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Life-cycle assessment (LCA) is a technique that is used worldwide by clients and their design team to assess the impact of their projects on the environment. The main advantage of LCA is in supporting decision making with quantitative data. LCA inventories can be either fully developed or streamlined. Fully developed LCAs are time-consuming and costly to prepare. Streamlined LCAs can be used as an effective decision-making tool when considering environmental performance during the design process, but with a loss of inventory completeness. Acknowledging the advantages and disadvantages of both types of LCA, this paper proposes a hybrid LCA method that uses input-output data to fill in those gaps routinely left in conventional LCA inventories. The developed hybrid LCA method is demonstrated using a life-cycle energy study of eight different road designs, including vehicle manufacture, maintenance, replacement, and operation. It was found that the road construction process was initially the most important, but in the long run the manufacture, use, and maintenance of vehicles using the road (which are an inevitable consequence of road construction) became paramount. CE Database subject headings: Life cycles; Inventories; Hybrid methods; Road construction.

It is commonly assumed that solar hot water systems save energy and reduce greenhouse gas emissions. The net energy requirement of solar hot water systems has rarely been analysed, including their embodied energy. The extent to which solar hot water systems save energy compared to conventional systems in Melbourne, Australia, is shown through a comparative net energy analysis. It was shown that the embodied energy component of the net energy requirement of solar and conventional hot water systems was insignificant. The solar hot water systems provided a net energy saving compared to the conventional systems after 0.5-2 years, for electric- and gas-boosted systems respectively. Keywords: Net energy analysis; Solar hot water systems; Australia

Embodied energy (EE) analysis has become an important area of energy research, in attempting to trace the direct and indirect energy requirements of products and services throughout their supply chain. Typically, input–output (I–O) models have been used to calculate EE because they are considered to be comprehensive in their analysis. However, a major deficiency of using I–O models is that they have inherent errors and therefore cannot be reliably applied to individual cases. Thus, there is a need for the ability to disaggregate an I–O model into its most important 'energy paths', for the purpose of integrating case-specific data. This paper presents a new hybrid method for conducting EE analyses for individual buildings, which retains the completeness of the I–O model. This new method is demonstrated by application to an Australian residential building. Only 52% of the energy paths derived from the I–O model were substituted using case-specific data. This indicates that previous system boundaries for EE studies of individual residential buildings are less than optimal. It is envisaged that the proposed method will provide construction professionals with more accurate and reliable data for conducting life cycle energy analysis of buildings. Furthermore, by analysing the unmodified energy paths, further data collection can be prioritized effectively. [ABSTRACT FROM AUTHOR]

Life-cycle assessment (LCA) is a method for evaluating the environmental impacts of products holistically, including direct and supply chain impacts. The current LCA methodologies and the standards by the International Organization for Standardization (ISO) impose practical difficulties for drawing system boundaries; decisions on inclusion or exclusion of processes in an analysis (the cutoff criteria) are typically not made on a scientific basis. In particular, the requirement of deciding which processes could be excluded from the inventory can be rather difficult to meet because many excluded processes have often never been assessed by the practitioner, and therefore, their negligibility cannot be guaranteed. LCA studies utilizing economic input-output analysis have shown that, in practice, excluded processes can contribute as much to the product system under study as included processes; thus, the subjective determination of the system boundary may lead to invalid results. System boundaries in LCA are discussed herein with particular attention to outlining hybrid approaches as methods for resolving the boundary selection problem in LCA. An input-output model can be used to describe at least a part of a product system, and an ISO-compatible system boundary selection procedure can be designed by applying hybrid input-output-assisted approaches. There are several hybrid input-output analysis-based LCA methods that can be implemented in practice for broadening system boundary and also for ISO compliance.