Sun Shading Systems

1. Introduction

When designing sunscreen systems, many variables must be considered, starting from the environmental and ergonomic conditions of the interior spaces, up to the energy calibration and the containment of consumption due to technical systems. Another decisive aspect is the morphological composition of the system, as well as the functionality that allows the regulation of the incidence of solar radiation and the lighting conditions.

The definition of solar screening refers to all natural or artificial mechanisms that are able to control light and heat flows. According to the UNI 8369 standard, from 1988, a screening is a “technical element with the function of specifically controlling radiant energy, lighting, heat flow and visibility of internal and external spaces”. Legislative Decree 192/2005 provides a more up-to-date definition: a screening is “a system that, applied to the outside of a transparent glass surface, allows a variable and controlled modulation of energy and light parameters in response to solar stress”. These definitions say nothing about what the environmental conditions must be for a screening system to be required.

The choice of adopting a shading 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 energy consumption containment has become increasingly important, and since then there has been a continuous succession of greater attention to try to reduce such waste, especially in the construction sector. New methods of thermal insulation have been studied, with a consequent reduction in the use of systems, both in winter and summer.

Over time, 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

Facade openings and their screening systems have always been subject to evolution. The functions they perform are varied, from simple protection from intrusions, to separation from the external environment, to the control of ventilation, lighting, noise and solar radiation.

Since the past, examples handed down that are at the origin of solar screening are numerous: for example, typical of Mediterranean architecture are the porticoes of buildings used by the ancient classical Greek and Roman peoples. Always in the same Roman environment, the Latin term tentorum, which defined the military tent, originated the word tenda, intended both as a separator of environments, and as a drape for windows.

The term velarium instead indicated the veil operated by ropes, above the stands of the Colosseum, to protect spectators from the summer heat during events. Later this curtain was used to protect windows. Initially, however, the separation by curtain was used mostly in public or noble buildings, since small popular houses were equipped with simple openings without protection.

During the Middle Ages, another type of screening, lighter, began to be used: the canopeum, made up of a wooden or canvas roof and supported by simple poles, used to cover canopies.

During the Renaissance, the use of textile elements to decorate and repair windows increased: velvet drapes, damasks, curtains, supported by simple rods or cables.

In England and France, towards the 18th century, there was an increasing tendency to decorate the facades and balconies of private homes with multicoloured awnings supported by fixed or semi-mobile structures: these had the dual function of decorating but also of protecting the interior from the heat and the sun.

Sunshades began to appear with the beginning of the construction of industrial buildings, characterized by very high and wide spans. Here, brightness and ventilation had to be kept under control, during the various seasons, by means of sunshade systems.

In the 20th century, many architects began to design their buildings by including solar shading, which were also seen as architectural elements.

3) Solar radiation

Solar radiation is the main source of energy for the Earth's surface; it reaches the Earth as direct radiation but also in a diffuse manner. The intensity of solar radiation depends on the height of the sun above the horizon and on the weather conditions. Furthermore, the percentage of direct or diffuse radiation has a great influence on the project; this is because solar radiation reaches the Earth with a precise direction while diffuse radiation reaches the globe from all directions. In this way, incident radiation can be shielded by means of some measures, while diffuse radiation is much more complex to manage.

Facades facing north receive less solar radiation, even during the summer season. Facades facing east receive most of the radiation before midday, while those facing west will receive it during the afternoon. Facades facing south receive solar radiation almost all day long; this is why it is preferable to optimize the glass surfaces on this side, to have maximum solar gain.

4) Classification of shielding systems

To understand the most suitable shielding system, you must first understand the type of radiation which will affect the surface of that building.

A screening system can be installed on individual windows or on the facade of the entire building. Effective screening must guarantee a maximum heat gain during the winter season and a Solar radiation control during the summer. Of course, one of the functions to be performed is also to ensure visual and acoustic comfort inside the structure.

Nowadays, shading systems are often a mandatory feature in the design of energy-efficient and low-consumption buildings. Technological developments in recent years have led to an ever-increasing range of products available, also thanks to the integration of the shading systems themselves into the facade components of the building in question. In fact, their use is no longer considered only functional but has acquired a new value also from an aesthetic point of view.

When designing a screening system, several considerations must be made:

• the climatic conditions of the place, to understand how much solar radiation will affect the building;
• the orientation of the building;
• the user, the type and the intended use;
• the height of the building;
• the construction system of the building;
• the characteristics of the screening panel materials;
• the incident energy flux and therefore the reflection coefficient of the flux obtained from the ratio between the intensity of the reflected radiation and the intensity of the incident radiation;
• the type of shielding.

There are many types of solar screens on the market. The legislation shows two categories in particular, but first of all a classification can be made taking into account whether these systems are part of the building or not: that is, whether the screen has the sole purpose of protect from the sun or if the function it's that too aesthetics, of facade cladding.

