Large-scale data centre operations are now being built. One of the largest, the QTS Atlanta-Metro Data Center has over 970,000 sq ft of total space, complete with its own on-site Georgia Power substation; this delivers 120MVA of utility power[i]. Electrical redundancy is achieved through two feeds from separate substations that power three on-site 40MVA transformers. There are also 46 standby generators to provide backup power protection through 23 independent uninterruptible power supplies.
This is just an example, albeit a very large one, of the sizes now being attained by large-scale data centre operations. So how do you build UPS systems that can offer the power protection, UPS efficiency and resilience coupled with the sheer capacity demanded by such large-scale data centre infrastructure? This post describes the horizontally- and vertically scalable PW 9500DPA modular UPS system as an example of how it can be done.
Large Scale UPS
While power demand measured in MW rather than kW is one challenge for many large-scale data centre designs, it’s usually accompanied by another; the likelihood that this already-large requirement will grow significantly in the years to come. The global data centre power market, which was worth USD 19.89 billion in 2017, is projected to grow to USD 32.36 billion by 2023; a CAGR of 8.45% for the period 2018 – 2023[ii].
To handle these factors, uninterruptible power supplies must, therefore, be highly scalable, yet offer sufficient UPS capacity to meet initial demand. Providing UPS capacity immediately for possible future demand would result in startup UPS installations that would be oversized. Therefore, inefficient both electrically and commercially. In addition, making accurate growth predictions is difficult. Yet future proofing must be provided somehow, to avoid restricting data centre infrastructure development.
Large application UPS scaling
KOHLER Uninterruptible Power’s PW 9500DPA modular UPS system offers one suitable data centre solution. Startup UPS installations could comprise of a single cabinet with one 100kVA UPS module. UPS capacity can then be incrementally scaled, to keep pace with growing demand, by plugging more 100kVA uninterruptible power supply modules into the cabinet as needed; each 9500DPA cabinet accommodates up to five UPS power supply modules, to give 500kVA capacity – or 400kVA, with N+1 electrical redundancy. The UPS modules are hot-swappable, so they can be added (or removed) without interrupting the power supply to the load.
Expansion by populating a single cabinet like this is known as vertical scaling. Further UPS capacity, up to a maximum of 3 MW, can be achieved by horizontal scaling: connecting up to six fully-populated cabinets in parallel. The uninterruptible power supply supports significant data centre infrastructure growth while remaining efficiently ‘rightsized’ throughout its operational life.
Energy demand at this elevated level highlights the need for uninterruptible power supply efficiency in today’s carbon-conscious climate. The PW 9500DPA modular UPS system contributes with a high online energy efficiency of 96%, which minimises cooling costs as well as system losses. This can be boosted to over 99% by running the UPS power supplies in eco-mode; however, eco-mode is often considered unsuitable for data centre design, as it involves exposing the critical load to raw incoming mains power during normal data centre operation.
Unlike most UPS power supplies, the system can maintain its high efficiency even when operating at significantly under UPS capacity. It does so by running in Xtra VFI mode, in which the number of uninterruptible power supply modules actively online is automatically adjusted if the load changes – a type of automatic, dynamic ‘right-sizing’ operation. Not-needed modules remain ready to share the load immediately if it increases, or if the mains supply fails.
The PW 9500DPA modular UPS system’s energy efficiency has been recognised by its inclusion on the Carbon Trust’s Energy Technology List for Enhanced Capital Allowances (ECAs), giving tax benefits to its users.
Whilst the KOHLER PW 9500DPA modular UPS system is a great candidate for large-scale data centre operations due to its capacity, scalability and energy efficiency, it also fulfils the most fundamental UPS power supply requirement – very high availability, rated at ‘six nines’ or 99.9999%.