Window blinds - Slat data

Slat data tab on Window Blinds Dialog.

 

This object specifies the properties of a window blind consisting of flat, equally-spaced slats. Unlike window shades, which are modelled as perfect diffusers, window blinds have solar and visible transmission and reflection properties that strongly depend on slat angle and angle of incidence of solar radiation. When in place, the blind is assumed to cover all of the glazed part of the window, including dividers; it does not cover any of the window frame, if present. The plane of the blind is assumed to be parallel to the glazing. When the blind is retracted it is assumed to cover none of the window. The solar and thermal effects of the blind’s support strings, tapes or rods are ignored. Slat curvature, if present, is ignored.

 

Side Elevation

 

The slat angle is the angle between the glazing outward normal to the slat outward normal.  A slat angle of 0° sets slats to be vertical and an angle of 90° sets them to be horizontal.

A slatted blind can be applied inside, outside or mid-pane.

Slat Properties

Blind to Glass Distance

For interior and exterior blinds, the distance from the mid-plane of the blind to the adjacent glass (m). See schematic above. Not used for between-glass blinds. As for window shades this distance is used in calculating the natural convective air flow between glass and blind that is produced by buoyancy effects.

Slat Orientation

The choices are Horizontal and Vertical. “Horizontal” means the slats are parallel to the bottom of the window; this is the same as saying that the slats are parallel to the X-axis of the window. “Vertical” means the slats are parallel to Y-axis of the window.

Slat Width

The width of the slat measured from edge to edge.

Note: if the Blind is applied mid-pane, the gap between the inner pane and the second pane must be at least large enough to accommodate the slat width. The gap thickness is defined by the Window gas selected in the Glazing component.

Slat Separation

The distance between the front of a slat and the back of the adjacent slat.

Slat Thickness

The distance between the faces of a slat.

Slat Angle

The angle (degrees) between the glazing outward normal and the slat outward normal, where the outward normal points away from the front face of the slat (degrees).

Minimum Slat Angle

The minimum allowed slat angle (degrees). Used only if WindowProperty:ShadingControl (for the window that incorporates this blind) varies the slat angle (i.e., the WindowProperty:ShadingControl has Type of Slat Angle Control for Blinds =ScheduledSlatAngle or BlockBeamSolar). In this case, if the program tries to select a slat angle less than Minimum Slat Angle it will be reset to Minimum Slat Angle. (Note that if the Minimum Slat Angle itself is less than the minimum allowed by Slat Width, Slat Separation and Slat Thickness, it will be reset to that minimum.)

Maximum Slat Angle

The maximum allowed slat angle (degrees). Used only if WindowProperty:ShadingControl (for the window that incorporates this blind) varies the slat angle (i.e., the WindowProperty:ShadingControl has Type of Slat Angle Control for Blinds = ScheduledSlatAngle or BlockBeamSolar). In this case, if the program tries to select a slat angle greater than Maximum Slat Angle the slat angle will be reset to Maximum Slat Angle. (Note that if the Maximum Slat Angle itself is greater than the maximum allowed by Slat Width, Slat Separation and Slat Thickness, it will be reset to that maximum.)

Slat Conductivity

The thermal conductivity of the slat.

Slat Beam Solar Properties

Slat Beam Solar Transmittance

The beam solar transmittance of the slat, assumed to be independent of angle of incidence on the slat. Any transmitted beam radiation is assumed to be 100% diffuse (i.e., slats are translucent).

Front Side Slat Beam Solar Reflectance

The beam solar reflectance of the front side of the slat, assumed to be independent of angle of incidence (matte finish). This means that slats with a large specularly-reflective component (shiny slats) are not well modelled.

Back Side Slat Beam Solar Reflectance

The beam solar reflectance of the back side of the slat, assumed to be independent of angle of incidence (matte finish). This means that slats with a large specularly-reflective component (shiny slats) are not well modelled.

Slat Diffuse Solar Properties

Slat Diffuse Solar Transmittance

The slat transmittance for hemispherically diffuse solar radiation. This value should equal “Slat Beam Solar Transmittance.”

Front Side Slat Diffuse Solar Reflectance

The front-side slat reflectance for hemispherically diffuse solar radiation. This value should equal “Front Side Slat Beam Solar Reflectance.”

Back Side Slat Diffuse Solar Reflectance

The back-side slat reflectance for hemispherically diffuse solar radiation. This value should equal “Back Side Slat Beam Solar Reflectance.”

Slat Beam Visible Properties

Slat Beam Visible Transmittance

The beam visible transmittance of the slat, assumed to be independent of angle of incidence on the slat. Any transmitted visible radiation is assumed to be 100% diffuse (i.e., slats are translucent).

Front Side Slat Beam Visible Reflectance

The beam visible reflectance on the front side of the slat, assumed to be independent of angle of incidence (matte finish). This means that slats with a large specularly-reflective component (shiny slats) are not well modeled.

Back Side Slat Beam Visible Reflectance

The beam visible reflectance on the front side of the slat, assumed to be independent of angle of incidence (matte finish). This means that slats with a large specularly-reflective component (shiny slats) are not well modeled.

Slat Diffuse Visible Properties

Slat Diffuse Visible Transmittance

The slat transmittance for hemispherically diffuse visible radiation. This value should equal

“Slat Beam Visible Transmittance.”

Front Side Slat Diffuse Visible Reflectance

The front-side slat reflectance for hemispherically diffuse visible radiation. This value should equal “Front Side Slat Beam Visible Reflectance.”

Back Side Slat Diffuse Visible Reflectance

The back-side slat reflectance for hemispherically diffuse visible radiation. This value should equal “Back Side Slat Beam Visible Reflectance..”

Slat Infra Red Properties

Slat Infrared Hemispherical Transmittance

The slat Infrared transmittance. It is zero for solid metallic, wooden or glass slats, but may be non-zero in some cases (e.g., thin plastic slats).

Front Side Slat Infrared Hemispherical Emissivity

Front-side hemispherical emissivity of the slat. Approximately 0.9 for most materials. The most common exception is bare (unpainted) metal slats or slats finished with a metallic paint.

Back Side Slat Infrared Hemispherical Emissivity

Back-side hemispherical emissivity of the slat. Approximately 0.9 for most materials. The most common exception is bare (unpainted) metal slats or slats finished with a metallic paint.

Openings

The openings data allows you to define the distance between the blind and the window and also define the fraction of the blind surface that is open to air flow on each side of the blind. The following opening multipliers are defined in the same way as for window shades. Note that, unlike window shades, there is no input for Air-Flow Permeability; this is automatically calculated by the program from slat angle, width and separation.

Blind Top Opening Multiplier

Defined as for Shades.

Blind Bottom Opening Multiplier

Defined as for Shades.

Blind Left-Side Opening Multiplier

Defined as for Shades.

Blind Right-Side Opening Multiplier

Defined as for Shades.