عوامل مؤثر بر تهویه غیرفعال دودکش خورشیدی (نمونه موردی: شهر اصفهان)

تهویه غیرفعال روشی کم‌مصرف از لحاظ انرژی است که می‌تواند هوای نامطلوب داخل را از ساختمان خارج کند. یکی از روش‌های تهویه غیر‌فعال استفاده از دودکش خورشیدی است که در یک کانال هوا، با استفاده از انرژی خورشید و با کمک پدیده اثر دود‌کشی تهویه فضاهای مجاور، تأمین می‌شود. در این پژوهش ابتدا عوامل مؤثر بر کارآیی دود‌کش خورشیدی از جمله مصالح، عرض دیوار جاذب، مساحت خروجی هوا از دود‌کش بررسی ‌شد. سپس تأثیر تعداد طبقات بر نرخ تهویه مورد مطالعه قرار گرفت و در نهایت در یک جدول مساحت فضاهایی که در طبقات مختلف دود‌کش خورشیدی قادر به تأمین نیاز تهویه آن است، ارائه شد. همچنین عملکرد دود‌کش خورشیدی در فصول سرد سال بررسی شد. به‌دلیل رایج نبودن ساخت دود‌کش‌های خورشیدی، امکان دسترسی به نمونه‌های اجرا شده وجود ندارد، از این‌رو شبیه‌سازی کامپیوتری مدل‌ها، در نرم‌افزار انرژی پلاس به‌عنوان روش جایگزین برای مطالعات میدانی انتخاب شد. مدل‌های دود‌کش خورشیدی متصل به یک ساختمان اداری هفت‌طبقه در اقلیم گرم و خشک شهر اصفهان در روز 31 تیرماه به‌عنوان نماینده یک روز گرم و ماه‌های گرم به‌صورت میانگین مورد بررسی قرار گرفت. نتایج نشان داد که افزایش ارتفاع دود‌کش خورشیدی، قدرت تهویه آن را بالا می‌برد. همچنین مناسب‌ترین مصالح و ابعاد بهینه دیوار جاذب، ورودی و خروجی هوا نیز مشخص شد.

Passive ventilation is an energy conservation method by which sufficient quantity of air is directed into the building in order to maintain desired air change and proper fresh air needed for inhabitants inside. There are many passive methods to achieve required interior ventilation. Solar chimney is a passive ventilation system that uses solar radiation to induce stack effect and to maintain ventilation of the adjacent spaces in the building. Solar chimneys usually consist of a glazed south wall, a duct and a mass wall for absorbing solar energy. Solar incidence transmitted through the glazing is absorbed by the wall and heats the air inside the chimney. Warm air flows upward due to buoyancy effect and as a result the interior air of the adjacent rooms will be drawn into the chimney and directed to the outside. Thus the ventilation rate of the interior spaces will increase and the desired fresh air is maintained. In the buildings of hot- arid climate, to prevent from direct solar radiation and entering dust, windows are usually closed during the day, and then ventilation of the interior spaces may be maintained by solar chimneys. By integrating a solar chimney into the south wall of a building thermal resistance of the wall will also improve. Advantages of a solar chimney in comparison to natural ventilation in buildings are: 1. preventing inside being viewed from outside, 2. maintaining inside ventilation with a low air velocity, 3. preventing dust, pollution and outside noise from entering inside, 4. providing thermal comfort during summer nights when outdoor air velocity is low and air temperature is within the comfort range. This paper investigates the specifications of the main parameters affecting the solar chimney’s efficiency such as the material of the absorber wall, the width of the wall and the area of the chimney’s inlet and outlet. The effect of the number of floors on ventilation rates is also studied, and finally the area of the interior spaces which may be ventilated by the solar chimney is introduced. Moreover solar chimney’s performance during cold periods is examined and discussed. Since the application of solar chimneys to buildings is not common and constructed models are not available for experimental studies, their performance is usually studied numerically or by simulation as substitute methods. Here the models under consideration were simulated in EnergyPlus software. We studied a seven-storey office building in hot-arid climate of Isfahan with an attached solar chimney on its south wall. The results revealed that by increasing the height of the chimney, the ventilation rate enhances. Furthermore, the most proper material for the absorber wall, the appropriate dimensions of the wall as well as the inlet and outlet air was identified. It was found out that the thermal mass of the absorber wall will affect the night ventilation and increases it. A double glazed south wall is effective for increasing the air flow rate inside the chimney. Overall, a solar chimney with optimum dimensions will result in 18.52% reduction of the building’s heating load during the year.

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