Dimensions

Openings tab in model data under External Glazing and Internal Glazing headers

You can use the Window to wall %  (WWR) data and Window height, Window spacing and Sill height to easily change the amount of glazing and its layout on the walls. The way this data is used for each facade type is described below.

Facade types

There are a number of standard facade types:

• 0-None - there is no glazing.
• 1-Continuous horizontal - glazing is generated in a continuous horizontal strip using Sill height, Window spacing and Percentage glazing.
• 2-Fixed height - glazing is generated with a fixed height at the specified Sill height and Window spacing, and width is calculated based on the Percentage glazing. This option uses Window to wall % but prioritises window height.
• 3-Preferred height - glazing is generated using the window height data and the Percentage glazing, but the Window height may be adjusted to achieve the required Window to wall %. This option uses Window height, Window spacing and Sill height but prioritises Window to wall %.
• 4-Fixed width and height - windows have fixed width and height. This option uses Window to wall % but prioritises Window Width, Height, Spacing and Sill height.
• 5-Fill surface (100%) - the entire surface is filled with glazing and there is no frame.

Window to Wall %

Often referred to as the Window to Wall Ratio (WWR) this setting can be used to change the amount of glazing for all openings at or below the current level in the building hierarchy. For example changing the WWR at building level changes the size of all windows in the model not overridden by other settings lower in the hierarchy.

When using the 2-Outer volume Zone geometry and surface areas option (typically one of the "External measurements " convention templates) it is important to understand that the reference surface area used when calculating the window area from the % value supplied is still based on the inner volume surface. This might seem surprising at first but the window dimensions must make physical sense and must be punched through both the inner and outer volume surfaces.

The image below illustrates a wall in a model using the "External measurements" template where a window has been created using the 3-Preferred height facade option with a 10% glazing ratio. You can see the black outline showing the available area where the window could possibly be sited. Areas outside this outline to the left and right are taken up by corners with adjacent walls. The % glazing calculation uses the black outline area as the reference area. In an extreme case where 100% glazing is specified the whole of this area would be filled with window, but of course the sides of the surface where there is a corner with an adjacent surface cannot contain a window and so do not take part in the calculation - even though they will form part of the surface used in the simulation.

Tip: If you need to ensure that the % window areas used in the simulation exactly match the % you define here then you should consider using the "Simple" convention template which ensures that 100% of all surfaces are available for containing windows by using zero surface thickness for all surfaces.

Window spacing

The spacing between the each window on the facade (in m or ft). The window spacing is the centre to centre spacing between windows, not the gap between windows.

Sill height

This is the height of the base of the window from the base of the block (in m).

Note 1: You can control the makeup of the building facades in greater detail by drawing individual windows at the surface level or by copying previously drawn windows at building level. In either of these cases glazing, vent and door facade layout model data is ignored.

Note 2: Flat roofs do not have default glazing set up using Roof glazing layout model data. To create openings on a flat roof you should go to the surface level and add them there.

Note 3: When the surface is non-rectangular, even with the 2 Facade type options that prioritise Window to wall % (3-Preferred height and 1-Continuous horizontal), the Window to wall % will not be perfectly maintained. For these surfaces, DesignBuilder calculates a rectangle that can accept the windows and starts from one end of the rectangle adding windows using the Window spacing data until no more fit into the rectangle. This results in an approximately correct looking facade but only prioritises Window to wall % in the rectangle, not accounting for the areas outside the bounding rectangle. For relatively large values of Window spacing on non-rectangular surfaces, no glazing may be generated. For example you may find that gable window surfaces have no default windows generated and it is often easiest to draw a window in this case.

Reveal

Reveal surfaces are associated with the setback of the glazing from the outside and/or inside surface of the parent wall. If the depth and solar absorptance of these surfaces are specified, the program will calculate the reflection of beam solar radiation from these surfaces. The program also calculates the shadowing (onto the window) of beam and diffuse solar radiation by outside reveal surfaces.

The following fields specify the properties of the window reveal surfaces (reveals occur when the window is not in the same plane as the base surface). From this information and from the geometry of the window and the sun position, the program calculates beam solar radiation absorbed and reflected by the top, bottom, right and left sides of outside and inside window reveal surfaces. In doing this calculation, the shadowing on a reveal surface by other reveal surfaces is determined using the orientation of the reveal surfaces and the sun position.

