Solar access indicators for urban planning

Abstract: Solar access describes the amount and distribution of sunlight in living environments. Access to sunlight is crucial for the health and sustainability of cities. It is vital for people and vegetation, and for energy production and conservation. The amount of sunlight entering the city space is restricted by the urban layout, as buildings obstruct solar access by shading each other and the surroundings. Scarcity of land and growing urbanisation drive the densification of cities. As cities are built taller and tighter, less sunlight can reach the urban fabric. This problem becomes especially critical for higher latitudes. Urban planners receive development directives that often stipulate higher densification of new and existing areas. Presently, some solar access aspects (daylighting and sunlighting) are legislated and evaluated at the late stages of building design, when it is often too late to change basic urban layout features to increase solar access. Thus, the urban planning level appears to be the appropriate design stage for solar access interventions. Having so many urban design objectives to deal with at this planning level, urban planners need simple methods to effectively introduce discussion of solar access into the design process. This thesis aims to contribute to this goal by investigating relevant metrics to identify suitable performance indicators for the purposes of solar access evaluation.In the first phase, a literature review was conducted to identify existing solar access metrics. The metrics were analysed and arranged into a metric taxonomy. The ways in which assessment metrics are typically formulated were also investigated, which led to structuring of the metric formulation principles. These guidelines may help analysts to select or formulate suitable metrics for specific design evaluations. In the next phase, the metrics that were identified from the literature review were further examined through correlation studies and statistical methods, including regression models. The study was conducted on neighbourhood models, typical for the Swedish context, including both generic design iterations and case studies. The relationships between metrics and urban density were investigated. The analysis identified four potential metrics (1. VSC, 2. SVF, 3. ASH_F, 4. RD_G) which can help assess solar access at the urban planning phase. They adhere to four design objectives for solar access, recognised as: 1) daylighting indoors, 2) daylighting outdoors, 3) sunlighting indoors, and 4) sunlighting outdoors. These metrics are well-correlated with urban density and with other metrics, yet remain relatively simple. Finally, two assessment methods that use and apply the identified performance indicators were suggested. Both models require the analyst to input the urban density and choose a target metric. Then, using the metric datasets created in this thesis, the assessment models return either 1) urban design proposals for a given development plot or 2) expected value ranges for a given metric to position the proposed design in reference to the previously simulated cases. The first method leaves less creative space for the planners, while the second method gives only reference values for estimation of the potential to improve a design. Future work should aim to focus on establishing metric thresholds, i.e., performance benchmarks, as this would further develop workflows for solar access evaluations. Evidence-based research is required to establish recommended solar access levels for the complex network of wellbeing and energy objectives.