The assessment can represent many different lifecycle stages of the goods or services. The two main ones are cradle to grave”, where goods are modelled from raw material extraction through manufacture, delivery, use and disposal, and “cradle to gate”, where goods are modelled from raw material extraction through to manufacture and packaging ready to be shipped to a wholesaler, retailer or end-customer. A third lifecycle is gate to gate which is used for modelling processes just within a single manufacturing organisation, say taking a set of off-the-shelf products and assembling them into a new product.
The impacts covered in LCA are very broad. They go far beyond carbon dioxide emissions or other greenhouse gases. For example, the standard impact categories include non-renewable resource use, acidification and ecotoxicity - see Figure1. Greenhouse gases are more correctly covered under global warming potential, where the global warming effects of different gases are appropriately factored and combined into a single figure expressed as Carbon Dioxide equivalent (CO2e).
The range of goods and services that contribute to the manufacture or use of a single product can be unexpectedly complicated, even circular.
The complexity of life cycle inventories, where the list of constituents for a given product are stored, can be demonstrated by the case of the mineral wool that might be used as an insulation material for ductwork and pipework. The inventory for this product contains many different inputs of products, recycled materials and natural resources including basalt, limestone, coke, electricity, water, rail transport, and many different outputs
of wastes including waste heat, particulates, and municipal solid waste, and different emissions to air, water and soil including carbon dioxide. All of these inputs themselves have inventories and their inputs will also have inventories, and so on. The ultimate aim is to compile the full list of outputs and emissions in sufficient detail for the analysis.
In fact, loops can often be found within the life cycle inventory analysis, where the impacts of all resource, material and process flows that cross the system boundary are analysed. For example, a product that has steel as a raw material means that coal is included as this is one of the inputs for manufacturing steel. But coal is mined and processed using equipment that includes steel.
The reliance on inventory data and the complexity of its analysis means that software is usually needed to carry out LCA. BSRIA was involved in the European CILECCTA project which developed a software package that takes account of both LCA and life cycle costing (LCC). This helps decisions to be made based on both environmental and economic performance of alternative construction materials, products, or building designs over their respective lifetimes.
The description of the mineral wool inventory, above, raises another important issue – that of the functional unit. As well as its ability to identify environmental hot-spots, LCA is also a comparison tool where one technical design can be compared with one or more alternatives to find out which is the best. To make the comparison fair, each solution has to be analysed on the basis of its performance. For example, two different insulation materials for pipework would be analysed on the basis of the U-value they provide. This would then need to be analysed to understand how much of the insulation would be needed in each case – for example, insulation for a 10m length of 50mm pipe might require x kg of mineral wool and y kg of expanded foam. The inventories stored in the database would both be compiled on the basis of 1kg of the insulation material and the various inputs and outputs would be scaled accordingly.