The heat loss from building windows is great. According to American record, the heat loss from windows is 30% of the building heat loss. In Sweden, the proportion can be 70%, while the number of our country is 50%. Practice has proved that improving the building envelope heat insulation performance, especially the windows heat insulation performance is the most economical and effective method. The insulating glass plays an important role in it. According to American record, heating energy consumption of buildings with grey insulating glass is 5494KJ per square foot, 1/3 of the single glasses buildings (the number is 17775KJ per square foot).
With the development of national economy, we have more strict requirements about the environmental protection, energy saving, the living conditions improvement and other issues and a number of regulations are formulated. The “energy conservation design standards” revised at 1995 (JGJ26095) (hereinafter referred to as the new standard) requires the heating energy consumption should be 50% of the 80s’ standards (building should be 30% and heating system should be 20%), it also has new requirements about the material and heat transfer coefficient of windows and doors.
The heat transfer coefficient of single glass is 6W/m2K, single frame double glasses steel composite window is 3.5W/m2K, and single frame double glasses plastic composite window is 2.6W/m2K. Insulating glass is a must if the window heat transfer coefficient is less than or equal to 2.5W/m2K.
According to the new standards, Beijing, Tianjin, Shenyang and Dalian can reach it by double glasses. However, the double glasses have the condensation problem, the problem would be worse with untight seal. Then the insulating glass replacing double glasses becomes an inevitable trend.
Though the requirement of heat transfer coefficient is stricter than before, there is a gap compared with overseas.
Now the main problem of insulation glasses usage is the cost. The cost can be paid back from energy saving. The record shows the energy saved during 4 or 5 years can pay back the cost in the cold region of our country.