Component blocks are a flexible way to apply shading to any part of the building and can be used to model more complex window shading systems not catered for by the in-built local shading systems that can be selected on the Openings tab. The issues to consider when using component blocks in this way are discussed below.
When using the zone inner geometry option for surface geometry, component blocks placed close to the window at building level may not be as close to the window in the simulation as might be expected from the view in the model. For example, in the simple model shown below a component block has been placed directly in front of a window, which cannot be seen as it is hidden by the component block. It is placed so that it touches the outer surface of the block. So one would think that it is touching the window in the simulation model and therefore no solar gain and light could pass round or through the component block shade.
However results from simulations will show quite a lot solar gain entering the window. This is because the window is actually placed on the zone surface which is on the inner surface of the block, the difference between the inner zone surface and the block outer surface being due to the External wall thickness. In this model the wall thickness is 0.23m so there will be a gap of 0.23m between the component block shade and the window in the simulation model. This can be seen in the example DXF output shown below which corresponds to the model above.
The DXF output above shows the gap between the window and the component block shade caused by the External wall thickness.
The solution in this case was simply to use either one of the External measurement Geometry conventions or a zero External wall thickness which removes the gap between window and shade.
As discussed elsewhere, shading of the ground by component blocks is only taken into account if the Model reflections and shading of ground reflected solar option is used. So if you use component blocks to model a local shading device and forget to include reflections in the simulations you will obtain higher than expected solar gains due to unobstructed ground-reflected solar gain.