Sun shading systems
by Denise Barbaroux
In the design of shielding systems, numerous variables must be considered, starting from the environmental and ergonomic conditions of the internal spaces, up to the energy calibration and the reduction of consumption due to the technical systems. Another decisive aspect is the morphological composition of the system, as well as the functionality that allows the adjustment of the incidence of solar radiation and the light conditions.
The definition of solar shading refers to all natural or artificial mechanisms that are capable of controlling light and heat flows. According to UNI 8369, of 1988, a shielding is a "technical element with the function of specifically controlling the radiant energy, lighting, heat flow and visibility of internal and external spaces". The Legislative Decree 192/2005 gives a more updated definition: shielding is "a system which, applied to the outside of a transparent glass surface, allows variable and controlled modulation of energy and light parameters in response to solar stresses". These definitions say nothing about the environmental conditions for a shielding system to be required.
The choice of adopting a shielding system should be conceived during the early stages of the building design, since their presence affects the energy balance, both in terms of heating and cooling, but also on the shape.
After the 70s the topic related to the importance of limiting energy consumption has become increasingly important, and since then there has been a continuous succession of greater attention to try to reduce these wastes, especially in the construction sector. New methods of thermal insulation have been studied, with a consequent reduction in the use of the systems, both in winter and in summer.
Over time, the architectural projects have been studied in a sustainable way, trying to contain the consumption of non-renewable resources and the quality of living, through energy performance but also through conditions of comfort and well-being.
2) Evolution of shielding systems - a bit of history
The facade openings and the relative shielding systems have always been the subject of evolution. The functions they perform are varied, from simple protection from intrusions, to separation from the external environment, to control ventilation, lighting, noise and solar radiation.
Since the past the examples handed down that are at the origin of the solar shields are numerous: for example typical of Mediterranean architecture are the porticoes of the buildings used by the ancient classical Greek and Roman peoples. Also in the same Roman environment, the Latin term tentorum, which defined the military tent, originated the word tent, intended both as a room separator and as a drape for windows.
The term velarium instead indicated the veil maneuvered by ropes, above the stands of the Colosseum, to protect spectators from the summer heat during the demonstrations. Subsequently this curtain will be used to repair the windows. Initially, however, the separation by curtain was used more than anything else in public or noble buildings, since the small public houses were equipped with simple openings without protections.
During the Middle Ages another type of shielding began to be used, lighter: the canopeum, formed by a wooden or fabric canopy and supported by simple poles, used to cover canopies.
In the Renaissance, the use of textile elements to decorate and repair windows was increasing: velvet drapes, damasks, marquees, supported by simple sticks or cables.
In England and France towards the eighteenth century the tendency to decorate facades and balconies of private homes with multicolored curtains supported by fixed or semi-mobile structures increased: these had the dual function of decorating but also of repairing the interior from heat and sun.
The sunscreens begin to make their appearance with the beginning of the construction of industrial buildings, characterized in fact by very high and wide spans. Here the brightness and ventilation had to be kept under control, during the various seasons, through sunscreen systems.
In the twentieth century many architects began to design their buildings by inserting solar screens, which were also seen as architectural elements.
3) Solar radiation
Solar radiation represents the main source of energy for the earth's surface; it arrives on Earth as direct radiation but also in a diffuse way. The intensity of solar radiation depends on the height of the sun on the horizon and therefore at what time of day it is considered, and on the weather conditions. Furthermore, the percentage of direct or diffuse radiation has a great influence on the project level; this is because solar radiation arrives on earth with a precise direction while diffuse radiation arrives on the globe from all directions. In this way, the incident radiation can be shielded through some precautions, while the diffuse radiation is much more complex to manage.
The north-facing facades receive less sunlight, even during the summer season. Facades facing east receive most of the radiation before noon, while facades facing west will receive it during the afternoon. The south-facing facades receive solar radiation almost all day; this is the reason why it is preferable to optimize the glass surfaces on this side, for maximum solar gain.
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