Energy codes provide a minimum standard for new construction of commercial buildings. Your local code may be a unique one developed by the state or municipality, such as California’s Title 24, or may be based on a version of ASHRAE 90.1 (1999, 2001, 2004, 2007) or the International Energy Conservation Code (IECC) (2001, 2003, 2006) standards. While the country is regulated by a patchwork of codes, all codes must be at least as stringent as ASHRAE 90.1-1999, the national energy standard.
On one point, all energy codes agree: Lighting controls are mandatory to eliminate waste and save energy.
Because many electrical contractors often find themselves in the role as lighting and control system designer, they should be aware of their applicable energy code(s) and offer code compliance as part of this service.
IECC and 90.1 both require indoor lighting systems in commercial buildings larger than 5,000 square feet be automatically shut off when not in use, with some exceptions.
How is that accomplished? First, the system could be scheduled to shut off at a time when it is predicted nobody will be there. According to the California Energy Commission (CEC), automatically shutting off lights after work hours can offer 5–10 percent energy savings.
Because scheduling is based on time of day, this strategy is best suited for controlling lighting where people work a predictable schedule, such as open offices, retail sales floors and similar applications. It’s also well suited for spaces that are intermittently occupied but where we want to keep the lights on, such as corridors, lobbies, parking lots, sidewalks and other public spaces.
While there are several options for scheduling, it is often implemented by low-voltage control systems, in which local controls are hardwired to low-voltage relays housed in an intelligent control panel with an integral processor and time-clock for programmable scheduling. Because each local control requires a wiring homerun, this type of control is economical for control of large public spaces. Other approaches to scheduling include building automation systems and digital ballast-based systems.
Codes require that each scheduling program be no larger than 25,000 square feet and not more than one floor. This ensures a minimum level of control flexibility. Each program, however, could contain identical schedules.
Second, occupancy sensors could be installed that monitor the space and turn off the lights when the spaces are unoccupied. According to the New Buildings Institute, automatically shutting off lights based on occupancy sensing can produce 25–45 percent energy savings in offices and classrooms.
Occupancy sensor-based shutoff provides economical distributed control, or ability to control a localized space, and also directly reacts when a space is unoccupied. Occupancy sensors are, therefore, ideally suited to enclosed spaces where there is an unpredictable rate of occupancy, such as restrooms, lunch/break rooms, meeting rooms, copy rooms and so on.
Codes require the occupancy sensor turn the lights off within 30 minutes of the occupant leaving the space, ensuring energy savings. Control manufacturers recommend a 15- to 20-minute time delay as a good compromise between energy savings and lamp life. If lamp life is a major concern, consider extended-life lamps and programmed-start ballasts.
ASHRAE 90.1-2007 also encourages occupancy sensor control of furniture-mounted task lighting, stipulating that it does not have to be counted as part of the installed interior lighting power if it is controlled by automatic shutoff.
The timer switch, which turns off lights in a single-load switch leg after a time period once the lights have been switched on, is a final form of automatic shutoff. This type of control is typically applied to storage rooms, mechanical and electrical rooms, supply closets and janitorial spaces.
Third, the control system could be set up to shut off the lights when it receives a command from another building control system such as a security system. When the building is vacated and the security system is armed, a signal is sent to the lighting control system to turn off the lights. This approach is often overlooked, but can be effective in retail and small office applications.
IECC and 90.1 both require installed controls for general lighting in enclosed spaces, with some exceptions. Two methods qualify: First, we could install occupancy sensors. This would satisfy both the automatic shutoff and space control requirements. Second, assuming a scheduling control system is being installed, we could install override switches.
Scheduling controls shut off the lights based on a time event, not whether the space is occupied. So that people working after hours do not suddenly find themselves in the dark, occupants should be given the capability of overriding the scheduled shutoff. IECC and 90.1 require manual controls located so that users can see the lights being controlled but allow remote manual control in appropriate applications.
Manual controls can be switches or dimmer-switches. ASHRAE 90.1-2004 and -2007 have another requirement: If the space is a classroom (with broad exceptions, including shops, labs and preschool through grade 12 classrooms), conference/meeting room or employee lunch/break room, it must have occupancy sensor control if a multiscene control, such as a dimmer, is not used. In addition, IECC and 90.1 have special requirements for guest rooms and suites in hotels and similar buildings.
If we give occupants working during the scheduled shutoff time override capability, we don’t want them turning the lights on in a large area or entire floor if they only need light in a small area, as this would waste energy. As a result, energy codes limit the maximum control zones for space controls. According to the IECC, the controlled area cannot be larger than 5,000 square feet (20,000 square feet for malls, arcades, auditoriums, single-tenant retail spaces and industrial spaces or arenas where captive-key override is used). ASHRAE 90.1 limits the coverage area at 2,500 square feet if the enclosed space is less than 10,000 square feet and 10,000 square feet if the enclosed space is greater than 10,000 square feet.
Additionally, if we allow occupants to override the scheduled shutoff, we eventually want the lights to automatically shut off after they’ve gone. Energy codes therefore limit the amount of time the override is in effect. IECC limits it to two hours, while 90.1 limits it to four. This can be accomplished with an intelligent control panel that conducts sweeps or uses conditional logic to turn off the lights or digital switches that have timed shutoff functionality incorporated into the switch. Digital switches also allow networking, which provides a simple way to control a load from multiple switch locations, including local and remote, and some offer dimming capability. During the next shutoff, if there is still an occupant in the area, these methods can override the shutoff again and so on until the occupant leaves.
Although not required by code, local occupants should be warned that the lights are about to shut off, if possible. For example, if the lights are about to be shut off, and as long as the lights are not high-intensity discharge, the panel can flick all or a portion of the lights off and on or cause an audible warning.
Light level reduction
IECC requires that occupants be given the ability to reduce lighting load in a reasonable uniform pattern by at least 50 percent in each indoor enclosed space, with some exceptions. ASHRAE 90.1 does not have such a requirement. Basically, this means bilevel switching, which the National Electrical Manufacturers Association says can generate 10–15 percent energy savings.
Three main options are available: First, we could circuit the lighting so that alternate rows, fixtures or lamps can be switched to achieve 50 percent light output and power input reduction.
Second, we could switch three-lamp fixtures so that the inboard lamp is electrically separated from the two outboard lamps, enabling 33 percent and 66 percent light output and power input reductions. If the lighting circuits are set up for bilevel switching, consider also setting up automatic scheduled shutoff of selected circuits to shed load during peak demand periods and/or in response to a utility request—as long as the switching effect will not irritate occupants—a strategy that can produce 5–15 percent energy savings, according to the California Energy Commission.
Third, we could install dimming. One exception to this IECC provision is occupancy sensors. If occupancy sensors are used, the enclosed space does not require bilevel switching. In fact, if occupancy sensors were installed in a private office, it would satisfy the automatic shutoff, space control and light level reduction requirements of IECC and 90.1.
Display/accent lighting control
ASHRAE 90.1 requires display/accent lighting be controlled independently of general lighting. This can be accomplished with an intelligent control panel with programmable switches.
By separately controlling display/accent lighting from general lighting in a store, for example, display lighting can be scheduled only during shopping hours, while the general lighting can operate during the store’s full operating hours.
DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.