Employing daylight to reduce electricity can be an attractive energy opportunity for building owners and operators, with lighting accounting for nearly 40 percent of all energy consumed in modern buildings.
Independent studies have demonstrated high energy-cost savings potential of 40 percent in open offices, 50 to 70 percent in private offices, and up to 50 percent in classrooms using daylight-harvesting control strategies. Daylight-harvesting controls can be effective in virtually any type of facility—office buildings, hospitals, educational institutions—where interior lights operate a majority of the time and ample daylight is available.
According to Craig DiLouie, speaking on behalf of the Lighting Controls Association, demand for good daylight-harvesting controls is growing, driven largely by green construction, particularly Leadership in Energy and Environmental Design (LEED) projects, and the latest generation of energy codes and standards now requiring it. He said the most significant recent developments in commercial daylight-harvesting technologies are digital control architectures, the promise of greater reliability with dual-loop sensing, and new opportunities for existing buildings with wireless controls and line-voltage dimming ballasts.
“The digital revolution sweeping lighting control is particularly advantageous for daylight harvesting, as it allows easy, remote, toolless and ladderless calibration and zoning via the control network,” DiLouie said, adding that digital systems also are able to provide control zoning as small as single lighting fixtures or ballasts to make the system truly responsive to gradients of daylight distribution. This architecture can easily be rezoned and recalibrated without rewiring and tools.
Industry experts are bullish on the potential for daylight-harvesting controls to help conserve energy where daylight is available for a space.
“Building owners and operators are challenged today with many tough economic concerns, and saving operating costs with daylight harvesting may not be on their radar,” said David Weigand, director of sales, Encelium Technologies, Teaneck, N.J. “Progressive contractors who are now performing regular service work for these folks have an opportunity to increase their business and save their customers money by proposing an integrated lighting control system.”
Daniel Trevino, product line manager for WattStopper, Santa Clara, Calif., notes that increasing awareness and education are important milestones to achieving greater market acceptance. He said it is important to gain a fundamental understanding of daylight-harvesting control concepts, including the sequence of operation and how application-sensitive controls will communicate with other automatic controls, such as occupancy sensors and wall switches. Another key aspect to a system’s performance is placement of photosensors for obtaining the most accurate light level data to optimize energy savings.
“Once the photosensor is correctly positioned in the space, the contractor needs to know how the device is calibrated or commissioned, even though he may not be the individual performing this work,” Trevino said.
When consulting with clients, contractors must learn how the customers intend to control the lights. The two choices are switching or dimming. Switching entails separate circuiting and control of alternate lamps/ballasts, fixtures or fixture rows. Bilevel or multilevel switching enables one or more steps between off and full output.
There are two types of dimming. Step dimming is typically similar to bilevel switching in control effect, but the change in lighting state occurs across all lamps, providing a uniform visual appearance.
Continuous dimming enables a smooth, continuous change in light level across the given dimming range that can produce greater energy savings in spaces like offices where daylight levels are highly variable and/or close to electric light levels. These systems typically present a higher initial cost and more sophisticated commissioning.
Another key decision point is whether the daylight--harvesting control system should be closed-loop, open-loop or dual-loop. Closed-loop systems measure the combined electric light and daylight level reflected from the task surface. This allows a set target light level that the controller maintains by adjusting electric light output through switching and/or dimming. The sensor “sees” the results of its adjustment and may make further adjustments based on this feedback, thereby creating a closed loop.
While some consider closed-loop systems to be more precise than open-loop, sensor placement is more critical in spaces where indirect general lighting is installed. Commissioning is regarded to be more complex in closed-loop than with open-loop systems, although some manufacturers have introduced closed-loop sensors with auto-commissioning capabilities.
Ideal applications for closed-loop systems include windows with blinds or shades and spaces with frequently changing lighting conditions. Ideal open-loop system applications include skylights or clerestories (rows of windows set into upper walls) without shades and spaces with relatively constant daylighting conditions.
