Buscador de Personas - SIGEVA - Universidad Nacional de Córdoba

Windows are architectural elements that have been developed for hundreds of years and play a keyrole in house functionality and other environments where the humans have developed their lives, transport and work. According to the Oxford Dictionary, a window is ?an opening in the wall or roof of a building or vehicle, fitted with glass in a frame to admit light or air and allow people to see out.? As the definition indicates, windows were created to meet the ventilation and lighting needs in homes, and for people to look through them. Etymologically the word ?window? comes from the language of Northern Europe, Old Norse vindauga, from vindr ?wind? and auga ?eye?. The initial implementation of windows consisted of an opening in the walls of rudimentary stone houses. Therefore, ventilation was easily and successfully achieved by making an opening in the walls; however, the entry of light was always accompanied by deficiencies in thermal insulation. The opening- type window had to be covered with animal skins or other available materials to prevent the entry of cold or heat due to unfavorable environmental conditions; however, the simultaneously entry of light into the environment was affected.During development, semi- or transparent materials were gathered and formed into sheets to allow the passage of light when achieving some isolation or at least preventing air circulation whenit was necessary. Among the different materials, minerals, such as lapis specularis were used inancient Rome, which is a type of translucent plaster; and sheets of this were assembled using smallpieces. Semi- transparent laminas of paper, which were sometimes greased, to improve the passage of light, were used by ancient people of Asia. Later, a hydrated phyllosilicate mineral of aluminum and potassium (muscovite) and commonly called mica was used in Russia and then in England in the Middle Ages, harnessing the ability of this material as an excellent thermal insulator.It is necessary to discuss glass in a separate paragraph, because it has its own history of discoveryand development. In the stone age, it was collected in small pieces of obsidian, a natural volcanicmineral for which a broad diversity of tools were made. Then, in Egypt small rudimentary pieceswere obtained and later in the Roman Empire the production techniques were perfected. This body ofItaly from the twelfth century. The most important activity was the production of containers, ornamental products, and the construction of stained glass windows for cathedrals and churches, in which religious figures were obtained by incorporating impurities from different minerals to achieve the final coloring of different pieces that were later assembled with lead. However, its cost was very high and was restricted to public buildings. In the twentieth century, with the mass production of laminates using the float method, thin, transparent, and regular sheets were achieved. Similary, the cost of production decreased and the use of glass in windows became widespread.In 1902, Benedictus invented the first laminated glass with cellulose acetate, which gave theglass excellent mechanical properties and resistance to breaking. This allowed it to be used safely as automotive window glass. Then, in 1907 Baekeland invented the first polymeric synthetic material, Bakelite and in 1922 Staudinger received the Nobel Prize for explaining the chemical nature of polymeric materials. Polymers quickly proved to be very versatile materials that could be laminated, and sheets that were equal to or even more transparent than glass, such as polymethylmethacrylate (Plexiglas), which was discovered in 1930, were achieved.Currently, buildings have a large number of walls and glazed ceilings, and the cost of the latteris approximately 25% the construction cost. The energy used by buildings is one- third of the totalconsumption in developed countries, which surpasses other areas, such as industries. Of this third,half of the energy in buildings is used for heating, ventilation, or cooling. Considering all the elements that make up a building, windows are the least energy- efficient elements. The thermal performance of glazed units is very rudimentary, because 50% of the energy is lost or gained through the windows, especially recently with the increased interest in building structures with large glazing. The thermal conductivity of glass is similar to that of bricks or concrete. However, the glass sheets are much thinner than the rest of the materials of the walls and the temperature gradient is large across the windows, and therefore, so is the heat transfer. Therefore, the windows alter the thermaldemand of buildings, which means that it is necessary to optimize these characteristics.To prevent sunlight from entering excessively, different strategies have been designed, whichincludes the implementation of fenestration devices. Currently, these are integrated with controldevices that can be operated manually or are automated, which covers windows with constantoptical properties. All these systems do not incorporate transmittance adjustments in the glazing and in many cases treatment of the glasses gives them opaque characteristics to avoid glare. This makes rooms dark and they require artificial lighting during the day and limit visibility to the outside. Faced with these drawbacks, current research is focused on the development of glazing that can dynamically change their optical properties, which are called smart windows. Figure 6.1 shows the evolution of windows and as an analogy, a sequence of human evolution.The driving force beyond scientific and academic interest is the large market for smart windows,because they function as a tool to improve energy efficiency, and can reduce approimately10% ofthe energy used by a building.

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