Fri 1 Feb 2008
Energy within
We are all familiar with the phrase sustainable development but, says Roger Hunt, sustainable manufacturing is perhaps even more important.
Measures such as insulation and air leakage are high on the agenda when it comes to reducing CO2 emissions resulting from housing. Indeed, reducing 'energy in use', in other words the energy used for purposes such as heating and lighting homes, is currently the chief goal of both government and housebuilders. Far less thought is given to the 'embodied' energy and carbon which is locked up in the lifecycles of the materials, products and processes used in construction.There is no one universally accepted definition of embodied energy. Go to Wikipedia and it states that "Embodied Energy refers to the quantity of energy required to manufacture, and supply to the point of use, a product, material or service." Read on and it becomes apparent that defining and comparing energy use is far from straightforward since the various methodologies and data used, and the difficulties that result, can give a wide range of embodied energy values for any given material.
What is clear is that embodied energy is an important component of the lifecycle impact of a home. Renovation and maintenance also add to the embodied energy over a building's life; although renovating may, in terms of embodied energy, be preferable to demolishing a building and starting again. That said; this argument has to be carefully considered since the additional insulation and other energy saving measures of a new home may outweigh the loss of the embodied energy stored up in the old.
This balance is an important consideration as Nick Jones, associate director of Inbuilt, a new RES Group company providing technical and consulting expertise in the research, design and delivery of sustainable built environments, makes clear.
"Even in new housing the energy used in the running of the home - the 'operational energy' - far outweighs the energy used to make and transport the materials that it is built of - the 'embodied energy'. However, as we move towards the zero carbon home the balance of importance starts to shift, although operational energy will always be more important."
This will undoubtedly mean that embodied energy gains greater currency but care needs to be exercised to avoid taking inappropriate conclusions from simple calculations. John Connaughton, a partner of construction cost and project management consultants Davis Langdon Management Consulting, points out that "In addition to the carbon emissions associated with energy use, some materials production processes - for example in the process of converting limestone to cement - involve chemical reactions that release CO2."
This highlights the fact it is embodied carbon rather than embodied energy that we should be considering. Connaughton explains that, with embodied carbon in construction, the 'so-called' 80:20 rule tends to apply. "A large proportion of the embodied carbon in a building is represented by a relatively small number of materials, due to their relative mass and carbon intensity.
"People used to think that embodied carbon, or energy, was an insignificant part of the total carbon emitted during the life of a building. But this isn't so. For many building types, we estimate that embodied carbon is about the same as the cumulative carbon emissions after fifteen years of building use. For dwellings this figure could fall to about ten years, but is still highly significant."
Considering the cradle-to-grave requirements of a construction method is a key part of understanding the embodied energy or carbon that will be used. Issues such as whether raw materials were obtained from local UK sources, whether recycled products or by-products were used and the environmental impact generated in the production process are all things that must be assessed.
Examples of how industry is managing these issues abound. With bricks and blocks a major element in many new homes, Colin Marshall, Tarmac Topblock's technical manager, is quick to stress that more than 97 per cent of the raw materials used in the manufacturing process of its lightweight aircrete blocks are sourced in the UK.
"Similarly, through our network of UK plants, all of our products are manufactured in the UK and supplied nationally to optimise construction options and minimise travelling distances. Only by looking at the impact of travel miles from raw materials to manufacture and on-site delivery can the true sustainability qualities of a product be assessed."
The story is much the same at H+H UK. As the manufacture of Celcon products, it claims that only around one per cent of the raw materials used in production are imported from overseas while, throughout the manufacturing process, energy saving, waste minimalisation and recycling are high on the agenda and follow right through into the packaging and transport of the products. With this involving everything from ensuring the polythene used for shrink wrapping has been minimalised to considering whether pallets are required, the complexity of measuring the environmental impact of any product is illustrated.
Brick manufacturer Ibstock is highlighting its carbon reduction and sustainability programme in its advertising. It has spent £55 million on energy efficiency over the last five years which, it claims, has made its factories five per cent more energy efficient and has reduced its C02 output to 28Kgs for each square metre of brick it produces. All Ibstock factory sites operate to the environmental standard ISO 14001 and, on average, its bricks include 18 per cent recovered and recycled material. Of course, every brick type varies in the materials and energy used in its manufacture so each has to be assessed individually in terms of embodied energy. For example, Ibstock's new unfired Ecoterre Earth Bricks have a very low energy input - as recycled heat is used from brick kilns - along with very low manufacturing waste and very high recyclability.
Thanks to its recent acquisition of Baggeridge Brick, Wienerberger has the capacity to reduce the carbon footprint of its Terca range of clay facing bricks. The company now has 14 manufacturing sites around the UK, meaning Terca bricks never have to travel far to reach customers as there is almost always a local factory which can supply the order should this be a key requirement of the customer.
It is not just the structural elements of a home which specifiers need to consider. Lifecycle assessments made by appliance manufacturer Electrolux show that, although the main environmental impact occurs during the use of the product, with 75.8 per cent of the life cycle impact down to consumer use of electricity and water, production accounts for 24.2 per cent if materials supply, manufacturing and transportation are taken into account. However, when it comes to the disposal phase, at least 75 per cent of the material can be recycled while another five per cent could be incinerated for heat recovery.
For specifiers, the need to understand the embodied energy or carbon within products is going to become increasingly important but, as Nick Jones explains, forming a clear picture is far from easy. "For some materials - especially those that are not heavily processed - transport is very important. There can be a big difference in the embodied CO2 between slate from Wales and that from half way around the world. This is not to say that we need to know distances from individual manufacturing plants to individual sites but we do need to get more detailed data than we have at the moment."
One of the most intriguing areas, and one where Jones sees that there is currently most interest, is in the energy or CO2 balance of products designed to save energy. "Does it take more energy to make insulation than it saves in its life? Does a photovoltaic cell take more energy to make than it generates? Clearly it depends on the specific case but, in all practical cases, products such as better windows and high insulation are all hugely positive in their contribution and even things like photovoltaic panels can reach their 'energy payback' within two to three years."
For specifiers seeking to address the issue of embodied energy and carbon, the data currently available is fairly basic but work is being done. At Davis Langdon, Connaughton explains that the company has developed an embodied carbon model for construction which estimates embodied carbon and allows the company's clients to identify savings through material substitution and other mitigation measures.
The BRE's Green Guide to Specification has been another source of guidance but is currently out of print as it is being revised for republication as a new printed version plus a web tool this year. The guide presents information on the environmental impacts of building elements and specifications by ranking them on a simple rating scale of A (the best performance), B, or C. Building elements such as walls, floors and windows are considered and, for each specification, have been examined and their environmental scores calculated. Behind the ratings lie full lifecycle assessment studies using environmental profiling methodology. All of which will prove increasing vital to housebuilders as carbon becomes an ever more important 'currency'.
First published in Show House Magazine February 2008.
The greatest care has been taken to ensure accuracy but some information contained within this article may have changed since it was first published.
Posted by Roger Hunt
in Sustainability on Fri 1 Feb 2008
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