پيشنهاد روشي براي پهنه‌بندي اقليمي ايران بر مبناي پتانسيل تهويه طبيعي (مطالعه موردي شهر يزد)

New Method for Climatic Classification of Iran Based on Natural Ventilation Potential (Case study: Yazd)

تقسيم بندي اقليمي يكي از ابزارهاي مفيد در سازماندهي اطلاعات مختلف در شرايط مشابه است. تاكنون انواع مختلفي از تقسيم بندي هاي اقليمي با اهداف متفاوت بر گستره كشور ايران پيشنهاد شده است. در زمينه طراحي ساختمان، وجود تقسيم بندي هاي مناسب با اهداف معماري، نقش مهمي در ايجاد ساختمان هاي منطبق با شرايط اقليمي و ميزان بهينه مصرف انرژي ايفا مي­كند. اين مقاله با بررسي تقسيم بندي هاي اقليمي موجود به تحليل كارايي و كاستي هاي هر سيستم در طراحي ساختمان و معماري پرداخته است. از جمله اين كاستي‌ها مي توان به عدم توجه به تفاوت در محدوده آسايش حرارتي و ميزان نيروهاي محركه باد در مناطق مختلف اشاره كرد. در نهايت با توجه به كاستي هاي موجود در سيستم هاي ذكر شده، روشي جهت پهنه بندي جديد اقليمي ايران بر اساس پتانسيل تهويه طبيعي پيشنهاد گرديده است. بدين منظور اتاقي از يك ساختمان اداري در شهر يزد با ويژگي هاي متداول ساخت، ابعاد و مصالح با استفاده از نرم افزار انرژي پلاس شبيه سازي شده و در دو ماه آوريل و ژوئيه، به عنوان دو ماه نمونه با شرايط دمايي به ترتيب معتدل و گرم مورد بررسي قرار گرفته است. مقايسه تطبيقي رفتار حرارتي ساختمان در چهار حالت بدون تهويه، تهويه روزانه، تهويه شبانه و تهويه روز و شب بهترين استراتژي تهويه وميزان آن را در هر ماه نشان مي دهد. به اين ترتيب با انجام شبيه سازي هاي مشابه، در ساير شهرها مي­توان بر اساس نوع تهويه و ميزان آن (پتانسيل تهويه) به دسته بندي شهرهاي مشابه پرداخت. چنين تقسيم بندي با ارائه تصويري مطابق از پتانسيل هاي موجود با واقعيت، رهنمودهايي مفيد را براي معماران، جهت طراحي ساختماني با بهره مندي از تهويه طبيعي و با حداقل نياز به سيستم هاي سرمايش و گرمايش مكانيكي، فراهم مي نمايد.

Introduction Climatic classification is one of the most useful methods in arrangement of information for similar places. Until now various kinds of climatic classification systems have been proposed for Iran concerning different goals. Buildings are affected by climatic situations in many ways. Due to this suitable recognition of climatic characteristics related to building design is essential. In this article assessing benefits of each climatic classification system for building design and architecture, defections of these systems have been noticed. Ignoring differences in thermal comfort zone and wind forces in various places are some of these defections. One of the most useful classifications for building design purpose is the HDDCDD system proposed by Khalili. This system is based on the thermal comfort condition in airconditioned buildings, ignoring natural ventilation potential. Depending on wind forces, natural ventilation could have significant effect on thermal comfort and though reduction of airconditioning systems usage and energy consumption. According to these, a new method has been proposed for Iran climatic classification based on natural ventilation potential and different thermal comfort zone.   Materials and Methods A typical office room in Yazd has been modeled for two months, April and July as moderate and hot month. An energy simulation program called Energy Plus was utilized to simulate the building thermal behavior. The required weather data had been derived from the Typical Meteorological Year (TMY) weather data used in EnergyPlus (EPW) weather file format. The simulations have been setup in four ventilation scenarios for each month: day ventilation, night ventilation, day and night ventilation and without ventilation. The results show thermal behavior of the simulated building affected by climatic parameters. The building also is taking advantages of natural ventilation potential which depends on wind speed and direction.   Results The results show day and night ventilation as the best choice of ventilation. The acquired results determine the ventilation potential to keep building indoor temperatures within thermal comfort zone. In this method, factors of weather data in conjunction with natural ventilation potential characterize the place. This method is based on the HDDCDD values according to the specific thermal comfort zone for each place. The values for CDD in April have been decreased from 7856.88 to 6.68, with no ventilation and day and night ventilation, respectively. In June the reduction was from 13285.97 to 348.81. This means that using natural ventilation could decrease energy consumption of the building effectively. Accordingly the CDD value for each city would be different using various kinds of natural ventilation. A new climatic classification would be achieved by defining cities with similar CDD value and ventilation scenario. These values represent the natural ventilation potential of cities which depends on local wind forces.   Conclusion According to various goals and distinction factors, a climatic classification system would be useful for special purpose. Only some of the climatic classification systems are created in conjunction with building design. A new method has been proposed for Iran climatic classification based on natural ventilation potential and different thermal comfort zone. A typical office room in Yazd has been modeled as the sle to evaluate the proposed method. Simulations have been setup for two months in four ventilation scenarios: day ventilation, night ventilation, day and night ventilation and without ventilation. The reduction in CDD values is various using each ventilation scenarios. On the other hand the values for each city would be different according to various climatic parameters. The resulted values for HDDCDD and natural ventilation potential show the best choice for ventilation. These values are the basic parameters to create the new climatic classification system based on natural ventilation potential proposed in this article. Applying similar simulations for other cities, it is possible to classify them based on values for natural ventilation potential and its type. Cities with similar CDD value and ventilation scenario would be in the same climatic zone. This method will consider available resources for wind as well as other climatic factors for selected city and also thermal comfort zone suitable for naturally ventilated buildings. Such classification will provide useful guidelines for architects to design naturally ventilated buildings with minimum need for mechanical cooling devices.