produced for the DETR by Professor Peter Tregenza in their Best Practice
Programme on energy efficiency. This goes through a number of ‘rules of
thumb’ and relates daylighting design to the different stages of the RIBA
plan of work. Architects can learn a lot from the commonsense approach
adopted in this little book, in establishing their initial design proposals
before checking these out with the methods of computation available.
The type and configuration of the window or windows, the nature of
the glazing and their surroundings will make a significant difference, and
whether the window is obscured by surrounding buildings, and how
much of the floor area has an unobscured view of the sky. All these and
other considerations need to be taken into account if an accurate
calculation of the overall daylight picture is to be made.
From the architect’s point of view, the physical modelling of a space
has advantages. Simple design models are a part of his design tools, and
have the advantage that they can be modified easily to accept changes to
the section and layout. Alterations to the interior reflectances can be
made and the interior effect photographed to show a client. Placing the
model below an artificial sky and using a grid of photocells; such models
at scales of 1/20 to 1/50 can be used to calculate the average daylight
factor, and if found to be unsatisfactory the model can be modified to
make the necessary changes to comply with the daylighting strategy, as
depicted by the brief. A simple alternative which may be used as a rough
check, is to place the model under an area of unobstructed sky.
It is not intended to go into the detail of the methods of calculation
which are available; architects’ offices will no doubt have the required
computer software to deal with the straightforward problems of the
calculation of the average daylight factor (DF) for buildings with
traditional side windows. It is most important to establish the correct
daylight strategy for a building in its environment, its orientation, and its
neigbouring buildings, together with a ‘client brief’ that recognizes the
advantages of the natural source.
The calculations for daylighting in large commercial buildings is
intimately bound up with the requirements of artificial lighting, and by
the means adopted for ‘daylight linking’. When calculating the levels of
daylight (DF) available during the day, this influences the level of the
artificial light which must be available, since considerable savings of
energy can be made by the sophisticated control systems now available.
Rather than duplicating the information on the methods of calculation
which are available elsewhere, there follows a design report which
46 Daylighting: Natural Light in Architecture
Rule of thumb. Daylight penetrationBuro Happold