“It is the weight of the glass which sets the limit in combination with the type of hardware you are using in the window,” says Magnus Fransson, President of Kronfönster AB in Växjö, Sweden. “We are now pushing the boundaries and are introducing a window with four glass frames intended to be used in passive or ultra energy efficient houses.”

“We can produce a four-paned window in a 110 × 140 cm size, but if it is a fixed structure, it can be made larger. The advantages of a four-paned window are that the costs of heating decrease. This is of great interest to passive houses but the window can also be used in environments where you need extra sound insulation.”

Less heat loss through windows

Many older houses have double paned windows. The inner window, due to its lower temperature together with a human’s body temperature, gives a sense of draft. With better insulation, the window’s temperature is raised thereby creating more comfort. One way to achieve this is to add an extra panel of glass. In the 80s, adding an extra pane of glass to reduce energy usage was revolutionary.

The next stage of development in the 90s was to introduce windows with inert gases like argon between the panes. Since then, building technologies have advanced even further. In 2009, Kronfönster launched its ‘Passive House’ concept, a four-paned window, that is even more energy efficient.

The frame of the four-paned ‘Passive House Ultimate’ window is made of steel, PVC and composite materials. It is maintenance free and does not need to be painted. With four panes as standard, and seals, this window offers low heat loss and insulates from outside noise as well.

The next step

Is a window with five panes the next step, or is it the glass itself that will change?

“Five panes is technically possible but the challenge is to keep the standard 90mm window thickness. If you are going to make room for five panes of glass, you still need to ensure a 16-18 mm air cushion between the panes, which is a technical challenge,” says Fransson.

“We use a new generation of low emission glass. This means there is a thin metallic surface on the outside pane that works as a filter. This means that shortwave radiation or light can enter but long wave radiation in the form of heat cannot get out. Krypton gas in between the panes increases the insulation even more. The U value in a four paned window is 0.6, which is a Swedish insulation record.”

‘Material developments are moving fast and who knows what properties future windows will have?” concludes Fransson.

This article was published in March 2012