تعيين الگوي بهينه حياط مركزي در مسكن سنتي دزفول

Determining Optimal Courtyard Pattern in Dezful Traditional Houses

استفاده از حياط مركزي الگوي بسيار كهني در ساخت و ساز مسكن بوده و به طور قابل ملاحظه‌اي در شهرهاي مختلف ايران مورد استفاده قرار گرفته، همچنين فضاهاي سكونتي با بهره‌گيري از تدابير مختلفي در اطراف اين حياط‌ها شكل گرفته‌اند. تناسبات حياط مركزي نقش عمده‌اي در تعيين ميزان انرژي تابشي جذب‌شده در سطوح مختلف حياط و ايجاد شرايط آسايش بصري و حرارتي براي ساكنين ايفا مي‌كند. شناخت الگوي بهينه حياط مركزي در مناطق مختلف كشور نيازمند انجام مطالعات دقيق در ميزان سايه‌اندازي الگوهاي مختلف حياط با تناسبات گوناگون است. براي رسيدن به اين مقصود كوشش شده تناسبات مختلف حياط در مسكن سنتي دزفول شناسايي شده و ميزان سايه دريافتي سطوح مختلف حياط در الگوهاي مختلف مورد ارزيابي قرار گيرد. جهت انجام اين تحقيق، نمونه‌هاي مختلف حياط با استفاده از برداشت‌هاي ميداني تعيين شده و با استفاده از شبيه‌سازي سه‌بعدي الگوها، سايه حاصل از ابعاد مختلف بر روي سطوح مختلف در ماه‌هاي گوناگون سال اندازه‌گيري شده است. با مقايسه ميزان سايه حاصل از هر نمونه با جدول نياز اقليمي شهرستان دزفول، بهترين نمونه از نظر مواقع نياز به سايه و آفتاب معرفي شده است. در بناهايي كه حياط آنها، داراي نسبت 1تا 4/1 ميان طول و عرض (حياط با فرم مربعي شكل) و همچنين نسبت طول به ارتفاع 1/1 تا 2/1 (عمق متوسط) باشند، مناسب‌ترين ميزان سايه در فصول گرم بر روي كف و جداره‌ها ايجاد خواهد شد. استفاده از اين الگوي بهينه، سبب افزايش سايه بر سطوح حياط، كاهش دماي جداره‌ها، كاهش بار سرمايشي ساختمان و افزايش آسايش ساكنين خواهد شد.

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° 22ʹ north and 48° 24ʹ 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.