Li, Jingjin

Pan, Changwei

Xie, Huahua

English

University of Utah E Publications

ISUF 2020: CITIES IN THE TWENTY-FIRST CENTURY   A COMPACT URBAN BLOCK DESIGN METHOD BASED ON ‘SOLAR ENVELOPE’ ---- CASE STUDY IN NANJING Jingjin Li, lecture, Southeast University, China,  Changwei pan,  Southeast University, China,  Huahua Xie, Southeast University, China,  ABSTRACT Maximizing the potential of passive utilization of solar energy in a high density urban block is an important goal in architecture and urban design. However, the current solar code in China focus more on single buildings rather urban blocks. This paper approach to apply ’Solar Envelope’ to design compact urban block forms with high passive solar potential. Firstly, the program of  ’Solar Envelope’ generation and solar radiation simulation are complied by Grasshopper a parametric platform. Secondly, different  blocks are implied to generate a series of compact urban block forms by ’Solar Envelope’. Thirdly, solar performance of the compact urban block and existing urban blocks are compared by simulation analysis, so as to achieve the balance between floor area ratio and solar quality. A pilot study of the ‘solar envelope’ for urban block in Nanjing demonstrates a significant improvement over the existing urban layout in terms of the solar insolation . INTRODUCTION  Solar insolation not only give us light and warm, but also affect our rhythm and behavior habits. solar insolation as an important natural resource has had an important influence on urban form since ancient times. Acoma pueblo ancient city adopts southward retreat and determinant layout to cope with different solar conditions in winter and summer（Knowles,R.L.2003，p.15）. Chinese traditional courtyard layout room sequences according to the relationship between different rooms and solar insolation orientation.  With the increase of urban construction density, the problem of solar insolation protection in urban environment becomes more and more prominent. According to the zoning law of New york, when the height of high-rise buildings on both sides of the street reaches a certain height, it is necessary to retreat from street according to a certain angle. A tower may then carry 25 percent of the plot area to unlimited heights （koolhaas,1978）. The solar insolation regulations currently adopted in China refer to the research on the height and spacing of buildings in Gropius in the 1920s. In the process of rapid urbanization, this method ensures the basic solar insolation demand of residential buildings in high-density cities, but it also leads to the monotonous form of urban blocks and the weak relationship between block building combinations and plots. According to the research of process type school, cities can be understood as four levels: elements, structure of elements, system of structures and organization of systems. The architectural combination in blocks corresponds to the structural level of elements, and plays an important role in connecting block combination and guiding building monomer（Karl Kropf，2009）. Therefore, how to balance solar insolation acceptance and diversified block shapes is the focus of this paper.    2 ISUF 2020 Cities in the Twenty-first Century BACKGROUND  Knowles first defined the obstacle angle principle in 1970s and put forward the famous 'solar envelope' principle. 'solar envelope' refers to generating a three-dimensional surface for a given site, and the construction inside it can guarantee the basic solar insolation demand of surrounding blocks. The Envelope is defined by space and time factors: block form, surrounding buildings, and the time period that needs solar insolation protection. These two aspects define the final size and shape of the envelope. To generate the ‘solar envelope’, There are two important concepts, ‘shadow fences’ and ‘cut-off  times’. The former refers to the range that the surrounding buildings can allow shadow to coverage, while the latter guarantees the solar insolation period of the surrounding environment. Generally, more time requirements of the surrounding environment will limit the amount volume of solar envelope. Different from the important influence of solar envelope in academic field, its application in practical projects is restricted to some extent. There are two main reasons: on the one hand, because the calculation method is relatively complex, solar envelope is considered to be more suitable for evaluating the construction intensity of small-scale regular square grid blocks, but it is difficult to apply to large blocks or irregular blocks. On the other hand, the envelope mainly pays attention to the solar insolation fairness between blocks, and gives less consideration to the solar insolation time of buildings in blocks. In order to solve the first problem, Carlo Ratti applied the 'solar envelope' model to the management and control of the main street in an urban design project in Milan through DEM model. A.Okeil put forward RSB block mode to maximize passive utilization of solar energy resources，which is combined with two L-shaped buildings diagonally （A.Okeil, 2010）. By combining solar envelope and solar fan, A. Vartholomaios put forward ‘RSBE’ (Residential solar envelope block)model, which solved the problem that the solar envelope paid less attention to the solar insolation conditions of buildings in the block（A. Vartholomaios，2015）.  