climatic aspects in urban design—a case study

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Building and Environment 38 (2003) 827–835

www.elsevier.com/locate/buildenv

Climatic aspects in urban design—a case study

Isaac G. Capeluto∗, A. Yezioro, E. ShavivFaculty of Architecture and Town Planning, Technion—Israel Institute of Technology, 32000 Haifa, Israel

Received 11 December 2001; received in revised form 13 February 2002; accepted 21 February 2002

Abstract

We present a case study of a design of a new business district in Tel Aviv city. In this work climatic aspects were taken into considerationin the very early design stages. For that purpose, two models SustArc (Proceedings of the ISES 1997 Solar World Congress, Taejon,Korea, 1997, p. 148) and FLUENT 5.0.2 (Fluent’s User’s Guide, Fluent Inc., NH, USA, 1999) were applied in order to achieve solar andwind rights. The new business district was designed as a high-density urban area and is located near an old low-rise residential quarter.SustArc was used as a design tool to create the solar envelope that shows the maximum available volume in which it is possible to buildwithout violating the solar rights of existing residential neighborhood, the main avenues and the pedestrian sidewalks. FLUENT, on theother hand, was implemented as an evaluative tool, in a trial and error method, until a design solution could be achieved, in which thewind rights of the residential neighborhood were preserved, while ensuring tolerable winds inside the business district. The paper presentsthe process of sun and wind controlled planning, as well as the recommendations. ? 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Solar rights; Wind rights; Urban design; Design tools

1. Introduction

During the conceptual design phase of urban districts, thedesigner deals with diAerent geometrical characteristics re-lated to the building’s height and width, in relation to theopen spaces and the pedestrian sidewalks. New buildingsmay create a diAerent microclimate, like changing the windregime and shading of existing neighborhoods, as well asin the new district. To protect solar rights, as well as windrights, is a complex task. Moreover, tolerable winds shouldbe achieved along the pedestrian sidewalks. The determi-nation of a preferable design solution becomes speciallycomplicated due to mutual inCuences. On the other hand,ignoring the solar rights at the stage of the preparation ofthe master plan may cause discomfort conditions around thebuildings beyond repair.DiAerent design tools for solar insolation conscious design

were developed. We can classify these tools into generationtools and evaluation tools. The generative design tools aidto deEne the proper geometry. Some examples are [1–6] fordetermining solar rights. These tools generate nomogramsthat present all possible solutions to a given problem. These

∗ Corresponding author. Tel.: +972-4-829-4013; fax: +972-4-829-4617.

E-mail address: [email protected] (I.G. Capeluto).

nomograms are called “Solar Envelopes”. The evaluationtools, on the other hand, analyze the performance of a givendesign. Some examples are Kroner and Abrey [7], Yezioroand Shaviv [8,9] and Capeluto and Shaviv [5] for evaluatingsolar rights for buildings and in open spaces among them.Heliodons are also used to evaluate the proposed design,namely a scaled down 3D physical model examined in thelaboratory.For microclimate and wind rights conscious design, there

are today only evaluative design tools. These are either windtunnel studies, or computational Cuid dynamics (CFD) sim-ulation tools. The CFD models are very powerful, requireheavy calculations, but provide detailed results that can showclearly the defects in suggested designs. As a result, new de-sign alternatives may be thought of and re-evaluated, untila good and satisfactory design is achieved.In the design of the new business district in Tel Aviv

(Fig. 1), we have used SustArc, as the design tool to evaluatethe proposed design (Fig. 2). We have also used SustArc tocreate the solar envelope that shows the maximum availablevolume in which it is possible to build while keeping thesolar rights of the existing neighborhood (Fig. 5). We usedFLUENT to evaluate the existing situation, the proposed so-lution and the mitigation design, in which the wind rights tothe residential neighborhood were preserved, while ensur-ing tolerable winds along the pedestrian sidewalks (Figs. 8

0360-1323/03/$ - see front matter ? 2003 Elsevier Science Ltd. All rights reserved.PII: S0360 -1323(02)00063 -X

828 I.G. Capeluto et al. / Building and Environment 38 (2003) 827–835

Fig. 1. An aerial view of the business district.

and 9). The paper presents the design process along withthe diAerent design tools implemented to create the solu-tions and to simulate and evaluate the proposed design. Us-ing these tools we could develop rules and design guidelinesthat ensure proper insolation and ventilation in the existingresidential neighborhood as well as creating good microcli-matic conditions inside the new business district.

Fig. 2. Sun-view presenting the shading of the main green avenue (the area adjacent to the tall buildings from the right) and the residential neighborhood(the long square on the right).

