Power Usage Effectiveness (PUE)

PUE is an acronym from Power Usage Effectiveness. It is the measurement of the energy efficiency of data centers physical infrastructure such as the power and cooling equipment. PUE is not a measure of how efficient the IT equipment is, rather it is the metric to quantify the overhead power that is consumed in supporting the IT equipment. According to the recent study, USA data center energy consumption is 2% of total USA energy consumption. This is equivalent to the energy consumption of 7 million households.

The formula to calculate PUE is, take all the energy or power that is used to operate the data center and divided by the amount of energy consumed by the IT equipment’s like servers, network switches and storage devices.

For example, let’s consider this 2N redundant data center. 47 percent of the electrical power entering the facility actually powers the IT load and the rest is consumed or converted to heat by the power, cooling and lighting equipment. This include devices like UPS, transformers, generators, chillers, pumps, fans, etc.… Let’s consider the total data center power consumed is 1000 kw and 470 kw is by the IT load. So the PUE of this data center is 2.13.

The theoretical best PUE that can be achieved is 1. That is, every watt consumed by the data center is consumed directly by the IT equipment. If the PUE is 3 or more, then the data center is considered as in efficient. According to the Uptime Institute Data center survey, the average PUE is between 1.8 and 1.9.

Few ways to lower the PUE level.

• First step is to know the PUE of your data center. If it is not determined, then have the energy assessment performed by the data center specialist. They can also provide the specific recommended improvements that often pay the cost of the assessment within a year. In many data center, the cooling systems uses more power than the IT equipment’s. So the improvements to cooling will generally have the biggest impact on the PUE in overall energy saving.
• Keep hot air and cold air from mixing. Since this mixing makes the cooling system very inefficient. So make use of containment solution like hot aisle or cold aisle containment or vertical docks which are very effective in separating the hot or cold air streams.
• Raise the temperature set point in the data center. The new ASHRAE guideline recommend rack temperature can be as high as 80°F or 27°C.
• Finally, calculate and manage PUE on a constant basis. This can be done by installing the meters and monitoring software.

     Reference: https://www.youtube.com/watch?v=BiglstCxGDI