A data centre

Data centres: failure is not an option

As data centres proliferate to keep pace with digital commerce, managers are desperate to curb energy use and cut costs.

The rise of Internet commerce has brought a deluge of digital transactions and a surge in the number of data centres around the world. To cope with ever-increasing data volumes, today's facilities now house complex IT equipment, computers and blade servers with critical cooling systems and more.

This double-whammy of growth and complexity brings new challenges to data centre managers desperate to strike a balance between energy efficiency, reliability, power performance and total cost of ownership.

As a result, the uninterruptible power supply (UPS) has become the linchpin of the data centre back-up chain, charged with providing vital protection to equipment in the event of an unexpected power disruption. And all at a reasonable cost.

"The crux of the problem for data centres is that even a very short outage can have a catastrophic outcome on availability," says Alex Greenhalgh, senior large systems and data centre manager at power management business Eaton. "For example, a cyclic event can take out all of the IT equipment and servers, and this equipment will have to reboot sequentially, which might take hours."

But as data centre challenges have grown, so UPS technology has evolved. In the past, data centre managers have chosen between offline and online UPSs, with many opting for the former to cut costs.

During normal operation, the offline, or passive standby, UPS will pass electrical power directly from the mains output to the critical load, and if a power outage takes place, the UPS turns on the inverter so power is then drawn from the battery. Such a set-up has clear disadvantages.

First, during normal operation, the critical load is exposed to raw mains power with no protection from transient power spikes. Furthermore, in the event of a more severe power outage, the changeover from mains operation to battery can take many milliseconds, hardly acceptable for sensitive IT equipment.

Line-interactive UPSs offer an affordable alternative. Here, a transformer or inductor is inserted between the main power source and load which enables the UPS power converter to condition incoming power on its way to the load. Still, this set-up doesn't completely isolate a critical load from fluctuations in mains power.

And so, online UPSs that permanently pass power from the mains through a rectifier/inverter chain to the critical load have emerged as the preferred set-up for data centres. These offer better power availability than passive and line-interactive UPS systems, protecting the critical load against power disturbances.

Online double conversion set-ups rectify AC power to DC power to supply the internal DC bus of the UPS. DC power is then inverted to AC power to support the critical load while batteries attached to the DC bus are float-charged during normal operation.

But while online double-conversion UPSs offer a high availability, the trade-off has always been data centre power system efficiency. Indeed, as more and more data centre managers turn to the latest online UPSs to ensure power availability to critical IT equipment, many UPS suppliers are also noting a rising interest in the use of economy modes of UPS operation in these systems, to boost efficiency.

As Patrick Brouhon, strategic marketing director of three-phase power at electrical equipment manufacturer Schneider Electric, explains, in an economy mode such as Schneider's Eco Mode the UPS only uses double conversion when needed to regulate the voltage. This can stretch the power supply efficiencies of today's UPSs by around 2 per cent.

But while economy mode is executed in firmware, only being enabled by the user, it has one clear risk; it exposes the IT load to raw utility power, without the conditioning supplied by the UPS. Still, despite the potential decrease in power availability, Brouhon reckons his customers are becoming more and more interested in this option.

"Eco Mode has existed for a while but hasn't been used," he says. "Now customers ask for it and we believe it reflects this trend for higher efficiency."

Eco Mode aside, suppliers are developing UPSs with state-of-the-art efficiency and energy optimisation modes, that promise to boost efficiency without compromising availability. For example, APC – owned by Schneider Electric – has integrated an efficiency booster mode (EBM) to its MGE Galaxy 7000 UPS line-up.

The new mode automatically places underused UPS modules into sleep or standby mode when the system load is much lower than installed capacity, boosting efficiency and reducing losses in parallel systems. Unlike UPSs operating in economy mode, EBM UPSs still operate as double conversion online units so critical load isn't exposed to utility power disturbances.

Similarly, Emerson Network Power, USA, has integrated so-called Active Eco Mode to its Liebert NX UPSs. This boosts the efficiencies of its double-conversion UPS systems but eliminates past economy mode issues by keeping the inverter and rectifier in an active state.

