Making the Switch

Making the Switch

Automated control strategies can cut lighting costs by as much as 50%. By James Piper.


Building lighting systems account for an estimated 35 percent of electrical energy use in commercial and institutional facilities today, making lighting systems a primary target in the effort to reduce building energy use. Managers have implemented programs that have reduced lighting energy requirements by lowering lighting levels or installing more efficient light sources.

Although many of these programs have reduced lighting energy requirements, they have not met their potential for lighting energy management.

Lighting energy management has three elements; providing the optimum lighting level for the tasks being performed, using the most efficient light source suitable for the application, and providing light during only those times when it is actually needed. By including lighting controls in their overall lighting energy management program, facility executives can achieve even greater energy savings — up to 50 percent of the total energy used for lighting. And by reducing the run time for lighting systems, good lighting controls can reduce maintenance requirements by increasing the interval between lamp replacements.

With lighting controls offering such good returns, why are they so often overlooked when lighting upgrade projects are implemented? In some cases, the facility manager simply does not consider lighting controls to be important. Some believe that lights are needed in all areas whenever the facility is open, and that all possible lights are turned off after hours.

Actually, only a portion of a building’s lights is needed at any given time. Lights frequently are left burning in unoccupied spaces simply because nobody thinks or takes the responsibility to turn them off.

Another reason that lighting controls are often ignored is that some facility executives believe that frequent switching of fluorescent lamps will increase operating costs due to shorter lamp life, and therefore encourage lights to be turned on at the beginning of the day, and left on until the facility is closed. While more frequent switching of fluorescent lamps will decrease lamp life, the energy cost savings achieved by switching off the lamp when it isn’t needed far exceeds the value of the lamp life lost, typically by a factor of 100 or more.

Some have had bad experiences with automatic lighting controls and are not willing to install any form of automatic lighting control. Early generation occupancy sensors, particularly if they were not well placed, allowed lights to turn off even while spaces were occupied, resulting in complaints and the bypassing of the controls by building occupants. Improvements in sensor design and installation practices have almost completely eliminated false shutdowns of lighting systems.

Automated lighting system controls can be used effectively in any building. Facility executives have a wide rage of options when selecting a system for a particular application. Systems range from ones that are stand-alone to ones that are part of a fully interoperable building automation system. While any system can be used to reduce building lighting energy and maintenance costs, systems are most cost effective when control strategies are matched to factors related to the building design and to occupant needs.

There are three lighting automation control strategies that can be used to reduce operating costs: scheduling, occupancy and daylight harvesting. In practically all applications, a mixture of different control strategies will be required to meet the needs of the facility.

Scheduling controls produce savings by turning lighting systems on and off on a set daily time schedule. Schedules typically vary by the day of the week based on building occupancy. By automatically turning off lights at a set time, the systems help facility executives avoid having building lights on during unoccupied hours, primarily at night and on weekends. Different schedules can be programmed for different areas of the building based on the use of the facility and the needs of the occupants.

Early generation scheduling control systems were little more than time clocks. Operators would set the tabs at the times when the time clocks were to turn the lighting system on and off. While the systems did help to ensure that lights would not be left operating when they were not needed, they were difficult to use. Every time lights were needed after normal operating hours, the settings on the clocks had to be changed. Similarly, turn-on times had to be set early enough and turn-off times had to be set late enough to accommodate those who came in early or went home late. The result was that lights were often operating when the space was unoccupied.

Today’s scheduling control systems are more sophisticated, flexible and easier to use. With built-in controls that allow users to temporarily bypass the system, lights can be brought on earlier or left on later to provide lighting for special functions.

Scheduling controls are used most widely in applications where building occupancy patterns are predictable and follow a set daily and weekly schedule. While the building can be divided into different control zones based on the occupancy of different areas, too many different control zones can make the use of scheduling controls difficult. Similarly, if areas within the building are unoccupied for more than an hour at a time during the day, it may be too difficult to take full advantage of scheduling controls. Occupancy controls may be required to give the flexibility required.

Occupancy Controls

Occupancy controls limit the operation of the lighting system based on the actual use of the space. Unlike scheduling controls, they do not operate by a pre-established time schedule. Instead, the system senses when the space is occupied and turns the lights on. When the system senses that there has been no activity in the space, it assumes the space is unoccupied and turns the lights off. To prevent the system from turning the lights off while the space is still occupied but there is very little activity, a time delay typically ranging from 1 to 15 minutes can be programmed into the controls.

Selection and placement of the sensor is key to the successful occupancy control application. For the system to operate properly, the sensor must be able to detect motion anywhere in the space, while ignoring vibration-induced false signals. Sensors can be wall or ceiling mounted. Multiple sensors can be used to provide better coverage, particularly in large or irregularly shaped areas.

There are two types of sensors used in occupancy controls: passive infrared and active ultrasonic. Infrared sensors detect changes in the energy radiated by the occupants of the space. To work properly, the sensors need a direct view of the occupants. Barriers that prevent the sensors from seeing portions of the room, such as work partitions, high shelving, and equipment, will cause the systems to turn the lights off even when the space is occupied.

For this reason, infrared sensors are best used in applications such as corridors, warehouses, and enclosed offices. They do not perform well in open offices, storage areas, or restrooms.

Ultrasonic occupancy sensors emit high frequency sound waves that reflect off objects in the space. If there is any movement in the space, the frequency of the reflected wave is changed and the control turns the lights on. Ultrasonic based occupancy sensors are best suited for used in open applications, such as open offices, classrooms, and large conference rooms. Ultrasonic sensors can be fooled by HVAC systems that cause high levels of vibration or airflow.

