Component Block

Construction tab in model data under Construction header

Component blocks can be used to include shading and reflection effects of objects such as local shading devices, awnings, adjacent buildings and trees. They can also be used to define ground and adiabatic adjacencies. The component block model data allows you to define the component block type, whether the component block shades and reflects in simulations, transmittance of the shading material and also a schedule for modelling seasonal variations in transmittance.

Component block type

You can change the type of the component block. Select from:

1-Standard - used for shading, reflection and visualisation.
2-Ground - used for setting ground adjacency, shading, reflection and visualisation.
3-Adiabatic - used for setting adiabatic adjacency, shading, reflection and visualisation.

For more information on the Component block types see Component Block under Working with Blocks (Building Level)

Component block shades and reflects

Switch this option on to include the component block as a shading/reflection surfaces in the simulations. Shading surfaces have the following effects:

Shade direct beam solar radiation.
Reflect solar radiation onto the building (if you select Model reflections in the calculation options).
Shade diffuse solar and long-wave radiation from the sky.
Shade diffuse solar radiation from the ground (if you select Model reflections in the calculation options).

Important note on ground reflection

Solar and light reflection from the ground is included even if the solar Reflections option is not used, but if Reflections are not calculated the ground plane is considered unobstructed, i.e., the shadowing of the ground by the building itself or by component blocks is ignored.

Shadowing of the ground by component blocks is only taken into account if the Reflections option is used.

Conclusion:Switch Reflections on for accurate shading calculations.

Note: all component block types cast shadows in the visualisations.

Material

The component block material is used to define the solar and visible reflectance of the block surfaces in Cooling design calculations and Simulations using real weather data when the model reflections calculation option is selected.

Note: Although component blocks are displayed in DesignBuilder as solid objects, non-flat component blocks are modelled in EnergyPlus as a group of surfaces and it is the reflectance and transmission of each of these surfaces that is being described here. The solar flux incident upon a building facade will be attenuated by each successive shading object located on a path between the facade and the sun position.

Maximum Transmittance

The transmittance of the component block during the simulation is calculated by multiplying the maximum transmittance by the time varying schedule value:

Transmittance = Max Transmittance x Schedule value

In most cases you will want component blocks to provide 100% shading for 100% of the time. In this case you can leave the Maximum transmittance and Transmittance schedule in their default states of 0 and On respectively. If you wish the component block to transmit solar and visible radiation you can define the extent and timing of the transmission. The component block transmittance is calculated during the simulations as the Maximum transmittance multiplied by the value of the transmittance schedule below. The maximum transmittance can have any value between 0 and 1. Note that if the component block is flat (i.e. it consists of 2 large surfaces and several smaller 'edge' surfaces) the block is represented in the simulations by a single shading surface. In this case the surface used will depend on the value of the Flat component block surface selection model option.

Tip: If your component block has a constant transmittance you can set the transmittance schedule below to On and set the constant transmittance for the block here.

For non-flat component blocks every surface is included in the simulation as a shading surface and the solar flux incident upon a building facade will be attenuated by each successive shading object located on a path between the facade and the sun position. The shading transmittance schedule you define is therefore modified to ensure that the overall transmittance of the block is the Maximum Transmittance value multiplied by the schedule you selected. This is done assuming that the component block is convex and that therefore solar rays can only pass through a maximum of 2 surfaces. The transmittance of each non-flat component block surface is set to square root of the value you defined to achieve this.

Note: non-convex non-flat component blocks will provide more shading than you specified during times when solar rays pass through more than 2 surfaces.

Note: there was a bug in the calculation of transmittance through multiple shading devices having fractional transmittance in EnergyPlus version 2.0 and earlier. We haven't yet verified that the bug has been fixed and so must recommend that you check results carefully when using fractional transmittance for component blocks.

Transmittance schedule

The component block transmittance schedule defines any time varying transmittance of the component block surfaces. By default, the component block is fully opaque for the whole year. The transmittance schedule can contain any value between 0 and 1. The transmittance schedule can be used to allow for seasonal transmittance change, such as deciduous trees that have a higher transmittance in winter than in summer. Transmittance based on time of day can also be used - a movable awning, for example, where the transmittance is some value less than 1.0 when the awning is in place and is 1.0 when the awning is retracted.

The following assumptions are made in the shading surface transmittance calculation:

Both sides of the shading surface have the same transmittance properties.
The transmittance is the same for both beam and diffuse solar radiation.
Beam solar transmittance is independent of angle of incidence on the shading surface.
Beam radiation incident on a shading surface is transmitted as beam radiation with no change in direction, i.e., there is no beam-to-diffuse component.
If two shading surfaces with non-zero transmittance overlap, the net transmittance is the product of the individual transmittances. Inter-reflection between the shading
surfaces (and between the shading surfaces and the building) is ignored.
For the daylighting calculation the shading surface’s visible transmittance is assumed to be the same as its solar transmittance.
Shading devices are assumed to be opaque to long-wave radiation no matter what the solar transmittance value is.

Note that shading devices only shade solar radiation when the sun is up, which is automatically determined by EnergyPlus from latitude, time of year, etc. The user need only account for the time-varying transmittance of the shading device in the transmittance schedule, not whether the sun is up or not.