The Dark Sides of the Modern Urban Design in the Persian Gulf Region

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1 The Dark Sides of the Modern Urban Design in the Persian Gulf Region MASOUD DALMAN 1, E SALLEH 2, OMIDREZA SAADATIAN* 2, CH. LIM 2, K. SOPIAN 2 1 Islamic Azad University- Bandar Abbas Branch, Iran 2 Solar Energy Research Institute (SERI) Universiti Kebangsaan Malaysia 436 Bangi, Selangor MALAYSIA *Corresponding author: omid.saadatian@gmail.com, Abstract: -- The Persian Gulf region grows rapidly due to the revenues gains from huge oil and gas recourses exploitations. This growth is sensible in all aspects of peoples life as well as in the design of urban areas. Taking the city of Bandar Abbas as a case study, this paper investigates modern urban fabric and vernacular urban fabrics by using thermal comfort and Computational Fluid Dynamics (CFD) methods. The results of this study imparts that modern urban fabrics are worse than vernacular urban fabric in term of thermal comfort. The results are beneficial for urban designers and policy makers of all countries of the Persian Gulf regions. Keywords: Persian Gulf regions; modern Urban Fabric, thermal comfort, CFD Nomenclature Mean radiant temperature from longwave and diffuse short-wave radiation MRT* (not including direct-beam radiation) ( C) Surface projection factor of a standing f p or walking person Beam radiation (on a plane I p perpendicular to the beam)( W/m 2 ) Average (short-wave) absorptive of the a k human body=.7 ε p Emissivity of the human body= W/m 2 K 4 (the Stefan-Boltzmann constant) ε i Emissivity of the surface T s,i Surface temperature (K) I d,i Diffuse radiation(w/m 2 ) F i View factor of the surface 1. Introduction The city of Bandar Abbas is located on a flat ground with 1 m above mean sea level at latitude of 27 11' N and a longitude of 6 22'E. This city experiences eight-months of extreme heat from April to November[1]. This city is the biggest port of Iran located in northern part of Persian Gulf and has experienced a rapid growth of urban area [2, 3]. This rapid growth has caused drastic changes in urban microclimate that has adverse impacts on human thermal comfort in the hot period of summers [3]. There are very few studies on the climate response in urban planning and design during hot and humid periods [4]. Therefore, the necessity of urban climate studies in the mentioned regions could be a big concern of the urban planners and designers. This study aims to find out a relation between thermal comfort situation and microclimatic characteristics of urban canyons within different fabrics in the hottest period of summers and to determine the role of the urban canyon orientation and dimension on wind circulation. 2. Theory and backgrand Existing literature supports the influence of urban design on cities thermal comfort conditions []. In this regard, this parameter is modified by the urbanized landscape as a whole, and by the physical design features of an urban canyon[6]. As another theory, Sellers ascertains the impacts of various features of the physical structure of ISBN:

2 the cities on the urban climates[7]. It is believed that urban climate and outdoor thermal comfort at the street level are significantly influenced by urban form [8]. It is imparted that the relationship between urban design and outdoor thermal comfort in hot and humid climates should be understood for developing appropriate climate-oriented urban design guidelines. Urban thermal comfort is significantly influenced by affecting factors including Height-to-Width (H/W) ratio of the urban canyons, street orientations, ground covers, and distance from the shore. However, Givoni believes that this effect mostly depends on the arrangements of buildings with different heights in the cities [9]. He suggests that urban climate should be controlled by urban planning and design since the structure of the city can be controlled by urban features. He also ascertained that buildings in urban area usually have thermal comfort problems due to their poor planning and climate consideration. Based on the latter discussion, the most important factors in urban thermal comfort are the influence of wind gustiness and Mean instantaneous wind speed. 3. Material and methods Computational Fluid Dynamics (CFD) simulations of wind speed are conducted as predictive models. A comparative investigation was conducted to discover the impacts of urban forms and layout on variation of the microclimatic factors and thermal comfort situation in modern fabrics and vernacular fabrics. Both selected areas are located near the sea shore. The two selected different fabrics are separated by an N-S street in South east of Bandar Abbas. Table1.Fabrics specifications Fabric Vernacular 1 Area (Hectare) Perimeter (Meter) Pathway coverage ratio (%) Buildings coverage ratio (%) % 74% Sit e H/ W Rati o 1. Prevailin g Orientati on WSW- ENE Ground Cover Asphalt ed 2 1 N-S Sandy Distan ce betwee n fabrics (m) 79 Fabric specificati on Modern Vernacula r Table 3: Modern fabric canyons specifications Canyon H/W Canyo Width( Wall Height(m) Orientatio Rati n m) n o M1 7. M2 1.8 M3 4.8 M4 3.1 S=3. E=3.1 E=4.4 E=3. N=4. W=3. W=7. W=3.4 WSW- ENE SSE- NNW SSE- NNW SSE- NNW There are four selected canyons in modern fabric, namely M1, M2, M3, and M4. The descriptions of these canyons are as follows: Table 4: specifications of the selected canyons in vernacular fabrics Cany on Width( m) T1 3.8 T2 3.2 T3 4. T4 2.3 Wall Height(m) E=3. 6 E=3. 7 N=2. N=3. 3 W=3. 6 W=3. 6 S=3.8 S=3.2 Canyon Orientat ion S-N H/ W Rat io.9 S-N 1.1 E-W.9 E-W 1.4 Modern % 8% (E=Eastern, W=Western, N=Northern, S=Southern) Table2. Inventory of selected canyons ISBN:

