THE REFRIGERATION MAGAZINE FROM ENGIE REFRIGERATION GMBH REFLECT. LOTS OF CHILL, LITTLE EXPENSE Various free cooling systems for the QUANTUM series

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1 THE REFRIGERATION MAGAZINE FROM ENGIE REFRIGERATION GMBH REFLECT #01 LOTS OF CHILL, LITTLE EXPENSE Various free cooling systems for the QUANTUM series THE KNOW-HOW TO BEAT LEGIONELLA Why legionella worldwide should fear German know-how TECHNOLOGY ALL OVER THE WORLD ENGIE Refrigeration realises innovative projects around the world

2 From unity comes performance: The air cooled QUANTUM Continuous improvement to technical solutions is what drives us like with the air cooled QUANTUM. This series provides free cooling and normal chiller operation in a single and compact design. In the air cooled QUANTUM, free cooling modules and chillers form a single unit. When outside temperatures are low, cooling can thus be provided without running a compressor. The same chiller fans are used for the necessary re-cooling in normal cooling mode and for cooling down the chilled medium in free cooling mode. This solution is not just smart, but also space-saving and highly efficient: The air cooled QUANTUM achieves an EER rating of up to 60. Ingenious Refrigeration Made by ENGIE Refrigeration. Optimal use of energies. engie-refrigeration.de

3 EDITORIAL A BREATH OF FRESH AIR: OUR HIGH-EFFICIENCY REFRIGERATION SOLUTIONS JOCHEN HORNUNG, CEO ENGIE REFRIGERATION GMBH A t ENGIE Refrigeration, we set ourselves ambitious targets. We want to keep on advancing our refrigeration solutions and supply all of our customers with cutting-edge technology and top-rate service. And so there s a hint of not one but several groundbreaking refrigeration solutions in the air at ENGIE Refrigeration. Our air-cooled QUANTUM series now comes with new, high-efficiency condensers. How you as the operator will benefit from this is explained from page 6 onwards. To check out the different variants of free cooling for air-cooled QUANTUM chillers, turn to page 8. We at ENGIE Refrigeration are among the very few manufacturers worldwide who offer all variations on free cooling external, integrated or with thermosiphon function. And we re always working on staying a step ahead in terms of innovation. So rest assured: we ve got the profitable and energy-efficient refrigeration solution you re looking for. Together, we ll meet your individual requirements in the best possible way. And we ll be more than happy to prove that ENGIE Refrigeration s claims aren t just hot air. With that, I ll leave you to enjoy reading. Best regards, yours Jochen Hornung REFlect Issue 01/2018 3

4 AIR is a mixture of oxygen, nitrogen, carbon dioxide and a myriad other gases. It also transports water vapour and dust. 1.2 grams is the weight of one litre of air under standard conditions; in other words, at a temperature of 20 C and at sea level. When air gets colder, the air molecules move closer together, increasing air density. For example, at a temperature of -20 C at sea level, one cubic metre of air already weighs 1.4 kilograms. 4

5 5 QUINTILLION KILOGRAMS is the weight of Earth s entire atmosphere. This means that, on average, each square metre of the planet s surface supports a mass of 10,000 kilograms of air. 10,000 litres of air are inhaled and exhaled by each human being every day. Over the course of a single lifetime, a healthy human being consumes up to 560 million litres of air. 7 NITROGEN N OXYGEN O MINUTES AND 3 SECONDS per cent nitrogen and per cent oxygen are contained in the air when we inhale. When we exhale, we have changed the composition to 78 per cent nitrogen and 17 per cent oxygen. is the current Guinness World Record for holding one s breath. World record holder is the Spaniard Aleix Segura. 1,057.8 hectopascals 15 BREATHS are drawn by an adult every minute. Children breathe 20 to 30 times per minute, newborns even take 40 to 50 breaths per minute. is the highest barometric pressure ever measured in Germany, recorded on 23 January 1907 in Berlin. The world record for highest barometric pressure lies at 1,085.7 hectopascals, measured on 19 December 2001 in Tosontsengel in Mongolia. REFlect Issue 01/2018 5

6 With their high-efficiency condensers, our air-cooled QUANTUM chillers meet even the most exact customer requirements. New condensers for air-cooled QUANTUM series THE GO-TO CHOICE What do a concert hall, a clinic and a pharmaceuticals corporation have in common? As distinct as they seem from one another, there s one thing they share: all three have the highest standards when it comes to cooling their building complexes. And now our air-cooled QUANTUM series with optimised-capacity condensers can meet these standards with even greater efficiency supplying the ideal climate even for the most demanding of applications. 6

7 Highly efficient and with optimised capacity: ENGIE Refrigeration now installs new condenser coils to cool the refrigerant in its air-cooled QUANTUM series units with optional free cooling. System operators gain real added value: the re-cooling capacity has been optimised overall and ensures optimum cooling output even where temperatures constantly remain high, a benefit enjoyed particularly when used in countries with long periods of hot weather. On top of this, the chiller s design makes it excellently suitable for areas with stringent noise requirements. Condenser power can of course be adjusted to suit your individual customer needs. The air-cooled QUANTUM chillers have a total refrigeration capacity of up to 1,800 kilowatts. A genuine all-rounder: the redesigned QUANTUM series supplies eco-cooling. The redesigned QUANTUM comes with greater capacity at lower noise and an identical footprint. Innovative refrigeration solution In addition, the chillers with the new condensers have been designed to keep their original footprint. This means that the space required for installation remains unchanged while refrigeration capacity is significantly higher. With the changes made to the condenser, the internal fans can run at lower speeds and power. This way, operators not only save on running costs but also considerably reduce their systems noise emissions. At the same time, the system scores greenie points: the fan s reduced power consumption logically entails lower carbon emissions. Furthermore, the air-cooled QUANTUM chillers can be operated using either R-134a or R-1234ze as refrigerant. If required, ENGIE Refrigeration can increase energy efficiency by setting up any standard QUANTUM model to include integrated free cooling, either modular or output-dependent. This innovative solution is ENGIE Refrigeration s answer to the market s increasing requirements. The new concepts are tailored perfectly to meet customer needs. For the toughest requirements The redesigned air-cooled QUANTUM series had its maiden performance with a customer from the pharmaceuticals industry. Since 2017, ENGIE Refrigeration has been taking care of optimum cooling in their production facilities. Thanks to its particular properties, the QUANTUM is especially suited for use in areas where noise needs to be controlled down to every last decibel, such as concert halls, hospitals and office buildings. REFlect Issue 01/2018 7

8 Free cooling systems for QUANTUM LOTS OF CHILL, LITTLE EXPENSE External, integrated or with thermosiphon function free cooling systems produce refrigeration highly efficiently and save energy costs. ENGIE Refrigeration is one of the few manufacturers to offer system operators all variants of free cooling. But putting the principle into operation does require certain conditions to be met. Many applications, for example process cooling or computer centres, require cooling not only in summer but also during the transition period, or even throughout winter. If outdoor temperatures drop below the temperature at which the chilled medium is supplied, you theoretically no longer need to produce cooling using cold vapour but can instead utilise a process of heat transfer between the ambient air and cold water. Referred to as free cooling, the advantage of this process is that you do not need to run the refrigeration system s compressors. The result is a lower electrical power consumption and thus greater energy efficiency. Free cooling offers system operators substantial energy cost savings. A tailored solution for your application To make sure that the chosen solution always provides the ideal balance between free cooling capacity, investment costs and system dimensions, ENGIE Refrigeration s portfolio includes various system solutions. All free cooling solutions come from the range of air-cooled QUANTUM chillers, and are integrated mechanically, hydraulically and in terms of control systems. The chiller s control system automatically switches from compressor mode to free cooling mode and back according to the operating conditions. Mixed operation is also possible. ENGIE chillers cover the entire spectrum of free cooling methods: external or integrated modules or thermosiphon function. On QUANTUMS with an external free cooling module, the module is fixed onto the chiller s base frame and integrated hydraulically. QUANTUMS with an integrated free cooling module come with additional water-air heat exchangers installed in the condenser modules. Flow through the sandwich structure with free cooling module and the condenser is produced by the same fan. QUANTUMS with thermosiphon function do not require additional heat exchangers. Two motor-driven ball cocks bridge the condenser and expansion valve in the refrigerant circuit to allow the refrigerant to circulate freely. The low ambient temperature causes the refrigerant to condense in the condenser. From there it flows into the evaporator, where it absorbs heat and evaporates. The chiller s condenser cannot run during thermosiphon or natural circulation mode. 8

