Is DC Power the Future of Data Center Design?

June 11, 2015 / by Benjamin Petschke

Improving data center efficiency continues to be the foremost issue in the industry, whether you are designing a new mission critical facility or optimizing your existing one. Now that huge increases in efficiency have been achieved in the air conditioning sector in the recent years, another sector, the power supply and distribution from the grid to the chip, is becoming the focus of the industry. There is enormous potential for increased efficiency by reducing losses through conversion, transformation and distribution. The transition from AC power supply to 380 VDC offers several significant advantages.


Today’s AC architecture is usually as follows:
  • 16.000 VAC from the grid into the building
  • Transformation to 480 VAC
  • Conversion to DC in the UPS for battery feed
  • Inversion to AC
  • Conversion to 480 VDC in the server power supply unit (PSU)
  • Transformation to 12 VDC in the PSU
The 380 VDC architecture is less complex:
  • 16.000 VAC from the grid into the building
  • Transformation to 380 VAC
  • Conversion to 380 VDC
  • Transformation to 12 VDC in the PSU
Advantages of 380 VDC power supply:
  • Increased efficiency from the grid to the chip: up to 10%
  • Reduction of investment cost for the electrical infrastructure: approx. 15%
  • Space requirement for the electrical infrastructure: approx. 25% lower
  • Installation costs: approx. 20% lower
  • Operating and maintenance costs reduced by up to 30%
  • Greater reliability through reduced complexity as fewer components are used. NTT research results show a tenfold increase in reliability.
  • Simplification of the integration of renewable resources such as photovoltaic, wind, fuel cells and other DC consumers and energy storage systems.
  • DC increases the power quality, no more problems with harmonic distortion. Phase correction is no longer necessary.
  • No need for synchronization to connect multiple sources.
  • No need for rectifiers or inverters for connecting batteries to the grid.
  • …and many more…
There have been attempts to use the proven -48 VDC architecture that is used in the telecommunication industry, but this entailed too many disadvantages. For the same capacity the required current is eight times higher which increases the cost of cabling. This is not feasible for data center applications in the high kilowatt or megawatt range.   

There are several challenges to master, besides the obvious advantages:
  • Experience and expertise must gathered and shared
  • The availability of DC components is still very limited and therefore still expensive
  • There are safety concerns in handling DC, however various analyses are available, proving that the handling of DC is not more difficult or dangerous than AC
  • The use of a DC power supply requires holistic planning from the grid to the chip
  • Cooperation between component manufacturers, server manufacturers, designers and data center operators is required
  • Standards need to be defined and established

Currently, companies like NTT and ABB are bringing this topic into the spotlight. In addition, many other companies, component manufacturers and associations (the Green Grid, EMerge Alliance…) are working on establishing this technology. IBM and HP are already offering servers with DC power supply. NTT built their first test data center with -48 VDC in 2006, followed by another with 380 VDC power supply in 2007. ABB supplied the 380 VDC power supply and distribution systems for the 1 MW Green data center in Switzerland in 2012. Today, there are approx. 25 data centers with DC power supply throughout the world.  Most of them are test or demonstration data centers with a capacity between 4 kW and 100 kW. Publications from ABB, NTT, Intel, HP, The Green Grid and others on this subject can be found online (many of them have been used for this article).

Air conditioning systems for data centers with 380 VDC need to be adapted accordingly. STULZ Germany offers a wide range of perimeter and row chilled water cooling models for 380 VDC. STULZ air conditioners are already in operation in many 380 VDC powered test data centers in Europe. Chillers in the 100 kW to 1,5 MW range are most likely AC powered at this time, as the required compressors are not available for DC. The implementation of DX air conditioning units with small capacities is currently under review.




Lower investment, installation, operating and maintenance costs and smaller footprint.

Experience and expertise is not yet widespread.

The availability of DC components is still very limited and therefore still expensive.

Holistic planning is required.

Standards need to be defined and established.



Increased efficiency.

Increased reliability.

Simplified integration of renewable resources.

Better quality power.

Safety concerns in handling DC.



It is obvious that DC Power is on the horizon and STULZ is part of the solution from the very beginning.  STULZ USA is exploring DC power as well, recently deploying a DC row based chilled water unit.  Time will tell how fast direct current power supply will enter the data center market on a large scale but we expect to see significant progress in the next 5 to 10 years.

What do you think?  Is DC Power the future of data center design? Share your thoughts in the comments below.

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As the mission critical cooling experts, STULZ is ready to help you decide what the best solution is for your data center.

Topics: Data Center Design, Energy Efficiency

Benjamin Petschke

Written by Benjamin Petschke

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