Frame and Dividers

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

If window frames and dividers are being modelled separately from the glazed part then the properties of the frame and dividers can be entered under the Frame and Dividers header on the Openings tab. A discussion on the methods that can used for modelling windows and frames in Glazing Assemblies.

Important Note: Frames and dividers are only applied to rectangular windows (default and custom) and not to other shaped windows. They are also not applied when using the Fill surface (100%) facade type. If you are unsure about whether frames and dividers will be applied to a window you can use the Visualisation rendered view to check.

A frame surrounds the glazing in a rectangular window (schematics below). It is assumed that all frame characteristics, such as width, conductance and solar absorptance, are the same for the top, bottom and side elements of the frame. If the frame elements are not the same then you should enter area-weighted average values for the frame characteristics.

If the glazing does not have a frame or dividers or if the whole glazing assembly properties are being modelled directly using the 2-Simple glazing definition method then you should uncheck the Has frame/dividers box.

If Has frame/dividers is checked and then you can enter:

• The construction of the frame and dividers,
• The number of horizontal dividers and vertical dividers,
• Frame width and divider with (see diagrams below for definition).
• Inside reveal and sill details

EnergyPlus window dimensions - technical information

For external windows on walls the following dimensions in the direction of the glazing normal can also be entered:

• Outside reveal depth
• Inside reveal depth
• Inside sill depth
• Outside divider projection
• Inside divider projection
• Outside frame projection
• Inside frame projection
• Divider glass edge-centre conduction ratio
• Frame glass edge-centre conduction ratio
• Divider type

The definition of the above dimensions is shown in the diagrams.

Reveal

Reveal surfaces are associated with the setback of the glazing from the outside/inside surfaces of the wall they are located in. 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.

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. This setting is used for EnergyPlus simulations but not for Visualisations and Radiance which use the Outside reveal depth to define the position of the window within the wall.

Note: Inside reveal depth data is provided to EnergyPlus in the same object as the frame and divider data, so when the Has frame/dividers option is unchecked this data is not provided to EnergyPlus and the equivalent of a 0 inside reveal depth will be simulated.

See also Outside reveal depth.

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.

Note: Inside sill depth data is provided to EnergyPlus in the same object as the frame and divider data, so when the Has frame/dividers option is unchecked this data is not provided to EnergyPlus and the equivalent of a 0 inside sill depth will be simulated.

Frame

Construction

Select the construction used to define the thermal properties of both the frame and dividers. In particular the frame construction is used to derive these EnergyPlus frame-related fields:

Frame conductance

The effective thermal conductance of the frame (in W/m2-K or Btu/h-ft2-F) measured from inside to outside frame surface excluding surface air films and taking frame and window geometry as associated 2-D conduction effects into account. Ideally the frame conductance should be obtained from THERM or some other 2-D calculation. DesignBuilder calculates the surface to surface conductance simply based on the material layers in the Frame construction. If you need to include particular 2-D conduction effects for the frame conductance then you should adjust the thickness or material properties of the layers of the frame construction.

Note: For metal frame windows DesignBuilder will calculate a very high surface to surface U-value for the frame construction, but the value that will be provided to EnergyPlus is limited to an maximum value of 500 W/m2k. This is in line with the limits used in the LBNL WINDOW program. This will have negligible difference on simulation as the corresponding thermal resistance is effectively zero in both cases (relative to the inside and outside film resistances).

Frame solar absorptance

The solar absorptance of the frame is derived from the surface properties of the outermost material layer. The value is assumed by EnergyPlus to be the same on the inside and outside of the frame and to be independent of angle of incidence of solar radiation. If solar reflectance (or reflectivity) data is available, then absorptance is equal to 1.0 minus reflectance (for opaque materials).

Frame visible absorptance

The visible absorptance of the frame is derived from the surface properties of the outermost material layer. The value is assumed to be the same on the inside and outside of the frame and to be independent of angle of incidence of solar radiation. If visible reflectance (or reflectivity) data is available, then absorptance is equal to 1.0 minus reflectance (for opaque materials).

Frame thermal hemispherical emissivity

The thermal emissivity of the frame is derived from the surface properties of the outermost material layer and is assumed the same on the inside and outside.

Frame width

The width of the frame elements when projected onto the plane of the window (in m or ft). It is assumed that the top, bottom and side elements of the frame have the same width. If not, an average frame width should be entered such that the projected frame area calculated using the average value equals the sum of the areas of the frame elements.

