Technical description

The Double Skin Facade system consists of:
The exterior and interior glazing:
The choice of the glass type for the interior and exterior panes depends on the
typology of the facade. In case of a facade ventilated with outdoor air, an insulating pane (=thermal break) is usually placed at the interior side and a single glazing at the exterior side. In case of a facade ventilated with indoor air, the insulating pane is usually placed at the exterior side, the single glazing at the interior side. For some specific types of facades, the interior window can be opened by the User to allow natural ventilation of the building.

The air cavity between the exterior and interior glazing:
The ventilation of the cavity may be totally natural, fan supported (hybrid) or totally mechanical. The width of the cavity can vary as a function of the applied concept between 10 cm to more than 2m. The width influences the physical properties of the facade and also the way that the facade is maintained.

The shading device
The shading device is placed inside the cavity for protective reasons. Often a venetian blind is used. The characteristics and position of the blind influence the physical behavior of the cavity because the blind absorps and reflects radiaton energy. Thus, the selection of the shading device should be made after considering the proper combination between the pane type, the cavity geometry and the ventilation strategy.

Openings
Openings in the external and internal skin and sometimes ventilators allow the
ventilation of the cavity.

The choice of the proper pane type and shading device is crucial for the function of the Double Skin Facade system. Different panes can influence the air temperature and thus the flow in case of a naturally ventilated cavity.

The geometry (mainly width and height of the cavity) and the properties of the blinds (absorbance, reflection and transmission) may also affect the type of air flow in the cavity. When designing a Double Skin Facade it is important to determine type, size and positioning of interior and exterior openings of the cavity since these parameters influence the type of air flow and the air velocity and thus the temperatures in the cavity (more important in high-rise buildings). The design of the interior and exterior openings is also crucial for the flow indoors and thus the ventilation rate and the thermal comfort of the occupants.
It is really important to understand the performance of the Double Skin Facade system by studying the physics of the cavity. The geometry of the facade, the choice of the glass panes and shading devices and the size and position of the interior and exterior openings determine the use of the Double Skin Facade and the HVAC strategy that has to be followed in order to succeed in improving the indoor environment and reducing the energy use. The individual facade design and the proper facade integration is the key to a high building performance.