Transparent Solar Protection
Modern architecture today represents spaciousness and transparency. Steadily growing glass elements for the outer building merge the outside with the interior. This is reflected worldwide in office and administration buildings from the last two decades, but also inthe private housing constructions that includes atriums, gables and winter garden glazing usingthat use increasingly large glass components. This style of construction only became feasible with the advent of solar protection glass. These types of glass reduce the greenhouse effect that mainly occurs in summer due to that fact that rooms can heat up to the point that they become unpleasant to be in.
Large window and façade surfaces allow a great deal of light deep into a building’s interior, thereby avoiding excessive use of artificial lightning. Despite this large amount of light that can nowadays penetrate deep into a building’s interior, one very important benefit of using sun protection glass is the immense number of options now available for minimizing the amount of heat energy that penetrates a building, as much as in order to limiting the extreme costs of air-conditioning, since it costs much more to cool down the interior of a building than to heat it up.
Wherever energy is saved – whether by reducing the amount of cooling power use or reducing the phases of artificial light – of course saves on the environment. ln this context, it is a logical consequence to certify these types of sun protection glass products acc. to e.g. LEED, Breeam, DGNB, or other worldwide-approved certification systems for sustainable constructions. (see > chapter 4.2).
Super-cooled interiors and overheated rooms are both uncomfortable to be in, and when rooms are overheated, it can be due to too much incoming solar energy (see > chapter 4.3). The floor, walls and furniture absorb solar energy and reflect it as long-wave heat radiation. For this reason, all efforts must be made to keep this energy outside the interior rooms to achieve an acceptable room climate – without air conditioning. This was previously achieved by constructing buildings using opaque building components that only had small openings in the walls.
Today’s architecture – which strives to create living and working areas that are close to nature and are open and spacious – has shifted away from this opaque way of construction towards transparency. Therefore it is essential to master the essential parameters of the sun protection using glass to create a functional and comfortable interior while also meeting other requirements, such as structural-physical guidelines while also achieving energy efficiency.
5.4 Energy flow through glass
An interaction occurs whenever solar radiation strikes a window: one part of this radiation is reflected back into the environment, another part is allowed to pass through unhindered, and the rest is absorbed. The sum of all three parts is always 100 % – transmission + reflection + absorption = 100 %.
5.5 Sun protection in summer
Modern insulated glass lets the short-wave solar radiation pass through without hindrance, but the majority of the short-wave heat radiation is reflected. This resultsmeans in solar heating gains in the cold seasons. ln summer, however, this solar radiation can result in overheating. Therefore, specific requirements need to be met to prevent this overheating that can result from these larger glass surfaces, starting with the solar input factor S, which must be determined as follows:
S = E (AW x gtotal) / AG
gtotal = g / Fc
Aw = glazed area in m2
Ag = total area of the room behind the glazing
gtotal = total solar energy transfer acc. to EN 410, minus reducing factors for the
additional solar protection measures
Fc = reducing coefficient for solar protection equipment
|Verglaste Fläche in m2||Glazed area in m2|
|Gesamtfläche des Raumes hinter der Verglasung||Total area of the room behind the glass|
|Gesamtenergiedurchlassgrad der Verglasung einschließlich Sonnenschutz, berechnet nach Gleichung (*)||Total energy transmittance from the glazing, including shading, calculated according to equation (*)|
|der Gesamtenergiedurchlassgrad der Verglasung nach EN 410||the total energy transmittance of glazing according to EN 410|
|Abminderungsfaktoren für Sonnenschutzmaßnahmen||Reduction factors for sun protection measures|
|Strombedarf für Kunstlicht||Electricity demand for artificial light|
|Kühl-Kälte-bedarf||Cooling refrigeration demand|
|Tranmissionswärmeverluste||Transmission heat loss|
|Solarwärmegewinne||Solar heat gains|
|Energiebedarf für Warmwasseraufbereitung||Energy demand for hot water|
|Interne Wärmegewinne (z.B. Personen, elektrische Geräte)||Internal heat gains (e.g. people, electrical equipment)|
|Lüftungswärmeverluste||Ventilation heat loss|
In addition to other energy sources (see figure above), the position and size of the glazing are critical. In general, windows or façades with large areas of glazing that face the east, west, and especially the south, must be equipped with suitable sun protection glazing.
5.6 Sun protection using glass
Early production of sun-protective glass was based on glass that was coloured en masse. Compared with clear glass, coloured glass increases solar radiation absorption but it also has a marked effect on how light is transmitted. The one version reduces the transfer of energy to approx. 60 %, and two panes of insulating glass, together with a normal pane made of float glass, version reduces the transfer of energy to approx. 50 % when the coloured glass thickness is 6 mm. The thicker the glass, the higher these values. Green-, grey- and bronze-coloured glass is used most often. Due to their own inherent colouring, they can significantly change the way interior colours are perceived. Advances in glass coating technology have produced a much broader range of colours that are also a lot more neutral in terms of the effect they have on interior colours.
Today’s sun protection glazing is based on coated glass rather than on coloured glass, and is produced using the magnetron-sputter-process (see > chapter 1.3.1).The multitude of coating varieties can be used for special applications. Guardian is focusing on this technology and developing new glass for a large variety of requirements.
Besides actual solar protection, which is constantly being refined, a great deal of research and development effort is being put into optimizing warehousing, processing and resistance to mechanical influences. Another essential requirement regarding coating is to offer versions for all products that can be laminated, pretempered and bent. Only with these parameters can the large spectrum of modern architecture be met in all aspects.
Sun protection coatings are normally on the outer pane and oriented towards the interspace (insulating glass position #2). A 6 mm thick outer pane is standard. A thinner counter-pane works against optical distortion caused by the insulating glass effect (see > chapter 3.1.3). lf the interspace is bigger than 16 mm due to fixtures in the interspace or for sound-dampening purposes; this effect has to be considered in the design. Static requirements often need thicker glass.
5.7 Solar control glass as design component
The trend today is toward design-oriented façades, which entail new designs in sun control glass.
Glass with low outside reflection can be produced, depending on the coating that is used. Glass façades can be built to neutralize the visible borders between inside and outside, yet remain energy efficient.
On the other hand, there are mirror or colour-reflecting coatings that allow for some architectural license, including realizing unconventional design concepts. Colour-coordinated balustrades, for example, enlarge the range of solar sun-control glass (see > chapter 8.2).
Such creative and additive glass designing is generally project-related and feasible once the physical construction rules have been taken into consideration. Digital or screen print techniques are available, as well as glass-like laminated glass. Please refer to > chapter 8.3 for more information.