Today's commercial buildings use between 30 and 50 percent of all AC electricity produced, transmitted, and distributed by centralized public and private utilities in the United States. These same buildings use a majority of the digital electronic devices that inherently run on DC electricity. As a result, much of the supplied AC power must be converted to DC at the device level to run such equipment as electronic ballasts, LEDs, lighting sensors and controls, HVAC controls, variable frequency drives, and actuators, not to mention computers and other IT equipment found in buildings. Moreover, the increasing amount of DC power natively generated from renewable and alternative energy sources, such as solar, wind, and fuel cells, also must be converted to AC electricity and synchronized to be compatible with existing AC distribution methods. But it is possible to use DC power without replacing the entire AC infrastructure.
"These conversions, in both directions, result in significant losses of electricity and associated wasted energy," notes Brian Patterson, chairman of the EMerge Alliance, an open industry association that is developing standards aimed at the rapid adoption of DC power distribution in commercial buildings. "They also add to the equipment and system's complexity and reduce the reliability of the overall electrical system."
DC power systems enable the use of simpler devices that don't have internal, electronic AC-DC and DC-AC converters, Patterson notes. These devices can be more reliable, portable, reusable, and individually addressable, and they can be reconfigured as quickly as a building's occupants' needs change. What's more, direct connection (without inverters) to one or more on-site DC alternative power sources can reduce energy costs and improve a building's environmental footprint, he says.
While incorporating a DC power platform into building infrastructure sounds simple enough, a significant obstacle to wider use of safe DC power in workplaces, data centers, and other commercial and institutional spaces is the frequently expressed misperception that a building would have to replace its entire AC power distribution system with a DC system. The reality is that hybrid AC-DC systems can offer many advantages for commercial facilities, particularly LEED and GridSTAR Net Zero energy buildings. "We believe that increasing demand for improved reliability and energy efficiency across all areas of commercial buildings provides the need for our broad, but modular, platform," Patterson says.
The hybrid system uses both AC and DC power sources to improve efficiencies, powering DC devices with DC power and legacy AC devices with AC power. Both portions of the system are typically interconnected at the distributed power source level. The DC portion is generally not redundant with the core AC system.
The more efficient conversion of AC power to DC — and the optional connection to native DC power from alternative energy sources — is done in bulk for all devices in a defined local area microgrid where a traditional AC system would normally be branched to circuits that feed individual electrical devices, such as light fixtures.
"EMerge is focused on eliminating many of the device-level conversions and aggregating them up at a higher level to improve efficiency, flexibility, and reliability," Patterson explains. "AC and DC systems can either co-exist and operate independently in the same space, or they can be interconnected, interoperatively providing the right form of power — AC or DC — for the loads."
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