公共健康视角下城市街区综合通风效能与规划响应研究

The Research of Urban Block Comprehensive Ventilation Efficiency and Planning Strategy in Public Health Perspective

建筑室内外的通风效能是确保城市空气质量与健康的重要方面,街区尺度上建筑群的空间形态则显著影响了室内外通风效能。本文归纳了八项室内外通风效能指标,通过对天津中心区107个地块的研究,将各项指标与常用规划指标建立相关关系。结论显示容积率与地块综合通风效能呈现显著负相关,但某些通风指标与容积率关系不大,需要单独考虑。通过对比城市常见的街区布局模式,发现综合体式的开发模式最不利于室内外通风,而小尺度的建筑群布局则具备更好的通风效能,商业与住宅混合的功能分配能够缓解高容积率地块的总体通风压力。本文希望通过对综合通风效能指标的建立,以及对建筑群空间形态—通风效能之间的相关关系的研究,为塑造公共健康视角下的健康城市街区设计提供理论支持。

Building indoor and outdoor ventilation efficiency is an essential part to urban air quality and human physical health.A poor ventilation condition may cause the accumulation of bacteria,virus and other pollutants,which is a threat to public health.It has been proved that urban spatial morphology and building arrangement strongly affect indoor and outdoor ventilation efficiency.Past studies about urban ventilation are mostly focused on single ventilation indicator and lack of connection between different indicators.Based on existing studies,this paper summarized eight outdoor and indoor ventilation efficiency indicators and proposes an evaluation method for overall urban ventilation.Also the correlation between ventilation indicators and common planning indicators is established.As a result,a quantitative analysis approach collaborating urban planning and public health is presented.This approach would not only reveal the ventilation defect in built urban blocks,but also figure out a fundamental direction for urban planning practices in early stage in perspective of urban public health as well.In this paper,107 built blocks that can fully reflect modern urban morphology in Tianjin’s core urban areas are selected.Each individual ventilation indicator,including frontal area ratio,frontal area density,average building height,site coverage,building shape coefficient,population density per unit f loor are,population density per unit building foot print area and population density per unit open space area,are calculated for each block.The overall ventilation efficiency of each block is evaluated and graded by adding up the scores of every individual indicator.The correlation between each ventilation indicator and planning indicator is further verified.The result shows that floor area ratio is significantly negative correlated with the block’s overall ventilation efficiency.Thus in early planning stage,floor area ratio can be used to control the overall urban ventilation.However,as floor area ratio is not correlated with every ventilation indicator,a more detailed controlling methods by using other planning indicators should be approached in detail planning stage.As average building height are positively correlated with frontal area index and population density per unit building foot print area,and site coverage are positively correlated with frontal area density and population density per unit open space area,these two common planning indicators can also be used as ventilation controlling indicators to optimize building outdoor and indoor ventilation.However,building shape coefficient and population density per unit floor area are not correlated with any common planning indicator which means they should be considered individually.Urban blocks in study area are then classified into five typical layout modes as mid-rise residential area,high-rise residential area,urban complex,commercial street and mixed mode based on its spatial morphology and land use characteristics.By comparing each ventilation indicator,a great ventilation efficiency variation is found between each layout mode.Also different layout modes face different ventilation problems and need targeted optimization.Mid-rise residential area faces the problem of low pedestrian level wind speed due to its high frontal area density.This can be solved by replacing some mid-rise buildings with high-rise buildings or by optimizing the building orientation.High-rise residential area has a less outdoor comfort due to its high wind speed dispersion.This problem can be solved by podium buildings around high-rise buildings to create a buffer space between high-rise buildings and pedestrian area.Commercial street has a poor indoor ventilation due to the high indoor population density and high site coverage indicator.By planning more open space and some high-rise buildings in proper place could lower the site coverage and enhance the indoor ventilation of commercial street.Urban complex mode has the worst overall ventilation efficiency with the lowest ranking in almost every ventilation indicator.Therefore,urban complex is not recommended in urban development and should be replaced by other layout modes although it is getting more popular in Chinese cities.What’s more,the land use and building function also affect population density among each block and further cause the ventilation efficiency difference.Therefore,a mixed land use urban block or commercial podium under high-rise residential buildings are recommended to improve the poor ventilation efficiency in commercial and office buildings.In summary,this paper proposes a comprehensive urban ventilation evaluation method in urban block scale by combining eight outdoor and indoor ventilation indicators in the perspective of public health.By using this method,the ventilation problems for built urban block can be detected.Also this evaluation method can be applied in planning practice in order to optimize urban overall ventilation.However,some future studies are needed as giving weight to each evaluation index and set recommendation value for each evaluation index according to different climate condition.