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

The history of window as a “wind-eye” 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 “international style”. In this movement Iran also was not an exception. Unfortunately today, the construction of diverse types of glass-covered buildings is a common practice in almost every city in this country. After the energy crises of 1970’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.Well-designed, 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.