Energy Advisor
Your guide to energy products for commercial buildings
|
Energy Advisor |
Lighting: Lighting Controls
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 light output 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 needed 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 fluorescents 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, and cut annual energy bills by $1.3 million. Overall, lighting controls have been shown to reduce lighting energy consumption by 50 percent in existing buildings and 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. To solve that problem, the lighting industry has developed a variety of devices, including timers and occupancy sensors.
Occupancy sensors. Occupancy sensors are most effective in spaces with a constant flow of foot traffic: for example, private offices, school classrooms, 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.
Three types of occupancy sensors are available: passive infrared (PIR), ultrasonic, and sensors that combine the two technologies.
PIR devices are the least expensive, 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 high-frequency sound above decibel levels audible to humans and animals, and 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 by 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 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.
Source: Paragon Electric Company, The Watt Stopper
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 single sets of contactors. Equipment may consist of mechanical devices—with motors, springs, and relays—or sophisticated electronic systems that handle several time schedules simultaneously. Mechanical switches may require correction for daylight savings or after a power failure, unless battery backup is available. However, battery backup can triple the price of a mechanical clock switch. 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 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 clocks current. For 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, and may damage the lamps.
Energy management systems. An energy management system (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 light sensors, 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 step-wise 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 bi-level 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 bi-level 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 then the more versatile continuous dimming ballasts. They typically offer two or three lighting levels. Step-dimming ballasts 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 starting 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 wide range of lighting output. They offer far 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 also 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. However, voltage is also reduced, which increases the life of standard incandescent lamps but may reduce life in halogen bulbs.
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, and long periods at very low light levels may shorten life. Dimming ballasts are often used to reduce artificial 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 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.
Source: Florida Solar Energy Center
Dimming is accomplished through the use of either low-voltage control or power line control. Most ballasts are controlled by a separate, low-voltage circuit. This approach requires additional control wiring, but the ballasts are compatible with a wide variety of dimming controls. For example, low-voltage controlled ballasts can easily be connected to energy management systems 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.
In recent years, it has become easier to dim compact fluorescent lamps as well as full-size fluorescents. New screw-based, dimmable compact fluorescent lamps (CFLs) provide dimming capabilities down to the range of 10 to 20 percent, and early reports claim that these products work well with most existing incandescent dimmers. These lamps cost just a few U.S. dollars more than standard CFLs. New hardwired CFL dimming products are coming to market as well, providing opportunities of dimming lights to even lower levels.
Personal dimming controls that 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.
HID dimming is more limited, because it is often 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 lamps promise to solve some of these problems and make HID dimming more feasible.
HID and fluorescent lights may also be dimmed with panel level controllers 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.
Building operators can achieve the highest levels of energy savings through the 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.
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. 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 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-to-5 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 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, photocells, 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.
Look for new products in the near future that incorporate the Digital Addressable Lighting Interface (DALI). DALI is a digital communications standard that a growing number of manufacturers are embracing. It is a nonproprietary standard that defines interfaces for digital communication between a controller and the various electronic components of a lighting system. The DALI concept was designed to close the gap between 0- to 10-volt systems—which are low in cost but lack flexibility—and complex building management systems, which provide lots of functionality but require costly equipment and a high level of system knowledge on the part of the user.
DALI supports the concept of individually addressable ballasts, which can be assigned to a control group after installation. These ballasts transmit their individual, digitally encoded identification number to a controller, which then assigns them to a control group and communicates the group's dimming or on-off instructions. If the configuration of the space changes, ballasts can easily be reassigned to another group without rewiring.
Copyright © 2004 - Platts, a Division of The McGraw-Hill Companies, Inc.