9 Estimating cooling requirements Free cooling can only work if the ambient temperature lies below the cold water temperature. Accordingly, it is especially suitable for applications with a comparatively high cooling water intake temperature of around 13 C. Operating costs can be cut especially where cooling is required not only in summer but also during the transition periods and in winter. Judging whether free cooling makes sense, and finding out which method is best suited, requires estimating the cooling requirements per season. Good starting points for estimates can be found in the standardised annual load profiles for process cooling and air conditioning in EU Commission Regulation 2016/2281 on eco-design requirements (see page 11). When choosing the best free cooling system, you need to consider a number of factors. The key factors are the achievable refrigeration capacity, achievable energy savings, investment costs and available space. Generally speaking, free cooling is always more efficient than compressor mode because the compressors are not required to run and thus consume no power. Choosing a free cooling system that matches requirements allows system operators to cut operating costs substantially. If year-round cooling is required, free cooling can make up around 70 per cent of annual operating time. To choose the right system, detailed knowledge of the cooling requirements throughout the year and selection of a matching QUANTUM chiller are indispensable. REFlect Issue 01/2018 9

10 ENGIE Refrigeration has the free cooling to match REAL ALL-ROUNDER: QUANTUM QUANTUM QUANTUM chiller with external free cooling module by ENGIE Refrigeration. T set Chilled medium 2 M Free cooling module Ambient air Refrigerant M Compressor Evaporator Fan Condenser Fan Condenser 1 M Chilled medium SAVES SPACE: QUANTUM Free cooling module QUANTUM with integrated free cooling offers high refrigeration capacity with a smaller footprint than our standard solution. T set Chilled medium 2 M Ambient air Refrigerant Compressor M Evaporator Fan Condenser Fan Condenser 1 M Chilled medium SAVES ENERGY COSTS: QUANTUM Fan Fan QUANTUM chillers Condenser Condenser with thermosiphon will fit a comparatively tighter budget. Chilled medium Motor ball valve M M Refrigerant Expansion valve Evaporator Compressor Ambient air M Motor ball valve 10

11 your requirements. At an ambient temperature of 7 C, the air-conditioning load profile specifies zero cooling requirements. For process cooling, however, the load profile lists 1,050 kilowatts (kw) required refrigeration capacity. This can be achieved using the following combinations of free cooling systems (the example assumes 13 C cold water at outlet/19 C cold water at intake): 1 external free cooling module: 100 kw (approx. 10 % of requirements) 2 external free cooling modules: 200 kw (approx. 20 % of requirements) 3 external free cooling modules: 300 kw (approx. 30 % of requirements) 4 external free cooling modules: 400 kw (approx. 40 % of requirements) Thermosiphon: 400 kw (approx. 40 % of requirements) Integrated free cooling: 1,050 kw (100 % of requirements) CROSS-COMPARISON: BENEFITS EXTERNAL FREE COOLING MODULES High EER in free cooling mode INTEGRATED FREE COOLING MODULES Extremely compact, high free cooling capacity DRAWBACKS Needs more space EER slightly lower in compressor mode USAGE EXAMPLE APPLICATIONS Lower power consumption in free cooling Can be combined with air conditioning High power consumption during transition period/in winter Process cooling, data centres THERMOSIPHON Low costs Combined mode not available as standard only thermosiphon or compressor mode Low power consumption in free cooling mode Can combine air conditioning and process cooling REFlect Issue 01/

12 QUANTUM P with improved performance A REAL POWER- HOUSE Compact outside, power inside: our water-cooled QUANTUM from the P (Powerline) series now comes with a refrigeration capacity of up to ten megawatts. This makes the ENGIE Refrigeration chiller the perfect choice for use in district cooling networks. QUANTUM P has the power despite being compact in size. 12

