Date Center Power Distribution Units
In the quest to become more efficient, an important facet of data center infrastructure that needs special attention is the data center power distribution strategy. With consumption costs and power densities rising, the traditional methods of distributing power to the racks are frequently challenged. Since power usage effectiveness and cooling costs account for a significant portion of a company’s budget, it’s important to examine which approach is right for your facility.
There are five approaches to data center power distribution used in data centers today. 2NSystems can help you choose the best one for your application.
Panelboard distribution allocates the main data center power to multiple wall-mounted panelboards. Panelboards may come pre-assembled by the vendor or can be assembled in the field by an electrical contractor, however this approach is very much custom engineered to meet the unique needs of the data center. Branch circuits or power cables are cut, terminated and connected in the field by the electrical contractor. Cables are run either in cable trays overhead, or run beneath a raised floor to provide power close to rack enclosures. Wall-mounted panelboards are a very low cost strategy, comprised of parts that could be secured in days to implement quickly. The panelboard distribution approach is custom engineered to meet unique needs of the data center.
Advantages
- Lower cost components lead to lowest first cost
- Can accommodate unusual and unique physical room constraints
- Greater flexibility in breaker and cable combinations
- Parts can be acquired quickly
Disadvantages
- Custom engineered installation rely on work and skill of electrician, and have increased risk of human error
- Cooling distribution could be affected by cabling restricting high volume air flow
- Environment is not readily changeable
- Tracing and removing cables is difficult due to power cables under the floor or in trays
Usually Used
- Smaller capacity installations and where lowest first cost is a priority</li
- Where IT changes are not likely or frequent</li
- Where there is low density per rack (if cables are in the air plenum)
Similar to those cables fed from the panelboard distribution method, power cables from field-wired PDUs to the enclosures can be run through flexible or rigid conduits or placed underfloor or in trays. Which method selected is variable based on local code requirements. A significant amount of wiring work is done onsite, including the cutting, terminating and connecting of each branch circuit, and routing them to the racks. In a raised floor scenario, special under-floor supports are engineered as well. For branch level metering, sensors are added and then programmed.
Advantages
- Greater number of monitoring options than panelboard
- Lower PDU cost than factory-configured or modular PDUs
- Can accommodate unique and unusual physical room constraints
- Allows for more strategic placement when compared to panelboards
- More flexibility is allowed to the electrician in breaker and cable combinations
Disadvantages
- Field-wired designs rely on work and skill of electrician, and have increased risk of human error
- Field-installed components like breakers and cables mean limited warranties
- Cooling distribution could be affected by cabling restricting high volume air flow
- Tracing and removing cables is difficult due to power cables under the floor or in trays
Usually Used
- When low first cost is a priority over factory-configured and modular distribution
- Where there is available floor space, but unique room constraints limit the use of factory or modular designs
- Where IT changes are not likely or frequent; growth of IT done at pod level
- When layout is unknown at the time of specification (actual ratings and lengths are not specified until closer to installation)
As the name implies, the factory-configured distribution’s wiring work is done in a controlled factory. The power distribution unit is configured to the customer’s specified requirements with factory-assembled breakers and pre-cut and terminated cables. These assemblies are all installed at the factory, so the only onsite work required is running the conduit from a subfeed breaker to the PDU’s input, and routing the pre-connect cables to the appropriate racks. By standardizing the solution, data centers can eliminate costly and time-consuming one-time engineering.
Advantages
- Improve reliability and minimize field work by using pre-fabricated breaker and power cable assemblies
- Better prepared for change as load requirements change
- Warranty of entire power distribution system, since components originate in factory
- Ability to accommodate unusual and unique room constraints
- Lower first cost than the modular distribution approach
Disadvantages
- Specific breakers and cable lengths require knowledge of the IT environment early on in the planning cycle
- Higher cost to install new cables and breakers as requirements change vs. modular distribution approaches
- Tracing and removing cables may be difficult due to the large volume overlayed in troughs
- Occupies IT floor space
- Heavier and perhaps costlier shipping weight
Usually Used
- Where data centers plan their future IT at the pod level
- When the data center requires portable equipment due to possibility of future moves
- Where low first cost is a priority and space is not constrained
The overhead/underfloor modular distribution, or busway, was the first alternative to the traditional distribution method that offered a more flexibly reconfigurable system. The power bus is generally installed over IT equipment rows. Onsite installation involves subfeed breaker install, securing the busway, running wire from breakers to the busway feed units and inserting the plug-in units and routing them to the racks. This approach makes changes easier and removes under-floor cabling. In the busway system, IT enclosures connect directly to the busway via plug-in units with breaker boxes. Generally, these systems are installed upfront for the maximum expected load.
Advantages
- No IT room footprint, more space is available for IT equipment
- Improved cable tracing and management, distribution cable from plug-in unit located directly above or below IT racks
- Cable inventory reduced
- Improved reliability from tool-less pre-assembled units eliminates field wire cutting and terminating
- Factory designed, tested and integrated components mean system-level warranty of the entire system
- Wider range of capacities available to address greater capacity needs
- Adds, moves and changes are easier because cables are not stacked
Disadvantages
- Height of ceiling could restrict overhead implementation. Space is required above racks (approx. 25″, 0.6 m); raised floor usage constrains underfloor implementation
- Field installation and integration of multiple bus sections necessitates more time and expense; can create unique problems
- If hung above enclosures may interfere with containment systems
- Advance thought of row placement and length required for busway placement
- Bus oversizing is more likely since it is built out on day one
Usually Used
- Where there is constrained IT floor space
- In larger facilities with an open plan and defined row layout
- Where there is a high level of confidence in final load requirement
- Where there is a high turnover rate of IT equipment requiring new circuits
Modular PDUs, unlike traditional breaker panels with bolted wire terminations, have a backplane in which the pre-terminated breaker modules are installed. Arranging this way eliminates on-site wire termination. For example, a row of new 24 IT enclosures and associated branch circuit wires and outlet strips can be installed in an hour, without cutting or terminating any wires.
A lot of data center projects involve the upgrading of an existing structure, typically involving the adding of capacity or installing a high-density zone. Floor-mount modular systems are suitable option for retrofit projects such as these, because installation is less disruptive than a traditional PDU. Modular PDUs can exist together with existing, traditional PDUs.
Modular PDUs can be directly integrated with the UPS system of a small data center into a compact arrangement. No separate UPS room required.
However there are some cases where there may be one or more zones within a data center that require only a small number of branch circuits. This can happen where there is a group of very high density racks or when a small group of racks are isolated by the environment shape or other constraint. Where this occurs, there are smaller modular PDUs that can mount directly to the IT rack, consuming zero footprint.
Advantages
- Pre-fabricated backplane and circuit modules promise a well-integrated and reliable system
- Pre-assembled modules require minimal field work
- Better capacity and change management for future load requirement changes
- Factory designed, tested and integrated components mean system-level warranty of entire system
- Easily scale additional PDUs when new IT demands are identified
- Ability to accommodate unusual and unique room constraints
Disadvantages
- Larger number of cables to inventory due to varying distances from PDUs to racks
- Cable tracing, adds, and changes can be difficult due to cable volume and size
- Takes up IT room space
Usually Used
- When flexibility is required to add/move distribution, i.e. uncertain growth plans or locations are not specifically defined in advance
- When the room has constraints in shape or height
- Where IT personnel prefers to reconfigure breakers and circuits without third party involvement
- Where deployment speed is a priority
- When retrofitting existing data centers with additional capacity or installing a high-density zone