B E DZ E D A report on energy efficient design principles applied to Beddington zero (fossil) energy development at Beddington, Sutton Otman Gusbi Introduction Beddington Zero Energy Development (BedZED) is a housing development designed by Bill Dunster Architects (now known as Zed Factory) in partnership with the Peabody Trust and the BioRegional Development Group. BedZED is the UK’s largest carbon-neutral housing development and was the first of its kind in the UK when completed in 2002.
BedZED is a mixed-use, mixed-tenure development that incorporates many innovative approaches to energy conservation and environmental sustainability. For this review I am going to examine how the designers of BedZED have used various technologies and design principles in their pursuit of making BedZED a truly carbon neutral development. The areas I am going to look at are the building’s fabric and the materials used in its construction, how the building utilises passive solar design, and finally the HVAC and building systems utilized in the development.
Building Fabrics & Materials Through the materials used in its construction and the design of its fabric, BedZED has tried to reduce its environmental impact in two ways. The first is by reducing its energy consumption and the second by reducing the embodied energy in the materials used to build the project. Despite being a zero carbon development, the first thing that struck me when visiting BedZED was that it didn’t look like an experimental piece of architecture.
The houses were clearly different to a standard housing development, but they looked modern and contemporary rather than a laboratory for testing new products and principles, only the slight glimpse of a wind cowl on the roofs and the photovoltaics (PVs) scattered on the facade gives this impression as you walk around the site. Inside, the interiors are pleasant and only the deep reveals on the windows and the exposed soffit gives you a clue that this is not a standard housing development.
BedZED works on the principle that if it can reduce the energy it consumes through hot water heating and space heating, the less energy it will have to produce to be a carbon neutral development. The building fabric is key in reducing the energy that is used in each of the dwellings and is dealt with in several ways. The most obvious way this is done is by ‘super insulating’ the buildings. BedZED houses have an additional 300mm of insulation than you would usually expect from a standard housing development, this takes the U-Value of the BedZED walls to an impressive 0. 1 W/m2K compared with 0. 45 W/m2K of a house built to 1995 Building Regulations . This extra insulation acts to keep out the cold from the outside but to also keep the internal heat gains from kitchens, occupants and electrical equipment inside the building. This has proven very successful and means that units require no central heating for large parts of the year, it is only when the weather is very cold that occupants have found that they need to use the heating system which is used as a back-up. This has allowed for an 88% reduction in space heating compared to the national average.
This is not the only way that the fabric is used to control the internal environment of the units. The extra insulation is used as a ‘jacket’ to the rest of the structure. The buildings are constructed from thermally massive materials that store heat during warm conditions and release heat at cooler times. For this to work the insulation jacket has to sit on the outside of the construction so that the concrete soffits and thermal blocks can be left exposed. One criticism I have of this is that it restricts the options for the occupants on how they can decorate their unit which was apparent in the show flat we looked around.
Some people may like an exposed soffit but others may like to apply a different finish to the ceiling which could upset the way in which the structure balances out indoor temperature fluctuations. The walls are not the only piece of the fabric that is designed to give the building a high thermal performance. A large percentage of heat on a standard building is lost through the windows as these are more difficult to insulate. As the windows are an integral part of the environmental strategy for the units (more on this later) the specification of the glass became ery important. The windows on the development are argon-filled triple-glazed units with a U-Value of 1. 2 W/m2K this is compared to 3. 3 W/m2K of a house built to 1995 Building Regulations. The windows are also a good example of how the architects have tried to reduce the embodied energy in its building materials. Embodied energy takes into account the energy used during a materials extraction, production and transportation and is often given a value as to how much CO2 this releases into the atmosphere.
For BedZED the designers went to great length to reduce the embodied energy in its materials. This can be done in many ways such as sourcing local materials to reduce transport miles or by recycling old materials to cut down on energy wasted during extraction and processing. The embodied energy of homes is less significant than the energy consumption during their lifetime so BedZED was designed primarily for exceptional energy efficiency during use and building products were selected to meet the thermal design criteria.
Nevertheless, from the tour we got round the project it became clear that the guides were keen to stress that environmental impact was considered at all stages of the design process. 52% of materials were sourced within a 35 mile radius of the site and recycled materials were used wherever possible. In some cases this wasn’t possible (the windows had to be sourced from Denmark as there was not a manufacturer in the UK who could build to the required specification) and in some cases I think the effort spent in sourcing recycled materials could have been spent better elsewhere.
