If daylight is to be at the heart of this equation, then the use of energy
for artificial lighting in buildings must be reduced by the intelligent use of
daylighting design; since it is now possible for the deficit in energy to be
made up by means of solar conversion... the use of photovoltaics,
powerful enough to generate sufficient energy to meet or exceed its
lifetime consumption.
Sustainable architecture is associated with minimizing all the different
aspects of energy consumption associated with the production of a
building from materials to construction methods and transportation,
together with the continuing operation of the building throughout its life;
but it is with the energy used for artificial lighting and the possible
economies associated with sunlight and daylight that we are concerned
with here... the development of a strategy for design, a strategy which
involves all the relevant criteria leading towards a holistic solution.
If we ignore the demands made upon a ‘passive’ structure, by aspects
of ventilation, air pollution, and the artificial lighting system, it is possible
to outline a simple four-point strategy for daylighting design, bearing in
mind that all the other factors need to be borne in mind to complete a
holistic approach towards the building design.
- A decision needs to be made on the siting of the building, differing as
to its location and site characteristics; in a green field or urban situation;
taking into account the orientation, sun path and location of existing
buildings or landscape. - The building function may determine the room dimensions, heights,
and subdivisions, bearing in mind the present and future needs of
occupation. Room height is a key decision, having a bearing on daylight
penetration and the desirable overall room depth as well as building
costs. - The window size and disposition. This is clearly the most
complicated design decision, since it must incorporate all the human
factors mentioned earlier, such as the provision of view, control of heat
gain and loss and the elimination of glare, as well as the more obvious
needs of functional vision.
The combined windows should provide an average 5 per cent daylight
factor for a substantial part of the floor space. From the architect’s
viewpoint, this may well appear as the most important decision, since it
will determine the appearance of the building elevations from the
exterior; but from a strategic point of view it will determine the success of
the daylighting approach.
It will be advisable to prepare a specification for the windows to
include the nature of the glass, its transmission value and other
characteristics. The types of glass are discussed in some detail under
the subject of energy later, but it is at this point that the needs of other
disciplines must be integrated, such as ventilation, sound attenuation and
energy conversion (PVs). - Finally control systems are a consideration, first, those controls
which relate to the outside condition, the control of sunlight and the
avoidance of glare; and second, those of the interior, the relationship with
daylight and the artificial lighting system, to facilitate ‘daylight linking’;
this will be crucial to effect the possible savings in energy.
Whilst the four-fold decisions outlined are a necessary start, they must
at each point be related to the other criteria for building design, not least
of which will be the question of structural possibility, durability and its
relationship to overall building costs, both initial and running costs,
which relate to overall sustainability.
8 Daylighting: Natural Light in Architecture