Synopsis

This tutorial explains how to use ECOTECT to calculate the sky factor for a planar surface, and the Vertical Sky Component (VSC) for a window.

Duration

You will need about 15 minutes to complete this tutorial.

Training and Accreditation

Successfully completing this tutorial fulfills one of the practical skills required for completing Level 3 of the Daylight Analysis training module.

Resources Required

To complete this tutorial, open the Bldgs-ShadingDesign-RtoL.eco file located in the Examples folder of your Ecotect installation.

Tutorial

Determining the Sky Factor for a planar surface

1. Open the specified example file, and select the Zone 8 roof object as shown in the following screenshot:
   

   Select the roof object of Zone 8.
   Then go to the Calculate»Sun-Path Diagram... menu item.
2. The following dialogue box appears, showing a sun path diagram for the selected object. The dark, shaded areas represent shadows falling over the geometric centre of the selected object.
   

   The sun path diagram shows shadows that fall over the geometric centre of the selected object.
3. To determine the sky factor for the selected object, we need to calculate a full shading mask. A full shading mask will also show when the selected object is only partially in shade, and in turn will tell us its sky factor percentage value. To do this, expand the Shading Mask section to the right of the sun path diagram, and then click the Calculate Shading button.
   

   Expand the Shading Mask section and then click Calculate shading.
4. Configure the surface shading dialogue box as shown in the following screenshot. Make sure the Displayed Data section is configured to Overshadowing perecentage. Click Ok to proceed.
   

   Configure the surface shading dialogue box as shown.
5. ECOTECT calculates the shading mask - depending on the accuracy specified, this may take a few moments. When done, the sun path diagram is redrawn with shades of grey, indicating when partial overshadowing occurs.
   

   ECOTECT calculates the full shading mask, which shows partial overshadowing as percentage values.
   In the bottom right hand corner of the sun path diagram, you will also see two additional percentage values - Overcast Sky Factor and Uniform Sky Factor. These are the sky factor values for the selected object, depending on whether you assume the sky uses the CIE overcast or uniform design sky conditions.
   

   Sky factor percentage values are shown in the bottom right hand corner of the sun path diagram.

Calculate the VSC for a window

1. The procedure for calculating the vertical sky component is exactly the same as for sky factor, except that it only applies to vertical surfaces. To demonstrate this, select the Zone 8 window instead of the roof object.
   

   This time, select the Zone 8 window.
2. Repeat the steps for calculating the full shading mask as above. This time, in the bottom right hand corner of the sun path diagram, you will see an additional percentage value for VSC. Note also that with vertical elements, half of the sun path diagram will be in shade, because the building itself will always shade one side of the window.
   

   Calculating a full shading mask on a vertical surface such as window automatically displays the VSC value in the sun path diagram, as defined by the Building Research Establishment.

Tips

• If when you calculate a shading mask and get a result of 0%, check that the surface normal for the selected object is pointing either outwards or towards the sun. Unless otherwise specified, ECOTECT only calculates the shading mask in the direction of the surface normal. To change this, when configuring the settings for the shading mask, check the box Check both sides of surface.
• When calculating the full shading mask, the Display Test Points dialogue box shows green dots in the 3D Editor for all the points used to generate the shading mask. Increasing the accuracy slider increases the number of points used.