Metering - You Can't Manage What You Can't Measure

Back from vacation and some key meetings, so back on the dais.

Metering is one of the least appreciated platforms in the data center. Metering is rarely integrated across the building, nor is it properly applied to critical power system. So, how ar you ever going to get a realistic PUE when your ruler is an inch short?

Metering challenges fall into two categories - location and quality. Metering typically occurs ar major electrical distribution points, and recently, has been appearing in the racks and cabinets of the data center in the form of localized power control. The challenge facing all metering is quality. When applying metering to the CP system, you should be srtiving for "Utility" grade metering for both the meter and the current and voltage instruments. This means less than a 2% error for the system.

One of the challenges is that the smaller current and voltage transformers typically have not been built to these standards. So, when you specify, be keen on the meter and instrument quality.

Moving on to location, it's absolutely vital that you meter as close to the IT system power supply as possible for a few reasons. First, low-power harmonics can adversely affect PUE calcs when you meter from a PDU or panel only. These low power calcs can yield widely divergent readings from the PDU or panel to the load simply by the impedance of the cable serving the load. Second, the most effective PUE is one that honestly measures the consumption of the IT equipment versus the entire plant.

One of the keener solutions is the use of a comprehensive power metering and control system on the cabinet itself. Several of the solutions in the marketplace offer Utility-grade metering while allowing you to control individual plugs on the power strips. Remember, focus on that metering quality and get the meter for the IT load on or as close to that load as possible.