It’s the way IT systems have been powered for decades: Large transformers feed power to distribution units via under-floor hard-wired circuits using rigid or flexible conduit.
Most data centers still use traditional methods, which means data center operators are forced to make circuit changes on energized wiring (“hot work”); under-floor cooling spaces are blocked with cables, reducing the efficiency of the cooling system; and, large transformer based PDU units generate waste heat that must be cooled, further decreasing the efficiency of the data center.
But significant changes in how power is used in data centers since this system was first introduced nearly 40 years ago have prompted the need for more efficient power distribution architecture. Increased power density, the use of a greater number of separate IT devices within a data center, and the need to add/remove devices on a continuous basis are widely recognized as challenges to the traditional power distribution system.
An ideal power distribution system would eliminate the need for under-floor cables, allow new circuits to be safely added or changed on a live system and enable all circuits to be monitored for power, among other attributes.
Newer approaches include modular power distribution and overhead power busways, which both have significant advantages compared to the traditional approach in terms of efficiency, power density, power monitoring and reconfigurability.
Some examples of how a modular power distribution system is ideally suited to a modern high density data center:
- Adding branch circuits: Plug-in, pre-made branch circuits can be installed in an energized system without exposure to live electrical wiring. Power monitoring is included in each branch circuit and is configured automatically when plugged in.
- Ability to remove or change a rack cabinet: The branch circuit unplugs at the rack, and the rack cabinet can be easily rolled out of the data center.
- Simplified planning: In the past, the number and location of PDUs had to be determined early in the design process – often before the final power density was determined. With a modular system, PDUs can be added later without any special preparation.
- Reliability: Wiring terminations are pre-made in a controlled factory setting, improving reliability. This reduces the likelihood of loose connections and other defects. Interference with other circuits during additions and changes is virtually eliminated.
- Air-flow interference: Under-floor cabling is eliminated, along with the associated air leakage caused by extra openings in the floor.
- Up-front cost: PDUs do not have to be installed in the initial build, reducing startup costs. Power distribution cost is incurred only if and when needed.
Busway to the rack
In the busway to the rack distribution system, IT enclosures directly connect to the overhead busway via breaker boxes. The busway is pre-installed over all IT equipment rows, which removes under floor cabling and facilitates changes to the system.
There are, however, drawbacks to this system. Busway must be sized in advanced to the maximum density and capacity because adding busway once the system is up and running is disruptive. Also, breakers are mounted on the overhead busway, requiring ladder access. In many cases, local codes prohibit this, necessitating chain or other actuators.
Both the modular and busway to the rack systems provide improvements to the traditional system in terms of scalability, efficiency, reconfigurability, manageability and power density. The modular system is particularly beneficial for data centers in which the layout is not precisely defined in advance, in retrofit applications and in cases where the room layout includes unusual shaped floor plan or obstructions.
For more information on power distribution architecture for data centers, as well as further details on the busway to the rack distribution system, see the APC by Schneider Electric white paper, A Scalable, Reconfigurable, and Efficient Data Center Power Distribution Architecture.