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BEST 2010: Birmingham City Council's BREEAM Excellent new offices

New BREEAM Excellent offices for Birmingham City Council are helping the city meet its CO2reduction targets.

Associated Architects director Matthew Goer says ‘no private offices will be allowed’ in its proposed offices for Birmingham City Council at Woodcock Street, ‘only meeting rooms, toilets and stores.’ By minimising cellular accommodation, cross-flow ventilation will be improved, providing optimum natural ventilation.

As part of its central administrative buildings business transformation programme, the council appointed Associated to design new offices at Woodcock Street, scheduled to open in September 2011, to accommodate departments from several existing city centre locations.

It needed a modern, flexible environment to achieve high levels of efficiency and introduce transformational change. It also wanted to meet these objectives with the minimum carbon footprint and be an exemplar for other large projects in the area known as the Aston Triangle.

The offices are in three four-storey wings, focused around four atria and the entrance is in a new landscaped public space, co-ordinated with pedestrian movement from local transport nodes. An adjoining pavilion supports complementary mixed uses.

Associated Architects’ proposal is sympathetic to its context and, together with the existing Aston University buildings, forms the fourth side of an urban space.

In 2008, the council occupied 55 buildings and its target is to reduce this figure to eight by 2012, by decanting from existing buildings, rationalising and optimising buildings which are to be retained, by increasing occupancy rates by 120 per cent and procuring new buildings, including Woodcock Street.

It also aims to reinforce corporate and department identity and achieve target occupancies of 7m2 per person, with attractive and stimulating working environments to improve staff productivity and flexibility, taking a whole-life cost approach.

The council is also committed to energy efficiency and sustainability, setting a BREEAM Excellent (2006) target at Woodcock Street.

Ventilation & solar control

Associated Architects has worked hard with services consultant Hoare Lea to provide a workable mixed-mode ventilation system at Woodcock Street, supplementing natural ventilation with displacement ventilation served by air-cooled chillers to provide comfort cooling where necessary. Fan coil units provide supplementary cooling in meeting rooms.

‘The aim is to fully naturally ventilate the building for the maximum percentage of the occupied year, dependant on acceptable external climate conditions,’ says Hoare Lea director Carl Saxon. ‘So we proposed openable panels with two functions.

These panels, manual at low level and automatic at high level, are integrated with the window system and twin central atria and a double skin south-west facade also assists with cross-flow ventilation of the offices.’

So the offices operate in two modes. In the first, there is displacement ventilation, full solar control, glare control and perimeter heating; in the second there is cooled mechanical displacement ventilation as well. In the second mode, tempered supply air passes through a 500mm-deep access floor and is distributed through floor diffusers.

Air is extracted at high level and through the atria, which have high-level automatically opening windows and useful heat energy is reclaimed in the central air-handling plant by heat recovery units. Internal sensors control the automatically opening vents, which have localised manual overrides.

Adjacent to each atrium, at high level, air movement is mechanically assisted. In really hot weather, displacement ventilation mode is automatically assumed.

Exposed concrete soffits provide thermal mass, helping to cool the internal spaces. These are cooled at night by natural ventilation through the automatically opening high level windows which pre-cool the internal space for the following day.

Associated Architects assessed numerous floor slab options, including simple steel beam and pre-stressed precast plank systems which were considered most cost-effective. The steel frame and floor plank sub-contractor then won the tender with a shear stud and plank proposal which significantly reduced plank depths and concrete volumes.

It was vital to maintain free air flow at high level within office spaces and to avoid stagnant air reservoirs. This led to the introduction of cellular beams with elongated cells to allow air to flow at high level and prevent temperatures building up above 26 degrees within 2m of finished floor level.

Energy

The offices have solar hot water heating, connected to the Aston Triangle’s combined heat and power (CHP) and the district CHP heating system, which provide low temperature hot water to serve perimeter radiators and trench heaters. Photovoltaic panels are currently being considered in lieu of solar hot water collectors.

According to simulation inputs, Woodcock Street will surpass Criterion 1 of Part L2A 2006 by 30 per cent and it has been predicted that, once all the suggested energy efficient measures are incorporated, the client’s carbon emissions targets will be met.

The elemental U-value is an improvement of 20 per cent on Building Regulations requirements, with the following break-down: external wall – 0.28W/m²K; external envelope/glazing/curtain walling – average 1.6W/m²K; flooring – 0.20W/m²K and roof – 0.16W/m²K.

According to EC Guide 19, the benchmark for an open-plan office with natural ventilation plus some mechanical ventilation and cooling (mixed-mode, for example) is to be interpolated between good practice levels for office types 2 (11kg CO2/m2/annum) and 3 (21.3kg CO2/m2/annum). Woodcock Street achieves 15.8kg CO2/m2/annum and therefore improves on this guide’s good practice levels.

Conclusion

Daylight-sensing luminaires will reduce the overall energy consumption and carbon will be saved by dimming the lights automatically within the daylight zone to the required level of 400 lux, however, BREEAM criteria for day-lighting and views out were not achievable for all workstations due to the deep plan.

Nevertheless, four generously proportioned atrium spaces bring natural light down into the five storeys of the building.

It’s notoriously difficult to get BREEAM points for daylight provision and this could be seen as a flaw in the BREEAM rating system. A pragmatic, not to say cynical, approach would be to not bother.

But because Associated Architects is driven by ecological conviction, rather than a passive box-ticking strategy, it has done its best to optimise the extent, level and quality of daylight at Woodcock Street, using the atria to admit high levels of daylight which minimise artificial light.

Associated Architects is on target for an 81 per cent BREEAM rating, which is well beyond the 71 per cent threshold requirement to be classified as ‘Excellent’. It should also be congratulated for achieving design quality on many levels and working hard to integrate natural ventilation, displacement ventilation, thermal mass and building construction.

Credits

Start on site August 2009
Contract completion September 2011
Contract duration 104 weeks
Gross internal floor area 23,435m (including 2,010m fourth floor plant room area)
Capacity 2,268 work stations
Form of contract and/or procurement NEC3 – Engineering and Construction Contract, Option C – Target Contract with Activity Schedule
Target project cost £38.5 million
Cost per m2 (gross) £1,514
Client Birmingham Property Services
Architect Associated Architects
Structural engineer Scott Wilson
M&E consultant Hoare Lea
Quantity surveyor Birmingham City Council Urban Design
Project manager Birmingham City Council Urban Design
Main contractor Thomas Vale Construction
Estimated annual CO2 emissions 15.8kg CO2/m2
Design air permeability 6m3/hr/m2 (at an applied pressure difference
of 50Pa)
Water consumption 4.5m3 per person per year
Commuting pollution 297kg per person per year
EPC (Energy Performance Certificate) rating
B (36)

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