High Voltage DC Systems for Data Centers Cut Power Use

February 11, 2008 Timothy Prickett Morgan

If you are running out of power and cooling in your data center and that is limiting your ability to add servers and storage for your company to support growing workloads, or if you are just simply tired of wasting energy, then Validus DC Systems wants to talk to you. The Brookfield, Connecticut, company has created a hybrid AC-DC power system for data centers that can cut energy consumption by as much as 40 percent, basically by eliminating AC power inside the data center and by running server and storage supplies at a higher DC voltage.

That sounds easy enough, but there is a lot of history of using AC power inside data centers and it takes a little retooling to make the shift to DC power. But that shift and the money it will save companies is the business that Rudy Kraus, founder and chief executive officer at Validus DC, is banking on. Validus was founded in 2002 and up until December 2007, when the company received $10 million in venture capital from Oak Hill Venture Partners, it was funded out of $4 million of private equity kicked in by Kraus through Data Support Associates, another company that Kraus co-founded. The company’s power systems are based on research done by Marcel Gaudreau, the former head of the Plasma Science and Fusion Center at the Massachusetts Institute of Technology.

“This is a system, it is not just a product,” explains Kraus, and that is probably the hardest message that his company has to convey to prospective customers. Like many of us who deal with servers and storage every day, and the heat they generate, the cooling they require, and the funds they burn up for all of that electricity, Kraus believes that AC power has no place in the data center–much as it has not ever had a place in the telecommunications equipment used throughout the world, which runs on DC. While AC power is wonderful in that it allows electricity to be transmitted over long distances and at very high voltages in relatively thin (and therefore relatively inexpensive) wires, considering that all of the equipment in a data center runs at 12 volts DC, it doesn’t make a lot of sense bringing AC inside the data center and then stepping it down a bunch of times and then converting it into DC power inside the power supply for a server or storage array. That, in a nutshell, is what Validus DC is all about.

Take a look at what happens in a typical data center to power a server today. Electric utilities bring high voltage lines running at 13.2 kilovolts AC to the outside of the data center. This power is stepped down to 480 volts AC by a transformer, which creates a bunch of heat in the process. Then, it goes into an uninterruptible power supply, which converts the AC to DC, runs it through a battery and some electronics to clean up the noise in the line, and then converts it back to 480 volts AC. After that, the electricity goes into a power distribution unit, stepping it down to 208 volts AC. Then it is run through a switched mode power supply, stepping it down to the 12 volts used inside the server itself. That’s a total of five conversion steps from the outside of the data center to the server or disk array, and the efficiency of the overall process, depending on the equipment, ranges from 40 percent to 72 percent, according to Kraus.

Now contrast this with the Validus DC hybrid power system. Power comes to the data center, just like before, at 13.2 kilovolts AC, and instead of going through a transformer, it goes through a rectifier that steps down the voltage and converts it to 575 volts DC power. Then, these power lines are fed into a DC/DC converter, which steps it down to 48 volt DC, and power supplies within the servers and storage are converted to accept this 48 volt DC power as an input, instead of using 240 volt or 120 volt AC lines. The resulting system has only two conversions and provides somewhere between 80 percent and 86 percent efficiency. And those 48 volt DC power supplies, which are used in the telco space, only have a nominal 10 percent premium at low manufacturing volumes and would be essentially the same price as 120 volt AC power supplies.

So here is how the Validus DC hybrid power system pans out in a real-world scenario. Take a big data center, with enough space to house 2,500 servers. That would require 2,777 square feet of data center, including space for nine CRAC units (eight for power and cooling, one for redundancy); such a setup would burn about 755 kilowatts of power, according to Kraus. Now, move over to a DC power system from Validus married to DC-powered servers from Rackable Systems. Because there is a lot less electricity transformation going on, you only need five CRAC units (with a sixth for redundancy). The Rackable designs also allow you to pack the servers tighter together because they don’t throw off as much heat, so you can put the same 2,500 servers into a 1,400 square foot data center, and you only burn 410 kilowatts to power and cool the servers. The energy savings alone–forget the cost of the CRAC units or the data center floor space–works out to over half a million dollars per year.

On a total cost of ownership basis spanning five years to power those 2,500 hypothetical servers, Kraus reckons that the DC equipment will cost only a nominal amount more than the AC systems (about $2 million), but operating costs for the AC system will come in at $19.3 million compared to $12.4 million for the DC system; overall costs including power and cooling equipment, maintenance, and operating costs are significantly higher for the AC way of doing things, at $21.6 million over five years compared to $14.6 million for the DC approach that Validus has engineered. Those numbers are just for single power lines. If you want fully redundant, fault tolerant power feeds, then the difference between AC, at $33.8 million over five years, compared to DC, at $17 million, is jaw-dropping.

There is just no question that, with numbers like these, Validus DC is going to be getting some calls now that its hybrid AC-DC power systems are generally available.

Validus DC also announced that it has inked at deal with Siemens Energy and Automation, to provide global support and services for the hybrid power system. The deal calls for Siemens to provide support in 69 countries from nearly 300 locations.

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