Frame outside projection

The amount by which the frame projects outward from the outside surface of the window glazing (in m or ft). If the outer surface of the frame is flush with the glazing then enter 0. This value is used to calculate shadowing of frame onto glass, solar absorbed by frame, IR emitted and absorbed by frame, and convection from frame.

Frame inside projection

The amount by which the frame projects inward from the inside surface of the window glazing (in m or ft). If the inner surface of the frame is flush with the glazing then enter 0. This value is used to calculate solar absorbed by frame, IR emitted and absorbed by frame, and convection from frame.

Frame conductance

The effective thermal conductance of the frame measured from inside to outside frame surface (no air films) and taking 2-D conduction effects into account. Obtained from WINDOW or other 2-D calculation.

Frame glass edge centre conduction ratio

The glass conductance near the frame (excluding air films) divided by the glass conductance at the centre of the glazing (excluding air films). Used only for multi-pane glazing constructions. This ratio is greater than 1.0 because of thermal bridging from the glazing across the frame and across the spacer that separates the glass panes. Values can be obtained from WINDOW for the user-selected glazing construction and frame characteristics.

Dividers

Dividers split the glazing up into separate lites. It is assumed that all divider elements have the same characteristics. If not, area-weighted average values should be used.

The schematic below show how DesignBuilder divider data is used to describe real glazing systems.

Divider type

The type of divider can be selected from these options:

• 1-Divided lite means that the divider elements project out from the outside and inside surfaces of the glazing and divide the glazing into individual lites. For multi-pane glazing, this type of divider also has between-glass elements that separate the panes.
• 2-Suspended is applicable only to multi-pane glazing. It means that the divider is suspended between the panes. (If there are more than two glass layers, the divider is assumed to be placed between the two outermost layers.)

Divider width

The width of the divider elements when projected onto the plane of the window (in m or ft). It is assumed that the horizontal and vertical divider elements have the same width. If not, an average divider width should be entered such that the projected divider area calculated using the average value equals the sum of the areas of the divider elements.

Horizontal dividers

The number of divider elements parallel to the top and bottom of the window.

Vertical dividers

The number of divider elements parallel to the sides of the window.

Divider outside projection

The amount by which the divider projects out from the outside surface of the window glazing (in m or ft). For Divider Type = Suspended, Divider Projection = 0.0. Used to calculate shadowing of divider onto glass, solar absorbed by divider, IR emitted and absorbed by divider, and convection from divider.

Divider inside projection

The amount by which the divider projects inward from the inside surface of the window glazing (in m or ft). If the inner surface of the divider is flush with the glazing, enter 0.0. Used to calculate solar absorbed by divider, IR emitted and absorbed by divider, and convection from divider.

Divider glass edge-centre conduction ratio

The glass conductance near the divider (excluding air films) divided by the glass conductance at the centre of the glazing (excluding air films). Used only for multi-pane glazing constructions. This ratio is greater than 1.0 because of thermal bridging from the glazing across the divider and across the spacer that separates the glass panes. Values can be obtained from the WINDOW program for the user-selected glazing construction and divider characteristics.

Divider properties defined by the Frame construction

The Construction is used to define the thermal properties of both the frame and dividers. In particular the frame construction is used to derive these EnergyPlus divider-related fields:

Divider conductance

The effective thermal conductance of the divider (in W/m2-K or Btu/h-ft2-F) measured from inside to outside divider surface excluding surface air films and taking 2-D conduction effects into account. Obtained from WINDOW 6 or other 2-D calculation. DesignBuilder calculates the surface to surface conductance simply based on the material layers. If you need to include particular 2-D conduction effects for the frame/divider conductance then you should adjust the thickness or material properties of the layers of the frame construction.

Divider solar absorptance

The solar absorptance of the divider is derived from the surface properties of the outermost material layer. The value is assumed to be the same on the inside and outside of the divider and to be independent of angle of incidence of solar radiation. If solar reflectance (or reflectivity) data is available, then absorptance is equal to 1.0 minus reflectance (for opaque materials).

Divider visible absorptance

The visible absorptance of the divider is derived from the surface properties of the outermost material layer. The value is assumed to be the same on the inside and outside of the divider and to be independent of angle of incidence of solar radiation. If visible reflectance (or reflectivity) data is available, then absorptance is equal to 1.0 minus reflectance (for opaque materials).

Divider thermal hemispherical emissivity

The thermal emissivity of the divider, assumed to be the same on the inside and outside.

Note 1: If you do not wish to model the shading/reflection effect of the reveal/frame/divider then simply set the projection/depth to zero.

Note 2: In the case where a window blind is applied mid-pane, any dividers that may have been specified for the window will not be applied in the model. EnergyPlus will generate a warning to this effect.