Environmental Impacts of Multi-Storey Buildings Using Different ...

- 112 -Table 9.1 (middle column) shows GWP coefficients (Kg CO 2 equivalent per Kg material) forall the materials in the different buildings used by Scion to input to the LCA modellingprocess. The right-hand column of this table shows the GWP for materials where carbonstorage in the timber is taken into account (see explanation below), which has a marked effecton the coefficients used for all timber products. The timber datasets are based on NewZealand log production.The report “Life Cycle Assessment: Adopting and adapting overseas LCA data andmethodologies for building materials in New Zealand” (Nebel, 2009) notes the following:All timber datasets are based on log production specific for New Zealand. The dataset forsawn timber is fully based on data that has been collected in a number of projects at Scion.Existing models from the GaBi database have been modified for particle board and plywoodas follows. The electricity mix has been replaced with the NZ grid mix and thermal energyfrom natural gas has been replaced with the respective Australian dataset. It should be notedthat most of the thermal energy in all datasets is generated from residual wood which isreflected in the renewable energy consumption.Primary energy and carbon stored in the timber have not been included in the datasetspresented, but need to taken into account when using the data, depending on the end of lifescenario. The carbon stored in the timber will be partially released in the case of landfillingand would be fully released in the case of thermal utilisation. In an LCA study the end of lifescenario needs to be defined and emissions of CO2 and/or CH4 as well as the potential longterm storage need to be taken into account. The stored carbon in wood products can becalculated as follows:Assumed 50% of wood mass is carbon.=> 1kg wood = 0.5 kg CarbonMolar mass carbon = 12 g/mol.Molar mass oxygen = 16 g/mol=> Molar Mass CO2 = 44 g/mol0.5 kg / 12 g/mol = 41.67 moles of carbon in 1 kg wood.41.67 moles x 44 g/mol = 1833.34 grams.=> 1 kg wood --> 1.83 kg of CO21.83 kg CO2 equivalents are sequestered per 1 kg of timber.Table 9.2Table 9.2Table 9.2 shows the GWP (in units of CO 2 equivalent) for the materialsused in the four buildings, obtained by multiplying the mass of different materials in Table6.1 by the coefficients for each material given in Table 9.1 (right hand column). Table9.3Table 9.3Table 9.3 shows the same data in the major groups of materials.Figure 9.1Figure 9.1Figure 9.1 shows the aggregated data from Table 9.3Table 9.3Table 9.3.It can be clearly seen that emissions from concrete production dominate the emissions fromthe Concrete building, emissions from steel production dominate the emissions from the Steelbuilding and emissions from aluminium play a significant part in the overall emissions of theConcrete, Steel and Timber buildings,. Whilst emissions from concrete are greatest for theConcrete building, they are notable in the other three buildings too.The carbon sink from wood and wood products is clearly apparent in the Timber andTimberPlus buildings (but is almost insignificant for the Concrete and Steel buildings whichhave few wood products). There are no net emissions from the timber materials in any of thebuildings. In the Timber and TimberPlus buildings, the carbon stored in the timber materialsgreatly exceeds the emissions associated with the production and manufacture of these timber