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Taking Control of Lighting
The use of lighting controls is on the rise, and many institutional and commercial facilities that have installed lighting controls realize a number of benefits. These benefits include energy and cost savings, as well as improved flexibility, convenience, productivity, safety and security.
Lighting controls are becoming more important to facilities for a number of reasons. Control technology has improved continuously, and building codes soon will require the use of controls. The choice for maintenance and engineering managers is not whether to install controls but which controls to install to control their building lighting systems.
The lighting requirements of ASHRAE/ IESNA 90.1-1999, Energy Standard for Buildings Except Low-Rise Residential Buildings, have been updated from the 1989 version. This energy standard is central to any discussion of lighting because it is the basis of most building codes. It already is the basis for federal buildings and was adopted for the 2001 version of the International Energy Conservation Code.
The standard is written in code language because states must certify that they have energy codes in place by July 15, 2004, that are at least as strict as 90.1-1999 or that provide reasons for non-compliance. The U.S. Department of Energy (DOE) is providing funding to states to assist with the incorporation of 90.1 in their building codes.
In the new standard, lighting controls are required more extensively than in the 1989 code. Scheduling or occupancy sensor controls now are required for buildings with a total interior lighting allowance of more than 5,000 watts. The only exemption is systems that require round-the-clock operation, such as emergency lighting.
Managers can choose programmable time controls, but they need to provide an independently programmed schedule for some areas and may not have more than one program per floor of the building. Alternatives to the scheduling control include occupancy sensors that turn off within 30 minutes after no occupancy is detected and an automatic shutoff control that receives signals from another control, such as a building management system.
The impact of adopting this energy code is apparent when one considers these statistics: About 90 percent of commercial buildings were built before 1986, and in most of these buildings, 50 percent of electrical energy use can be attributed to lighting systems, according to the New Building Institute. By comparison, in newer buildings, only 30 percent of electrical energy powers lighting systems.
Lighting controls save money by controlling the hours systems are on or by reducing lighting system power. Electricity is paid for in kilowatt hours (kWh), and kWh costs drop when either the hours of use or the kW drop. In many cases, reducing kW will generate more cost savings than reducing hours because it reduces peak demand and its associated high cost.
Many lighting systems are switched with circuit breakers. After many years of operation, breakers used this way can fail to trip on overload due to spring wear. This situation can be a serious safety problem. If breakers are required to switch lighting loads, switch duty (SWD) breakers should be used.
Managers must be aware that some lighting systems — high-intensity discharge (HID) and heavy tungsten loads — have high inrush current when switched. Breakers used for these applications must be rated for these loads. Instead of breakers, managers should consider switches, relays and contactors, which are better for switching lighting circuits – if they are used. But when building occupants do not turn off lights, automatic controls might be more desirable.
Timers, central controls and occupancy sensors provide automatic means to control the time lighting systems operate. Time controls and centralized time-of-use scheduling are best suited to buildings that operate on highly predictable schedules that do not change often.
Lighting surveys often reveal that facilities have bypassed timers and central control systems, largely out of frustration from constantly changing building schedules. A better solution for non-predictable schedules is distributed controls that use occupancy recognition strategies to automatically turn on lights when people are present and turn lights off after the room is no longer occupied.
A pilot study in a Boulder, Col., federal building found that the use of energy for lighting dropped 50 percent after the installation of occupancy sensors.
Two principal technologies used for occupancy sensors are passive infrared (PIR) and ultrasonic. PIR sensors react to body heat and sense occupancy by detecting the difference in heat from a body and the background. A lens creates “fingers” of detection zones, so PIR sensors use line-of-sight sensing to “see” an area to control it.
The most common mistake in applying PIR sensors is using a wall-box unit in restrooms. An entrance is a good location for a switch, but it does not allow the sensor to see into the restroom. Consequently, the sensor will time out and turn out the lights while people are still in the room. Ceiling-mounted ultrasonic units work better.
Ultrasonic sensors use volumetric detectors and broadcast sounds above the range of human hearing, then measure the time it takes the waves to return. These units can detect persons behind obstructions, but they also are sensitive to air movement from HVAC diffusers.
