مطالعه رفتار حرارتي مصالح رايج در ساخت ديوار ؛ مطالعه موردي: ساختمان هاي مسكوني شهر تهران

Evaluating the thermal performance of wall construction materials; Case study: Residential buildings of Tehran

پوسته ساختمان به عنوان واسطه اصلي بين فضاي بيرون و درون، نقش اساسي در كنترل شرايط محيطي و تامين آسايش ساكنين ساختمان ايفا مي‌كند. در سال هاي اخير، با توجه به ضرورت كاهش و جلوگيري از صدور گازهاي گلخانه‌اي، اهميت مسيله طراحي و اجراي سيستم‌هاي ساخت و ساز كه با كم‌ترين استفاده از سيستم‌هاي فعال توانايي تامين آسايش حرارتي براي ساكنين را دارا باشند، آشكار است. بررسي اين امر كه مصالح جديد و سيستم‌هاي ساخت ديوار رايج تا چه حد مي‌توانند آسايش حرارتي ساكنين را تامين كنند، پرسشي است كه اين تحقيق در پي پاسخ آن است. اين تحقيق با استفاده از نرم‌افزار شبيه‌سازي انرژي IES-VE ، به شبيه‌سازي نحوه رفتار گونه هاي مختلف ديوار كه از تركيب بلوك هاي سفالي، ليكا، هبلكس و عايق حرارتي ساخته شده و در ساختمان‌هاي مسكوني شهر تهران متداولند، مي‌پردازد. ضمنِ پرداخت و تحليل نتايج، مواردي از قبيل نقش متفاوت جرم حرارتي و عايق حرارتي، تعريف ويژگي‌هاي حرارتي ديناميك و رفتار دوره‌اي مصالح در مواجهه با شرايط ناپايدار محيط بيان مي‌گردد. نتايج تحقيق نشان از لزوم استفاده از محاسبات شرايط ناپايدار به جاي روش مرسوم محاسبات پايدار مي‌دهد. همچنين از ميان گونه‌هاي ديوار معرفي شده، ديوار ساخته شده از دو رديف بلوك ليكاي ?? سانتيمتري با ? سانتيمتر عايق در ميانه آنها مناسب‌ترين عملكرد را از نظر توانايي تامين آسايش حرارتي داراست.

This study examines thermal performance of conventional wall construction materials and systems used in typical residential buildings in the city of Tehran; these materials are used instead of traditional heavyweight materials used in vernacular architecture of the region and represented appropriate potential in moderating outdoor weather conditions and providing thermal comfort for occupants. The necessity of this study is due to the important role of the building envelope, as an interface between indoors and outdoors, in control of the heat transfer and moderating weather conditions. With growing concern about climate change and global approach to cut CO2 emissions, application of construction systems which can help reduce energy consumption and associated carbon emissions are desired. As the wall area constitutes the largest part of the building envelope, its contribution to heat loss through the fabric is significant. Moreover, due to growing rate of the number of residential buildings in Tehran, there is a great potential of energy saving in improvement of the residential building’s envelope. The steady state thermal analysis is not an appropriate/ sufficient way of evaluating thermal performance of the building envelope as the indoor condition is the result of the dynamic response of the building fabric energy system to dynamic outdoor weather conditions. Therefore, apart from insulating capacity of the wall, its useful thermal mass which is a function of heat capacity, density and thermal conductivity of the composing layers of the wall, has an important role on its cyclic performance especially when the outdoor temperature starts cycling below and above indoor temperature. Therefore, a dynamic simulation tool (IES-VE) was used to analyse thermal performance of common wall construction alternatives in Tehran. These wall types are mostly made of hollow clay, LECA (Lightweight Expanded Clay Aggregates) and AAC (Autoclaved Aerated Concrete) blocks in combination with insulating materials (Expanded Polystyrene) and were tested on a reference building selected as a sample of typical residential buildings in Tehran. Indoor temperature resulted by each wall type was plotted against comfort temperature of the residents of Tehran in order and the deviation on indoor temperature from comfort temperature was measured to evaluate the level of comfort provided by each of these construction details. According to the results from the simulations, wall type L2 made of two layers of LECA blocks (100 mm) with a layer of polystyrene (50 mm) in between has the best performance in terms of providing indoor comfort condition among total six wall types introduced. Results show that there is a potential of 50% energy saving by application of wall type L2 instead of L1 (made of 200 mm hollow LECA blocks) which have the best and worst performance in terms of deviation of indoor temperature from comfort temperature.