According to the US Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE), daylight harvesting technology can offer significant energy savings by offsetting a portion of the electric lighting load. In addition, it generally improves occupant satisfaction and comfort, while the use of windows can provide visual relief, contact with nature, time orientation, the possibility of ventilation and emergency egress. Key technologies involved in daylight harvesting include fluorescent dimming ballasts, daylight sensors, controllable window shades and occupancy sensors.
Daylight harvesting potential is found particularly in spaces that are predominately daytime-occupied, according to the EERE. Solar analyses of the site should assess the access to daylight by considering what is detectable from the various potential window orientations.
“The location of the daylight sensor in relationship to the windows is one of the most important design considerations of daylight harvesting,” said Michael Jouaneh, marketing manager for Lutron Electronics Co. Inc., Coopersburg, Pa.
The sensor should be placed one to two window heights away from the nearest window for side-lighted applications, he said. When daylight enters a space from a vertical wall area through windows or glass walls, etc., it is termed sidelighting.
In addition, the windows should be oriented in a position that allows the most natural light, according to Mike Crane, product marketing manager for Hubbell Building Automation Inc., Austin, Texas.
“A study by Heschong Mahone Group found that as much as 25 percent of a typical building’s square footage is within 20 feet of a perimeter wall and could be a daylighting opportunity,” said Dave Weigand, national sales and market manager, Leviton Manufacturing Co., Little Neck, N.Y.
“Daylighting design should incorporate the entire building, and all design elements of the project need to be coordinated to maximize the daylight contribution,” Weigand said.
For instance, toplighting—using openings that allow daylight to enter the space from above—is typically implemented in schools, retail, warehouses and manufacturing facilities.
A building designed for daylighting but without integrated controls will not minimize lighting energy use or maximize space functionality and user satisfaction. Control techniques range from the simple to the extremely sophisticated and are most successful when building occupants can easily understand their operating characteristics.
“It is extremely helpful to educate occupants in how the lighting controls work so that they are less likely to be surprised or annoyed by their operation,” Weigand said.
Savings and benefits
For the building owner and tenants, daylight harvesting delivers cost savings through reduced energy consumption.
“The owner can typically save 25 to 75 percent on lighting costs, depending on the location of the building and how much natural light is available,” Crane said.
Also, if the daylight harvesting or lighting control systems are tied into other systems, the building has reduced wear and tear and reduced operating costs for the owner and tenants.
“And, if the daylighting system and controls are integrated with an energy management system, facility managers are better able to control energy consumption and make operational decisions in real time,” he said.
Another benefit derived from daylight harvesting is increased comfort.
“Most spaces are over-lighted because there is enough daylight inside. Daylight control makes spaces more comfortable by reducing electrical light levels when daylight is abundant,” Jouaneh said.
Also, using controllable window shades adds to the comfort of the people inside by eliminating harsh sun glare while maintaining views of the outside.
“People are more productive working in spaces that are not over-lighted and that effectively use daylight. For example, there are studies that show students perform better when more daylight is present in the classroom,” Jouaneh said.
Currently, high demand exists for daylight harvesting in commercial and educational buildings, Jouaneh said.
“Demand is being driven by high energy costs, the green movement and building energy codes that either require daylight harvesting in some instances or provide incentives for using the technology,” he said.
Modern daylight harvesting systems, however, are easy to install and provide flexibility. In configuring a daylight harvesting system, electrical contractors need to understand for what light levels the room has been designed and be able to measure the light levels at each task or workstation.
“Those two pieces of information are critical if the contractor is going to effectively program the daylight harvesting system and deliver a valuable solution,” Crane said.
Contractors that can use physical models, lighting and daylighting computer simulations, and whole-building energy simulation programs can provide their customers with a daylight harvesting system that will provide real impact on building energy use and savings and add value to their services.
BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 or firstname.lastname@example.org.