Facebook’s Prineville, Ore., data center achieved a water usage effectiveness rating of 0.22 liters per kWh for the 12 months to the second quarter of 2012, a result the social networking giant calls “a strong level of efficiency.”
In a blog post for OpenCompute.org. Facebook’s Daniel Lee calls the WUE “a great result” but qualifies that statement by saying that, to Facebook’s knowledge, no one else has publicly released WUE scores for data centers. Facebook is hoping other data centers will start releasing their measurements so the industry can begin setting benchmarks.
WUE, by definition, is an annualized calculation, but the company will be reporting its WUE results on a quarterly basis with those results eventually becoming a 12-month trailing metric, Lee says. The measurement only records water used in the data center’s computing processes and not any water used for plumbing or offices, although Facebook does use such water-saving techniques as waterless urinals, the post says.
The Prineville center uses 100 percent outside air economization coupled with a direct evaporation cooling and humidification misting system. Typical data centers do not use outside air economization, relying instead on the recirculation of up to 100 percent of the air used to cool their server room with cooling towers and a central chilled water plant, Lee says.
This uses far more energy and water than Facebook’s system, Lee says, comparing it to using a window mounted air conditioning unit instead of a window fan when outside air temperature is cooler. Facebook’s reliance on outside air also eliminates the need for water-intensive cooling towers, the blog post says.
In a column written for Environmental Leader in July, John Collins, segment manager for data centers at Eaton Corporation, detailed water efficiency strategies in data centers. In the column Collins advocates the use of air-side economization – similar to the system in use at Facebook’s Oregon data center. However, such technology is not well suited for every data center, and works best in cooler northern climates, such as Oregon, Collins argues. What Collins describes as “especially progressive” data centers have begun using recycled water sources rather than drinking water for their cooling.