Page T2.2 . 16 June 2004                     
ArchitectureWeek - Tools Department
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    Daylighting Prediction Tool Online


    The tool offers a comparative, reliable, and quick analysis of the annual amount of daylight available in perimeter offices and classrooms as well as the lighting energy performance of automated lighting controls (occupancy sensors, photocells) relative to that of standard on/off switches. Blinds can be either manually or automatically controlled. The user can choose among 361 building sites across the Northern hemisphere.

    To reduce simulation times from hours to minutes without compromising simulation accuracy, daylight coefficients for a comphrehensive set of building geometries have been precalculated with the Radiance raytracer. An online simulation run typically takes between one and three minutes, given moderate traffic on the server and a fast Internet connection.

    Lightswitch User Behavior Model

    Field studies reveal that current daylight evaluation methods tend to overestimate lighting energy savings due to daylight. One reason for unrealistic expectations is that these methods do not consider how occupants manage their electric lighting and shading controls. So it's important to model user behavior along with physical lighting variables.

    A unique feature of the Lightswitch Wizard is a strong emphasis on the description of the user (occupancy and behavior) and the lighting and blinds control systems. User occupancy is characterized by arrival and departure times on weekdays, which are processed by a stochastic occupancy model that breaks up the working day through temporary absences from the workplace.

    A user behavior model combines annual illuminance profiles and occupancy profiles with behavioral patterns that are based on field studies throughout the Western world. The model predicts how building occupants use their lighting and blind controls (if available). For example, the model predicts when users will lower window blinds in response to glare, or when they will switch on the electric lighting.

    Users wanting to analyze more complex geometries can download NRC's expert daylighting analysis software DAYSIM which operates with the same models as Lightswitch Wizard but allows input of user-defined building geometries.

    Future Developments

    The Lightswitch Wizard was originally developed within the framework of a three-year NRCan/NRC project, "Towards Realistic Daylighting Energy Savings in Office Buildings" that ended in April 2004. Now the software developers are linking the Wizard output to daylighting credits for the LEED rating system from the U.S. Green Building Council.

    Ongoing developments are supported by BC Hydro and the Climate Change Plan for Canada, Technology and Innovation R&D Initiative. Over the next four years, the Wizard will be further coupled with the whole-building simulation program ESP-r from the University of Strathclyde to allow for a total energy analysis of daylighting systems.

    Discuss this article in the Architecture Forum...

    Dr. Christoph Reinhart is the project manager for the Lightswitch Wizard and a research officer in the Indoor Environment Program of the National Research Council Canada.



    ArchWeek Image

    Lightswitch Wizard, from the National Research Council Canada, can compare two lighting scenarios.
    Image: National Research Council Canada

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    One of three data entry screens for setting up the two scenarios.
    Image: National Research Council Canada

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    Setting the parameters for comparing two perimeter offices.
    Image: National Research Council Canada

    ArchWeek Image

    Specifying occupant behavior and lighting controls is a unique aspect of Lightswitch Wizard.
    Image: National Research Council Canada


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