By Carolin Hubschneider, Fraunhofer IBP, Germany and Robert Weitlaner, HELLA Sonnen- und Wetterschutztechnik GmbH, Austria
Brief Concept Description
Common devices used for daylight management and solar shading are:
- Venetian blinds (also known as louvered shutters): they consist of multiple horizontal or vertical slats, which can be fixed or movable. The cross section of slats can have different shapes, such as C-shape, Z-shape or S-shape. The surfaces are in general mostly diffuse with specular reflection gloss of 30 to 80 GU but specular, micro-facetted or retroreflective surfaces are also available (for in-between or internal use only).
- Roller shutters: they are curtains made of many horizontal profiled bars, mostly made of aluminium, plastic or wood, hinged together. Roller shutters can be raised to open and can be closed tightly for solar protection and darkening purposes. To widen the possibilities of daylight control, the use of translucent / transparent hinge-connectors and the integration of translucent bars and bars with movable slats is also possible.
- Textile screens: they consist of a movable screen called rolled screen if a fabrique is flat and pleated/ cellular shade if the fabrique is pleated. The textile has different light transmission according to colour and the material of the fabric. Common materials are acryls, polyesters or PVC-coated glass-fibres or polyesters. In general, a clearer view to the exterior is obtained with smoother surface of the yarn and edges of the openings of the fabrique.
Such shading devices are used to control the incident solar radiation, protect against glare, distribute daylight into the room and also reduce heat losses. Their performance in these tasks depends on many factors including type of device, optical characteristics, material, installation and also mounting position.
Architectural and Technological Integration into the Envelope
These devices can effectively control solar gains when they are installed on the exterior of the façade, as they can significantly reduce direct solar radiation transmission and secondary heat transfer, limiting the risk of overheating of the building (lower g value of the complex fenestration system: window + device). In this case, however, their limited resistance to wind is an issue in medium/high buildings. Additional guiding elements (guide rails or guide cables increase the wind stability. Placed in the interior of the building, these shading devices can achieve good daylight control, but they do not significantly contribute to the reduction of the solar gains. In some cases, as for daylight redirection louvers made of specular material, the device is installed in-between the glass panes and is protected from dust and wind loads.
Venetian blinds, louvred shutters and textile screens can be installed a) in front of the façade or b) integrated into it (plastered box), as shown in the table below.
Integration into the Building: System and Comfort
A significant improvement of the performances is achieved when shading devices are automated. If the manipulation of the device is let to the user, the frequency of manipulation (e.g. rate of change) can drastically lower: in a field study on office buildings (Blindswitch 2017), it was found that only 6,2% of the blinds was operated at least once throughout the day. The implementation of automatic controls allows instead self-adjusting operation base on, for example, climatic conditions or presence of occupants. The coupling with environmental sensors (e.g. photo-sensors, temperature sensors and presence sensors) is however required for automation, so that an improved control of daylight and visual comfort as well as a smart management solar heat gains can be achieved. This additional investment in environmental sensors could be potentially exploited for other advanced controls, such as thermostats regulation or artificial lighting use.