Carbon Negative Cement

 Cement produces around 5-6% of carbon dioxide emissions because the manufacturing process depends on burning vast amounts of fossil fuels to heat kilns to more than 1,450C. The production of cement also relies on the decomposition of limestone, a chemical change which frees carbon dioxide from the rock as it converts to calcium oxide. The 2 billion tonnes of cement used globally each year creates more emissions of carbon dioxide than the aviation industry. Some projections suggests that there will be a 50% increase in the amount of cement consumed by 2020 further increasing emission of carbon dioxide.

 

An Imperial College London spinoff, Novacem, have developed a new type of cement based on magnesium oxide – the chemical most familiar to consumers as talcum powder. As carbon dioxide isn’t present in magnesium oxide no carbon dioxide is released. An additional carbon saving is achieved because Novacem only needs to heat the materials to about 800 degrees Celsius instead of 1450 degrees Celsius. Novacem claim that biomass could be used as a fuel to power the process instead of traditional fossil fuels. The process not only requires much less heating, it also absorbs large amounts of CO2 as it hardens, making it carbon negative.

Apparently, the processing of the ingredients for traditional cement releases 0.8 tonnes of carbon dioxide per tonne of cement. When it is eventually mixed with water for hardening each tonne of cement can absorb up to 0.4 tonnes of CO2, but that still leaves an overall carbon footprint of 0.4 tonnes of carbon dioxide per tonne of cement. The production of Novacem's cement creates a total of 0.5 tonnes of carbon dioxide per tonne of cement. But the Novacem cement formula absorbs far more carbon dioxide as it hardens - about 1.1 tonnes. So the overall carbon footprint is negative - i.e. the cement removes 0.6 tonnes of CO2 per tonne used. It is claimed that magnesium silicates are abundant worldwide, with 10,000 billion tonnes available.

Novacem are reported to be building a small-scale test plant to see if the concrete works and it hopes to have a larger-scale plant operating by 2011 and full-scale production underway by 2013.

Novacem was a finalist in the Carbon Trust’s Innovation Awards 2009.

See www.novacem.com and http://www2.technologyreview.com/article/418542/tr10-green-concrete/ 

BedZED - Sustainable Homes

The Beddington Zero Energy Development, or BedZED for short, is the UK’s largest carbon neutral development. It provides 82 residential homes with a mixture of tenures and sizes. The project also includes buildings for commercial use, an exhibition centre, a children's nursery and a show flat so that visitors may see what it is like to live at BedZED.

Buildings are constructed from thermally massive materials that store heat during warm conditions and release heat at cooler times. In addition, all buildings are enclosed in a 300mm insulation jacket.
BedZED houses are arranged in south facing terraces to maximise heat gain from the sun, known as passive solar gain. Each terrace is backed by north facing offices, where minimal solar gain reduces the tendency to overheat and the need for energy hungry air conditioning.

Where possible, BedZED was built from natural, recycled or reclaimed materials. All the wood used has been approved by the Forest Stewardship Council or comparable organisations.
BedZED homes and offices are fitted with low energy lighting and energy efficient appliances to reduce electricity requirements. Visible meters are mounted in homes and offices so the occupiers can keep tabs on their electricity consumption.

BedZED receives power from a small-scale combined heat and power plant (CHP). In conventional energy generation, the heat that is produced as a by-product of generating electricity is lost. With CHP technology, this heat can be harnessed and put to use. At BedZED, the heat from the CHP provides hot water, which is distributed around the site via a district heating system of super-insulated pipes. The CHP plant is powered by off-cuts from tree surgery waste that would otherwise go to landfill. Should residents or workers require a heating boost, each home or office has a domestic hot water tank that doubles as a radiator.

Making the roof areas green with sedum plants helps increase the site’s ecological value and its carbon absorbing ability, as well as giving the occupants private gardens. Next to the green roofs are the photovoltaic panels to generate electricity.

Transport energy accounts for a large proportion of the energy consumption of any development. A green transport plan promotes walking, cycling and use of public transport. A car pool for residents has been established. BedZED has good public transport links, including two railway stations, two bus routes and a tramlink. On-site charging points for electric cars and a free public electric vehicle charging point is already available in Sutton town centre. BedZED's 10-year target is to produce enough electricity from photovoltaic panels (which convert sunlight into energy) to power 40 electric vehicles. It is hoped that a mixture of private cars and vehicles available through the car club will minimise fossil fuel use as the community settles. For owners of electric vehicles energy and parking will be free of charge.

To find out more search Google for “BedZed” or visit http://www.zedfactory.com/projects_mixeduse_bedzed.html

Green Roofs

Green roofs are vegetated layers that sit on top of the conventional roof surfaces of a building. Usually a distinction is made between extensive and intensive. These terms refer to the degree of maintenance the roofs require.

Intensive green roofs are composed of relatively deep substrates and can therefore support a wide range of plant types: trees and shrubs as well as perennials, grasses and annuals. As a result they are generally heavy and require specific support from the building.  Intensive green roofs (what most people think of as roof gardens) have in the past been rather traditional in their design, simply reproducing what tends to be found on the ground, with lawns, flower beds and water features.

However, more contemporary intensive green roofs can be visually and environmentally exciting, integrating water management systems that process waste water from the building as well as storing surplus rainwater in constructed wetlands. Because of their larger plant material and horticultural diversity, intensive green roofs can require substantial input of maintenance resources – the usual pruning, clipping, watering and weeding as well as irrigation and fertilisation.

Conversely, the green roofs that have received the greatest interest recently are extensive green roofs. They are composed of lightweight layers of free-draining material that support low-growing, tough drought-resistant vegetation. Generally the depth of growing medium is from a few centimetres up to a maximum of around 10cm. These roof types have great potential for wide application because, being lightweight, they require little or no additional structural support from the building, and because the vegetation is adapted to the extreme roof top environment (high winds, hot sun, drought, and winter cold) they require little in the way of maintenance and resource inputs. Extensive green roofs can be designed into new buildings, or retro-fitted onto existing buildings. 

Because of their very wide range of environmental and economic benefits (in particular their insulation and cooling properties, ability to significantly reduce rainwater runoff from roofs, and their value in promoting biodiversity and habitat in built-up areas), green roofs have come to be important elements of sustainable and green construction in many countries. Moreover, because they can be highly visible, they also clearly outwardly signal an intent for sustainable building and can give a very positive and distinctive image to a building or development.

Some benefits include:

Research from around the world indicates that Green Roofs reduce annual run-off from roofs by at least 50%, and more usually by 60-70% - contributing to urban drainage and flood alleviation schemes. Moreover, the rate of release following heavy rainfall is slowed, reducing the problems associated with storm surges. With an increasing need for developments to have limited water run off, the Environment Agency now highlight the use of green roofing and the Agency have been supportive of supplementary planning documents which refer to green roofs.
Green roofs (and other practices such as natural ventilation) reduce the need for air conditioning in the summer and as a result reduce CO2 emissions. Poorly protected and insulated roofs can lead to substantial overheating of spaces beneath them. This can lead to the need for increased air-conditioning. A green roof not only acts as an insulation barrier, but the combination of plant processes and soil processes reduces the amount of solar energy absorbed by the roof membrane, thus leading to cooler temperatures beneath the surface. Research by Nottingham Trent University has shown that at an average temperature of 18.4°C, the roof temperature of a normal roof can reach 32°C whereas the temperature beneath a green roof is only 17.1°C. A study conducted in Chicago, USA, recently estimated that building energy savings to the value of $100,000,000 could be saved each year if all roofs were greened, as the need for air conditioning would be reduced.

Green roofs can help to reduce heat loss from buildings during the winter when root activity of plants, air layers and the totality of the specific system create heat and thereby provide an insulation membrane. However the efficiency of green roofs as thermal barriers is dependent on the amount of water held within the system. Water retention can increase the amount of heat lost through the system and therefore any efficiency gains are dependent on daily conditions. It is therefore difficult to provide accurate figures on the net effect of green roofs on energy efficiency during the winter months. The study at Trent University on the temperatures under membranes of standard roofs and those under green roofs also showed that green roofs appear to have a positive effect in winter. With an average temperature of  0°C the temperature of a standard roof is 0.2°C whereas the temperature under a green roof 4.7°C

New developments lead to a loss of habitats – green roofs can contribute to biodiversity and address local biodiversity action plans. In particular they have been shown to favour many rare invertebrates found on brownfield sites, as well as ground-nesting birds such as skylarks.
Green roofs contribute to a greener urban environment and quality of life for communities in high density developments.

A roof life is at least doubled with the addition of a green roof, thereby reducing resource use in roof replacement and repair.

For more details (including several case studies from Sheffield) please check out the following web sites:

www.livingroofs.org
www.groundwork-sheffield.org.uk