Managing Uncertainty in Environmental and Cost Life Cycle Studies of Building Design

Abstract: The building and construction sector accounted for 39% of energy and process-related carbon dioxide emissions in 2018 and global emissions from buildings increased by 2% for the second consecutive year. It is therefore important to find building design solutions that minimise the climate impact of buildings. At the same time, the production of residential houses and commercial buildings must be cost-efficient in order to provide housing and workplaces at reasonable prices.Several studies have recently pointed out that although the energy used for operating the buildings has a large environmental impact, the manufacturing, replacement and waste management of building material and products can represent an equally large share of the total environmental impact of buildings. It is thus important to consider the complete life cycle when evaluating the design alternatives of buildings. There is a risk of missing important environmental and economic aspects if only a portion of the life cycle is addressed during the evaluation. This will lead to faulty conclusions and sub-optimal solutions of the building design.Available and mature life cycle tools for evaluating buildings and other products are life cycle assessment (LCA) and life cycle cost analysis (LCCA). Even for simple products, the manufacturing chain from raw material acquisition, production and use through to waste management is complex and intertwined with material flows of products outside the studied object. This means that even if the methods are mature there are many assumptions and choices to be made when evaluating the effect on for example the environment and cost of a building during its life cycle. Conducting an LCA and LCCA for products and buildings is therefore time- and resource-demanding even for products with set production lines. It is easier to make changes in the early design stages when there are fewer decisions that have been set, and the design freedom is larger. However, this also means that there is less data to base the life cycle studies on. As there are larger degrees of freedom, there are more available options to consider. When evaluating a design alternative based on the design process information, such as which products to use, manufactures, installations, user patterns and assembly methods might not have been decided yet. Conducting LCAs and LCCAs under these circumstances naturally involves greater uncertainties in the results than for products with fixed systems.The work described in this thesis consists of a number of studies in which methods and procedures have been developed to facilitate evaluating building design alternatives using life cycle tools. The Effect and Consequences Evaluation (ECE) method describes how to establish the technical system boundaries in a consistent way. Its focus is on managing secondary effects that arise in different parts of the building as an effect of the design alternative. The secondary effects were shown to have significant impact on the results in a case study. The Decision Choices Procedure (DCP) was also developed within the project. It provides a means to manage choices and their options in a structured way when life cycle tools are used as design decision support. Another studied issue was how to obtain reliable data on the materials and products used in buildings. A process enabling contractors to report data on site in a form that facilitates life cycle studies was explored for an office building. To demonstrate how to utilise the developed methods and procedures several case studies were conducted. Four case studies were made to evaluate each issue separately and an additional one to demonstrate how to combine the methods when conducting an LCA and LCCA, concerning how to optimise insulation thickness in a building. The emphasis of this study has been more on accuracy of the results rather than simplification in order to mitigate erroneous conclusions regarding environmentally friendly, cost-effective alternatives for the building design. However, a simplification of life cycle studies does come from providing a structured and more consistent process of managing technical system boundaries and uncertainties in design optimisation. Adopting the approach described in this study will likely provide design conclusions with higher quality as well as save time and effort when conducting the study.

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