Water Usage Effectiveness (WUE)

Water Usage Effectiveness (WUE) is an important measure which, alongside PUE, provides a more holistic view of a data center’s environmental impact. WUE represents an important evolution in how we think about the impact of the data center, because there are tradeoffs between PUE and WUE. In most instances, comparing sites with like-for-like operating conditions, adiabatically cooled mechanical systems use less power than those that are just air cooled, but they do so with significant water use. In some locations where water is scarce it may sound rational to avoid water use on site for the rejection of heat, but one must dig deeper.

How to strike the balance that will produce the most ‘sustainable’ outcome really depends on local factors. For example, given that renewable power generation uses less water than traditional Rankine cycle-based plants, a more power-intensive air-cooled data center using renewable energy could have a smaller total water footprint than an evaporatively assisted data center in the same location. Conversely, in locations where power is generated by way of a Rankine cycle, an evaporatively cooled data center could use less water than the air-cooled equivalent.

A Shift Toward WUE≈0 Cooling Systems
Our design standard has also evolved as customers’ thinking about sustainability has evolved. For example, our new design leverages closed loop chillers in most markets—more sustainable because it uses almost no water. This is one of the ways Stream is responding to customers’ focus on sustainability beyond PUE and commitment to water efficiency. At Stream’s new Phoenix data center, for example, we leverage closed-loop chillers to minimize our water usage. At full build, the campus will support up to 280 MW of critical load in 2 million square feet of data center space.

Explore more in the article Water Is Life.