Housing Development & Management, Department of Architecture and Built Environment, Lund University, Lund, Sweden.
Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden.
Int J Biometeorol. 2018 Mar;62(3):373-385. doi: 10.1007/s00484-017-1380-7. Epub 2017 Jun 14.
Due to the complexity of built environment, urban design patterns considerably affect the microclimate and outdoor thermal comfort in a given urban morphology. Variables such as building heights and orientations, spaces between buildings, plot coverage alter solar access, wind speed and direction at street level. To improve microclimate and comfort conditions urban design elements including vegetation and shading devices can be used. In warm-humid Dar es Salaam, the climate consideration in urban design has received little attention although the urban planning authorities try to develop the quality of planning and design. The main aim of this study is to investigate the relationship between urban design, urban microclimate, and outdoor comfort in four built-up areas with different morphologies including low-, medium-, and high-rise buildings. The study mainly concentrates on the warm season but a comparison with the thermal comfort conditions in the cool season is made for one of the areas. Air temperature, wind speed, mean radiant temperature (MRT), and the physiologically equivalent temperature (PET) are simulated using ENVI-met to highlight the strengths and weaknesses of the existing urban design. An analysis of the distribution of MRT in the areas showed that the area with low-rise buildings had the highest frequency of high MRTs and the lowest frequency of low MRTs. The study illustrates that areas with low-rise buildings lead to more stressful urban spaces than areas with high-rise buildings. It is also shown that the use of dense trees helps to enhance the thermal comfort conditions, i.e., reduce heat stress. However, vegetation might negatively affect the wind ventilation. Nevertheless, a sensitivity analysis shows that the provision of shade is a more efficient way to reduce PET than increases in wind speed, given the prevailing sun and wind conditions in Dar es Salaam. To mitigate heat stress in Dar es Salaam, a set of recommendations and guidelines on how to develop the existing situation from microclimate and thermal comfort perspectives is outlined. Such recommendations will help architects and urban designers to increase the quality of the outdoor environment and demonstrate the need to create better urban spaces in harmony with microclimate and thermal comfort.
由于建筑环境的复杂性，城市设计模式会极大地影响特定城市形态的微气候和室外热舒适度。建筑物高度和朝向、建筑物之间的空间、场地覆盖率等变量会改变街道层面的太阳能获取、风速和风向。为了改善微气候和舒适度条件，可以使用城市设计元素，如植被和遮阳设备。在湿热的达累斯萨拉姆，尽管城市规划当局试图提高规划和设计质量，但城市设计中的气候考虑因素几乎没有受到关注。本研究的主要目的是调查城市设计、城市微气候和四个不同形态建成区（包括低层、中层和高层建筑）的室外舒适度之间的关系。本研究主要集中在暖季，但对其中一个区域的凉爽季节的热舒适条件进行了比较。使用 ENVI-met 模拟空气温度、风速、平均辐射温度 (MRT) 和生理等效温度 (PET)，以突出现有城市设计的优缺点。对各区域 MRT 分布的分析表明，低层建筑区域的高温 MRT 出现频率最高，低温 MRT 出现频率最低。研究表明，低层建筑区域比高层建筑区域导致更具压力的城市空间。研究还表明，密集的树木有助于提高热舒适度条件，即减少热应激。然而，植被可能会对风的通风产生负面影响。尽管如此，敏感性分析表明，考虑到达累斯萨拉姆的阳光和风向条件，提供遮荫是比增加风速更有效的降低 PET 的方法。为了减轻达累斯萨拉姆的热应激，从微气候和热舒适度的角度概述了一套如何发展现有情况的建议和指南。这些建议将帮助建筑师和城市设计师提高室外环境的质量，并展示在与微气候和热舒适度和谐共处的情况下创造更好的城市空间的必要性。
