Robin Koffler, general manager of Riello UPS discusses the evolution of UPS design in line with data centre (DC) growth and transformation - and choosing the right technology for DC installations

UPS systems have evolved greatly over the past decade, and it’s an evolution that has been driven by the rise of the data centre, in which the need to use power more effectively and control lifetime costs of equipment is as important as the need for mission-critical power protection.

UPS Evolution
The first thing to go was the transformer. Old UPS designs contained internal transformers, which performed multiple roles such as voltage step down, power conversion and harmonic conditioning. However, they were inefficient, not optimally located and without them UPS have greatly reduced in size. Other advantages provided by transformerless UPS are they are lighter in weight and consume far fewer raw materials in their manufacture.

Eco mode UPS
Since the introduction by The Green Grid of PuE (Power Usage Effectiveness), UPS manufacturers have developed newer, more energy efficient designs containing fewer components and with renewed inverter technologies that consume less energy. Many newer UPS designs offer energy efficient operating modes, eco mode or ‘smart’ mode, which if used can provide a 2-5% energy reduction. It’s a step up from the basic ‘standby’ or ‘line-interactive’ mode in which the system switches to mains power and has the UPS operating on standby when suitable conditions prevail. This mode, however, is not suitable for mission critical data centres because of the potential availability and power quality issues associated with operating on mains power. Power quality is as important in the data centre as power protection.

Double conversion online UPS powers the load continually through its inverter and  acts as a conditioner and voltage stabiliser, thus ensuring a supply of clean energy to connected loads.

Efficiency and TCO
Even without eco mode operation, newer UPS designs can offer much better efficiency figures than their predecessors with the average now around 96-98%. Silicon controlled rectifiers (SCRs) in old UPS designs have been replaced by isolated gate bipolar transistors (IGBTs), which are capable of much higher speed switching and higher power handling, and this reduces energy loss within the UPS.

Analogue controls have been replaced by digital signal processing controls (DSPs), which operate more quickly and intelligently and reduce the number of components in the unit.

Key to energy efficiency is how the UPS draws energy from the mains, termed Input power factor, which in a unit offering optimum efficiency should be rated high (0.99). The higher the input power factor, the lower the reactive power (wasted energy). How a UPS utilises energy while protecting loads is also key, as is how they deal with total harmonic distortion (THDi) to produce a pure sine wave input current that, again, reduces energy wastage.

But energy efficiency is not just about installing equipment with the highest efficiency ratings, it is about TCO (total cost of ownership) and lifetime costs of owning and operating power systems and equipment and key to this is the management of consumables (such as batteries, fans and capacitors) so that they are replaced less often. Maintaining battery-friendly ambient temperatures (21-25 degrees centigrade) is key to this as is regular and routine service and maintenance.

Flywheel UPS Systems
Rotary UPS have been around as long as static UPS but a somewhat newer kid on the block is the flywheel UPS system, offering higher capacity, greater efficiency and lower lifetime costs as the flywheel itself is virtually maintenance free. A flywheel is a mechanical device that rotates at speeds in excess of 30,000 rpm in many cases, and produces kinetic energy, which is then stored and supplied to connected loads in the event of a mains failure.

Everything in modulation
Modular UPS is also a design influenced greatly by the needs of the data centre. Comprised of individual units of 15kVA; up to eight of them can be connected together in one cabinet that utilises a ‘drawer-style’ approach to offer a maximum (per cabinet) of 120kVA. With modular UPS there are no shared components; each unit is a fully functioning UPS in its own right. Units can be easily slid out and ‘hot-swapped’ for maintenance or repair, which can then be done offsite.

Key to their scalability is that systems can be right-sized and expanded incrementally by adding new units one at a time and simply sliding them into place. Historically, UPS systems have been oversized to meet the needs of tomorrow, today. A scenario that is wholly unacceptable in today’s efficiency-conscious data centres.

Containerisation
Anyone visiting a large data centre today will be used to seeing car park or outdoor space occupied by one or two ISO-type shipping containers – inside which can be found a turnkey power protection system, delivering robust and reliable power protection quickly and efficiently. Power containers are the new solution for meeting urgent power protection needs or for quickly increasing capacity to cover data centre expansion without the lengthy and costly process of building bricks and mortar facilities.

Choosing the right UPS for DC
The criteria for choosing the UPS to suit the application will vary from installation to installation and the different types and sizes of data centre: small to medium, large data centre or co-location operations. Each will have its own list of criteria and priorities but they will undoubtedly include: criticality, availability, runtime required, load type and rating, configuration, maintenance and building considerations.

The majority of data centre UPS applications are mission critical which demands an uptime of 99.999% and this in turn demands resilient UPS with redundancy built in and onsite generators to supply continuous back up power in the event of a mains power cut.

There is now far more choice of UPS for data centre applications and rather than a simple grey box that sits in the corner waiting for the lights to go out, today’s units offer sophisticated and intelligent operation and right-sized but scalable power protection. In addition, they serve a valuable secondary (but equally important) purpose – that of power conditioning and voltage optimisation – thus playing their part in optimising data centre energy use.