Exterior shadings

Exterior shadings are very effective. However, they must be robust to withstand the elements and therefore cost more. External shadings such as awnings must be withdrawn when there are strong winds, which can conflict with the need for solar control.

Penetration through the building envelope, necessary for mechanical operation, is in conflict with the need for air tight envelope construction.

Awnings

• Tall windows need an awning that projects far out, which is therefore more exposed to wind damage. In addition, the further the projection, the greater the side opening through which solar radiation is admitted.

• The awning should be 15 cm to 20 cm wider than the window opening to reduce sun penetration from the sides.

• Italian awnings are more suitable for tall windows. The top part is located in side runners and the bottom part projects outwards in the same way as an ordinary awning (see Figure 9.6.3).

• Awnings are more efficient if they have a dark colour. A light colour will increase the primary solar transmittance of the fabric and also increase the solar gains reflected from the light backside of the awning into the room. A very light-coloured awning captures reflected solar radiation from the façade and the ground.

• Awnings are more efficient on a south façade than on a west or east façade.

Source: Helena Bülow-Hübe

Figure 9.6.3 Italian awning

Source: Helena Bülow-Hübe

Figure 9.6.3 Italian awning

Exterior Venetian blinds

• A standard construction has aluminium slats in widths from 50 mm that can be tilted. Slats wider than 50 mm are stronger and have a stiffened edge. The shading performance is not very different due to the slat width. The slats are located in side runners to make the blind quieter and better able to resist strong winds. The exception is the 50 mm slat that can be guided at the sides with a plastic-coated wire.

• There should be sufficient space above the window to allow full access to winter sun when the blinds are retracted. When retracted, the external Venetian blind should be protected by a cassette.

Horizontal overhangs

• A horizontal slatted baffle should be capable of supporting snow loading.

• A sloped roof above a horizontal slatted baffle should have cleats to prevent snow avalanches from destroying the shading system.

• Slatted baffles may be combined with an inclined or vertical mantle.

Roller screens

• Roller screens are external screens that can be rolled up or down. The screen is guided by side runners in a track. The fabric is translucent PVC-coated polyester or glass fibre.

Figure 9.6.4 A horizontal slatted baffle combined with photovoltaics on the vertical mantle

Source: Björn Karlsson

Figure 9.6.4 A horizontal slatted baffle combined with photovoltaics on the vertical mantle

Source: Björn Karlsson

• The fabric is 'transparent' from the dark side to the light side. The screens provide a relatively good view out but less privacy at night. In districts where dust particles, sand or similar substances are numerous, these may clog up the fabric, with the result that it is less transparent and the view of the outside is restricted. However, the fabric is easy to clean.

• A screen requires less room above the window than, for example, an external Venetian blind.

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