Define shading features

Example of simple shading and window design option analysis

Shading surfaces may refer to exterior features of the building that cast shadows on the facade or glazed surfaces, or features on the site that cast shadows. This page also discusses modeling interior shades.

The input process to define shading features may involve drawing shading geometry, or specifying shading features with numerical inputs.

Adding exterior building shade geometry

Shades are drawn as geometrical features - typically as flat 2D planes to represent window overhangs or fins.

Adding exterior building shades with numerical input

Shading projection factor calculation

In some software tools, shades may also be specified using simple numerical inputs. This is typically accomplished by selecting a window surface, and indicating that it has a shade. Users then specify whether it is horizontal, vertical, how high it is mounted above the window (e.g. for horizontal shades), or it's location to the side of the window (e.g. for vertical fins). Other inputs such as length, depth, projection factor, angle of tilt may be provided but the exact inputs are software dependent.

Adding site shading features

Shadow cast on project (shown in blue) by adjacent building modeled as a shading object (shown in pink).

BEM tools can account for solar impacts due to shading from nearby buildings and trees. This is done by modeling them as shading objects. Typically, the shading objects are modeled using a low amount of detail - for example, a nearby building may be modeled as a box or series of planes rather than accounting for all of the detailed geometrical features. Similarly, a tree (or group of trees) may be modeled as a triangular shading object (for a single tree) or a plane (for a group of trees or forest surrounding the site). BEM simulation engines will calculate the percentage of each surface being shaded by adjacent objects, and reduce the direct solar radiation received by the surfaces by that percentage.

Some BEM tools allow for shading objects to be "scheduled." This feature is designed to model operable shades, but can also be used to account for deciduous trees that lose their leaves in the winter. The schedule could be defined so that the trees are "opaque" during the spring and summer (when there are leaves on the trees and therefore they cast shadows), and "transparent" during the fall and winter when the leaves fall and shadows are no longer cast. More detailed schedules could be defined that vary the amount of transparency in the different seasons and months to account for gradual growth and fall of leaves.

Adding interior shades/blinds

Interior or exterior movable shades can also be modeled in some tools. If evaluating these operable shades, be sure to understand how the controls are represented by the simulation tool. And for interior shades, the impact on solar heat gain is complex and is affected by the performance of the glazing itself, so make sure to choose realistic values.  

Simple box model approach

If a complex shading system is being considered, it is often desirable to simplify its geometry during the early stages.

See also: Simple box model shading simplification