Technologies for measuring power at the device level

While not displacing the UPS, the PDU adds insight into power consumption for data center managers.

While not displacing the UPS, the PDU adds insight into power consumption for data center managers.

by Patrick McLaughlin

In early June, the United States Environmental Protection Agency (EPA; www.epa.gov) officially launced its Energy Star program for data center facilities. We have chronicled the program’s development over the past several months and in this issue (page 29) we report on NetApp’s Research Triangle Park, NC data center that claims to be the first to achieve the EPA’s Energy Star rating. It is a safe bet to say the NetApp facility will not be the last to achieve the rating. In recent years increasing emphasis has been placed on data center energy efficiency by government, industry and in many cases, whoever pays a facility’s electric bill.

When the EPA was establishing the Energy Star program for data center facilities, a process that was almost three years from beginning to completion, it gathered energy-use information from 121 data center facilities of various types. Those types include standalone facilities, those enclosed within other facilities, and all tier levels.

Facilities gunning for the Energy Star rating provide to the EPA their energy-use measurement taken from their uninterruptible power supplies (UPSs), not their power distribution units (PDUs) if they have them. The reason the EPA opted for UPS readings rather than PDU readings is that of the 121 facilites from which the agency gathered information, more than 100 provided data from UPS meters and 42 provided data from PDU meters. The EPA’s goal was to make the program as widely accessible as possible, and more facilities will have the opportunity to participate with the measurements taken from UPSs.

UPS and PDU

While the Energy Star program singles out the UPS as the practical means of measuring power consumption, with increasing frequency savvy data center managers are also using PDUs for that purpose because in many cases the PDU can better pinpoint energy consumption at a rack or even a device level.

“Typically the UPS generates power and measures input and output power in terms of kVA [kilovolt-ampere] and kilowatts,” explains Chuck Heller, product marketing manager for 3-phase UPS technologies at Chloride Power (www.chloridepower.com). So with the UPS, “you have an idea of what your efficiency is going to be, with kilowatts out and kilowatts in,” he says. “How much real power did you bring in and how much real power are you able to put out? That’s a good way to measure a lot of the efficiency within a data center, but it does not cover everything.”

In terms of energy efficiency, Heller says the information provided by a UPS can be used as part of a formula to determine savings. “If you know you’re saving X number of kilowatt hours per year by optimizing load and other measures, you not only save whatever those losses were, but also the energy needed to cool that. The number typically used is 1.7. That multiple takes into account cooling reduction. Take whatever efficiency you gain and multiply it by 1.7” to determine the amount of savings garnered from increasing energy efficiency.

The PDU is physically located further “downstream” in the data center. Calvin Nicholson, senior director of product management and software development with Server Technology (www.servertech.com), describes the physical setup. “Most cabinets contain a PDU, which distributes power to all the devices in the rack.” If most do, then how come only 42 out of 121 facilities used data from PDUs in their reports to the EPA? It’s because not every PDU is equipped with the technology to report consumption figures.”The key is the adoption rate of what we call intelligent PDUs or cabinet PDUs.

“As the product matures, more and more users are seeing the value of an intelligent PDU and are implementing them,” Nicholson says.

Server Technology manufactures PDUs with a wide range of capabilities, including basic units that provide power without any level of consumption reporting, units with a local meter that allows users to ensure they are not exceeding the rating of a particular drop, and more-intelligent units that measure not only power consumption but in some cases temperature and humidity levels as well.

“Some of our intelligent models are switched units,” Nicholson explains, “which allow users to turn lights on and off and conduct a remote reboot.”

The dynamic for power supply and measurement is not really UPS versus PDU, but really UPS and PDU. “UPSs will always have a position in the data center,” Nicholson says. “But with the UPS you’re not going to get down to the device level.”

Increasing intelligence

Two of the most recent product/technology introductions from Server Technologies are referred to by their acronyms POPS and PIPS. POPS stands for per outlet power sensing. For PIPS, the “I” stands for “inlet.”

“POPs has been shipping since the latter part of last year,” Nicholson says. “It fits in with what groups like The Green Grid (www.thegreengrid.org) are discussing about Level 1, 2 and 3 measurements.”

The levels of measurement, as spelled out in a white paper authored by The Green Grid, increase the frequency and granularity of power measurements. Level 1 calls for at least monthly measurements from a UPS and the main distribution panel feeding all cooling equipment. Level 2 involves daily collection of data from PDUs and from the distribution system used to power all the facility equipment. And Level 3 specifies continuous measurment from each individual piece of information technology equipment.

Nicholson says the POPS capability is at the forefront of detailed measurement. For Level 3, “You need to be measuring at the device and doing so continuously,” he says. “That’s what we’re doing with the POPS devices.”

He says that some data center managers have been seeking this type of data for a little while. “Some time ago we noticed certain markets were becoming cost-conscious and understanding the price of power was going up while availability was going down. We could see a need to control power rather than just higher densities.”

Nicholson believes that today there is more of a market for this type of detailed information from intelligent PDUs than there had been. “We developed a POPS-style design years ago,” he recalls. The industry apparently was not willing to pay for such capability at that time. He says when developing the POPS products, Server Technology was able to reduce some costs due to overall electronics pricing. But a more significant factor in POPS succeeding in the marketplace is users’ recognition of what it offers. “People are starting to understand the value of measurements,” Nicholson says. “The cabinet PDU is really the smartest thing in the cabinet besides the server itself.”

The company also offers the Sentry Power Manager software suite, which manages the intelligent devices that are deployed and also acts as a middleware tool for other data center systems. It’s the software package, Nicholson explains, that allows clear and detailed reporting of the data that these intelligent PDUs collect.

More power efficiency

Chloride’s Heller says one developing trend that may significantly affect overall data center efficiency is the adoption of a nominal 400-volt power supply in the United States. It’s used in other parts of the world and, “There’s a movement afoot in the U.S. to start using this system in data centers because it has efficiency advantages.”

Chloride, based in the United Kingdom where 400-volt power systems are common, is developing a new product line based on this system, Heller says.

Patrick McLaughlin is our chief editor.

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