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Clarks Houndwood Site, Street: Housing Design Brief
Visits to Exemplar Schemes, 26th April/5th May2004
Summary of Findings
Avonmouth Combined Heat and Power Plant (26th April 2004)
Power point presentation here
CHP Background and Technology
Avonmouth CHP plant is run by Compact Power and has been developed since the company was formed in 1992. It is the first commercial plant of its kind. Compact Power actually provide the power for CHP and not the CHP itself.
The plant produces renewable energy through the processing of various types of waste including pharmaceutical and clinical waste, shredded tyres, municipal solid waste and sewage sludge. Compact Power are paid for the safe disposal of these waste products and the resultant heat and/or power created are a beneficial by-product that can then be used to heat and power homes and business. This type of process should be used as a last option process once all materials possible have been recycled or composed.
The aim of the visit was to understand the technology behind CHP and to gain increased insight into whether CHP would be feasible on the Houndwood site. The process of waste disposal and energy production goes as follows:
1) Feed preparation: Waste is fed into two compacter shredder machines where it is chopped up and formed into sausage shaped lengths of waste which form air locks within two pipes.
2) Pyrolysis: Waste is heated without oxygen to 800(C. Methanes and other simple gases are driven off leaving a carbon char of solid, inert materials.
3) Gasification: Carbon residues are percolated by steam to produce hydrogen and carbon monoxide. The remaining inert solids can then be safely disposed of via landfill. The gas is spun through a cyclon at this point to remove any particulates.
4) Oxidation: Gases are then held at 1250(C for 12 seconds to remove any remaining particulates and organic pollutants. This is a process of 'oxidisation' and is the opposite of internal combustion. The cylinder is held at a very high temperature and oxygen is then sucked in to act as a bellow.
5) Energy recovery: The addition of oxygen results in the release of large amounts of energy in the form of heat. The hot gases pass through a steam boiler and the steam created is then used for power generation or CHP applications.
This process is considered particularly successful as it does not generate dioxides, which enable it to process ridged plastics. It also utilises a catalytic converter to ensure extremely low output of Nox (noxious gases). The minimal amount of solid waste left over after the process is completed is not harmful. As a result the environment agency consider the process to be the cleanest combustion process anywhere in the world.
Is CHP suitable for the Houndwood Site?
If a CHP development were to be suitable on the site it would need to be viable. The bigger the requirement for energy and the bigger the plant, the more viable this kind of process would be.
Roger Green of Compact Power stated that we would need to consider the summertime heat load for the housing development (which is the lowest level of power that will ever be required) and base the size of a CHP on this. In reality he considered that a plant for a housing development of 400 units would not be viable. However if other uses for the power can also be found, then the reality becomes more feasible, e.g. the distribution centre and/or the swimming pool at Milfield. In respect of the proposed CHP plant at Morlands, he confirmed that it would be possible to pipe heat a matter of miles but of course this has cost implications, which will again affect the viability of any plant. Juggling heat stores so minimal energy is being used when demand is low at night is another way of making smaller plants economically viable.
In terms of the size of plant, Mr Green considered that an NT4 would be the smallest plant that could be used for the Houndwood site. This is twice as powerful as the Avonmouth plant but not twice the size. The NT4 would require a building 14m high and would need 15,000 tonnes of fuel per year and is good at producing heat but weaker a producing electricity. In terms of fuel, the plant could utilise waste and or Biomass fuel. It was noted that every project based solely on biomass (except for straw burning in Ely) had failed. Waste is good because the plant will get paid to process it, then benefit from the energy produced. Getting a fuel supply is often the hardest part of setting up a small CHP development. It should be remembered that only 7% of all waste is municipal and 97% is industrial, commercial and agricultural.
There are other examples of CHP on a similar scale. Compact Power are setting up a private plant in Broham, near Melksham. This two megawatt plant will serve a housing development of a similar scale to that proposed on the Houndwood site, plus a furniture factory an abattoir and some offices. A range of fuels have been identified for this plant including sawdust from the furniture factory, clinical waste from a nearby hospital, waste from the abattoir, waste from a nearby rubber factory and the municipal waste from the housing development.
Key points to Note:
* Gasification is a last option once all options for recycling and composting have been exhausted.
* A CHP for 400 units may not be viable - the more uses the better, link in with existing housing, distribution centre etc.
* Heat can be piped, may be possible and preferable to share CHP with Morlands.
* Of site provision likely to be preferable as the plant will need to be of a considerable size.
* Finding a supply of fuel is likely to be the hardest part of the process - a mixture of waste and biomass is likely to be the most viable option.
* Any CHP plant that relies on biomass or recycled waste products is unlikely to be compatible with the development of the Houndwood site at Street for housing.