3 The Physiological Equivalent Temperature (PET) is introduced as a model, which works based on the Munich Energy-balance Model for Individuals[1]. The basis of PET is the air temperature in a typical indoor setting in which the heat share of the human body balanced with the same core and skin temperature as under the complex outdoor conditions [11]. PET also allows the assessment of thermal conditions in a physiologically significant way. PET as a thermal comfort index; take into account four climate factors that affect comfort conditions: Ta, Mean Radiant Temperature (MRT), RH %, and air movement. Based on the goal of this study which is to compare the thermal comfort conditions of different canyons and fabrics rather than calculating an exact comfort level, the Physiological Equivalent Temperature (PET) index, observed in recent outdoor studies was selected. Although the activity level and clothing rate are not considered in PET index, an index with capability of considering these parameters is not necessary. Because of significantly less variation of such parameters in the study area, the other indices like Predicted Mean Vote (PMV) and Standard Effective Temperature (SET) were only used for comparing the situation [12, 13]. The PET index which is expressed in degree Celsius is calculated using Rayman software (ver. 1.2). Another important factor to calculate comfort condition is MRT. The MRT rate for study urban canyons, according to VDI could be calculated as below:.2 f.. *4 p ak Ib MRT = MRT + ε p. σ.2 n * 1 4 ak. Idj MRT = ( εi. σ. Ts, i + ) Fi σ ε i= 1 p The CFD method was used in order to gain a proper understanding about the likely air flow within different canyons compared to recorded field data. Basically, CFD is about numerical simulation of fluid flow processes and shows the air flow process occurring inside and around building spaces. In the study the following formulas were used to calculate the thermal comfort variables. α met α δ met h u( h) = umet hmet δ Or: V met1 V z1 Where: Where: α met1 metg = α Z1 ZG met δ met = 27 m is the Layer Thickness for the meteorological site (assumed to be of type Country ) α met =.14 is the Exponent for the meteorological site (assumed to be of type Country ) h met = is the measurement height for the meteorological site (assumed to be 1 m) Log Law model: V Z = V Where: ref [log( Z / Z ) / log( Z ref / Z )] V z = the mean wind speed at height Z V ref = the mean wind speed at some Z ref = the reference height Z = the height for which the wind speed V z is computed Z o = the roughness length or log layer constant. Data analysis and results According to calculated comfort indices and microclimate data of the study area, each canyon has different environmental characteristics and consequently comfort situation. Open spaces ISBN:

4 which allow breeze to pass through have better condition of comfort and semi enclosed and enclosed spaces which are not along the prevailing wind and restricted free air flow are in discomfort condition during the summer period. The adapted microclimate and thermal comfort investigation with CFD simulation method serves to articulate the subjective nature of collected field data and to examine the linkages among the referred methods. The calculated thermal comfort indices were estimated for the sample s hottest day of the year in July 1, 21 to indicate the upper limits of comfort zone with air flow of 1 m/s and average data of Ta and RH% obtained during the study period from 1-1 July 21. The highest rate of each index in canyons of vernacular fabric at the peak of the day s temperature is around 3 degrees lower than those of canyons of modern fabric. In general, the canyons with N-S and SSE-NNW orientation show lower rates of calculated indices due to significantly higher rates of air flow. Table presents the maximum and minimum rates of calculated thermal comfort indices for each canyon. Tmrt-C Mean Radiant Temperature Hour T1 T2 T3 T4 M1 M2 M3 M4 Fig 1: Mean radiant temperature (Tmrt) inside the canyons PET(C) Canyon PET(Celsius) Hour T1 T2 T3 T4 M1 M2 M3 M4 Fig 2: PET ( C) inside the canyons PMV PET/ C SET*/ C Min. Max. Min. Max. Min. Max. T T T T M M M M Table : variation of thermal comfort indices during July days (min. and max. values) The discomfort index of eight selected sites in which the data were collected during the hottest period of a year, indicates a discomfort condition during the whole day hours. However, it should be mentioned that air flow and shadow effect, were not considered in this index. The calculated discomfort index for January, compared to July, indicates the different thermal comfort situation in the moderate and the hottest months. ISBN:

5 Fig 3: Discomfort index (DI) in January (entire area) and July for eight canyons These figures present a comparison of two different wind profile modelling conducted according to the study area conditions. The plotted wind profile in the study area shows dissimilar variation of height to speed ratio especially between 2 to 6 meter levels. According to registered data of field measurements (which is in 2 meter height) and Table 6, the ASCE (1999) model is more reliable than ASHRAE. Height (m) Wind profile of study area(ashrae and ASCE) ASCE ASHRAE Wind speed (m/s) Fig 4: Mean wind profile using ASHRAE and Log Law(ASCE,1999) models The simulated and recorded wind speeds have a reasonable relation in terms of calculated mean speed and the calculated correlation coefficient (Table 6). The selected data of recorded and simulated wind speed explains the swing rate hours of wind magnitude in a day. Wind speed rate changed to stronger from 8 a.m. and reaches to peak around 2 to 3 p.m. and then goes to zero m/s around 8 to pm. According to CFD results, the selected canyons shows different characteristics in recorded wind speed but simulated wind speed is more similar to recorded on in all canyons. Figures 14 and 1 indicates the differences in wind speed recorded during study period and shows higher air movements in vernacular fabrics especially between 12 p.m. to 1 p.m. 6. Conclusions It is concluded that modern fabrics function poorer than vernacular fabrics of the Persian Gulf regions. Besides, lower thermal comfort values (PET, PMV, SET and Tmrt) in vernacular fabric canyons with N-S orientations compatible with prevailing southward winds by more than 3 degrees Celsius. Higher wind speeds were registered in N-S oriented canyons compared to other canyons with different orientations. Computational Fluid Dynamic (CFD) and particularly Micro Flo (IESve) software were found to be accurate tools to simulate and predict airflow. References [1] M. Dalman, E. Salleh, A. R. Sapian, O. M. Tahir, K. Dola, and O. Saadatian, "Microclimate and Thermal Comfort of Urban Forms and Canyons in Traditional and Modern Residential Fabrics in Bandar Abbas, Iran," Modern Applied Science, vol., pp. 43-6, 211. [2] A. Burke and M. Elliott, Iran: Lonely Planet, 28. [3] M. Dalman, E. Salleh, O. Saadatian, C. H. Lim, and K. Sopian, "Effects of urban canyons and thermal comfort in persian Gulf," in IEEE Business, Engineering & Industrial Applications Colloquium, IEEE, Ed. kuala Lumpur, 212. [4] O. Saadatian, L. C. Haw, K. Sopian, and M. Y. Sulaiman, "Review of windcatcher technologies," Renewable and Sustainable Energy Reviews, vol. 16, pp , 212. [] E. Johansson, "Influence of urban geometry on outdoor thermal comfort in ISBN:

6 a hot dry climate: A study in Fez, Morocco," Building and Environment, vol. 41, pp , 26. [6] D. Pearlmutter, P. Berliner, and E. Shaviv, "Integrated modeling of pedestrian energy exchange and thermal comfort in urban street canyons," Building and Environment, vol. 42, pp , 27. [7] A. Henderson-Sellers, Future Climates of the World: A Modelling Perspective: Elsevier, 199. [8] G. Z. Brown and M. DeKay, Sun, Wind & Light: Architectural Design Strategies: J. Wiley, 21. [9] B. Givoni, Climate Considerations in Building and Urban Design: Van Nostrand Reinhold, [1] K. Steemers and S. Yannas, Architecture, City, Environment: Proceedings of PLEA 2 : July 2, Cambridge, United Kingdom: James & James, 2. [11] K. Hiyama and S. Kato, Ventilating Cities: Air-Flow Criteria for Healthy and Comfortable Urban Living: Springer, 212. [12] Dalman, M., Salleh, E., Sapian, A, and Saadatian, O., (213). "Thermal Comfort in Traditional and Modern Urban Canyons in Bandar Abbas-Iran" Pertanika Journal of Social Sciences and Humanities 21 (2), P-P, 212 (In Press) [13] O. Saadatian, K. Sopian, L. C. Haw, N. Asim, and M. Y. Sulaiman, (212)."A review of opportunities and challenges in research and development," Renewable and Sustainable Energy Reviews 212, in press. ISBN: