Power usage effectiveness

Power usage effectiveness (PUE) is a measure of how efficiently a computer data center uses energy; specifically, how much energy is used by the computing equipment (in contrast to cooling and other overhead).

PUE is the ratio of total amount of energy used by a computer data center facility to the energy delivered to computing equipment.

PUE was developed by a consortium called The Green Grid. PUE is the inverse of data center infrastructure efficiency (DCIE). An ideal PUE is 1.0. Anything that isn't considered a computing device in a data center (i.e. lighting, cooling, etc.) falls into the category of facility energy consumption.

The PUE metric is the most popular method of calculating energy efficiency. Although it is the most effective in comparison to other metrics, the Power Usage Effectiveness comes with its share of flaws. This is the most frequently used metric for operators, facility technicians, and building architects to determine how energy efficient their data center buildings are. Some professionals even brag about their Power Usage Effectiveness being lower than others. Naturally, it is not a surprise that in some cases an operator may “accidentally” not count the energy used for lighting, resulting in lower Power Usage Effectiveness. This problem is more linked to a human mistake, rather than an issue with the Power Usage Effectiveness metric system itself.

One real problem is PUE does not account for the climate within the cities the data centers are built. In particular, it does not account for different normal temperatures outside the data center. For example, a data center located in Alaska cannot be effectively compared to a data center in Miami. A colder climate results in a lesser need for a massive cooling system. Cooling systems account for roughly 30 percent of consumed energy in a facility, while the data center equipment accounts for nearly 50 percent. Due to this, the Miami data center may have a final Power Usage Effectiveness of 1.8 and the data center in Alaska may have a ratio of 1.7, but the Miami data center may be running overall more efficiently. In particular, if it happened to be in Alaska, it may get a better result.

Additionally, according to a case study on Science Direct, "an estimated PUE is practically meaningless unless the IT is working at full capacity".

All in all, finding simple, yet recurring issues such as the problems associated with the effect of varying temperatures in cities and learning how to properly calculate all the facility energy consumption is very essential. By doing so, continuing to reduce these problems ensures that further progress and higher standards are always being pushed to improve the success of the Power Usage Effectiveness for future data center facilities.

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