title: Outdoor thermal comfort and airflow in relation to urban form in Amman, Jordan: A residential setting analysis
Creators: name: Ayyad, Yara
Publisher: name: University of Liverpool Repository
Year: 2020

description: Rapid urbanisation and economic growth have put a significant pressure on urban planners to create layouts and buildings’ forms that are sustainable, healthy, and thermally comfortable for urban occupants. In the context of semi-arid climate, the built environment is often afflicted with high pedestrian comfort levels due to the increase in phenomena such as urban heat islands (UHI). The main aim of this research is to identify the key elements for enhancing the outdoor thermal comfort and airflow for pedestrians in a residential setting in the semi-arid climate of Amman in Jordan, through studying the urban geometrical parameters and their effects on the urban microclimate. The study followed an optimisation process that allowed a different variation of the designed proposals to be tested and simulated in terms of airflow and thermal comfort. The process analysed the urban elements on three different levels, the mesoscale (street grid layout), the microscale (compound layout) and the urban canyon scale. ENVI-met is a computational fluid dynamics (CFD) model that assesses the effect of meteorological parameters (e.g., air temperature, wind speed and relative humidity) on the built environment, in which it is used to simulate and evaluate proposed scenarios to find out the best configuration in terms of thermal comfort and airflow. A validation study was performed on ENVI-met using Amman configurations to test the model’s sensitivity and accuracy in predicting the microclimatic parameters change in the urban environment. The research proposed five different common street layouts to test out the geometrical aspect of the street grid. The results showed that wind speed values were found to change greatly for different orientations. However, Physiological Equivalent Temperature (PET) levels were more sensitive to the different grid geometries rather than their orientation. The research also proposed two grid designs for an empty plot in Amman based on the findings of the street grid analysis which comprised of a layout with streets oriented in the wind direction and an adjusted version of the wind flow proposal with perpendicular intersections for better land distribution. The results showed that the adjusted layout produced better PET values due to better shading geometry. Wind direction analysis showed that PET levels across the plot increased when the approaching wind angle was parallel to the streets and showed a significant decrease when directed at 45°. Compound design proposals showed that compound 1’s design with the wind flow transition produced higher PET levels when compared to strips of buildings design that allowed for better ventilation and controlled shading. The urban canyon scale analysis showed that increasing the buildings height enhanced the PET and airflow, while orienting the design in the (West-East) direction showed lower PET values when compared to the (North-South) orientation. The vegetation analysis showed airflow is enhanced with lower Leaf Area Density (LAD) values, due to less resistance from trees’ foliage.