عنوان مقاله [English]
Urban microclimatic conditions have a very serious impact on the energy consumption of buildings, outdoor comfort conditions and pollutants concentration. Urban heat island phenomenon in combination with global climatic change deteriorate the microclimatic conditions that are characterized by increased ambient temperatures, longer duration of hot spells and more frequent heat waves )Santamouris, 2007, 2011). Various studies performed have shown that urban heat island may increase the cooling energy demand of urban buildings between 20 and 100% (Hassid et al., 2000; Santamouris et al., 2001; Papadopoulos et al., 2001; Kolokotroni et al., 2009; Ihara et al., 2009 ). Mitigation techniques are aiming to counterbalance the heat island phenomenon by the intensive usage of green spaces. Applications of highly reflective materials, decrease of the anthropogenic heat, solar control of open spaces, use of environmental heat sinks and increase of the wind flow in the canopy layer, and more importantly than these cases using cool paving materials in paths and roads. This paper presents a study by the goal of investigating the influence of urban transportation network covers and paved surfaces on microclimatic conditions using common brick, cement concrete, and asphalt (with basalt) materials. The first case is applied in paving of the pavement tradition cities of Iran and two other cases are applied in paving of the pavement modern cities of Iran. The purpose of this research is presenting the performance of three materials used as paving materials in urban network pavement and investigating their impacts on reduction or increase of the arrogance heat island phenomenon and on the peak ambient temperature during a typical summer day. This try to improve outdoor comfort conditions of urban space, as the result of a real project in Tehran (Iran), in order to recommend the best paving materials.
In this study, to investigate the effects of surface coating on the temperature and on wider scale urban spaces, the following stages have been carried out. The first, texture design of site based on the requirements specification and the field space divided by type of land uses, the second, collection of the atmospheric raw data from Mehrabad weather station, corresponding to July as the hottest month in Tehran. The third gathering the specifications of Asphalt, Concrete, Cement and solid bricks, and entering details of each one in configuration editor of Envi-met. Forth, designing the site in Eddi program in Envi-met, to defines type of material (asphalt, cement concrete, and solid brick), land cover of the site on the net, program of soil model on three separate models for simulation. Fifth, definition and locating 7 virtual receptor on the site in Envi-met as reference points in recording and receiving atmosphere data during simulation process to statistical analysis and numerical simulation (quality of site selection of receptors show all changes of temperature for each of the models).
ENVI-met is a three-dimensional microclimate model designed to simulate the surface-plant-air interactions in urban environment with a typical resolution of 0.5 to 10 m in space and a typical time frame of 24 to 48 hours with a time step of 10 sec at maximum. This resolution allows analysis of small-scale interactions between individual buildings, surfaces and plants. Typical areas of application are Urban Climatology, Architecture, Building Design or Environmental Planning, just to name a few.
The energy budget is calculated at the ground surface. The results are the surface temperature and humidity as well as the fluxes of sensible and latent heat. The ground surface and the walls are used as boundary conditions for the atmospheric model (ground surface and walls) and for the soil model (ground surface).The temperature of the walls and the roofs is calculated for each grid point with respect to surface orientation, albedo and heat exchange with the temperature inside the building. The heat exchange between the building walls/roof and the atmosphere can be calculated using the wind field, the surface temperature and the local turbulence.
3. Results and Discussion
This research has showed that the use of brick (made of clayey) paving material contributes to the reduction of the peak ambient temperature (potential temperature) during a typical summer day up to 2◦C and 0.5◦C compared with asphalt (with basalt) cement concrete paving materials, respectively. At the same time, the surface temperature in the site was decreased by 10◦C in brick paving material compared with asphalt (with basalt) paving material and 4◦C in comparison with cement concrete paving material, while comfort conditions have been improved considerably in the assessment with Comfort index.
Heat island increases temperature in urban areas, increases the energy consumption for cooling purposes and affects the global environmental quality of cities. The use of advanced mitigation techniques highly contributes to decrease temperatures and improve comfort in open urban areas. Autochthonous and tradition cool paving materials, e.g., brick, presenting a high solar reflectivity and emissivity have been proposed as an effective mitigation technique when applied to open spaces against asphalt (with basalt) and cement concrete materials. Although many experimental data are available to evaluate the performance of brick material in isolated buildings, very limited information is available concerning the mitigation potential of the brick material when applied in open urban areas. The results of the specific climatic conditions in the three-dimensional microclimate model ENVI-met of site fabric have showed that the extensive application of brick pavements, under the specific climatic conditions, may reduce the peak daily ambient temperature during a typical summer day up to 1.5 ◦с while surface temperatures were reduced up to 10◦C against cement concrete and asphalt pavements. In parallel, calculations of the thermal comfort conditions in the site fabric space have shown that brick crossings improve considerably comfort conditions. In particular, under strong wind conditions, advection phenomena may dominate and the impact of local convection and radiation phenomena will be diminished. In addition, for lower levels of the ambient temperature and solar radiation, the summer contribution of brick paving material is expected to be reduced. Finally, the use of brick paving materials is not expected to decrease the ambient temperature during the winter period. The overall analysis has shown that the use of brick crossings is an efficient strategy in order to reduce the intensity of heat island in urban areas and to improve the global environmental quality of open areas. Therefore, it can be concluded that the use of brick paving materials is a very efficient mitigation technique to improve thermal conditions in urban areas of Iran.