: “The electric motor of the ‘Wilo-Stratos GIGA’ has exceeded energy efficiency class IE4 from the day we launched it. That class has been the best one according to the current standard, so we had no choice other than hinting at the pump’s significantly superior efficiency by resorting to the designation “> IE4”. We are delighted that the standard has now drawn level with our technical development and we can appropriately label the Stratos GIGA series as an IE5 class pump.”
To achieve this high electric efficiency, the glanded pump has been fitted with an EC motor. EC stands for “electronic commutation”. This means that the type of rotor construction incorporated in the pump, using permanent magnets, causes the current to change its direction and thereby create the necessary rotating electric field. The rotating field propels the rotor, which in turn powers the pump impeller via the motor shaft. Synchronous EC motors have a lower loss rate than asynchronous AC motors. Another technological difference is that AC motors depend on the fixed rotating field of the power supply and can therefore only be controlled via an additional frequency converter.
“The precise tuning of electronics, EC motor and impeller in a system is what delivers the superior overall efficiency of the ‘Wilo-Stratos GIGA’ when compared to a free combination of AC motor and frequency converter. We were also able to achieve weight savings of up to 55 percent and a reduction of the unit size of up to 39 per cent in comparison to conventional pumps,” Jörg Keller continues, as he explains the advantages that go beyond energy efficiency: “The control electronics offer a wide range of options to adapt to the given hydraulics and load profile of a system, which in turn increases the efficiency of the entire system.”
Control technology for improved efficiency
A further characteristic, which is particularly helpful in achieving a sustainable reduction of operating costs by replacing pumps in the case of unknown grid structures of existing systems, is to have a wider spread of rotational speeds. In the case of the ‘Wilo-Stratos GIGA’, the spread is up to three times wider than for comparable controlled pumps; it ranges from 500 to 5,130 rotations per minute. The advantage is an energy-efficient operation of the pump at different partial loads.
Pre-configurable control modes allow the pump electronics to adjust its rotational speed to the prevailing demand. When in control mode “constant differential pressure” (Δ p-c), the pump maintains a constant differential pressure set point across the entire bandwidth of volume flows. This setting is used for boiler circuits in which the pump serves as a feeder for the heat exchanger or a hydraulic shunt. In this scenario, the delivery head remains unchanged while the generated heat quantity varies. (see Figure 1).
Secondary consumption circuits have different characteristics. Activation of the thermostatic valves positioned at different locations throughout the piping network causes the pressure to fluctuate incessantly. When the pre-configured control mode “variable differential pressure” (Δ p-v) is activated, the Stratos GIGA adapts its performance to the variable demand of the consumers along a pump curve. The delivery head increases in line with the increasing volume flow along the same pump curve (see Figure 2).
Differential pressure set points can also be adjusted via a building automation system. Depending on the type of operation, this will increase the efficiency even further. The ‘Wilo-Stratos GIGA’ features plug-in modules to network the pump electronics with the building automation system via different types of bus systems - Modbus, BACnet, CAN, PLR or LON.
Hydraulics and increased efficiency
A lot of energy can be saved by adjusting the piping networks to suit the actual demand. But the cost of replacing the existing pipes with smaller ones is frequently prohibitive. It is however possible to reduce the size of the pump to better suit the demand, thereby providing an optimised duty point, provided that the hydraulic duty chart of the supply grid can be determined.
Two pumps working in parallel may be installed in distribution grids dealing with a small number of peak loads, meaning loads that are significantly higher compared to partial load conditions. In order to prevent expensive building works on the existing pipes, Wilo offers double-pump systems that can be connected to an existing piping network. The newly launched high efficiency inline double pump ‘Wilo-Stratos GIGA-D’ is a good example. Each pump side has its separate electronics that communicate with each other. This allows for different operating modes: from a scenario where one unit serves as the main pump and the other one as a standby pump for emergencies to a system that is fine-tuned to deliver energy efficient parallel operations with efficiency-optimised switching patterns for both pumps in peak-load operation.
IE labelling is far from sufficient for optimising the energy efficiency of pump systems. Instead, the factors to consider are the overall efficiency of a pump as well as the hydraulics and the load profile of the individual supply grid. In the case of optimisation measures for existing buildings, for example triggered by an energy audit or in the context of energy management systems, specialist technicians find it frequently difficult to determine the system curve and to effectively optimise the piping network. The replacement of old pumps with electronically controlled pumps using EC motors offers significant energy savings, even in these scenarios. The magnitude of these effects depends on the pump’s efficiency and other characteristics. Index values provide guidance for specialist technicians. What’s new is that the IEC 60034-30-2 standard now provides for the new energy efficiency class IE5 for electric motors. These high efficiency motors have previously been labelled ≥ IE4.
The hydraulic efficiency of pumps is of equal importance, which is why the IE class of glanded pumps is now complemented by the MEI index. For glandless pumps, the EEI index is already common place, which uses a realistic load profile to express the overall efficiency comprised of electric and hydraulic efficiency with electronic control. The same logic could be applied to glanded pumps. How soon the committees will provide for this option in the relevant standards remains to be seen.
To make it easier for specialist technicians to identify the most economic pump solution for the respective scenario, Wilo offers an online database which automatically calculates the all crucial life cycle costs.