Lighting Controls Save Energy - EPM Archives

Greater availability of simple controls through improved technology and stricter building codes make the choice not whether to install lighting controls but which controls to install.

The lighting requirements of ASHRAE/IESNA 90.1-1999 are important because they are the basis for other building codes, including the International Energy Conservation Code (IECC) and codes covering federal buildings. ASHRAE 90.1 requires scheduling or occupancy sensors for most buildings larger than 5000 square feet. Users can choose programmable time controls, occupancy sensors, or automatic shutoff controls.

These lighting controls save money by controlling the time that the systems are in operation. Utility bills decrease when hours-of-use decrease. When systems are not needed, they can be turned off, but widespread myths inhibit many energy-saving actions.

Misperceptions

Many believe that continuously operating fluorescent lights is cheaper than turning them off for short periods of time. Actually, turning off fluorescent systems saves energy.

A second myth says that turning off lights shortens lamp life and increases maintenance costs. In truth, fluorescent lamps last many years more if they are turned off when not in use. Switching may shorten the average rated life of fluorescent lamps; however, switching extends the service life, which includes the time the lamps are off.

T8 lamps operated continuously have an average rated lamp life of about 34,000 hours (calendar life of 3.9 years). Turning these lamps off for 12 hours each day decreases the average rated lamp life to 30,000 hours, but the service life increases to 6.8 years.

Switching

Circuit breakers are often used to switch lighting systems. Breakers can eventually fail to trip on overload due to spring wear. Switch duty (SWD) breakers should be used when switching lighting loads. HID and heavy tungsten loads have high inrush current and breakers need to be rated for peak inrush current. Switches, relays, and contactors are better ways to manually switch lighting circuits. However, automatic controls such as timers, central controls, and occupancy sensors are best when people do not turn off lights

Time controls are best suited for applications where predictable schedules do not change often. Control systems are frequently bypassed by users, usually as a result of their frustration from continuously changing schedules.

A better solution for intermittently occupied spaces is occupancy sensors that turn lights on when people are present and automatically turn lights off when the spaces are vacated.

There are three technologies used for occupancy sensors, passive infrared (PIR), ultrasonic, and sound. PIR sensors react to body heat; they sense occupancy using line-of-sight sensing. The most common mistake in applying PIR sensors is using a wall-box unit in restrooms. While the entrance is a good location for a switch, it does not allow the sensor to "see" into the restroom. The sensor will often time out and turn lights off on occupants. Ceiling-mounted ultrasonic units work better for this application.

Ultrasonic sensors use volumetric detectors that transmit waves above the range of human hearing, then measure the time for the waves to return. Ultrasonic units can detect persons behind obstructions, but are sensitive to air movement from HVAC diffusers. Sensors that "listen" for sounds in a space usually have integrated PIR sensors.

There are dual-technology models for use where no single type will do the job. Dual technology sensors can solve difficult situations, such as false offs.

Occupancy sensors are often blamed for reducing lamp life, when the problem is usually caused by a poor ballast choice and delay setting. Rapid-start or program-start ballasts are recommended for switching applications. When instant-start ballasts are used, lamp life can be reduced, especially at short delay settings.

Photocells are relays that operate on the presence of light to turn on outdoor lighting at dusk and off at dawn. Photocells fail on (fail-safe). They should be aimed north. When aimed east or west they are biased by the directionality of east/west exposure. If aimed south, they degrade faster from the intensity of the southern exposure.

Power Savings

Kilowatt-hours also are reduced when power (in kilowatts) is reduced. In many cases reduction in power demand reduces cost more than time of operation savings because peak demand charges are also reduced.

Dimming can save energy costs by reducing the power portion when contemporary controls are used.

Conference rooms traditionally have two lighting systems—an incandescent dimming system with wall box dimmers and a fluorescent system to provide ambient lighting. These rooms can be upgraded by removing the incandescent system and replacing the ballasts in the fluorescent system with line-voltage dimming ballasts that connect to existing incandescent wall-box dimmers. The principal benefit is lower maintenance costs from not having to frequently replace incandescent lamps.

Daylight harvesting couples photosensors to fluorescent luminaires to reduce power while optimizing illumination levels for occupant comfort. The sensors and electronic dimming ballasts provide independent zones to control the light from a small number of luminaires. The photosensor reads the ambient light, and, if the daylight is sufficient to light the space, the connected electronic dimming ballast is signaled to reduce light output to its minimum value. As conditions change, the photosensor output signals the dimming ballasts to increase the light output to supplement the daylight.

Data loggers can help identify applications where lighting controls can save energy. A simple, low cost light on/off HOBO logger (www. onsetcomp.com/) or occupancy loggers (www.wattstopper.com or www.sensorswitch.com/) can take the guesswork out of the savings calculation. Lighting controls can reduce energy and cost and are required to meet energy codes. They should be high on every energy manager’s short-term action list.