Evaluating the effects of Urban planning Principles on Outdoor Thermal comfort with an emphasis on Wind flow through Large Eddy Simulation: the case study of row housing pattern in Isfahan

Introduction :

Along with the rapid growth of urbanization and the issues of global warming, environmental pollution, the urban heat island, and climate change, thermal comfort has turned into one of the most influential factors in adaptation of the design of climate-related urban open spaces. Today, the high temperature in human-made areas has doubled the need to consider thermal comfort in open urban spaces. Thus, wind flow is regarded as one of the most influential climatic parameters, where the speed and movement of the wind affect human thermal comfort.

Theoretical Framework :

The traditional architecture and urban planning applied in the city of Isfahan, Iran makes up a unique local examples of Iranian architecture, which has been forced to provide many climatic solutions due to the hot, dry climatic conditions. In the past half century, however, a new pattern has emerged in building massing models as a result of the changes in the forms of housing space into different types of dense multi-family housing. Due to their extension and pervasiveness in Iran, these terraced housing models can be considered as part of the new urban planning trend in the country. Because of the increase in density and building surface ratios, however, part of the self-purification capacity of the urban environment has vanished, and certain construction models have become common in different climates with unfavorable conditions. As many cities are looking for solutions to apply compression and massing as far as possible, the drawbacks of the previous model have become more prominent, and a need has arisen for solutions to the current situation, in order to reduce the probable adverse consequences in the future. The consequences that may arise from this trend include a lack of thermal comfort in open urban spaces, an increase in heat exchange between indoor and outdoor spaces, and a rise in energy loss as a result. A master plan and an auxiliary force to urban designers and planners, the Booklet for Urban Planning and Building Regulations of the city of Isfahan always seeks to modify this pattern in the current situation. In the present study, therefore, attempts are made to consider the existing directions in the booklet and examine the role of physical factors in wind flow and its extent in the new fabric of the city.

Due to its applied nature, this research uses the descriptive-analytical method and documentary and field techniques for data collection. Moreover, the large eddy simulation (LES) model is used for analysis of the defined scenarios.

In order to achieve its purposes, the present study was designed in three phases. Thus, the effective physical indicators were first extracted through examination of the theoretical foundations related to thermal comfort, and their overlap with the directions in the Booklet for Urban Planning and Building Regulations of Isfahan was then studied. In the final step, LES was conducted through definition of the probable scenarios based on terrace housing models of the dominant line in the new fabric of Isfahan. An analysis of the simulation of different scenarios confirmed that an increase in lot coverage ratio, among the extracted indicators, caused a sharp decrease in speed ratio, while an increase in building height led to a decrease in speed ratio, and density exhibited a different effect, which could be interpreted along with the other criteria.

Based on the results, lot coverage ratio is the most effective parameter on air flow in the area, and density is not a suitable criterion for such measurement. Moreover, the effect of a change in lot coverage ratio on wind speed is greater than that of a change in building height. As for passage width, the fluctuations in speed ratio on narrow streets are far more limited than those on wide alleys and streets. Thus, speed is higher at the beginning and end of an alley than at the middle. In scenarios where building height is set between 10.5 and 14 meters, therefore, proper conditions are provided for urban air quality, ventilation, and air pollution.