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Real routes to green living

Stephen Cousins

Designing sustainable homes to fit the way people live could make an energy-efficient future a reality

The Energy Bunker was a flagship project of the Hamburg IBA, supplying heat to 3000 homes and electricity to 1000.
The Energy Bunker was a flagship project of the Hamburg IBA, supplying heat to 3000 homes and electricity to 1000.

One of the world’s biggest experiments in sustainable construction, the Internationale Bauausstellung (IBA international building exhibition) in Hamburg, came to a close last November following a seven-year research and development phase that saw an entire district of the city transformed with new energy efficient infrastructure and buildings.

The IBA was no traditional building exhibition. Backed by the Hamburg Ministry of Urban Development and Environ­ment and around 40 private investors, it encompassed over 60 structural, social, economic and cultural projects spread across 35km2 covering the Elbe islands.

Under the theme Cities and Climate Change (others included Cosmopolis and Metro­zones) the exhibition aimed to show how a city can grow simultaneously with sustainability. Central to this was the ‘Renewable Wilhelmsburg’ climate protection scheme, on the city’s largest river island, where several dedicated sustainable energy production projects were set up to provide heat and power to its 50,000 residents.

These projects included the ‘Energy Bunker’, a World War II ruin retrofitted with renewable technologies; and the Energy Hill, a former toxic landfill site converted to harness solar energy and wind power to supply around 4,000 households with electricity. Renewable Wilhelmsburg will be expanded to meet the district’s total power requirement by 2025 and its heat requirement by 2050.

Meanwhile, in the suburb’s centre, the ‘Building Exhibition within a Building Exhib­ition’ included several cutting edge sustainable demonstration apartment blocks featuring the latest smart facade technologies. These included the Woodcube, a five-storey block built almost entirely of untreated timber and designed to be the first fully-biodegradable building with zero net carbon emissions throughout its life cycle. The BIQ apartment building has the world’s first bioreactive facade – growing microalgae in glass tubes and using it to produce energy and control light and shade (RIBAJ September 2013).

Sustainable capacity

‘The exhibition’s most innovative approach was to prove that our cities have the capacity and ability to create a great deal of their energy demand sustainably and by themselves,’ explained Uli Hellweg, managing director of IBA Hamburg. ‘Our three new energy and heating grids, which include the Energy Bunker, a district heating grid under Wilhelmsburg Central and a deep geothermal energy grid now under construction, will be able to deliver 13-15% of Wilhelmsburg’s housing demand by 2015. And by 2050, despite a 40% population increase, we expect to be able to meet the entire demand of the district’s housing stock through energy performance improvements to buildings and five sustainable heat and power grids.’

IBA Hamburg’s most publicised project is the Energy Bunker, which inhabits the concrete shell of a former air raid shelter. For 60 years the structure’s outer shell, with its 3m-thick walls, served as a war memorial.

Realising the opportunity to sustainably reuse the existing structure, and its capacity to function as a decentralised heat and power station for the local neighbourhood, IBA Hamburg kitted it out with renewable technologies, including solar panels and a wood chip burner that feeds into a gas combined heat and power unit. It also built-in the capability to harness waste heat from nearby industrial machinery.

Power generated by the solar panels is channelled into Hamburg’s electricity grid, but perhaps the building’s most innovative feature is its large-scale heat buffer, whereby heat and waste heat produced by the various systems is stored in around two million litres of water housed in large tanks inside the structure.

‘This approach has great potential. Housing typically creates a large heating demand in the evening and overnight during autumn and winter, which means ramping up your central energy plant’s power and size accordingly,’ said Innes Johnston, partner and engineering team leader at consultant Max Fordham. ‘But a large store of water can be heated constantly at a lower temperature during the day, and discharge it at night. It means you can run energy plant pretty much constantly at a lower heat load, increasing energy efficiency. Plant can also be much smaller, maybe half the size,’ he added.

The Energy Bunker has been supplying local households with electricity, hot water and heating for over a year and once fully operational, in 2015, it is expected to generate around 22,500MWh of heat and almost 3,000MWh of electricity, heating around 3,000 homes and supplying electricity to 1,000. This will save roughly 6,600 tonnes of CO2 a year.

The Smart is Green block in Wilhelmsburg pioneers the use of phase change materials on a big scale.
The Smart is Green block in Wilhelmsburg pioneers the use of phase change materials on a big scale.

