Windows SUSTAINABLE GLAZING TECHNOLOGY.ppt

Windows SUSTAINABLE GLAZING TECHNOLOGY * Window facts One square metre of ordinary glass can let in as much heat as would be produced by a single bar radiator. In winter, heat lost through a window can be ten times more than through the same area of insulated wall. High mass buildings can benefit from larger areas of glazing than would be optimum for a lightweight building. Double glazing is beneficial for all orientations. Variables that alter the thermal effectiveness of glazing systems. Regional climatic conditions. Form and layout. Thermal mass and insulation Positioning of windows Locate and size windows and shading to let sunshine in when the temperature is cold and exclude it when it is its hot. Use thermal mass to store the sun’s heat and provide night-time warmth in cold conditions. Locate window and door openings to allow natural cooling by cross ventilation. Provide seals to openings to minimise unwanted draughts. Glazing “heat flow”, defines the transmission of heat through a glazing unit. This includes the sheets of glass, films, coatings and frames. There are 3 ways “heat flow” occurs. Convection Conduction Radiation Conduction = movement of heat energy through the glass and frame materials from the air on the warmest side to the air on the colder side. The greater the difference in temperatures – the more heat flow. Different frame and glass materials have varying ability to conduct heat, specified by the U-value. The lower the U-value – the less heat is transmitted. U-value Components Aluminium frame - 10.0 Timber frame - 2.8 3mm clear glass - 5.9 Double glazing (uncoated) – 2 x 3mm glass with 6mm air gap - 3.1 SYSTEMS Aluminium frame with 3mm clear glass - 6.9 Aluminium frame with double 3mm clear glass and 6mm gap - 3.8 Timber frame with 3mm clear glass - 5.5 Timber frame with double 3mm clear glass and 6mm gap - 3.0 Primary method to limit conduction: Double glazing creates