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

- 57 -For more information see:http://www.greenhouse.gov.au/yourhome/technical/fs52.htmEmbodied energy usually includes energy from fossil fuels as well as energy from renewablefuels, based on the assumption that there is a limit on how much renewable energy can beharnessed. The supply of electricity from hydro or wind is for example restricted and shouldtherefore also be used efficiently in order to replace as much fossil fuels as possible. In orderto address this issue only harnessed renewable energy should be considered, e.g. electricitygenerated from hydro energy, or thermal energy from combustion of biomass. In this case, forexample, the calorific value of biomass is included. Harnessed renewable energy is differentfrom energy that is captured within a product, but not used for energy production, for examplethe solar energy required for the photosynthesis to grow timber.In currently available commercial databases, including the widely used Ecoinvent database aswell as the GaBi database non-harnessed solar energy for photosynthesis is also included.This is done to keep the energy balance intact because a calorific value is assigned to alltimber products. This means there is an output of energy (calorific value of timber) andtherefore an equivalent input of energy, i.e. solar, is required. However, this can be seen asdistorting the overall use of renewable energy, because the solar energy for timber productioncan not be utilised in any other way. In the LCA data for building materials in New Zealand(Nebel et al. 2009) non-harnessed energy has therefore been excluded. However, as the NZdata does not cover all materials, it needs also to be consistent with available databases inorder to be able to mix NZ with data from those to provide a full range of materials and thisoption has therefore been provided too. Not all materials used in the four buildings analysedin this report are available in the new New Zealand dataset, e.g. NZ specific LVL andWestern Red Cedar data are not available and the data had therefore to be sourced from theGaBi database.For the purpose of this project a sensitivity analysis has been done that compares the analysisof renewable plus non-renewable as well as only non-renewable embodied energy. For thetimber products used from the GaBi database the solar contribution has been subtractedmanually for the key timber products for this comparison, using the calorific value of theproducts. The results are indicative – because wood fibres are for example used in fibrecement and it was not possible to determine the accurate amount of all timber used in allprocesses. The results are shown in Figure 6.2 and indicate that the conclusions drawn fromjust the non-renewable proportion of the embodied energy are valid for the total embodiedenergy use (the results for the non-renewable energy follow an almost identical trend to thenon-renewable & renewable energy combined). Therefore, the primary energy figures in thisreport will refer to the non-renewable proportion of primary energy only.