A new take on energy efficiency

Tuesday, November 29, 2016

Reducing consumption of energy – we all know why it’s important. From a business standpoint, lower energy consumption equates to lower production costs. From an environmental perspective, lower energy utilization reduces CO2 emissions which helps stave off the dangerous consequences of climate change.

The principle of reducing consumption of energy also has a major role to play in ensuring a stable and sustainable energy supply. Unused energy is conserved. And what is not consumed is not transported, saving on expansion and maintenance of the grid and its infrastructure. Energy efficiency can therefore be talked about as an energy source in itself and, today, that approach goes under the name of Efficiency First.

The transformation from product-level to system-level optimization

More than 50% of global electricity is consumed by motor systems. And 30% of global electricity consumption is used in industrial electric motor systems.

During the last decade, in order to capitalize on the vast potential for energy savings, the focus has been on the energy efficiency of motors. Legislation pushing for more efficient motors and different motor technologies is already in place and is gradually being intensified around the world.

In Europe, International Efficiency (IE) standards have been defined to categorize the energy efficiency of motors. These range from IE1 for standard efficiency up to EI4 for super premium efficiency. Since January 2015, machinery and system manufacturers using new motors with a rated output power between 7.5 and 375 kW have been required to achieve at least efficiency class IE3. From 1 January 2017, this requirement will also apply to motors with a rated output power of 0.75 kW or more.

Similarly, the energy-saving potential related to the use of AC drives is well recognized. Adding a drive to an application running at fixed speed will immediately create savings, and to such a degree that regulations stipulate that IE2 motors can be operated as an alternative to IE3 motors, when used in combination with an AC drive.

In short, the focus of energy savings has been on product-level efficiency. According to ZVEI, the German Electrical and Electronic Manufacturers’ Association, efficiency improvements at product level can address 10% of the total savings potential. Using variable speed in applications such as pumps, fans and compressors can address 30% of the total energy savings potential. But, by far the largest potential for energy savings lies in system- and process-level optimization. In percentage terms, we are talking about a massive 60%. Many different measures must be taken to improve the performance of processes and systems, but AC drives themselves have the most important role to play.

AC drives’ role in system-level optimization

System-level optimization is possible thanks to several key elements in AC-drive technology:

Motor independence – Drives that are independent from control systems and motor technology. This freedom enables you to choose the motor technology (induction (IM), permanent magnet (PM), or high-efficiency synchronous reluctance (SynRM)) and motor manufacturer that best suit your application to ensure its peak performance and optimized energy consumption.

Open availability of efficiency data (also in part-load conditions) – This data can be used to optimize the design of a system. Tools to calculate energy efficiency are continuously being developed.

Use of energy-optimized motor control – This is essential to harvest the efficiency potential of electric motors and to ensure your drive is always perfectly adapted to the attached motor and changing loads.

There is a strong relationship between power and flow. A 20% reduction in flow creates a 50% reduction in power usage. Being able to control the flow enables us to control the process and provide higher system-level optimization at plant level which was not possible without using drives. The use of drives also increases the coordination between different machines in a plant or a process.

When talking about efficiency, there is a major difference between motors and drives. To make a motor more efficient, you need to add more functionality into it which, in turn, increases its cost. To make a drive more efficient, you can change the performance level of some components. But, it is important to remember a drive should be used to optimize the performance of a motor. Any drive can control the speed of a motor, but not all drives can get the best efficiency out of a motor. For higher efficiency, we need to focus on advanced drive control. Control methods, such as maximum torque per ampere, reduce power consumption and improve performance of the system.

Hardware features built into the drive (such as DC chokes) result in a more efficient system. This built-in functionality also reduces costs and eliminates the installation space required for external components.

Intelligent heat management is another target of system-level optimization. Features such as back-channel cooling and availability of liquid-cooled drives result in significantly reduced heat loads in switchrooms. This enables the use of smaller air-conditioning systems to optimize space requirements, improve efficiency and drive down costs.

System optimization leads to energy-neutral operation

An excellent example of the advantages of system-level optimization is the Danfoss Drives case story related to the Marselisborg wastewater treatment plant.


The extensive use of AC drives, energy-efficient components and real-time online process control combined with energy production based on the methane from the plant’s digester, has enabled this full-scale facility to operate on a completely energy-neutral basis.

The Marselisborg wastewater treatment plant has transformed its focus beyond minimizing energy consumed, to maximizing net energy surplus. Nowadays, the facility has net production of both electricity and heat, and supplies the district heating system in Denmark’s second-largest municipality, Aarhus. The plant produces 194% energy – that’s 94% more than is needed in the wastewater facility and enough to cover all the electricity needed for water production and distribution and wastewater pumping into the canalization network. It brings the whole water cycle in the catchment area of 200,000 people into energy neutrality.

AC drives will continue to play a major role in reducing energy consumption. But, it is the focus on system-level efficiency that enables companies like Danfoss Drives to further strengthen our customers’ competitive edge and enable the world of tomorrow to do more with less.

Author: Aksel Jepsen, Head of Industry Affairs, Danfoss Drives