Energy Efficiency of Translucent Structures
One of the nowadays priority directions of science and technology in Russia and the world is a more efficient use of thermal energy. The matter of transition to a reasonable consumption of energy sources and energy independence as the priority in countries policy has become so obvious that argue with this fact is just meaningless. Our country’s position on this issue is reflected in the Federal Law № 261-FL “About energy conservation and improving energy efficiency and amendments being made to certain legislative acts of the RF ”, adopted in 2009 year. According to this law, buildings, structures, and other facilities must comply with the energy efficiency requirements – balance between beneficial effects from energy sources use and expenditures on their use.
Meanwhile, there are a lot of ways to improve the energy efficiency – this is the introduction of efficient lighting systems, and the modernization of the heating systems and hot water supply systems, energy-saving technologies and equipment, instrumenting buildings by modern metering devices, carrying out of energy surveys, and, of course, using of energy-efficient building envelopes, including translucent ones.
Today is almost impossible to imagine any city architecture without buildings glass facades. Although, translucent structures in most cases are the primary source of heat loss – they account for 40–50% of the total heat loss. To understand and choose the most effective solutions should be considered, what increases the heat loss in the translucent structures?
Heat transfer always takes from warmer to cooler medium. It includes three basic types of heat transfer: heat conduction, convection and heat radiation.
Heat radiation is an electromagnetic radiation that emits a substance with a define temperature, due to its internal energy. The radiation takes about 70% of the heat loss. The material resistance to radiation is characterized by emission coefficient (from Lat. Emission – emission ability).
The less emission factor, the more thermal energy will be reflected from the material back into the room. If we talk about translucent structures, the main protection method from radiation is use of double glazing windows with low-E coating.
Glass with low-E coating – it is a burnished float glass, on which surface by spraying is applied comprising free electrons special coating of semiconductor oxide black or colored metals. Today are used two types of low-emission glazing: K-glazing (hard) and i-glazing (soft). The difference between K-glass and i-glass is in their emissivity coefficient, as well as its production technology. K-glass is created by coating its surface by chemical reaction at high temperature (pyrolysis method) of a thin layer of metal oxides InSnO2; i-glass is produced by vacuum deposition and is a threelayer (or more) structure of alternating layers of silver and the dielectric (BiO, AlN, TiO2, etc.). Emission coefficient of ordinary glass is about 0.84, K-glass-0.2, i-glasses-0.04.
This difference gives the energysaving effect: burning characteristics of double-pane glass unit with low emission glass higher than triple- pane glass unit with ordinary glasses. At the same time, in addition to the effect of energy saving, the glass units with low emission glass have another advantage: the double-pane glass unit with low emission glass is 10 kg/m2 lighter than a triple-pane one (with glass thickness – 4 mm), which ensures a longer service lifetime of window sash and reduces the load on window hardware.
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