Solar Control Devices on Glazed Facades : Optimising the shape of an outer Slat Array as function of latitude, climate and solar control strategy.

The arrays of external movable slats are one of the most effective solar control devices on transparent building envelope elements. Furthermore, they significantly affect the image of the building. For a south facing glazed façade it is normally assumed that slats with the major axis horizontal are convenient, while for the east and west orientations it is better to arrange their major axis vertically. Therefore, intermediate inclinations should be appropriate for intermediate orientations of the façade. The optimal shape of a slat array depends on a number of factors such as: visible solar paths, which are defined by the Latitude and orientation of the façade, local climate and building's energy balance; the latter determines the relative weight of energy demand for heating, cooling and artificial lighting. If the slats are equipped with PV cells, the energy balance of the building must also take into account their electricity production. If the slats are movable and/or combined with other devices, such as internal curtains, any solar control strategy reduces the incoming luminous flux, and this increases the period of use of the lamps, with the necessary consequences on energy demand and comfort. Therefore, the part of the sky that the façade sees through the slats become important, and this depends on the inclination of slats longitudinal axis. In reference to a typical office room with a fully glazed exterior wall, in a northern Italian climate, in this work is proposed a computer method for finding the optimal slope of the slats longitudinal axis as a function of: local climate, façade orientation and various solar control strategies. The analysis was performed only by means of computer simulations. With regard to the case study in the examined climate the results show that the optimal arrangement of the slats major axis varies significantly depending on the solar control strategy adopted.