Dimming Ballasts, Occupancy Sensors Can Reduce Costs
By Lindsay Audin January 2008 - Energy Efficiency
Upgrading the energy efficiency of lamps, ballasts and fixtures can cut lighting energy by more than 40 percent. So what’s left to cut by using controls? Possibly another 40 percent.
Leaving lights on when unneeded is one of the most common ways energy is wasted in buildings. In addition, controlling peak electric demand, either to minimize tariff charges or to earn incentives from a utility or grid operator, is becoming a raison d’être for controls all by itself. And there is always the possibility to replace some electric lighting with daylight through photoelectric dimming. Taken together, these options could cut lighting costs and energy use by another 20 to 40 percent.
Some of the same control equipment may be used in architectural dimming to set scenes for presentations or events, adding flexibility and value to many spaces. An ever-widening variety of controls exists to adjust, minimize or automatically shut off lighting. Getting the most out of these options — be they for architectural or energy efficiency purposes — requires a clear understanding of their benefits and pitfalls. While significant savings are possible by eliminating unnecessary lighting, such savings are not guaranteed. Careful specification and commissioning is essential to ensuring good results.
Major Pieces of the Puzzle
A quick look at a typical lighting control design may reveal:
- Dimmable ballasts, either continuous or step-dimming.
- Some form of occupancy sensing, or scheduling built around occupancy, such as timers.
- A panel-based automation system, which schedules lighting and its intensity, that is either part of the overall building management system or works in tandem with it.
More sophisticated systems may also involve photoelectric light sensors that adjust light levels based on ambient daylight and lumen depreciation.
Many facility executives have adopted controls in a piecemeal fashion, resulting in overlapping systems that don’t work well together. Occupancy sensors may act alone to shut off room lights, while selected fixtures may be dimmed or shut off through sweep or other centralized systems. Daylighting sensors may work through a third system to dim the same fixtures in areas having windows or skylights. While such a piecemeal approach is rarely optimal, it’s not surprising that it is common because the technologies and economies of these options have appeared and varied over time.
To simplify design and construction, cut installed costs and avoid operational problems, many lighting practitioners suggest a coordinated approach. Fortunately, a variety of computerized control systems are available that may be programmed to deal with the sophisticated routines required to handle multiple control schemes while working with many legacy controls. Most are compatible with major controls protocols, such as BACNet or LonMark, though capabilities vary widely.
Even as such centralized systems become more common, however, controls components, both stand alone and integrated, continue to evolve.
Switches and Sensors
Consider a series of switches that transmit a radio signal to a receiver. The receiver cycles power via a relay that controls either a particular fixture or a bank of fixtures. While battery-powered transmitters in wireless switches have been around for more than a decade, the new wireless technology requires no batteries or other power source. The trick is in the finger pressure applied to the switch; that energy is converted, via a piezoelectric crystal, into a small burst of power that runs the transmitter long enough to send a signal to the receivers. A lot of wiring and labor is avoided, and altering fixture and switch layouts may be a lot easier.
Demand/response switching may soon also be commercially available. A relay built into such a switch shuts off a portion of non-critical room lighting, and an LED on the switch plate lets occupants know that light levels have been temporarily lowered to cut peak demand. Communication to the relay may be by power-line carrier, wireless or other method. An unacceptable reduction may be manually overridden by cycling the switch.
The latest crop of occupancy sensors is yet another step above its predecessors. While both ultrasonic, infrared and combinations of them have been around for decades, software built into sensors is both more flexible and complex. Today’s occupancy sensors may provide many of the following options:
- The usual sensitivity and time-delay settings.
- An LED that shines whenever motion is detected.
- Manual on/off to override the sensor for a defined period.
- An adjustable light sensor to keep lights off if ambient light is sufficient.
- Ability to observe occupant motion patterns to “learn” right time delay and sensitivity.
- Choice of an audible warning several seconds before lights are about to shut off.
- “Smart” override that keeps lights on even when no motion is sensed, and off even when motion is sensed, within a defined period, such as for school tests and A/V events.
To comply with bi-level switching requirements, some units are equipped with a pair of small toggle switches that can keep 50 percent of lights off while the other 50 percent are switched by the sensor.
With regard to learning occupant motion patterns, sensors have improved since such auto-calibration technology first appeared around 1995. When confused or depowered, early models tended to conservatively default to the longest delay time (30 minutes) before working their way down to the right period, resulting in lost savings. More recent versions default to the shortest period (30 seconds) and then work their way up to the right delay interval.
One innovation that is being seen more often is integration of occupancy sensors with light fixtures. Bi-level stairwell fixtures containing sensors have been around for several years, dimming but never shutting off while stairwells are unoccupied. Now this option is showing up in other locations.
