By Michael Rothenborg
More severe and frequent heat waves. Heavier winds. Higher air pollution and more complications for people with respiratory diseases.
These are some of the consequences of climate change in the world’s cities, where high-rise buildings are affecting air flow, and the urban heat effect means higher temperatures in areas with a lot of concrete and not much blue-green infrastructure such as parks or lakes.
That’s why climate change necessitates a better urban design, Jens Christian Bennetsen, senior project leader in Ramboll and an expert in advanced flow engineering concludes.
“Higher temperatures and exacerbated air pollution, together with growing and aging urban populations, requires better urban design, to allow sustainable population growth in urban areas”, Jens Christian Bennetsen says. He will be presenting important conclusions on advanced flow engineering at a Cop22 side event about Sustainable Cities on Saturday.
Ramboll has been working in this field of climate engineering for 15 years. The method is to study the urban landscape of a particular area by assessing its natural systems: its landforms, hydrology, vegetation and climate on a virtual workbench scale. Creating more sustainable urban design requires an understanding of the urban microclimate – its wind distribution, pollutant level and thermal comfort characteristics – at every stage of the design process.
Improve the outdoor comfort in Riyadh
In collaboration with Henning Larsen Architects Ramboll has been conducting urban design for King Abdullah Financial District, Riyadh, Saudi Arabia. In July the average daily temperature ranges beyond 40 degrees Celsius, and low humidity, intense solar radiation and strong dusty winds also play a big part in the individual physical and psychological conditions and comfort.
“The computational capacity available nowadays allows us to calculate local microclimates using Computational Fluid Dynamics (CFD) modelling inside the urban city. Relative wind speeds can be computed and the probability of their exceeding certain values can be calculated to evaluate the wind comfort for various pedestrian activities”, Jens Christian Bennetsen explains.
In this study, numerical CFD simulations were performed for two planned building layouts. The results show that the integration of technical knowledge can qualify the planning process and improve the overall outdoor comfort level – thus avoiding the need to introduce mitigating measures at later stages in the project.
3D simulation in Hong Kong
Ramboll’s air ventilation assessments typically entail identifying open playgrounds, bus stops, footbridge entrances and other important pedestrian areas.
For that purpose, Ramboll has applied the 3D air simulation tool “Computational Fluid Dynamics” – a way of investigating the flow, energy transport, chemical reactions, combustion, etc., in an urban setting.
The tool is also being used to improve the environmental hygiene in Hong Kong - and also in the Danish town Køge, where Ramboll is analysing how local winds from the open sea affect the planned city development to maximize comfort.