Lighting Control Testbeds at the General Services Administration: Showing Promise for Lighting Energy Reductions
Lighting represents 26 percent of a commercial building's electric load, which roughly translates to 10 percent of a building's operating costs. Advanced lighting controls can greatly reduce that load, but so far, U.S. commercial building owners and operators have not reaped those energy savings—only one percent of those buildings use lighting control systems.
Given the potential savings, why are so few of these systems being used? One reason is that relighting can be costly—especially in existing buildings, where it's impossible to predict what barriers might be encountered during the installation. Unfamiliarity with these systems also deters some potential users from taking advantage of these technologies. Overcoming these two obstacles could greatly increase the use of advanced lighting controls.
Toward Increased User Acceptance
Francis Rubinstein and Joy Wei of the Environmental Energy Technologies Division (EETD) at Lawrence Berkeley National Laboratory (Berkeley Lab) teamed with the U.S. General Services Administration for a Commercial Building Partnership (CBP) study to address the issue. The CBP program was established by the U.S. Department of Energy to demonstrate leading edge technologies, integrated design, and other strategies that could significantly reduce energy consumption in commercial buildings. The study's goal was to develop affordable advanced controls to eliminate wasted lighting energy in existing commercial buildings.
The ambitious goals of the Building Technology and Urban Systems Department's lighting team are to achieve 80 percent lighting energy savings in existing commercial buildings with controls that cost $2 per square foot (ft2) installed by 2015, and to work with industry to create the next-generation controls.
Berkeley Lab addressed this challenge in a couple ways. Rubinstein and others conducted a meta-analysis of estimates of energy savings identified in the literature, spanning 240 savings estimates from 88 papers and case studies, categorized into daylighting strategies, occupancy strategies, personal tuning, and institutional tuning. That study revealed that the average energy savings potential of the various approaches is 24 percent for occupancy controls, 28 percent for daylighting, 31 percent for personal tuning, 36 percent for institutional tuning, and 38 percent for multiple approaches. It also revealed that simulations in the literature significantly overestimated—by at least 10 percent—the average savings obtainable from daylighting in actual buildings.
"There weren't really any surprises," says Rubinstein. "Those numbers were consistent with what we had seen in demonstration projects we had conducted."
Demonstrating Individualized Lighting and Controls
The CBP study then set out to measure energy savings at 10 demonstration sites in seven federal buildings in California and Nevada.
They started by replacing the existing lighting with workstation-specific lighting that consisted of a new energy-efficient luminaire with a built-in occupancy sensor and individual-controlled digital dimming ballast centered over each workstation (Figure 1). This system enables users to control both occupancy sensing and light level tuning for each workstation, so users could set lights as they pleased. Similar relighting arrangements have achieved 40 percent lighting energy savings and greater occupant satisfaction with workspace lighting. Using data loggers at the circuit level, the team gathered pre-retrofit and post-retrofit lighting power use data under various operating scenarios for all of the sites, which enabled them to calculate and compare pre-retrofit and post-retrofit energy use.
They also documented lighting conditions with standard photometric surveys and conducted occupant surveys to gauge user acceptance of the controls, to help determine which controls are most likely to be used. The duration of each demonstration varied from one to two years.
Proven Lighting Energy Reductions
The advanced lighting controls were found to lower energy consumption and lighting energy use intensity (EUI, the energy consumed by a building relative to its size) at all of the sites, although the installation of new fixtures resulted in similar or increased installed lighting power density (LPD; watts per square foot for a given space).
The before-and-after measured lighting energy use differed dramatically from site to site, ranging from a 0.75 kilowatt-hour per ft2 per year improvement at the Chet Holifield Federal Building in Laguna Niguel, California, to a 4.29 kilowatt-hour per ft2 per year difference at the Roybal Federal Building in Los Angeles, California. The before-and-after energy savings in the buildings studied ranged from 26 percent to 66 percent, with an average savings of 46 percent (Figure 2).
Given that the controls allowed users to implement institutional tuning and scheduling, personal control, and occupancy sensing, the study also looked at each of these options individually, to determine the energy reductions from each. At the Roybal site, where lights operated almost 24/7, the highest level of reductions came from institutional tuning and scheduling, then from occupancy controls, and to a lesser extent, from the use of personal controls.
