The magazine of Friedhelm Loh Group

The magazine of Friedhelm Loh Group

How Bosch Rexroth conserves resources
Experience – Engineering

Really saving energy

Blue e+ chillers. More than 15 per cent of the energy consumption associated with machine tools goes on cooling. Chillers from the Rittal Blue e+ series efficiently reduce this energy consumption, as the test installation in a CNC lathe at Bosch Rexroth in Elchingen, Germany, has shown.

Text Ruth Lemmer ––– Photography

One small step, but a giant impact for GoGreen. Scientists from PTW Darmstadt unpack their measuring equipment in the workshop. Working by hand, they install their electricity meters on four CNC machines at the Bosch Rexroth production plant in Elchingen. The devices are a neat way of showing how much electricity is being used to cool the machines and keep them running smoothly. The rest of the work is done far away – data on the current flows is sent back to the university, where the scientists perch in front of their computers, eagerly evaluating the measurements.

Bosch Rexroth has set up the in-house energy management consultancy GoGreen at its headquarters in Lohr am Main. The group, which has a global workforce of just under 30,000 employees, wants to ensure it is operating on an energy-efficient basis. GoGreen has developed a universal system – dubbed Rexroth 4EE (Rexroth for Energy Efficiency) – that all the group companies can use to lower their CO2 emissions.

The consultancy also participates in research projects – such as the ETA-Transfer project led by the Institute of Production Management, Technology and Machine Tools (PTW) at Technische Universität Darmstadt, examining the energy efficiency of machine tools used in production. “The aim of projects like this is to find solutions that will boost energy efficiency and can also be implemented on a practical level,” explains Leo Pototzky, GoGreen Project Manager at Bosch Rexroth.

The Elchingen plant run by Bosch Rexroth makes hydraulic pumps that help keep construction machinery, agricultural equipment and forklift trucks moving. Various components for the axial piston pumps are manufactured on a DMG GMX 250-type CNC lathe. “In November 2017, as part of the Transfer project, we retrofitted a new Blue e+ chiller from Rittal to one of the four CNC lathes,” Pototzky recounts. The lathe has a total connected load of 75 kilovolt- amperes and is run in three-shift operation four to six days a week.

The blue e+chiller needs


percent less electric energy




kWh saved by Bosch Rexroth with the cooling units.

Energy efficiency wins out

On the face of it, nothing has changed. The machine operator does the same as always – enters the workshop and walks from lathe to lathe, checking on the display that chips are being removed with millimetre precision from the metal workpiece in the gigantic drilling machine.

After all, the new additions retrofitted to the CNC lathe are buried deep in its inner workings. That’s where the Blue e+ chiller feeds in the cooling medium, which flows through the spindles that conduct the heat away from the drive technology. In the chiller, an inverter-controlled DC compressor generates the cooling output needed. To ensure the machine tool’s enclosure is also efficiently climate controlled, the existing compressor cooling unit was replaced by a device from the Blue e+ series, too.

The scientists at PTW Darmstadt measured and precisely documented the energy consumption both before and after the retrofit. A distinction was made between two operating statuses on the machine – working and operational, i.e. when components are being machined as opposed to when machine tools or components are being changed. To ensure the scientists could carry out a detailed analysis, the consumption of all the units in the machine was measured separately and over the course of a week. The main difference in the energy consumption between the two machine statuses lies in the power consumed by the drive train and the system for supplying the cooling lubricant.

  • Flexible performance classes

    The all-important energy efficiency parameter for cooling is the Energy Efficiency Ratio (EER), This defines the ratio of cooling output to the electrical power used. The higher the EER, the better. Conventional chillers that use hot-gas bypass control exhibit an EER of 1. The new Blue e+ chillers from Rittal achieve an EER of up to 4. At the heart of this efficiency enhancement is a variable-speed compressor that always provides just as much cooling output as is currently required. Rittal uses precisely controlled DC synchronous motors to drive the compressors. This ensures the Blue e+ chillers run at optimum speed, saving up to 70 per cent of energy compared to chillers using hot-gas bypass control. Another technical innovation is the micro-channel technology in the heat exchangers, which helps reduce the volume of refrigerant used by up to 55 per cent and thus benefits the environment.

    The Blue e+ chiller series comprises three models with cooling outputs of 2.5, 4 or 5.5 kilowatts. An integrated flow sensor in the cooling medium circuit and fill level monitoring further boost reliability. There is also an overflow valve installed in the cooling medium circuit that opens automatically as soon as the cooling medium circuit is closed at the point of use. A filter mat monitoring system promptly notifies the user when the filter mat needs to be replaced. The units can be used worldwide with all common mains frequencies and voltages – and are very user friendly. The control panel, which features a touchscreen display, depicts all messages in plain text – and in 21 languages. The Blue e+ app transmits data wirelessly, while RiDiag III parameterisation and diagnosis software can also be used with the new series via a USB connection or by linking up to the IoT interface through a range of network protocols.


The results were impressive. The new Blue e+ chiller consumes a good 50 per cent less electrical energy than the old recooling system, while the saving achieved by the cooling unit in the enclosure even exceeded 80 per cent. “If we project that over the course of a year then, depending on the capacity utilisation of the CNC machine, we get a saving of more than 10,000 kilowatt hours,” Pototzky calculates. “This example shows us just how much potential is still waiting to be tapped in lots of areas.”

Another positive effect is that the temperature accuracy of the refrigerant flow, which amounted to more than two degrees Celsius on the old recooler, has been improved by the new Blue e+ chiller to +/-0.1K when in steady state. This can have a positive impact on quality when manufacturing precision-turned parts. By enhancing  energy efficiency, Go- Green has been able to identify an annual potential saving of 14 million euros for the Group – a saving of up to 50 per cent for each plant.

The energy-efficient chillers and compressor cooling units in the Blue e+ series are already playing their part in realising those savings at the Elchingen plant. Go- Green is not only taking shipping companies, the food sector and movie production by storm – it’s also making its mark in mechanical engineering.

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