Good Controls Design Key to Saving Energy with Daylighting

By Craig DiLouie

Published March 2005

Daylighting has become a more important feature of mainstream construction due to the sustainable design movement. Daylighting is the use of daylight as a primary source of illumination in a space.

“Spaces that are daylit provide an improved sense of well being,” says Chris Meek, Research Associate for the Daylighting Lab and a Lecturer in Architecture at the University of Washington. “Increased access to daylight versus no daylight in classrooms has been correlated to large increases in student test scores. Similarly, extremely large increases in retail sales have been attributed to the illumination of grocery stores with daylight via skylights.”

These and other studies have been conducted by the Heschong Mahone Group and illustrate significant potential benefits of daylighting in commercial spaces.

“Many studies over the last 50 years have shown that workers prefer to have daylight and views in their work space,” he adds. “When looking at the bottom line, owners need to recognize that 80-90% of their costs are often in staff salaries and benefits. Anything that enhances staff performance pays back at an enormous rate, and if you are careful, the project can save a great deal of energy.”

These productivity and energy savings benefits have been recognized by the U.S. Green Building Council’s LEED Rating System, Lightfair International (which launched a specialized education program), and the 2005 version of California’s Title 24 energy code.

Daylighting and LEED: Lighting is related to achieving at least 8 points and as many as 22 points in these sections: Sustainable Sites, Energy & Atmosphere, Indoor Environmental Quality, and potentially Innovation & Design Process. Daylighting, which intersects with LEED requirements in Indoor Environmental Quality, Credit 8.1: Daylight and Views, can earn 1 point. This credit requires that 75% of all critical visual task-occupied space must achieve a daylight factor of 2%, and occupants in 90% of regularly occupied spaces must have a direct line of sight to vision glazing.

Daylighting and Title 24: “The 2005 Title 24 is the first instance of skylights being required by a building code for energy savings,” says Lisa Heschong, Principal of the Heschong Mahone Group.

Title 24 now identifies skylights combined with daylighting controls as the baseline efficiency standard for big box-type spaces.

A prescriptive provision requires skylights in these big box buildings, specifically skylights with controls to shut off the lights when daylight is available. The provision applies to buildings >25,000 sq.ft. with >15 ft. ceilings, and to spaces directly under a roof and with general lighting power density of >0.5W/sq.ft. For these spaces, at least one-half of the floor area must be daylit using skylights. The skylights must have a glazing material or diffuser that effectively diffuses the skylight.

In addition, for daylit areas larger than 250 sq.ft., at least one control is required to either control 50% of the power, control fixtures in vertically daylit areas separately from horizontally daylit areas, or maintain uniform levels by means of dimming or alternating lamp/fixture switching. For daylit areas over 2,500 sq.ft., general lighting has to be controlled separately with either automatic multi-level daylighting control or multi-level astronomical time switch, both having to meet requirements of Section 119 (Section 131, 143).

(For more information about Title 24, click here.)

Seventy-five percent of all commercial space in the United States is one-story and directly under a roof, representing significant potential for skylights in office, school, gym, retail, warehouse and similar buildings.

For a daylighting strategy to be successful, the designer must effectively design the electric lighting system and specifically, an effective controls strategy.

Electric Lighting Design: “The key is to have an overall vision of how the lighting system and lighting controls integrate with the daylighting scheme,” says Doug Paton, Daylighting Product Line Manager for The Watt Stopper.

“Lighting is a tremendously important architectural element that has far-reaching impacts on energy consumption, operating costs, aesthetics and ambience, user satisfaction, worker productivity, and the environment,” says Stuart Berjansky, Senior Product Manager, Dimming for Advance Transformer Company. “Lighting is often relegated to low-priority status within the design/build process, when in reality it should be considered upfront and incorporated into the entire building design for maximum effect and benefit.”

In short, electric lighting and daylighting systems should be designed so that they are integrated and complementary. For example, when warm color temperature fluorescent sources (<3500K) are used in conjunction with very cool daylight (>5000K), the lights may appear yellow. To mitigate this effect, many designers specify lamps with a neutral-white color temperature of 3500-4100+K.

Controls are a major area of integration. Daylighting entails the use of daylight as a primary source of illumination. Since daylight is generally available during hours when most commercial buildings are occupied, daylighting is often feasible. However, if the lights are operating at full output when there is ample daylight available, then no energy is being saved and the owner is wasting money. If the building is heated or cooled, daylighting may even result in a net increase in energy consumption if daylighting controls are not present.

“Demand for daylighting controls continues to increase as more buildings are designed for sustainability,” says Paton. “Lighting controls make a daylit space an energy-saving opportunity.”

The strategy is called daylight harvesting. “To some lighting enthusiasts, daylight harvesting may mean use of some active and dynamic method of increasing the quantity of daylight entering a building, but these applications are still rare,” says Pekka Hakkarainen, PhD, Director, Technology & Business Development for Lutron Electronics Co., Inc. “There are emerging technologies in skylights and controllable louver systems that provide such active dynamic control. More commonly, daylight harvesting means simply making use of daylight and reducing electric light intensity in the building. These applications are seen in many public buildings, educational facilities and higher-end office buildings.”