In spaces that were used by many people but owned by no one, such as grand jury rooms and filing and conference rooms, occupancy controls resulted in deep energy savings. Often, lighting in such spaces had been left on continually, regardless of whether they were occupied or not. Institutional tuning and scheduling also contributed to energy savings in these spaces.
Some potential energy reductions were not fully realized because some controls were not consistently implemented in similar spaces.
"Lighting in some rooms used occupancy sensors, while others were controlled with a manual switch," said Wei. "In some instances, occupants thought all of the rooms were controlled by occupancy sensors, so they left the conference room lights on all the time. That underscored the need for consistent programming and occupant training."
Further savings were considered to be possible from eliminating standby power at night and through continued fine-tuning of the system throughout the study. For example, three buildings that revised their operational sequences after their initial performance checks were able to increase their savings 6 percent to 14 percent beyond those initial checks.
How Do the Savings Pencil Out?
Energy saving measures are always appealing, but if they aren't cost-effective, they aren't likely to be adopted. In looking at cost-effectiveness, the team chose to estimate savings-to-investment ratio (SIR) over simple payback, because the SIR approach accounts for savings throughout the life of the equipment—past the simple payback time frame.
"The SIR approach looks at the energy savings over the lifetime of the equipment, at least 15 years, accounting for the time value of money," says Wei. "An investment is considered cost-effective if the sum of the benefits is greater than the costs. The GSA, Department of Defense, and other federal buildings generally use such life-cycle cost methods."
The study found that because of high installation costs for the new lighting equipment, only 2 of the 10 demonstration sites proved to be cost-effective using site-specific rates of $0.09/kilowatt-hour (kWh) in Nevada and $0.11/kWh–$0.13/kWh in California. On average, the retrofits would achieve cost-effectiveness with energy rates of $0.24/kWh or pre-retrofit installed LPDs of 1.3 watts/ft2. However, the lighting EUI in the eight non-cost-effective buildings was lower than the national average, 4.5 kWh/ft2/year, to begin with, so they were already operating more efficiently than the average lighting system. With less room for improvement, less energy was saved.
If the buildings operated above the national average lighting EUI, all of the retrofits would be cost-effective with energy rates greater than $0.17/kWh—and most would be cost-effective at rates above $0.13/kWh, such as those found in some areas of California.
Strategies for Success
What do these results mean in terms of expanding the use of advanced lighting systems? As previously mentioned, cost-efficient systems and familiarity and ease of use are the most critical considerations to ensure the installation and effective use of such systems, and in those areas, the outlook is promising.
"Equipment and labor are the two biggest cost factors," says Rubinstein. "We can make it cheaper to install the system if we preserve the existing luminaire spacing and avoid redesign. We can reduce labor costs even more by using wireless controls, which will mean we don't have to wire above the ceiling."
"Still, if occupants don't buy into using these controls properly, we won't see those deep energy reductions we're looking for. Good training of occupants and facility managers is essential. If the users understand the benefits and are able to easily control the lighting to meet their needs, there's a good chance these systems will achieve their energy-reduction potential."
Demonstrating the advantages of lighting systems that report energy use in real time for utilities, regulators, and building code compliance are also likely to boost the chances for the success of these systems, as will making commissioning simple, automatic, and transparent.
"The success of advanced lighting controls relies on awareness of their potential benefits, cost of installation and operation, and ease of use for occupants and building management," says Wei. "As that understanding advances, resulting in improvements in responsive lighting systems and allowing for easier installation and greater flexibility, we should begin to see these systems become more widespread."
Alison Williams, Barbara Atkinson, Karina Garbesi, and Francis Rubinstein (Lawrence Berkeley National Laboratory) and Erik Page (Erik Page & Associates). 2011. A Meta-Analysis of Energy Savings from Lighting Controls in Commercial Buildings. [PDF]
Williams, Alison, Barbara Atkinson, Karina Garbesi, Erik Page, and Francis Rubinstein. 2012. "Lighting Controls in Commercial Buildings." LEUKOS 8(3) 161–180.
Wei, Joy, Abby Enscoe, and Francis Rubinstein. 2012. Responsive Lighting Solutions. Lawrence Berkeley National Laboratory. [PDF]