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Sep 02 2015

Fujitsu LCT: How Hot Water Can Keep Your Data Center Cool


With server performance and density growing on an annual basis and data centers ever expanding, keeping the appropriate operating temperature can turn into a real challenge both from a technical and a financial perspective. This is particularly true for so-called scale-out environments, i.e. farms of server clusters that handle massively parallel workloads, as well as for high-performance computing (HPC). With Fujitsu's new Cool-Central® Liquid Cooling Technology in place, administrators can sit back and chill out.

Typical data centers today spend up to 40% of their total energy consumption on cooling. In a world of rising energy costs, this may easily cause electricity bills to shoot up to six- or seven-digit amounts, depending on company and data center size. Since only very few companies can afford to 'waste' that much money, the demand for efficient, cost-effective cooling solutions is constantly increasing, and ICT infrastructure vendors have put together numerous solutions of varying quality, some of which hardly live up to their promise – either because they're not as potent as needed or because they cost a small fortune themselves.

As a leading infrastructure vendor, Fujitsu has a long history of delivering eco-friendly, energy saving systems and solutions. Our first "green PC," the PCD-4 LsI with automated power saving functions, debuted more than two decades ago, and since the millennium we have introduced an array of innovations ranging from halogen-free motherboards (2002) through server and storage pooling concepts (2005) to low-voltage servers (2007). Among our latest achievements were the well-established Cool-safe® design and its equally popular successor Cool-safe® ATD (for: Advanced Thermal Design), which enabled servers to operate within a higher ambient temperature range of up to 40 °C (104 °F), whereas regular systems could at best tolerate up to 35 °C (95 °F). As a result, DC air-conditioning systems kicked in at a later point in time, and air-conditioning expenses dropped by 5 to 6% per additional degree. Our freshly introduced Cool-Central® Liquid Cooling Technology (or Cool-Central® LCT for short) points into the same direction – only this time, we're targeting a different group of customers, namely those who run scale-out environments and/or HPC data centers. Following a preview in spring this year, the concept convinced analysts and CIOs alike and received the prestigious German Data Center Award only weeks later, in the category Air Conditioning and Cooling. The official product launch took place in mid-July – fittingly during a period of extreme temperature levels.

How It Works
Cool-Central® LCT relies on the fact that liquid (water) is far more effective as a 'cooling medium' than air, approximately by a factor of 1,000. Since a large part of the server heat is directly removed by water, the traditional DC air conditioning can be sized much smaller, which results in savings in investment and operational costs. Cool-Central® LCT was developed in collaboration with Asetek, a leading provider of liquid cooling solutions for "anything IT" headquartered in Aalborg, Denmark. It builds on Asetek's concept of a cooling distribution unit (CDU), which is basically a 10.5 inch rack extension that connects to each system via tubes with quick-connects (cf. Fig. 1).


Fig. 1

Fig. 1: FUJITSU rack with RackCDU extension and PRIMERGY CX400 M1 server nodes


These carry a special coolant – technically, a mix of deionized water and eco-friendly anti-freeze and anti-corrosion additives – directly to an arrangement of pumps and cold plate units that sit atop CPUs, GPUs and RAM, replace air heat sinks and circulate the coolant through the server (see picture at the top). The coolant then 'picks up' the heat and is returned into the cooling distribution unit, where it enters a heat exchanger that serves as the second stage of the cooling system (cf. Fig. 2). Here, the server liquid encounters a facility liquid. The two liquids travel across the exchanger in reverse directions, with each being confined to a separate loop so the fluids won't mix. During the process, heat is transmitted from the coolant to the facility liquid, which enters the heat exchanger at a temperature of 40° C (104° F) and leaves at a scorching 60° C (140° F).


