Effective daylighting solutions consisting of toplighting
and side-lighting--or a combination of both--should not only optimize energy savings, but also provide benefits that clients will find compelling in tandem with the design criteria.
Optimal Daylight Factor for Energy Efficient Toplighting System (QC-06-058)
This study examines the impacts of aperture size for four combinations of toplighting strategies and glazing types on the total yearly energy loads for a prototypical open office space in four climates.
Changes to lighting standards include improvements to daylighting and daylighting controls, space-by-space lighting power density limits, thresholds for toplighting
and revised controls requirements and format.
The design of a toplight system needs to take into consideration different toplighting types, including aperture size and orientation, electric lighting control, and, most importantly, the local climate.
In order to compare the effectiveness of different toplighting strategies and determine toplight glazing sizes for optimum energy efficiency, simulations based on hourly local weather data must be performed to estimate annual daylight availability and building energy use.
Combining the results of daylight simulations with an annual building energy simulation captures the interaction between lighting and total building energy use and provides a more complete picture of the changes in building energy consumption caused by the installation of different toplighting strategies.
They showed that the toplighting design based on the 2% daylight factor provides too much daylight, and that smaller glazing areas are necessary to optimize energy savings and visual comfort.
This study investigates four different combinations of toplighting strategies with clear and diffuse glazings in a range of climates by combining the results from a sophisticated lighting simulation program based on raytracing, Radiance (Ward 1994), to the DOE 2.
5%, and 2% daylight factors for each glazing and toplighting type.
The Four Toplighting Systems: Three Toplighting Strategies and Three Glazings
The four toplighting systems considered in this study and their abbreviated names are as follows (see Figures 1 and 2):