DC Power Could Reduce DataCenter Energy Use by 20% While Improving Reliability

Researchers at the U. S. Dept. of Energy’s Lawrence Berkeley National Laboratory have teamed with Silicon Valley giants, including Sun Microsystems, Intel, Cisco and others, to demonstrate technologies that could save billions of dollars a year in the energy costs of operating data centers, as well as improve reliability and lengthen equipment life. A demonstration project is taking place this summer at a test facility at Sun Microsystems in Newark, Calif., with more than 20 high-technology companies participating.

Eliminating power conversion losses by using direct current (DC) instead of alternating current (AC) from the utility grid for electricity throughout a data center can trim its energy needs by 10% to 20% and improve reliability. Preliminary measurements from the demonstration center in Newark support this estimate.

Researchers in Berkeley Lab’s Environmental Energy Technologies Division

(EETD) proposed this technology demonstration, and the California Energy Commission’s Public Interest Energy Research (PIER) program sponsored the work.

The Berkeley Lab team, which consists of project leader William Tschudi, Steve Greenberg and Evan Mills, conceived the project and provided oversight for the demonstration’s planning and design, which is being executed by private-sector firms ECOS Consulting and EPRI Solutions under a contract with Berkeley Lab. The partner companies have provided technical advice, equipment and staff to set up the demonstration facility.

“[Data centers] can use 100 times the electricity of a typical office building on a square-foot basis,” says Tschudi. “Energy costs of $1 million per month are not uncommon in large data centers that require megawatts of electricity.”

“We’re excited to be able to demonstrate and evaluate the efficiency merits of two different data center DC power-delivery approaches and expect our results can inform data center operators, facility designers and this global industry regarding efficient options for future designs,” says My Ton of ECOS Consulting.

A number of strategies can be used by designers and managers of these facilities to decrease their power needs, such as optimizing airflows to get the most out of the cooling system, upgrading the energy efficiency of the cooling system or moving to liquid cooling, and facilities managers are increasingly implementing them.

DC power offers a complementary strategy for improving energy efficiency. In the typical data center, the power-distribution system provides 480-volt AC power to a transformer, which then steps it down to 208-volt AC to feed racks of servers.

Individual power supplies—typically, these are redundant—within each server convert this into a voltage appropriate for the unit’s needs. These individual supplies are often inefficient, generating substantial heat, which the room’s air-conditioning system must remove at great expense. Waste heat can also impose limits on the number of servers that can be housed in a data center and jeopardizes reliability if not handled properly.

Some servers on the market can run on DC power—typically at 48 volts DC, which is the standard in the telecommunications industry. The demonstration shows how a DC-powered data center could skip the conversion from 480 to 208 volts and provide DC power directly to the servers. The demonstration DC center converts high-voltage AC directly into high-voltage DC power and then steps down the high-voltage DC power to low-voltage within the IT equipment. By skipping or consolidating conversion steps, this approach can save as much as 20% of electricity usage overall.

However, substituting DC power in data centers as a replacement for conventional AC power has not yet made significant inroads into many data centers because the technology is unfamiliar to many facilities engineers. There is reluctance within the industry to switch to new technologies without field experience showing that the switch could be done safely and would have operational and economic benefits, without causing unanticipated problems

This project is actually two demonstrations. One shows off a DC architecture at a facility level, distributing 380 volts DC, and the other is a rack-level implementation of DC power supplied at 380 volts within the rack.

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