Reliable, easy-to-install, electronic dimming ballasts and photo sensors can easily integrate with building automation systems and save you a lot of money.
Many facilities have improved efficiency of their lighting systems and enjoyed notable savings. These facilities could be saving even more with the use of lighting controls during peak load periods, when the marginal utility cost is high. Aside from saving money, occupants want simple lighting controls that are responsive to their needs. They're placing emphasis on controls for added value, to further enhance workplace lighting systems. Amenities such as flexibility and individual control are high on their lists. However, most central control systemscan't respond to individual needs, so distributed controls serve many of these functions.
Managing occupancy control strategy. We employ this type of control strategy in intermittently occupied areas, to turn lights on when people are present and off (after a time delay) when the area is unoccupied. This strategy works best in areas where occupants negligently leave the lights on. Chances are this happens a lot in single-person offices. Field tests show single-person offices are occupied an average of five hr a day, but the lights are on an average of 14 hr a day.
The best way to identify areas for occupancy controls is to take measurements as inconspicuously as possible. Knowing they're on camera, people tend to alter their behavior. An occupancy/lighting logger may provide more realistic evaluation data. With this, you can record data for periods of occupancy/no occupancy and lights on/off for a period, usually a week. You can then download the data from the logger to a PC or laptop and calculate the savings.
Occupancy monitoring for controlling lighting. Occupancy sensors are the most popular distributed lighting control system. Knowing which technology to use can make a difference in your long-term results. Two major sensor technologies are passive infrared (PIR) and ultrasonic.
PIR sensors respond to energy sources and sense occupancy by detecting difference in heat from a body and its background. They need to "see" an area to control it, employing line of sight sensing. Two characteristics to understand when applying PIR sensors are: (1) detection of movement across the field of coverage is easier than moving to or from the sensor and; (2) the zones of detection broaden as you get further away from the sensor, reducing sensitivity. The sensor can easily detect hand motions close by, but it detects only large motions from a distance.
You can mount PIR sensors on the wall or ceiling. The ceiling-mount sensors usually transmit low-voltage signals to a switching unit, normally mounted on a j-box. Wall box-mounted units fit standard wall switch electrical boxes. It's important to remember that PIR sensors use line of sight sensing. In many applications, such as in bathrooms, the wall switch location can't "see" into the room. You can easily determine wall box sensor coverage after installation by walking the periphery of the room and watching the light-emitting diode (LED), located on the face of the unit. The LED indicates occupancy by either being on steady, or flashing at a slow rate. Wall-mounted PIR sensors located near a light switch (often near a door), tend to activate the lighting when people walk by the door outside the room. Placing tape over part of the lens can help to prevent this from happening.
Be careful regarding the lighting load on wall box sensors. If the lighting load is below the minimum loading value, the lights can flash on and off erratically. Avoid overloading the sensor, which can reduce the life of the electronics and shorten usable life. Most PIR wall box sensors now employ zero-crossing relays to avoid the inrush problem inherent with low THD electronic ballasts.
Ultrasonic sensors are another option to consider. These devices detect changes in high-frequency sounds and transmit and receive sounds above the range of human hearing. They use the Doppler principle to detect any shift in frequency of the reflected waves. Ultrasonic sensor coverage is 360 degrees. This type of sensor is most sensitive to small movement close to its detector (10 ft to 20 ft). As you go further away from the sensor (40 ft to 50 ft), sensitivity reduces. Sensors are usually separate from the relay that switches the lighting load, using low-voltage wiring between the sensor and switching unit.
Adjusting the sensors. Usually, you need to make only two adjustments. A delay adjustment determines the amount of time the control will keep lights on after there is no detection of motion. Choose a setting based on occupancy patterns and lamp replacements. Setting this adjustment too low will shorten lamp life.
You'll typically find a sensitivity adjustment on ultrasonic sensors. This makes the sensor more or less sensitive to motion, including vibration. For ultrasonic sensors, you must adjust this control to prevent detection of air movement (such as air from an HVAC diffuser). When adjustment of the sensitivity control doesn't solve the problem, changing the sensor to a dual-technology type may work.
Some occupancy controls don't need adjustment. The newest occupancy recognition controls require no manual adjustments, cutting down costly commissioning time. They contain microprocessors that analyze occupancy activity, and adjust sensitivity and time delay settings to meet the needs of the controlled area. We sometimes call these types of occupancy controls adaptive sensors. They "learn" a room's use pattern or "signature" and continuously adjust the sensor settings for maximum performance.
For example, a common problem with older controls typically occurs during installation. In one test, when installers leave occupancy sensors in the "test" mode, the lighting system short-cycles (constantly going on and off), which severely affects lamp life. These third-generation lighting controls provide additional benefits, such as lighting energy monitoring capabilities; more accessible dimming; and the ability to respond to real-time utility pricing methods.
