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 variations in transmittance at different times of the day, seasons etc. For example they can be used for modelling deciduous trees which shade more in the summer when they have leaves than they do in winter when the leaves have fallen.

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 all external reflections and shading of ground reflected solar 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).

Note: Solar and light reflection from the ground is included even if the solar Model 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 Model reflections option is used. Conclusion: Switch Model reflections on for the most accurate shading calculations.

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

Level

This setting allows you to associate component blocks with either the building or the site, depending on whether they are in some way part of the building or a fixed part of the site layout. Most of the time you won’t need to change it, but for some simulations it can be important to attach component blocks to the site rather than the building. For example if you are trying to optimise a building’s orientation using the parametric or optimisation tools, or using the ASHRAE 90.1 automated baseline or UK DSM tools, you should leave component blocks that represent building structures such as shades and canopies set to the default building level. However for component blocks that represent fixed site objects such as other buildings or site topography, you should set these to be site level objects to ensure that they are not rotated with the building as part of any parametric variations.

Select whether the component block is considered to be part of the building or the site, choosing from:

1-Building - the default option where the component block is considered to be part of the building and so is rotated with the building as part of parametric and optimisation studies where the Building orientation is varied. Typically, any component blocks used to model building shading, should be given this assignment.
2-Site - the component block is considered to be part of the fixed wider site, perhaps representing an existing building or a tree and so is not rotated with the building as part of parametric and optimisation studies.

Note: It is especially important to make the correct setting here for UK DSM and ASHRAE 90.1 Appendix G PRM buildings because any 1-Building level standard component blocks are removed from the auto-generated notional and reference/baseline buildings. This is done based on the assumption that they represent shading devices that must be excluded to be in keeping with code rules. If the component block is intended to represent another building or other site object make sure to use the 2-Site setting.

Tip: Any component blocks that need to remain in contact with building including ground component blocks must use the 1-Building option. This may not be obvious because you may consider the ground to be part of the site, but the important point to remember is that ground component blocks are used to create ground adjacencies for the building surfaces and so they should be considered as part of the building.

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.

Important Note: Component blocks do not absorb or conduct heat in any way - their only effect on building surfaces in simulations is related to the shading and reflection of short-wave solar radiation and light. In cases where the component block touches the building, the material associated with the component block and the thickness of the block are not used in any way to modify the conduction of heat.

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 façade will be attenuated by each successive shading object located on a path between the façade and the sun position.

Flat surface position

If the component block is determined by DesignBuilder to be flat (based on the Maximum flat surface thickness threshold accessible on the Advanced tab of the Model options dialog) then you can control how the single surface used to represent a flat component block in simulations is defined. Choose from:

1-Upper surface, where the uppermost of the 2 largest component block surfaces is used.
2-Lower surface, where the lowermost of the 2 largest component block surfaces is used.
3-Midway surface, where a surface midway between the lowermost and uppermost large component block surfaces is used in simulations.
4-All surfaces, where flat components are represented using all surfaces like non-flat component blocks.

Maximum Transmittance

Warning 1: In EnergyPlus v9.4 used in DesignBuilder v7.3 there is a bug in the calculation of solar radiation through multiple partially transmitting shading surfaces as recorded in EnergyPlus Issue 6420. The bug applies only to non-flat component blocks and non-zero values as Maximum transmittance for flat component blocks.

You are advised not to enter any value other than 0 here for non-flat component blocks until EnergyPlus 23.2 has been included in DesignBuilder.

Warning 2: Also, for flat, partially transmitting component blocks you must ensure that the blocks are either rectangular or triangular in shape. More complex shaped flat, partially transmitting component blocks will not transmit solar radiation and light as expected.

Flat, partially transmitting component blocks must be rectangular or triangular in shape to ensure correct solar and light transmission.

This is the maximum solar transmittance of the entire component block to be used in EnergyPlus simulations. 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

You will generally 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 surface position above.

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 façade 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.

Note: In the IDF shading surface data generated for each non-flat component block surface, the transmittance is set to the square root of the Maximum Transmittance value you entered to achieve this.

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

Transmittance schedule

The component block transmittance schedule defines any time-varying transmittance of the component block surfaces (for EnergyPlus simulations only). 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. The table "Modifying Characteristics of Various Species of Trees" in "Landscape Architectural Graphic Standards" by Leonard J. Hopper, 2007 contains some data on tree solar transmission.

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: Shading devices only shade solar radiation when the sun is up, which is automatically determined by EnergyPlus from latitude, time of year, etc. So you only need to account for the time-varying transmittance of the shading device in the transmittance schedule,for times whether the sun is up. In other words for times when the sun is not up, it doesn't matter what value of transmittance is contained in the schedule.