Stroud Co-Housing Development (26th April 2004)
Co-housing in Stroud web site - out of date but with plans and details
Development site and principles
The Stroud Co-Housing development is a site of approximately 1 hectare set on a relatively steep hillside close to Stroud Town Centre. The development is currently 80% completed and when finished it will comprise of 35 units (15 flats and 20 houses) plus a common house in the centre of the site for use by all residents.
Co-Housing is a term coined by a booked called "Co-Housing: a Contemporary Approach to Housing Ourselves" by American authors McCamant and Durrett. It is based on a form of cooperative housing with is popular in Denmark and increasingly in the US. It is thought that as many as 5% of the Danish population live in co-housing settlements.
Co-Housing is based on a few key principles. In the case of Stroud these include the following:
1) The whole site is pedestrianised. In order to make this possible an area for parking is provided at the top of the site and has space for a maximum of 25 cars. A car sharing system will be used when the site is finished.
2) A large common house is provided with a dining room and kitchen, plus a playroom and library. Each person also has self-contained accommodation with full services.
3) The development is owned by a freehold company, the same as a block of flats and this company, made up of the residents has control of the site and responsibility for its maintenance.
4) Entrance into the Co-Housing scheme is self-selective - the only criteria are: a) Residents must agree to the principles of Co-Housing;
b) Residents must be able to afford to buy in.
5) Residents are involved in design of the site from a very early stage and have had the opportunity to design their own interior (80% of residents brought into the scheme before planning permission was even granted).
Construction
Sustainable living is part of the ethos of Co-Housing as living in a more communal manner can lead to reduced levels of consumption through the shared ownership and use of resources. Members and architects of the Stroud Co-Housing development were keen to include sustainable development features from the outset. This has been achieved to varying degrees during the construction.
Building features:
* Timber frame construction with recycled newspaper insulation inside the walls; however walls are not as thick as originally intended due to financial constraints;
* Rockwool insulation for sound proofing between floors and triple glazed windows all of which help to keep heating bills low at approximately £80 per year.
* Ultra low flush toilets minimise water wastage but no grey water recycling could be provided due to financial constraints.
* The development is the largest solar energy development in the country with photovoltaic panels on all of the houses. These cells create instantaneous energy which is either used immediately in the property or is sold back to the national grid, giving the residents positive credit for use of mains power when the PV cells are not producing energy. In general units import more power then they export and the price of buying and selling depends on the individual electricity company. In the case of this development a standard fee for buying electricity at approximately 6p per unit and electricity is sold back to the grid for a profit for 11p per unit.
* Although there are no Solar Thermal Panels in use on the site currently, special boilers are provided to enable their addition in the future.
* Buildings are mainly three stories and in close proximity - the layout works due to car free space and steep slope of site altering levels.
* Around the buildings a Sustainable Urban Drainage System has been implemented to replicate the drainage patterns of open land and avoid flash flooding run off which can be caused by impermeable development.
* There is no private open space attached to properties; all open space is communal.
Development Successes
In terms of marketability the scheme has proved extremely successful with all units sold and keen interest from many more people. In Denmark and the USA the market value of Co-Housing has been higher then average due to high demand and a few early sales of Stroud properties has also shown an impressive rise in value.
In terms of sustainability the solar panels are a real success and well integrated into the site to offer minimal visual impact. Elsewhere sustainable features are more limited and the lack of recycling features and general refuse storage is a clear shortcoming. In operation the site has been important in the development of Stroud Car Share scheme and the lack of cars on the development is a positive sustainable contribution.
Key Points to Note:
* High density appearance successful due to steep gradient of site;
* Scheme has proved successful and highly marketable;
* Attractive, usable and well designed interiors;
* Good consideration of sustainable principles but limited implementation in some respects;
* Excellent use of photovoltaic cells for electricity generation and successful car sharing scheme.
* Strong emphasis on community management and participation.
Greenfields Housing Development, Maidenhead (5th May 2004)
Site Context
The Greenfields sustainable housing development is part of a larger housing estate of 250 maisonettes, which was built in the 1950s. The sustainable housing site was previously occupied by an area of garaging that had become derelict and underused. The area was developed by Maidenhead and District Housing Association in 2001/2 with 27 properties; 19 one bedroom flats and 8 two/three bedroom houses. All of the properties are social rented units let by M&DHA.
The site is sustainably located 3 minutes walk from a mainline train station and within walking distance of Maidenhead Town Centre.
The aim of the development was to provide a good quality development utilising environmentally sustainable practices and materials as follows:
* Solar gain minimises heating and lighting bills through the utilisation of the south east facing site with large windows (and conservatories for the houses).
* Passive ventilation is provided by a central ventilation and servicing tower in each block and automatically by the electronic opening of ventilation outlets when the temperature exceeds 18(c. A rain sensor will automatically close these outlets if it starts to rain.