Lumen depreciation compensation benefits. Designers sometimes "over design" lighting systems to compensate for light loss. Depreciation factors, such as dirt accumulation on fixtures and room surfaces, play a part at the designing level. These factors affect the number of fixtures required to provide a target light level. The lumen depreciation compensation strategy allows designers to meet light levels without over designing, for a more effective lighting system.
The system works like this: A photo sensor detects the actual light level and provides a low-voltage signal to an electronic dimming ballast that sets the actual light level. When lamps are new and room surfaces are clean, the area requires less power to provide the design light level. As lamps depreciate in their light output and surfaces become dirty, the input power and light level increase gradually to compensate for the light loss. Some experimental building management systems use a depreciation algorithm to adjust the output of the electronic ballasts instead of relying on photo sensors.
Taking advantage of dimming opportunities. The use of dimming controls offers a broad range of benefits: improved building aesthetics; increased employee productivity; reduced pollution; and substantial energy and cost reductions. Dimming provides excellent energy savings, especially in spaces using daylight to illuminate the area.
The Lighting Research Center published the results of a study it performed on private offices at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. The project found occupants highly value dimming functionality and use both manual switching and dimming. The location of dimmers does matter; people prefer to have a dimmer conveniently located at their desk. The study showed that the status of the reset also matters, i.e. occupants whose lights are automatically restored to a preset value of reset dim the lighting in higher proportion than those whose lighting was not reset.
Further results of the study showed lighting controls save energy. Experimenters achieved the following reductions of energy usage for lighting compared with the existing lighting strategy: occupancy sensors, 46% manual switching, 9% dimming, 6%
These results show promise. Handheld PIR remote controls, much like the ubiquitous TV remote, can control the light level of overhead cubicle fluorescent lights.
Dimming electronic ballasts for fluorescent lamps. Electronic ballasts with dimming functions operate fluorescent lamps at high frequency, just like fixed-level electronic ballasts. Separate low-voltage control leads from each ballast is what distinguishes them from electronic ballasts for fixed-light applications. You can group these Class 2, low-voltage control leads together to create control zones independent of the power zones.
Many of the new-generation ballasts now provide overvoltage protection of the control leads in case line voltage accidentally applies to the low-voltage leads. Several electronic dimming ballasts now accept low-voltage telephone cables and connectors, instead of being hard-wired. The control method of choice is 0VDC to 10VDC, although a new group of dimming ballasts accepts the AC line phase control signals from incandescent wall-box dimmer controls, dimming the fluorescent lamps accordingly.
Dimming ballasts divide into two categories, based on dimming ranges:
• Energy management applications: 100% to 5%, and
• Architectural dimming applications: 100% to 1% (or less).
It was just a few years ago that dimming ballasts for energy-management applications could only dim down to 20%. In the last few years, this lower level has dropped to 5%, where it remains.
Recent developments in dimming electronic ballasts bring their promise closer to reality. Most manufacturers of electronic ballasts now have dimming products, including 1-, 2-, or 3-lamp versions. Ballasts are available for dimming most linear fluorescent lamps, including the new T5 HO lamps.
Many of the new products start the lamps at any dimmer setting. Most of the units available today measure less than 15% total harmonic distortion (THD) throughout the dimming range, and come in a small package.
Several manufacturers also have new dimming ballasts for rapid-start (4-pin) compact fluorescent lamps (CFLs). Most of these offerings are for the higher-wattage CFLs (26W to 42W). Currently, the lowest dimming limit is 10%, while some dim to 20%. Dimming range varies with the manufacturer.
Many of the new OEM units accept the AC phase-control signals from incandescent wall-box dimmer controls. This makes upgrading an older incandescent downlight system to an energy-efficient CFL system easy, with no new wiring required.
A quick way to expand your understanding of dimming strategies is to get a free CD-ROM from the National Dimming Initiative (NDI). The goal of the NDI is to provide you with information about the benefits associated with lighting controls and fluorescent dimming products.
When lighting controls respond to occupants' needs, strategies such as occupancy control and dimming can provide savings and improve the work environment.
Lighting Research Center Documents
National Lighting Product Information Program; Specifier report on photo sensors, Vol. 4, No. 3, March 1998. For copies, call (518) 276-8717. There's a $15 fee.
National Dimming Initiative
CD-ROM is available on dimming strategies and benefits associated with lighting controls and fluorescent dimming products. For a free copy, call (847) 390-5136.
Fetters is a Certified Lighting Efficiency Professional and President, Effective Lighting Solutions, Inc., Columbus, Ohio.