Fig. 2

Fig. 2: Heat exchanger inside the RackCDU - 60 °C hot water from the servers (red) and supply of 40 °C "cold" water (blue)


The facility liquid then exits from the data center in the regular way (e.g. via a tube system beneath a raised floor) and may either be cooled down through an external dry cooler or – even better – be used for waste-heat recycling. The excess heat drawn from the servers can be used for office heating. In short, Cool-Central® LCT enables companies to implement a closed-loop cooling system that will help them achieve excellent results with regard to both Power Usage Effectiveness (PUE) and Energy Reuse Efficiency (ERE), two of the key metrics for building energy-efficient data centers or increasing the efficiency of existing ones. For a more detailed and vivid description, please see the video on Fujitsu's YouTube channel.

Compatibility and availability
The liquid cooling solution is now available for PRIMERGY CX400 M1 scale-out servers equipped with either PRIMERGY CX2550 M1 or CX2570 M1 cluster nodes. As per usual, Fujitsu will not only deliver tailor-made PRIMERGY CX400 M1 configurations with Cool-Central® LCT pre-installed, but also offers comprehensive consulting and support services on a project basis, helping customers to evaluate existing cooling infrastructures, find the right size for a new solution, calculate that solution's TCO, and implement and maintain fresh scale-out server configurations. Day-to-day management is particularly easy, because Cool-Central® LCT is fully integrated into our ServerView® suite and can be controlled from its central dashboard.

Usage scenarios and benefits
Still the question remains, why should companies invest in a potentially expensive new cooling technology and when and how well will that investment pay off? The answer in a nutshell is: Cool-Central® LCT will help them save money, increase data center performance, and reduce their carbon footprint. A more in-depth look reveals these tangible advantages will take effect in the short and medium term:

  • Cuts in power consumption and overall cooling costs: Liquid cooling allows for up to 50% less cooling power and costs through highly efficient coolers with low operating costs.
  • Increasing rack density/server performance: Today a fully configured HPC server rack with 80 compute nodes already requires 35+ kilowatts (kW) at peak performance – more than is needed to supply ten family homes with heating and domestic hot water. Future configurations with higher rack densities – that is, more server nodes aggregated in a single enclosure – could eat up more than twice as much energy as current models and are likely to appear by the end of 2016. Cool-Central® LCT enables us to build extremely dense HPC and cluster configurations for upcoming HPC scenarios and thus future-proof our scale-out servers.
  • Reducing the carbon footprint: As outlined above, water-based liquid cooling enables companies to not only reduce their energy consumption, but also recycle excess energy they would have blown into the air before. With Cool-Central® LCT in place, they can now use that energy to heat (or cool) office space, break rooms, cafeterias, warehouses and, of course, their data center. In short, they will lower their greenhouse gas emissions.
  • Reducing the cost of planned data centers: While the initial investment may appear high, liquid cooling ultimately pays off if a company plans to restructure existing data centers or build new ones. The reasons are manifold; however, the most obvious is that higher rack densities means they can house more servers in the same or a smaller floor space than today. Moreover, the air conditioning system won't have to be as complex and powerful as in a traditional setting, which also lowers the cost.

Let's take a look at a real-world scenario to calculate possible savings: In a data center populated with 1,000 PRIMERGY CX2550 M1 server nodes, the initial cost for building an adequate air-cooling infrastructure would amount to roughly 1.2 million dollars (1.07 million euros). Its total power consumption would add up to 796.7 kW per year for server operation and cooling. By contrast, with Cool-Central® LCT the initial cost amounts to 972,000 dollars (865,100 euros) while annual power consumption clocks in at 696.4 kW. Further assuming that electricity costs won't exceed US-$0.15 (€0.13) per kWh, the TCO of the air-cooled data center may easily run up to 3.85 million dollars, or 3.43 million euros, whereas the liquid-cooled edition arrives at 3.3 million dollars, or 2.9 million euros. These numbers speak for themselves – and provide a surefire killer argument for future scale-out server deals!


Intel, the Intel logo, Xeon, and Xeon Inside are trademarks or registered trademarks of Intel Corporation in the U.S. and/or other countries.

Florian Frimmel


About the Author:

Florian Frimmel

Global Product Marketing Manager, responsible for PRIMERGY tower and scale-out servers, at Fujitsu 


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