Ever since George Westinghouse and Nikola Tesla won their "battle of the currents" against Thomas Edison in the late 1800s, electricity generation and distribution systems from the power plant to the end user have been built around alternating current (AC) instead of the kind Edison favored – direct current (DC).

Now an alliance that includes lighting and electronic controls manufacturers, construction firms and building materials makers are pushing a renaissance for Edison's current of choice.

"What we're doing is devising a hybrid layer in the building that can use low-voltage direct current," said Brian Patterson, chairman of the EMerge Alliance.

The idea is that an electrified ceiling – and maybe walls and floors, or even furniture-powering a shifting array of lighting, audio, and sensor and security equipment without the need for re-wiring, he said.

"We're not going to eliminate AC in the building, we're going to complement it with DC –and we can do it very safely and inexpensively by doing it in low voltage," he said. The type of power EMerge is looking at – Class 2 as defined by the National Electric Code, a North American standard – is so low that you couldn't feel it, unless you touched your tongue to the ceiling, he said.

While AC has huge advantages over DC for transmitting power, Patterson said, many of the devices in use in buildings today have to convert it into direct current, with resulting efficiency losses, he noted. The common example is a computer, with its AC-to-DC adapter that gets warm as power is converted to heat – lost in the conversion process.

But lots of other gear used in buildings need direct current, including many types of lighting, he said. Electronic ballasts, which control current for some fluorescent and high-intensity lights, use direct current, as do light-emitting diodes, or LEDs, he said.

The alliance is working on standards for a low-voltage DC system that could "open up a whole wave of cost savings, improved sustainability and a whole level of flexibility with a plug and play mentality," he said.

Patterson is general manager of business development for the building products division of Armstrong World Industries, a major maker of interior ceilings and floors, walls and cabinets with net sales of $3.5 billion last year. Armstrong is also a founding member of the EMerge Alliance.

Other EMerge founding members include Johnson Controls, which makes HVAC, security and building management systems; Nextek Power Systems, which makes DC power systems for buildings; Osram Sylvania, which makes lighting systems; and WAVE, a joint venture of Armstrong and steel products maker Worthington Industries, which makes ceiling suspension systems.

Other participants include Webcor, a major California construction company, and the utility Southern California Edison. So is microplasma lighting startup Eden Park Illumination. Eden Park is looking to office ceiling tiles as a first market for its microplasma lights, which can be made of glass or flexible material that sandwiches n aluminum mesh with tiny cavities filled with phosphors, which illuminate when a current is passed through them.

Investments into ways to make lighting more efficient and functional has been on the rise, with light-emitting diode, or LED, startups getting a lot of attention from venture capital firms and large lighting companies alike (see Lighting the Way to Efficiency).

But that also means that new types of lighting systems are more likely to become more obsolete more quickly, as new technologies supplant the old, Patterson said – yet another reason to seek to make switching them out as cheap and easy as possible.

Of course, any building-wide, low-voltage DC system will also have to deal with the efficiency losses of converting AC grid power, Patterson said. Still, building-scale conversion will be more efficient than converting power on an item-to-item basis, he said.

Then there are renewable energy sources to consider, he said. Solar photovoltaic systems and fuel cells, for example, provide DC power that has to be converted to AC via an inverter to be integrated into the electricity grid or building power systems connected to it.

Using that power as direct current without conversion, however, means "you can get a pretty big pick-up, sometimes on the order of 30 percent," compared to the efficiency losses involved in converting renewable-generated to AC, and then sometimes back to DC again, he said.

EMerge's electrified ceiling concept is being tested in several facilities around the country, Patterson said, though he wouldn't say where.

But the concept has the support of Clark Gellings, vice president of technology for the Electric Power Research Institute. In fact, Gellings said he's been promoting the idea for years.

"The majority of appliances and devices around us have, somewhere at the core of their operation, direct current," he said. Efficiency gains, while yet unproven, could be particularly good for devices he calls "PV-DC," or devices made to run on direct current directly fromsolarphotovoltaic systems.

Using DC in buildings does present some safety issues that will have to be dealt with through new equipment, Gellings said. Still, "we probably have the technolgoy, the components and the smarts. We just haven't done it yet."

EMerge's Patterson says that a key early target market will be buildings that incorporate renewable energy generation, given the efficiency advantages that low-voltage DC systems could provide them.

Given that buildings account for about two-fifths of the nation's energy usage, making them "greener" by incorporating energy efficiency or renewable energy technology into them is a field that's seen growing interest from investors (see Green Building: Cheaper Than You Thought).

Retail and office buildings as well as schools will be other early target markets, since they're likely to see more "churn" in switching lighting and other electrical equipment to suit changing needs, he said. Using low-voltage DC could cut the mechanical and electrical plumbing costs of those conversions by a third to a half, he said.

EMerge is aiming to have a set of standards for low-voltage DC systems in place by early 2009, and Patterson said devices made to utilize it could be on the market by the middle of next year.

As far as barriers to EMerge's goals, "I would say the skepticism is borne out of the fact that the building industry in general is a slow to change industry," he said. "Like all good things, this will have to stand the test of time."