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Daylight Harvesting Technologies Embrace the Power of the Sun


11/18/2013 12:00PM

by Brent Protzman, Lead Architectural Engineer at Lutron Electronics

The evolution of architectural lighting

Daylighting is a relatively new term for an ancient practice. In the millennia before the introduction of electricity, buildings had to rely on available daylight to illuminate interior spaces.

More recently, as electric lighting sources and technologies improved, daylight became almost passé. Evolving building codes, new energy regulations, and a renewed emphasis on sustainability lighting professionals to once again embrace daylight as a practical, aesthetic, and symbolic element of good building design.

The dynamic nature of daylight

The greatest challenge of using daylight as a primary light source is that it is dynamic, and somewhat unpredictable – there are seasonal and cyclical patterns, but daylight also changes from day-to-day, hour-to-hour, and even from one building façade to the next.

Automated shading solutions, digital dimming technologies, and daylight sensors can work together to compensate for these constant changes in daylight, minimizing the need for electric light by incorporating dynamic fenestration (automated shades, solar-adaptive software, and window sensors) into total light management systems.


Figure 1: Automated shades maximize the amount of daylight entering a space to minimize
or eliminate the need for electric light, increasing Daylight Autonomy.

 

One of the most powerful motivators to use daylight more effectively is code compliance. As of October 18, 2013, ALL state commercial building codes must meet or exceed ASHRAE 90.1-2010 standards that include mandatory requirements for daylight harvesting technology. Other building standards, including IECC and Title 24, are following suit by including similar daylighting requirements in their updated recommendations.

Which leads us to the concept of Daylight Autonomy…

The concept of Daylight Autonomy is designing a space such that it maximizes the amount of useful daylight, thereby minimizing the need for electric light. The final product has to embrace daylight while minimizing or eliminating glare, and maximize energy savings by reducing the use of electric light.

Automated shade control offers the best solution

Dynamic fenestration, including automated shade control, is the ideal lighting design strategy for addressing both energy saving and glare management. The best solutions combine automated shade control with solar-adaptive software, and cloudy-day/shadow sensors that allow the shading software to evaluate and respond to real-time daylight conditions. By using the same software to control electric light, the electric light can be used only to supplement available daylights, minimizing or eliminating lighting energy use whenever possible.

Figure 2: Solar-adaptive shading, like Lutron Hyperion systems with window sensors, adjusts shades throughout the day based on the position of the sun, and environmental conditions.
 

Automated shading allows the lighting system to respond to environmental factors related to both energy use and glare. As related to energy use, automated shading control works to maintain a consistent light level in all environments, and can extend the useful daylight zone (the area inside a space where enough glare-free daylight is available for daylight harvesting) inside the perimeter of the space.

Manual shades can generally achieve a useful daylight zone of 10 feet inside the perimeter windows. Because automated shades respond to real daylight conditions, they can extend the useful daylight zone to 20 feet inside the perimeter, allowing for higher daylight autonomy.

 
Figure 3: Automated shades can extend the useful daylight zone to significantly
increase lighting energy savings2. 
 

To mitigate glare, it is important to choose a shade manufacturer that offers a broad selection of fabrics, allowing the lighting designer or architect to choose the appropriate transmittance level based on the building’s location and orientation.

A recent study conducted by Purdue University and Lutron Electronics, analyzed the benefits and energy-saving potential of solar adaptive, automated shading control systems. Results show that perimeter private offices with daylight harvesting strategies in place can further reduce lighting energy usage by 65% through the use of automated shades2.

Forward thinking lighting design will increasingly call upon the well-documented benefits of sunlight to create spaces that are comfortable, energy-efficient, sustainable, and code compliant. The Masters of ancient architecture relied on building techniques that simultaneously captured and tamed the sun’s potential – automated shading systems bring daylight back into the mainstream of modern design.

Sources

1Steffy, G. (2008). Architectural Lighting Design. John Wiley & Sons, Inc., New York, NY

2Lutron Electronics Co., Inc. worked with Purdue University to analyze the benefits and savings potential useful daylight zone up to 10 feet of Lutron’s Hyperion automated shading systems. The results showed the impact of how automated shades significantly reduce annual lighting energy usage. Savings are based on energy simulation of a perimeter private office with a lighting power density of 0.9 W/ft., a standard clear double pane glass, and a shade fabric with 5% transmittance and a 76% reflectance. Values shown are the average of three window to wall ratios: 20%, 40%, and 60%. Daylight harvesting system required.