CIBSE AWARDS WINNER BROCKHOLES
to ensure good views out and excellent levels of natural light, minimising the requirement for artificial lighting. The windows are made from high-specification double-glazed units, combined with a low conductivity timber frame and thermal- break edge-spacers to produce a unit with an overall U-value of 1.1 W/m2
K. Pochee
says this gives the units ‘a comparable thermal performance to triple glazing but with better light transmission’. As a result, daylight factors exceed 4% in all the main spaces, and even in secondary spaces, such as WCs, the daylight factor is still above 2%. Any artificial light required is provided by
bare fluorescent tubes suspended beneath the roof. The lack of a diffuser significantly increases light output. A reflective panel mounted above the bare lamps helps direct light downwards. The fittings also incorporate daylight controls and presence detectors to turn off the lighting when there is sufficient daylight or rooms are empty. In addition to daylight, the glazing
also admits passive solar heat from the low winter sun. In summer, external awnings are used to prevent rooms from overheating. As well as providing shade, says Pochee, the awnings allow views out beneath the sloping canopy, while enabling air to flow freely through the open windows.
It was clear from the outset that environmental performance was top of the client’s agenda
accuracy of the calculations,’ says Pochee. One result of these studies was that concrete, rather than steel, was used to construct the floating pontoon. This was cast in-situ, around polystyrene void formers. ‘Its construction means that, even if the concrete pontoon does spring a leak, it will still float,’ reassures Pochee. The pontoon has a rustic appearance,
thanks to a series of narrow, barn-like buildings with tall, pitched roofs and no ceilings. Their walls and roofs are formed from structural insulated panels (SIPs), topped by an oak shake roof. Pochee is particularly pleased with the
façade design, which he describes as ‘an environmental conditioning machine’, and waxes lyrical about the part the windows, insulation, apertures, shading, glazing specification and air tightness have contributed to the environment and servicing strategy. The buildings have been designed
with areas of carefully orientated glazing 32 CIBSE Journal September 2012
A breath of fresh air A series of rooflights, positioned close to the roof ridge, open to allow warmed air to rise out of the buildings as part of a natural ventilation strategy. These are predominantly orientated north to avoid over-exposure to the summer sun, with retractable blinds fitted beneath to help prevent summer overheating. The buildings that make up the visitors
centre are naturally ventilated, with the exception of a few rooms such as the toilets and kitchen. In winter, fresh air enters buildings through a row of small, low-level vents positioned beneath the windows. The vents are opened and closed using a building management system (BMS), depending on room temperature and CO2 levels. When it is very cold the vents open far enough to allow 4 l/s/person of fresh air to enter the space increasing to 8 l/s/ when the weather is mild. Ventilation rates can be increased in summer by manually sliding open the 2m-high windows because of the building’s relatively low thermal mass. ‘We’re implementing a marquee strategy: if you
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Ioana Marinescu
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