بهينه سازي دودكش خورشيدي و تاثيرات آن بر تهويه طبيعي جهت كاهش بار سرمايش ساختمان ها

Effect of Solar chimney optimization on natural ventilation for reducing cooling load

امروزه در پي افزايش مصرف انرژي و محدود بودن منابع آن معماران به دنبال كاهش مصرف انرژي در ساختمان¬ها با استفاده از انرژي¬هاي تجديد پذير مي¬باشند كه اين امر سبب روي آوردن به سيستم¬هاي غيرفعال خورشيدي شده است. از سيستم¬هاي غيرفعال مناسب براي كاهش مصرف انرژي در ساختمان¬ها مي¬توان به دودكش خورشيدي اشاره كرد. دودكش خورشيدي با استفاده از گرماي خورشيد و خاصيت ترموسيفون سبب ايجاد تهويه طبيعي در ساختمان¬ها و به دنبال آن كاهش نياز به انرژي براي سرمايش مي¬شود. در اين پژوهش يك نمونه مدل از اتاق فرضي در شهر يزد كه در آن يك دودكش خورشيدي با 30 سانتي¬متر ضخامت جرم حرارتي از جنس آجر به يك فضاي يك طبقه رو به جنوب شرقي متصل است در نرم¬افزار انرژي¬پلاس مدل سازي و توسعه يافته است تا اثر دودكش خورشيدي بر تهويه طبيعي اتاق مورد مطالعه قرار گيرد. پس از معرفي مدل و نحوه عملكرد دودكش خورشيدي، به شرح پيش فرض¬هاي نرم¬افزار استفاده شده در پژوهش و الگوريتم حل آن پرداخته شده است سپس با استفاده از شبيه¬¬سازي¬، ارتفاع، عرض دودكش خورشيدي، ضريب انتقال تابش شيشه پوشش دهنده و فاصله بين شيشه و ديوار جاذب مورد مطالعه قرار گرفته است. نتايج نشان مي¬دهد كه نرخ تهويه طبيعي ايجاد شده توسط دودكش خورشيدي با افزايش عرض، ارتفاع، ضريب جذب انرژي خورشيدي ديوار جاذب و ضريب عبور تابش شيشه افزايش مي¬يابد و با افزايش فاصله شيشه و ديوار جاذب كاهش مي¬يابد. در اين بين فاصله شيشه از ديوار جاذب دودكش خورشيدي كمترين تاثير را بر روي نرخ تهويه طبيعي دارد.

In the modern era, due to developing the urbanization, increase of energy demand and growing costs, the use of passive solar systems, replacing fossil fuels with renewable energies to keep these valuable resources, are important needs for the building industry because much of the energy consumed in buildings. Although achieve an ideal design without the need for energy is difficult, appropriate measures and using the passive systems can dramatically reduce energy consumption. Since 40% of energy consumption has accounted in the building sector there is serious need to use passive heating equipment. Solar chimney is a vertical shaft that utilizes solar radiation to enhance the natural ventilation in buildings. This is achieved as a result of the fact that the solar energy causes a temperature rise as well as a density drop in the air inside the thermal chimney. The drop in air density causes air within the thermal chimney to rise and be expelled out of the top of the chimney. The air which leaves the thermal chimney is typically replaced with outside air that is first drawn through the building to provide natural cooling. This building feature is typically composed of an absorber wall, an air gap and a glass cover with high solar transmissivity and is designed to maximize solar gain in order to increase the chimney effect and thus the air flow generated by the chimney. Solar chimney serves as an excellent natural ventilation strategy for reducing buildings consumption. Solar chimney relies on the buoyancy-driven natural convection to induce airflows in a vertical channel or inclined channel. However, solar chimney as a passive ventilation strategy has not been completely understood despite continuous research effort devoted to the topic over an extended period of time, especially large-scale solar chimney, and so their exact performance can seldom be predicted accurately. In the past decade, solar chimney as a passive ventilation strategy has attracted so much attention in various investigations. Solar chimney has affordance to change into Trombe wall and reduce Heating load of buildings with latent heating. Since this system has double capability for heating and cooling this passive solar system can widely use in every place. In this paper an assumption module which in a solar chimney with 30cm depth of concrete thermal mass integrated to a one-story south-east faced zone was developed for and implemented in EnergyPlus program to determination effect of thermal chimney on natural ventilation. This study described the design concept of the solar house, the basic concept of thermal chimney, posits of software and Modeling algorithm in the EnergyPlus program to predict the performance of thermal chimney. In this study using parametric analysis, height and width of thermal chimney, absorption coefficient of absorber wall, transmittance of glass cover and air gap width between glass and absorber wall was investigated in the solar house under hot-arid climate condition of Yazd to propose the best condition of solar chimney to enhancement of natural ventilation in the module.