In practice: Capgemini's carbon-cutting Merlin data centre

With data centres accounting for 40% of Capgemini's total emissions and 70% of energy use, IT consulting firm's decision to develop an ultra-sustainable, energy-efficient data centre has driven great results, helping to push the company beyond a carbon goal one year ahead of schedule.

The low-carbon systems utilised throughout the facility have resulted in a 45% reduction in energy use compared to an industry-standard data centre

The low-carbon systems utilised throughout the facility have resulted in a 45% reduction in energy use compared to an industry-standard data centre

The challenge

A rapid expansion of innovation driven by Information Communication Technologies (ICT) has heightened the importance of data centres - the repositories for billions of gigabytes of information - in processing, and distributing large amounts of data. But as the global reliance on data centres has grown, so has the strain on energy supplies, hampering efforts to contain global warming.

As of 2016, data centres consume around 3% of global electricity supplies and account for around 2% of greenhouse gas emissions. In fact, the 416.2TWh of electricity consumed by data centres around the world is much higher than the UK’s total consumption of around 300TWh. Experts have also warned that the rising growth of data centres will lead to the consumption of three times as much energy in the next 10 years.

The solution

The global rise in technological innovations has created a unique business opportunity for consulting, technology and outsourcing services company Capgemini to reduce carbon emissions.

In September 2010, Capgemini opened its 'Merlin' data centre. Located in Swindon, Wiltshire, the state-of-the-art, 3,000m2, high-specification facility set a new benchmark for low-energy data management. It utilises a 'modular' design, consisting of purpose-engineered modules and components to offer scalable data center capacity with multiple power and cooling options.

The company focused the centre's sustainability credentials on its Power Usage Effectiveness (PUE) – the total amount of energy used by a data centre facility compared with the energy delivered to computing equipment. The average PUE for the industry at the time was between 2 and 2.5, and has fluctuated between 1.67 and 1.8 since then. The Merlin centre has steadily operated with PUE readings of between 1.08 and 1.12, making it still one of the most sustainable centres globally on that metric. By comparison, Facebook designed its data centre in Oregon to have a PUE rating of 1.07, while Google claims that its data centres have an average PUE of 1.12.

Project development

The focus of the Merlin data centre was two-fold: both operational and embedded carbon were targeted during the design phase, while Capgemini was also hoping to deliver cost and time benefits as well.

One of the first aspects that had to be decided upon for the project was the location. Data centre performance and energy consumption can significantly vary based on the local weather and climate. Capgemini noted that the northern parts of the UK were cooler, which would reduce energy costs by utilising fresh air cooling rather than air conditioning systems. However, a climate that was too cool could also bring damper weather conditions, meaning that more energy would be required to dehumidify the air. Eventually, Capgemini settled on the "geological sweetspot" of Swindon, due to its relatively balanced heat and humidity levels.

Another key aspect of the project that Capgemini focussed on was the embedded carbon within the infrastructure of the centre. Merlin was built from modular, easy-to-construct components delivered by companies that specialised in constructing field hospitals – another type of building that needs to be constructed, deployed and moved quickly. The infrastructure design was influenced by resource constraints built around the need to minimise the use of water, optimise energy performance and heat management, and to impliment re-usable, recyclable and renewable materials. The components used within the development of the Merlin data centre can be repurposed, and at least 95% of the material used in the design is recyclable.

The cost

The cost of the project was estimated to be between a third to half of the cost of a traditional centre. Time of construction only took 22 weeks, as opposed to the typical 12 to 18 months for centres. From a construction perspective, the cost of deployment is a fraction of the cost of deployment of a traditional centre. Capgemini received a return on investment on the original capital expenditure – which it was unable to disclose – in two years.

Low-carbon credentials

Merlin offers power savings of 91% compared to an industry average. A traditional data centre of Merlin’s capacity using the UK grid mix of electricity would emit between 7,000 and 7,500 tonnes of carbon annually. If Merlin was using the UK grid mix, it would be emitting approximately 4,000 tonnes of carbon each year. However, because Merlin is sourcing renewable energy, it only emits 330 tonnes each year – a 95% improvement against the industry average.

The systems utilised in the centre have resulted in a 45% reduction in energy use compared to an industry-standard centre with a 1.8 PUE reading. This is due to a number of key onsite sustainability solutions being identified and deployed.

The modular design of the centre makes it easier to separate sections of the building into 'hot' and 'cool' isles. A lot of the equipment used in the facility requires different levels of heat to stop particualr components from overheating. An innovative design approach of stacking equipment using racks, rather than placing components on the floor, significantly reduced the volume of air needed to cool the equipment.

Waste heat from the equipment in the data centre is also captured and used to dehumidify the air, creating further reductions on energy costs, while a Building Management System (BMS) controls air flow to ensure that isles remain at ideal temperatures. The BMS was designed to deliver efficient climate controls. It is accountable for the containment of hot and cold air, while using minimal energy from the 12 variable-speed fans that move air around each module.

The cooling unit uses fresh air cooling for external temperatures up to 24C, with an evaporative cooling system controlling temperatures up to 34C. For external temperatures above this – it has been tested up to 48C – a Direct Expansion (DX) refrigerant cooling system acts as the final backup. The net result is close to 100% fresh air cooling, which represents a reduction in cooling energy of 92% compared with a conventional data centre with around 50% fresh air cooling. The BMS also displays a live PUE figure so staff can see current efficiency levels in real-time.

Merlin also uses flywheel technology for uninterruptible power supply (UPS), which acts as a battery backup if the electrical power fails. However, flywheel technology eliminates the use of batteries, many of which were lead acid versions, by storing kinetic energy instead. The energy losses in the transformer and UPS are low at only 60kw per 1,000m2, and energy losses on battery systems are at least twice as high compared to using flywheels.

Sensor lighting has also been added to the system to reduce energy consumption in unoccupied data modules, and a raft of autonomous features means that Merlin requires less staffing in the first place, which again reduces energy consumption and temperature variants.

Additional benefits

As the modules are factory-built, they can be transported to the site for installation which reduces the construction impact from the outset. The lifecycles of these modules can also reach 60 years based on durability and maintenance.

Additionally, the modules of the data centre can be moved to a new location or, if needs be, extended at the current location. Since Merlin opened, Capgemini has added an additional module and increased the size of the centre by about 40%. The entire data centre can be fully re-commissioned in three months.

Many UK data centres are designed with maintainability in mind, but do not have generators capable of continuous running. However, Merlin has been accredited by Uptime Institute as one of the three 'Tier 3' data centres operating in the UK, reflecting its minimum life span of 30 years.

The choice of location also reflected a desire to select a sustainable, brown-field site to avoid unnecessary construction emissions, pollutants and environmental damage.

Capgemini’s unique approach to construction and management, coupled with a “geological sweet spot” means that it has been difficult to copy and match the outputs of the centre, but aspects have since been applied to the firm’s other centres across the UK.

Matt Mace


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