Rio Architects' Innovate Green Office in Leeds has achieved the highest ever BREEAM rating.
Here is a British building which takes passive design seriously.At the Innovate Green Office in Leeds, called the UK's greenest building because it achieved the highest ever BREEAM rating of 87.5 per cent when assessed last year, there is not a single renewable technology in sight. This project exemplifies what passive design can achieve, starting from first principles – orientation, exploitation of thermal mass, optimisation of plan depth and building section to maximise daylight, and a heavily insulated envelope.
Not only have all the obvious moves been realised, but extensive study of different options during the design phase meant that the project was thoroughly assessed for its environmental performance before the design was even finalised.
Client Innovate Property, a niche developer of serviced workspace, challenged its design team – Cardiff-based Rio Architects, structural engineer Scott Wilson and King Shaw Consulting Engineers – to deliver a commercially viable green building. As early design fees escalated, Innovate approached regional development agency Yorkshire Forward to fund prototype research prior to acquiring its Leeds Thorpe Park site. Yorkshire Forward eventually contributed approximately £1 million to the £6 million scheme to fund the difference between a conventional and a green office.
innovate_orientation
To maximise daylight penetration, the building is sited east-west rather than the north-south orientation typical of many sustainable projects. South-facing buildings require large overhangs to screen out the midday sun, but these sunscreens block out much useful daylight on cloudy days. With an east-west orientation, morning sun is not a problem and the effect of the strong afternoon sun is controlled by the thermal mass which delays internal temperature increases until the close of the working day.
British Council for Offices (BCO) guidelines were carefully reviewed to reach what King Shaw's Doug King refers to as 'a compromise between what was fundable by institutional lenders and the aspirations of low-carbon design'. Maximum summertime temperatures were agreed at 26?C (as at Bennetts Associates' Wessex Water Operations centre in Bath) rather than BCO's standard of 22?C, and lighting levels to 400 lux rather than the current 500 lux guideline.
innovate_section
The 13.5m plan depth of the two office wings and the 5.5m-wide atrium were calculated to maximise daylight penetration into the building, providing 400 lux to the work surfaces during 80 per cent of the working year. Internally, ceiling height was set at 3.075m to allow stratification of warm air without discomfort to occupants.
Due to the high occupational density of the building and the IT loads, the initial aspiration for a naturally ventilated building proved unfeasible. The design team opted to maximise the building's capacity as a thermal store to keep air conditioning loads to a minimum, choosing concrete over a steel-frame structure. TermoDeck hollow-core concrete floor slabs were specified along with prefabricated concrete planks for the exterior walls.
innovate_thermodeck
innovate_wallpanel
Exposed concrete is used for floors, roof and external walls, making the building an enormous thermal store. The use of hollow-core TermoDeck concrete slabs (see diagram above) for the floors and roof means that air is circulated through the slabs for pre-heating or precooling depending on the season. Precast wall planks are exposed internally to further increase the building's thermal capacity. As a result, maximum cooling loads are
shifted to evening, reducing the overall chiller capacity.
TermoDeck acts as a thermal labyrinth by circulating air through
perforations in the concrete slabs. 'TermoDeck meant that we could engage with every ounce of concrete,' says Shaw. The building's concrete fabric stores solar gain, releasing it in the unoccupied evening hours, and it is
also well-insulated, with some 250mm of expanded polystyrene insulation glued to the exterior of the planks.
innovate_insulationplinth
250mm-thick blocks of expanded polystyrene insulation glued to the exterior of the concrete planks result in a U-value of 0.15 for walls. Fixed vertical fins on the east and west elevations screen out 60 per cent of the midday sun. The glazing ratio of approximately 40 per cent optimises daylight gain and heat loss. Double-glazed argon-filled windows by IdealCombi have a U-value of 1.67 W/m2K.
The result is a building which is 80 per cent more efficient than a typical comparable air-conditioned office, according to Shaw. The highly insulated envelope means that the proportion of energy required for space heating is dramatically reduced – from 44 per cent for a comparable air conditioned building to 12 per cent – and is met primarily by internal gains using mechanical ventilation with heat recovery.
Electrical demand for lighting, the next largest energy load, is also reduced because the building is designed to a high 4.5 per cent average daylight factor, which means that electric light is only required for 20 per cent of the working year. Other factors which contributed to the high BREEAM score include rainwater harvesting and vacuum drainage, as well as reduction of embodied energy through the use of recycled materials (Lytag aggregate in the concrete and recycled steel from UK mills for the rebars) and the specification of local materials for bulk orders where possible.
The Innovate building's BREEAM assessor Elliott Carter, of sustainability consultant Eight Associates, says the project has been used as a case study for BREEAM's recently introduced Outstanding category and the BRE will use it to show how to achieve the new rating.
As for costs, cost consultant Mike Bezzano of Mirus Management Services says that the building cost approximately 25 per cent more than the comparable steel-framed prototype created by the design team, with a 14-year payback at current energy prices. 'That could easily be down to seven at the rate energy prices are increasing,' says Bezzano. And in the meantime you're helping to save the planet.
Source - AJ
Author - Hattie Hartman