2. Sun, winds and urban design

There are many places in which urban design take intoconsideration solar rights and winds protection. Let us men-tion a few: New York, Boston, Chicago, Philadelphia, Pitts-burgh and San Francisco, in the USA, Calgary, Edmonton,Halifax, London, Montreal, Ottawa and Toronto, in Canada[10]. Many tall buildings were built during the past in all ofthe above cities. These tall buildings caused diAerent prob-lems, like shading, loss of daylight, and creation of strongwinds around the tall buildings on one hand, and at the sametime avoid good ventilation by creating wind stagnation atsome parts around them. From the accumulating experience,the city leaders and designers recognized the need to con-trol the changes in the microclimatic conditions created bya proposed design. In many cities, large projects, includ-ing tall buildings, require wind studies, as well as shadingevaluation. Nevertheless, in most places, the planning con-trol for wind protection and solar insolation are not manda-tory and are not imposed by standards, but rather open tonegotiations with the developers.DeEning urban standards can be carried on along three

diAerent approaches [10]:

a. Prescriptive and descriptive standards, in which the ex-act physical solution is given. For example, the speciEcmaximum height of buildings in the inner city neighbor-hood of San Francisco is dictated along with the angle ofthe slope of a plan that cut the upper Coors further fromthe street.

b. Performance standards, in which the expected perfor-mance of the design is given. For example, Boston zoningordinance dictates for some downtown areas, that “Nonet increase in shadow is permitted between 8 a.m. and

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2.30 p.m.”. In San Francisco for example a performancestandard is set for the maximum allowed wind velocity sothat “a building formwhich causes wind speeds to exceed11 miles=h in areas where people walk and 7 miles=h inareas where people sit, should not be used”.

c. Discretionary review, in which a comprehensive studyis required as part of the environmental impact study(EIS) process. For example, in New York, sponsors oflarge development projects are required to conduct windstudies. The expected wind velocities in new or existingopen spaces shall not exceed the mean wind velocity inexisting comparable open spaces.

There are not yet urban standards and legislation in Israelabout howmuch a building can shade neighboring buildings,open spaces, or what is the maximum allowed wind speed.As for solar rights, we were contracted to develop legislation[11] and we hope that our future recommendations will beimposed. However, in many cities, the Israeli ministry of theenvironment demands from every developer, who intends tobuild high-rise buildings, a discretionary review for windsand shading, as part of the EIS. As there are not yet urbanstandards, the results of the study are not always imposedon the project.The shading study is usually an evaluation process, carried

by diAerent computer codes, while the wind assessment isin most cases a wind tunnel study. In the following chapterwe shall demonstrate the approach to deal with planningcontrol for sun access and wind access and protection [12]that was carried out in the design of a new business districtin Tel Aviv.

3. Planning control for sun and winds in a new businessdistrict

A new business district is being planned in the heart ofTel Aviv on an area of 250; 000 m2. The urban density waschanged from 200% to 450%. As a result, the developerswish to build in the area many high-rise buildings 40 sto-ries and above. Existing low-rise residential buildings thatsurround this new business district will be aAected by thehigh-rise buildings (see Fig. 1).The new master plan of this district was not approved yet,

and the residents of neighboring communities can submitobjections to the new plan, which they did. The designersof the Tel Aviv City planning department produced a 3Dmodel of the site, in which they assumed that all developerswould build the maximum allowed (a likely outcome). Themodel allows the visualization of the spatial drawbacks inthe preliminary design. In particular, it was found that thenew buildings create a high wall that would deprive the sunand winds (coming mainly from west) from the existingbuildings (Fig. 2). Therefore, the designers of Tel Aviv Cityplanning department decided to adopt certain rules for thedesign of this new business district so as to ensure sun andwinds in the existing residential neighborhood.

The Tel Aviv climate is hot and humid, and the sea breezehelps in summer to bring about thermal comfort in openspaces, as well as indoors. Therefore, the proposed high-risebuildings should not block the sea breeze. Moreover, tallbuildings can create strong winds at the foot of the buildings.This fact complicates the situation, as near tall buildings thewind velocity may change very fast from extremely strongwind to no breeze at all.The sun in Tel Aviv is undesirable in summer but it can

cause any open space and parks to be a very pleasant and en-joyable place to stay in winter. Therefore, permanent shad-ing, even if needed in summer, compromises winter sun. Adynamic solution, like shading open spaces and sidewalks insummer by deciduous trees that supply winter insolation, ispreferred. In general, at least one pedestrian sidewalk shouldbe exposed to winter sun to provide thermal comfort in win-ter. The other sidewalk, which is shaded by the building inwinter, can be protected from the summer sun by permanentshading devices, or by evergreen trees. On top of it, in Is-rael there is a requirement by law, for every residential unit,to have solar panels for hot water. It is mandatory, there-fore, that these panels will be exposed to the sun the yeararound.

