دکتری شهرسازی، استاد دانشکده هنر و معماری، دانشگاه تربیت مدرس، تهران، ایران.
استفاده از حیاط مرکزی الگوی بسیار کهنی در ساخت و ساز مسکن بوده و به طور قابل ملاحظهای در شهرهای مختلف ایران مورد استفاده قرار گرفته، همچنین فضاهای سکونتی با بهرهگیری از تدابیر مختلفی در اطراف این حیاطها شکل گرفتهاند. تناسبات حیاط مرکزی نقش عمدهای در تعیین میزان انرژی تابشی جذبشده در سطوح مختلف حیاط و ایجاد شرایط آسایش بصری و حرارتی برای ساکنین ایفا میکند. شناخت الگوی بهینه حیاط مرکزی در مناطق مختلف کشور نیازمند انجام مطالعات دقیق در میزان سایهاندازی الگوهای مختلف حیاط با تناسبات گوناگون است. برای رسیدن به این مقصود کوشش شده تناسبات مختلف حیاط در مسکن سنتی دزفول شناسایی شده و میزان سایه دریافتی سطوح مختلف حیاط در الگوهای مختلف مورد ارزیابی قرار گیرد. جهت انجام این تحقیق، نمونههای مختلف حیاط با استفاده از برداشتهای میدانی تعیین شده و با استفاده از شبیهسازی سهبعدی الگوها، سایه حاصل از ابعاد مختلف بر روی سطوح مختلف در ماههای گوناگون سال اندازهگیری شده است. با مقایسه میزان سایه حاصل از هر نمونه با جدول نیاز اقلیمی شهرستان دزفول، بهترین نمونه از نظر مواقع نیاز به سایه و آفتاب معرفی شده است. در بناهایی که حیاط آنها، دارای نسبت 1تا 4/1 میان طول و عرض (حیاط با فرم مربعی شکل) و همچنین نسبت طول به ارتفاع 1/1 تا 2/1 (عمق متوسط) باشند، مناسبترین میزان سایه در فصول گرم بر روی کف و جدارهها ایجاد خواهد شد. استفاده از این الگوی بهینه، سبب افزایش سایه بر سطوح حیاط، کاهش دمای جدارهها، کاهش بار سرمایشی ساختمان و افزایش آسایش ساکنین خواهد شد.
Determining Optimal Courtyard Pattern in Dezful Traditional Houses By Relying on Shadow Analysis
Courtyard form is a very ancient element of a building structure in Iran and has been in place in Iranian houses for ages. A look at the plan of old houses in Iran as well as other countries in the region show that the structure of buildings are formed around the yard with several strategies. Solar radiation entering the courtyard space is received by different surfaces and will affect the thermal conditions of the buildings. The amount of received radiation generally depends on several factors including climatic conditions, location, orientation, the surrounding environment, proportion, the time during the year and the form of the courtyard. The absorbed solar radiation will increase the surface temperatures and consequently the temperature of the adjacent zones will be affected. This effect on thermal conditions in the courtyard space is reflected on the thermal behavior of the surrounding spaces. Therefore, it is necessary to ensure an optimum amount of shadow and irradiation in the courtyard space for an efficient courtyard performance through the year. It is evident that this can be achieved through properly configuring and proportioning the courtyard’s form and surfaces. Using an improper pattern not only will cause poor courtyard performance but will also increase the cooling and heating loads of the building because of the existence of too much shadow when solar radiation is needed or receiving plenty of irradiation when it is not desirable. The courtyard building is suitable for use and enjoyable if special arrangements are made in the design of the building. This includes the internal envelope’s finishing and materials, as well as the proportions of the physical parameters of the courtyard form, which are the most important element and the focus of the present study. Dezful is one of the cities of Khuzestan province in southwestern Iran which is located on latitude 32° 22' north and 48° 24' east. This city has severe summer climate conditions and on some days the temperature reaches 52 degree centigrade. In traditional buildings of Dezful, different passive design strategies have been used to control climate conditions and obtain thermal comfort inside the building. One of these strategies is creating a micro climate condition by using courtyards as a design pattern. For the present study, 15 cases of the courtyards in traditional buildings of Dezful have been selected. Generally, when more solar radiation is received in building, solar heat gain would be greater. Since solar radiation is the only thermal factor considered in this study, cooling loads for building is referred to the variation in the obtained solar radiation. Two different indices have been used to classify cases. These indices have been introduced as N1 (ratio of width to length of the courtyard) which defines elongation of form and N2 (ratio of length to height of courtyard) which shows the depth of form. From each classification, one case is selected and used for this study. The investigated cases have been modeled using three-dimensional simulation by Townscope software. An image processing is used to calculate the amount of shadows in different proportions on courtyard surface levels by Imagej software. The amounts of shadows have been measured in different months of the year on vertical and horizontal surfaces. Generally, in summer, the solar radiation received by horizontal surfaces is more than that obtained when the surface is vertical. Therefore, shadows on vertical and horizontal surfaces ave been measured separately. The total amount of shadows of each sample has been compared in the research with the climate requirement table of Dezful and the best sample regarding the needed periods for irradiation and shadow have been introduced. The optimum ratios of a courtyard building are defined as that which ensures minimum energy requirement throughout the year to achieve comfort in the building. Results show that courtyards with length to width ratio of 1 to 1.4 (near to square form) and height to length ratio of 1.1 to 1.2 had the most proper shade on different courtyard surfaces. Results also showed that for the purpose of reducing the cooling load in summer, deep and square shape courtyard forms were the most preferable. The self-shading of the courtyard building acts to reduce the need for cooling by an average of about 4%. By using this proportion, the amount of shadow on the courtyard will be optimized. This will accordingly result in reducing the temperature of the walls – what would help the cooling load in summer and also maintain warmth in winter. Courtyards with suggested proportion in buildings make great advantages for thermal condition of building. However, it must be mentioned that this passive strategy is not enough for achieving thermal comfort in building. Rather, a series of other strategies must be used to create more favorable thermal condition. They include thermal mass, proper insulation, good orientation and ventilation.
کلیدواژه ها [English]
Dezful Historical Context, Central Courtyard, Shadow Analysis, Proportion, Solar radiation