A first subdivision of the shieldings is given by UNI 8369-4, according to which the systems are divided as follows:

• tax
• dark
• roller shutter
• sunblind
• veneziana
• tent
• blackout panel closure
• sun screen
• mosquito net

We can trace back to four categories of screening, regardless of the type of product used: based on the morphology, i.e. the shape of the devices, which can be horizontal or vertical slats, panels or grids, the position with respect to the closure (internal, external or intermediate), the fixed or mobile movement, and the plane of arrangement with respect to the closure (horizontal, vertical parallel to the facade, vertical orthogonal to the facade, inclined).

The most used among all these typologies are essentially the panels with slatted elements, since they do not require complex support structures and their production is not that elaborate and difficult.

These panels are a versatile and adaptable solution, both thanks to the easy design by experts and thanks to the fact that they can also be an aesthetic element of the facade.

This category of panels also includes: tends, the subject of many studies and research especially in recent years, especially regarding their fabrics, movement and external appearance. In fact, curtains can be made of different materials, such as fiberglass, PVC, polyester, polyvinyl, all treated in such a way as to obtain the appropriate resistance characteristics.

Nowadays the use of has also become very popular expanded metal, gratings, nets and wire mesh: these materials have often been considered poor and have never been used much, in fact they were used mostly to hide secondary parts of buildings, but they have become pieces to be shown and exhibited, to complete and adorn the appearance of the building itself.

As regards the screens divided according to their position with respect to the closure, with respect to the outside, to the inside and in an intermediate position, the external position is the most used, since it is more efficient, given that it protects from radiation and therefore from overheating: in fact, this identifies the solar radiation before it passes through the glass and enters internally in the form of heat.

The internal position is definitely not recommended, as it tends to block radiation once it has already entered. The intermediate position includes the solar screen placed in the gap between an external glass panel and an internal one, and can be considered an ideal solution, because in this way the system is not exposed to atmospheric agents, but at the same time prevents the diffusion of heat inside.

We then move on to fixed and mobile screens; fixed screens cannot change their position after installation, while mobile ones can tilt at different angles, to prevent the entry of solar radiation, both during the year and during the day. The movement of these screens can be rotating or sliding, horizontal and vertical.

Finally, the last category provides panels based on the plane of their position with respect to the closure; therefore, there are horizontal or vertical systems, parallel or orthogonal with respect to the closure, and inclined systems. The horizontal or vertical position depends mainly on the angle of incidence of solar radiation on the facade: facades exposed to the south are preferable to have horizontal screening, while to the east and west, vertical screening is recommended.

3 Case studies

Bologna City Hall – Designer Mario Cucinella

The new single headquarters of the Municipality of Bologna was built by the studio of architect Mario Cucinella between 2003 and 2008. The concept of the building was born from the fragmentation of the volume into three distinct blocks of different heights, one 12 high, one 10 high and the last 8 high. On the ground floor of the structure there are commercial spaces and services, such as a nursery, a bank and a restaurant. The other floors house the offices of the municipality.

The screening system, which characterizes the complex, is composed of a metal roof covering all three buildings, which almost resembles a sail: in this way the structure remains raised above the roof level by about three meters and is supported by steel columns, which also support a metal framework, equipped with braces, which supports the sunshades, made of aluminum tubes. The screening of the sunshades is fixed and therefore not adjustable; for this very reason, already in the design phase of the structure, the inclination of the pitch and the position of the tubes were chosen to optimize the screening.

The system covers the façade but also covers the terrace on the roof of the 12-storey building, where machinery and systems are located: all this to reduce the heat input, so as to improve the operating conditions of the machines. The façades to the east and west are not equipped with screens, but silkscreened solar control glass has been installed; to avoid glare, a system of internal roller blinds has been chosen, which have a light transmission coefficient of 14% and an energy transmission factor of 23%.

Markthauser – Massimiliano Fuksas

The building, located in the city center of Mainz in Germany, was completed in 2008 by the Fuksas studio. The construction faces a historic square, a place characterized by the presence of eclectic and historic buildings, which are almost all reconstructions. Fuksas' idea was to "create a building with a sense of history but without rhetoric".

The most innovative aspect of the building is the external layer, the second skin: the white laminated ceramic surface covers the structure almost completely, and is composed of many unequal windows and openings, leaving the ancient facade free and visible in the front part.

The screening system is continuous but at the same time filtering. The facade structure is made of aluminum uprights connected to the concrete slabs; on this metal framework, glass and opaque parts are inserted alternately.

Building U15 – Cino Zucchi Architects

The project places great attention on the theme of energy efficiency, therefore on solar orientation and environmental quality.

The structure of the envelope is composed of a double skin: it is therefore divided into an internal wall, completely transparent, which acts as a continuous facade and where frames and surfaces join together in a single element with curvilinear shapes, and an external part consisting of a fixed sunshade system, with perforated aluminum sheet panels. The shades of the panels range from bronze to gold, and these colors were chosen both as a decorative element and as protection from direct sunlight. Each individual sunshade panel is specifically designed and is inserted into the building with a precise orientation, depending on the internal intended use.