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Fig. 5.1.2 shows the interior of the hall
during the daytime and fig. 5.1.3 at night time, showing the
similarity in lighting conditions from both daylighting and
artificial lighting.
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The artificial lighting is designed to
provide 300 lux at night. The efficiency of the system at night
is reduced due to the light losses encountered in the velarium.
However, the glare free light and energy savings from
daylighting still make the system more efficient than a
standard hall, overall.
Daylighting
The daylighting levels frequently exceeded
300 lux. In the summer this increases to above 1000 lux
between 09.00 and 18.00. In spring, light levels exceed 500 lux
for at least two-thirds of the school hours.
For 60% of the time the artificial lighting
is not needed, fig. 5.1.4. The hall is used from 09.00 to 21.00
and the daylight reduces the annual electricity requirements by
32% - saving £1300 per year, at 1990 prices. The
potential reduction is 48% (£1900), which would be
achievable if there were ideal controls.
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Problems
A major problem associated with the
daylight was overheating due to solar gains through the
rooflights. These are exposed to the direct sunlight, with no
shading of the actual glazing. This was aggravated by poor
heating control and poor air quality, due to insufficient
ventilation. The solar gain overheating could be solved by
reduced glazing areas, the addition of removable shading and/or
the provision of better extract ventilation from the roof
space.
Control of lighting is by manual switching,
operated by a vigilant caretaker. This
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5.0 Examples of Good Practice
In addition to the survey of designers and cost
professional experiences a number of sports halls have been examined in
some detail. The aim is to assist designers to better appreciate the
impacts associated with daylighting of sports halls. The review covers
design features, problems, advantages, costs and any impacts on other
aspects of a building specification. The merits of a range of concepts
are taken into consideration and combined to give design guidance.
Two existing projects have been documented in work
by DETR. These are summarised here.
5.1.1 Brune Park, Hampshire
The main lighting problem identified with Brune
Park has been in the control of the lighting, and to some extent the
choice of luminaires. This latter is partly a problem of vintage, and
lighting technology has advanced significantly since it was constructed
in 1986.
The hall is lit by rooflights (9% of the floor
area) and metal halide lamps (33 x 400W), both located in the apex of
the roof space behind a diffusing sail cloth (velarium). It diffuses
both artificial and daylighting, contributing to a glare free
environment. This achieves very good illuminance without excessive
glare.
The hall is 30m x 16m and was designed by Jackson
Greenen Down and Partners in association with a daylighting consultant
from Hampshire County Council. Previous designs of sports halls in
Hampshire had used the velarium approach and its success prompted its
use here. The long axis of the building is located 28 degrees off
north-south. Mature deciduous trees are located to the south of the
hall, providing some degree of shading to the partially glazed end wall
(double glazing).
The rooflights are twin-wall plastic panels (on
either side of the roof apex, 3 m below the ridge and 1.8 m in depth),
with an additional layer of plastic following the roof profile. The
light transmission of the rooflighting and velarium is 60%. The amount
of light entering the hall is therefore about 35% of the external
levels. There is no shading for the rooflights. The daylight factors
are shown in fig. 5.1.1. In the centre of the hall they approach 5%.
This is sufficient to play without the requirement for artificial
lighting. The walls are reflective and daylight factors are 1.5% at the
edges of the hall.
increases the savings over what might be
anticipated had control been given to, for example, reception or
the users. Automatic control, linked to the daylight levels, would
provide ideal control, but only if alternative (high frequency
fluorescent) lights were used.
Users report the lighting as very satisfactory.
Most are unaware of the daylighting behind the velarium.
The building cost £495,000 (1990 prices),
with the velarium costing £14,500 - a significant item in the
design.
Savings
The total installed lighting power in the sports
hall is 13.2 kilowatts, using high-pressure mercury halide lamps. The
power density is 27.5 watts per m2, which is over twice that of standard best practice of
12 watts per m2. The main reason behind this is due to the velarium,
which reduces the effective output of the lights into the hall by 30%.
This high power density, related to the benefits gained from a glare
free and uniform light source has to be assessed.
Improved switching (automatic controls) is limited
using the present lighting system. A change to high frequency
fluorescent tubes, with dimmable daylight linking, would significantly
improve the present energy savings of 32%, to at least 48% savings over
the non-daylit alternative using the present lighting arrangement.
Savings are calculated by analysing the hours of
daylight available and measuring/calculating the levels that are
available in the hall for which these times would be satisfactory for
playing under. These values are then multiplied by the appropriate
power rating of the lights (if they were all switched off or total of
groups of lights to be switched off at specific illuminance levels) to
give a kilowatt hour rating. This can be compared with the hours that
the artificial lighting would normally be on if the hall was not daylit
and the corresponding kilowatt hours.
