Heelis, National Trust Hq, Swindon
good links between departments. Heelis takes daylighting and natural ventilation of offices in a new direction and demonstrates how a building can be architecturally enticing, an outstanding place to work and highly sustainable, with very low running costs.
Building Form
The design team settled on a two-storey, deep-plan building with the main public elevation, internal layout and roof all orientated to face due north-south to control solar gain and daylighting. The roof was pitched at a 30° angle to maximise potential output from photovoltaic panels (PVs). Rooflights were placed on the north-facing side of the pitched roof, and the PVs were cantilevered off the south side to provide shading to the rooflights, so limiting high solar gains. First-floor voids bring daylight from the rooflights to the ground floor, and two courtyards allow ventilation into the centre of the deep plan. To provide thermal mass for summer night-time cooling, the roof is formed from 80 mm thick exposed pre-cast concrete panels with high levels of insulation.
Daylighting
Artificial lighting can be a significant proportion of a building’s running costs, and maximising the use of natural daylight was one of the main drivers in the design. There are first-floor mezzanines within the open-plan spaces, and two thirds of the office can be directly roof lit. Artificial lighting is controlled by detectors and dimmers, keeping electrical energy for lighting to an absolute minimum.
Natural Ventilation
It was decided that the building should be naturally ventilated, using the stack effect, which uses the bouyancy of hot air to exhaust at high level, thus introducing fresh air into the lower occupied level. Air is introduced through automatic opening windows and panels. The windows are at high level and can be left open at night without compromising security. Manual opening windows and an over-ride facility for all of the automatic windows give the occupants a degree of control. Air exhausts via openable roof lights under large roof cowls, known as ‘snouts’. Propeller fans in some ‘snouts’ provide mechanical back-up during still, hot periods. The automatic openings are controlled by the building management system (BMS) to maintain comfortable temperatures within the building. In summer these are achieved by ventilating at night to cool the exposed concrete roof soffit and first-floor slab. This thermal mass absorbs the internal gains during the day and emits them at night, thus smoothing out the effects of fluctuations in external temperature. Unlike air-conditioned buildings, it is not possible to dictate exact internal conditions with natural ventilation; rather the aim is to achieve reasonable conditions for most of the time.
Winter Ventilation
In a well-insulated and well-sealed building, roughly half of heat loss in winter is due to ventilation for fresh air. A fully naturally ventilated building would do this via the external openings and thus lose warm air to outside. By passing the stale exhausted air through a heat exchanger (using fans to drive the air), heat can be extracted and used to preheat incoming cool fresh air. This reduces the ventilation heat loss by about 70% and is yet another way to reduce the overall running costs of the building.
Cooling
The building is predominantly naturally ventilated, but in areas with stricter environmental requirements, eg central IT equipment, mechanical cooling is provided. Local fan coil units within the rooms run on water fed from roof-mounted chillers. The chillers operate on Care 45, a hydrocarbon refrigerant that is the HCFC 22 replacement with the lowest global warming potential (GWP) and also has a zero ozone depleting potential (ODP).
Photovoltaics
The photovoltaics, which provide the shading to the rooflights have a primary purpose of generating electricity. At 1300m2 the array is one of the largest in the country and provides up to 15% of the total electrical load of the building.
Sustainable Design
The team defined sustainability targets early on, and this helped guide the design to achieve a BREEAM rating of ‘excellent’. The use of PVC was avoided by careful specification of materials, including low smoke and fume cabling (LSF) and cast iron above-ground drainage. Waterless urinals help reduce the overall water consumption.
Winner of the RIBA Sustainability Award 2006
International FX Interior Design Award 2005
Best Commercial Building, Brick Awards 2005
AJ100 Sustainability Award 2006
BCO Innovations Award 2006
BIFM Sustainability Award 2006
BIFM New Build Award 2006
OAS/IAS Best Bespoke Development 2006
Building Sustainability Awards 2006 shortlist
Dedalo Minosse International Prize 2006
British Construction Industry Award 2006
For a detailed account of the sustainability strategy for Heelis, see the new edition of Environmental Design: An Introduction for Architects and Engineers
(ISBN 0-419-23760-7) published September 2005.
Architects: Feilden Clegg Bradley Architects
Location: Swindon
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