How UPS efficiency impacts data centre PUE

Power Control
14 Oct 2020

PUE (Power Usage Effectiveness) is the widely accepted metric used to determine the overall energy efficiency of a data centre. Expressed as a ratio, almost all operators strive to achieve a perfectly efficient facility, running as close to 1.0 as possible.

Data centres in particular pay great attention to PUE and over the years it has become an industry benchmark for efficiency. However, there are indiscretions on how PUE is accounted. Many report design PUE figures, which are often not reflective of true operational efficiency.

Design PUE is an estimation of the amount of energy consumed by equipment such as UPS (Uninterruptible Power Supply) systems, cooling and servers. Reporting PUE based on a hypothetical analysis is disingenuous and leaves room for significant error.

It is however understandable as to why data centre operators may want to push for presenting design PUE figures. The likelihood is that these will always paint a ‘greener’ picture. With such tight PUE margins and growing competition to deliver the best efficiency figures, it would now make sense for all facilities to follow the same rules when it comes to reporting PUE statistics.

Theoretical analysis will always have its place, particularly in the design phase; hence the acceptance of design PUE. Not only does it provide efficiency targets but it also encourages manufacturers to deliver more efficient solutions. This has been notably evident with the UPS market, where not so long ago inefficient low load figures were being hidden and UPS efficiency was almost always reported only at full load. Nowadays, UPS manufactures are expected to present complete efficiency curves which cover the complete load spectrum; something that should be adopted for data centres as a whole.

Today’s data centres are under immense pressure. They now provide the computational backbone for the internet, acting as information factories that shape the modern users’ experience. As the population becomes more reliant on their services, the number of data centres, and their rack density increases annually.

Unsurprisingly there have been claims that data centre PUE is in fact on the rise and achieving the gold standard of 1.1 is becoming increasingly challenging. This is largely due to the growing amount of power being drawn for data centres and a focus of the sustainability of such power consumption. It is a somewhat ironic concept that the principle driver of data centre efficiency has been highlighted by the increased scale of data centres needed to support the growth of sustainable innovations such as electrical vehicles (EV).

The 2019 Global Data Centre Survey carried out by the Uptime Institute presented findings to support the opinion that data centre efficiency plateaued over the four previous years and was predicted to rise in 2020. Although, advances in electrical equipment can pick up some of the blame, other factors that are beyond human control also need to be considered. Unpredictable weather patterns that deliver very high temperatures and the subsequent need for greater cooling is just one of the bordering factors.

As an industry though it is expected that the PUE trajectory will start to fall again and head towards the long predicted 1.1 PUE ratio. This will be the result of the closure and repurposing of smaller data centres, which historically have always declared high PUE figures. Hyperscale data centres, co-location facilities and new builds continue to contribute to bringing the PUE line down.

Achieving industry leading PUE needs to be measured based on operational efficiency as design PUE can be very misleading. The Uptime Institute recently revealed that on average data centres are operating at a PUE of 1.59, so for every 1.59 watts in at the utility meter, only 1 watt is being delivered to the IT load. These are still very reasonable figures, especially when considering that only a few years ago the average operating PUE was nearer 2.0


To find out how Power Control Ltd could lower PUE figures and to discover more about its high efficiency UPS systems, please contact or call the office direct on 01246 431431. For additional product and service information please visit