Impact of Urban Built Form and Urban Density on Building Energy Performance in Different Climates
Creators: name: Ahmadian, Ehsan
Publisher: name: University of Lincoln
Year: 2023

description: Cities are recognized as the main consumers of energy on the planet, and to optimize their energy consumption and enhance the potential of using renewable energy sources, built form and density are considered highly influential factors. The energy efficiency of compact built forms has been debated by many studies. Meanwhile, urban density, as an attribute of urban form, has yet to be well defined due to the diversity of density indicators used in literature. Hence, there is a lack of integrated guidelines for urban density indicators and their relationships with urban built forms in urban energy studies. This thesis establishes a framework to demonstrate the inter-correlation of urban built form, density and energy for residential buildings, and the impact of climate as an influential parameter is investigated by adopting a mixed methods research approach. It primarily identifies the relationship between the urban built form and density by introducing a novel indicator of urban form termed the Form Signature. It demonstrates the simultaneous correlation of two selected density indicators with influential variables developed from the geometry of four selected urban built forms. An urban energy simulation software package, CitySim, is adopted to conduct sensitivity analyses. The simulation models are validated against data from a known building group. An energy indicator, termed Energy Equity, is also introduced that simultaneously considers the amount of building energy demand as well as energy generation by building-mounted PVs. Cross case study analysis is undertaken to examine the impact of climate on urban energy performance, where four cities (London, Singapore, Helsinki and Phoenix) are chosen based on the specific climatic criteria. Meteonorm software is adopted to generate climate file relating to each case study. The investigation is further complemented by analysing future scenarios to examine the impact of climate change and technological developments (i.e. the penetration of EVs into the transportation sector) on the energy efficiency of urban areas of the future. Graphical results of the Form Signature indicator prove that the term ‘high density’ is crucially dependent on the definition of the density indicator. The resulting graphs provide a robust platform for the analysis of contexts such as climate, economy, social issues and energy. Overlaying results of building energy simulations over the Form Signature graphs indicates the relationship of energy with urban built form and density. Results show that buildings with a greater number of storeys and greater plan depth (equivalent to low values of plot ratio and variable values of site coverage) have lower energy demand. When PV generation is also considered, low number of storeys and great plan depth can improve the energy performance of buildings (equivalent to low plot ratio and high site coverage). Having identical geometric variables, tunnel-court form (that is introduced in this study) provides the greatest density while pavilion form provides the lowest (~80% lower than tunnel-court). The energy performance of tunnel-court form is also the highest in all considered climates, while pavilion form shows the lowest energy performance (between 27% and 67% for cooling-dominated buildings and between 7% and 32% for heating-dominated buildings). Nevertheless, if density remains constant and geometric variables are changed, the opposite becomes true. An important conclusion is that the site plans with similar built forms and densities may have different energy performance since the same value of density can be achieved by different combinations of geometrical variables. Increasing the cut-off angle reduces building energy demand in cooling-dominated buildings (i.e. in Singapore and Phoenix) between 6% and 56%, while increase building energy demand in heating-dominated buildings (i.e. in London and Helsinki) between 2% and 16.5%. Therefore, increasing density through cut-off angle is not always energy efficient as it depends on climate. In general, building energy demand in London is the lowest among the case studies, while it is the highest in Singapore (up to 219% higher than London). London also shows the highest value of Energy Equity (demonstrating the best energy performance) and Helsinki shows the lowest (up to 51% lower than London). Considering future scenarios, the total building energy demand in 2050 will be 48% higher than at present, on average. A recommendation for future urban planning in London, for instance, is that court and tunnel-court forms will be more energy efficient, and possessing a lower number of storeys, small cut-off angle and greater plan depth will further improve their energy performance and reduce their emissions. The holistic outcome of this study provides urban energy planning guidelines that can be used by various stakeholders in the built environment.