Examples of superinsulated window frames

Some popular highly insulated window frame constructions on the market include the following:

Frames made of prefabricated sandwich structures of wood/polyurethane/wood or wood/cork/wood. These materials are available today and there is no difference in the production compared to a standard wooden frame, except for the depth of the frame (see Figure 9.5.5). Basic wooden frames with an additional separate shell made of cork, PU, expanded polystyrene insulation (EPS) or plastic profile filled with thermal insulating material. These shells are mounted on the external side of the wooden construction. The shell is not glued onto the wood and, hence, can easily be separated at the end of its lifetime for waste disposal (see Figure 9.5.6).

Thermal coefficients of the frame Uf (W/m2K) Width (mm) (W/mK)

Reveal/lintel 0.72 135

Spandrel 0.78 135

Thermal coefficients of the frame Uf (W/m2K) Width (mm) (W/mK)

Reveal/lintel 0.72 135

Spandrel 0.78 135

Source: www.passivehouse.com

Depth of glazing rebate (mm) Uw(W/m2K)

Materials: wood-PU-wood in sandwich layer construction.

Glass edge system: reinforced polycarbonate with embedded stainless steel layer (0.1 mm). j Frames of this type are also available with aluminium clad at the outer surface. SandW>lCk pMK

Figure 9.5.5 Window frame made of a wood-

Thermal coefficients of the frame Uf (W/m2K) Width (mm) (W/mK)

Reveal/lintel 0.76 148

Spandrel 0.76 148

Depth of glazing rebate (mm) Uw(W/m2K)

Materials: wood-PU-wood in sandwich layer construction. Glazing: 44 mm (4/16/4/16/4).

Glass edge system: reinforced polycarbonate with embedded stainless steel layer (0.1 mm).

Thermal coefficients of the frame Uf (W/m2K) Width (mm) (W/mK)

Reveal/lintel 0.71 120

Spandrel

0.71 120

Depth of glazing rebate (mm) Uw(W/m2K)

Materials: plastic (PVC) profiles filled with thermal insulating foam. Glazing: 36 mm (4/12/4/12/4).

Glass edge system: profile made of thin stainless steel sheet (0.2 mm).

Source:

www.passivehouse.com

Figure 9.5.6 Wooden frame with an additional thermal insulating shell

Source:

www.passivehouse.com

Figure 9.5.7

Thermally insulated plastic profile

Thermal coefficients of the frame Uf (W/m2K) Width (mm) (W/mK)

Reveal/lintel 0.71 125

Spandrel

0.71 125

Source: www.passivehouse.com

Figure 9.5.8 Thermally sseparated aluminium frame with minimal thermal bridges

Depth of glazing rebate (mm) Uw(W/m2K) Materials: Shell: aluminium.

Core: tight PU foam (I = 0.06 W/mK) with minimal thermal bridges. Glazing: 44 mm (4/16/4/16/4).

Glass edge system: reinforced polycarbonate with embedded stainless steel layer (0.1 mm).

Thermal coefficients of the frame Uf (W/m2K) Width (mm) (W/mK) Depth of glazing rebate (mm) Uw(W/m2K)

Reveal/lintel Spandrel

127 127

Materials: plastic (PVC) profiles filled with thermal insulating foam. Glass fibre reinforced profile instead of steel.

Glass edge system: reinforced polycarbonate with embedded stainless steel layer (0.1 mm).

Source:

www.passivehouse.com

Figure 9.5.9 Plastic profile and glass fibre-reinforced profile instead of steel profile

Thermal coefficients of the frame Uf (W/m2K) Width (mm) Wg (W/mK)

Depth of glazing rebate (mm) Uw (W/m2K)

Reveal/ lintel Spandrel

Materials: wood fibre-reinforced profiles filled with thermal insulating foam, wooden shell inside. Glazing: 44 mm (4/16/4/16/4).

Glass edge system: reinforced polycarbonate with rolled stainless steel layer on surface (0.025 mm)

Thermal coefficients of the frame Uf (W/m2K) Width (mm) Wg (W/mK)

Depth of glazing rebate (mm) Uw (W/m2K)

Reveal/ lintel Spandrel

Materials: wood fibre-reinforced profiles filled with thermal insulating foam, wooden shell inside. Glazing: 44 mm (4/16/4/16/4).

Glass edge system: reinforced polycarbonate with rolled stainless steel layer on surface (0.025 mm)

Source:

www.passivehouse.com

Figure 9.5.10 Wood fibre-reinforced plastic profile; no steel for stiffening is necessary

Plastic frames are made of extruded profiles, mainly out of PVC. Here the main chambers have to be filled with polystyrene, PU or other thermal insulating materials, or they have to be very narrow 5mm diameter) (see Figure 9.5.7). Conventional plastic frames lack these insulation properties.

• Thermally separated frames with aluminium shells are available. This frame has the functionality and appearance of an aluminium window, but the core is completely made of tight polyurethane foam with X = 0.06 W/mK and with minimal thermal bridges in the construction (see Figure 9.5.8).

• Further developments will be highly strong profiles, which will not need to be reinforced by steel. Profiles made of glass fibre, reinforced materials (see Figure 9.5.9) or wood fibre-reinforced materials (Figure 9.5.10) are now ready for production.

9.5.4 Positioning of highly insulated windows in a super-insulated wall

When placing the window in the wall, an extra thermal bridge effect has to be taken into account. Typical thermal bridge coefficients (^pos) with optimally designed positions are about ^ = 0.01-0.03 W/mK. The value is higher at the spandrel, for here the frame cannot be covered by an insulation layer because of the weep outlet. At the reveal of the window the frame is normally covered by thermal insulation and the thermal bridge effect can be almost diminished (^pos = 0).

The limit of heat losses for windows in passive houses should be UW,pos 0.85 W/m2K (Central Europe), including the thermal bridge effect of positioning the window in the wall. The indicated values of ^pos refer to a super-insulated wall with UwaU 0.15 W/m2K. Many conventional positioning design details result in large thermal bridge effects (Hauser and Stiegel, 1992, 1997; Hauser et al, 1998; Hauser et al, 2000).

In highly insulated walls, windows are often deeply inset in the wall opening (that is, 30 cm to 40 cm). This can result in the wall section shading the window from solar gains and daylight. One solution to reduce this effect is to bevel the sides of the opening (see Figure 9.5.12). This solution has been applied for centuries - for example, in the Swiss Graubunden region.

Not like this: unfavourable positioning causes high thermal bridge effects and increases the thermal losses dramatically (Wp0s = 0.06 W/mK; Uw^ = 0.93 W/m2K).

Optimal: the window is placed in the middle of the thermal insulation layer of the wall; framing should be minimized by careful structural engineering (Wpos < 0.014 W/mK; UWp0s = 0.82 W/m2K).

Not like this: unfavourable positioning causes high thermal bridge effects and increases the thermal losses dramatically (Wp0s = 0.06 W/mK; Uw^ = 0.93 W/m2K).

Optimal: the window is placed in the middle of the thermal insulation layer of the wall; framing should be minimized by careful structural engineering (Wpos < 0.014 W/mK; UWp0s = 0.82 W/m2K).

Note: UWall = 0.12 W/m2K; the U-value of a single window is, in both cases, the same: Uw = 0.78 W/m2K: Source: www.passivehouse.com

Figure 9.5.11 Design details for positioning a window in a wall

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