Energy and Water Environmental Trade-Offs of Data Center Cooling Technologies

Historically, the rising cost of energy has been a huge driver for data center energy efficiency, and the contribution of this consumption to climate change is ever more evident. As the industry begins to look beyond energy consumption, it has become aware that environmental impact derives not just from energy consumption, but also from our use of natural resources. To ensure optimization measures do not cause a burden shift, these interdependent issues should not be considered in isolation. Data centers consume energy to power and cool IT equipment. Current optimization efforts largely focus on the operation of cooling technologies. These can be categorized simplistically according to their use of air or water to remove the heat created by the IT equipment. Design decisions are based on the theoretical energy consumption, and resulting running costs that a certain technology has in a given location. However, water is a valuable natural resource and currently it is difficult to expand this analysis to consider its consumption alongside that of energy. It is also difficult to understand whether indirect impacts of water and energy consumption outweigh any savings of one technology over another during operation. For example, water is consumed during the production of energy, the amount of which depends on the source of generation. To understand these impacts a life cycle approach is required. Such an approach acknowledges that water and energy are consumed from the moment raw materials are extracted and combined into process materials, to the point that it is used and then disposed of. A full life cycle impact of the different cooling technologies in a data center would consider the impacts of operation as well as those embodied in them. This, however, is a time-consuming process. Instead, the industry needs life cycle based tools and metrics that can expedite this decision process. Using life cycle assessment (LCA) to determine a single numerical value for total environmental impact, the work in this paper provides simple equations that allow designers to understand the environmental implications of their water and energy use in different parts of the world. A number of theoretical case studies are then used to demonstrate its application. Future work should look to include embodied impacts.