Taming the Power-Hungry Distribution System
Energy management strategies for mission-critical buildings
As power density in modern data centers increases, more focus has been placed on improving efficiency in the power distribution infrastructure. Dramatic changes, such as switching to 600-V direct current (DC) distribution systems have been explored, but there are some practical and affordable options to significantly improve efficiency without making major changes to the existing power delivery infrastructure. Recent advancements in power distribution products can reduce energy, cabling, and cooling costs. As an added bonus, new modular power distribution schemes and products also make the data center more adaptable and easier to manage.
Let’s take a look at how any data center can increase efficiency and adaptability simply by making smart choices in the major building blocks of power distribution which include: Uninterruptible power systems (UPSs), Power distribution units (PDUs), Power distribution racks (PDRs), and Enclosure power distribution
units (ePDUs).
The UPS: From Behind the Scenes to the Data Center Floor
In traditional data center designs, a large, three-phase UPS stood alone in a separate room, providing conditioned power and battery backup for the whole data center, perhaps even the entire building. These UPSs fed PDUs on the data center floor.
Advances in UPS technologies have greatly improved the efficiency of these large UPS systems. In the 1980s, a state-of-the-art UPS was 75% to 80% efficient at best. With the advent of faster switching devices in the 1990s, efficiency jumped to 85% to 90%, and later to 90% to greater than 94%.
Even higher efficiency is now possible. In the past few years, manufacturers have introduced UPSs, specifically for high-density computing environments. These types of modular UPSs operate at an industry-leading 97% efficiency in normal operation. Even at less than 30% load, where one would expect much lower efficiency, this type of UPS is indeed more efficient than others at full load.
Even small increases in UPS efficiency can quickly translate into tens of thousands of dollars. The savings compound with data center size. High UPS efficiency also extends battery runtimes and produces cooler operating conditions, extending the product’s operational life.
The Backbone of Efficient Distribution
PDUs provide efficient and flexible distribution for today’s data centers and promote efficiency by streamlining cabling and increasing airflow. In a traditional distribution scheme, the PDU feeds a panelboard, and separate branch circuits deliver power to racks. Excessive cabling can restrict airflow under the raised floor.
PDUs can dramatically streamline cabling requirements by using subfeed breaker distribution rather than panelboard/branch circuit distribution. The subfeed distribution wiring can be connected to PDRs that sit at the end of rows, closer to rack loads. This arrangement has the added benefit of being able to handle moves, adds, or changes more easily, since branch circuit cables only have to be managed up to the PDR, and not all the way back to the PDU.
In addition to the obvious cost savings of less cabling, cooling efficiency is also increased by reducing airflow restrictions under the raised floor. Some data centers have been designed with 4-foot (or taller) raised floors to compensate for excessive wiring. These higher raised floors add cost and compromise the structural integrity of the floor.
Use high-efficiency transformers. Look for PDUs that can use energy-efficient TP-1-compliant transformers that meet the requirements of the Energy Policy Act of 2005. The TP-1 standard calls for distribution transformers to be 1% to 2% more efficient at their typical loading level (30% to 50%). Although TP-1 transformers are more expensive, they pay for themselves in five to six years by significantly reducing energy costs—and they continue to deliver cost savings for the remainder of their 20- to 30-year lifespan.
High-Density PDRs—Optimizing Three-Phase Distribution to the Rack
Further simplification can be achieved by using high density power distribution racks (HD-PDRs), which can be optimized for pure three-phase distribution to the rack. The HD-PDR can contain up to eight panelboards, ranging from 12- to 42-pole positions. These panelboards are rated from 225 A up to 800 A, to support high-power three-phase distribution from the panel.
Three-phase distribution allows more power to the racks with less wiring. The smaller 12- and 24-pole panelboards that are available allow more effective use of space in the unit for installation wiring and operational maintenance. Distributing three-phase power to the racks enables power changes at the rack level, rather than the PDU level, allowing the Information Technology (IT) staff to make power changes for additions of new IT equipment to the rack.
HD-PDRs can support separate input sources to feed dual-corded loads or rack-mounted transfer switches. This can reduce the amount of cabling required by approximately 25% using dual-source PDRs. Minimizing cabling along the rows and to the racks improves airflow and, therefore, thermal efficiency of the room and
racks (Figure 1).
ePDUs —Power Distribution for the High-Density Rack
In high–power density environments, three-phase, rack-mounted ePDU products are quickly being recognized as the optimal solution for rack power distribution. These ePDUs are the perfect complement to the PDR (although ePDUs are certainly compatible with standard remote power panels and can even be directly connected all the way back to the PDU).