According to Heschong Mahone, energy savings from daylighting controls can range from about $0.5/sq.ft. to $0.75/sq.ft., depending on the building type, location, operation and local cost of energy. Primary factors include the amount of daylight available and the occupancy pattern, plus the control strategy. In addition, since ample daylight is often available during utility peak demand hours (usually 3 to 6 pm), daylight harvesting can reduce demand charges, particularly valuable if a “ratchet clause” is in effect.

Using Controls to Integrate Lighting and Daylighting: There are basically four options available:

• Manual dimming. Occupants can be given the capability of dimming the lights in an area. However, this will probably not result in maximum energy savings.
• Automatic shutoff. This can be accomplished using one of two methods. The simplest method is to use a timeclock. On a regular schedule, the entire fixture can be shut off or individual lamps can be shut off to achieve dual light levels, typically 100% and 50%. The other method is use a light sensor combined with a relay and switch. The light sensor measures ambient daylight and if enough light is measured, the fixture or individual lamps within the fixture are switched off. Staging the switching in a fixture by enabling shutoff of, say, two lamps, then the other two lamps, is often called stepped switching.
• Automatic stepped dimming. Similar to automatic shutoff, stepped dimming can be based on a time-of-day schedule or on sensed quantity of daylight. However, with dimming, light output is gradually reduced, which is less jarring than lights switching on and off. Stepped dimming is often called bi-level dimming because the strategy often involves two levels of light output, usually 100% and 50%. However, if more flexibility is required, stepped dimming can involve three levels of light output.
• Automatic continuous dimming. Based on a schedule or sensed quantity of daylight, fixture light output can be gradually dimmed over the full range, from 100% to 1/5/10% (fluorescent) or 100% to 50% (HID).

Choosing the right strategy depends on the application requirements.

When the 1920s era building at MontgomeryPark in Baltimore was renovated to feature state-of-the-art lighting, Sam Himmelrich, Jr. of Himmelrich Associates, the property developer, opted for a daylight harvesting system using photocells. The sensor essentially sends a signal to the local lighting system, telling it how much dimming to engage based on available daylight levels. “Continuous dimming with daylight trackers was an effective and affordable approach at MontgomeryPark,” says Himmelrich. “The system works, it’s straightforward and simple for end-users to operate, and it minimizes energy use and maintenance requirements.” Advance Transformer supplied more than 2,000 Mark VII dimming ballasts for the project, in addition to some 1,300 Centrium non-dimmable electronic ballasts for areas where photocells were not installed. The building’s first tenant? The Maryland Department of the Environment.

Manual Dimming. Manual dimming is a simple strategy but does not provide programmable control and generally does not provide maximum energy savings because the level of control is dependent on the vigilance of the user. In a manual dimming strategy, the user should have control over their immediate work area via an easily accessible control device. Individuals with responsibility for larger spaces, such building managers, should have authority to control larger control zones. Even if an automatic control strategy is chosen, local user manual override may be desirable.

Automatic Shutoff. Automatic shutoff can provide a low-cost option and is suitable for applications where there is ample daylight that is highly predictable. However, if the entire fixture is shut off, occupants may complain about interruptions (lights suddenly activating and de-activating for no understood reason) and lights being off (again for no apparent reason). In these situations, it is often good practice to educate users about how their control system works, and that their building is using this strategy to save energy.

“Good daylighting control will not annoy occupants,” says Paton. “In fact, if designed correctly, daylighting control has the ability to delight occupants.”

Stepped Dimming. Stepped dimming is popular for HID lighting systems as a lower-cost option for spaces where full light output is needed quickly after switching on (as HID Lamps require a warmup and restrike time). (Click here to learn more about HID dimming.) Stepped dimming is also suitable for fluorescent systems in spaces where daylight levels are variable, where ample daylight is not predictable. In addition, stepped dimming is often considered desirable for spaces with major motion activity such as walking and shelf stocking.

Continuous Dimming. Because continuous dimming follows the daylight pattern very closely, it not only is often more acceptable to occupants, but can produce higher energy savings, particularly in areas with highly variable cloud cover. Continuous dimming also responds to changes in light output due to dirt depreciation on fixtures and lamps, and lamp lumen depreciation due to lamp aging. Lighting systems are generally overdesigned to compensate for these light loss factors, with an initial light output that is typically 15-25% higher than at end of life. By maintaining a constant light level, dimming can compensate for this overdesign and increase energy savings. According to Heschong Mahone, lumen maintenance dimming can result in an additional 5-10% energy savings over the life of the lamps.

Continuous dimming also provides the highest degree of flexibility, particularly for spaces where daylight levels are variable during the day. In addition, continuous dimming can provide greater uniformity of light levels in daylit spaces where some areas receive lower amounts of daylight than others. Continuous dimming is often considered desirable for spaces with minor motion activity, such as reading, writing and conferencing—such as offices and classrooms.

