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Electrically heatable glass and windows are relatively new products, which help solve problems in the design of buildings and vehicles. The idea of heating glass is based on the use of energy-efficient low-emissive glass, which is generally simple silicate glass with a special metallic oxides coating. Low-emissive coating decreases heat loss by approximately 30%. Heatable glass can be used in all kinds of standard glazing systems, whether wood, plastic, aluminum or steel. Heatable glass based on low-emissive coatings was first produced in high volume in the early 1980s. Today, heating glass is used in the construction of many kinds of buildings and in mass production of vehicles, ships and trains. Heatable glass removes discomfort and other disadvantages induced by the low heat-insulating features of silicate glass. The effect of “cold glass” disappears when the surface of the glass is heated. Condensation is eliminated, along with ice and snow covering, the window’s heat losses are compensated and room comfort is improved. Heatable glass can be used as the principal system of heating and can be combined with floor and ceiling heating. Such combination helps reduce the total rate of heat loss of the building, thereby lowering heating expenses. Also, the active area of the room can be used more efficiently, as massive window-sill radiators are not needed. Initially, heating glass was produced by sputtering ordinary glass, and stable quality could not be guaranteed. A technological breakthrough took place in 1989 when the mass production of low-emissive glass began. The glass was coated during the manufacturing process. == Standard windows == * Window construction Windows play a significant role in room comfort. As a result, the area of glazing of buildings is constantly being increased. Window technologies always in progress and it is common today to use low-emissive glass. In spite of progress the low temperature of glass surface is still the problem of constructive glazing. Heatable glass helps to solve problems concerning low surface temperature and increase the level of comfort in the room significantly. Heatable glass can be used in practically all kinds of glazing systems made of wood, plastic or aluminum. Heatable glass and multiple glass panes can be used both in blind and openable constructions. Multiple glass panes made of heating glass can have one or two chambers. The advantages of multiple glass panes are their hermiticity and ability to decrease heat transfer significantly. * Optical transmission and heat losses of windows If the temperature in the building is higher than the temperature outside, the heat leaks through the elements of construction. Windows are usually the most vulnerable elements of the building in terms of heat losses. The heat loss though window constructions is about 20-25% of total heat loss. Heat insulation of translucent constructions can be improved by increasing the number of glasses and chambers of multiple glass panes, but will result in increased construction cost and decreased optical transmission. The reasonable alternative is the usage of low-emissivity glass, which is practically the same as ordinary glass in terms of optical transmission, but it also reflects the heat radiation back into the room. The major indicator which characterizes the ability of glass to reflect heat radiation is its emissivity (E) or the "emission factor". The emission factor of ordinary glass is 0.83; the factor for low-emissive glass can reach 0.03, so that more than 90% of accumulated heat will be reflected back into the room. The lower the emission factor is, the more effective is the material to reflect the heat, and the more heat it will accumulate. To compare, the emission factor of a multiple glass pane with two chambers, which is made of ordinary glass, is the same as the emission factor of a multiple glass pane with one chamber, which was produced with usage of low-emissive glass. Besides energy-efficient functions in cold seasons of the year, low-emissive glass possesses the ability to reflect the excess of outside heat energy in summer seasons; the optical transmission coefficient is affected insignificantly in this way. The additional factor of reduce of heat transfer of multiple glass panes is the usage of low thermal conductivity gases – Ar or Kr – to fill the chambers. In present-day multiple glass panes Ar is more often used, which helps to reduce heat losses by 10-20%, though the cost of multiple glass panes is insignificantly increased. * Influence of window surface temperature on comfort There are two reasons why people feel discomfort when they are close to a cold window surface. First, a cold window is the reason for outflow of heat, which is produced by the cutaneous covering of the individual. Second, a cold window provokes the circulation of air, which is felt like a draft. In order to reduce these factors the heating radiators are always placed under window sills. As far as people can feel cold and heat, the actual temperature of environment is not the only factor which defines the total level of comfort. In reality, the heat radiation of surrounding surfaces has a greater influence than air temperature. If the window surface is cold then to maintain the comfort atmosphere it is necessary to increase the heating temperature, but it will also increase energy consumption. The problem of cold window can be solved effectively with the help of heatable glass. These windows allow to maintain the optimal comfort level and temperature of the room. The air temperature can be decreased at least by 1 degree if the temperature of surrounding surfaces has the same significance. You also do not have to install heating radiators and free the additional space for that. Besides, when turned off the multiple glass panes made of heatable glass act like ordinary low-emissive glass. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heatable glass」の詳細全文を読む スポンサード リンク
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