The global demand for electricity is about 20,000 TWH; The ICT (Information and communication technology) industry uses 2,000 TWH, while data centers use about 200 TWH, or 1% of the total. Therefore, data centers are an important part of energy consumption in most countries and regions. It is estimated that there are more than 18 million servers in data centers worldwide. In addition to their own power needs, these IT devices also require supporting infrastructure, such as cooling, power distribution, fire suppression, uninterruptible power supply, generators, etc.

To compare the energy efficiency of a data center, IT is common practice to use “Power usage efficiency” (PUE) as a metric, which is the ratio of the total energy used by the data center to the energy used by IT. The ideal PUE is 1, which means that all energy is used for IT and the supporting infrastructure consumes no energy.

Therefore, to maximize the reduction of PUE, it is necessary to reduce the consumption of supporting infrastructure such as cooling and power distribution. Existing traditional data centers typically have a PUE of about 2, while large hyperscale data centers can reach below 1.2. In 2020, the global average is about 1.67. This means that, on average, 40% of total energy consumption is non-IT consumption. However, the PUE is a ratio that does not capture the total energy consumption, which means that if the IT equipment consumes a high level of energy compared to the cooling system, the PUE will look low. Therefore, IT is also important to measure the total power consumption as well as the efficiency and life cycle of the IT equipment. In addition, from an environmental point of view, the method of power generation, the amount of water consumed (including power generation and on-site cooling) and whether waste heat is used should also be considered.

The PUE concept was first proposed by the Green Grid Consortium in 2006 and published as an ISO standard in 2016. Green Grid is an open industry consortium of data center operators, cloud providers, technology and equipment vendors, facility architects, and end users working to improve the energy and resource efficiency of the data center ecosystem and reduce carbon emissions globally.

PUE is still a common way to calculate energy efficiency in data centers. At Munters, for example, PUE is assessed on a peaking and annualized basis for each project. When calculating PUE indicators, only IT load and cooling load are considered in the calculation of PUE. This is called partial PUE (pPUE) or mechanical PUE (PUEM). Electrical engineers use peak pPUE to determine the maximum load as well as the size of the backup generator. The annualized pPUE is used to assess typical power consumption over a year and to compare it with other cooling schemes. While PUE may not be a perfect tool, it is gaining support with the adoption of other measures such as WUE (water use efficiency), CUE (carbon use efficiency), and methods such as SPUE (server PUE) and TUE (Total PUE) that enhance PUE relevance.