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LD+A The Magazine of the Illuminating Engineering Society of North America

Lighting Research & Education

Smart Corridors Light the Way to Energy Efficiency

Managing the lighting in secondary spaces such as stairwells, lobbies and service rooms based on occupancy can carve a big chunk out of overall energy use

BY NICOLE GRAEBER AND KONSTANTINOS PAPAMICHAEL

I f a light dims down to the minimum recommended illumination level in a secondary space and no one is around to see it, does it really make a difference? Research shows yes—it makes a big difference in reducing lighting energy use.

Laboratory and field testing of prototype systems that dim corridor lights down to 50 percent or less of full output during vacancy periods and increase to full output during occupancy show significant reduction in lighting energy use and great potential for effective electricity demand response.

Far from missing the luxury of fully illuminated empty corridors, occupants report that they enjoy the welcoming light-level change and the satisfaction that comes from being in a more eco-friendly space.

For a number of reasons—including budget restrictions, legislative statutes, as well as growing eco-consciousness—building owners and facility managers are seeking ways to increase building energy efficiency. When it comes to lighting, they are looking for maximum load shed and energy savings at minimum investment cost. With approximately 35 percent of energy use in California’s commercial buildings attributable to lighting1, adaptive lighting retrofits provide a relatively easy strategy for reducing energy consumption. Lighting is also ideally positioned to shed load during critical peak electricity demand events.

Certain building types attribute more of their energy use to lighting than others according to the commercial lighting profile compiled by the California Energy Commission2. But common among all building types are secondary spaces, such as corridors, stairwells, lobbies and service rooms, which are usually fully illuminated at all times. Managing lighting in these spaces based on occupancy proves to be a very effective strategy for energy savings and peak demand reduction. It’s an easy strategy, too, with networked control solutions commercially available for both retrofit and new construction projects.

Bi-level lighting systems use occupancy detection technologies to switch or dim the lights from full output during occupancy to a lower level during vacancy. In addition to providing significant energy savings, when networked, these systems can provide a very effective demand response approach, reducing lighting in transient areas, where building occupants are not usually performing tasks. The required technology is widely available and current R&D is under way to improve the occupant experience.

Typical corridor lighting in commercial buildings operates 24 hours a day, seven days a week. This is because public spaces require a minimum level of illumination3 for safety at all times, making corridors and similar secondary spaces a large factor in the total energy use attributed to electric lighting in California’s commercial buildings.

Figure 1.

A survey conducted by UC Davis on the campus’s lighting energy use indicates that corridors are one of the largest lighting energy use spaces (Figure 1). Incumbent lighting systems in corridors and stairwells are typically equipped with the building’s standard: non-dimmable ballasts operated with wall switches or from panel boxes.

BI-LEVEL APPROACHES
The current market offers a number of adaptive, bi-level lighting systems. The simplest versions of occupancy-based adaptive systems use step- or full-dimming ballasts paired with occupancy sensors and wired communications. More advanced systems offer additional control capabilities such as scheduling and tuning, which are easily run independent of a building’s management system (BMS), or tied in at a later date at the discretion of the customer. This solution is often appropriate for retrofit installations, where tying into the BMS may not be easy or cost-effective. Systems on the market today offer wired and wireless communication strategies between system components.

In addition to adaptability based on occupancy, scheduling and tuning, the most advanced systems include the ability to adapt to available daylight if appropriate for the space. These systems are usually incorporated into the BMS but can also operate independently. Linking the systems to the BMS allows lighting loads to be easily controlled via existing building scheduling. This feature also enables users to participate in automatic demand-response programs offered by utilities, and to reap the benefits of participation, namely, lower energy bills and incentive payments from utilities offering demand-response programs. These solutions are appropriate for both retrofit and new construction applications.

In addition to enabling further energy savings, tuning capabilities also give facility managers control over quality factors such as lumen maintenance. Lighting is often designed to initially over-illuminate spaces. This ensures that, even as light output degrades over the course of a lamp’s life, light levels will remain adequate. With a tunable lighting system, this is easily remedied by trimming the initial occupied level down to the design light level. The end users’ total experience with the system is improved as they’re able to find that sweet spot between energy savings and light output, providing just the right amount of light, where and when it is needed.

FIELD WORK
With support from government and utility partners, the California Lighting Technology Center (CLTC) is demonstrating and evaluating various smart corridor technologies in the laboratory and in the field. The evaluations focus on energy savings, demand-response effectiveness and occupant response, while continuing research and development projects aim to improve occupant experience through networked occupancy sensing.

Figure 2.

Results from monitoring occupancy in corridors and stairwells of educational and office buildings show occupancy rates range between 6 percent and 36 percent. Figure 2 shows the typical pattern of a secondary space.

One case study, sponsored by the California Energy Commission’s Public Interest Energy Research (PIER) program, took place in Bainer Hall at the University of California, Davis campus. The demonstrated lighting systems successfully implement bi-level strategies by pairing occupancy sensors and dimmable light sources in corridors. High- and low-trim levels are set according to occupants’ preferences, meeting goals for both energy-savings and visual comfort.

Results from three different technology installations at Bainer Hall show average savings of 73 percent with payback periods ranging from four-and-half to eight years, which can be significantly reduced with incentives offered by local utilities. In larger, building-wide applications, incurred installation costs are offset by broader energy savings, resulting in a shorter payback period.

Corridors and stairwells are proving to be suitable locations for interior smart, bi-level lighting; the same seems to be true for other secondary spaces subject to lighting level requirements, such as lobbies and service rooms. Exterior spaces, such as parking lots and garages, also lend themselves to occupancy-based bi-level lighting controls. Adaptive roadway lighting is yet another bi-level application with energy-saving potential. And several experimental control technologies are already available for early adopters.

The next step for the smart, bi-level lighting strategy is achieving widespread implementation in commercial and exterior applications. This can be facilitated by continuing inclusion of bi-level strategies in building and energy codes and by offering utility incentives to customers who install adaptive control technologies.

REFERENCES
1 Itron, Inc. “California Commercial End-Use Survey (CEUS).” Prepared for California Energy Commission: CEC-400-2006-005. March 2006. < http://www.energy.ca.gov/ 2006publications /CEC-400-2006-005/CEC-400-2006-005.PDF>
2 Itron, Inc. “California Commercial End-Use Survey (CEUS).” Prepared for California Energy Commission: CEC-400-2006-005. March 2006. < http://www.energy.ca.gov/ 2006publications /CEC-400-2006-005/CEC-400-2006-005.PDF>
3 National Fire Protection Association 101: Life Safety Code. 2012. CA Title 24/NFPA 101 requires that buildings’ means of egress be illuminated at all times the buildings are occupied. California’s Department of General Services typically interprets this as “a minimum of not less than 1 footcandle at the walking surface.”

November 2011