Assessment of the Effect of Modern Transformation on the Traditional Settlement ‘Ksar’ of Ouargla in Southern Algeria
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Frontiers of Architectural Research (2013) 2, 322–337 Available online at www.sciencedirect.com www.elsevier.com/locate/foar RESEARCH ARTICLE Assessment of the effect of modern transformation on the traditional settlement ‘Ksar’ of Ouargla in southern Algeria Moufida Sebtia, Djamel Alkamaa, Ammar Bouchairb,n aResearch Laboratory LACAMOFA, Department of Architecture, University Mohamed Khidder Biskra, Biskra 07000, Algeria bResearch Laboratory CBE, Department of Architecture, University of Jijel, East of Algeria 18000, Algeria Received 18 February 2013; received in revised form 16 May 2013; accepted 17 May 2013 KEYWORDS Abstract Ksar; The architecture of the Ouargla Ksar has long been recognized as an example of adaptation to harsh Traditional settle- climate in the deep desert of Algeria. Over the last few decades, it has undergone some changes in ment; its initial urban structure, due to accelerated and uncontrolled modern urbanization, that had Ouargla; negative implications and devaluation of its thermal characteristics. This article tries to understand Desert; the bioclimatic concept of adaptation of this Ksar and assess to what extent its morphological Transformed; transformation has impacted its microclimatic conditions. This assessment is made through a Comfort comparative study between two different areas: one untransformed and the other transformed. A referential weather station situated in the suburbs was also exploited for consolidation of comparison. The investigation was undertaken using site measurements and observations. & 2013. Higher Education Press Limited Company. Production and hosting by Elsevier B.V. All rights reserved. 1. Introduction centuries to guarantee its survival within the climatic constraints of southern Algeria. The climate has been the fl The Sahara, from the Neolithic era, has always been an area foremost environmental factor that in uenced the evolu- of great change. Man has adapted and persisted through the tion of vernacular settlements and building design. It is well known that southern Algeria is one of the most arid lands of the world. The prevailing outdoor environmental conditions fl nCorresponding author. Tel.: +213 34502688; fax: +213 34502688. that in uence inhabitants comfort are mainly of four types: E-mail addresses: [email protected], high temperatures and intense solar radiation; high glare fl [email protected] (A. Bouchair). from direct and re ected sunlight; dust storms, mainly in Peer review under responsibility of Southeast University. the afternoons; in some regions with cold winters, cold winds in the winter season; low annual rainfall, torrential rain causing severe floods. In general the south of Algeria has a typical desert climate with variations between seasons 2095-2635 & 2013. Higher Education Press Limited Company. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foar.2013.05.002 Assessment of the effect of modern transformation on the traditional settlement ‘Ksar’ 323 and between day and night temperatures. The climate is (few days per year) and the relative humidity is low hot and dry during the summer with cold nights and mild especially during the summer. Wind is the main factor for days during the winter. The rainfall occurs mainly in winter the desert topography. Sandstorms occur during certain Figure 1 Location of the wilaya of Ouargla, Algeria. Table 1 Monthly average temperature (period 1997–2008). Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean Mean temperature (1C) 11.6 13.7 17.8 22.5 29.9 32.1 35.7 33.1 30.8 24.9 16.9 12.3 23.44 Table 2 Monthly average rainfall (period 1997–2008). Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean Mean rainfall (mm) 11.13 0.92 3.46 4.03 1.29 0.13 0.58 1.56 5.58 13.4 7.53 2.71 52.3 Figure 2 Location of the Ksar in the city of Ouargla. 324 M. Sebti et al. times of the year, usually in March and April. Regarding the internal migration from one time of day to another, or from Sirocco, it occurs at an average of 10 days/year during the one season to another, between parts of the house or areas period from May to September months. Protection against that provide more comfortable indoor conditions. the devastating effects of wind on the inhabitants has The basic factors influencing thermal comfort are the become a major problem to deal with. The use of screens surrounding air temperature, radiant temperatures of the and obstacles is one of responses. Under these harsh surrounding surfaces, humidity of the air, and air move- conditions and inhospitable surroundings the vernacular ment. In order to illustrate how thermal interactions affect settlements survive using passive means to provide comfort human comfort, the explanation below describes the body of