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Improving the thermal insulation of windows

机译：改善窗户的隔热效果

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Possibilities of improving the thermal insulation of existing windows were examined on the basis of calculations done with the aid of computer programs WINDOW and FRAME. The U-value of current three-pane windows is roughly 1.7 W/m(sup 2)K. For wooden windows it is slightly smaller than the above value and for plastic windows slightly greater. In wooden windows the light opening has the worst thermal insulation and thus there has been little need to develop the frame and the sash. Using a glazing with a low U-value is unprofitable if the U-value of the frame and sash is not lowered simultaneously. It is easy lower the U-value of a window to 1.2 W/m(sup 2)K by changing the glass, but lowering it to 0.8 W/m(sup 2)K would need major development of frames and sashes. It is now possible to buy three-pane sealed glazing unit with U-values at the centre of the glazing of about 0.7 W/m(sup 2)K. However, use of these glazings requires substantial changes to the frames and casements. The spacers of sealed glazing units also need improvements. Heat loss at the edge of a sealed glazing unit is especially high in fixed windows and in windows with one sash when an aluminium spacer is used. The difference in the mean u-value of a 1200 mm * 1200 mm fixed window can be as high as 25 % when an aluminium spacer is used instead of a silicone spacer, if the u-value at the centre of a glazing is 0.62 W/m(sup 2)K. The U-value of the windows manufactured for the study was measured and computed with the programs that had been obtained. The computed and measured values differed from each other by less than 5 %, which is smaller than the accuracy of the measurement.

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