There are many advantages of using three-phase, 208-V power down to the ePDU level, as opposed to just using a plethora of single-phase 120-V rack power strips:
- Three-phase distribution can transfer almost twice as much power (1.73 x) as equivalent 208-V, single-phase circuits over the same size conductors and three times the power as 120-V single-phase circuits.
- When switching from single-phase 208 V to three-phase 208-V distribution, only one extra wire is run in each power drop, which is a 25% or 33% increase in copper, compared to a 73% increase in power delivery.
- Using higher voltage ePDUs in the rack reduces the number of cables that need to be brought in and managed. A few high-power ePDUs replace an unwieldy web of cabling and a mass of low-power plug strips. The result is greatly simplified cable management, more space available in the rack, and improved air flow and thermal efficiency.
Modular Power Distribution
With data center devices smaller than ever—often served by dual or triple power supplies—a single rack of equipment might produce 40 or more power cords to manage. Power consumption per rack is higher than ever, and continuous uptime is essential. What’s the best way to distribute power to racks in the era of modularity?
As discussed earlier, a far better alternative is to use a rack power module to provide “plug and power” distribution from a UPS or panelboard to an ePDU or directly to IT equipment. Select a rack power module that can deliver power in an organized manner to loads of various voltages, input power cord types, and output receptacles—supporting a broad range of applications.
In order to truly support modularity, the rack power module should be adaptable to serve either of two roles:
Primary power distribution from the UPS to a PDU. A Rack Power Module (RPM) can be hardwired, delivers high power (36 kW), provides metering and monitoring, and has 12 poles of distribution breakers—essentially bringing the characteristics of a panelboard into a portable 3U box.
Secondary power distribution from a PDU or panelboard to IT equipment. Where one formerly had many long cable runs (home runs) from a panelboard to enclosures, the rack power module simplifies the cabling and makes it easier to track the power path when adding or changing IT equipment.
For either application, the modular approach has fewer cables to manage and greater flexibility, both for changing the IT equipment and the distribution system that powers it.
As shown below in Figure 2, modern enclosure-based PDUs can be installed in many locations and removed and redeployed as needed, making it easy to support moves, adds, and changes in IT systems.
The Challenge of Monitoring Modular Power Distribution
Data center managers could rightfully wonder if modular power distribution might be more difficult to monitor. After all, there will be dozens or even hundreds of ePDUs to track, compared to a few power distribution racks. In the past, managing all those rack-level power distribution devices has been problematic, for a couple of reasons:
- With older or very basic ePDUs, there is typically no visibility into current flow at this level. If an overload condition or tripped circuit were imminent, customers wouldn’t see it coming.
- With newer ePDUs networked over the company LAN, users typically have to point their Web browsers to each device to see its status—a time-consuming and tedious proposition.
Those compromises are no longer necessary. With the latest ePDU products and software, you can monitor and manage network-connected power distribution components at the rack level via one Web-based user interface and one IP address. Straightforward and budget-friendly software is available to aggregate power data from a virtually unlimited number of ePDUs and UPSs on an IP network into a cohesive, enterprise-wide view. Going modular doesn’t have to compromise visibility; in fact, it extends visibility further to the edge of the distribution system.
What to Look for in Modular Power Distribution
- Compact size, such as 3U for a rack power module, 1U, or 2U for an enclosure-based PDU
- Ability to mount the device anywhere, not just in one vendor’s rack or a specified slot
- Installation options that conserve valuable U space and support easy cable management
- Ability to easily move, redeploy, and swap out ePDUs without tools or an electrician
- Ability to install ePDUs horizontally or vertically, multiple units per rack
- Display of load currents for load balancing and protection during moves, adds, and changes
- Ability to monitor ePDUs over the network through IP communication
- Sufficient power capacity and receptacles to meet projected needs for 12–18 months
- Additional functionality, such as remote control or receptacle-level metering, if possible
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When considering modularity—plan ahead. When evaluating components for the data center power infrastructure, look for the ability to support modular expansion and redeployment later. There may be some incremental additional investment—such as a parallel bus bar in an enclosure to support a modular UPS, for example—but once that initial setup is done, one just needs to purchase additional modules as needed, plug them in, and go.
There are more options than ever to capitalize on modular architectures to tailor the power system for your unique data center requirements and the velocity of change. As you plan to upgrade power systems or build a new facility, seek to create a power infrastructure that is as adaptable as the IT infrastructure.
Author's Bio: Imran Ahmad is a product manager for Eaton.
