G-value: A pane of glass g-value indicates the heat gain as the sun sends into space. The higher the g-value, the more solar heat can pass through the glass.
A modern double-pane now has a g-value of approximately 50-55%. By using built-in blind or pleated blind is possible to reduce the heat gain by as much as 85%. This has a major impact on the amount of energy to be consumed to establish a proper cooling of the room, for example. with air conditioning.
U-value: A glass pane u-value expresses the ability to keep heat from escaping. So the lower the value, the better the insulating properties.
A built-in blinds reduces the pane U-value significantly. The reason for this is that the blind reduces thermo pane convective know that it shares the wide cavity in two narrow space, thus preventing the pane gas in the ventilated from the hot surface to the cold surface. At the same time reflects one lameloverflader Venetian blind, a large part of the radiating heat and prevent it from disappearing through the glazing pane.
A venetian blind closed may reduce a window's U-value of up to 35%. In an energy glass reduction will not be as great, but typically 20%. In one test, the u-value decreased from 2.7 W / m²K when the blind was up to 1.75 W / m²K when the blind was closed. What does this mean in practice?
We consider ourselves a relatively large building with a glass area of 1,000 m² located in Denmark. The office is closed every night at. 17 and opens every morning at. 7 weekdays. When the last person goes home becomes the blinds closed and is opened again when the first person comes to work.
In the months of October to April, we expect an average outside temperature of 0 degrees Celsius in the hours blinds are closed, while the inside temperature of 20º Celsius. The blinds will also be opened and closed on weekends.
Energy consumption in windows between the hours. 17 and 7 without blinds:
14t * 212d * 2.7 W / m²K * 1,000 m² * 20K = 160,272 kWh
(Timer * days * W / m²K * m² * temp. Diff. Outside / inside).
(W / m²K = expression of heat loss through a building).
Energy consumption due. Windows between the hours. 17 and 7 with the blinds closed:
14t * 212d * 1.75 W / m²K * 1,000 m² * 20K = 103,880 kWh
That is a savings of approximately 56,000 kWh. per year or 56 kWh per m² window surface.
This corresponds approximately to 5,600 liters of oil