Design considerations

In order to achieve successful daylighting design, the following aspects should be considered:

• The amount of glazing has a clear influence on the amount of daylight available, but more window area is not always better, it may simply increase contrast.

• Large windows admit light but also provide heat gain and heat loss routes and thus potential thermal discomfort, especially from cold draughts near the windows.

• Allocation of rooms to facades should be appropriate to the activity -to do this successfully will require consideration of the issues at the building planning stage.

• The amount of sky which can be seen from the interior is a critical factor in determining satisfactory daylighting.

• High window heads permit higher lighting input as more sky is visible.

• External obstructions/buildings which subtend an angle of less than 25° to the horizontal will not usually exclude use of natural daylight.

• If there are many external obstructions the room depth should be reduced.

• Daylight normally penetrates about 4-6 m from the window into the room.

• Adequate daylight levels can be achieved up to a depth of about 2.5 times the window head height.

• Rooflights give a wider and more even distribution of light but also permit heat gains which may cause overheating.

• Generally rooflights provide about three times the benefit of an equivalently sized vertical window.

• Rooflight spacing should be one to one-and-a-half times the ceiling height.

• Where single sided daylighting is proposed, the following formula gives a limiting depth (L) to the room:

(L/W) + (L/H) < = 2/(1 - Rb) where L = room depth, m W = room width, m H = height of top of window, m Rb = average reflectance of internal surfaces

(Adrian Pitts in Smith, P. and Pitts, A.C. (1997) Concepts in Practice -

Energy, Batsford).

• In non-domestic buildings, the window area should be about 20 per cent of the floor area to provide sufficient light to a depth of about 1.5 times the height of the room.

• Internal reflectances should be kept as high as possible.

Examples

One of the most dramatic techniques for channelling daylight into the deep interior of a building has been devised by Foster Associates for the Reichstag building.

The original design was for an all encompassing canopy but this proved much too expensive. Initially Norman Foster opposed the idea of reinstating a dome since this was emblematic of an era best forgotten. However, he yielded to pressure and used the dome as an opportunity to create something dramatic.

It is effectively a double dome, with the lower portion sealed from the upper space (echoes of Wren at St Paul's Cathedral). The upper cupola is a public space which permits views into the chamber. The spectacular feature is the cone designed by Claude Engel which is sheathed in 360 mirrors that reflect daylight into the lower chamber. Sun-tracking shading prevents direct sunlight from reaching the chamber. The cone houses air extract and heat exchange equipment. The motorised shading and the heat exchange equipment is powered by photovoltaics (Figure 14.1).

Design Climate Change

Figure 14.1

Reflective cone in the Reichstag

Figure 14.1

Reflective cone in the Reichstag

Figure 14.2

Atrium between existing buildings, Sheffield Hallam University

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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