# PUE: Every data center is different

Power usage effectiveness, or simply PUE, is one of the basic and most effective metrics for measuring data center energy efficiency. It is calculated by taking into account the total power consumed by a data center facility and dividing it by the power consumed by the IT equipment.

So, basically the PUE is calculated like this:

PUE = Total power into data center/IT equipment power

Let us take an example to see how PUE is calculated – and where the UPS comes into that calculation. Consider that the power entering the data center (measured at the utility meter) is 100 kW and the power consumed by the IT load (measured at the output of the UPS) is 50 kW; PUE will be calculated as follows:

PUE = 100/50 = 2

A PUE value of 2.0 is typical for a data center. But what does this mean?

For every watt required to power a server, two watts of power are consumed. Since you are paying for every watt of power entering your data center, every watt of overhead represents an additional cost.

There are two major ways which improve data center energy efficiency: Reduce the power going to the support infrastructure – and reduce losses in the power system. But there are many other factors, that still may affect your PUE.

Redundancy, for example, will increase PUE. There will always be tradeoffs between availability and energy efficiency. Data center equipment—from cooling equipment to UPSs to server power supplies—will run more efficiently when they are heavily loaded.

So one conclsuion while thinking about PUE is, that it is important for energy efficiency to do your math. But PUE is still only one piece of a puzzle. For real efficiency you need a more comprehensive energy management plan, that considers not only IT but facilities as well.

And as many data center operators will tell you: Every data center is different.

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