Towards an integrated multi-scale zero energy building framework for residential buildings
In most developed economies, buildings are directly and indirectly accountable for at least 40% of the final energy use. Consequently, most world cities are increasingly surpassing sensitive environmental boundaries and continue to reach critical biophysical thresholds. Climate change is one of the biggest threats humanity faces today and there is an urgent need to reduce energy use and CO₂ emissions globally to zero or to less than zero, to address climate change. This often leads to the assumption that buildings must reduce energy demand and emit radically less CO₂ during construction and occupation periods. Certainly, this is often implemented through delivering ‘zero energy buildings’. The deployment of residential buildings which meet the zero energy criteria thereby allowing neighbourhoods and cities to convert to semi-autonomous energy systems is seen to have a promising potential for reducing and even eliminating energy demand and the associated greenhouse gas emissions. However, most current zero energy building approaches focus solely on operational energy overlooking other energy uses such as embodied energy and user transport energy. Embodied energy constitutes all energy requirements for manufacturing building materials, construction and replacement. Transport energy comprises the amount of energy required to provide mobility services to building users. Zero energy building design decisions based on partial evaluation and quantification approaches might result in an increased energy demand at different or multiple scales of the built environment. Indeed, recent studies have demonstrated that embodied and transport energy demands account for more than half of the total annual energy demand of residential buildings built based on zero energy criteria. Current zero energy building frameworks, tools and policies therefore may overlook more than ~80% of the total net energy balance annually. The original contribution of this thesis is an integrated multi-scale zero energy building framework which has the capacity to gauge the relative effectiveness towards the deployment of zero energy residential buildings and neighbourhoods. This framework takes into account energy requirements and CO₂ emissions at the building scale, i.e. the embodied energy and operation energy demands, and at the city scale, i.e. the embodied energy of related transport modes including infrastructure and the transport operational energy demand of its users. This framework is implemented through the development of a quantification methodology which allows the analysis and evaluation of energy demand and CO₂ emissions pertaining to the deployment of zero energy residential buildings and districts. A case study, located in Auckland, New Zealand is used to verify, validate and investigate the potential of the developed framework. Results confirm that each of the building (embodied and operational) and transport (embodied and operational) energy requirements represent a very significant share of the annual overall energy demand and associated CO₂ emissions of zero energy buildings. Consequently, rather than the respect of achieving a net zero energy building balance at the building scale, the research has revealed that it is more important, above all, to minimise building user-related and transportation energy demand at the city scale and maximise renewable energy production coupled with efficiency improvements at grid level. The application of the developed evaluation framework will enable building designers, urban planners, researchers and policy makers to deliver effective multi-scale zero energy building strategies which will ultimately contribute to reducing the overall environmental impact of the built environment today.