China's increasingly severe environmental pollution has casted a shadow over the heaven in former days. As some researches may indicate, in many Chinese cities, the increasingly serious air pollution has constituted a threat to residents' health and quality of life. Even the Yangtze-river delta, which is recognized as the pioneer of the economic and social development, cannot be able to survive. The frequently viewed heavy fog in recent years is just the disastrous effect due to the pollution of the environment, which could be further intensified by the temperature inversion in winter. Furthermore, the environmental pollution can also lead to the economic losses through traffic accidents, postponed or cancelled flights etc.
In response to these conditions Frey Architecture Ltd. was invited by the planning administration in Kunshan City to strive for establishing the overall strategies to improve the ecological environment so as to develop a sustainable city. The prevention measures can be divided into three types: short-term measures – by which the polluted air will be replaced by fresh air; Interim measures, which focus on lessening the content of atmospheric pollutants; Long-term measures, which highlight the reduction or prevention of air pollutant emissions from industrial and residential perspectives. As the anterior part of the weather modification plan the urban air corridor project has aroused great concern from the municipal government.
In this demonstrative project a series of necessary analysis and evaluations will be adopted in the air duct structure of Kunshan city. Due to the impeded air circulation in winter the pollutants are always congested without sufficient evacuation, the air quality is thus of great worries. The ventilation therefore becomes an appropriate entry point of the green city construction.
It is the basic principle of laying down the strategy of ventilation that is to progress gradually from macro to micro scales, while the result from the upper level of planning builds up just the basic framework of the next. The administrative grade in the project is 'city', whose climate behavior has been defined as in the mesoscale, with which the methods of analysis and planning are also characterized.
The basic data of the analysis of climate conditions in the perspective from ventilation in Kunshan city contain two parts: urban data, which indicates the GIS data and meteorological data, which mainly refer to the wind-rose diagram as well as the statistics of air pollution. In order to acquire the 3D model of the city, the height of the building can be added into the corresponding architectural planes inside the Basic data. The model displayed the different density and height distributions of buildings in the entire urban zone.
Three dominate ventilation corridors were developed by means of precisely calculating in analysis within 100m roughness accuracy along the prevailing wind direction of Kunshan city. Among them, red represents the unit with high roughness and length thus blocked ventilation; the yellow unit signifies medium building density, by which only weak ventilation could be realized; the blue expresses that the roughness and the length are close to zero, so that the ventilation of high quality could be guaranteed -- these areas can strike great importance to the equipment of air corridor as well as the climate balance.
The effect of corridor ventilation planning should not only reflect in the reduced air pollutants, but also be examined through people’s feeling of comfort, which is determined by six main parameters, namely temperature, humidity, wind speed, clothing, metabolism, and radiation. To enhance the air flow in a warm environment can have a positive impact on the thermal comfort: the body feeling temperature will be decreasing as the evaporation being accelerated with heat loss. As an example mentioned in the international standard ISO 7730, when the temperature is 29 °C and the wind speed is 0.82 meters/second, the body feeling temperature will reach just 26 ° C. When Cities are lacking in ventilation or only possessing unilateral ventilation, the body feeling index would almost be the same. Improving urban air quality while raising the air pressure on building facades and increasing the frequency of draught will contribute to improving indoor thermal comfort as well as reducing the energy consumption of air conditioning in summer. Additionally the time of ventilation via window-opening in winter will be reduced.