13 Hub for economics and trade, creative cultural centre and hip district with cutting-edge architecture: founded in 1996, the Euroméditerranée urban development project in Marseille in southern France is one of the largest in Europe. ENGIE Refrigeration keeps it cool: two QUANTUM P chillers are used on-site to produce a cooling power of eight megawatts. The capacity is now to be increased to 16 megawatts. The chillers shine through their outstanding energy efficiency. ENGIE Refrigeration has supported Marseille in sustainable urban development this way since Full speed ahead ENGIE Refrigeration has further improved its capacities for district cooling projects of this scale. Because customer demand for especially powerful chillers has been increasing, our refrigeration specialists have advanced the QUANTUM P series: QUANTUM P is now available with the refrigerant R- 134a and a refrigeration capacity of up to ten megawatts. Using the refrigerant R-1234ze allows for a refrigeration capacity of up to eight megawatts. Both variants can be supplied with 8 to 16 compressors. ENGIE Refrigeration delivered the first 5 of these chillers, together reaching a total refrigeration capacity of 25 megawatts, to southeast Asia only a few weeks ago. Each of these chillers is 3.5 metres wide, 7.3 metres long and weighs a total of 31,100 kilograms. The next orders are already being put together. High power, high flexibility System operators benefit particularly from the modular design of the QUANTUM P series. We can cater to customer requirements with full flexibility and easily adjust the chillers to the requested refrigeration power. Because a QUANTUM P can be dismantled into five parts, it is also simple to transport and can even be fitted into tight chiller rooms. Furthermore, the chiller can be set up to operate under a variety of conditions. Equipping it with titanium interior piping, for example, allows it to run using seawater. Its high refrigeration capacity makes the QUANTUM P especially suitable for producing cooling in district cooling networks like that for Marseille s Euroméditerranée: networks of this kind use a pipeline system to supply multiple consumers with cooling generated in a refrigeration centre. At the consumer s site, all that is normally installed is a transfer station. Because district cooling networks have substantial thermal storage capacity, ENGIE Refrigeration chillers can be integrated into and operated within a smart grid especially well. Pioneering solution Alongside the particularly high refrigeration capacity, our QUANTUM P chillers offer all the customary benefits of our QUANTUM series. The chiller has outstanding energy efficiency under partial load. The redundancy included in its design makes it a paragon of reliable operation. At the same time, this redundancy massively simplifies compressor maintenance: the compressors can be serviced while the chiller is running. This allows QUANTUM P to supply highperformance, high-efficiency, pioneering cooling. A single QUANTUM P chiller can be fitted with up to 16 compressors. Felix Rutschke, working for the Application Technology & Test team within ENGIE Refrigeration is testing the QUANTUM P at the new test bench in Lindau. REFlect Issue 01/

14 Interview with Manfred Hofmann THE KNOW-HOW TO BEAT LEGIONELLA What was the impetus behind drawing up the 42nd Federal Immission Control Act? In 2013 in Warstein and in 2010 in Ulm, Germany saw serious outbreaks of Legionellosis; there were even fatalities. The legionella each time proliferated in re-cooling systems. Legionella become a danger when they reach a certain concentration or when they ecome airborne as an aerosol. Manfred Hofmann is responsible for various training courses around the topic refrigeration. This year most training courses includes information about 42. BImSchV. 14

15 What was the impetus behind drawing up the 42nd Federal Immission Control Act? In 2013 in Warstein and in 2010 in Ulm, Germany saw serious outbreaks of Legionellosis; there were even fatalities. The legionella each time proliferated in re-cooling systems. Legionella become a danger when they reach a certain concentration or when they become airborne as an aerosol. How acute a risk do legionella pose in Germany? We hadn t had any problems with them in Germany for decades. In Warstein and Ulm, the re-cooling systems had been serviced poorly or incorrectly. Based on the system principle, the coolant temperature in 90 per cent of all refrigeration systems lies between 35 and 45 C. This is also the temperature at which legionella proliferate rapidly. What measures can be taken to combat the bacteria? If necessary, you need to cleanse the cooling water using biocides. You also need to add drip strainers to the design to minimise dripping. Legionella aren t actually a problem at all with the right technology. What steps does the new law prescribe? The Immission Control Act requires system operators to inspect their systems; that is, to conduct a simple water test for legionella, at intervals of no more than 14 days. And every three months, you have to perform a lab test. There s a reference value specific to each system. What do operators have to do if the test is positive? The water has to be sent to a lab and the causes need to be identified. And then corrective action has to be taken. If the test shows more than 100 times the reference value, immediate action using the latest technology is required. You are also obliged to document your research into the causes and the action taken in your system s operating log. What technical measures are available to system operators? In general, proper maintenance should be performed and systems should be upgraded to the state of the art. Technological progress won t stop. In the past, the threat of legionella could have been neutralised each time by employing the latest technology and controls. ENGIE Refrigeration, for example, specifies annual maintenance, an inspection every five years by a publicly appointed and accredited expert as well as maintaining a system operating log including a service log. How can ENGIE Refrigeration assist its customers in complying with the new law? ENGIE refrigeration systems and our specifications for their use already comply fully with the new Immission Control Act. We also provide our customers with instructions on how to operate the systems based on the legal requirements and offer very good training courses on technical and legal aspects. What additional costs are refrigeration system operators facing? The operating costs have become slightly higher but the safety gain is considerable. We supply our customers with a comprehensive package that provides the ideal combination of technology and service. How great is the risk posed by legionella in other countries? The 35 to 45 C that legionella require for propagation can be found anywhere in the world. Differences in the various global regions lie in how technology is maintained and in the attitude towards health hazards. Many societies have far less stringent safety requirements than we do here in Central Europe. How can Made in Germany act as an example in terms of fighting legionella? Germany and Europe lead the field globally when it comes to technology, efficiency and safety. Less developed nations use our import regulations to secure orders. Our service and sales partners export German expertise for combating legionella to customers all over the world. REFlect Issue 01/

