Beddington Zero Energy Development BedZED

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Though this project featured in the first edition, BedZED has still not been surpassed as a pioneer development. It is not just another low-energy housing scheme, it is a prescription for a social revolution; a prototype of how we should live in the twenty-first century if we are to enjoy a sustainable future. This project was introduced at the foundations stage in Architecture in a Climate of Change (pp. 76-78). The scheme now has its first residents and it is appropriate in this volume to consider the completed product (see Fig. 15.13).

It shares many of the objectives of the Malmo development though being on a much smaller scale and so makes an interesting comparison. The main difference is that there is a just one design team led by Bill Dunster Architects who is one of the UK's top evangelists for ecologically sustainable architecture.

To recapitulate, the Innovative Peabody Trust commissioned this development as an ultra-low energy mixed-use scheme for the London Borough of Sutton. It consists of 82 homes with 271 habitable rooms, 2,500 m2 of space for offices, workspaces, studios, shops and community facilities including a nursery, organic shop and health centre, all constructed on the site of a former sewage works - the ultimate brownfield site. The housing comprises a mix of one- and two-bedroom flats, maisonettes and town houses.

Peabody was able to countenance the additional costs of the environmental provisions on the basis of the income from the offices as well as the homes. Though the Trust is extremely sympathetic to the aims of the scheme, it had to stack up in financial terms.

In every respect this is an integrated and environmentally advanced project. It is a high-density development along the lines recommended by the Rogers Urban Task Force.

It realizes an overall density of 50 dwellings per hectare plus 120 work spaces per hectare. At such a density almost 3 million homes could be provided on brownfield sites with the additional benefit of workspaces for the occupants, radically cutting down on the demand for travel. This density includes the provision of 4000 m2 of green space including sports facilities.

Figure 15.14 South elevation with work spaces at ground level and roof gardens serving dwellings opposite
Figure 15.15 Masonry wall construction (courtesy of Bill Dunster)

Excluding the sports ground and placing cars beneath the 'village square' the density could be raised to 105 homes and 200 workspaces per hectare.

Some dwellings have ground-level gardens whilst the roofs of the north-facing work spaces serve as gardens for the adjacent homes (see Fig. 15.14).

The energy efficiency of the construction matches anything in the UK or mainland Europe. External wall consist of concrete block inner leaf, 300 mm of rockwool insulation and an outer skin of brick adding up to a U-value of 0.11 W/m2K (see Fig. 15.15).

Roofs also contain 300 mm of insulation, in this case styrofoam with a U-value of 0.10. Floors containing 300 mm of expanded polystyrene also have a U-value of 0.10. Windows are triple glazed with Low-E glass and argon-filled. They are framed in timber and have a U-value of 1.20. These standards of insulation are a considerable improvement over those required by Part L of the latest Building Regulations in the UK. Masonry external and internal walls and concrete floors provide substantial thermal mass, sustaining warmth in winter and preventing overheating in summer. In traditional construction up to 40% of warmth is lost through air leakage. In the case of BedZED great attention has been paid to maximizing air tightness which is designed to achieve two air changes per hour at 50 pascals.

One of its primary aims was to make the most of recycled materials and the main success in this respect was to obtain high-grade steel from a demolished building as well as timber. The majority of all the materials were sourced within a 35-mile radius.

Materials containing volatile organic compounds (VOCs) have been avoided as part of the strategy to use low-allergy materials.

Ventilation becomes an important issue as better levels of air tightness are achieved. In this case the design team opted for passive natural ventilation with heat recovery driven by roof cowls. A vane mounted on the cowls ensures that they rotate so that incoming air always faces upwind with exhaust air downwind. The heat recovery element captures up to 70% of the heat from the exhaust air.

The energy efficiency drive does not end there. South-facing elevations capitalize on solar gain with windows and their frames accounting for nearly 100% of the wall area. Sun spaces embracing two floors on the south elevation add to the quality of the accommodation (see Figs 15.16 and 15.17).

According to the UK government's method of measuring the energy performance of buildings, the Standard Assessment Procedure for Energy Rating of Dwellings (1998) (SAP), BedZED achieves 150. Until the 2002 revision of the Regulations dwellings were required to achieve around SAP 75. It is predicted that space heating costs will be reduced by 90% against a SAP 75 building. Overall energy demand should be reduced by 60%.

BedZED aims to reduce domestic water consumption by 33%. This is to be achieved by the use of water-saving toilets, dishwashers and washing machines. Toilets normally use 9 litres per flush; regulations now stipulate a 7.5 litre maximum. Here 3.5 litre dual flush toilets are

Figure 15.17 South elevation with PVs integrated into the glazing

provided, producing an estimated saving of 55,000 litres per household per year. Taps are fitted with flow restrictors; showers that rely on gravity replace baths in single bedroom flats. As the scheme uses metered water it is expected that these measures will save a household £48 per year. On average, 18% of a household's water requirements will be met by rainwater stored in large tanks integrated into the foundations.

