Guest post by Jim Brodrick, U.S. Department of Energy
There’s a great deal of interest these days in occupancy sensors as a way to save energy in outdoor commercial lighting applications. Done right, they can increase the energy savings from a lighting system that’s already efficient – such as one based on LEDs, whose inherent controllability makes them especially suited to sensors. That’s why, already, a number of regulatory and utility efforts (e.g., ANSI/ASHRAE/IESNA Standard 90.1-2010, California’s Title 24, and Illinois ComEd’s Smart Ideas program) are encouraging their use in parking lots and garages – which means we’re likely to be seeing lots of installations in the very near future.
But because occupancy sensors are still relatively new to the outdoor lighting market, “doing them right” is not always a simple matter. And if they’re done wrong, their potential energy savings drain away into the sand. To help ensure that this doesn’t happen, DOE has come out with a new GATEWAY report, Use of Occupancy Sensors in LED Parking Lot and Garage Applications: Early Experiences. It describes the results at four sites – two parking lots and two parking garages – where LED lighting was controlled by occupancy sensors.
The additional energy savings obtained from the use of the sensors – that is, the savings beyond what resulted from converting to SSL from the incumbent technology – spanned the spectrum in terms of success, ranging from 76 percent at one location to no additional savings at another location. Why such disparate results? They were due to a variety of issues encountered across the four sites, which dragged down the performance of the sensors – most of which did fairly well but could have done even better.
Some of these issues may have been caused by using components that had not been specifically designed for the application at hand; for example, up till now most occupancy sensors haven’t been designed for fully exposed outdoor installations, because the incumbent lighting technologies aren’t that compatible with dimming or frequent cycling. Others stemmed from shortcomings in product design or problems with manufacturing quality control. Still others resulted when the equipment wasn’t appropriately paired with the needs of the application or wasn’t properly integrated with the operating environment. Then there was the question of whether or not the system was ever thoroughly commissioned (i.e., “test-driven” to make sure it was working properly) following installation, and whether it was optimized for the application.
This early in the game, it’s not surprising that there are some growing pains and lessons learned accompanying the use of occupancy sensors. Because user characteristics and ambient environments can differ widely from site to site, the greatest success from the use of occupancy sensors may come from designing equipment and deployment strategies for the particular application at hand – and perhaps even from customizing on site, in terms of operation.
When it’s done right, combining occupancy detection and bi-level dimming systems with efficient exterior lighting can significantly increase the energy savings achieved. But in order to maximize performance and minimize user inconvenience and negative effects, prospective buyers should be sure to select the equipment carefully and consider how it will be integrated into a coordinated system.
It’s also important to keep in mind that potential energy and cost savings have their limits, and that different approaches to achieving those savings often compete with one another. For example, a control system that’s set up to turn the lights off completely is capturing 100 percent of the possible energy savings while those lights are off – regardless of the efficiency of the light source. Whether such an approach makes sense depends on the characteristics of the particular installation.
At this early stage, simply installing occupancy sensors in parking lots and garages doesn’t guarantee you’ll get energy savings, or that the energy savings you do get will be worth the initial cost. But the potential is there, waiting to be tapped by those who are willing to do their homework. The four installations covered in the new GATEWAY report can teach us a lot about how to avoid the pitfalls and get the full benefits of this promising technology.