solar access shading and building form geometrical study of the traditional housing cluster in sanaa

8/14/2019 Solar Access Shading and Building Form Geometrical Study of the Traditional Housing Cluster in Sanaa

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S O L A R ACCESS~SHADING A N D B U I L D I N G F OR M : G E O M E T R I C A LSTUDY OF T t lE TI~XD!TIONAL HOUSING CLUSTER IN SAN A'A

K H A L E D A . A L - S A L L AL, PH.D.

Faculty of Engineering, Departmer, of ArchitectureSana 'a , Republ ic of Yemen

A B S T R A C T

The study emp loys three-dimensional compu ter modeling for visualizing the solar access and shading inthe tradit ional housing d ust er o f Sa na'a historical ci ty. I t investigates the geometrical relat ionships amongthe building form and the sun location, and motion, in the crit ical t imes of the year I t also investigates themethods for controll ing the different componen ts of the solar energy (solar radiation, sunlight , daylight)and i ts potential impact on the thermal performance of the houses. I t analyzes the results and establishesdesign rules of thumb that are graphically and textually described. The rules of thumb are valuable designtools in the ini t ial s tages of design and for evaluating design al ternatives or exist ing buildings.

K E Y W O R D S

Solar access; solar shading; solar heating; three-dimensional modeling; San a'a architecture

INTRODUCTION

To maintain com fort with minimal cost , the people in Sa na'a have depended on guidelines and rules ofthumb for orienting and shaping their ci ty, buildings, and bu ll in g elements for hundreds of years. There

has not been any kind o f studies that investigate the solar access and sb.ading for buildings in Sana 'a. As acontribution for exploring the values of the v ernacular arc.Ntectnrc in Yemen, this study exp lores theissues of solar access and shading in the housing cluster of the historical ci ty of San a'a. The objectives ofthis study are threefold: to plot and e~am ine the solar access and shading in a selected case study ofhousing cluster, to analyz e i ts performance w ith respect to solar heating, shading, and daylighting, and todevelop and present the rules of thumb in formats that can aid the architectural design. The most chal-lenging demand for solar access in Sa na'a is solar space heating in winter. Sola r access for domestic hotwater can be easier to achieve because much o f the solar collection occurs during the higher sun angles ofspring and summer. Access for daylighting is also less demanding because of the year-round use of thesun and because of both diffuse sky radiat ion and reflected sunlight are useful. Thus, daylighting can beachieved with co nsiderably less solar access than for space heating. I t is generally agreed that solar accessshould be maintained, if possible, from 9 AM to 3 PM during the winter months. During those six hoursove r 80% of a w inte r's day total solar radiation will fall on a bu ilding (I_e, hner, 1991.)

Tile tradit ional housing du ster contains several tower houses that surround the urban garden and at tached

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Fig. 1 Shadow pattern of a pole, cast on south wall (a) and cast on southeast wall (b).

to the social square and the road. Some of these housesreach up to ni ne floors; yet, the majority are three to f ivefloors high. They were bui lt of squared black volcanic stoneon the lower levels, and of baked brick above that (Lewcock,1986; I_~me, 1~,~8.) Sana' a house looks outwards in order toprovide its occupants with fascinating views and access tothe comfortable climate. Being a tower building and lookingoutwards gives the windows of the old S ana 'a house asignifi cant role. They are responsible to provide the occu-pants' needs of daylighting, winter heating, summer cooling,outdoor view, and aesthetics (AI-Sallal and Cook, 1992.)The selection of a housing cluster for the study depended

primarily on the availabili ty of data. The one selected,however, was judged to be sufficiently representative for thetypical housing duster in Sana' a and appropriate for thepurpose of the study. It contains a garden in the center of thecluster surrounded by tower houses at the north and north-east sides, a mosque at the northwest side, and the marketand caravanserais at the south and east sides. The garden islinked to the road that includes another row of houses fromthe north side. The road is linked to the social square whichexists i n the northwest side and includes al-Shahidaynmosque and other houses.

SHADOW PATTERN

A shadow pat tern is a composite of all shadows cast duringthe winter hours when access to the sun is most valuable.The shadow pattern of a pole (area = lm x lm, height = 12m) at 9:00 AM, 12:00 Noon, and 3:00 PM for the wintersolstice day, December 21, was determined using computermodeling, as seen in lower part of Fig. l(a). The upper partof Fig. l(a) shows the shadow for these hours cast on avertical wall. The clear distance between this wall and thepole was determined, as 6 m, so that the shadow cast on thewall did not exceed the height of two floors (the averageheight of two floors in a vernacular Sana 'a house is 6.5 m.) Fig. 2 Shadow pattern on December, 21

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along the south-southwest boundary of the garden does not block the south sun from the housing sectionbecause they are single story buildings. The placement of the mosque on the south side of the socialsquare does not block the south sun from the housing section that exists around the social square. That is

because of the relatively low height of the mosque that balances with the north-south depth of the socialsquare. The road directions of the case study maximize solar access to buildings because the roads runmostly east-west which allow the sun to reach south facades. In fact, placing the roads along the east-westaxis was dominant in most parts of the Mstofical city of Sana'a. The size and proportion of the garden andthe social square permit appropriate solar access to the housing sections located along their boundaries.That i s because the dimension of any side of the garden or the social square boundaries exceeds the mini-mum clear distance, 6m, explained in section Shadow Pattern. Also, the proportion of east-west to north-south dimensions (1.66:1) of the garden m~'dmizgs south solar access to large number of buildings. Thenarrow roads i n some parts of the case study hinder the solaraccess for some buildings.

CONCLUSION AND RECOM~IviENDATiON

o The mare activity spaces in the Sana 'a house should beoriented toward south and the service spaces should beoriented toward north with minimal openings.

Buildings that are most demanding for solar accessshould be placed along the north-northeast boundary ofthe urban garden or the social square.

Buildings that are one to two floors high, such as themarketplace, should be placed along the south-southwestboundary of the urban garden or the social square.

Roads should run east-west in order to allow south solaraccess for maximum number of buildings.

For four-floors buildings dominated areas, the roads thatrun east-west should not have less than 6m width and theroads that run northeast-southwest, or northwest-south-east, should not have less than 9m width. The samemethod can be applied to determine the appropriate roadwidths for high building dominated areas.

REFERENCES

A1-Sallal, K. A. and J. Cook (1999.). Sana' a historicalwindows: integration between comfort and aesthetics. InProceedings of 17th National Passive Conference ofAmerican Solar Energy Society (S. Bur ley and M. E.Arden, ed.), Vol. 17, pp. 197-202, ASES, Boulder.

Lechner, N. (1991). Heating, Cooling, Lighting: DesignMethods forArchitects. Wiley Inc., New York.

Lewcock, R. (1986). The Old Walled City of Sana 'a.

United Nations Educational, Scientific, and CulturalOrganization, Paris.

Lane M. B. (1988). Sana'a : Pilot Restoration Projects.UN-DPiUNESCO YEM,'88/O06

Fig. 4 Shadow pattern on June, 21.

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solar access shading and building form geometrical study of the traditional housing cluster in sanaa

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