DaylightFactor Extension

Introduction

Daylight Factor (DF) is used to study daylight illuminance levels under overcast sky conditions. It depends on space geometry, materials and external obstructions (environment buildings and relief), regardless of climate data for building location.

Daylight factor is defined as the ratio of the inside illuminance to the exterior diffuse horizontal illuminance on an unobstructued plane, for a standard CIE Overcast Sky luminance distribution.

The advantages of DF are its ease of apprehension, speed of calculation and independence of climate. But the fact that it does not take into account the direct radiation of the sun (weather, season and time) is a limitation.

DF is a good indicator of the behavior of the project in an unfavourable climatic situation (overcast sky).

DF indicator is part of environmental standards in many countries.

Daylight factor calculation affects lighting strategies:

• selection of interior and exterior materials taking advantage of natural light,
• positioning and sizing of the openings.

Daylight factor simple or BREEAM

The extension allows calculation of the daylight factor according to two modes:

• a conventional method of calculating DF, described below,
• a BREEAM mode taking into account BREEAM requirements for the criteria of DF and uniformity, detailed on DF BREEAM calculation.

Calculation of the daylight factor for standard EN 17037

The EN 17037 standard provides a framework for calculating the daylight factor (criteria, specific sensor grid).

The extension Daylight Factor (EN 17037) is dedicated to this standard, the Daylight Factor (EN 17037/UK) for the UK variant.

How To Use DaylightFactor Extension

1. Open SketchUp model. Follow recommendations to prepare your model for DL-Light calculations.

2. Open DaylightFactor dialog from toolbar or menu option Extensions -> De Luminae -> Daylight Factor -> Activate extension and enter the parameters of the calculation.

   

   Fields description:

   • Project name - Project name is used during export and for output filename generation. The SketchUp model name is used by default.

   • Results - Directory where model will be exported for calculation.
     When calculation is started model geometry and resulting files will be saved in df_output subdirectory.
     For SketchUp projects stored on network disk (Windows), see Work on a copy of the model.

   • Mode - Calculation mode selection:

     • Keep default value "DF classic",
     • For the mode "DF BREEAM", read: DF BREEAM calculation.
     Nota: To determine the influence of a sensor on the result, the default setting is to assign to each sensor a weight proportional to its coverage area. On the contrary, for the BREEAM calculation each sensor has the same weight. See "Coverage area of sensors" in preferences.

   • Details - Surfaces may require different density of sensors. Level of details definition is directly connected to number of sensors or their density on surfaces. Big unobstructed surfaces may need lower level of details with few sensors only, while smaller surfaces or surfaces with complex obstructions may require very high level of details. Level of details determines number of sensors for calculation, and has a major influence on calculation time and results accuracy.

     DL-Light allows to choose:

     • the sensor grid applicable by default to all calculated surfaces,
     • different sensor grids for some surfaces ("exceptions" button).
     

     See sensors selection for more information on the choices of proposed sensors.

   • Units - Results units:

     • Percent [0-100%] - classic DF representation.
     • Normalized [0-1] - Representation on a 0 to 1 range.
     
     Nota: in BREEAM mode, a BREEAM representation is automatically applied

   • Ground albedo - Reflection factor of the ground. Value can be selected from drop-down list or defined custom value in next dialog.

     
     

   • Location - Building location coordinates. Location can be based on SketchUp model location, current Weather file location or be Custom. Below is dialog for Custom location definition.

     

     A weather file can be selected to facilitate the model location and détermination of time zone. See page Weather data.
     Important : For this calculation, the weather file is only used for location and time zone selection.

   • Time zone - Display of the time zone used for the calculations.

     If a weather file is used, the time zone is defined by this file. Otherwise, a selection list allows you to choose the time zone.
     Nota: when a model is located in SketchUp, SketchUp proposes a time zone based on the longitude of the place. This value is sometimes wrong, especially for European or Asian countries.

3. Define materials characheristics for energy calculation.

   Since calculation is done with validated Radiance tools it is necessary to 'attach' physically based material to each layer in SketchUp. Note that materials should be defined with their solar reflectance and transmittance.

   The tab to choose materials:

   

   Materials panel consists of two main parts:

   • SketchUp layers table contains the list of all layers defined in the SketchUp model. Each row contains SketchUp layer name and attached material name if any. If text in a row is grayed, it means that the corresponding layer is not visible in the model. The table is updated in real time, as the SketchUp model is modified.
   • Materials tree contains all materials libraries available for DL-Light extension. Some of them are provided when extension is installed and others can be imported or created by user. Subtree 'Model materials' contains materials currently attached to SketchUp layers.
     To explore available libraries and add new ones, see Materials libraries dialog.

   To attach a material, select in the table layer(s) and either double-click on the chosen material in the tree or select the material in the tree and press Attach/Detach button.
   To detach from the layer(s), select it and click Attach/Detach button.
   To revert all layers to previous state press Revert button.

4. Palette of false colours can be defined with precision. 3 options for palette are given, Automatic, Gradient and Custom:

   
   • Automatic palette is generated during calculation and is based on calculated results for selected surfaces. This is the best option for first calculations, when user doesn't have idea about possible resulting values
   • Gradient palette enables global palette manipulations - definition of minimal and maximal palette values, number of colors and start and end color. It is very useful once user have idea of resulting values, but want to experiment with colors.
   • Custom palette gives full freedom to add/delete/modify each color separately. Good for creation of final results for representation, when some surface areas should be highlighted for example.

5. After all data are entered in DF dialog, select one or few surfaces and press Render or button.

   

   Calculation time depends on number of selected surfaces, level of sensors details and model complexity.

6. When results are imported, selected surface will have appropriate false colors and Palette is opened.

   
   

7. Results analysis.

   • The Report dialog displays the distribution of results over current palette, and calculation input parameters.

     

   • Show/Hide Sensors and Values explores results directly in the model for each sensor.

     

8. For further calculations in the same model:

   • To run calculation on surfaces simply select them and Render .
   • It is possible to modify the parameters of the calculation: to change the density of sensors to improve the visualization of the results (for all the model or a specific surface), to modify the palette of colors... Whatever the change, use the Render button. Previously calculated surfaces will be updated with the new settings.

   DL-Light uses a calculation cache algorithm. It automatically detects if a surface requires recalculation or if a previous result can be reused. By default, the cache keeps the information of the last 10 calculations (value configurable in the preferences).

9. Archiving results:

   DL-Light allows to archive all the results of a calculation: reports, textures and calculation steps (exported Radiance model, weather file, ...). This archive can be reloaded on the model, subject to using exactly the same model as during the calculation.

   See the page Archiving results for more informations about this feature.

   • To archive the calculation results, click on the button Archive.
   • To load the results of a previous calculation, click on the button Load

   See the page Comparison of results for more informations about comparison of archives.

10. Snapshots:

    Current SketchUp model view with imported results can be exported with palette or without palette to png format. To explore created images user can open folder where they are saved .
    This option is not supported in trial version of the extension (see license information).