The advent of lower cost electronic ballasts for HID fixtures has led to bi-level warehouse, gymnasium and big box store lighting where fixtures may be dimmed approximately 50 percent, yielding considerable savings. Such lighting is often left on 24/7 due to its typically long warm-up time. The same is now being offered in parking lot lighting, with an additional level of sophistication involving communication between adjacent light poles.
Careful with Daylight
Displacing electric lighting with natural daylight holds the promise for significant savings, but success with this strategy is often elusive. Recent findings now confirm what had been mostly anecdotal concerns.
In 2007, Heschong Mahone, a lighting consulting firm, surveyed existing daylighting systems that use window light. In this study, only 25 percent of the sidelighting photoelectric controls were working properly, and 52 percent were not operating at all, apparently having been intentionally disabled due to occupant complaints, never having been commissioned, or because they were incompatible with an existing building management system.
Considering the expense of such systems, which may cost more per square foot than fully upgrading fixtures with new ballasts and lamps, end users may wish to involve an experienced daylighting consultant and require a performance bond.
Similar issues have arisen with regard to the Digital Addressable Lighting Interface (DALI) protocol, which allows electronic ballasts to be manipulated individually for maximum control under a variety of scenarios, including daylighting. While some have had great results with DALI in new construction, issues have risen when trying to retrofit existing facilities with this powerful technology. Insufficient commissioning has sometimes been its bane, with complaints of overall cost, complexity and maintenance also being heard.
While the management issues may require more experience and rigor when commissioning or handling details, installation costs may come down if the need for dedicated wiring can be avoided through wireless control methods.
While no final wireless DALI standard has been settled, several promising protocols, such as ZigBee, are being deployed to that end.
Before making decisions, facility executives should be clear about exactly how much more they are willing to pay for the last increment of control. Once fixtures have been upgraded, and occupancy sensors shut them off much of the time, the cost per kwh to save more may be greater. Trimming that last kwh may have a surprisingly long incremental payback.
Avoiding Common Missteps
As with any device that may involve programming, adjustment and maintenance, it’s important to accommodate the learning curves of the people who will be using and maintaining the controls. To ensure their longevity and continued successful operation, lighting controls must be easily understood by cleaning and maintenance personnel. Also, allow sufficient time and resources for proper commissioning, or controls may be damaged or disabled.
Even something as simple as a slide dimmer may require a bit of training. At one site where manual dimmers had a separate push button on/off control, cleaning personnel did not understand it and simply dimmed lighting to minimum when they were finished at night. At their lowest level, many dimming systems continue to pull 25 percent of full wattage, thus wasting a lot of power if left on overnight or during weekends. In another case, instead of adjusting daylight sensors to respond to a complaint, maintenance personnel lacking training simply taped over them, ensuring lights remained at full output all the time.
Getting all the components of such systems to work together may require careful attention to specifications. Several experienced lighting designers have pointed out, for example, that merely specifying installation of “dimming ballasts” and “dimmers” does not ensure their compatibility. The lowest cost two-wire ballast/dimmer combination may, for example, be unable to dim down to the level needed in all locations and may not work with daylight sensors unless an intermediate system is involved.
At electric supply stores, lighting controls are not yet as routinely available as lamps and ballasts. When some dimmers fail, or are about to, light levels may be limited or stuck at a low setting or else the lights may be shut off entirely, requiring immediate replacement of the control. If the right unit is not readily available, the likely result is replacement with a standard toggle switch. Maintaining savings and avoiding occupant complaints may therefore require stocking of exact replacement parts as part of a facility’s inventory. That task may be simplified by specifying that the installation contractor provide a few of each crucial device as part of the turnover of the job.
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Free Help is Available
Both industry and various energy-related agencies provide very helpful guidance on lighting controls.
The New Buildings Institute offers a good manual on lighting controls issues and options in chapter 8 of its Advanced Lighting Guidelines (circa 2004), which may be found on-line.
The Lighting Controls Association, a non-profit organization run by the National Electrical Manufacturers Association (NEMA), is dedicated to educating the professional lighting community about applying lighting controls. Its members include most of the major U.S. and foreign controls firms. LCA offers a free e-mailed newsletter on the latest technologies and findings. Back issues are available at its Web site, which is a great place to get up-to-speed on many lighting controls issues. It also offers online 24/7 short seminars covering many aspects of lighting controls.
— Lindsay Audin
Lindsay Audin is president of EnergyWiz, an energy consulting firm based in Croton, N.Y. He is a contributing editor for Building Operating Management.