Impacts of High-Rise Buildings Form on Climatic Comfort with Emphasis on Airflow through ENVI-met Software

Sustainable design (also called environmental design, environmentally sustainable design, environmentally conscious design, etc.) is the philosophy of designing physical objects, the built environment, and services to comply with the principles of social, economic, and ecological sustainability. Generally speaking, Environmentally Sustainable Design endeavors to reduce the impacts of the construction on the natural environment, in addition to improving the comfort of inhabitants.

Human climatic comfort as an important factor of attending people in urban open spaces is one of the most effective varieties for creating Sustainable urban places in order to achieve viable lively social living in urban areas. Owing to the fact, improving the quality of life and human comfort should be taken into account by urban studies and urban experts. Thus, the importance of climatic studies connected to open space and utilizing the results to access a better spatial structure in urban projects is undeniable. In terms of climate comfort, there are several factors affect the human life and the responsiveness of urban spaces to the human needs. One of the most important factors of climate comfort is the airflow. In this regard, airflow defines as the motion of air passes through objects especially high-rise buildings. The amount of air can be measured by its volume or by its mass.

In this study, the optimum usage of air flow to improve the quality of climatic comfort around high-rise buildings has been taken into consideration. Actually, this research aims to apply the airflows for designing urban spaces especially in high-rise areas. In fact, the appropriate usage of airflows has been considered as an important approach of creating responsible urban space to meet the needs of human comfort. Hence, this paper tries to answer these questions: “How does wind behave around Ekbatan buildings?” And “In response to the human comfort, which forms are preferred regarding the existing air flow patterns in Ekbatan complex?”

Several studies about air flow’s effects and difficulties around high buildings have been conducted by researchers such as Arens (1981), Penwarden (1973), Aynsley (1976), Davenport (1976).In addition, in Iran ,Ranjbar (1389), Tahbaz (1370, 1386), Razjouyan (1372, 1386) carried out researches on architectural aerodynamic and airflow around urban blocks.

The research method of this paper is a practical analytics. Required information for this study is collected via observation, literature review, and documentaries. In this paper, three steps have been followed: First, The descriptive- annalistic method used for understanding the present situation. Second, Simulation technique (by ENVI-met software) employed to observe and analyze the relation between the shape of high-rise residential buildings and wind behavior in the case study. Third, a logical argumentation to reach the conclusion. 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 min space and 10 sec in time. Typical areas of application are Urban Climatology, Architecture, Building Design or Environmental Planning, just to name a few. ENVI-met is a prognostic model based on the fundamental laws of fluid dynamics and thermo- dynamics. The model includes the simulation of: flow around and between buildings, exchange processes of heat and vapor at the ground surface and at walls, turbulence, exchange at vegetation and vegetation parameters, bioclimatology and pollutant dispersion.

The selected area is in Ekbatan complex located in Tehran, Iran which consist of three phases. The modeling area is selected from three phases with different types of residential buildings. The reason for selecting Ekbatan complex is the variety of buildings in forms and public spaces surrounded them and as well as airflow concerns in this area. Climatic data entered into the software is May average data in 2013.

Eventually, the best form for Ekbatan residential buildings was evaluated according to the human comfort against wind. For more explanation, some of the most important rules for urban designing based on airflow comfort have been verified here. When wind strikes buildings, especially high-rise buildings, the wind that flows down the facade, causes to accelerating wind speeds near the windward corners. The increase in wind speed directly depends on the height. Besides, Wind is funneled between two buildings causing wind acceleration between them. According to the simulations, the behavior of wind, particularly the speed of wind, changes while passing through the buildings.

Furthermore, the spatial pattern of Ekbatan complex has been analyzed from different aspects of airflow. The optimized plot has been presented based on three axes. As follow:

1. Analyzing the physical pattern of the location. In other words, this axis tries to understand how buildings were organized next to each other in an adjacent unit.

2. Recognizing the most important environmental factors which affect the desirable urban design. Academically speaking, this step aims to identify environmental aspects of cases.

3. Presenting the optimized-plan. In this section, three alternatives have been simulated by the software. The Structural elements on the drawings and simulation software are Residential blocks, Commercial blocks, the vegetation and green land cover and floor coverings Including asphalt, concrete pavement and dust. It should be noted that the simulation started from 6 am and took 12 hours to analyze.

Finally, some practical strategies (based on software analyses) have been presented for the future developments. For instance, wind speed in backside space of the buildings against air flow, is very low and sometimes it turns to zero. These situations lead to random air movements and consequently wind turbulence. In these cases buildings that step back can be used to reduce undesirable downward wind flows. Wide facades that face the prevailing wind are often undesirable in comparison to less width facades.

In conclusion the study shows that the forms and physical features of the blocks have significant impacts on the wind behavior. According to the analysis, proposed plan has been formed mostly base on controlling and optimizing airflow. However, it should be noted that to achieve proper design and in Consistent with climate, it is unavoidable to have a comprehensive view of all aspects of climate as well as physical aspect.