16 Efficient and non-flammable Starting April 2018, QUANTUM chillers will be available with the refrigerant R-513A. Suitable for both new and already operating systems, it comes with safety rating A1 and a low GWP value (GWP = global warming potential) of only 573 (IPCC AR5). Furthermore, R-513A is non-flammable while providing almost the same refrigeration capacity and energy efficiency as R-134a. R-513A is a pioneering refrigerant in that it meets the requirements of EU Regulation 517/2014 (F-gas regulation). Experts on-site ENGIE as exhibitor on CEBIT and Data Center World. Artificial intelligence, augmented and virtual reality, blockchain and the Internet of Things (IoT): these and other things will be the focal, pioneering topics at CeBIT And the specialists from ENGIE Refrigeration and its sister company ENGIE Deutschland GmbH, Germany s market leader in building control technology, energy services and facility management, will be there too. The world s largest trade show for computer technology will be held from 11 till 15 June at the Hanover trade fair grounds. There ll be lots to see for visitors, for example in the 360 dc pavilion in hall 12, stand D79, where you can check out the technical design aspects and operating principles of energy-efficient solutions for computer centres. ENGIE Refrigeration will also present at Data Center World in Frankfurt am Main on 7 and 8 November. Our experts will be on site at Germany s largest get-together of computer centre specialists to answer any questions you might have about refrigeration solutions for computer technology. Get in touch in advance and we ll arrange appointments for personal consultation. 16

17 Sponsor of EV Lindau Dedicated to the home advantage Refrigeration and ice hockey a perfect match. ENGIE Refrigeration has been a sponsor of the ice hockey team EV Lindau (EVL) since At ENGIE Refrigeration, we love the cold. We operate at international level but remain deeply rooted in our home region on the German shores of Lake Constance. So dedicating ourselves to ice hockey in the region came easy to us: ENGIE Refrigeration is the main official sponsor of EV Lindau. The team is nicknamed the Islanders in reference to the island town of Lindau. Right now, the team s doing great: since 2016, the men s first team has been playing in Germany s ice hockey Oberliga (literally: upper league), finishing tenth for the 2016/2017 season. EV Lindau actively fosters junior talent and officially maintains several junior and school teams. ENGIE Refrigeration has a three-year sponsorship deal with the Islanders, including as a jersey sponsor. Jochen Hornung and Patrick Meier, Head of Marketing Lindau Islanders Club: both wearing the new shirts of the Lindau Islanders Club. Diverse training offers Take on the future At its head office in Lindau on Lake Constance, ENGIE Refrigeration provides job training for junior personnel. At present, there are 13 young people completing job training as mechatronics engineers for refrigeration technology. Job training at ENGIE Refrigeration offers a great outlook: refrigeration specialists are highly sought for on the labour market. Since 2017, four young adults have been on our team to complete their job training as mechatronics engineers for refrigeration technology. And we re expanding our job training offer: starting September 2018, ENGIE Refrigeration will offer a three-and-a-half-year job training course for systems engineers and a two-year job training course for industrial electricians in the field of systems technology. On top of that, junior personnel can also enlist in a dual degree course to complete a bachelor s in mechanical engineering in the field of design and development or a bachelor s in electrical engineering in the field of automation. This makes up a total of twelve traineeships at ENGIE Refrigeration a focused effort to train our own next generation of technicians and managers. Instructor Wolfgang Steur (right) explains the cut-away model of the Turbocor compressor the core element of a QUANTUM chiller to trainees.

