Data centers go green

In an increasingly networked world, we are storing more and more data. So much so that the volume of data stored doubles every 18 months. This poses a tremendous challenge to the beating heart of our global networks; the world's data centers. As the volumes of data increase, so too do the requirements for safety, availability and infrastructure in data centers. In Frankfurt, Citigroup operates its largest data center outside of the USA. The highly energy-efficient facility is the world's first center of its kind to receive LEED (Leadership in Energy and Environmental Design) Platinum certification, thanks in part to technology from Siemens.

Data centers link the worlds of IT and infrastructure. Their primary task is to save and protect data. Yet at the same time, the buildings and infrastructure must be operated safely and efficiently. Ultimately, there is little difference between data centers and traditional industrial infrastructures. So it is with good reason that they are known as the ‘factories of the 21st century'. The IT infrastructure in such data centers requires a great deal of energy. For operators, availability, reliability and energy efficiency are therefore top priorities. This requires an uninterruptible and redundant power supply, and intelligent safety and security technology. Further innovative features such as smart lighting and cooling control can also lower energy consumption appreciably. Reliable building automation cools and conditions the air as required and prevents the servers from overheating. Finally, cold aisle containment allows the cold air cooling the servers through a raised floor to be directed in a more targeted manner, thus reducing the air volume required. This offers further valuable energy savings. In addition, the warm exhaust air can be utilized for local heating through the use of heat pumps.

Today, 'green technology' is no longer just an optional extra in data centers; it is essential for ensuring energy-efficient and sustainable operations.
Urs Iten, Director of Global Portfolio Management for Data Centers

Citigroup's success with Siemens

“At Citigroup we’ve had great success with free cooling, i.e. relying on cool outside air, and we use our building automation system to adjust the cooling performance to our actual demand,” says Dirk Hatzmann, Senior Vice President of Technology Infrastructure at Citibank NA's Frankfurt branch, who is also overseeing the Citigroup data center in Frankfurt.


Citigroup's Frankfurt Data Center (FDC) comprises three building complexes. Firstly, the center's offices are located in a 1,500-m2 building. A second complex measuring 9,500 m2 is used for deliveries and warehousing. And the third, largest complex with some 21,000 m2 of floor space houses a two-story server room, with infrastructure such as the cooling station, the sprinkler system (including water tanks with a capacity of 2 million liters), and an emergency power system with a 600,000-liter diesel tank. Throughout the site, Siemens solutions ensure reliable automation, security and energy supply.


The Desigo building automation system from Siemens plays a central role in maintaining high energy-efficiency and meeting the requirements for LEED certification. This innovative building management system enables individual control and continuous monitoring of heating, ventilation and cooling technology. In addition to the two Desigo management stations, the system also includes 1,600 fire detectors with the associated Sinteso fire control panels, and early fire detection via smoke extraction systems. Sensors and 160 sensor-activated cameras monitor the 1.3-km perimeter fence and interior. The 168 door sensors ensure the buildings are secure, and are connected to an intrusion detection system. All signals from the security and fire safety systems come together in the danger management system (GMA Manager).


“Our motivation was to continuously save energy,” says Norbert Heberer, who supervises the data center along with a team of ten staff. “Building automation allows us to individually control and continuously monitor the heating, ventilation and cooling technology that is so vital to us.” When operations began in 2008, the data center used 900 kilowatts of electricity. With additional utilization and occupancy, the electricity requirement now far exceeds 1 megawatt. “One challenge was to continually adjust the power supply and cooling capacity to the actual demand, from the planned 5 megawatts of total capacity to the starting load of 900 kilowatts, and then to the current level of about 1.5 megawatts,” Heberer adds. “When operations started, we had a less efficient ratio of consumed energy to server energy demand, giving us a power usage effectiveness, PUE, of 2.8.”

A professional approach

To adjust the power supply and cooling capacity, Siemens technicians analyzed the complete electrical supply and optimized the cooling control. “Now all the dependencies of free cooling, pumps and chillers operate together as a bundle and can be controlled as demand dictates,” explains Heberer. To adjust energy efficiency based on demand and lower the PUE value, lighting was tied to access control so the lights would turn on only when the server rooms are occupied. In addition, the air conditioning in the server rooms was set to the optimal operating point. Now, the same level of server security is assured with less cooling capacity. Air pressure in the cold aisle was also lowered by 10 pascals.

“Throughout this project, we benefited from the experience and commitment of the Siemens technicians. They were prepared to forge new paths and supported us quickly and competently, even devising custom solutions for particular challenges,” praises Hatzmann. As a result of this collaboration and the measures implemented, the current PUE of the Frankfurt Data Center is 1.5 – almost half of the initial value. Yet Citigroup and its partners remain ambitious and are aiming for even greater energy efficiency.

All the FDC stakeholders now benefit from custom solutions that were developed collectively. “Everyone involved in this project learned a great deal”, sums up Hatzmann. “Technology, solutions and processes go hand-in-hand, and we are very satisfied with the results. The dedicated technicians from Siemens made essential contributions to the project’s success.”


Author: Urs Iten, Director of Global Portfolio Management for Data Centers, Siemens AG

Picture credits: Citigroup

For data centers, safe and reliable power must be ensured at all times to protect the stored data. Thus, Siemens solutions include a comprehensive portfolio for power supply, across all voltage levels and throughout the entire lifecycle. For example in the CitiGroup Data Center, if a power failure were to occur, two independent uninterruptible power supply units and the emergency power supply would take over, ensuring continued energy for at least 72 hours. This means that the FDC meets the Tier IV standard awarded by the Uptime Institute.

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