Dimming is often considered to be better design practice in terms of occupant perception. When lamps are switched, the sudden change of light output is noticeable to occupants, and the occupants are suddenly being told they have less light, which can be irritating. When lamps are dimmed, light level decreases but the human eye may perceive a higher light level than is actually recorded by a light meter. For example, 1% measured light is actually perceived as 10%, 5% as 22%, and 10% as 32% (following the square law). In addition, research conducted by the Lighting Research Center suggests that people do not notice changes in light levels from dimming as much as they do from switching. (For more information about both of these phenomenon, click here.)

When designing a continuous dimming system, an important consideration will be the creation of control zones. All lamps in a given control zone are dimmed and regulated by a controller and a photosensor. For gaseous discharge lighting systems, each lamp is dimmed using a dimming ballast.

Continuous dimming is achievable using either analog or digital ballasts.

Analog ballasts are currently the most popular type and may be 0-10VDC, two-wire phase-control, three-wire phase-control or wireless infrared.

Digital ballasts are a more recent introduction and offer new opportunities in dimming and lighting control. Benefits include greater granularity of lighting control, reconfiguration without rewiring, possibility of providing an estimate of energy consumption, and smaller control zones than was previously practical. Most digital ballasts are compatible with the DALI protocol. (For more information about dimming ballast technology, protocols and application, click here.)

“A major technological trend that is positive for the industry is the continued drive towards cross-compatibility among various controls manufacturers,” says A. J. Glaser, President of the Lighting Controls Association and HUNT Dimming.

Controls Application Tips: When planning a controls system to integrate with a daylighting strategy, consider the following tips:

• Integrate lighting and lighting controls design into the initial planning and design process.
• Design control circuits parallel to the daylight contours to create control “zones” that match daylight availability/coverage patterns.
• Allow users to manually override automatic controls.
• Consider integrating automatic lighting control with automatic window shades, blinds or other devices that can reduce direct glare and heat gain.
• Adapting existing buildings for dimming is often not difficult, but adapting them to daylighting can be. Single-story buildings with simple roof structures are often easiest to upgrade for daylighting, particularly spaces with high ceilings.
• Specify commissioning services as a separate item, to be bid separately.
• Light sensors should be located carefully to synchronize the availability of daylight with coverage from the electric light fixtures. “The location of the photocell should be indicated on the bid documents,” says Paton. “Unfortunately, the mounting requirements are manufacturer-specific. It is crucial to understand that a location that is selected based on the recommendations of one manufacturer may not work on another manufacturer’s product.”
• Write a sequence of operation for the lighting controls. “This is a great tool for clearly communicating the intent of the controls system design,” says Paton.
• Provide specific guidelines and expectations for checkout and verification of the lighting controls.
• Demand performance specifications from the controls manufacturers. “Carefully read and follow the photocell [light sensor] placement guidelines in your designs.”

“New daylighting controls that measure light in the same way that people perceive it will significantly improve daylighting control,” says Paton.

“The commissioning process has been simplified in the last several years, and manufacturers have trained technicians who know how to perform this job in a high-quality fashion,” says Hakkarainen.

“If daylighting is done correctly, from specification of complementary equipment to proper installation and commissioning, it works,” says Glaser.

Solutions: Below are a number of products from LCA members that can be used to save energy via daylighting:

The Watt Stopper’s ezDALI digital dimming and scene controls use the DALI communications protocol to provide full-featured, individual ballast-level dimming. Users create lighting environments (scenes) via push-button programming for a variety of common activities, then recall those scenes with the push of a button. Comprised of wall-based controllers, a power supply, DALI-based ballasts and a communications databus, ezDALI provides 1-100 percent dimming for linear fluorescents and 3-100 percent for compact fluorescents.

The SYLVANIA Quicktronic DALI Dimming Ballast combines digital control technology with full-range continuous dimming. This allows for greater flexibility and control of the lighting environment than can be achieved with traditional 0-10VDC dimming systems. System 32 DALI is available in one- and two-lamp models, either T5 or T8, that operate from 120V through 277V, eliminating "wrong voltage" wiring errors and reducing the number of models in inventory by half.

Lutron Electronics’ Sivoia QED is a window treatment system designed to provide quiet operation, easy control of sunlight, simple installation, natural and electric light integration, and a range of aesthetic options. With the push of a button, users can control both the penetration of daylight and also dim electric light levels in both commercial and residential environments.

Leviton’s new line of Z-MAX lighting control relay systems combine lighting energy management features with extended service life. The new family of relays offers a solution for complying with energy codes based on the ASHRAE 90.1-1999 standard, which requires that timed-scheduling systems or occupancy sensors be used to reduce lighting usage in buildings of 5,000 square feet or larger. The Z-MAX Relay System Control Modules feature a built-in astronomical time clock.

HUNT Dimming’s Simplicity Series digital dimming systems now offer enhanced daylighting capabilities within its custom LCD touchscreen controls, which operate with the company’s microprocessor-based dimming panels, pushbutton control stations and handheld infrared remote controls. Options for making daylight adjustments include graphic program screens using custom AutoCAD layout drawings.

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