Life cycle assessment of multi-glazed windows
In 1987 the World Commission on Environment and Development proposed a reduction in per capita energy consumption of 50%. Increasing demands, and initiatives of this nature, produce a need for more reliable assessment methods, measurement tools and improvement regimes. Since the late 1960's Life Cycle Assessment (LCA) has become an increasingly important tool for engineers, technologists, scientists, designers, managers and environmentalists alike. LCA enables the effects which products, processes and activities have on local, regional or global environments to be assessed, adopting a holistic, or whole life approach to design methodologies. The design of window systems has a large impact upon LCA results generated. Thermal performance properties influence energy consumption patterns throughout a lifetime of use, while appropriate use of materials, window positioning and size have a knock-on effect on lighting control functions and air conditioning demands. In developing countries, residential sectors account for between 20% and 30% of the total energy used (30% in the UK). Windows in dwellings alone account for 6% of the total UK energy consumption. This thesis addresses an ongoing need to focus on sustainable development, using LCA as an assessment tool to develop a greater understanding of the window life cycle, and to highlight improvements which are necessary to lessen its environmental impact and make the processes involved more benign. To do this successfully requires that the demands of modern day living, and the comfort conditions expected, be incorporated into design criteria, whilst ensuring that the needs of future generations are not compromised by today's activities. Along with rising demands to improve efficiency and decrease energy consumption in buildings, comes an expectation for continual improvement in building interiors. To this end, both the aural and visual haracteristics of window installations become paramount, in addition to the well researched thermal performance criteria. Much research has focused on investigating the social and physiological benefits associated with improved interior environments. The correlation between worker satisfaction and performance has been well proven. If complete physical well-being is satisfied then an individual's mental well-being is less likely to be affected by the additional stressors of environmental dissatisfaction. An optimisation model has been developed, linking the thermal, aural and visual performance of varying window designs, such that an "advanced" window system is created. Two outputs are generated from the model, which may be used to evaluate the "optimum" window design in terms of energy consumption and global environmental impact. Optimisation of energy consumption incorporates embodied energy, thermal performance and electric lighting demand, over the life cycle of a window. Global environmental impact optimisation is similar, but evaluation is based on energy generation, and greenhouse gas production. Finally, a flowchart for optimisation guides the user towards a glazing solution which offers sufficient noise attenuation, whilst minimising thermal losses and electric lighting demand. Each output provides a guide for design, leaving room for judgement, and is not intended to be followed definitively. Recommendations for improvements to manufacture systems and production of multiglazed windows are offered, based on sustainable development criteria. Future research needs, which are necessary to minimise the total environmental impact resulting from multi-glazed window production, are also discussed.