Improve energy efficiency, reduce power consumption, lower
energy costs
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Efficient Data Center Power Configurations
Many data centers predate the industry’s focus on
efficient technologies. From design through
technology selection and installation, initial costs
and uptime were the focal points because power was
not a major expense or energy availability a
consideration. Concerns about costs related to power
consumption and the impact of the data center on the
environment had not entered the corporate
consciousness.
Today, energy is an issue, a big issue. US data centers
consumed 61 billion kWh of electricity in 2006, while an
estimated 70% of the electricity in the U.S. is generated by
fossil fuels. The economic and environmental consequences
render some legacy data center designs irrelevant and
wasteful. The legacy 480V—208V power distribution
architecture is a prime example. The components (UPS, PDU,
and server power supply) are older and lose roughly 40% of
the incoming electricity during transformation and
distribution.
In its defense, this power distribution approach was
designed with a minimal power envelope in mind. Its
inefficiencies are amplified in the context of high density
installations, where rack loads can conceivably eclipse
30kW.
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UPS Double Conversion
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Isolated PDU
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Isolated PSU
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Server
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Improved AC Power Distribution
Data centers can no longer afford to waste 40% of incoming
electricity. For this reason, they are investigating new power
technologies and distribution designs. Modern architectures
achieve overall efficiencies between 80-90%; according to the
Green Grid, a 4% difference exists between the most and least
efficient. In addition, performance curves for newer equipment
are steeper and better sustained across the loading curve, making
them significantly superior at lighter loads. ]
Here are some AC Distribution schemes:
480V—208V Power Distribution (Present Day)
The present day 480V—208V distribution design is the same as
its predecessor, except it uses the highest efficiency components
on the market today. The overall efficiency, depending on the
load, ranges, between 80%-85%, a significant improvement over
the legacy design.
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UPS (Double Conversion or Line
Interactive)
ENHANCED
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Isolated PDU
ENHANCED
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Isolated PSU
ENHANCED
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Server
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600V—208V Power Distribution
600V-208V is most commonly used in Canada and closely resembles
the present day 480V-208V design. The only difference is the
higher input voltage into the UPS.
The overall efficiency of the design ranges also between
80-85%.
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UPS (Double Conversion or Line
Interactive)
ENHANCED
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Isolated PDU
ENHANCED
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Isolated PSU
ENHANCED
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Server
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480V/277V Power Distribution
This power scheme distributes electricity in a three-phase Wye
configuration at 277V—the phase to neutral voltage in 480V 3
phase power. Instead of stepping down to 208V, the voltage remains
constant through the PDU, improving the efficiency of design.
This power distribution scheme achieves efficiencies between
85-90% depending on the load and is considered the US equivalent
of 400/230V and 415/240V, though currently server power supplies
are not readily available to accept 277V.
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UPS (Double Conversion or Line
Interactive)
ENHANCED
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PDU
ENHANCED
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Isolated PSU
ENHANCED
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Server
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415V/240V Power Distribution
This design is typically employed outside the United States.
Since most US facilities have 480/277V available, they would
have to convert to 415V at the UPS level.
This scheme is another high efficiency approach, achieving
85-90% efficiency based on the load.
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UPS (Double Conversion or Line
Interactive)
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Isolated PDU
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Isolated PSU
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Server
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DC Power Distribution
The last few years have seen a renewed interest in distributing
Direct Current (DC) power throughout the data center. There
are multiple points, including the UPS and server power supplies,
where incoming AC power is converted to DC. Losses occur during
each conversion, the severity of which depends on the equipment.
Proponents see DC power distribution as a way to minimize electrical
losses, thus achieving a more efficient design.
Here are some of the DC Power Distribution Schemes:
480Vac to 48Vdc Power Distribution
The 48Vdc power distribution design is most common in telecom
deployments. It achieves efficiencies of 85%-90% based on the
load.
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Isolated Double Conversion UPS
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Isolated PDU
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Isolated PSU
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Server
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480Vac-575Vdc-48Vdc Power Distribution
This design distributes 575Vdc power from the UPS to minimize
distribution cabling losses and cost. The efficiency levels,
like most of the other present-day designs, ranges from 80%
to 85% depending on the load.