inhabitants as demonstrated by Bouchair and Dupagne temperature control mechanisms and how environmental (2003) and Bouchair (2004). In addition to the use of climate conditions affect them. For example, when we are uncom- responsive buildings, people adapt their behavior and activities to the diurnal or seasonal climate changes: the Street Palm grove Palm grove Cul-de-sac Dwelling Road Gate Gate Gate Figure 5 Typical tissue of Ouargla Ksar showing hierarchical Gate arrangement of streets and their irregular form. Market Gate Gate Gate Streets Culs-de-sac Figure 6 Market place occupying a large square with modern Figure 3 Compact cellular layout of Ouargla Ksar. inadaptable building material. Figure 4 (A) Typical cul-de-sac in the Ouargla Ksar and (B) typical covered passage of a street in Ouargla Ksar. Assessment of the effect of modern transformation on the traditional settlement ‘Ksar’ 325 Figure 7 Modern transformations within the Ksar: (A) extension above street in the Ksar and (B) insertion of collective housing. Figure 8 Measurement instruments: (A) environment meter 8820 and (B) hot-wire anemometer. fortably hot in the direct light of the sun, we can cut off the of sight of the body. If the MRT is below the body radiant energy coming directly from the sun by stepping into temperature, the radiant heat is a positive number, and the shade of a tree. Since air is a poor absorber of radiant the body is losing radiant heat. If the MRT is above the body heat, nearly all radiant exchanges are with solid surfaces to temperature, radiant heat is negative, and the body is which we are exposed. Radiant heat may travel toward or gaining radiant heat. away from a human body, depending on whether the It should be kept in mind that the body loses radiant heat radiating temperatures of surrounding surfaces are higher according to its surface temperature. For a comfortable, or lower than the body's temperature. In a cold room, the normally dressed adult, the weighted average temperature warmer body or its clothing transmits radiant heat to all of the bare skin and clothed surfaces is about 27 1C. In still cooler surfaces such as walls, glass, and other construction air at a temperature near skin temperature, radiant within view. If there is a cold window in sight, it will exchange is the principal form of heat exchange between typically have the largest impact in terms of draining heat the body and its environment. The MRT affects the rate of away and making the body feel colder. By closing the radiant heat loss from the body. Since the surrounding drapes, a person can block the radiant transfer in the same surface temperatures may vary widely, the MRT is a way that a person can cut off the radiant energy from the weighted average of all radiating surface temperatures sun by stepping into the shade of a tree. The rate of radiant within line of sight. It can be calculated as follows: transfer depends on the temperature differential, the MRT=∑(Tθ)/360, where T is the surface temperature and thermal absorptivity of the surfaces, and the distance θ the surface exposure angle (relative to occupant) in between the surfaces. The body gains or loses heat by degrees. radiation according to the difference between the body The thermal effect of humidity on the comfort of surface temperature and the MRT of the surrounding sur- sedentary persons is small, that is, comfort is maintained faces. The mean radiant temperature (MRT) is a weighted over a wide range of humidity conditions. In winter, the average of the temperatures of all the surfaces in direct line body feels no discomfort over a range of relative humidity 326 M. Sebti et al. Trajectory 2: Transformed tissue Trajectory 1: Untransformed tissue Figure 9 Locations of the two trajectories investigated in the Ksar of Ouargla. Covered passage Cul-de-sac 1 Cul-de-sac 2 Road Square Meteorological station 46 44 42 40 38 36 34 32 Teperature (°C) 30 28 26 05 09 12 17 21 Mean Time (h) Figure 10 Position of measuring points on trajectory 1. Figure 12 Variation of air temperature in trajectory 1 Covered passage Cul-de-sac 1 Cul-de-sac 2 Road Square 46 44 42 40 38 36 34 32 Teperature (°C) 30 28 26 05 09 12 17 21 MEAN Time (h) Figure 11 Position of measuring points on trajectory 2. Figure 13 Variation of radiant temperature in trajectory 1. Assessment of the effect of modern transformation on the traditional settlement ‘Ksar’ 327 Table 3 Variation of air temperature in trajectory 1. Measurement points Designation Time of the day Mean temperature 05 h 09 h 12 h 17 h 21 h 1 Covered passage 32.7 35.1 41 38.5 36.1 36.68 2 Cul-de-sac 1 32.7 35.1 40.4 40 36.2 36.88 3 Cul-de-sac 2 32.6 35.2 40.6 41.2 36.9 37.3 4 Road 32.3 35.5 40.6 40.1 36.3 36.96 5 Square 32 36 43.6 40.6 36.2 37.68 Mean 32.46 35.38 41.24 40.08 36.34 37.1 Meteorological station 28 40.1 42.8 41 34.3 37.24 Table 4 Variation of radiant temperature in trajectory 1.