|| Print This Page ||
Lighting controls help to make commercial buildings more comfortable, productive, and energy efficient. These controls can turn lights off when they are not needed or dim them so that no more light than necessary is produced. The two functions can be employed individually or in tandem to provide even greater benefits. The equipment used to achieve these functions ranges from simple timers to intricate electronic dimming circuits.
The benefits of lighting controls can be significant. In one prominent example, Lockheed Martin cut energy use by 75 percent after applying daylighting and dimmable fluorescent systems extensively at one of its buildings in Sunnyvale, California. Elsewhere, TRW installed occupancy sensors in 8,000 rooms at its Space and Defense Park campus in Redondo Beach, California, resulting in annual energy savings of $1.3 million. Overall, the addition of lighting controls to existing buildings has been shown to reduce lighting energy consumption by as much as 50 percent—sometimes more—and by at least 35 percent in new construction. Lighting controls can also reduce peak loads and provide a load-shedding capability.
The simplest way to reduce lighting energy consumption is to turn the lights off when they are not in use. All electric lights feature manual switches for that task, but these are not used as often as they could be. The lighting industry has developed a variety of devices to solve that problem.
Occupancy sensors. Occupancy sensors are most effective in spaces where people move in and out frequently in unpredictable patterns: for example, private offices, lecture halls, auditoriums, warehouses, restrooms, and conference rooms. Occupancy sensors are less likely to be effective in open-plan offices, where one or more people may be present throughout the day, or in reception areas, lobbies, retail spaces, or hospital rooms. The three most common types of occupancy sensors are: passive infrared (PIR), ultrasonic, and those that combine the two technologies.
PIR devices are the least expensive and most commonly used type of occupancy sensor. They detect the heat emitted by occupants and are triggered by changes in infrared levels when, for example, a person moves in or out of the sensor's field of view. PIR sensors are quite resistant to false triggering and are best used within a 15-foot radius.
Ultrasonic devices emit a sound at high frequency—above the levels audible to humans and animals. The sensors are programmed to detect a change in the frequency of the reflected sound. They cover a larger area than PIR sensors and are more sensitive. They are also more prone to false triggering. For example, ultrasonic sensors can be fooled by air currents produced by a person running past a door, moving curtains, or the on-off cycling of an HVAC system.
Hybrid devices that incorporate both PIR and ultrasonic sensors are also available. These take advantage of the PIR device’s resistance to false triggering and the higher sensitivity of the ultrasonic sensor.
More details are available in the Purchasing Advisor on Occupancy Sensors.
Timed switches. Timed switches operate based on either elapsed time after triggering or on programmed schedules using clock time. Elapsed-time switches, also called timer switches, typically fit into or over a standard wall-switch box and allow occupants to turn lights on for a period that is determined either by the occupant or by the installer (see Figure 1). Lights go off at the end of that interval unless the cycle has been restarted by the occupant or manually turned off sooner. Time intervals typically range from 10 minutes to 12 hours. Elapsed-time switches are much simpler to specify than occupancy sensors, are less prone to user maladjustment, and are low in cost.
Elapsed-time switches are an inexpensive means of controlling lights in irregularly used spaces.
Courtesy: Paragon; Watt Stopper/Legrand
Elapsed-time switches may be mechanical or electronic. Mechanical units, typically set by the user, are basically spring-wound kitchen timers connected to a relay. These items are subject to mechanical failures if used in high-traffic areas. Time intervals on electronic switches are typically set by the installer using a hidden set-screw. These electronic devices look like conventional toggle switches, so occupants are usually unaware of the presence of the device, which reduces vandalism and theft. Elapsed-time switches are also an easy, economical means of complying with energy codes that call for automatic lighting controls.
Clock switches control lights by turning them on and off at prearranged times, regardless of occupancy. They are most useful in locations where occupancy follows a well-defined pattern, such as a retail outlet. They are typically placed in electric closets that house lighting power panels. These devices cost relatively little to install and can control large loads with a single set of contactors. Equipment may consist of mechanical devices—motors, springs, and relays—or sophisticated electronic systems that handle several schedules simultaneously. Mechanical switches may require correction for daylight savings time or after a power failure unless battery backup is available, but battery backup can triple the device’s price. Electronic devices routinely include battery backup and can be easily programmed to adjust for shifts to and from daylight savings time or for holiday schedules. The latest electronic clock switch includes a 10-year lithium battery and the capability to receive time signals from the National Institute of Standards and Technology to keep the clocks current.
