A case study and critical assessment in calculating power usage effectiveness for a data centre

•A case study PUE calculation is carried out on a data centre by using open source specifications.•The PUE metric does not drive improvements in the efficiencies of IT processes.•The PUE does not fairly represent energy use; an increase in IT load can lead to a decrease in the PUE.•Once a low PUE is achieved, power supply efficiency and IT load have the greatest impact on its value. Metrics commonly used to assess the energy efficiency of data centres are analysed through performing and critiquing a case study calculation of energy efficiency. Specifically, the metric Power Usage Effectiveness (PUE), which has become a de facto standard within the data centre industry, will be assessed. This is achieved by using open source specifications for a data centre in Prineville, Oregon, USA provided by the Open Compute Project launched by the social networking company Facebook. The usefulness of the PUE metric to the IT industry is critically assessed and it is found that whilst it is important for encouraging lower energy consumption in data centres, it does not represent an unambiguous measure of energy efficiency.