5.1.2 Mountbatten, Hampshire
Mountbatten school sports hall, constructed in 1986
and designed by the same architects as Brune Park, achieves good
average levels of horizontal illuminance. It uses rooflights, high
level glazing and reflective walls in conjunction with fluorescent
uplighting.
The inside of the hall is pictured, during the day,
in fig. 5.1.5 and at night, in fig. 5.1.6. The average daylight factors
are good (3%) at the edges of the hall, but only 1.25% - 1.5% in the
playing area.
Shading of the hall is provided by large eaves to
the south. The rooflights are triple-glazed, clear glass and located at
5 m above floor level and 0.9 m in depth. The end wall windows are
double-glazed, 2.3 m x 4.8 m. The total window area is about 9% of the
floor area.
Daylighting
Daylight levels are frequently above the 400 lux
provided by the artificial lighting. However, uniformity is poor in
relation to the playing spaces and has to be supplemented most of the
time by the artificial lighting.
The use of daylighting saves £570 per year
(1990 prices) compared to the predicted £1400. This is
significant, but could be improved by using a more integrated lighting
control system. Fig. 5.1.4 shows the energy savings from using
daylighting.
Artificial Lighting
The electric lighting is fluorescent tubes (192 x
70W), arranged in groups of three, in two rows along the outside edges
of the central, opaque ceiling. The lights shine on the ceiling, but
create glare problems due to the dark underside of the reflectors and
the striped effect of the corrugated ceiling.
Control of the lighting is with manual overall
switching, photoelectric sensors and microwave occupancy sensors. The
lamps are wired so that the outer rows of tubes are on circuit A and
the inner rows (towards the centre of the hall) are on circuit B. If
the light levels are above a certain limit then circuit A will switch
off, followed by B at higher daylight levels. All lights come on when
people enter the hall, followed by the reduction in artificial
lighting, should the daylight levels be sufficient.
Problems
The lighting controls have not been well received.
The existence of two circuits leads to a stepped response and is not
popular with the users. Also starting with all the lights on and
subsequent reduction in lighting in response to daylighting leads to
occupants complaining of a dimming in the light levels. The operators
of the hall like the idea of the automatic control, but wish that it
operated better. Improved design of the automatic controls and the use
of high frequency dimming fluorescents, to alleviate the stepped
response of the light switching would be beneficial.
The advantages of the uplighting are not as
apparent here because of the lighting on the corrugated ceiling casting
distracting stripe shadows.
Lining the underside of the central ceiling with a
smooth surface would reduce the effect of the stripes and a proportion
of light leakage through the reflectors would reduce the contrast
between them and the bright ceiling.
Most users were satisfied with the light levels,
though 60% preferred to have the artificial lights on in the daytime.
Other problems include overheating, poor acoustics (hard surfaces) and
poor daylight distribution.
The building cost £321,000 (1990 prices),
with £6800 attributed to the inclusion of rooflights. The
inclusion of microwave occupancy sensors and photocell light levels
sensors costs approximately £400 to £500 extra, including
wiring, at today’s prices.27
Savings
The total installed lighting power in the sports
hall is 13.4 kilowatts, using high-pressure mercury halide lamps. The
power density is 28 watts per m2, which is, again, over twice that of standard best
practice of 12 watts per m2. The reason for this can be attributed to the
uplighting, where the light output needs to be higher than the
equivalent downlighting system.
Improved logic of the automatic controls and a
change to high frequency fluorescent tubes, with dimmable daylight
linking; with smooth finish to the ceiling, would significantly improve
the present energy savings of 14%, to at least 34% savings over the
non-daylit alternative using the present lighting arrangement.