The above research summary raises a question: whether the solar envelope method can be applied to Chinese urban design to balance the urban solar insolation quality and the diversity of block shapes, and to construct the relationship between buildings and plots.     Figure1.Research evolution of solar envelope research  3 ISUF 2020 Cities in the Twenty-first Century METHODOLOGY  A case study was proceed in Nanjing，four urban blocks with different shapes near east hill were selected for empirical study, total site area is about 95,000㎡. Dongshan Park is on the east side of the site, and urban roads are on the west and north sides. Three targets are need to achieve in this design. First, due to the influence of the existing hill, the building height of the block is strictly limited. Second, the design needs to provide as much floor area ratio as possible under the limit of limited height and solar insolation. In addition, The climate in Nanjing is hot in summer and cold in winter,  the urban environment needs to take into account the dual needs of winter solar insolation and summer shading. Therefore, this paper puts forward a combination of solar envelope and building height gradient adjustment method.  Three different scene models  are designed for the same site, and evaluates the three models by comprehensively comparing their form and solar insolation indexes.  1. Workflow compilation: Based on GH, the workflow to generate ‘solar envelope’  is constructed, which includes five parts: climate information input, block boundary import, solar insolation time setting, solar envelope generation and geometric parameter statistics. The climate information of Nanjing used in this study comes from the official website of energy+, and the solar insolation time is set at 11-1 o'clock on the winter solstice. 2. Application of solar envelope: apply the previous workflow to the actual site, set up the sideline to generate the initial solar envelope and perform Boolean operation with the building control red line to form the largest potential building volume in each block.  3. Building layout inside the envelope: In the interior of the formed envelope,three different block models are designed to fit the envelope, model 1 is combined with tower and slab buildings, model 2 is combined with tower, slab and courtyard buildings, model 3 is combined with tower and courtyard buildings.  4.Solar insolation simulation and geometry indicators calculation: Solar insolation and geometric index calculation are carried out for three scenes respectively. Solar insolation time includes total and average building insolation time in summer solstice and winter solstice.Total Solar insolation time means the amount solar insolation received by the building surface which is calculated by the plug-in of ladybug while the average solar insolation time(Ast) is calculated by the equation:   Figure2. Work-flow of solar-envelope by grasshopper Figure3. Site condition and initial solar envelope 4 ISUF 2020 Cities in the Twenty-first Century Ast= Total Solar insolation time/ gross floor area. Morphological indicators include: total building area, floor area ratio（Far）,building coverage ratio(Bcr),open space ratio（Osr）and mean elevation height（Meh）,the calculation methods are as following equations: Far = gross floor area / site area, Bcr = footprint area of building / plan area， Osr =(1-Bcr)/Far， Meh= building volume/ footprint area of building.  5.Data comparison: comprehensively compare the solar insolation and morphological indicators of the three models, and clarify the advantages and disadvantages among the different models.  FINDINGS   Solar Envelope: According to the generation results of solar envelope, the generation volume of solar envelope is closely related to the block size, which is mainly affected by the depth of the block in the north-south direction. The maximum height of the cover is 95m for the block on the north side of the site, and about 50m for the block on the south side. Block form: According to the difference of building heights and enclosing degrees, three different building layout models are formed in the solar envelope. Model 1 is the combination of slab and tower. According to the height restrict of the envelope, tower buildings are added in three plots on the north of the site, and the height of tower buildings is between 30m and 54m. This model is widely used in the current residential area design in China, with the main goal of meeting the solar insolation of buildings in the block, which is lack of consideration of urban interface. On the basis of the first model, the second model adopts the combined of courtyard buildings with a height of 9- Figure 4. Three 3D models and geometry indicators 5 ISUF 2020 Cities in the Twenty-first Century 27m along the west urban roads. In the third model, only three tower buildings on the north side are reserved, and the rest adopt the layout mode of enclosed buildings with the step back form. By the step back of the building height, a larger building area can be obtained under the strict of building height control(Figure4).  