Layered approach

The capacity for long term heat storage was a concept exploited by the Smart is Green demonstration apartment block.

Designed by Zillerplus Architekten und Stadtplaner München, the five-storey Passiv­haus building features a ‘layered’ facade that combines a vertical garden to create a heat shield in summer, highly insulative glazing, and large transparent panels of phase change materials (PCMs) that store and release heat throughout the year and effectively enable the building to generate more heat than its residents require.

The salt hydrate-based PCMs are in a constant state of flux between solid and liquid and in the process of changing between the two states, thermal energy is absorbed or released at a constant temperature. The materials absorb solar warmth during the day and release it into apartments at night, and absorb excess heat from inside during the day to prevent apartments from overheating.

Although not a new technology, this is thought to be the first time PCMs have been installed in sufficient quantities to deliver the year-round heat that Passivhaus requires.

‘PCMs offer a simpler answer than solar thermal water storage, as they don’t require pipes, pumps or a water store, and the translucency of the PCM curtains is novel,’ said Max Fordham’s Johnston. ‘They are interesting for retrofitting although one issue is the high cost of rolling out PCMs on a large scale development.’

Standing alongside is another Passivhaus block, built almost entirely of timber using traditional-based techniques and no man-made adhesives, glues, wood preservatives, insulation materials, chemicals, paints or plastics.

Designed by Architekturagentur from Stuttgart, the Woodcube is mostly biodegradable and will produce net-zero carbon emissions throughout it’s lifecycle.

‘We tried to achieve a CO2 balance for all materials used in the Woodcube,’ said client Ralph Frenzel at DeepGreen Development. ‘While concrete (used in the basement), or glass and metal (windows), produced emissions during manufacture, the huge amount of wood used more than offset this thanks to carbon sequestration.’

With a U value of 0.16 W/m2K, the walls’ thermal performance is almost as good as a conventional Passivhaus and the entire building was erected in just five weeks by four workmen using just hand tools and a single crane.

Efforts to reduce carbon emissions during the building’s manufacture included harvesting local wood and drying it in the open air for two years to avoid the use of ovens. This also increases the timber’s strength as sap produced in the summer can cause weaknesses. Meanwhile, a photovoltaic system on the roof, LED lighting and a smart metering system dramatically cut the building’s heating demand and energy load.

‘Our greatest challenge was convincing the authorities that using so much exposed, non-chemically treated wood would still provide sufficient fire protection,’ said Frenzel. ‘Typically in Germany you are not allowed to build this high using timber, but we were able to show that these thicknesses would still deliver 180 minutes of fire protection before the structure lost stability and static functionality.’


This project shows that if you listen to residents’ needs you can design accordingly This is especially important in cities

Long term impact

Other projects at IBA Hamburg had a less obvious, but potentially longer term, impact on approaches to sustainable development. The Global Neighbourhood residential development, started in 2009 and due for completion in mid-2014, involves the modernisation, reconstruction and expansion of several streets in Wilhelmsburg. Rather than work to standard German housing designs, residents were given a central role in the design process through inter-cultural planning workshops and direct dialogue with students from Hamburg University who asked about residents’ living situations and their concept of ‘home’. Their comments helped form the basis of the redesign competition, which was won by Krause-Feyerabend- Sippel Architektur + Innenarchitektur.

‘The Global Neighbourhood was all about innovation in how a project is approached,’ said Thomas Beney, principal consultant on climate change at consultant Capita Property and Infrastructure. ‘It’s all well and good designing buildings with energy efficient facades, renewable technologies and heat recovery systems, but if it doesn’t work culturally or a family likes opening windows to get fresh air, it falls flat. This is especially important in cities, which have a mix of cultures and dense populations. This project shows that if you listen to residents’ needs you can design accordingly.’

Hamburg’s commitment to the ongoing monitoring of projects also sets it apart from other exhibitions and demonstrator projects, adds Johnston. ‘Feedback on the performance of buildings is a historic problem, but it is vital to help the industry move forward and learn from its mistakes. The IBA’s Hamburg Energy Partnerships will meter and audit buildings in use and feed the results back into design. It’s perhaps this, above all, that will determine whether Hamburg’s innovations will become applicable elsewhere and on a larger scale.’


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