January-February 2010
Taming the Power-Hungry Distribution System
Energy management strategies for mission-critical buildings
Photo: Eaton
As power density in modern data centers increases, more focus has been placed on improving efficiency in the power distribution infrastructure. Dramatic changes, such as switching to 600-V direct current (DC) distribution systems have been explored, but there are some practical and affordable options to significantly improve efficiency without making major changes to the existing power delivery infrastructure. Recent advancements in power distribution products can reduce energy, cabling, and cooling costs. As an added bonus, new modular power distribution schemes and products also make the data center more adaptable and easier to manage.
Let’s take a look at how any data center can increase efficiency and adaptability simply by making smart choices in the major building blocks of power distribution which include: Uninterruptible power systems (UPSs), Power distribution units (PDUs), Power distribution racks (PDRs), and Enclosure power distribution
units (ePDUs).
The UPS: From Behind the Scenes to the Data Center Floor
In traditional data center designs, a large, three-phase UPS stood alone in a separate room, providing conditioned power and battery backup for the whole data center, perhaps even the entire building. These UPSs fed PDUs on the data center floor.
Advances in UPS technologies have greatly improved the efficiency of these large UPS systems. In the 1980s, a state-of-the-art UPS was 75% to 80% efficient at best. With the advent of faster switching devices in the 1990s, efficiency jumped to 85% to 90%, and later to 90% to greater than 94%.
Even higher efficiency is now possible. In the past few years, manufacturers have introduced UPSs, specifically for high-density computing environments. These types of modular UPSs operate at an industry-leading 97% efficiency in normal operation. Even at less than 30% load, where one would expect much lower efficiency, this type of UPS is indeed more efficient than others at full load.
Even small increases in UPS efficiency can quickly translate into tens of thousands of dollars. The savings compound with data center size. High UPS efficiency also extends battery runtimes and produces cooler operating conditions, extending the product’s operational life.
The Backbone of Efficient Distribution
PDUs provide efficient and flexible distribution for today’s data centers and promote efficiency by streamlining cabling and increasing airflow. In a traditional distribution scheme, the PDU feeds a panelboard, and separate branch circuits deliver power to racks. Excessive cabling can restrict airflow under the raised floor.
PDUs can dramatically streamline cabling requirements by using subfeed breaker distribution rather than panelboard/branch circuit distribution. The subfeed distribution wiring can be connected to PDRs that sit at the end of rows, closer to rack loads. This arrangement has the added benefit of being able to handle moves, adds, or changes more easily, since branch circuit cables only have to be managed up to the PDR, and not all the way back to the PDU.
In addition to the obvious cost savings of less cabling, cooling efficiency is also increased by reducing airflow restrictions under the raised floor. Some data centers have been designed with 4-foot (or taller) raised floors to compensate for excessive wiring. These higher raised floors add cost and compromise the structural integrity of the floor.
Use high-efficiency transformers. Look for PDUs that can use energy-efficient TP-1-compliant transformers that meet the requirements of the Energy Policy Act of 2005. The TP-1 standard calls for distribution transformers to be 1% to 2% more efficient at their typical loading level (30% to 50%). Although TP-1 transformers are more expensive, they pay for themselves in five to six years by significantly reducing energy costs—and they continue to deliver cost savings for the remainder of their 20- to 30-year lifespan.
High-Density PDRs—Optimizing Three-Phase Distribution to the Rack
Further simplification can be achieved by using high density power distribution racks (HD-PDRs), which can be optimized for pure three-phase distribution to the rack. The HD-PDR can contain up to eight panelboards, ranging from 12- to 42-pole positions. These panelboards are rated from 225 A up to 800 A, to support high-power three-phase distribution from the panel.
Three-phase distribution allows more power to the racks with less wiring. The smaller 12- and 24-pole panelboards that are available allow more effective use of space in the unit for installation wiring and operational maintenance. Distributing three-phase power to the racks enables power changes at the rack level, rather than the PDU level, allowing the Information Technology (IT) staff to make power changes for additions of new IT equipment to the rack.
HD-PDRs can support separate input sources to feed dual-corded loads or rack-mounted transfer switches. This can reduce the amount of cabling required by approximately 25% using dual-source PDRs. Minimizing cabling along the rows and to the racks improves airflow and, therefore, thermal efficiency of the room and
racks (Figure 1).
ePDUs —Power Distribution for the High-Density Rack
In high–power density environments, three-phase, rack-mounted ePDU products are quickly being recognized as the optimal solution for rack power distribution. These ePDUs are the perfect complement to the PDR (although ePDUs are certainly compatible with standard remote power panels and can even be directly connected all the way back to the PDU).