* Cellulose-recycled newsprint is used as insulation to retain as much heat as possible within the buildings reducing the energy requirement for heating.
* Sun pipes pipe down and amplify natural daylight to provide light for interior corridors.
* Roofs are planted with Alpine Sedum, which acts to fix some pollutants from the atmosphere and absorb rain avoiding flash urban flooding. The walls are faced with untreated Western Red Cedar, which should last for 60 years if maintained.
* Rainwater is harvested and stored in underground storage tanks and mixed with used bath and sink water then disinfected and used to flush toilets, minimising fresh water use. This has proved more successful in houses where the pumps could be stored internally then in the flats where pumps are stored externally.
* Photovoltaic cells are featured on each property at a cost of £10,000 per property (funded by the DTI) and were retrospectively fitted. The power from this is collected in one box and shared between the developments as a whole.
Key Points to Note:
* Small size of development - The project manager admitted that economies of scale would have made the development more profitable if unit numbers were increased.
* Solar panels were highly visible and seemed outdated compared to those at Stroud Co-Housing.
* Buildings attractive from the front with some nice architectural features such as the simple design and two storey conservatories. Design was let down by deep (heavy-looking) roof structures and unattractive porches).
* An especially dark area was produced at the rear of the buildings where most sunlight was blocked out by the considerable building height.
* Good use of sustainable features including PV energy generation, grey water recycling and use of materials.
Beddington Zero Energy Development (Bedzed) (5th May 2004)
Article and pictures here.
Background and Key Features
The Bedzed development comprise 82 residential unit, 14 live/ work units, employment space, community facilities a green water treatment plant and an on-site 130 kW CHP plant. The development was largely completed two years ago and was a partnership between Bio Regional Development Group, Bill Dunster Architects and The Peabody Trust who were site developer and owner.
The 82 homes are divided three ways by tenure with 1 third social rented, 1 third shared ownership key worker housing and 1 third private market housing. The live/work units were originally designed to be purely work units but were converted to live/work when marketing highlighted a lack of demand. Planning permission is currently being secured to change the use of the live/work units officially to live units with positive encouragement to work. This is because the business rates payable on live/work units was proving a disincentive to their occupation.
The community space comprises a social centre, sports pitch and clubhouse. At the time of our visit the sports pitch was out of use as it had been dug up to lay gas mains.
The development is designed as a series of parallel terraces. Key design features are:
* East-West alignment;
* Houses face south to maximise solar gain;
* Work spaces face north, in the shade zone - now to become housing "with a positive encouragement to work";
* Extensive use of solar panels (777 m2 in all) to produce the energy to run 40 electric vehicles (currently only one electric van and two mopeds);
* All buildings operate on basis of super insulation, thermal mass and solar gain;
* Temperatures within units are designed to self-regulate at around 17oC;
* All buildings have cowls at roof level, providing ventilation without using energy and with minimal heat loss;
* Development generates as much energy on site as is needed to operate year-round (this has not yet occurred due to problems with the CHP and hence a back up mains gas supply has recently been added)
* Whole development is carbon neutral (will be when the CHP is running properly!);
* All construction materials possible are sourced locally (over 50% of materials from within a 35 mile boundary) e.g. wood chip fuel for CHP comes from managed wood in nearby Croydon;
* Materials have been reclaimed or recycled wherever possible, e.g. steel girders reclaimed from Brighton Train Station.
* Porous paving and sedum roofs soak up rain water and prevent rapid run off leading to urban flooding.
Bedzed has been built without grants or subsidy, except the solar panels (funding from EU 5th Array and DTI Field Trials). The development has an estimated 10 year payback time for savings in energy costs in relation to increased construction costs. The Local Authority (Owner) sold land at a marginally reduced cost to the developer based on forecast of energy savings.
Green life styles initiatives in use on the site include:
* Composting;
* Local food links;
* Source segregation recycling (aimed to achieve 60% recycling);
* Car club: combined LPG/petrol vehicles; (links into capital wide scheme);
* Living Machine carries out grey and black water recycling on-site ; tops up SUDS rainwater collection system which is then used to flush toilets;
* All kitchens have visible meters for electricity and hot water to act as an incentive to reduce consumption.
Key Points to Note
* Houses attractively designed but seemed small inside (6.3m column grid);
* High densities achieved 100 units per ha on some areas of the site, 50 units per ha on the site as a whole including sports pitch.
* Terraces are close/compact; approx 6.3m between each; works well;
* Gardens to maisonettes located on roofs of separately owned properties on other side of road - potential maintenance disputes in long term?
* Live/work units poor quality interior light and suffer from lower demand.
* Extensive and rigorous use of sustainable principles is to be admired, including green life styles;
* CHP has been problematic and is still not working to capacity, can only utilise a particular prepared fuel.
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