For data centre and ICT installation operators, the economic, legislative and social impact of an excessive carbon footprint cannot be ignored. Although this impact is large, and expected to grow, mitigating steps can be taken by choosing the best available UPS technology and deploying it correctly
Data centre and ICT installation operators regard energy efficiency as a key factor in their selection process for UPS systems; however the priorities driving their efficiency strategies can vary. In this article, Alan Luscombe, marketing director at Uninterruptible Power Supplies, a Kohler company, looks at these priorities, steps that users can take to meet them, and the associated impact of the power consumption savings made.
UPS users’ views on energy efficiency are usefully revealed in surveys that UPSL conducts periodically. The most recent found that 62% of respondents regarded rising power costs as the primary driver for reducing power consumption, while 30% cited ‘reducing their carbon footprint’. These results are unchanged from those obtained in the previous survey. The economic aspect of rising costs appears to be dominant, with 85.1% of respondents agreeing with the statement that ‘Rising power costs are a major concern for my business’ – a slight increase from the previous figure of 80.3%. Concern for the environmental, legislative and social aspects, although lower, is still significant. Just below 65% of the respondents viewed increasing environmental legislation as a major concern to their business – and over 70% have a carbon reduction policy in place.
Increasing social and legislative pressure
All of these pressures are likely to rise as time passes. The energy gap, and with it energy pricing, is expected to increase as demand rises while power stations using outdated technology are taken off line. Meanwhile, concerns for the environment continue to grow. Shareholders, potential investors, employees and customers want to know more about an organisation’s energy policy, which they regard as part of their corporate social responsibility. Managers who choose the cheapest rather than the most environmentally friendly piece of equipment must justify their decision to their Board. The Government, through the Department of Energy and Climate Change (DECC) has legislation and initiatives to motivate and reward energy reduction, while penalising organisations which fail to act.
This legislation includes the CRC Energy Efficiency Scheme, formally known as the Carbon Reduction Commitment This is a mandatory carbon emission reporting and pricing scheme covering nearly all organisations in the UK using more than 6,000 MWh per year of electricity. It requires organisations to report their electricity and gas related carbon emissions, and buy allowances for every tonne of carbon they emit. Participants’ energy use and emissions records are also published. This means that organisations can both cut costs and improve their reputation by reducing carbon emissions.
More recently, DECC has announced an Energy Savings Opportunities Scheme (ESOS), under which large enterprises will be required to undertake assessments to identify cost-effective ways to invest in energy efficiency. They do not have to act on the results of their assessments, but on average a large business can benefit from annual savings of £56,400 in return for a £15,000 per year investment in energy saving measures. This equates to a £1.9 billion benefit to the UK as a whole.
Improving efficiency through transformerless technology
Data centre operators have possibilities for improving their UPS efficiencies – and, as UPSs are typically relatively large electrical systems, doing so can contribute significantly to overall energy reduction strategies. Today, UPS efficiency improvement comes primarily from using transformerless technology. However, efficiency can be increased further by operating in Eco mode, if the installation’s circumstances allow this to be done safely.
Transformerless UPSs have been made possible through advances in power semiconductor technology and the introduction of the Insulated Gate Bipolar transistor (IGBT). This allows the inverter to produce an output RMS voltage directly compatible with the critical load requirement. The inverter is fed by a solid-state DC boost converter; its higher input and therefore output voltage eliminates the need for a step-up transformer.
Transformerless topology brings many advantages, the most important of which are improved efficiency and a higher, stable power factor. Fig. 1 compares transformerless vs transformer-based efficiencies. Note that the transformerless curve is not only significantly higher than the transformer-based, but it also remains nearly flat right down to 25% loading.
Fig.1: UPS Efficiency Curves – Transformerless vs Transformer-based
Transformer-based UPSs present a lagging power-factor load to the incoming mains supply, which declines from unity as the UPS loading reduces. By comparison, transformerless UPSs inherently produce an input power factor which is much closer to unity and less load dependent. This draws lower input currents, minimises cabling and switchgear sizing, and sometimes reduces electricity running costs.
Fig.2 below shows a comparison between transformer-based and transformerless power factor/loading curves.
Fig 2: UPS Input Power Factor Comparison
As an example of the cost savings possible, consider a 500 kVA system with 95.5% efficiency and 100% loading. Switching from transformer-based to transformerless will achieve a cost reduction of £19225 over five years for every percentage point saved.
However under certain circumstances transformerless technology also offers further advantages and additional energy savings. The object of UPSs is to provide clean power with availability as high as possible – and a key way to improve availability is to use a redundant configuration that can tolerate the failure of a single module. Fig 3 shows a 1+1 redundant system in which either 120 kVA module is entirely sufficient for the load if the other fails. This improves availability, but during normal operation each module is only 42% loaded. As Fig.1 above shows, this will make very little difference to efficiency in a transformerless system – but the transformer-based equivalent’s efficiency will drop by about 3%. Further losses will arise due to the steep reduction in the transformer-based UPS’s input power factor.
Fig.3: Parallel Redundant UPS System
‘Economy mode’ operation
‘Economy-mode’ or ‘Eco-mode’ operation of a UPS offers an opportunity for further efficiency, although each user must balance the real and perceived risk applicable to his situation against the possible savings. During most of its operational life, when power conditions are normal, a UPS in Eco-mode is in a Bypass state, with power from the mains fed directly to the critical load. If the mains power deviates from the voltage limits specified by the ITIC/CBEMA power quality curve (The ITIC/CBEMA curve represents the withstand capabilities of computers in terms of the magnitude and duration of the voltage disturbance), the installation’s static switch transfers the load to the UPS output.
Although in theory this exposes the critical load to a risk of power loss, it may not be a problem in practice. Much modern ICT equipment can ‘ride through’ a power break of 20 ms or longer, although a maximum of 10 ms is considered safer. Either way, a standard UPS static switch can sense and operate within about 4 ms. Meanwhile, Eco-mode can yield efficiencies up to 98-99%, since UPS losses are eliminated during normal operation.
Choose and apply best technology to minimise carbon footprint
Eco-mode popularity has improved over the years, partly because rising energy costs inevitably render it more attractive. However the improved tolerance of ICT hardware is also an important factor, as it reduces the mode’s real or perceived risk. In fact this is a reflection of the current climate. Data centre operators are under increasing economic, social and legislative pressure as described, to reduce their carbon footprint. Yet, as the environment is changing, technology is changing too. Choosing the right technology, and deploying it correctly, can help to mitigate the pressure for carbon footprint reduction.