Glazing of windows & doors
Single glazing, double glazing or triple glazing? Here we explain the main characteristics, compare the performance and describe advantages of quality double glazed windows and doors.
Single glazed doors and windows waste a lot of energy. Close to windows it is often not comfortable, in winter it's too cool and too hot in summer.
Then, people often think the window is not tight but in reality it is usually because the glazing is insufficiently insulated. Modern insulated windows outperform conventional single glazing in several areas significantly.
Also known as U-factor or U-coefficient. It is the overall heat transfer coefficient. The U-value describes the energy conducted through building materials or components under standardized conditions. The lower the U-value the better a component’s thermal insulation.
GLAZING - Thermal performance Australia (PDF-file)
“A low U-value will improve both summer and winter performance”
A simple formula can help you quantify the impact of different U-values
U x T x A = watts
U: U-value of the component or system.
T: Difference of air temperature in degree Celsius.
A: Area of the component.
Example of energy loss:
70m², 3 mm clear glass (single glazing) windows. Difference in air temperature, outside to inside: 15°C.
5.9 [W/m² K] x 15 [°C] x 70 [m²] = 6.195 [kW]
This is equal to the energy consumption of about 100 conventional 60 watt light bulbs.
Virtually every type of energy generation or use produces carbon dioxide (CO2), which is made jointly responsible for the climate change. Windows and doors with modern double glazing not only create a more pleasant living environment but also save energy, that is good for the environment and additionally saves even money.
Glazing is glazing – far from it!
As the table above shows, choosing quality low-e double glazing can save about 2/3 of energy compared to the low-quality double glazing, frequently used in Perth and Australia. As an additional benefit, these glass panels provide increased sound insulation, reduce solar energy radiation and can decrease the transmission of light if desired.
What is Low-e glass?
The technical enhancement and optimization of glass never stops. In Europe low-e double glazing is used since 1995. During a special process, a nanometer-thin coat of noble metal is burned in the inner surface of the outer glass.
This metal layer is so thin that it is invisible to the naked eye, thus short-wave light (visible light) can pass the layer. However, a majority of long-wave light (energy intensive infrared light) is reflected back to the outside.
The main objective of low-e glass and window glass with excellent U-values is to keep the internal temperature as constant as possible without air-conditioner or heater.
Sun protection glass
Sun protection glass reduces the cooling load in summer and can be designed to either transmit more or less natural light into the room. Responsible is an invisible-thin layer of noble metal on the inner surface of the outer pane. A lower Solar Heat Gain Coefficient (SHGC) generally also reduces the Visible Light Transmittance (VLT). The metal coating can also cause a mirror effect of the glass front, which for example is used for architectural design.
The presently best glazing for residential buildings is triple glazing. These achieve U-values of 0.7 and lower. Although normally the house walls have better thermal insulation values, the extremely low energy loss values of modern triple glazing exceed ordinary Perth house walls by far. However, triple glazing is relatively expensive compared to double glazing. Thus, the use of triple glazing for thermotechnical reasons in Australia only makes sense if the remaining building envelope also has a good thermal insulation.