High grade reclaimed materials such as structural steel are not off-the-shelf products and there needs to be a willingness to work at securing a reliable supply of materials and extra time in designing connection details that can accommodate a range of sizes. As materials used in a buildings construction account for just 2-3% of the UK’s CO2 emissions (compared to 29% for domestic household energy consumption) I think that if sourcing recycled and sustainable materials can help reduce costs then it is justified. This was the case with the recycled aggregates and the timber window frames which were cheaper and had less environmental impact.
In a project like BedZED, which is a showcase for environmental thinking and in some ways an exemplar project, I can understand why so much time and effort went into sourcing these materials but if the thinking and attitudes are to be rolled-out on a mass scale by other developers then I think it will become unviable. Firstly, the supply of reclaimed materials such as steel would fail to keep up with demand and secondly the risks involved would be too much for a developer to consider. On BedZED the risk for the structural steel was absorbed by understanding clients and structural engineers , but this wouldn’t always be the case.
Passive Solar Design Passive solar design involves utilizing the heat and light given off by the sun in the design of buildings to reduce the need for artificial light and space heating. BedZED has been designed with this as a key principle to help reduce its energy consumption. The basic orientation of the site allows the residential units to face south to take advantage of solar gain whilst work units face north to gain from increased natural daylight. The south facing residential units have an unheated sunspace that creates a buffer between the sunspace and the living areas in the unit and trapping heat.
In the summer the windows can be opened up to create open-air balconies. Whilst this system works well at reducing energy consumption through using less heating and artificial day lighting, I have concerns that it could lead to the living spaces overheating in the summer. Our tour guide assured us that the system worked well for the vast majority of residents for the vast majority of the year but confided that in some cases residents had complained of it being too hot during the daytime on particularly hot days. However, due to most residents not being at home during the day this wouldn’t be a problem for a large percentage of residents.
Another problem I found when visiting the show flat was that it was quite gloomy in the main living area, despite it being a moderately sunny day outside. If it was overcast I think it could be a bigger problem. The tour guide tried to blame the lack of light by claiming it had recently been redecorated with darker colours and furnishings, contributing towards a lack of daylight. To me, this is no justification as residents should be able to decorate their environment as they see fit and not have to worry about poor day lighting. The work units have been designed the other way around.
Offices often suffer from overheating during the summer due to internal gains from machinery and office equipment. To combat this, the work units face north meaning they benefit little from solar gain. A north facing orientation also allows for greater overall level of day lighting during the day, helped by roof lights to cut down on the amount of artificial lighting needed. As it was not possible to see the units on the tour it is difficult to say how well this works and during the winter I can imagine artificial lighting to be essential. Energy Production & HVAC Systems
For BedZED to be carbon neutral it not only has to reduce the amount of energy it uses but needs to generate it own energy, to match its consumption, through renewable sources. To do this BedZED has chosen to use a combined heat and power (CHP) plant. It was felt that in the current market a small-scale CHP plant was the most viable option for generating enough power to supply the development, PVs and wind driven turbines were considered but proved uneconomical although PVs are used to power the electric cars available on site. In conventional energy generation heat is given off and lost to the atmosphere.
In a CHP plant this heat energy is captured and used to heat water which is then distributed around the site via a district heating system of super-insulated pipes. The fuel for the CHP plant comes from off-cuts from tree surgery waste that would otherwise go to landfill. These wood pellets are a carbon neutral fuel as they give off as much CO2 when burned as hey absorbed whilst growing. In theory the system works well and for this scale of development I think it was the right solution to generate enough power. However, the CHP plant has been be set by problems.
Due to the equipment not being readily available on the market, the system used was a prototype. When problems started occurring due to tar forming on the equipment, maintenance costs soared and eventually the firm supplying maintenance went bankrupt and the plant had to be shut down. Since 2005 BedZED has ceased to be a carbon neutral development whilst new plant is obtained. The problem is that until there is more of a market for the equipment costs will continue to be high and sourcing suitable plant will become difficult. The other problem is that if they do become more popular, it will be difficult to satisfy the demand for fuel.
BedZED are lucky that they are one of few using this technology therefore they can find the wood pellets easily. The CHP plant uses 1100 tonnes of fuel per year which would be difficult to satisfy if more schemes used this technology. However, it could be used in the short-term whilst the prices of solar technologies fall. The compound for the CHP plant I found this part of the site to be a little bit unsightly and I think more could’ve been done to hide the plant away and maintain the pleasant streetscape environment. It is unfortunate that it has to be placed next to the playing field and the comunity centre (ZEDBar)
The other technology used in the development that is not usually present in a standard housing development is the ventilation system. To keep the fabric heat losses to a minimum, the units were constructed to be as airtight as possible meaning ventilating the units by traditional means became a problem. The solution was to use a wind driven system that used specially designed wind cowls on the roof. These cowls are designed to spin and pick up wind that is flowing around the building. This incoming air then forces the stale air in the building out through a separate section of ducting.
