The Analysis of the Role of Green Walls in Reduction of Heat Islands in Tehran

With the development of urbanization and population growth in the use of land for construction of residential and industrial areas and other infrastructure and turning to remove more vegetation,construction materials and non-systematic misuse of cities,urban areas have forced some changes that pollution and poor air quality,dehydration,high temperatures are some of its results.The temperature difference between the central and dense big cities and its suburbs is named Urban Heat (Thermal) Islands that enter the city to a self-destructive cycle.In this way the hot and polluted air increase the city temperature in the central and dense big city,due to closure of wind passing ways and absorption heat by the most of materials in city surfaces and decreasing humidity,so we use more utilities and electricity for temporary relief.However,the generated heat return to the cycle by the facilities,causing to be warmer and upper city temperature and enhance heat islands.This has devastating and fatal effects on human health.It causing many diseases and encounter with loss of water resourses,drought and more polluted air.Then must find ways to reduce this phenomenon at the same time,such as:Planting trees(especially the shady type of them),vegetation(with increasing humidity and cooling environment),the use of reflective surfaces(rooftops and sidewalks,walls of buildings that organize most of city areas)which includes cool paving such as light-colored materials and create shadows on the floor, also porous and pervious paving,ligh-colored roofs,green roofs,use of green walls in the building,reduce facility outcome heat by using natural ventilation,reducing the height of buildings for local winds passage.In this research,one of the strategies have been fully reviewed namely the green walls and its role in reducing urban heat islands.And present the best model by examining a few built examples in Tehran.Correlation Research methodology is descriptive-analytic.Some results of this research are as follows:Green wall on the facade of the building acts as insulation and prevents thermal fluctuations by creating an air layer.Some of the radiated rays is reflected by the leaves of plants and the others are absorbed by plant  and it cause surface evaporation and moisturing to the environment.By using of green wall in canyon(due to high altitude of buildings or topography)can prevent of absorption and storage of too much sun radiation energy during the day and also of anthropogenic heat.