Civil Engineering Reference
In-Depth Information
Light transmission efficiency is greatest if the tube is short and straight. In longer,
angled, or flexible tubes, part of the light intensity is lost. To minimize losses, a high reflec-
tivity of the tube lining is crucial; manufacturers claim reflectivity of their materials, in the
visible range, of up to 99 %. At the end point (the point of use), a diffuser spreads the light
into the room. Devices using optical fibres to transport daylight are also under development,
with interesting perspectives in refurbishment thanks to their very small diameter.
In view of the small dimension of the fibres, an efficient daylighting set-up requires a par-
abolic collector to track the sun and concentrate its light. Light pipes can be also used in new
construction and refurbishment, to transport daylight through thick roof structures and attics.
Heliostats
A heliostat tracks the movement of the sun. It is typically used to orient a mirror, through-
out the day, to redirect sunlight along a fixed axis towards a stationary target or receiver,
which can be an interior building space, a light pipe or an atrium.
In the case of daylight applications, a heliostat can be used to improve the amount of
natural light in very deep, very high or scarcely illuminated building areas. In the case of
building applications, a heliostat is typically composed of a movable mirror that follows
the movement of the sun, and a fixed mirror oriented towards the interior of the building.
Example: Heelis office building, Swindon, UK
Heelis, the new headquarters of
the National Trust in Swindon, materializes the relationship between natural light,
solar shading, ventilation and thermal storage. Heelis received the “excellent”
Building Research Establishment Environmental Assessment Method (Breeam)
scoring. The building shows the possibility to integrate energetic strategies with
low cost technological solutions.
Some of the innovative solutions include:
• natural light for solar passive gain (Victorian shed);
• indirect natural light integrated with an artiicial luorescent system con-
trolled by sensors that
• keep the minimum luminance;
• photovoltaic panels;
• natural ventilation by stack effect (light metal snouts);
• lightweight steel structure (Fig.
3.8
).
Fig. 3.8
Heelis: A section of the building showing the indirect lighting system and the natural
ventilation strategies (Feilden Clegg Bradley Studios).
Design
(Arup Associates). Feilden Clegg Bradley Studios; 2005