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Isolated Double Conversion UPS
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Isolated DC/DC Step Down
Converter
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Isolated PSU
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Server
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480Vac—380Vdc Power Distribution
This design distributes 380Vdc to the server power supply, achieving
greater efficiency and minimizing losses in the distribution
cabling. It achieves 90% at 30-50% of capacity with the overall
efficiency decreasing slightly as the load nears full capacity
380Vdc has been widely discussed in the industry. Mark Monroe,
Sun Microsystems’ Director of Sustainable Computing, had this
to say on the topic: “So we decided to run the datacenter at
380 volts of DC power. Now, DC power is more dangerous than
AC power, so there are safety issues, and we had a hard time
finding electricians to hook up the 380 volt DC power”
If Sun had difficulty finding qualified electricians, it’s
reasonable to assume that the majority of data center professionals
don’t have a background in 380Vdc. The lack of trained personnel
could present a safety issue for those working with the power
components
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Isolated Double Conversion UPS
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PDU
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Isolated PSU
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Server
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Conclusions
New, enhanced technologies are available that improve efficiencies
in power distribution. The latest UPS systems and PDUs achieve
efficiencies in the high nineties, while some server power supplies
have reached or exceeded the ninetieth percentile.
These best-of-breed technologies, however, may be in stark
contrast to the equipment already within a data center. In a
2008 whitepaper, Lawrence Berkley National Labs estimates “a
typical AC system in today’s data center would have a UPS that
was about 85% efficient, and power supplies around 73% efficient.”
For these existing data centers, the question remains: In terms
of complexity and cost, how feasible is it for a legacy data
center to employ next generation power distribution?
The simplest exercise would involve a hardware refresh. If
an organization, due to tax incentives or corporate protocol,
refreshes its hardware every 3-5 years, the latest server products
may be shipped with highly efficient power supplies. If the
LBNL projections are correct, the improved power supplies would
have a noticeable impact on the overall power distribution efficiency.
DC distribution, the subject of the LBNL whitepaper, seems
most suited for new or specialty data center applications. Though
the most efficient of the designs we discuss above, a wholesale
change to DC distribution is impractical for an existing data
center. And before DC power distribution would even be viable
for a new facility, especially the highly efficient 380Vdc design,
the market must support it. There are no rack power distribution
products or server manufactures that support 380Vdc power (though
some are available at 48Vdc telecom voltage).
One of the Top 10 recommendations of Data Center Pulse, an
end user group, asked for server power supplies to support 277Vac,
which would eliminate the intermediate transformer loss between
the UPS and the load. 277V is the phase to neutral voltage of
480V 3 phase power. In addition, a prominent power/cooling manufacturer
believes worldwide standard 400/230Vac would rival the best
DC design in efficiency and would be far less complex to operate.
The lesson learned is that any improvement to components
in a conventional 480—208Vac design results in greater efficiency.
A running change to the power distribution scheme, however,
may be impractical for an existing facility due to complexity
and the risk and cost of prolonged downtime. A green field data
center is well poised to take advantage of the latest product
advances and architectures.
How much can your organization save by
having a more energy efficient Data Center?
Having a very efficient data center will certainly yield
very dramatic costs savings, but even modest improvements in
efficiency can significantly reduce your power consumption
and consequently your energy related costs. Try our
Interactive
data center efficiency
calculator and track how slight improvements can have a
substantial payback!
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Bibliography
Lawrence Berkeley National Labs. (2008). DC Power for
Improved Data Center Efficiency. Berkeley: Lawrence Berkeley
National Labs.
Rassmussen, N. (2007). AC vs DC Power Distribution for
Data Centers. Retrieved March 2, 2009, from APC Corporate
Site:
http://www.apcmedia.com/salestools/SADE-5TNRLG_R5_EN.pdf
Sun Microsystems. (2007, March). Sun Microsystems is Building
Energy Efficient Data Centers. Retrieved March 23, 2009,
from Sun Microsystems:
http://www.sun.com/emrkt/innercircle/newsletter/0307sponsor.html
The Green Grid. (2008, December 1). Quantitative Efficiency
Analysis of Power Distribution Configurations for Data Centers.
Retrieved March 10, 2009, from The Green Grid:
http://www.thegreengrid.org/Global/Content/white-papers/Quantitative-Efficiency-Analysis
About 42U
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