4. Planning control for sun access

“Solar Rights Envelope” deEnes the space of all possiblesolutions for the determination of a design that does notviolate the solar rights of existing buildings and open spacesduring a given period of the year (See Fig. 3). The modelSustArc creates such an envelope [5,6].In the design of the new business district, the use of so-

lar envelopes was recommended to protect the solar rights.The requirement was to achieve solar access during the en-tire winter, between 8 a.m. and 3.00 p.m., in the residen-tial neighborhood, as well as in the main avenue that is theonly existing green open area. The solar envelope that ful-Ells the above requirement, as well as the obtained shape ofthe buildings under this envelope, are presented in Fig. 4.Although the requirements were only to ensure solar ac-

cess to the residential neighborhood, we added the demandthat the main two avenues from west to east will be exposedto the sun during the same period. This is in order to en-sure that the morning and afternoon walk from the railwaystation to work, is in the sun (see Fig. 6). On top of it, werequired that the main inner street parallel to the main greenavenue would have solar access during lunchtime from 12.00to 13.00. These requirements will allow the people to enjoywalking in the sun to the two avenues (A and B in Fig. 6)that lead them to the main green avenue, to have lunch in thegarden, or in the planned restaurants along the green avenue.Fig. 5 presents the solar envelope that was accepted as

design guidelines for the relocation or reshaping of the tallbuildings in the business district. All buildings higher thanthis envelope (these are the buildings that can be seen above


Fig. 3. The solar rights envelope.

Fig. 4. The solar envelope that ensure solar rights in the existing residential neighborhood as well as in the main green open space.

Fig. 5. The solar envelope that ensure solar rights in the existing residentialneighborhoods as well as in the main avenues and streets.

the net of the envelope) must be displaced to another loca-tion, or should be reshaped (see Fig. 6). This is a descrip-tive approach, in which all possible consistent solutions are

Fig. 6. The maximum allowed Coors for each building, keeping solarrights in the existing residential neighborhoods as well as in the mainavenues and streets.

given in advance. However, we mixed the descriptive ap-proach with the performance one, by allowing some excep-tions, as long as the shading caused by these buildings is notabove a given standard. But, till such standard will exist, adiscretionary review approach might be necessary.Based on these design guidelines a new scheme was sug-

gested by the city planners, that follows the solar envelope


Fig. 7. Design guidelines on building mass as proposed by the city planners. View from south–east.

(see Fig. 7). Until now, few tall buildings have already beenrelocated and reshaped, so that they will not stick out fromthe given solar envelope.

5. Planning control for wind access and protection

Contrary to other cities, where the requirements were onlyto protect from high wind velocity around tall buildings, thedemand in our case was to ensure good ventilation to theresidential neighborhood located east to the business cen-ter. The situation today is, that in the business district, mostof the buildings are seven Coors high and are in a verybad physical condition. Therefore, the majority of the build-ings should be demolished and replaced by new ones. Theonly exception is the Erst row of buildings near the free-way that are seven Coors and new. Today, one can feel inthe neighboring residential quarter the good breeze comingfrom the west. The proposed new tall buildings, thirty Coorsand above, may block the breeze. As a result, the residentsof this quarter objected to the new design on the groundof wind rights. The question that was raised, therefore, waswhat should be the ventilation corridors inside the businessdistrict tissue, so that good natural ventilation will remainin the residential neighborhood, as well as in the new busi-ness district. This fact complicated the situation, as in manydesign alternatives the very solution for ensuring the breezein the residential quarter, may cause excessive winds in thebusiness district (see Figs. 9 and 10).There are not yet design tools that can create the enve-

lope of all possible solutions that satisfy wind requirements,or wind protection. Therefore, performance approach andevaluation technique were applied by using a CFD simula-tion model FLUENT 5.0.2 [13]. We required the following:wind velocity in the main avenues and streets should be insummer at least 2 m=s in walking areas, and 1 m=s in sit-ting areas. In winter, wind velocity in the main green av-

Fig. 8. The wind rose as measured in site.

enue should not be higher than 5 m=s in walking areas and3:5 m=s in sitting areas. In other streets, where people movefast, it can reach up to 9 m=s . In the residential neighbor-hood, the breeze should be similar to what exists today.FLUENT is a very powerful tool. It requires heavy cal-

culations, but gives detailed results that can show the windpattern in any plan or cross-section (see Figs. 9 and 10).We used FLUENT with the k–� turbulence model, to eval-uate the existing situation. We compared it with the pro-posed design (Fig. 9) and with the design based on the solar


Fig. 9. Simulating winds in the business district by using FLUENT: Top left—existing situation. Top right—proposed design. Bottom—parametric analysis.

envelope (Fig. 10). Many diAerent design alternatives wereproposed and evaluated, until a design solution was found,in which the wind rights of the residential neighborhood arepreserved while ensuring tolerable winds inside the businessdistrict.

