Taming datacentre emissions: flywheels and third-generation UPS

Chloride routinely detects 450,000 mains power interruptions per month, each capable of bringing servers down and mostly bridged using battery power.

Chloride routinely detects 450,000 mains power interruptions per month, each capable of bringing servers down and mostly bridged using battery power. Of these, the vast majority last for a fraction of a second.

The conventional solution to providing back-up power is to use batteries, but flywheels are now a viable alternative energy source, often used in conjunction with batteries to provide short-term energy before the battery takes the load, potentially extending the life of the battery.

The latest flywheels spin at 36,000rpm on magnetic bearings in a near total vacuum, and although the energy stored in their spin must, like batteries, be kept topped up with a trickle of mains power, they can extend the life of conventional batteries. More datacentre managers are now prepared to entrust their critical load to the successful start-up of a diesel generator with power provided by a flywheel, often combined with a smaller-rated battery system.

A less energy-intensive approach is being adopted by the latest generation of datacentre UPS now emerging from development. These have the traditional battery-backed 'double conversion' mode of operation offering over 95% operating efficiency as well as two further modes of operation which enable them to achieve up to 98% efficiency while still maintaining the highest level of AC power protection.

Early evidence from the use of this new generation of less battery-intensive devices in the context of the UK power supply suggests that these systems reduce cooling costs by 400%. This is likely to be a substantial proportion of total cooling power, which is itself usually protected by a separate UPS on a different bus to the primary load.

At the least temperamental end of the spectrum, hydrogen fuel cells are already established as a power source in some UPS applications where the required support time is measured in hours instead of minutes. These convert a relatively inert ethanol/water fuel mix into hydrogen, which is then used by the fuel cell to generate electricity. While they require a conventional UPS with some batteries to provide power while the reaction begins, their fuel tanks allow them to provide uninterrupted power for a day or more dependant on the fuel available. But this is still an emerging technology in datacentres, and cannot fulfil the sudden demands for power made by IT loads without some level of battery back-up.

Efficiency matters. While it may be true that computers are providing more processing power for less input power, total energy demand seems to be ever-increasing and cooling demands are growing in a curve that directly correlates to growth in MIPS and overall density. Energy is unlikely to get cheaper, although it will hopefully become less carbon intensive. Future-proofing power supply hardware no longer means over-specifying UPS. As a result, first principles should be revisited and further energy waste can be eliminated.

UPS technology is currently moving forward in the achievement of exceptionally high efficiency. The energy savings made possible will, in some cases, pay for the cost of the UPS system in just a couple of years, sometimes less. As we enter an age when we are going to be forced by legislation to reduce our energy consumption, investment in a high-efficiency UPS system can be a convenient, economical and profitable way to comply with the need to reduce energy consumption.

This was last published in February 2010

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