There are many advantages of using three-phase, 208-V power down to the ePDU level, as opposed to just using a plethora of single-phase 120-V rack power strips:
- Three-phase distribution can transfer almost twice as much power (1.73 x) as equivalent 208-V, single-phase circuits over the same size conductors and three times the power as 120-V single-phase circuits.
- When switching from single-phase 208 V to three-phase 208-V distribution, only one extra wire is run in each power drop, which is a 25% or 33% increase in copper, compared to a 73% increase in power delivery.
- Using higher voltage ePDUs in the rack reduces the number of cables that need to be brought in and managed. A few high-power ePDUs replace an unwieldy web of cabling and a mass of low-power plug strips. The result is greatly simplified cable management, more space available in the rack, and improved air flow and thermal efficiency.
Modular Power Distribution
With data center devices smaller than ever—often served by dual or triple power supplies—a single rack of equipment might produce 40 or more power cords to manage. Power consumption per rack is higher than ever, and continuous uptime is essential. What’s the best way to distribute power to racks in the era of modularity?
As discussed earlier, a far better alternative is to use a rack power module to provide “plug and power” distribution from a UPS or panelboard to an ePDU or directly to IT equipment. Select a rack power module that can deliver power in an organized manner to loads of various voltages, input power cord types, and output receptacles—supporting a broad range of applications.
In order to truly support modularity, the rack power module should be adaptable to serve either of two roles:
Primary power distribution from the UPS to a PDU. A Rack Power Module (RPM) can be hardwired, delivers high power (36 kW), provides metering and monitoring, and has 12 poles of distribution breakers—essentially bringing the characteristics of a panelboard into a portable 3U box.
Secondary power distribution from a PDU or panelboard to IT equipment. Where one formerly had many long cable runs (home runs) from a panelboard to enclosures, the rack power module simplifies the cabling and makes it easier to track the power path when adding or changing IT equipment.
For either application, the modular approach has fewer cables to manage and greater flexibility, both for changing the IT equipment and the distribution system that powers it.
As shown below in Figure 2, modern enclosure-based PDUs can be installed in many locations and removed and redeployed as needed, making it easy to support moves, adds, and changes in IT systems.
The Challenge of Monitoring Modular Power Distribution
Data center managers could rightfully wonder if modular power distribution might be more difficult to monitor. After all, there will be dozens or even hundreds of ePDUs to track, compared to a few power distribution racks. In the past, managing all those rack-level power distribution devices has been problematic, for a couple of reasons:
- With older or very basic ePDUs, there is typically no visibility into current flow at this level. If an overload condition or tripped circuit were imminent, customers wouldn’t see it coming.
- With newer ePDUs networked over the company LAN, users typically have to point their Web browsers to each device to see its status—a time-consuming and tedious proposition.
Those compromises are no longer necessary. With the latest ePDU products and software, you can monitor and manage network-connected power distribution components at the rack level via one Web-based user interface and one IP address. Straightforward and budget-friendly software is available to aggregate power data from a virtually unlimited number of ePDUs and UPSs on an IP network into a cohesive, enterprise-wide view. Going modular doesn’t have to compromise visibility; in fact, it extends visibility further to the edge of the distribution system.
What to Look for in Modular Power Distribution
- Compact size, such as 3U for a rack power module, 1U, or 2U for an enclosure-based PDU
- Ability to mount the device anywhere, not just in one vendor’s rack or a specified slot
- Installation options that conserve valuable U space and support easy cable management
- Ability to easily move, redeploy, and swap out ePDUs without tools or an electrician
- Ability to install ePDUs horizontally or vertically, multiple units per rack
- Display of load currents for load balancing and protection during moves, adds, and changes
- Ability to monitor ePDUs over the network through IP communication
- Sufficient power capacity and receptacles to meet projected needs for 12–18 months
- Additional functionality, such as remote control or receptacle-level metering, if possible
When considering modularity—plan ahead. When evaluating components for the data center power infrastructure, look for the ability to support modular expansion and redeployment later. There may be some incremental additional investment—such as a parallel bus bar in an enclosure to support a modular UPS, for example—but once that initial setup is done, one just needs to purchase additional modules as needed, plug them in, and go.
There are more options than ever to capitalize on modular architectures to tailor the power system for your unique data center requirements and the velocity of change. As you plan to upgrade power systems or build a new facility, seek to create a power infrastructure that is as adaptable as the IT infrastructure.