California’s Title 24-2005 energy code, for example, requires daylighting control in daylit areas larger than 250 sq.ft., and ASHRAE 90.1-2010 and future versions of IECC will likely contain similar daylighting control provisions.

LEED-NC v.2.2 encourages the introduction of daylight into at least 75% of regularly occupied building areas. The Advanced Buildings Benchmark requires that lighting in daylighted areas be controlled by a daylighting control system. The ASHRAE Advanced Energy Design Guide for Small Office Buildings requires daylight dimming controls for luminaires within 12 ft. of North/South window walls and within 8 ft. of skylight edges. And the Northeast Collaborative for High Performance Schools encourages daylighting throughout school buildings and automatic daylighting controls controlling at least 40% of the connected lighting load.

To be successful, however, daylighting control projects require special attention to placement of photosensors and predicting daylighting impacts, integration of daylight and electric lighting, and potential energy savings.

“Daylighting and electric lighting do not inherently know how to play together in the same space,” says Judie Porter, CEM, LEED-AP, program manager for Architectural Energy Corporation. “Add photosensors to the mix without understanding exactly what the sensors see or how the electric lighting responds to the control settings, and the results may be undesirable.”

One example, she says, is using the software to identify glare issues, which can make a space uncomfortable. “We have seen examples of a Band-Aid, such as paper taped on glazing, used to remedy a high daylight illuminance design in a computer room with a low task illuminance criterion,” Porter adds. “We have also seen photosensors rendered useless by occupants taping over the sensor because they were placed or commissioned improperly and light levels in the room were not adequate.”

With proper planning and design of the daylighting controls, she points out, these problems can be avoided in many projects.

Enter SPOT, or the Sensor Placement + Optimization Tool. Aimed at lighting and daylighting designers, energy consultants, electrical engineers and students, this new free software tool helps designers to quantify electric and daylighting with associated energy use in a given space and across all seasons.

The latest version of SPOT (v.4.0), released in May 2008 and funded by the California Energy Commission’s Public Interest Energy (PIER) Program and Energy Design Resources, recently earned Lightfair International’s highest honor for the Most Innovative Product of the Year. SPOT also won top honors in the Research, Publications, Software and Unique Applications category, and the Attendee’s Choice Award by popular vote.

“SPOT enables designers to simulate and understand the impact of their designs and achieve optimal photosensor system selection, placement and settings—helping them to find the best balance between required annual light levels and energy savings,” says Jennifer Scheib, staff engineer for Architectural Energy Corporation and co-developer of SPOT. “Light levels and energy savings can be compared among differing designs for specific geographic locations.”

Version 4.0 includes performance characteristics for specific photosensor manufacturers (based on the 2007 NLPIP Specifier Report on Photosensors by the Lighting Research Center). It can also be used to calculate compliance with daylighting metrics for LEED and the Collaborative for High Performance Schools (CHPS) rating systems, enabling the generation of printable reports.

SPOT uses a Microsoft Excel platform with a RADIANCE engine, handles toplighting and sidelighting daylight sources, and can model any electric light source using existing IES files. The program has two main functions: Design Tool followed by an Analysis Tool.

The Design Tool consists of all geometric and site inputs and calculates electric lighting performance and annual daylighting results and performance. “It’s simple enough for most lighting designers and others to navigate and understand,” says Scheib.

The Analysis Tool provides recommended photosensor placements for the analyzed space.

“These recommended placements provide good starting points for analysis and typically require further iteration to fine tune the photosensor system design,” says Zack Rogers, staff engineer for Architectural Energy Corporation and SPOT lead developer. “The iterative process requires more technical knowledge.”

The software produces commissioning reports for the analyzed photosensor system to aid with field implementation. A DOE-2 output function has been added, enabling the annual electric lighting simulation to be integrated into a whole-building energy analysis.

“SPOT reflects the growing importance of quantifying light in a space,” Rogers points out. “Designers can use SPOT to evaluate the daylight and electric lighting in any type of space using a variety of electric lighting control strategies. It plays a unique role in providing the kind of information necessary for design teams to more consistently and successfully integrate daylighting and electric lighting, and it is neutral to the type of technology or manufacturer’s equipment specified.”

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