تهويه طبيعي در شوادون‌هاي شهر دزفول با بهره‌گيري از مدل‌سازي CFD

Natural ventilation effect on Shavadoons in Dezful by applying CFD modeling

تهويه طبيعي يكي از موثرترين عوامل در ايجاد آسايش حرارتي است. اين عامل با بهره‌گيري از كوران هوا، كاهش رطوبت نسبي و افزايش تبخير سطحي موجب ايجاد شرايط آسايش در اقليمهاي گرم و مرطوب ميشود. در دوران معاصر با توجه به اهميت انرژي‌هاي تجديد‌ناپذير از جمله سوخت‌هاي فسيلي و هم‌چنين افزايش آلودگي‌هاي زيست‌محيطي، نقش تهويه طبيعي در ساختمان به لحاظ سازگاري ساختمان با محيط‌زيست حايز اهميت است. سازندگان بنا در دزفول به عنوان يكي از شهرهاي اقليم گرم و نيمه مرطوب جهت تعديل شرايط آب و هوايي در مسكن به ساخت فضايي در عمق 5 تا 12 متري در زيرزمين پرداخته‌اند. اين فضاي زيرزميني به نام شوادون(Shavadoon) به عنوان يكي از راهكارهاي مناسب جهت انطباق با محيط و ايجاد شرايط آسايش حرارتي با استفاده از ثبات دماي سالانه زمين و تهويه طبيعي است. اين پژوهش در ابتدا به شناسايي عوامل مشترك و انتخاب شرايط كالبدي تاثيرگذار در تهويه شوادون مي‌پردازد، سپس اثر تهويه طبيعي را در گونه‌هاي مختلف شناسايي‌شده با استفاده از مدل‌سازي CFD جهت ايجاد شرايط آسايش حرارتي مورد بررسي قرار مي‌دهد.

Natural ventilation is one of the most effective factors in thermal comfort. According to the importance of nonrenewable energies such as fossil fuels and the increase in recent environmental pollution, ventilation plays an important role in buildings. Using air flow, reducing humidity and increasing surface evaporation, creates comfort condition in hot and humid climates. The city of Dezful, due to its special geographic situation, topographic conditions and the environmental systems, devoted particular climate Conditions to itself; so long-term warming has caused many problems for the citizens. In Dezful- as one of the warm and humid cities- builders have applied conglomeration soil to build a space at the depth of 5 to 12 meters underground to moderate and adapt the house climatic conditions. This underground space is called Shavadoon which is one of the suitable approaches to create thermal comfort by using earth annual temperature stability and natural ventilation. Earth temperature is less than outside temperature in the summer and higher in the winter. Expect the Caspian, Persian and Oman coasts, Iran old houses have basement often, and especially in the summer, dwellers went into the basement for thermal comfort. To recognize and analyze the natural ventilation condition and main effective criteria, twelve houses which have Shavadoon have been studied first; Based on this study the depth and area of Shavadoon, Darizeh -Darizeh is a pit 1 meter in diameter in order to supply light & vertical ventilation in shavadoons. Shavadoons reach the yard by darizeh - cross section area and geometric shape of plan are the most effective parameters on natural ventilation in shavadoons, changing the parameters result in significant changes in the air flow. On average by increasing house area, shavadoon area has been increased, the proportion between depth of shavadoon and yard area is also significant. So with more yard area the depth of shavadoon has been increased directly. Four separate phases have been taken to consider the parameters which will be analyzed separately. The results are presented in comparison. There are different ways to study natural ventilation in internal spaces, such as real-scale testing, wind tunnel and modeling approaches. In this study, CFD modeling is used by Design Builder software. The research method of this study is descriptive research and the method of gathering data is based on library and field studies and the analysis method is causal and based on modeling results. The history of this study goes back to the 1930s and early 1940s when there were plentiful interests in air conditioning engineering, caused numerous published books and articles. The air flow Knowledge inside the indoors is notable for three reasons: thermal comfort, indoor air quality and the decrease in building energy consuming. Studies show that in the last two decades attentions to the "air flow" in terms of modern science have been significantly increased. There is another article (in 2008) which defined and analyzed Dezful’s shavadoons, while a comprehensive investigation about air natural flow and the operation of natural ventilation in this place is not available. The final results show that, in the classification of the considered shavadoons which were selected to be analyzed, the maximum depth is 11.8 m and minimum depth is 4.7m. The desired result has been concluded from the one with the minimum depth. Darizeh cross section is another effective parameter. The calculated velocity in darizehs which have different cross section along them is better than the ones which have the same cross section. Then, the location of Darizeh was analyzed. The best natural ventilation will take place when the darizeh is placed in sahn- shavadoon center-which makes balanced ventilation along the shavadoon. Next condition takes place when darizeh is in terminal cat- shavadoons have some small rooms which are called cats- which the air flow is desirable along Shavadoon but the amount of air flow decreases in adjacent cats. Finally Shavadoons, based on their appearance, are classified in to two types, pure space (without Cat) and Chalipa space. The results of analysis showed air flow and air circulation was better in pure space, however Chalipa form is better in structure and architecture.