18 Vienna, Austria ENGIE Refrigeration GmbH worldwide Technology all over the world From Lindau to the wide world: ENGIE Refrigeration provides its customers with tailored solutions and services for profitable and energy-efficient refrigeration and heat utilisation all over the world and in a myriad different ways. REFlect presents some of the projects. Tehran, Iran Nice and cool With eleven storeys, 500 beds and around 64,000 square metres of usable space, the International Neuroscience Institute (INI) in Tehran is the world s largest Neurology clinic. Opened in 2017, it is four times as large as the INI in Hanover, Germany, which served as its template and is also chaired by the Iranian Professor Majid Samii. The building complex, which is shaped to look like a brain, is supplied with a pleasant and energy-efficient climate by three QUANTUM chillers. They flexibly adjust cold-water production to the cooling requirements. Total refrigeration capacity: approx. 10 megawatts 18 Aspiring to higher things At 140 metres, the IZD Tower is not only the highest office tower in Vienna, it is also Austria s greenest office building thanks to eco-friendly building technology and low energy costs. One contribution to the outstanding energy balance is made by ENGIE Refrigeration: the existing cooling system, consisting of two ice storage tanks and a chiller, was replaced with two air-cooled QUANTUM chillers with free cooling. Refrigeration capacity is 4.4 megawatts. Over the course of one year, the system supplies 4.3 gigawatt-hours of cooling that s 30 per cent more than the previous system. Total refrigeration capacity: approx. 4.4 megawatts

19 Nouméa, New Caledonia Koropi, Greece Cool South Seas Get well soon In New Caledonia s capital Nouméa, around 1,500 kilometres east of Australia, ENGIE Refrigeration helps a private hospital keep its cool. At tropical outdoor temperatures, two type X105 watercooled QUANTUM chillers with a refrigeration capacity of 900 kilowatts each, ensure a pleasant room climate for patients and personnel and protect sensitive medical equipment. The chillers are protected from electromagnetic radiation by EMC filters. Another clinic on the island has been running with four QUANTUM chillers without problems since Boehringer Ingelheim Ellas specialises in producing consumer healthcare products such as medication for treating diabetes and high blood pressure, anti-aids drugs and painkillers and other medicines in tablet form. When producing medicine, temperature and humidity need to in perfect accordance to the specifications. That s why, since 2017, the Pharmaceuticals company has been operating with three type X080 QUANTUM chillers and one type X040 QUANTUM that can also be used as a heat pump. Besides the production facilities, ENGIE Refrigeration also keeps the offices cool. Total refrigeration capacity: approx. 1.8 megawatts Total refrigeration capacity: approx. 2.7 megawatts Loßburg, Germany Black Forest power ARBURG is world leader in the manufacture of machines for plastics processing. ENGIE Refrigeration provides cooling for some of the production sections and takes care of the air conditioning in the German HQ plant. To do so, ENGIE Refrigeration has installed two type X060 QUANTUM chillers and one type X030 QUANTUM. The deal was clinched thanks to QUANTUM s outstanding energy efficiency under partial load and to the twin condenser technology. The latter allows ARBURG to use heat recovery and put the lion s share of the produced heat to use elsewhere. Total refrigeration capacity: approx. 1.5 megawatts REFlect Issue 01/

20 IMPRINT PUBLISHER ENGIE Refrigeration GmbH Josephine-Hirner-Straße 1 & 3 D Lindau Phone: Fax: refrigeration@de.engie.com engie-refrigeration.de EDITORIAL RESPONSIBILITY Tatiana Köhler, Head of Marketing and Communications EDITORIAL DEPARTMENT Publik. Agentur für Kommunikation GmbH TEXT/EDITING AND DESIGN Tatiana Köhler, Katja Krimme and Jessica Lenz PICTURE CREDITS German Trade Fair, Hannover, Jan Potente, istock, ENGIE Refrigeration GmbH, ENGIE Deutschland GmbH March 2018 Optimal use of energies.