The cowls are also fitted with a heat exchanger so that in winter up to 70% of the heat from the outgoing stale air can be transferred to the cooler incoming air. This has the effect of reducing the need for heating and therefore reducing energy consumption. The system also acts as an extract for the bathrooms and kitchen so stale air and odours do not linger in the units. It has been claimed that this system is better at reducing allergens coming into the building such as pollen and traffic pollution so the internal environments are cleaner and healthier.
Again, in theory the system should work well but in practice there are a few problems. On days with very little wind the system struggles to cope, this is especially prevalent in the summer when stale air accumulates quicker. Residents had also complained that in the summer the flats get uncomfortably hot during the day. This is partly due to the solar gain problems discussed earlier but also due to the fact that the air coming into the ventilation system is also warmed by the heat exchanger.
Although this heat is a problem for any type of ventilation system during hot weather, many residents felt as though conventional methods of ventilating the room may have worked better. Also, new technology is available now that can bypass the heat exchanger at certain temperatures. Wind Cowls and Roof Gardens I feel that the wind cowls are a little bit out of character with the rest of the development and could be integrated more subtly. The bright colours make them stand out too much, and whilst I appreciate that the architects may have wanted to make a feature of them, I feel as though they detract from the rest of the development.
Through the Q&A session with one of the architects at the end of the tour it is my understanding that the cowls were one of the sticking points in receiving planning permission and I think things could’ve been made easier by toning down the colours used. Conclusion It is clear from the statistics and figures on energy usage at BedZED that the development has been a tremendous success, despite the problems the development has had with its CHP plant. In my opinion, the project shows developers that this type of scheme can be profitable, successful but at the same time environmentally aware.
Over the coming years this is going to become very important if the Government is serious about its commitments to reducing CO2 emissions in the UK, and BedZED gives other developers an indication on how they may reduce their own CO2 emissions and eventually meet the Government’s aim of all new housing being carbon neutral by 2016. However, I think BedZED can only used as a guide and the exact same formula cannot just be copied and rolled out across the entire country.
BedZED was able to capitalise on certain benefits as it was the only development of its type at the time. Issues such as the supply of its CHP fuel from local tree cuttings are not sustainable in the long-term and figures suggest that London would only be able to support a maximum of 50 of this type of development from its annual tree-cutting supplies. This along with being other factors such as being able to source reclaimed steel and materials will not be possible in a mass market situation.
What developers need to take from BedZED is that sustainability issues need to be taken into account from the very start of the design process and that they need to employ professionals who have a strong understanding of the principles of sustainable design. For me, what BedZED has been most successful at is enabling people to live sustainably, within their share of the earth’s renewable sources, without sacrificing a modern, urban and mobile lifestyle. This has been done through a range of technical but also some very simple techniques.
It is easy for designers to design facilities and services that make it easy to reduce waste and landfill, recycle waste and reduce car use. These often come with very little cost to developers and can be achieved with simple ideas such as designing in community spaces where local produce can where local produce can be sold or by simply specifying more efficient household appliances within units. However, the simplest thing that developers can do is to make the fabric of the buildings perform to a high standard and this is what I think has been most successful at BedZED.
It is such a simple thing with good designers to detail an airtight fabric and, despite costing slightly more, specify high levels of insulation and materials with a high thermal mass. BedZED has shown that by doing these simple things energy consumption can be reduced dramatically, and whilst developers are often reluctant to do this due to the cost implications, BedZED has gone some way towards showing developers that these type of features, with the reduced energy bills that they bring, can actually add value to the property in the long run.
Tables demonstrating added value at BedZED Carbon neutral buildings do cost more to build. Facilitating carbon neutral lifestyles requires investment in infrastructure and on-going initiatives. If carbon neutral developments are rolled out on a significant scale, the build costs will be greatly reduced through bulk buying of specialist components and build up of onsite skills. In housing, the market for sustainable buildings has been clearly demonstrated at BedZED. FPD Savaills have showed that buyers are willing to pay up to 20% premium for innovative design and green features. Bibliography
Reports BioRegional Development Group, BedZED Total Energy Strategy inc. Green Transport Plan, November 1999 Dunster, B. , BedZED General Information Report, Housing Efficiency Best Practice Programme Lazarus, N. , Beddington Zero (Fossil) Energy Development: Toolkit for Carbon Neutral Developments Part I, Department for Trade & Industry publication Lazarus, N. , Construction Materials Report: Toolkit for Carbon Neutral Developments – Part II, Department for Trade & Industry publication Websites www. arup. com www. bioregional. com www. exusenergy. com www. peabody. org. uk www. zedfactory. com
