Cutting out sunlight and glare

Building performance issues

PatrieAllemann

Protection against sunlight and glare is provided by additional elements around the opening. The task of these elements is to regulate the amount of daylight and solar radiation entering the interior, perhaps even exclude it completely. A secondary function is to provide privacy at night.

There are many ways of incorporating sunlight and glare protection measures into the architecture of a building. However, certain building performance aspects must be considered if efficient, functioning protection is to be achieved.

Sunshading: the brief

Depending on the geographical location of a building, its exposure and the construction of its facades, solar energy can enter through the openings and lead to overheating of the interior in spring, summer and autumn. We prevent this by installing a suitable sunshading system. Basically, sunshades reduce the amount of heat radiation admitted by reflecting it. The total energy transmittance (g-value) is the means we use to assess the effectiveness of the protection, or to compare it with other systems. The g-value is the total of radiation transmitted plus secondary heat emissions to the inside and is determined through measurements or calculations. An efficient sunshade is distinguished by a high degree of reflection, which reduces the g-value accordingly. To prevent overheating of the interior, this reflection must take place before the radiation strikes the glass. If the solar radiation passes through the glass first, some of this radiation is absorbed lotal radiatior

Reflection

Transmitted radiation + long-wave infrared radiation

Secondary heat emissions

Transmitted radiation + long-wave infrared radiation

Secondary heat emissions

Outside Glass Sunshade Inside

Fig. 75: Internal sunshade that the visual relationship with the outside world remains essentially undisturbed. Depending on the form of the sunshade, an interesting intermediate layer can also be created between inside and outside which can even provide useful floor space (e.g. loggia). However, a fixed sunshade can respond to the changing solar trajectory (daily and seasonal) to only a limited extent.

A movable sunshade can be constantly adjusted to suit the position of the sun and to regulate the incoming sunlight according to individual needs. Owing to the diversity of types many design options are conceivable. During the planning it is important to consider the minimum and maximum dimensions of the respective systems. However, these dimensions vary only slightly among manufacturers of the same systems. Whereas the minimum dimension depends on the size of the opening, the maximum dimension mainly depends on the properties of the materials employed and the degree of exposure to the wind.

Total radiation

transmitted radiation + secondary heat emissions

Outside Sunshade Glass Inside Fig. 74: External sunshade by the internal sunshade and converted into long-wave infrared radiation. This radiation can no longer be reflected back through the glass and promotes a temperature increase inside the building. Optimum sunshading can therefore only ever be fitted externally.

Types of sunshading

Sunshades can be designed as movable or fixed components. Examples of fixed sunshades are canopies, horizontal and vertical screens (brise-soleil), loggias and fixed louvres. Such elements form a vital part of the f acade design. One advantage of the fixed sunshade is

Fig. 76: Fixed sunshade as a tangible intermediate layer with brise-soleil (top) and loggia

Le Corbusier: Unité d'habitation, Marseille (F), 1947

Fig. 76: Fixed sunshade as a tangible intermediate layer with brise-soleil (top) and loggia

Le Corbusier: Unité d'habitation, Marseille (F), 1947

lotal radiatior

Reflection

Total radiation

Fig. 77: The components of the sunshading system are housed behind an aluminium fascia and are therefore concealed when not in use.

Gigon/Guyer: Broelberg development, Kllchberc (CH), 1996

Fig. 77: The components of the sunshading system are housed behind an aluminium fascia and are therefore concealed when not in use.

Gigon/Guyer: Broelberg development, Kllchberc (CH), 1996

Various types of movable sunshading

Roller shutters: These consist of non-adjustable slats guided in channels at the sides of the opening. When not in use the slats are rolled up around a spindle mounted near the window/door head or folded into a bunch (folding roller shutter). The degree of light transmittance is determined by the slat profile (interlinked or separate), the reflection by the material and its colour. Today, the slats are usually of aluminium, which combines a high degree of reflection with minimum maintenance. By contrast, the wooden shutters often preferred in the past require more maintenance. As an option, roller shutters can be pivoted outwards and upwards to allow indirectly reflected daylight to enter the room. The maximum/minimum dimensions for roller shutters without this feature are approx. 50/450 cm for the width and 50/400 cm for the height. During planning, the maximum permissible area of approx. 10 m2 must be considered. The maximum dimensions must be considerably reduced on facades exposed to high winds (e.g. high-rise blocks).

Louvres: In contrast to the slats of the roller shutter, the angle of each louvre can be varied about its longitudinal axis, which enables flexible control and redirection of the incoming light. The louvres, which are made exclusively of aluminium, are guided in channels or by thin steel wires. When not in use the louvres are stored as a compact bunch at the window/door head. The minimum dimensions are similar to those for roller shutters, but the maximum dimensions depend on the louvre profile. Special care must be taken with louvres exposed to high wind loads.

Rollerblinds: These are made of fabric and when not in use are rolled up at the window/door head. Light transmittance and degree of reflection are determined by the type of fabric. Light-coloured fabrics can scatter the incoming

Fig. 79: Roller shutter with angled positioning option integrated into the wall access from inside

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