Watt Reduction Factor Extension


The Watt Reduction Factor extension calculates on surfaces the ratio of the solar irradiance (W/m²) to the theoretical irradiance of an identical but virtual surface without surroundings. The ratio is represented by a percentage between 0% and 100%.

DL-Light extension WRF

Operating principle

The Watt Reduction Factor can be interpreted as the normalization of a standard Watt calculation by the maximum reachable with the local climate.

This indicator enables to compare surfaces and to interpret their performance according to their geometric characteristics, minimizing the influence of climate and orientation.

This indicator is useful for performance optimization of a building, especially for low-energy houses.


- This extension has parameters very close to the Watt extension.

- In practice, a automated double Watt calculation is performed. The cache for the calculation is partly shared with Watt extension, in order to speed up calculation when using both extensions.


How To Use Watt Reduction Factor Extension

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

  2. Open Watt Reduction Factor dialog from toolbar WFR dialog icon or menu option Extensions-> De Luminae -> Watt Reduction Factor -> Activate extension and enter the parameters of the calculation.

    DL-Light extension WRF Reduction Factor General tab

    Fields description:

  3. Define materials characheristics for energy calculation. Defined materials have influence for calculations 'with interreflections'.

    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 of choice of materials:

    DL-Light extension WRF Materials tab

    Materials panel consists of two main parts:

    To attach a material, select in the table layer(s) and either double-click on required 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:

    DL-Light extension WRF palette tab
  5. After all data are entered in Watt dialog, select surfaces and press Render or run_selected button.

    DL-Light extension WRF Sketchup selection

    Calculation time depends on the 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 and Report dalogs will be opened.

    DL-Light extension WRF Sketchup result imported - automatic palette
  7. Results analysis.

  8. For further calculations in the same model:

    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).

    For example if a calculation has just been made for the "summer" season, then the season is changed to "winter" for a recalculation, and finally recalculated for "summer":

  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.

    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 snapshot_with_palette_icon or without palette snapshot_icon to png format. To explore created images user can open folder where they are saved open_snapshot_folder_icon.
    This option is not supported in trial version of the extension (see license information).

    DL-Light extension WRF Sketchup model snapshot image