Foulwater is treated in a sewage treatment plant housed in a greenhouse. It is a biologically based system which uses nutrients in sewage sludge as food for plants. The output from the plant is of a standard equivalent to rainwater and therefore can supplement the stored rainwater to be used to flush toilets.

Household waste normally destined for landfill will be reduced by 80% compared with the average home.

The energy package

The principal energy source for the development is a combined heat and power unit which generates 130 kW of electric power. This is sufficient for the power needs of the scheme. The plant also meets its space heating and domestic hot water requirements via a district heating system served by insulated pipes. The CHP plant is reckoned to be of adequate output due to the high standard of insulation and air tightness and the fact that the peaks and troughs of seasonal and diurnal temperature are flattened by the high thermal mass.

A combustion engine generates the heat and power, producing 350,000 kWh of electricity per year. It is fuelled by a mixture of hydrogen, carbon monoxide and methane produced by the on-sight gasification of wood chips which are the waste product from nearby managed woodlands. The waste would otherwise go to landfill. The plant requires 1100 tonnes per year, which translates to two lorry loads per week. In the future rapid rotation willow coppicing from the adjacent ecology park will supplement the supply of woodland waste. Across London 51,000 tonnes of tree surgery waste is available for gasification. It is worth restating that this is virtually a carbon neutral route to energy since carbon taken up in growth

BIO-FUELLED CHP

GRID

BIO-FUELLED CHP

GRID

Figure 15.18 Wood chip gasification plant within the development (courtesy of ARUP and BRE)

is returned to the atmosphere. Excess electricity is sold to the National Grid whilst any shortfall in demand is met by the Grid's green tariff electricity. It is predicted that the scheme will be a net exporter to the Grid (see Chapter 8 and Fig. 15.18).

There is a further chapter to the energy story. Figure 15.17 illustrates the inclusion of PVs in the south-glazed elevations of the scheme. They are also sited on southerly facing roofs. Their purpose is to provide a battery charging facility for electric vehicles. How the decision was made to dedicate the PVs to this role is worth recording.

Originally the idea was to use PVs to provide for the electricity needs of the buildings. Evacuated tube solar collectors would provide the heating. It turned out that this arrangement would involve a 70-year payback timescale. If the electricity were to be used to displace the use of fossil fuels in vehicles, taking into account their high taxation burden, the payback time would be about 13 years. So it was calculated that 777 m2 of high-efficiency monocrystalline PVs would provide a peak output of 109 kW, sufficient for the energy needs of 40 light electric vehicles covering 8500 km per year. It has to be remembered that, in a project like BedZED, the energy used by a conventional car could greatly exceed that used in the dwelling. As a yardstick, a family car travelling 12,000 miles (19,000 km) per year produces almost as much carbon as a family of four living in a typical modern home.

The aim is that the 40 vehicles would provide a pool of cars to be hired by the hour by residents and commercial tenants. Other car pool schemes have indicated that hiring a pool car to cover up to 13,000 km a year could save around £1500 in motoring costs. And that is without factoring in the potential avoided cost of pollution. With congestion charges levied on vehicles using streets in London and soon in other major cities, the exemption of electric vehicles provides an even greater incentive to adopt this technology.

The co-developers Peabody and Bioregional agreed as part of the terms of the planning consent to enter into a Green Travel Plan, which meant a commitment to minimize the residents' environmental impact from travel. On-site work and recreational facilities, together with the electric vehicle pool of 'Zedcars', more than satisfy that commitment.

A diagram produced by Arup summarizes the ecological inventory of the project (see Fig. 15.19).

This development has come about because the right people were able to come together in the right place at the right time. The idea came from Bioregional Development Group, an environmental organization based in Sutton who secured Peabody as the developer. Peabody

Figure 15.19 The ecological inventory of BedZED (courtesy of ARUP and BRE)

is one of the most enlightened housing associations in Britain. Bill Dunster was engaged on the strength of Hope House, which he designed as an ecologically sound living/working environment and which served as a prototype for BedZED. Chris Twinn of Ove Arup and Partners worked with Bill Dunster when the latter was with Michael Hopkins and Partners so he was a natural choice as adviser on the physics and services of BedZED. The project happened due to a fortuitous conjunction of people committed to the principles of sustainable development. In future, developments of this nature must not rely on the chance collision of the brightest stars in the environmental firmament.

For a more detailed description of this project, refer to 'General Information Report 89, BedZED.2 The conclusion to be drawn from these case studies is that sustainable design is a holistic activity and demands an integrated approach. Reducing the demand for energy and generating clean energy are two sides of the same coin. Examples have been cited where buildings and transport are organically linked with building integrated renewables providing power for electric cars. BedZED and to some extent Malmo are signposts to new and much more sustainable and agreeable patterns of life. This book has been an attempt to illustrate how the link between buildings and renewable technologies can form a major part of the green revolution which must happen if there is to be any chance of stabilizing atmospheric CO2 at a level which leaves the planet tolerably inhabitable.

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