Feature
Electrical metres enable data center managers to easily measure power quality and performance with accuracy.
Which type of data center metre is right for you? A comparison of various electrical metres
Embedded metres are cost-effective and should be implemented whenever possible.
If “you can’t manage what you can’t measure,” then electrical metres provide the critical power measurements needed to manage data centers. Specific types of metres serve various purposes, from tracking electricity consumption to triggering critical alarms to analyzing power quality to reporting power usage effectiveness (PUE). Which type of metre to incorporate into a data center design depends on what needs to be measured, and therefore managed.
Pros and cons of the different types of electrical metres
Stand-alone power quality metres and power metres both measure electrical power parameters (energy, voltage, current, power factor, frequency) precisely and accurately. Power quality metres provide more accurate engineering data and monitor the quality of electricity (harmonics, voltage disturbances) but are more expensive and complicated devices.
Although primarily protective devices, digital relays, electronic trip units, and UPSs often include embedded metres that measure power parameters. Leveraging these devices’
built-in metering capability avoids the higher cost of stand-alone metres. Trade-offs include less accurate data, limited or no power quality monitoring, and, in the case of digital relay and electronic trip unit embedded metres, difficulty in accessing the data.
Both UPS metres and embedded metres in power distribution units (PDUs), remote power panels (RPPs), and busways can serve as a cost-effective proxy for measuring IT load for PUE reporting. Note, however, that any non-IT loads powered through these devices would be inaccurately counted as IT load.
By measuring power on an outlet-by-outlet basis, metered rack PDUs calculate IT loads most effectively, avoiding the kind of complicated mapping needed when metering at the branch circuit level. Metered racks cost about 50% more than basic PDUs and measure data less accurately than the other upstream metres. In addition, using them in only some racks gives an incomplete picture of the IT load.
In sum, embedded metres are cost-effective and should be implemented whenever possible.
More detailed guidance on the advantages and disadvantages of different metres, a cost comparison, and sample measurement points can be found in APC by Schneider Electric white paper #172, “Types of Electrical Metres in Data Centers.” Go to
www.apc.com > Support > White Papers
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