Power usage effectiveness (PUE) has become an industry-accepted energy efficiency metric for data centres. It requires accurate measurements to be taken of the power consumed by IT equipment and separately from the overall power consumption of the entire facility. Wendy Torell, a senior research analyst at Schneider Electric’s Data Center Science Centre, explains
There are of course several valid approaches to calculating PUE, the appropriate method being determined purely by the business objectives for measurement.
The most accurate is to take continuous measurements of the power expended by the various IT and infrastructural elements in a data centre to calculate how PUE varies over time in accordance with changing IT load conditions, available support infrastructure systems and especially the outside climatic conditions.
Even so, there are various options available for continuous metering and monitoring, which will depend on the particular purpose and surroundings of each data centre. The various factors that should be considered when choosing how to acquire, aggregate and analyse data on a continuous basis for accurate calculation of PUE are discussed in a new white paper from Schneider Electric, the global specialist in energy management and automation.
The paper, entitled ‘Continuous Metering and Monitoring of PUE in Data Centers’, discusses the drivers that can affect how one chooses to deploy the most appropriate data acquisition and aggregation tools for one’s needs. It also discusses the four levels of PUE reporting as set down by the Green Grid. Level 0 does not cover continuous monitoring at all; Level 1 requires only monthly measurements and is intended for situations in which only the IT equipment in a data centre is powered via the Uninterruptible Power Supply (UPS); Level 2 requires daily measurements and takes a more granular approach to measuring power consumed by the IT equipment by measuring at the PDU output.
This is important in cases where the UPS also supports infrastructure equipment such as air handlers; Level 3 reports IT load most accurately, as the meters are at the IT rack level. It also comes with added complexity, however, as there are many more meters that must be aggregated together. Level 3 ultimately helps you understand why your PUE is trending up or down over time, and most important, what you can do about it.
The paper goes into some detail as to how costs can be minimised even as one deploys the greater number of meters needed for the most accurate data acquisition possible. It also discusses how additional metering can be installed in a working data centre without causing downtime and thereby incurring unnecessary costs.
Finally it demonstrates the various methods that can be deployed to aggregate all the data from several measurement points using Data Centre Infrastructure Management (DCIM) management software and the tradeoffs that should be considered before deciding on the most appropriate course.
White Paper No 204 ‘Continuous Metering and Monitoring of PUE in Data Centers’ is available for immediate download here