One thing to note: If your space has fluorescent lighting, make sure that electronic switches do not use a triac relay. Triacs may trickle a small amount of current to ballasts and lamps, even when they are off, which may damage the lamps.
Energy management systems (EMS). An EMS performs the same function for lighting as a clock switch, but with more sophistication and additional features. A typical EMS is designed to handle a variety of loads, including HVAC, but pure lighting-management systems are also available. Systems are now becoming available that combine on-off and dimming capabilities in an EMS.
A common EMS feature is a sweep mode that automatically cycles lights on or off, one section or floor at a time, signaling occupants that lights will soon be shut off. Occupants can then override the shutdown in their area by pressing a local switch or by phoning in a code to the EMS.
Dimming controls are usually used to match lighting levels with human needs and to save energy. When combined with photosensors that measure local light levels, dimming controls can correct for dirt buildup in fixtures and lamp lumen depreciation. Dimming controls are also used to modulate lamp output to account for incoming daylight. Dimming may be accomplished in either a stepped or continuous fashion.
Step dimming. The most familiar form of step dimming is the three-way incandescent lamp. For non-incandescent lamps, two means of step dimming are available: banks of lamps may be put on different switching circuits, or ballasts designed specifically for step dimming may be applied.
The first of these two methods is often referred to as bilevel switching, even though more than two levels may actually be available. For example, in a system with three-lamp fluorescent fixtures, one switch may operate the center lamp in each fixture, while another operates the outer lamps. This arrangement makes three lighting levels possible (one lamp, two lamps, or three lamps lit), yet the term “bilevel” is still often used to describe such a system.
Step-dimming ballasts offer more light control and energy savings than nondimming ballasts but cost less than the more versatile continuous-dimming ballasts. Step-dimming ballasts typically offer two or three lighting levels, and they can be used with occupancy sensors so that the sensors are able to dim the lamps rather than turn them off, which can reduce on-off cycling and extend lamp life. These units also offer a viable way to reduce lighting levels during noncritical hours and to shed peak demand in common areas such as corridors.
Step-dimming ballasts are especially useful for high-intensity discharge (HID) lamps. HID lamps typically require long warmup times, so they are not suited to being switched on and off by occupancy sensors. Better results can be obtained by switching the lamps between low power and full power.
Continuous dimming. Continuous-dimming controls let users adjust lighting levels over a range of lighting output. They offer more flexibility than step dimming and are used in a wide variety of applications, including mood-setting and daylight dimming. Dimming can be accomplished on all lamp types found in commercial buildings: incandescent, fluorescent, and HID.
Incandescent lamps are the easiest to dim. The introduction of semiconductor-based dimming controls for these lamps means that dimming is accompanied by a reduction in energy consumption. However, these dimmers cause the filament to run cooler, reducing color temperature and making the lamp appear more yellow. In addition, power does not vary linearly with light output, and lamp efficacy is reduced during dimming. But voltage is also reduced, a factor that increases the life of standard incandescent lamps though it may reduce life in halogen bulbs under certain conditions.
Fluorescent lamps may be dimmed for two purposes: energy savings and architectural effect. Energy-saving dimmers typically dim down to 20 percent, while architectural dimmers may reduce light levels to 1 percent or less. Unlike incandescent dimming, fluorescent dimming does not extend lamp life; in fact, long periods at very low light levels may shorten lamp life. Dimming ballasts are often used to reduce electric light output whenever sunlight is available. In one test, dimming ballasts helped cut peak demand by almost 40 percent (see Figure 2). Dimming can also be used in load-shedding strategies—better to have employees work briefly under slightly lower light levels than be forced to send them home because of a power failure.
In a test at the Florida Solar Energy Center, dimming cut average workday power consumption for lighting from 157 watts (W) to 70 W per fixture.
