Document Type : Research Paper
Assistant Professor of Urban Design, Shiraz University, Shiraz, Iran
M.A. student of Urban Design, Shiraz University, Shiraz, Iran
Improving people's thermal comfort in outdoor spaces is one of the most important goals of achieving the desirable design in these spaces. Today, the issue of thermal comfort in the " manufactured environment" is considered as a vital factor that affects health and the level of mental comfort of urban residents. Special attention to the issue of thermal comfort of people in outdoor spaces is of fundamental importance due to its direct impact on cognitive function and efficiency and as an important principle, it should be considered in the process of designing open urban spaces. Because comfortable outdoor spaces within urban fabrics can provide opportunities for people to participate and increase their social participation. Residential textures, as the core of urban areas, require high energy to meet the cooling and comfort needs of their residents. Also, this challenge stems from the undesirable design of these textures in modern times. It is essential to control "local micro- climate" in order to achieve the thermal comfort of the residents. The aim of this study was to investigate the micro-climate conditions of old and middle textures of Shiraz city on a summer day with extreme heat stress, so that during the hottest hour of the day, the correlation between the geometry of old and middle textures with comfort index Thermal "PMV" was measured and the thermal comfort conditions in the old and middle textures were studied.
In order to conduct the present research, descriptive-analytical research method has been used in the context of library studies and quantitative measurement using two software ENVI-met 4 basic and SPSS. The most important advantage of this software is that it is one of the first models that seeks to produce the main processes in the atmosphere and calculates all the important meteorological factors. "Envi-met" software has been used in various studies, but in this study, the research method of those studies that have provided a basis for conducting our research has been studied. The aim of this research is to measure the thermal comfort on a hot summer day with the maximum air temperature in different climates, all studies have been done using " Envi-met " software and have been mainly based on "simulation". In this study, a simulation for the date of 21 July in the "thirty-year period" was performed. For this purpose, the weather data entered into the " Envi-met " software based on the 30-year weather data taken from the official sites of Shiraz city and using Autodesk Ecotect software for an average of 30 years, 21 July has been taken to simulate the hourly output that has been entered into the " Envi-met " software for date of "21 July ". The "PMV" thermal comfort index for the selected areas located in the old and middle textures was extracted between 9 am and 16 pm and specifically at 15 pm with maximum temperature. Then, using "SPSS" statistical software to analyze the correlation between air temperature variables (° C), wind speed (m/s), relative humidity (%), Mean radiant temperature (° C) and urban geometry parameter "Sky view factor" with the "PMV" thermal comfort index at 15:00 pm in each of the "old and middle" textures.
Results and discussion
According to statistical analyzes and results obtained in both textures, it was found that in the middle texture, the correlation rate of "PMV" thermal comfort index with the variables of "Sky view factor" coefficient (0.885) and" Mean radiant temperature" (0.689) and in the old texture has a strong and positive correlation between "PMV" thermal comfort index and "wind speed" (0.935) and "Sky view factor" (0.762). It can be said that "Sky view factor" coefficient as one of the components of urban texture geometry in both textures, has a very positive and direct correlation with "PMV" thermal comfort index. Also, according to the obtained outputs related to the thermal comfort index "PMV", in the old and middle texture and according to the 7-degree ASHRAE standard (ASHRAE Standard 55,2004: 2) related to the "PMV" index was determined. The old texture feels less heat stress than the middle texture between 9 a.m. and 16 p.m., and especially at 15 p.m. And it is in the range of more thermal comfort, which is due to the special geometric features of the old texture, such as the street orientation, aspect ratio and sky view factor compared to the middle texture.
According to the results obtained related to the thermal comfort index "PMV", the selected points in both old and middle textures were determined that the old texture studied in time intervals and according to the Ashri standard, is in the range of low and medium heat stress and has more thermal comfort than the middle texture. Thus, the old and middle textures with their specific spatial layout, absorb different amounts of solar energy during the day and as a result, different levels of thermal comforts are created that organic urban layouts, such as old texture with higher levels of shading, are more efficient during the summer and provide more thermal comfort.