REFURBISHMENT CASE STUDY OFFICE BLOCK
Lighting was carefully designed to avoid impacting on the cooling load limit
solution that balanced high performance glazing with solid elements. In the end the designers opted for high performance neutral-coloured glazing with a G-value of about 0.3 and low level solid elements on each floor. However, even with this type of glazing, to keep the solar gain within manageable limits a 500 mm band of fritting had to be added to the top of the glazing to provide additional shading. The windows are fitted with internal blinds
for glare control. To prevent heat build-up close to the glazing, NDY and AHMM developed a neat return air detail. According to Hall, when the sun hits the blind, the blind heats up and the heat form changes from radiant to convective. Their solution has been to incorporate a return air slot detail in the box housing the blind to remove this convective element as it rises upwards.
Carbon footprint: Recycling the structure
Re-use of the existing structure helps limit the carbon footprint of the development and significantly reduces the transport and disposal of demolition and construction waste, which reduces emissions and minimises dust creation.
The omission of unnecessary finishes and fixtures such as suspended ceilings helps expose the thermal mass and also reduces the
28 CIBSE Journal May 2012
amount of energy embodied in the finishes and their maintenance.
Using the concrete carbon calculator and data from the University of Bath, NDY estimated that the retained structure accounts for 39,500 tonnes of concrete, or about 30,000 cu m, which is equivalent to about 7,400 tonnes of CO2 or running the operational elements of the building for 13 years.
Careful detailing has also been used
to extract air from beneath the soffit in areas where the floor plates have been extended. An existing downstand beam marks the outer limit of the original floor plate; this protrudes into the offices from the soffit. The intrusion impacted the flow of warm air along the soffit back to the return air grille at the cores. Tests by NDY in Germany had shown that without intervention, returning warm air at high level would dislodge from the soffit at the obstruction and fall into the occupied zone. In another neat solution, to overcome this particular challenge the engineers designed an extension to the extract system to draw air through a shadow-gap created between the plasterboard ceiling panels of the new floor plate extensions and the downstand beam. The extract air is carried from high level to the floor void through ducts concealed within the webs of the steel columns that support the new structure. Once in the floor void, the warmed air is routed back to the main return air ducts in the cores. The scheme also includes openable windows controlled by the occupants at will. About half of the windows can be opened. Hall says that because the displacement ventilation system is designed to use outside air for much of
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