1.4 Rules of Thumb
Daylighting, because of its variability, is complex
and hence benefits from simple guidance so long as this is used as the
basis, rather than the end point of good design.
General
• The
daylight factor is a good basis for early design thinking. The average
daylight factor can be approximated for an outline design and inversely
- the required area of window for good daylighting can be approximated
from basic data.
• It is
important to understand the difference between daylight, sunlight and
skylight.
• Big issues
to resolve are ensuring adequate daylight is available without
generating glare particularly from low level winter sun, heat gains in
summer and heat loss in winter and incorporation of daylight linked
controls so that energy, cost and environmental benefits can be reaped.
Typical Illuminance Values
• 300 - 500
lux is expected for play and must be supplied by artificial lighting
for night-time activity.
• Typical
outdoor illuminance (CIE Standard Overcast Sky) - 5000 lux. NB: this is
considerably exceeded for 85% of the time between 8.00 and 17.00 in the
UK.
• Outdoor
summer sunshine maximum illuminance - 100,000 lux.
• Sunpatches
in sports halls can be up to 60,000 lux and will cause problems.
Daylight Factor Values
• A daylight
factor of 5% or more will create an acceptable environment for play
when daylit only.
• A daylight
factor of 3% will require artificial lighting for uniformity.
• A daylight
factor of 2% or less will require use of artificial lighting most of
the time.
Optimising Natural Light
• Ensure that
electric lights remain off when there is sufficient daylight, apart
from those necessary for contrast minimisation at the perimeter.
• Ensure that
daylight does not produce glare as this can lead to a
blinds-down/lights-on situation.
• Ensure that
daylight is usable through good distribution using the appropriate use
of splayed reveals, light shelves, prisms, etc.
• Avoid dark
internal spaces/surfaces which absorb useful daylight.
• Ensure that
lighting controls take account of daylight availability, playing area
layout and user needs; careful integration of manual and automatic
control often provides the most effective solution.
Window Size
• A sports
hall can have a daylit appearance if the area of glazing is at least
25% of the total wall or at least 9% of the ceiling area.6
• The minimum
of 9% unshaded rooflight glazing to total ceiling area should be
considered as giving the least solar heat gain compared with adequate
daylight levels and heat losses.
• In general
a glazing area of 30% of the total wall area (southerly aspect) is the
optimum for overall energy conservation; considering combined heat
losses and solar gains. However, this is undesirable for sports halls,
as a southerly aspect can lead to excessive glare problems and
overheating.
• Higher
daylight factors are required for solely toplit halls (3% minimum, with
5% preferable), as walls will appear poorly lit and a room gloomy if
the same considerations are used for rooflights as are taken for
vertical windows.
• Areas of
the hall from which there are no direct views of the sky, eg side
windows and concealed rooflights, have a low level of daylight;
typically 1/10th that of an equivalent position near a window.7
• Playing
surfaces that are closer to a vertical window than twice the height of
the window head above the floor, receive adequate daylight for most of
the daytime.
• Imagine
that the sports hall floor is mirror-like (in some cases it is).8 If a person
would see a light source reflected then, in practice, there will
probably be reflected glare.
Glazing Type
• Uncoated
double glazing should be a minimum specification.
• Low-e
coated, gas-filled double glazing is a reasobale substitute for triple
glazing - saving money and materials.
• Low-e
coatings, tints and integrated shading all improve solar heat
gains/losses but also reduce daylight levels need consideration.
Window Location
• Avoid
direct sunlight access, especially in players’ field of view.
• Avoid
distracting views out of windows (for non-recreational activities).
• Optimise
window location in relation to heat gain/loss and light levels.
• Integrate
daylight with artificial lighting.
• Rooflights
in combination with clerestories are most appropriate for daylighting
sports halls.
Orientation
• North
facing windows avoid sunlight.
• North
facing windows avoid solar gain and lose heat.
• North
facing glazing must compensate for heat effects.
• South,
South-East and South-West facing windows receive sunlight.
• South,
South-East and South-West facing windows receive solar gain.
• South,
South-East and South-West facing glazing must - in combination with
solar shading, blinds and controls minimise the worst effects of glare,
minimise solar gains when not required and maximise when they are
useful.
Site Layout
A sports hall needs to be carefully planned in
relation to its orientation and location so that sunlight control can
be easily integrated into the design. Factors to consider include the
need to9 :
• allow
adequate sky light and sunlight to reach existing or possible future
adjacent buildings;
• ensure that
the new building itself has adequate skylight, whilst sunlight is
restricted. Views are less important for a hall.
Seasonal Variations
• Pay
attention to the glare effect of low winter sun.
• Summer sun
will cause overheating if windows are unshaded.
• Shoulder
months will either compromise the shading and orientation design if
they are not catered for by adaptability.
Controls
The use of daylight indoors will only save
electricity and money if it is adequate for play at least some of the
time and if the artificial lighting is controlled in response to the
levels of daylight. There are a variety of control systems available,
from the simple switch to fully integrated computer systems.
1.5 Areas for Future Research
• Guidance on
modelling.
• Guidelines
on retrofit of daylighting duing major building repairs.
• A survey of
sports facilities to establish and communicate the potential savings in
basic terms, and to set strategies in easily understood terms on no
cost, low cost and cost beneficial measures of energy conservation from
appropriate use of daylighting and daylight controls on a facility by
facility basis is highly recommended.
• Design
development of ergonomic controls is highly recommended
• A
demonstration project which documents the design and modelling process
with post occupancy evaluation of cost benefits is highly recommended.
• Research
into colour of balls and shuttlecocks.
