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RAG Aktiengesellschaft

  • RAG Aktiengesellschaft

  • Germany, Essen

  • 76 kW

  • CyberCool CSI 841A, CyberCool CSI 662GES, CyberRow 210CW

  • Efficient cooling for IT infrastructure and cooling circuit for comfort cooling

  • Variable cooling due to scheduled increase in IT load

The Customer

RAG Aktiengesellschaft was founded in 1968 and for decades provided a safe and reliable supply of coal. After more than 200 years, industrial coal mining in Germany came to an end in 2018. This led to the closure of RAG’s last two mines, Prosper-Haniel and Anthrazit Ibbenbüren. However, the company’s responsibility did not end at this turning point. Rather, RAG focused on the task of seeking sustainable solutions for the post-mining landscape.

These involve in-perpetuity work to deal with the consequences of mining. This work includes management of mine water, polder areas, groundwater treatment and monitoring systems on the Ruhr and Saar rivers and in Ibbenbüren. However, the requirements for management and monitoring have grown ever more stringent over the years, and this also applies to the control centers that were formerly operated locally at the various mining sites.

The challenge
Our solution
The result
Our product
Our product

To centralize management and safety monitoring processes and make them more efficient, RAG decided to build a new control room at the Pluto site in Herne-Wanne. Here, modern monitoring systems should enable all water management sites in the Ruhr, on the Saar river and in Ibbenbüren to be monitored centrally in future. A key feature of this project was the appreciably higher level of safety required for this in-perpetuity work. The IT infrastructure is fully redundant in structure, for example. The two server rooms are 100 percent redundant, with each server room additionally having a separate UPS and battery room. The cooling solution was also extremely important, as cooling circuits needed to be installed both for the IT infrastructure and for comfort cooling in the building. The requirements were clear: the cooling system must not be visible from the outside, and it must run on Free Cooling. Moreover, the system must be designed for an IT load that was initially still low due to the new build.


The changing loads posed a particular challenge. Finally, RAG Aktiengesellschaft decided on a solution from STULZ. The possibility of Mixed mode combining Free Cooling and DX cooling was a primary factor in their decision.

In all, STULZ supplied a CSI 841A indoor chiller with condenser for comfort cooling, two CSI 662 GES indoor chillers with integrated Free Cooling function, two matching dry coolers and eight CyberRow CRS 210CW row coolers for the IT infrastructure.

The air conditioning was installed by Dr. Starck Gebäude- und Umwelttechnik GmbH from Siegburg. One important aspect was the need to keep the chilled water circuit for the comfort cooling completely separate from the IT cooling. The varying load conditions were another factor: the initially low load of 12 kW, comprising 3 kW from the monitor wall and 9 kW in total from the server rooms, UPS and battery, will increase to approximately 72 kW when all building is complete.

The two water-cooled CSI 662 GES chillers support the Indirect Free Cooling demanded by the client and each delivered a cooling capacity of 76 kW. Therefore, one unit can already cover the entire future load, providing N+1 redundancy and ensuring availability. What's more, the STULZ systems can cope with fluctuating loads and therefore the initial low load of just 12 kW without problem. At the same time, RAG gains particular benefits from the engineering prowess of the STULZ specialists. For the chillers have two compressors – an On/Off compressor and a modern EC compressor that can work in partial load mode – which share the load between them. This is a real bonus for these project requirements. 

If the load increases between 15 and 50 percent, the capacity of the EC compressor rises to 100 percent, while the On/Off compressor remains off. If, on the other hand, the load rises by 50 percent, on comes the On/Off compressor, and gets straight to 100 percent of its capacity, to cool the load. A rise in load from 50 to 100 percent causes the On/Off compressor to deliver another 100 percent of capacity.

In addition, the EC compressor switches itself back on, and can increase capacity steplessly to 100 percent. Moreover, the CSI 662 GES is equipped as standard with a Free Cooling brazed plate heat exchanger. Therefore, the compressor and associated DX brazed plate heat exchanger can be fully bypassed and switched off based on the outside temperature, controlled by a three-way valve. Rising outside temperatures are no problem either. This is thanks to Mixed mode, which enables an infinitely variable combination of Free Cooling mode and DX mode.

For row cooling (cold aisle solution), the intelligent standby manager used in the STULZ solution is impressive. As four CRS 210CW CyberRows each with a capacity of 9.8 kW were installed in each IT room, three of the four installed row coolers are already able to cool down the maximum heat load. This way, N+1 redundancy has also been achieved for the row coolers. However, thanks to the STULZ standby manager, the fourth unit does not remain on standby, but also runs continuously. 

The STULZ solution therefore achieves greater energy efficiency: since four units are in operation, each individual row cooler has less to do, and the amount of moving air per unit also decreases.

CyberCool Indoor

STULZ CyberCool Indoor provides powerful, highly efficient chilled water cooling with a minimal footprint and is perfectly suited for cooling medical equipment, IT and facilities. The unit's modern design and compact construction allows it to be installed inside the building easily, as well as integrated in existing systems. The version with EC compressor was developed for especially stringent project requirements.

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In the CyberRow, in-line air conditioning unit, innovative horizontal air conduction has been enhanced with state-of-the-art technology that works with power, flexibility and efficiency – directly at the rack. Fluctuating server rack loads, space restrictions, lack of a raised floor, existing high-density server technology – these are exactly the cases from server rack cooling practice for which CyberRow was developed.


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