April 5, 2012
Data centers are finding that they must deploy more and more power to their racks. High-power requirements at data center racks are driven by high density such as racks filled with 1U “pizza box” servers or multiple blade server chassis in one rack. Racks of network storage devices can also drive high demand for power.
When considering power demand it is important to determine and design for peak actual demand. Designing to IT equipment nameplate ratings is excessively high. Designing for average power consumption may not be sufficient for periods of peak demand.
Many data center managers are doing a good job conserving energy – decreasing PUE, raising data center temperatures, using air-side economizers to reduce energy consumption for cooling—but average power consumption at the rack may still go up. In fact, the increased efficiency means more power is available for servers which supports data center growth.
Since IT equipment vendors want to be able to sell their products globally, virtually all IT equipment is designed with power supplies that automatically adjust to voltages from 100V up to 240V. Another voltage that is being used more and more around the world for high-density data centers is 400V input converted to 230V at the outlets.
A single-phase 120V at 100A (80A rated) circuit provides 9.6kVA. A single-phase 208V at 60A (48A rated) circuit provides 10.0kVA. A three-phase 208V at 40A (32A rated) provides 11.5kVA. A single-phase 230V at (48A rated) circuit provides 11.0kVA. A three-phase 400V at 20A (16A rated) circuit provides 11.1kVA.
Running higher voltages at lower currents means smaller cables that use less copper, weigh less, take up less space, and cost less. Running three-phase power instead of single-phase power means fewer cables which simplify deployment as well as the benefits of smaller cables, less copper, less weight, and less cost.
Plugs and receptacles are also less expensive at higher voltages and lower current ratings. For example, a 30A 400V three phase Wye (16.6kVA) plug (Hubbell NEMA L22-30P) costs $32 and the receptacle costs $41. A 60A 208V three phase Delta (17.3kVA) plug (Mennekes IEC309 460P9W) costs $166 and the receptacle costs $216. The plug / receptacle combination is $73 vs. $382.
There are other benefits to higher voltages. By eliminating voltage transformations, 400V power reduces energy costs by approximately 2-3% relative to 208V distribution and approximately 4-5% relative to 120V distribution.
Consolidating data centers may reduce total power consumption but concentrate power demand in one data center or one row of high-density racks. A 42U rack filled with 1U servers consuming 250W each draws 10.5kW which would require two three phase 208V, 50A circuits providing 14.4kVA each. Blade server adoption continues such as deploying up to five HP BladeSystem® C7000 chassis in one rack requiring two three-phase 208V, 80A or 100A or two three phase Wye 400V, 50A or 60A rack PDUs. (These examples allow sufficient headroom should one of the feeds fail and support the North American requirement for 80% derating).
High power, such as 400V power distribution, is a good way to achieve higher power densities such as a rack full of 1U servers or a rack with several blade servers. It is also a good way to increase data center capacity. Efficiency is improved because higher voltages have somewhat reduced transmission losses. Higher voltages can deliver the same power at lower amperages which means thinner wire using less copper can be safely deployed. The savings continue with less expensive lower amperage plugs and receptacles.
High-density racks can be deployed in small, medium, or large data centers. Even in our own small data center, we’ve increased temperature set points to where our cooling capacity has increased to support higher density rack loads. The total power consumption of a small data center may not be great yet there may be racks with multiple blade servers or densely packed 1U servers that consume as much power as similar racks in a multi-megawatt data center.
Three-phase and high voltage power may be the right solution for you regardless of the size of your data center.
Learn more about Raritan's intelligent power distribution units for high voltage and high density racks.