Some occupancy controls in use both types of sensors to help improve their accuracy in determining whether the space is occupied.

Occupancy controls are best used in applications where occupancy does not follow a set schedule and is not predictable. Typical applications include private offices, conference rooms, classrooms, library stack areas, storage rooms and warehouses.

Daylight Harvesting

The third lighting automation control strategy is daylight harvesting. Daylight harvesting systems allow facilities to minimize lighting energy use by making use of the available daylight, supplementing it with artificial lighting as needed to maintain the required lighting level. What has made the systems efficient is the development of low-cost, dimmable electronic ballasts for fluorescent fixtures. These ballasts provide full dimming capabilities for fluorescent lamps from 100 percent of rated light output down to as low as two percent, without causing flicker or noise.

Daylight harvesting systems use a photo sensor to measure the total lighting level within a space. If the level is too high, the system’s controller reduces the light output of the fluorescent lights. If the level is too low, the controller increases the light output of the fluorescent lights. Multiple sensors are often used in large areas, each controlling a separate bank of lights in order to maintain a uniform lighting level throughout the area. The result is a system that minimizes lighting energy use while maintaining uniform lighting levels.

Daylight harvesting systems are best used in those spaces that have relatively large areas of windows or skylights. Typical applications included high-rise office buildings, classrooms and retail facilities.

The Digital System

Lighting control systems are going digital. Digital lighting control systems have been developed as stand-alone systems or as part of building- wide automation systems. In a digital system, each segment of the lighting system has its own device-specific address. That allows commands to be issued to specific portions of the building’s lighting system, such as to turn lights on or off, or to dim them.

Digital systems can perform the same lighting automation functions that independent, stand-alone systems perform, only better. They can schedule the operation of lights in any area within the facility. They can override the set schedule to match changes in operating schedules. They can monitor occupancy patterns in an area and adjust the operation of the lighting systems as required.

Digital systems also give facility executives the ability to control building lighting energy use from any location. In addition to providing a central control station for the building’s lighting systems, most digital systems are Internet compatible, allowing managers to monitor and control building lighting systems from any location that has Internet access.

The ability to remotely control building lighting systems is particularly important for facilities facing high or uncertain electricity costs. One method of reducing those costs is to limit the facility’s demand for electricity during peak-use periods when rates are the highest. During these times, the lighting control system can turn off as many lighting system components as possible, or dim those systems that are equipped with dimming ballasts. With building lighting systems accounting for such a large portion of the electrical load, any reduction in lighting load during peak-rate periods will translate into savings, in both energy use and energy demand charges.

Another benefit of digital lighting control systems is their ability to monitor the operation of the lighting systems. At the minimum, the digital system can receive feedback from each lighting system, confirming that it is on or off as commanded. The digital system can also monitor the number of hours that the lights are operated in a given area, as well as the number of times the lights are turned on, the most important factors in determining lamp life. Using this information, managers can schedule the group relamping of particular areas in the building before the number of lamp burnouts becomes excessive while ensuring that the lamps have been used for as long as possible.

Most facility executives can expect to achieve a 25 to 40 percent reduction in lighting energy use by implementing an automated lighting control program. Most facilities will recover their investment in lighting automation in two years or less. The actual savings and payback that will be achieved depend on a number of factors, including how the facility uses lighting, the type of lighting systems installed, the hours that lighting is required, the lighting level needed, when the lights are required and the ability of the facility to make use of daylighting.

The savings that a facility can achieve will also be greatly enhanced if the facility can use portions of the lighting system to reduce its peak load. This is particularly important for those facilities that are purchasing electricity in a deregulated market.

In determining the actual savings that can be achieved in a particular facility, executives will have to closely examine all aspects of lighting use within their facility. Spot checks of facilities during off hours will help to identify how frequently lights are left operating after hours when the facility is unoccupied. Similarly, spot checks of areas such as private offices, classrooms and conference rooms will help to identify how often lights are left on in unoccupied spaces during normal operating hours.

Another method that facility executives can use to better quantify the potential for savings is to use a logging system in representative areas within the facility. These systems are designed to monitor the occupancy of a given space and record the time when lights are left on but the space is unoccupied. A rule of thumb that can be followed is that any area where the lights are found to operate for two hours or more when the space is unoccupied will benefit from automated lighting controls. By carefully selecting representative areas, it’s possible to project the savings for the entire facility.

Projecting the savings that can be achieved by daylight harvesting systems will require a more detailed analysis that examines the available sunlight on a daily basis for a typical year.

A successful lighting automation program requires careful planning. One size does not fit all when it comes to applying lighting automation systems. Differences in facility construction, room layouts, lighting requirements, code requirements and building automation system capabilities will, to a great extent, determine the type of system that is best suited for a particular facility.

Start by examining all aspects of the lighting systems in the building. What type of lighting is installed? When is the lighting needed? Is lighting required continuously while the building is open, or is the need intermittent? What activities are being performed in the building? How will automated lighting systems impact those activities? Remember, most systems will use a combination of all three lighting control strategies.

Identify individual lighting systems in the building where savings can be achieved through the use of automated lighting controls. Estimate the savings that automated lighting controls will produce. Finally, use the estimated savings to convince financial managers of
the value of the lighting automation program.

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By James Piper, P.E., PhD., a consultant and writer with 25 years of experience in the facilities field. This piece copyright 2002 Energy Decisions, a GreenBiz News Affiliate.