Solar tubes in DesignBuilder Daylighting
Posted by Luis Sousa on 14-Sep-21 10:10 AM
DesignBuilder v7.0 does not have the solar tube object for the Daylighting calculation.

One work around would be to use rooflights but this will only be applicable for blocks with external roof.

Its more complicated with basement zones without external roof surfaces. However, this may be achievable by:

1. Use the Add surface tool to extrude the pipe shape from the ceiling to the roof level.

If the pipe has conical shape then these objects will need to be created using an Outline block.  
The Clone tool can be used to copy these objects and create an array of solar pipes.
These pipes can then be converted to building block type (Convert Outline block option) and merged to the block below using Boolean operation with the Union option  .

2. Create the upper floors with an Outline block

3. Remove the block intersections by selecting the building block with tube and the outline block.

4. Then, use Boolean operation with the Subtraction option to remove the intersecting section of the tube.

5. Use Convert Outline block option to convert the upper block to a Building block.

6. Apply a window on top of the solar tube geometry.

The final geometry should be similar to this:

Solar tube settings:

Note that the surface reflectance of the materials in the light pipe walls (partitions) needs to set to very high value as light pipe tubes are mirrors to reflect the light.

You need to assign the suitable material Surface properties and Specularity values of innermost layer on Surface properties tab (Edit material dialog).

For further information please refer to the text from our DesignBuilder Program Help below:


Enter a specularity value for the material surface to define the way that light reflects from it. The value entered must be between 0 and 1. A value of 0 provides purely diffuse reflection, while a value of 1 gives no diffusion, representing mirror-like behaviour.

Note: the Visible absorptance must also be adjusted to complete the surface property behaviour for Radiance and Daysim calculations.

Specular reflection is the mirror-like reflection of light from a surface where each incident ray is reflected, with the reflected ray having the same angle to the surface normal as the incident ray. Some devices used to enhance daylighting performance such as light shelves and blinds with directional reflection properties require a non-zero value of specularity.

Finally, use a high number of light bounces on your Daylighting simulations.

Article update: 14.09.2021