Data centres have a self-evident obligation to provide their users with a reliable data processing resource as contractually agreed. However, according to a Data Centre News[i] article, these users’ CIOs are under increasing pressure to obtain another assurance from their data centre partner; their commitment to an eco-friendly policy that’s compatible with their own. This should cover emission reduction, ensure sustainability, and, where possible, use renewable energy. Businesses trading with suppliers that fail to make this a priority can themselves be exposed to accusations of contradictory environmental policies.
Today, all data centres handling mission-critical applications use UPSs to protect their sensitive ICT equipment from mains-borne spikes, noise and other aberrations during normal operation, and enough battery autonomy to permit a generator start-up or a graceful system shut-down if the mains fails. However, as the UPSs are handling the facility’s entire critical power intake, their power efficiency significantly impacts that of the whole facility.
Accordingly, to facilitate their customers’ increasingly insistent expectations of demonstrably green behaviour, data centres must ensure that they are operating with UPSs of the highest possible efficiency. More efficient UPSs save not only on the electrical power they consume directly, but also reduce the related power needed for cooling.
Improving UPS efficiency can be achieved using one or more of three available factors; transformerless topology, operation in eco-mode, and using a mode such as Xtra VFI when a UPS is significantly under-loaded. We look at these factors below:
Transformerless topology: This is by now a well-established design approach, used within most modern static UPSs. It has enabled many UPS advances – in particular the concept of the modular UPS – because of the reduction in size and weight that it achieves. However, it also provides significant energy savings, which can be up to 5% for the whole load spectrum above 25% of the UPS’s capacity. Overall efficiencies can be up to 96%.
Transformerless UPSs also present an input power factor that’s closer to unity and less load-dependent than transformer types. This reduces the input current magnitude, and sometimes saves on electricity running costs.
Eco-mode: Data centres with critical loads as described almost entirely use on-line dual-conversion UPSs, as the UPS rectifier and inverter circuits shield the load from mains power disturbances during normal operation. However, some losses are inevitable as the supply passes through these stages. Accordingly, a decision can be made to operate the UPS in Eco-mode; this is a form of offline operation, in which mains power is routed directly through to the load – not through the rectifier and inverter – under normal circumstances. If the mains supply starts to fail, the load can be switched to the inverter output, which is supplied by the battery until mains power is restored.
While eco-mode operation can boost efficiency to 99% or better, it exposes the critical load during most of its operational life to any spike or other aberration appearing on the mains. For this reason, most data centre operators don’t use eco-mode. Nevertheless, it’s an option where the load is considered sufficiently robust to survive mains problems, or if there is very high confidence in the mains power quality.
Xtra VFI mode: This is available on the PowerWAVE 9500DPA; when enabled, it automatically adjusts the number of active modules according to load requirement. Modules that are not needed are switched to standby but remain ready, primed to start and transfer to active mode if the load increases. The efficiency improvements achieved by this mode of operation are especially significant when the load is less than 25 percent of full UPS system capacity.