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conventional servers and put greater strain on UPS. This again demands a modular approach. A modern UPS can be 8–10 per cent more efficient than

a 10-year old unit – equating to savings of around £10,000 a year for 80kVA – a typical power requirement for many medium-sized businesses. Ultimately, efficiencies of more than 99 per cent can be achieved. Remember that a greener strategy can result in tax-saving possibilities, through the government’s Enhanced Capital Allowance (ECA) scheme.

‘For example, from 2013, the UK’s older coal-fired

power stations will start to be shut down. Wind, tidal power, solar photovoltaic (PV) and heat pumps, are very important, yet they cannot yet make up the shortfall that will occur, and new nuclear will not be available for many years. In addition, the rapid increase in decentralised and renewable power sources will have a significant effect on the grids,’ concludes Digilio. The government has set itself a major task in trying to

meet legally binding 2020 carbon reduction targets. Electric vehicles (EVs) will become another part of the electric power jigsaw. A recent study (by WWF-UK) indicated that at least 1.7m EVs will be needed by 2020, and 6.4m by 2030, if the UK is to achieve its targets. Assuming that charging will mostly be carried out overnight, and ignoring losses, a National Grid estimate was that the near instantaneous power demand would be about 2GW (around 4TWh annually). To power all 30m UK EVs that might be required at some stage could result in a 12-15 per cent electrical power output increase (50-60TWh). Such scenarios pose a risk to supply security, though the full extent – worryingly – is not known.

Saving energy With today’s ever-increasing economic, social and regulatory pressures to reduce energy use, achieving high UPS availability at the expense of efficiency is no longer acceptable. Symantec research has shown that 97 per cent of IT managers are implementing a green IT strategy, green IT budgets will increase over the next year, and two- thirds are prepared to pay a 10 per cent premium for the greenest technology option. A first step is to ‘design for demand’. In adopting a modular

UPS architecture, and sizing the power infrastructure according to immediate load needs, significant energy can be saved. For example, installing smaller scalable modular UPS that meet the initial power demand – then scaling it up as the demand grows. A dedicated control system is essential. Cloud computing – the real-time delivery of IT infrastructure,

services and software over the internet – has already become the ‘next big thing’ and many readers of ECA Today will already be using ‘The Cloud’, perhaps without even knowing it. However, one area that is still overlooked is the impact it has on IT infrastructures. For example, most cloud data centre virtualisation host servers demand more power than

30 ECA Today September 2011

Fig.1: A schematic of an online (double conversion) UPS – the output is independent of input mains supply voltage and frequency variations (courtesy APC)

UPS technologies UPS system choice is largely determined by capacity, redundancy, scalability and total cost of ownership. It is important to seek early professional advice so that the right solution is chosen to match the application. There are three main technology (topology) types of UPS.

These are static (purely electronic) UPS, rotary (flywheel) UPS and diesel-powered (engine-coupled) UPS. The static UPS is so-called because (apart from cooling fans) it has no moving parts. There are three static types: offline, online and line-interactive. There are also hybrids, which are not covered here. Offline UPS – The simplest and least expensive, this

provides limited surge and spike protection. It is the most energy efficient type because charger and inverter do not operate at all times. However, the disadvantage is that an offline system can fail when it is most needed. Offline UPSs work as follows: in normal mode, an AC circuit is fed directly to the load, while a feed charges a standby battery via a DC charger. Power passes from the mains directly to the load, with the secondary circuit charging standby batteries. If mains power failure occurs, the UPS detects the voltage reduction and automatically switches the load so that it is fed by standby batteries via a DC/AC inverter. Online UPS (double conversion) – This more expensive

Fig.2: A schematic of a line interactive UPS. The output is dependent on input supply frequency variations, but mains supply voltage variations are conditioned (courtesy APC)

type (typically rated 10kVA or above) is suitable for operation with a longer-term backup system, such as a genset. After passing through a surge filter, the mains voltage is converted from AC to DC via a rectifier. This charges the batteries and feeds the second (double) conversion from DC back to AC via an inverter to feed the load. This type of UPS is more reliable because the inverter runs continuously. Also, there is greater protection against surges, spikes, sags, brownouts, electrical noise and harmonics. Although the type is the benchmark for power protection, the disadvantage is that it is relatively inefficient, especially at part load. To counter this, economy modes improve efficiency. Line-interactive UPS – This type (also 10kVA or above)

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