نقش شيشه (پنجره) در رفتار حرارتي ساختمان

Fenestration Through the Ages and Its Role in Today’s Energy Dilemma

پنجره ها و بازشوها از مهم ترين بخش هاي هر بنا است. تاريخ پنجره و مصالح پوششي آن، قدمتي به بلنداي تاريخ معماري دارد. در فرهنگ هاي مختلف قبل از اختراع جام شيشه، از پوست حيوانات گرفته تا كاغذهاي روغني براي پوشش پنجره ها استفاده مي شد. پس از وقوع انقلاب صنعتي در غرب و به مدد مصالح نوين و پيشرفت تكنولوژي، استفاده از شيشه در بنا رشد چشمگيري يافت. هرچه جام هاي شيشه اي بزرگتري توليد شد، پنجره ها هم بزرگتر شدند. بزرگي جام ها به جايي رسيد كه حتي در مواردي نماي ساختمان ها به صورت تمام شيشه ساخته مي شد. اين موضوع معناي پنجره را تغيير داد و پنجره ها ديگر تنها روزنه يا حفره اي درون ديوارها نبودند. اين رويه در قالب سبك بين المللي به ديگر كشورها راه يافت. با اينكه اين سبك هم آهنگ با اقليم و معماري بومي ايران نبود امّا در ايران هم گسترش پيدا كرد. با وقوع بحران انرژي، پژوهشگران صنعت شيشه و پنجره بر آن شدند تا راهكارهاي نويني در جهت بهبود رفتار حرارتي شيشه و پنجره ارائه كنند. اين نوشتار با مروري كوتاه بر سير تاريخي تحوّل شيشه در معماري، راهكارهاي بهبود رفتار حرارتي آن را مورد بررسي قرار داده است. اين راهكارها در دو بخش ارائه شده اند: در بخش نخست عوامل خارجي و شرايط فيزيكي مؤثر در رفتار حرارتي شيشه و پنجره بررسي شده است. اين بخش شامل بررسي تأثير محيط پيرامون بر رفتار حرارتي پنجره، موقعيت و جهت گيري پنجره و نقاب سايه است. در بخش دوم، پنجره ها از نظر اجزا و مواد و مصالح تشكيل دهندۀ آن ها بررسي شده اند. در اين بخش انواع شيشه ها و قاب هاي پنجره معرفي و از نظر ميزان اتلاف انرژي و شاخص هاي ديگر با هم مقايسه شده اند.

The history of window as a ldquo windeyerdquo is as old as the history of architecture. But the history of glass as window glazing is relatively new. For centuries windows were covered with materials other than glass. In china and Japan oiled paper made of rice, protected by a sliding wooden shutter, allowed light in and kept cold drafts out. Colored chunks of glass in cement frames were used in Syria and Egypt. Thin slabs of marble were used by Romans. Even the windows of the early new England houses were covered with stretched animal skins. During the middle ages small pieces of colored glass were used only in windows of very important churches. Window glazing as we know it today is practically the product of the industrial revolution in England. In the first decades of the 20th century glass manufacturers began to produce large sheets of glass. This trend caused windows to become larger and larger, to the point that the whole walls and ultimately the facades of some buildings were covered with thick sheets of glass. This trend of using glass and usually steel structures in building design became known as the ldquo international stylerdquo . In this movement Iran also was not an exception. Unfortunately today, the construction of diverse types of glasscovered buildings is a common practice in almost every city in this country. After the energy crises of 1970rsquo s, an extensive research in architectural glazings and window frames has been undertaken by different institutions and glass manufacturers to improve the thermal behavior of windows and to develop the new more efficient glazing materials and window frames. The aim of this study is to investigate: The external forces and physical conditions influencing the thermal behavior of architectural glazing under different circumstances. The impact of environment forces, orientation of windows and their shading. The materials, components of windows, different types of glazing and window frames. The final part of this study contemplates on the thermal behavior of window frames made of different conventional and new materials. Windows in almost every climate can considerably alter the amount of purchased energy required to maintain comfort. Welldesigned, they can actually provide a net energy gain poorly designed, they can be an enormous energy burden. This study provides design strategies to make windows more energy efficient.