Reducing adverse air flow

Urban life 18 October 2016 Steve Lo

From skyscrapers in Hong Kong to new urban spaces in downtown Køge, Denmark: Managing wind and air pollution problems.

4 min

By Michael Rothenborg, October 2016

With more than half the Earth’s population now living in urban areas, some changes in the indoor and outdoor climates of cities are bound to occur. Climate scientists’ greatest concern is traditionally the urban heat island (UHI) effect – city areas where temperatures can be several degrees higher because there is lots of concrete and little blue or green infrastructure like lakes, rivers and parks. But another effect – air flow – can also cause serious health problems.

Skyscrapers or other prominent buildings change the wind flow through a city, which can, for example, interfere with the intake of fresh air in buildings. Air pollution at street level can also worsen, or wind can strengthen and hinder pedestrians or cyclists or even compromise safety.

The problem has been described in scientific papers, including a survey by the US National Library of Medicine that examines “High-Rise Buildings versus Outdoor Thermal Environment in Chongqing” and concludes that cities can improve their urban thermal environment if they change their architectural and engineering structures and layouts.

Better layout of city blocks

Drawing on 15 years’ experience in the field of climate engineering, Ramboll has reached the same conclusion.

Ramboll designers study the urban landscape of a particular area by assessing its natural systems: its landforms, hydrology, vegetation and climate. 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.

In Hong Kong, the SARS outbreak in 2003 caused nearly 300 deaths, thus prompting the city to take measures to improve its environmental hygiene. The aim was – and is – to mitigate the urban heat island effect and other negative consequences of urbanisation through initiatives that promote a better layout of city blocks.

“Since 2005, air ventilation assessments have become an essential part of town planning, concentrating on how planning can influence and improve the general living environment, quality and sustainability of Hong Kong,” explains Steve Lo, environmental consultant at Ramboll Environment & Health in Hong Kong.

3D air simulation tool

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 can also be used on a smaller scale. In the Danish town of Køge, Ramboll is analysing how local winds from the open sea affect the planned city development – and using the findings to optimise the shape and location of buildings and thus create pedestrian and living zones that afford maximum comfort for future residents.