Dual-loop technology, being developed by WattStopper in partnership with the California Lighting Technology Center (CLTC), represents a new-generation technology that combines the advantages of open-loop and closed-loop sensing to increase overall reliability and is particularly well suited to skylighting applications, such as big box retail buildings.
According to Andrew Lawler, national sales manager for Lutron Electronics Co., Coopersburg, Pa., radio frequency wireless photosensors are now available for commercial building applications where it is too costly or impossible to run control wires, such as for outdoor lighting and in parking garages, warehouses and retrofits. Photosensors can be placed on the ceiling, and light switches can be replaced with a wireless switch or dimmer that will automatically adjust light levels when sufficient daylight is present.
“Wireless technologies provide an opportunity for the electrical contractor to be more competitive on their bids by recognizing some labor savings,” Lawler said.
Unlike an analog system, occupants can override a digital system’s photosensor by using programmable low-voltage manual controls. The entire system can be programmed, calibrated and adjusted over a network, with no tools or ladders.
One of the benefits of a digital architecture is that it enables a daylight-harvesting system to have control zones. Zones can be as small as the lighting covered by a distributed controller such as a single ballast or lighting fixture. Smaller loads can be grouped into larger zones as needed. As space needs change, the lighting can be rezoned without rewiring.
“The ultimate goal in daylight harvesting is to get to a dimmable zone controlled application. In the past, generally, you had to have a separate dimming control system in addition to your relay control added cost and complexity and now, especially with the digital lighting systems, it’s all part of the system,” said Bob Freshman, marketing manager for lighting and energy solutions, Leviton Manufacturing Co., Melville, N.Y.
Industry experts caution that more effort needs to be made to qualify daylight before implementing controls.
“As daylight-harvesting controls become more popular, specifying professionals need to have clear guidelines for identifying where daylight harvesting controls should be implemented and where they should not,” said Eddie Hickerson, Schneider Electric, Palatine, Ill., field services and application engineering manager.
Energy codes and standards are now beginning to regulate the minimum size of control zones. DiLouie commented that the latest generation of commercial building energy codes and green construction codes and standards, including ASHRAE/IES 90.1-2010, IECC 2009, California Title 24-2008, ASHRAE 189.1 and CALGreen, address daylight harvesting. While each requirement is slightly different, the common theme, he said, is to identify primary zones of high, consistent daylight levels in the building, and separately circuit and control general lighting in these zones. Beyond this basic requirement, the code/standard may require or provide incentive for (through design power credits) automatic bilevel switching or dimming and expansion of daylight harvesting into secondary as well as primary daylight zones.
ASHRAE 90.1 2010, for example, defines a sidelighted daylight zone’s width as window width plus 2 feet on either side, limited only by 60 or more inches of partitions. Depth is defined as one window height (distance from floor to top of window), limited only by 60 or more inches of partitions. Contiguous windows produce a single daylight zone. Any electric lighting in the daylight zone must be controlled separately from other general lighting in the space.
Additionally, ASHRAE/IES 90.1 2010 also requires that daylight-harvesting control systems be commissioned, with specific requirements related to document turnover and performance testing.
“Overall, daylight harvesting is a welcome addition to energy codes, but ideally all of these codes and standards will harmonize their different approaches in the future to avoid confusion,” DiLouie said.
LEED 2009 encourages daylight and daylight harvesting. IEQ, Credit 8.1, awards one LEED point for introducing at least 25 foot-candles of daylight into at least 75 percent of regularly occupied building areas. Daylight-harvesting controls can then be used to earn energy points.
“Our main mantra is ‘sunlight’s free, so use it.’ The purpose of daylight-harvesting controls is to harness available light and take advantage of it because energy costs are not going down,” Leviton’s Freshman said.
MCCLUNG, owner of Woodland Communications, is a construction writer from Iowa. She can be reached at email@example.com.