سنجش تغییرات هندسه بافت شهری بر شرایط آسایش حرارتی بیرونی مطالعه موردی: بافت مسکونی قدیمی و میانی شیراز

تامین آسایش حرارتی شهروندان در فضاهای باز به‌عنوان اصلی مهم جهت حضور آن‌ها در فضاهای بیرونی بافت‌های مسکونی تلقی می‌شود. هدف پژوهش حاضر، سنجش تغییرات هندسه بافت شهری بر دمای محیط و آسایش حرارتی بیرونی در دو بافت مسکونی قدیمی و میانی شهر شیراز است تا با شناخت رابطه بین متغیرهای اقلیمی موثر بر آسایش حرارتی و خصوصیات هندسه بافت‌های مذکور، امکان ارائه راهکارهای مناسب جهت افزایش کیفیت فضاهای بیرونی در دو بافت ارائه گردد. جهت انجام پژوهش از روش تحقیق توصیفی -تحلیلی در بستری از مطالعات کتابخانه‌ای و سنجش کمی با استفاده از دو نرم‌افزار envi-met و spss بهره برده شده است. در مرحله اول با استفاده از منابع کتابخانه‌ای مولفه‌های هندسه شهری موثر بر آسایش حرارتی در فضاهای بیرونی شناسایی شد. سپس با بهره‌گیری از نرم‌افزار انویمت به شبیه‌سازی نقاط منتخب در این دو بافت پرداخته و شاخص آسایش حرارتی «pmv»، برای نقاط مشخص در گرم‌ترین ماه سال بر اساس اقلیم شیراز و داده‌های آب هوایی سی‌ساله استخراج گردید و توسط نرم‌افزار «spss» تحلیل شد. نتایج نشان می‌دهد که رابطه معناداری میان «ضریب دید به آسمان» به‌عنوان یکی از مولفه‌های هندسه بافت مسکونی منتخب با میزان آسایش حرارتی در بافت‌های قدیم و میانی وجود دارد و مقادیر عددی به‌دست‌آمده شاخص «pmw»، با استناد به استاندارد 7 درجه‌ای اشری نشان داد که میزان آسایش حرارتی در بافت قدیم بیشتر از بافت میانی است و این موضوع ناشی از جهت‌گیری معابر و میزان محصوریت آن‌هاست.

Evaluation of Variation Geometry of Urban Texture on Outdoor Thermal Comfort Conditions Case Study: Old and Middle Residential Fabric of Shiraz City

Extended abstractIntroductionImproving 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 microclimate 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. MethodologyIn order to conduct the present research, descriptiveanalytical research method has been used in the context of library studies and quantitative measurement using two software ENVImet 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. Envimet 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 Envimet software and have been mainly based on simulation. In this study, a simulation for the date of 21 July in the thirtyyear period was performed. For this purpose, the weather data entered into the Envimet software based on the 30year 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 Envimet 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 discussionAccording 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 7degree 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. ConclusionAccording 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.