Quantifying the sustainability of the built environment : the development of a complete environmental life cycle assessment tool

[摘要] ENGLISH ABSTRACT: Sustainability is becoming an increasingly important aspect in all facets of engineering. It is in particular animportant consideration in the structural engineering industry, due to the prominence of the negative impactthis industry has on the environment, both on a national and international scale.The problem, however, is that sustainability is a mostly unknown and highly debated topic. It is not onlydifficult to quantify, but even difficult just to define. In the field of structural engineering it is an especiallydifficult task to consider sustainability. It is still a very new field of research and difficult to apply. It is thereforeimportant that continued research be done in order for there to be a better understanding of howsustainability should be considered and applied in the context of structures.In an attempt to assess the environmental impact of building structures, there are two basic approaches thatare followed. The first, the application-oriented method, is a simple, points-based system. The second, theanalysis-oriented method, makes use of detailed indices and factors to quantify the impact. This study aims todevelop an analysis-oriented method, specifically designed for the complete life cycle of buildings in the SouthAfrican environment. This is accomplished by continuing the work that was started by Brewis (2011), andcontinued by Brits (2012).Brewis developed the approach for the pre-use phase, while Brits developed the approach for the end-of-lifephase. Both focussed their application on low-cost housing development. However, the approach is definedfor the use of the analysis of a building envelope. The details of developing the environmental life cycleassessment (LCA), as well as the approaches for the pre-use phase and the end-of life phase are discussed inChapter 3.The study develops the use phase of the proposed environmental life cycle assessment for buildings in Chapter4. It discusses in detail the two main components of the use phase, namely maintenance and operation. Whilemaintenance is concerned with the replacement of building materials in the structure, the operationcomponent is concerned with the energy needs during the use phase.It is determined that the energy use that is directly related to the building envelope is the energy required forthe space heating and cooling of the building. This is due to the fact that the thermal properties of the buildingenvelope influence the thermal environment within the building, and thereby impact the use of energy toregulate that thermal environment.In order to make the most use of both of these components within the application of the proposed LCA, it wasdecided to model a residential building structure that uses consistent energy to regulate the thermalenvironment within the structure.However, it is not only the objective to use the proposed LCA as an assessment tool, but also as a comparativeand optimisation tool. Therefore one component, the external walls, was selected as a variable component.This component was varied to form a total of nine different buildings. These nine buildings were then used in acomparative study in order to try to determine an optimum choice of external walling system, based on theresults of the environmental impacts determined in the LCA. It is also used to try to explain exactly how and towhat extent the external walling system contributes to the environmental impact, and what useful applicationvalue we can gain from this knowledge. The results showed that a minor increase in the materials impact (due to attempts to improve the thermalcapacity of the external walls) were in most cases countered by a decrease in the energy impact, which inseven of the eight alternative external walling systems led to a net decrease in environmental impact (EI)categories one to four. It was also found that with the increase of the R-value of the external walling systems, the environmentalimpact of the building steadily decreased, in terms of four of the five impact categories.The only exception to these trends was found in the fifth impact category: waste generation. The reason forthis is the fact that energy impact in this environmental impact category is negligible, and therefore does notcontribute much to the net change in environmental impact.

[发布机构] Stellenbosch University