It is assumed that:

• The window is an exterior window (EnergyPlus does not consider reveals for interior windows).
• The reveal surfaces are perpendicular to the window plane.
• If an exterior shade, screen or blind is in place it shades exterior and interior reveal surfaces so that in this case there is no beam solar on these surfaces.
• If an interior shade or blind is in place it shades the interior reveal surfaces so that in this case there is no beam solar on these surfaces.
• The possible shadowing on inside reveal surfaces by a window divider is ignored.
• The outside reveal surfaces (top, bottom, left, right) have the same solar absorptance and depth. This depth is not input here but is automatically determined by the program—from window and wall vertices--as the distance between the plane of the outside face of the glazing and plane of the outside face of the parent wall.
• The inside reveal surfaces are divided into two categories: (1) the bottom reveal surface, called here the "inside sill;" and (2) the other reveal surfaces (left, right and top).
• The left, right and top inside reveal surfaces have the same depth and solar absorptance. The inside sill is allowed to have depth and solar absorptance values that are different from the corresponding values for the other inside reveal surfaces.
• The inside sill depth is required to be greater than or equal to the depth of the other inside reveal surfaces. If the inside sill depth is greater than zero the depth of the other inside reveal surfaces is required to be greater than zero.
• The reflection of beam solar radiation from all reveal surfaces is assumed to be isotropic diffuse; there is no specular component.
• Half of the beam solar reflected from outside reveal surfaces is goes towards the window; the other half goes back to the exterior environment (i.e., reflection of this outward-going component from other outside reveal surfaces is not considered).
• The half that goes towards the window is added to the other solar radiation incident on the window. Correspondingly, half of the beam solar reflected from inside reveal surfaces goes towards the window, with the other half going into the zone. The portion going towards the window that is not reflected is absorbed in the glazing or is transmitted back out into the exterior environment.
• The beam solar that is absorbed by outside reveal surfaces is added to the solar absorbed by the outside surface of the window's parent wall; similarly, the beam solar absorbed by the inside reveal surfaces is added to the solar absorbed by the inside surface of the parent wall.
• The net effect of beam solar reflected from outside reveal surfaces is to increase the heat gain to the zone, whereas the effect of beam solar reflected from inside reveal surfaces is to decrease the heat gain to the zone since part of this reflected solar is transmitted back out the window.
• If the window has a frame, the absorption of reflected beam solar by the inside and outside surfaces of the frame is considered. The shadowing of the frame onto interior reveal surfaces is also considered.

The schematics below show how DesignBuilder reveal data is used to describe real glazing systems.

FAQ: Why does DesignBuilder require both Inside and Outside reveal depth data when wall thickness is available to calculate one reveal depth from the other?

 

Although it is possible for inside reveal depth to be calculated from the outside reveal depth and the wall thickness, DesignBuilder allows both Inside and Outside reveal depths to be defined giving greater flexibility for situations where it is not possible to enter the wall thickness as accurately as one might like. For example the wall thickness may be entered as zero for simplified modelling. In such cases having direct control over the reveal depth data is an advantage.

Outside reveal depth

The outside reveal depth gives the extent to which the glazing is offset into the wall. As shown in the above diagram it is the distance from the exterior surface of the wall to the glazing outer surface (in m or ft).

Note: The outside reveal depth is used in EnergyPlus, Visualisations and Daylighting calculations.

Note: EnergyPlus models outside reveals through the co-ordinates of the window, which are offset into the zone so the window and the base surface don't lie on the same plane. DesignBuilder provides window co-ordinates to EnergyPlus in this way and there is no specific data item in the IDF data to define it.

Inside reveal depth

The inside reveal depth is the distance (in m or ft) from the innermost surface of the window to the interior wall surface as shown in the diagram above.

Inside sill depth

The inside sill depth is the distance (in m or ft) from the innermost surface of the window to the innermost end of the sill as shown in the diagram above.

EnergyPlus window dimensions - technical information

The FenestrationSurface:Detailed window data written to the EnergyPlus IDF input file will usually have a slightly smaller area to the area defined in DesignBuilder. This is to account for the frame which is included in the window area defined in DesignBuilder but excluded from the IDF window area. In cases where the frame option is switched off in DesignBuilder the frame area in the IDF data will exactly match the area set in DesignBuilder.