Power Usage Effectiveness (PUE) – How Efficient Is Your Data Centre?

Data centrePower Usage Effectiveness (PUE) is a metric used to determine the energy efficiency of a data centre. PUE is calculated by dividing the amount of power entering a data centre by the power used to run the computer infrastructure within it.

Created by members of the Green Grid, an industry group focused on data centre energy efficiency, PUE is expressed as a ratio, with overall efficiency improving as the quotient decreases toward 1. According to the Uptime Institute, the typical data centre has an average PUE of 2.5. This means that for every 2.5 watts in at the utility meter, only one watt is delivered out to the IT load. Uptime estimates most facilities could achieve 1.6 PUE using the most efficient equipment and best practices.

Determining PUE:
Figure 1: Take a measurement of energy use at, or near the data centres utility meter. For data centres not on a separate meter, you will need to estimate the amount of power being consumed by the non-data centre portion of the building and remove this from the equation.

Figure 2: Measure the IT equipment load after power conversion, switching and conditioning is completed. The most useful measurement point is at the output of the computer room power distribution units (PDUs). This measurement should represent the total power delivered to the server racks in the data centre.

By dividing these two figures, your data centre PUE can be determined.

Reducing PUE:
One of the biggest energy users in a data centre is not the equipment itself, but the means of keeping this equipment cool – essential to prevent downtime and allow data centres running at their optimum.
In fact, as much as 45% of the energy cost of a data centre can relate to HVAC, with 3% of the UK’s total electrical energy usage thought to be attributable to data centres.

With HVAC accounting for so much of the energy used by a data centre, improving PUE focuses largely on the supporting cooling system. Cooling towers and Air Handling Units (AHUs) draw in air from the outside, air that is potentially full of dust, leaves and pollen, all of which can clog system filters. To ensure these HVAC systems work to their optimum, filters must be kept clean and in good working order – a simple step that can offer big savings on fuel bills.

Reduced airflow will result in a unit working harder to meet its cooling targets, therefore using more energy, increasing the likelihood of breakdown. For example, according to Johnson Controls’ study, when condenser flow rate is reduced by 20% in mechanical and absorption chillers, full load energy consumption is increased by 3%. Best practices in building maintenance and operations can reduce HVAC usage by 10 to 20 percent, with poor maintenance increasing energy usage by 30 to 60 percent.

ECEX Air Intake Screens
ECEX Air Intake Screens stop airborne particulates from entering a system in the first-place, to ensure cooling is kept constant, risk of breakdown is reduced and maintenance requirements are cut. This can be achieved by external, pre-filtration media. A solution that can be applied at the specification stage, or retrospectively, to improve the operational efficiency of existing cooling equipment, this approach is a relatively low cost option for what can be a big problem, with pay-back through reduced energy consumption in a very short timeframe.

For more information, speak to one of our experts:
Call: 01635 244 100
Email: sales@ecex.co.uk