As the buildings are not yet designed, and for the mas-ter plan only general information about the mass of thebuildings is required, we assumed simple shapes, and con-ducted parametric evaluation, in order to End the inCuenceof each design option on the wind pattern. Also, as the


Fig. 10. Simulating winds in the business district by using FLUENT: Top left—existing situation. Top right—proposed design according to the Solarenvelope section. Bottom left—parametric analysis: Seven Coors buildings along the pathway. Bottom right—parametric analysis: Adding trees at theentrance of the ventilation corridor.

simulations are CPU time intensive, we shorten the eval-uation procedure by presenting in the same plan diAerentwidths for the ventilation corridors, as well as diAerentwidths for the north–south streets. In this way we could

learn from the same run, what is the preferred width of theventilation corridors.Fig. 8 presents the standard meteorological wind mea-

surements on site, 10 m above the ground. From this Egure


Fig. 11. Ventilation corridors as requested by the city planners.

one learns that the desired winds in the hot seasons comemainly from the west and northwest and in general the windvelocity is about 3:5 m=s. To ensure wind rights, we carriedsimulations for these two directions. In all simulations weassumed a wind proEle appropriate for the urban roughnessand wind velocity of 3:5 m=s at the entrance.Figs. 9 and 10 show few of the simulations results and

only for winds coming from the west. In general, the windcoming from northwest gave better results than what isshown here. Figs. 9 and 10 top left present the existing situ-ation; i.e. all buildings are seven Coors high. The widths ofthe north–south streets are 16 and 36 m according to the ex-isting situation and widths of the east–west streets are 36, 24and 12 m. The latter are the ventilation corridors that shouldallow the sea breeze to reach the residential neighborhood.According to the wind pattern obtained, we required thatthe north–south streets should be at least 36 m in order notto have wind stagnation in the street. The ventilation corri-dors should be at least 24 m, preferable 36 m. For the 12 mwide ventilation corridor, the wind velocity in the residen-tial neighborhood is too low, even in the existing situationof seven Coors high buildings. Therefore, we deEned thewind pattern examined area as the area east to the 24 and36 m ventilation corridors only. Based on these recommen-dations ventilation corridors were designed and required bythe city planners (see Fig. 11).Fig. 9 presents the simulation results for the proposed de-

sign (top right) and parametric analysis for mitigation (bot-tom left and right). We can see that cutting the building in45◦ at the exit of the business district, improves the ven-tilation in both the main green avenue and the residentialneighborhood (bottom left). On the other hand, changing theplan of the middle tower from square to round deterioratesthe microclimate conditions.Fig. 10 presents the simulation results for the proposed de-

sign according to the solar envelope section (top right) andparametric analysis for mitigation (bottom left and right).We can see that the design according the solar envelopepreserves also the wind rights. However, the wind velocity

along the east–west pathway is too high, and should be re-duced. Adding seven Coors high buildings along the 36 mwide pathway, reduces the high velocity wind speed in thispathway, but also reduces a little bit the wind velocity inthe residential neighborhood. Adding trees at the entranceto the ventilation corridors reduces the wind velocity insidethe ventilation corridors, and also in the residential neigh-borhood. However, the wind pattern obtained is quite satis-factory (bottom right).

6. Summary and conclusions

This work presents a case study in which, for the Ersttime, the solar rights envelope was used in Israel for the de-sign of a new business district in Tel Aviv, keeping solarrights in a high-density urban area. Using this solar envelopewe could determine the maximum allowed heights of thebuildings that ensure proper insolation in the existing resi-dential neighborhood as well as in the new business districtand the main green avenue. The requirement to build underthe solar envelope is a prescriptive=descriptive approach.To protect both, the solar and wind rights, the solar en-

velope was created Erst, this envelope was then evaluatedusing a CFD technique to ensure the wind rights and tol-erable winds inside the business district. From the manysimulations performed (only few of them shown here) wefound that it is not easy to use the prescriptive=descriptiveapproach, as was done in the solar rights requirement. Onlyfor the determination of the geometry of the ventilation cor-ridors to ensure wind rights, such an approach can be ap-plied. However, for the wind control, a standard performanceapproach should be applied. This is because the winds pat-tern depends on the exact geometry of all buildings around.Changing the geometry of one building can inCuence thewind pattern around other buildings. Therefore, performancestandards should be established, and the wind pattern aroundthe building should be evaluated against these standards, bycertiEed tools and users.


Acknowledgements

This research was supported by the fund for promotionof research at the Technion. Research Number 022.732, and022.751.

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climatic aspects in urban design—a case study

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