Urban Geometry: The Effect of Height Diversity and Buildings Configuration on Thermal Performance and Cooling Load at Urban Scale. A Case Study in Dubai / UAE
The British University in Dubai (BUiD)
Urban geometry and buildings morphology are important factors that affect both thermal behaviour of the spatial environment as well as a building’s energy performance. This research aims to explore the effect of the urban block with different building configurations on energy performance at the urban level. For this aim, a literature review was conducted to identify the previous and recent studies relevant to this research topic. It has been proven that the compactness element is a key urban geometry variable that controls the desired thermal performance of the built environment in hot climates. However, the previous studies have primarily focused on traditional methods of increasing the shading effect, such as by increasing buildings height / canyon width H/W ratio to provide the required compactness for desired solar access and energy saving target. This research attempts to provide alternative methods to achieving the required compactness and increase the shading effect by adapting building height variations and configurations in urban block design. As observed in the previous literature, the energy consumption assessment and the strategies that can be adopted to reduce this consumption are generally implemented and evaluated on the scale of individual buildings. Therefore, further investigation of both the diversity in building heights and the effect of this on the energy performance, and the evaluation of the energy consumption at the urban scale is required to fill the gap identified in previous literatures. This study utilised two software packages to simulate a base case urban configuration and evaluate this case against the proposed suggested scenarios of different configurations. The proposed scenarios depending on the urban configuration sustainable strategies were implemented and simulated to find the effect of adopting these strategies on the building’s total energy performance within the case study area, i.e., the Dubai / UAE local context and weather characteristics. Three groups with 56 proposed scenarios were simulated, where in different ratios of building height variation were implemented in the first two groups, and different building configurations were adopted for the third group. The research found that a significant variation in building height reduces the cooling load more than a gradual height variation, and consequently offers more energy saving. The variation along the short direction of the urban block has a greater positive effect and the saving in cooling energy consumption reaches 4.6 %. The significant variation in building height along the short axis of the urban block provides more shading to the canyons and the adjacent buildings compared to the base case. This over shading reduces the air temperature by 1.1 ͦ C within the canyon and directly reduces the conduction heat gain through the buildings envelop. This is in addition to the other effect represented by reducing the direct solar access to the building surfaces and decreases the solar energy gained by the buildings envelop through direct radiation. Furthermore, building orientation plays a significant role in the thermal performance of the urban block, and it contributes to the total cooling load energy saving of the urban block by 6.6 % at the peak time of cooling demand. Moreover, the research found that the variation in building heights will increase the wind velocity by up to 23 %, and this improvement in air flow affects the outdoor air temperature positively. This positive effect of the height variation on the outdoor air temperature of the urban canyons reduces the conduction heat gain through the buildings envelop by 4 %, and consequently reduces the energy required for cooling purpose. In addition, the alternative arrangement of the buildings within the block is another geometrical variable that affects the thermal performance of the built environment. It has been found that the alternative, or stagger arrangement, provides more shading effect on both canyon and building surfaces. However, this arrangement reduces the wind speed due to the obstruction created by the buildings mass and decreases the air velocity in the canyons. On the other hand, this type of configuration improves the distribution of the air around the buildings block and consequently enhances the outdoor thermal comfort around most of the buildings within the urban block. The reduction of 1.9 ͦ C in outdoor air temperature, and 4.9 % in cooling load is achieved by increasing the H/W ratio of the main canyons from 0.96 to 1.2. Therefore, designing the urban block with a significant diversity in building heights, or gradual height variation will have the potential of a shading effect and wind speed increase to enhance the thermal performance of the urban block. Finally, adopting the rectangular shape of the urban block, creating diversity in building heights and alternative building morphology are some of passive urban design strategies that can be followed for the optimised urban block configuration, with high efficient morphology and less environmental impact. This prototype is recommended for the new urban development in the UAE and other areas of the same climate zone.
Buildings -- Thermal properties., height diversity, buildings configuration, United Arab Emirates (UAE), cooling load, thermal performance, energy performance, energy consumption, sustainable energy