Paper: Reviving the War of Currents

Opportunities to Save Energy with DC Distribution in Commercial Buildings

Distributed-generation resources and many of the electrical loads in today’s buildings fundamentally produce and consume direct current (DC). The solution for decades has been for each device to convert alternating current (AC) into low-voltage DC through power supplies, lighting ballasts, and motor drives. Our estimates show that today’s commercial office buildings lose about 13 percent of their electricity every year simply distributing and converting power from the utility meter down to the point where it can power equipment. The loss is even higher for high-performance designs, like zero net energy (ZNE), which possess additional power-conversion stages for on-site generation, such as photovoltaics (PV).

We examine an alternative approach: DC distribution “islands” within commercial buildings that eliminate the need for repetitive power-conversion steps. We summarize the state of the industry-led effort for DC distribution, including current technology, demonstration projects, cost-effectiveness, and ancillary benefits. Significant market barriers to implementation exist, for example, the trades have little to no experience with DC, and there are few DC-powered products available today. With these barriers, tapping into the energy savings will not be easy. However, the best opportunity exists in ZNE commercial office buildings where designers can leverage synergies between DC loads and PV power generation. In ZNE commercial office buildings, we estimate that the elimination of redundant conversion steps and smaller, less-efficient power conversion devices could shave building electric consumption by as much as 8 percent.

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