Ensinger expands bar product range and recommends
precise Uw value calculation Bars lend the window and consequently the whole building a unique design character. The use of glazing bar windows may even be a requirement for development planning or the restoration of listed buildings. In October 2014 Ensinger added a new muntin bar size 25.4 mm x 9.4 mm to its product range. Thus the Thermix muntin bar sizes 11.4 mm and 9.4 mm are each available in widths of 21.4 mm, 25.4 mm and 31.4 mm.
The muntin bars are available to match the Thermix® TX.N® plus spacers in six colours, and on request individual colour requests can be implemented (see “Muntin bars for Leipzig Opera House”). Supplementary accessories such as cruciforms and end pins ensure secure connections. Configured as rectangular hollow chamber profiles, Thermix® muntin bars are far easier to process than duplex solutions using spacer profiles. Thermix® muntin bars are manufactured from glass fibre-reinforced plastic. The materials are UV-resistant and free of fogging, and the polymer used has impressively low thermal conductivity.
Muntin bar: Superb appearance and energy credentials But how does the bar generally affect the window’s thermal transmission coefficients? First of all, an important distinction must be made: Is the window fitted with a structural bar, a decorative bar or a muntin bar? A “real” or structural bar used to join several insulating glass units to form a single window is the most inefficient in thermal technology terms. Decorative bars and muntin bars are significantly better here. They are mounted in the space between panes and only appear to divide the insulating glass. Unlike the use of internal decorative bars, when using muntin bars the window producer additionally mounts ornamental strips on the outside of the glass. These make the window appear like a real glazing bar window (see info box “The bar makes all the difference”).
In accordance with DIN EN 14351-1, table J.1, the Uw value is calculated by adding a flat-rate value to the Uw value of a window without bars. In practice, however, this method is actually highly imprecise and shows the bar in a detrimental light, as the added value is based on a “worst case scenario”. When performing a precise calculation, the opposite is shown to be the case: If a “warm” system is used made of engineering plastic, such as the Thermix® muntin bar, the increase in the Uw value is only in the hundredths.
Precise calculation of the Uw value with bar To calculate the thermal transmission coefficient (Uw) of a glazing bar window, in addition to the known variables only the length and the Ψ value (in other words: Psi value) of the bar are required. The calculation formula is as follows: Underlying Ψ values for the Thermix® muntin bar have been calculated by the Window Technology Institute ift Rosenheim for double and triple-glazed units, and are shown in the Ensinger data sheet. Ensinger will be pleased to calculate the Ψ values for different insulating glass constructions made with Thermix® muntin bars on request.
To facilitate the calculation of thermal transmission coefficients for architects, planners and window producers, from middle of September, Ensinger will be providing an updated, easy-to-use Uw calculator on its website www.thermix.de/en which will provide fast, accurate results. Other online helps from Ensinger include a window configurator and a heating cost calculator, which demonstrates with just a few clicks how effective thermally optimized windows can be in reducing heating costs for households.
