Lighting can use up to 30 percent of electricity in facilities, according to the U.S. Department of Energy. Light-emitting diodes (LEDs) offers opportunities for greater system efficiency, design, aesthetics, operations, and maintenance. Adopting building-level DC power-distribution microgrids as part of the building infrastructure can benefit these areas.
For example, at the luminaire level, locally available DC power eliminates the need for a power supply to convert AC line voltage for use by LED devices, resulting in lower conversion loss and improved efficiency at the fixture of up to 15 percent. Multiply these improvements by the number of lighting fixtures and other electronic devices in a building, and the savings add up quickly.
As luck would have it, many of the electronic components eliminated in that front-end conversion are responsible for limiting the life of LED systems. In most cases, it is not the LED that fails in the system but the power supply or other electronic components responsible for converting AC power to DC power and controlling power quality and performance. So another bonus is improved overall system reliability.
From a building operation and maintenance perspective, the benefits of DC power grids go beyond decreasing energy use to include reduced labor costs and fewer facility interruptions. While the backbone distribution is done with higher voltage — Class 1 wired — AC or DC power, the final distribution is accomplished with isolated Class 2 wired and powered grid or wiring bringing 24-volt DC power throughout the occupied space. This makes several safety and maintenance practices much easier.
When technicians need to change modular walls, furniture or even just traffic patterns in an area, a modification in the lighting design often comes with it. These modifications typically require significant rewiring or new circuits and recommissioning of control systems. The process can include shutting off circuits and providing temporary lighting while the system is reconfigured.
But with a DC power grid, safe, low-voltage, hot-pluggable buses already are distributed throughout the space. Particularly in facilities using wireless control systems, the only required tasks are a physical reconfiguration of fixtures and possible software reprogramming.
Electricians can add or upgrade fixtures easily without new wiring, since power comes from the electrified ceiling grid already in place. At this low voltage, the power level is so-called touch-safe, so electricians can relocate luminaires without the need to shut down the circuit, a technique often called hot-swapping.
If the task is troubleshooting or repairing one fixture, safe and more efficient maintenance can take place without disrupting operations. Electricians can temporarily remove or swap out faulty fixtures and repair them at a remote site when convenient. They can be de-bugged while powered up on the bench in most cases, because the input power is touch-safe Class 2 — less than 100 volt-ampere at 24 volts DC. This benefit means electricians do not have to perform such maintenance while on a ladder, which can be awkward and unsafe.
Brian T. Patterson is the chairman of the EMerge Alliance. Patterson's extensive technical and work history in electronics, fiber optics and building technologies has resulted in his holding many patents in those fields. He is also the general manager of business development for the building products division of Armstrong World Industries, a founding member of the alliance.
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