The ultimate evolution of the IGU for nearly zero energy buildings (nZEB). Three panes, two Argon-filled cavities and double Low-E magnetron coating to halve heat losses compared to standard double glazing.
The third pane physically halves gas convection. Two low-emissivity coatings (Faces 3 and 5) lower the thermal transmittance Ug to values approaching 0.5 W/m2K.
In harsh climates or for Passivhaus architecture, double glazing is no longer sufficient. Inserting a third central pane revolutionises the thermodynamics of the window, creating a transparent element that insulates almost as well as a brick wall.
In a double-glazed unit, the optimal space for Argon gas is 16 mm; beyond this measure, the gas triggers vertical convective motion that worsens insulation. The third pane divides a very thick cavity into two separate, sealed chambers, cancelling out convection. Above all, it provides an extra surface to host the magnetron coatings: using two Low-E coatings (Faces 3 and 5), a double trap for thermal infrared is obtained, halving transmittance compared to the standard.
Three layers of normal glass would create a dense visual filter with a greenish light. The central pane in extra-clear (low-iron) glass, free of iron oxides, is therefore mandatory. Structurally, each pane adds 2.5 kg/m2 per millimetre: a large French door can weigh over 100 kg, requiring heavy-duty hardware.
European and international references applicable.
Cold climates, Passivhaus and nZEB standards. Caution: the central third pane can overheat in hot climates. Use toughened glass (ESG) for the central pane on south-facing facades.
Mandatory standard for zero-energy houses, exploiting winter solar gain while eliminating thermal losses.
PRC.27 · Open the processExtreme use at altitude where Face 6 temperature must remain mild even at -10 degrees C outside.
PRC.27 · Open the processNon-opening glazed walls for full-glass living spaces without the cold wall sensation.
PRC.10 · Open the processAsymmetric systems where the third pane mass eliminates low-frequency noise (heavy traffic).
PRC.27 · Open the processEvery millimetre of glass thickness weighs exactly 2.5 kg/m2. Designing large opening triple-glazed panels, the sash weight can easily exceed 250 kg, requiring steel tracks and motorised mechanical carriages.
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