In a further move to boost efficiency for enterprise-scale data centre facilities, Emerson recently unveiled its latest generation of Trienergy UPS. Trinergy Cube uses an adaptive algorithm that continually monitors power supply and load conditions, automatically selecting the most efficient operating mode.

Flexible and modular

But as UPS manufacturers jostle to boost efficiencies, data centre managers are also grappling with capacity constraints. Long gone are the days when huge areas of unused floor space existed, today's capacity shortages now threaten to strain overall resources and negatively affect data centre performance levels.

Pleasingly, however, pretty much every component of a data centre's infrastructure has been designed to be modular, and this includes the UPS system. Described by some as 'pay-as-you-grow', a modular set-up allows infrastructure to be added, when needed, and for many is nothing short of an industrial revolution. 

"Data centres were originally custom-designed, with the building, electrical and mechanical systems bespoke to customer requirements," says Zahl Limbuwala, chief executive of Romonet, a supplier of software for data centre modelling. "But now, three, four or more modules can be bolted together on-site... [we're] moving from a bespoke, cottage industry to [one based on] pre-integrated, pre-fabricated modules."

And as Limbuwala adds: "Building the same product over and over reduces costs and helps to make manufacturers more aware of performance, specification, failure modes, and improving the product."

Modularity brings other advantages. While past infrastructure upgrades demanded the entire data centre was shutdown for, sometimes, several days, modules can now be quickly added, and removed, as load grows and shrinks, helping data managers optimise total cost of ownership. What's more, multiple smaller UPS modules can be integrated together to provide the redundant power protection of, say, one very large UPS.

The big picture

While data centre managers can adopt the very latest modular, online UPSs to boost efficiencies, maintain reliability and drive down costs, some industry players are adamant cost-cutting must take place even before the data centre is switched on. As Romonet's Limbuwala says, the complex interaction of all components in a data centre can impact on energy efficiency.

"Data centres used to be designed and engineered in a predictable way, and were expected to be highly reliable," he says. "But even [today's] small data centres have a lot of moving parts and a lot of electrical parts, all of which have a finite life and all of which fail eventually."

Limbuwala believes the biggest challenge now facing any data centre manager is actually understanding how a building reacts to its load and elements. By way of example, he cites how air-handling units have typically housed fans running at fixed speeds, irrespective of room temperatures and air flow. In the past a data centre manager would simply switch off these units to save energy.

"But now, systems control the speed of fans, depending on the load," he says. "To turn off half the fans will cause the remaining fans to ramp up speed to maintain the ambient temperature settings. And running these at double speed, uses three times the energy."

Consequently, today's data centres are adopting the very same building management systems – controlling light and thermostats – that offices have used for some time. With this in mind, design engineers at Romonet have developed simulation software that uses an underlying model to create a virtual environment to which actual data centre characteristics can be compared.

The model lays out how the data centre should perform in a given configuration for a particular environment, so the user can detect deviations at any given point in time. A user can compare the reality of operations with the model's forecasts of running costs to detect, say, when power usage isn't optimised.

"For example, at a given external temperature and load, if the meter should read 10kW but actually reads 12kW, the software will reveal why this has taken place and where that extra 2kW came from," explains Limbuwala.

Importantly, a data centre manager can also use the model to create different scenarios to accurately assess any trade-offs associated with using different UPSs. Efficiency curves are produced so the manager can assess these relative to the costs of buying and maintaining different systems.

As well as using the software to pre-plan centre design, the software can be used to ensure equipment and the data centre perform at an optimum level. Indeed, the company offers a subscription so businesses can use a software service model that plugs into the data centre to monitor or analyse operations, producing alerts as well as weekly or monthly reports.

"With such software, managers still have control of their facilities but with much better visibility," says Limbuwala. "For example, they can predict what will happen if, say, they turn a dial three points this way.

"A lot of the knock-on effects are much less intuitive than they used to be so managers can become more reliant on intelligent systems to help run a data centre efficiently."  

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