Geometry indicators:  the  floor area ratio of model 1 is lowest in the three models which is about 1.6, the floor area ratio of model 3 is highest about 2.13, and the floor area ratio of mode 2 is about 1.74. Model 3 has the highest building coverage rate around 0.39, and model 1 has the smallest coverage rate close to 0.28. The open space ratio of model 1 is 0.45 which is highest in the three models , model 3’s open space ratio is lowest around 0.29. Compared to the variation among the three models of the floor area ratio , coverage ratio and open space ratio, the average height of the three models is similar range from 17.9m to 19.7m, among which the average height of model 1 is the largest and model 3 is the lowest. Solar insolation time: Figure 5 indicates that among the three models, model 2 and model 3 have a larger total solar insolation time on the winter solstice, in which model 2 show the maximum solar insolation time of about 215,995 hours and model 1 has the minimum solar insolation time of about 208,246 hours. However, in terms of average solar insolation time, model 1 shows the maximum solar insolation time of about 1.38 hours in winter, while model 3 shows the minimum solar insolation time of 1.07 hours.  Model 1 shows the minimum amount of solar insolation time in summer solstice which is about 334,005 hours, while model 3 and the maximum sum of solar insolation time about 401,245 hours. Compare to it’s highest total solar insolation in summer solstice,the average solar insolation time in summer solstice of model 3 is lowest in the three models which is about 1.99 hours. The average solar insolation time of model 1 and 2 is about 2.21 and 2.24 hours. Compared with the total solar insolation time, the average solar insolation time can reflect the solar quality of the urban block form more accurately. Although the solar insolation time in winter is limited, model 3 provides better shading effect in summer. 6 ISUF 2020 Cities in the Twenty-first Century  CONCLUSIONS With the development of computer technology, the solar envelope method has certain possibility in urban design projects which has positive significance in ensuring solar rights among blocks. The application of this method in blocks with similar solar insolation conditions to Nanjing can achieve higher development intensity under the condition of limited land height. Different layout buildings have a significant impact on the temporal and spatial distribution of solar insolation. Based on the study of different building combination models , the dual requirements of solar access in winter and shading in summer can be better considered.Further research needs to pay attention to the organization of the building layout inside the solar envelope, to make full use of the inner space of the envelope on the basis of ensuring the solar insolation of the building  to balance the relationship between environmental quality and construction capacity. REFERENCES Knowles,R.L.. The solar envelope: Its meaning for urban growth and form[J]. Energy and Buildings, 2003(35), 15–25. Kropf, Karl. Aspects of urban form[J].Urban Morphology,2009,13(2):105-120. Koolhaas,R.(1978).Delirious New York: a retroactive manifesto for Manhattan. Oxford: Oxford University Press. Eugenio Morello, Carlo Ratti. Sunscapes:“Solar envelopes”and the analysis of urban DEMs[J]. Computers, Environment and Urban Systems,2009(33):26-34.  Figure 5. Simulation results of solar insolation time of three models  7 ISUF 2020 Cities in the Twenty-first Century Ahmad Okeil. A holistic approach to energy efficient building forms[J]. Energy and Buildings,2010(42):1437-1444 A. Vartholomaios. The residential solar block envelope: A method for enabling the development of compact urban blocks with high passive solar potential[J]. Energy and Buildings, 2015(99):303-312. CORRESPONDING AUTHOR Jingiin li, Lecture,School of Architecture, Southeast university, 2#Sipailou, Nanjing,Jiangsu province,210096,China. seuljj@163.com  

A compact urban block design method based on 'Solar Envelope' - case study in Nanjing

https://epubs.utah.edu/index.php/ISUF2020/article/download/4236/3618

A compact urban block design method based on 'Solar Envelope' - case study in Nanjing

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