Source: E Source; data from Florida Solar Energy Center
HID dimming is more limited because it is accompanied by color shifting, reduced color-rendering index, increased flicker, adverse impact on lamp life, and inadvertent lamp shutdown during line-voltage variations. New electronic dimming ballasts for metal halide lamps promise to reduce the severity of some of these problems and make HID dimming more feasible. (See the Purchasing Advisor for Metal Halide Ballasts for more information.)
HID and fluorescent lights may also be dimmed with panel-level controllers, commonly called power reducers, that lower circuit voltage upstream of the ballasts. This approach is best applied in overlit situations with large banks of lights that are switched simultaneously, such as in retail stores, supermarkets, and large open-plan offices. Dimming levels are usually limited to 25 percent or less.
Dimming is accomplished through the use of either low-voltage or power-line control. Most ballasts are controlled by a separate, low-voltage circuit. This approach requires additional wiring, but the ballasts are compatible with a wide variety of dimming controls. For example, low-voltage-controlled ballasts can easily be connected to EMSs that offer 0- to 10-volt output channels. Power-line-controlled ballasts can dim fluorescent lamps with standard incandescent wall dimmers installed directly on the line-voltage switch leg—no extra wires necessary. The ballasts are not compatible with all dimmers, however, so ballast and dimmer should be checked for compatibility. Personal dimming controls, which allow individuals to control light levels in their own work areas, are also becoming more widely available. Such dimming controls have been shown to cut energy use and increase worker satisfaction levels.
In recent years, it has become easier to dim compact fluorescent lamps (CFLs) as well as full-size fluorescents. New screw-based, step-dimmable, and continuously dimmable CFLs provide dimming capabilities down to the range of 10 to 20 percent, and these products work well with most existing incandescent dimmers. These lamps cost two to three times more than standard CFLs. New hardwired CFL dimming products are on the market as well, providing opportunities to dim lights to 5 percent of maximum output or even lower levels.
Building operators can achieve the highest levels of energy savings through a combination of dimming and on-off strategies. However, the total savings achieved by implementing both strategies will be less than the sum of the savings gained by implementation of each individual strategy. The reason for this is simple. Take for example a system that combines occupancy sensing and dimming. Dimming cannot save energy when occupancy sensors have already shut off a lamp, and the occupancy sensors save less energy when they turn off lights that otherwise would have been dimmed.
Low-voltage digitally controlled ballasts. These ballasts use control protocols such as DALI (digitally addressable lighting interface), LonWorks, and BACnet, or other proprietary protocols. One key advantage of these digitally controlled ballasts is that each is assigned an identifier, or “address,” and can be controlled individually on a single network. This allows the lighting to be easily controlled from a central location in a building without requiring a dedicated control wire between each ballast and the central control point. The control protocol can be delivered over a dedicated control network or over the Ethernet network already present in most office buildings.
Some protocols, such as DALI, are designed for use over a dedicated low-voltage network, but DALI-to-Ethernet converters are available so that DALI can be used in buildings with existing Ethernet networks without the need to run additional control wires. Some digital ballasts include a built-in DALI interface; others use a proprietary protocol. You can add conventional low-voltage controlled-dimming ballasts to digital lighting control systems by using special interfaces that connect to DALI systems and convert the DALI commands to standard 0- to 10-volt direct current (DC) control signals.
Wireless lighting controls. A typical wireless lighting control system consists of a set of sensors, actuators, and controllers that communicate via radio waves rather than wires. Although wires are still required for the lighting equipment itself, using radio waves instead of wires to transmit control signals offers a number of potential advantages in terms of ease of installation and maintenance as well as flexibility.
Wireless lighting controls have been available for a number of years, but their use has been limited to a few niche markets such as high-end homes, conference rooms, and classrooms that often need a large variety of lighting scenes. These systems are installed to provide amenities—they're not aimed at energy savings—and they lack the reliability and flexibility to be applied throughout a commercial facility. Newer, more-capable wireless systems, some of which are available today, may broaden the wireless lighting controls market considerably if costs can be brought down.
