What is Power Usage Effectiveness (PUE)?

Power Usage Effectiveness, or PUE for short, is a key metric for the energy efficiency of data centers. In 2007, Green Grid, a consortium of computer and chip manufacturers, defined this value. The PUE value indicates how efficiently a data center uses its supplied energy. The closer the PUE value is to 1.0, the more efficiently the data center operates.

In an era where energy demand continues to rise due to increasing data volumes and the growing use of cloud services, optimizing energy efficiency is becoming increasingly important. Data center operators must therefore constantly work to lower their PUE value. This allows them to both save costs and minimize their ecological footprint.

PUE Calculation

To calculate the PUE value, the total energy consumed by the data center is divided by the energy used directly by the IT infrastructure. IT infrastructure includes servers, storage systems, network equipment, and other relevant devices. The resulting figure indicates how much energy is used to operate the IT systems and how much flows into other areas, such as cooling and power conversion. A PUE value of 1.0 would theoretically mean that 100% of the energy is used exclusively for IT. In practice, however, this is hardly achievable.

Significance

A low PUE value is the goal of every data center. It means that the energy expenditure for non-IT-relevant processes such as cooling or power conversion is minimal. For example, Google achieved an average PUE of 1.2 for its data centers in 2017. This shows that only 20% of the energy is required for processes other than IT operations. In contrast, a data center with a PUE of 4 would mean that 75% of the energy flows into these processes.

Optimization Opportunities

Data centers are major energy consumers, and cooling is often one of the largest energy items. A data center typically uses around 35 to 50 percent of its energy requirement for cooling. This is also where the greatest potential for energy savings lies. Data center operators often use “free cooling,” where they use outside air to cool the server rooms. This method does not require energy-intensive chillers and can significantly increase energy efficiency.