Environmental Engineering Reference
In-Depth Information
windows are found to have lower overall impacts compared to aluminum
or PVC windows. A review of the available LCAs on windows (Salazar and
Sowlati, 2008), however, concluded that lifetime environmental impact is
not strongly determined by the choice of material as no one material has
an advantage in all impact categories. It is the design features, such as
thermal transmittance coefficient of the entire window and air tightness
of the window to limit the operational energy losses, that define the
environmental impact in the use phase (Tarantini et al., 2011). Use-phase
impacts therefore dominate the lifecycle impacts for windows.
PVC window frames have a thermal conductivity that is at least 1-2 orders
of magnitude lower than that of aluminum and about the same as that
of wood windows. A PVC window with double glazing significantly lowers
thermal losses compared to standard aluminum frames and helps make
homes energy efficient ( Table 5.6 ). Toughness of a PVC-extruded profile
can match that of aluminum frames. But plastic windows are less durable
compared to the aluminum windows (though still better than wooden
frames in this regard).
Table 5.6 A Comparison of Leading Materials Used in Window
Frames
Frame
Embodied
energy
(MJ/kg) a
Carbon
emissions a
Thermal
conductivity
(W/(m·K)
Mean
estimated
lifetime b
(years)
kg eq
CO 2 /kg
Aluminum 214 (34.1)
11.2 (1.98) 205
43.6
PVC
77.2
2.41
0.19
24.1
Hardwood 7.8
0.47
0.07-0.17
39.6
a Hammond and Craig (2012). Value for recycled metal is shown in parenthesis.
b Asif et al. (2005) for each material.
5.4.3 Foam Insulation
Plastic foam insulation is typically made of rigid polyurethane (PU),
polyisocyanurate, or expanded polystyrene (EPS). The thermoset foams
 
 
 
 
 
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