What's Happening from Environmental Building News
A Surge of Popularity for Efficient DC Power
In a digital world, why are we still using analog power? That’s the question posed by Brian Patterson, general manager of business development for Armstrong Ceilings and chairman of EMerge Alliance, an industry association that is trying to change the way power is distributed. EMerge promotes the idea that a long-term switch from alternating current (AC) to direct current (DC) for power distribution is crucial to our energy future. EMerge, which includes a variety of members, from Johnson Controls to Herman Miller to Underwriters Laboratories, has started the ball rolling by developing standards for “microgrids” in commercial buildings that allow hybridized use of AC and DC.
In the 1890s a power struggle between Thomas Edison and Nikola Tesla—known as “the war of the currents”—resulted in a standard AC grid. At that time, AC was the better choice, because no one had the technology to efficiently transmit DC power over long distances. Edison stood to make a great deal of money building a large number of small DC power plants, but rural electrification would have been impossible without AC.
Now things have changed. Not only can we transmit DC power at high voltages over long distances, says Patterson, but also many devices at the end of the line are native users of DC. In general, any device with a transistor, silicon chip, rechargeable battery, or diode—which includes almost all electronics, electric cars, LEDs, and even some variable-speed motors—runs on DC current. You don’t always see the
rectifier that converts AC power from the wall outlet to the DC power used by your device, but if you have a laptop, it’s the brick on your power cord. That brick gets hot while your laptop is plugged in because of all the energy wasted when the AC current is rectified: that
conversion loss is at the heart of the trouble with AC current. What’s worse, Patterson says, is that most of our renewable power sources generate DC current, and it is transmitted in that form from solar arrays and wind farms, only to be converted to AC on the grid and then back to DC in our devices.
Worst of all are data centers. They buy AC grid power, convert it to DC for the uninterruptible power supply device, convert it back to AC to go through the wires, and then back to DC again for use by each and every server. Intel, among others, has been researching the energy benefits of DC microgrids for data centers for five years now, and research scientist Guy AlLee told
EBN that Intel’s pilot data center using 380V DC power has realized 7%–8% better energy efficiency than the highest-efficiency data centers running on AC power. Other advantages include 15% savings on capital costs, 33% space savings, and 200% reliability improvement, resulting in large short- and long-term cost savings.
That 200% average reliability improve-ment—meaning the device lasts twice as long—applies to LED fixtures also, according to Patterson, because the electronics are simpler and run cooler when the power does not need to be rectified in the device. Intel has converted half of the lights in one of its office buildings to LEDs running on 24V DC current. AlLee said pre-liminary results suggest that the LEDs perform at least twice as well as T8 fluorescents running on AC. With additional sensors, he said, they are anticipating a possible 75% energy savings over the lights in the other half of the building.
DC microgrids are new, and users are helping work out the kinks with pilot projects like these. Keith Pehl, president of Optima Engineering in Charlotte, North Carolina, loves the results of connecting a DC microgrid to his building’s PV array. One major advantage, Pehl told
EBN, is that the low voltage makes the lighting completely flexible; the “plug-and-play” light systems can be safely moved from place to place without hiring an electrician or cutting the power—perfect for retail spaces, museums, or other buildings that need to move lighting around frequently.
Pehl sees one drawback to using PV to run his lights, though. “It works really well, but peak power production is when you need lights the least”—especially in Optima’s LEED Platinum building, which incorporates daylighting. Pehl has recommended DC lighting to a few clients in the last couple of months, but none have chosen it so far. Pehl expects the rapid expansion of cheaper LED lighting options to make DC micro-grids more popular in commercial buildings.
“I think this field is the next big thing,” AlLee said. “It feels like the transition from telephones to the Internet.” AlLee said that DC power distribution is “readily deployed in the third world,” but he also believes that the legacy infrastructure in North America will gradually switch back to DC.
– Paula Melton
May 1, 2011
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Photo: Armstrong Ceilings
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Source: EMerge Alliance
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