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Part 3: UPS Energy Saver Mode, High Voltage DC Power Cut Data Center Energy Use
By James McEnteggart
February 2012 -
New UPS systems and high-voltage power supply are the two major trends in infrastructure design and engineering to reduce power consumption. DC power is a rare solution in the United States today, but worth considering the potential benefits and risks to save energy.
Manufacturers have modified the designs of new UPS systems with an "energy-saver" operating mode, which increases their power efficiency by approximately 90 percent operating at any load. Owners have been cautious to adopt this new operating mode until the new systems prove themselves, but more owners are willing to consider it today.
Operating a UPS in energy-saver mode has clear advantages over the conventional operating mode of older UPS systems, whose efficiency falls into the 30 to 40 percent range at low loads. Even as the load increases on an older unit, it never achieves a higher efficiency level than about 80 percent.
High-voltage power supply is an effective way to cut capital costs and power requirements, and it is an idea whose time has finally come. Until two or three years ago, most computers purchased in the United States were equipped with a 110V or 220V power supply. Now some organizations use 277V power supplies. A few use a 400V wye system, which yields a 240V phase-to-neutral voltage.
Running at these higher voltages not only reduces the capital cost of wiring as the system uses fewer, smaller wires, but at higher voltages, the current is lower, so less energy is lost through the wire.
One downside is the fact that high-voltage computer equipment is still a custom order even though it is more available. This means longer lead times for the initial purchase, as well as replacement parts.
More important, running at 400V is not yet standard. Most power in commercial buildings is delivered at 480V, and transformers step it down to 208V, 110V, or 120V — the standard voltages that are common in the United States. If the data center is going to run 400V IT support power, the owner must custom-order UPS systems that take in 480V and step it down to 400V, or provide external transformers to change the voltage.
High-voltage power supply is a win-win for a new facility or major addition. In a retrofit the benefits would not likely outweigh the additional costs.
Running a data center on DC power saves energy by reducing the energy losses associated with the number of power conversions typically required in a conventional data center. In a conventional data center, utility power is delivered as AC, it is converted to DC to charge the UPS batteries, and it is re-converted to AC power at the computer's power supply, which then converts it back to DC. Energy is lost at each conversion, making this approach less efficient than a DC system, which efficiently converts AC to DC once at high voltage and then distributes it to the computer's power supply, which reduces the DC voltage to the proper level using electronics. This approach reduces the number of conversions and boosts the overall efficiency.
Part 1: PUE is One of Many Metrics for Data Center Energy Performance
Part 2: Free Air, Water-Cooled Servers Increase Data Center Energy Efficiency
Part 4: In Data Centers, Simplicity of Design, Commissioning Saves Energy