Daylighting Calculations

DesignBuilder provides 3 types of daylighting calculations:

1. Daylight illuminance distribution under static sky conditions with reports on average daylight factor, uniformity etc. Data is generated for each zone calculated using the Radiance ray-tracing simulation engine. Standard reports detailing eligibility for LEED EQ8.1, BREEAM HEA 01, Green Star IEQ4 and LEED v4 Daylighting BD+C credits Option 2 daylighting credits are provided. Navigate to the Daylighting screen and the Illuminance tab to view these daylighting results.
   
   
2. Annual Climate Based Daylight Modelling (CBDM) through the Daysim simulation engine (which is also based on Radiance). Standard reports are generated for LEED v4 Daylighting BD+C credits Option 1 as well as general sDA, ASE and UDI distribution plots and summary reports.
   
   
3. Daylighting integrated within EnergyPlus simulations allowing savings in electric lighting to be calculated based hour-by-hour on daylight availability throughout the year.

The rest of this section covers the detailed Radiance and Daysim methods of calculation of daylight.

Model Data Used in Radiance and Daysim

For both the Radiance and Daysim calculations, the DesignBuilder uses the following data from the model:

• Surface visible reflectance and specularity of materials on the innermost and outermost layers of constructions used in building surfaces. The outermost material layer surface properties are used for component blocks and assemblies.
• Window glazing transmittance and diffusion properties.
• Detailed geometry description including the 3-D surfaces, window frames and dividers etc as seen on the Visualisation screen.
• Site ground reflectance is used to create a ground plane that reflect light in a diffuse manner.
• You can select which zones are regularly occupied with regard to Radiance and Daysim daylighting calculations using the Include zone in daylighting calculations option on the Activity tab.

For Daysim only:

• The occupancy schedule over the year is used to define the hours where daylight is required in each zone. Hours outside this schedule are not considered when assessing the daylight performance of the zone.
• The same hourly weather file selection used in EnergyPlus simulations is used to define the sky conditions through the year.

Additional data entered on the Calculation options dialog is used to define the details of the calculation and, in the case of Radiance some further information on the sky light distribution is provided. The above data is passed to the simulation engine which calculates the distribution of illuminance on the working plane using a backward ray-tracing method. This is done either for single static points in time (Radiance) or over the course of the whole year (Daysim). Once the calculations have been carried out, the daylight data can be displayed in a range of formats.