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Daylight is free, and many spaces inside buildings are daylit, yet electric lighting is left on unnecessarily. Daylight harvesting harnesses this free, natural light, using such building control system strategies as light sensing, occupancy sensing, and shade control, while automatically adjusting the energy use of HVAC and electric lighting systems.
The results? Reduced overall energy costs, coupled with healthy and productive working environments. Daylight harvesting technologies include photocells, occupancy sensors and centralized or distributed control systems. The strategy can be implemented during building design and planning or even retrofitted flexibly at a later time.
"Retrofitting holds many cost-effective daylight harvesting opportunities, making it an attractive option for many facility managers," says Cheryl De Los Santos, manger, marketing communications, Leviton. "Hardwired or wireless technologies can be added to existing systems, as part of one large overhaul or in stages. For example, a facility may begin a daylight harvesting initiative by implementing photocells in skylit spaces, then windowed areas, and finally adding a new, centralized control system with strategic scheduling."
One major takeaway surrounding daylight harvesting is the fact that energy-saving opportunities track with energy consumption during the course of an ordinary day, says Rita A. Renner, director of marketing & communications at WattStopper.
"That is, when energy consumption is peaking, the savings opportunity with daylighting controls also is peaking," Renner says. "The time when daylight contributions are highest, typically from noon until around 4 p.m., is often when the energy or load profile of a facility is highest, as well. So incorporating daylighting control also can provide some opportunities to reduce demand charges in addition to capturing regular energy savings. Reducing the lighting load also can reduce the cooling load, realizing additional savings."
Energy codes also have begun to recognize this opportunity. ASHRAE 90.1-2010 and IECC 2012 incorporate mandatory daylighting control requirements. In California and a few other jurisdictions, these have been already required for a few years.
Dimming strategies are becoming more popular as ways to reduce energy use. "Dimming strategies will allow for more energy savings than on/off strategies alone," says Brian Dauskurdas, Lutron's director, global energy solutions. "Once you add dimming to your building, additional energy saving lighting control strategies can be implemented above and beyond basic automatic lighting shut-off. For instance, continuous daylight dimming (i.e., unobtrusively lowering electric lights when daylight is available) can be done with dimming. Also, light level tuning, personal light control and demand response lighting also can be done with this strategy."
As mentioned above, dimming strategies offer the ability to capture additional energy savings, even when lighting is in use. Various code-making bodies are including multi-level control requirements in emerging codes.
Beyond energy savings, there are other reasons why facility professionals should consider dimming, notes WattStopper's Renner.
"Providing adjustable light levels can boost individual worker productivity," Renner says. "Research suggests when workers have control over their own lighting in their personal work environments, they often will select lower light levels to accommodate personal preferences."
According to the LightRight Consortium, personal lighting control not only saves energy but also increases occupant comfort and productivity. "Distributed control systems allow for individual control of lighting loads, providing the ultimate in precise settings and user satisfaction," De Los Santos of Leviton says.
Daylight Harvesting, Other Dimming Strategies Help Lower Energy Costs