Select the type of control based on the usage of the space. Consider occupancy sensors and timers if the space use is unpredictable. Typical examples might be warehouse aisles and hotels or any space that is unoccupied in an unpredictable fashion for more than 30 percent of the time. Consider timed switches if space use is predictable and not part of a 24-hour operation. Light-sensitive photoswitches and timed switches work well for exterior lighting used on facades, signs, and in parking areas. If daylight is available, consider dimming ballasts with photosensors or multilevel switches.
In choosing between step-dimming and continuous-dimming controls, it is helpful to know how occupants will use the space. Step-dimming controls are more practical in spaces that receive ample amounts of sunlight; where fixtures are mounted outside the field of view; and where there is little concern for distracting occupants, such as hallways and atriums. In contrast, continuous-dimming controls are best in areas where the fixtures (or lamps within the fixtures) are in the field of view and where there is a concern for distracting occupants, such as classrooms and office spaces.
Even at today’s prices, wireless solutions can be attractive in some applications. These include small buildings that have been underserved by technology in the past, office buildings where high churn rates lead to frequent reconfiguring of space, and old buildings that are being converted to modern office spaces. Wireless systems may pay off now in buildings eligible to participate in demand-response programs, where a high incentive is paid to shed load. As the systems become more widely used and costs come down, the market may expand to larger buildings and then to new construction. New products being introduced today based on a networking concept called “mesh networks” may be the key to bringing costs down.
In spaces where there is a need to vary light levels, either during the day or after hours, manual dimmers or multilevel switching will work well.
Select the right type of control for the expected load profile. For a space with predictable 9:00-to-5:00 work hours and limited weekend use, select controls that will reduce peak demand. In that scenario, occupancy sensors and photosensors will help reduce demand in tenant spaces, and timed switches can be used in public areas. In a facility with extended hours of occupancy, occupancy sensors and manual dimming or multilevel switching can help to reduce unpredictable use. In spaces that are always open, use photosensors in conjunction with dimming ballasts to cut daytime energy use, and use manual dimming and multilevel switching to account for lighting preferences and cut energy use at night. Manual controls work best in spaces such as gymnasiums or conference rooms that are lit for specific events. Manual dimming and multilevel switching are the best energy-saving options in those situations.
Evaluate cost-effectiveness. Users will achieve varying levels of energy savings based on the types of spaces in which they implement occupancy sensors, as shown in the table for occupancy sensors. More precise estimates require random surveys of occupant patterns or the use of dataloggers to record current usage. For daylighting, actual scale models or full-scale mockups are sometimes used to estimate the savings potential. Once building operators estimate potential savings, they can use the incremental cost of the controls to calculate a simple payback period.
Test system compatibility. All the components in a lighting control system—including ballasts, controller, photosensors, occupancy sensors, and switches—must be compatible. Achieving this can be tricky when each item may come from a different manufacturer. A small-scale test will help sort out compatibility issues before a large installation is specified.
Commission lighting control systems. Almost all lighting controls require commissioning so that they operate as intended. For occupancy sensors, time delays and sensitivity need to be adjusted for each workspace. When it comes to photosensors for daylighting systems, the sensitivity must be set for local room conditions. Commissioning may initially be done by a professional, but the best results come when occupants are involved in fine-tuning the system to meet their needs.
Advanced capabilities—such as individual control of lighting levels and ballast diagnostics that can provide energy and maintenance data—appear to fall into the “useful” rather than “must-have” category. That could change if researchers are able to quantify worker productivity benefits resulting from individual control of workspaces. Until then, or until the incremental cost of sophisticated systems like those based on DALI becomes negligible (which could happen if production volumes were to increase dramatically), these systems will remain a niche market technology best suited for offices in Class A facilities.
Existing buildings represent a huge opportunity for both energy savings and demand-response programs through the use of lighting controls. The costs of wiring to retrofit controls has been prohibitive, but we expect wireless controls to begin to make a difference if equipment costs can be reduced. There is a good chance that can happen, as it has with all kinds of electronic devices. Systems based on open protocols have the best chance of meeting the cost goals because they can spur competition and because they enable similar components to be manufactured for a wide range of applications, making it more likely that volumes will be large enough to lead to lower costs. For example, members of the ZigBee Alliance are developing products for a range of applications including HVAC and appliance control in addition to lighting.
Copyright 2006 - Platts, a Division of The McGraw-Hill Companies, Inc.