Sensors feature two adjustments – delay and sensitivity. The delay adjustment sets the time that lights are on after no occupancy is detected. Technicians should not set delays for less than 10 minutes so that lamp life is not affected. The sensitivity adjustment makes the unit either more or less sensitive to motion. Ultrasonic units are adjusted so they are not sensitive to air movement.
Managers should specify the correct occupancy sensor technology for each application. For example, they might consider using dual-technology models for locations in which neither PIR nor ultrasonic sensors alone will meet difficult challenges, such as false shutoffs. Both technologies must agree on occupancy conditions before switching.
Photocells are light-sensitive switches that operate when light falls on them. They turn on outdoor lighting at dusk and turn it off at dawn. A built-in time delay prevents lightning from turning off lights.
Photocells fail in the on, or failsafe, position. They should be aimed toward the north to view the reflected light of the north sky. If they are aimed east or west, they are biased by the directionality of exposure. When aimed south, the intensity of the southern exposure degrades them much faster.
Cadmium sulfide photocells are the least expensive type, but they degrade from daily exposure to the sun, which causes a loss of sensitivity and erodes energy savings by keeping the lights on longer than necessary. To avoid this situation, managers should direct that photocells be changed when workers are changing HID bulbs, or they should specify photocells with silicon sensors that last longer and do not degrade as quickly or easily.
Dimming using contemporary controls can save energy by reducing the kW portion of kWh. Managers can expect savings of 75 percent when they specify individual manual desktop dimmers, according to the Boulder pilot study, and several subsequent studies have verified this finding. When building occupants have a local dimmer that is easy to use, they tend to set their light level lower than 100 percent.
Conference rooms traditionally have two lighting systems — an incandescent dimming system with wall box dimmers and a fixed-light fluorescent system to provide ambient lighting. To cut energy costs, managers might consider having the incandescent system removed and replacing ballasts in the fluorescent system with line-voltage dimming ballasts that connect to existing incandescent wall-box dimmers.
Aside from energy savings, the lower maintenance cost is the principal benefit because this strategy eliminates the high labor cost associated with replacing incandescent lamps frequently.
New technology has emerged in recent years that increases the opportunities to apply daylighting techniques cost-effectively. The goal of daylight harvesting is to couple photosensors to fixtures in ways that reduce energy use while optimizing illumination levels for occupant comfort.
New sensors and electronic dimming ballasts provide distributed control that operates independently to detect conditions in small areas and controls the light from a few fixtures in that area.
In an active daylighting design for fluorescent lighting, a photosensor reads ambient light. If the daylight is sufficient to light the space, the connected electronic dimming ballast receives a signal to reduce light output to its minimum value.
As sky conditions change, the photosensor signals the dimming ballasts to increase the light output of fixtures to supplement the daylight. The change must occur slowly, using a fade control to avoid disturbing building occupants.
Lighting controls can save energy and provide many other advantages, but only for facilities that learn how to specify, install and operate them correctly.
John L. Fetters is a certified lighting efficiency professional and principal of Effective Lighting Solutions in Columbus, Ohio.
Switching Myths Debunked
Many facilities professionals believe a number of myths surrounding lighting system operation that tend to get in the way of energy and cost savings.
For example, there is the belief that continuously operating fluorescent lights is cheaper than turning them off for brief periods of time. Actually, turning off fluorescent lights saves energy, extends overall lamp life and reduces replacement costs. Turning off one T8 fluorescent tube for 1/2-hour each day saves enough money in energy over the life of the tube to pay for the tube.
A second, related myth holds that lights shouldn’t be turned off because it shortens lamp life and increases maintenance costs. Actually, fluorescent lamps will run more hours when operated continuously, but they will last for many more years if they are turned off when not in use. Although switching shortens the average rated life of fluorescent lamps, it extends calendar life — the time between lamp changes, including the time the lamp is off. Since lamp changes are based on calendar life, the average rated life should be of little concern to maintenance managers.
For example, T8 lamps operated continuously result in a rated lamp life of 34,000 hours, a calendar life of 3.9 years. Turning them off for 12 hours each day decreases the average rated lamp life to 30,000 hours but extends the calendar life to 6.8 years. This means the relamping interval increases from 3.9 years to 6.8 years, reducing maintenance labor costs.
— John L. Fetters