How Low Can PUE Go?

By combining the latest energy-efficient design and components with easy-to-calibrate modules, we have driven PUE in the data center down almost as low as it will go. This should pave the way to a more integrated approach to environmental impact.

Eric Lisica, Operations Director, EvoSwitch

The EvoSwitch PUE

With the announcement last week of the new 7.5 MW three phase build-out of the EvoSwitch AMS1 Campus, now is a good time to reflect on the relationship between energy efficiency, design and operations in the data center. Looking back over the last decade, a lot of colocation providers have been hesitant about releasing PUE figures, but this has never been the case with EvoSwitch. Back in 2009 we stated our aim to reach a PUE of 1.2 in our new builds, and we set out the significant savings (70-80%) that would create.  We also offer real-time PUE reporting using over 8000 power monitors, despite the fact that there is currently no standard-related obligation to report this data. Today, we have a design PUE of 1.2 for our new builds, but experience shows that we can actually operate consistently below this figure.  In AMS1 Campus Hall 6, this means a day-to-day PUE range of 1.1 to 1.15.

Adiabatic Cooling

How are we beating our own design PUE?  Partly because of conservative estimating.  In 2011 we were one of the first companies to use Indirect Adiabatic Free Cooling systems, so we were not sure how effective they would be. Since then the systems – and the way we have learned to use them – have outperformed assumptions.

A key factor in PUE reduction is optimizing set points. This requires a careful balancing of the inlet and return temperatures for each module. For instance, where our SLA specifies no more than 24 degrees at inlet point, but when we measure an exit/return temperature of say 30 or 40 degrees, we can recalibrate that module to bring down exit temperature.  Because the modules we use are individually adjustable we can go through this optimization process at more points on the data floor, giving us a greater overall efficiency gain.

A Perfect Fit

This level of granular control and variation would not work for many data center operators, but it fits perfectly with our retail proposition, and we expect to be able to improve further on it in the new data halls. Our customers want to be able to customize their space in terms of power density, rack numbers, UPS capacity, so we have made our latest 88 rack module even more modular. We can easily make it smaller and add interconnecting sections to enlarge it, as well as tuning UPS capacity up and down.

Sustainable Facilitators

The net impact of all this is that we are approaching rock bottom for PUE.  If your power overhead is 10% and the ultimate possible figure is 3% (a PUE of around 1.06 or 1.07) then there are only a few percentage points left to be gained.  We will of course continue to close that gap – when you are operating a 22 MW facility those percentage points still involve a significant financial and environmental impact.

Bringing PUE as low as it can go should open the way for other sustainability priorities. More transparent reporting on PUE and renewables, the integration of embodied impact with operational impact, WUE, and the optimization of server deployment and software are just some of the other ongoing challenges. As I said in Data Center Sustainability: The Next Dimension, by improving on PUE, multi-tenant data centers are reaching the boundaries of what they can do in their own domain. Operators with a genuine commitment to the environment can no longer be simply sustainable facilities, they should become sustainability facilitators.