Principles
Energy payback time The energy payback or amortisation time is the period required by a building material or product to harvest the same amount of energy as was used for its production (fig. 1.32). Photovoltaic panels, for example, have an energy payback time of two years, insulation materials, in contrast, have a payback time of only two to six months.
Global warming potential for the insulation of a brick wall using a variety of products
Energy yield factor The energy yield factor expresses how much more energy a product saves or yields during its lifetime compared to the amount of energy required to produce it. For a photovoltaic module measuring one square meter, the factor is approximately 8; in the case of insulation material, the factor is 15 to 30. The production of, for example, one square meter of insulation material, a 10-cm-thick mineral wool panel, requires one litre of oil. This same insulation material reduces the amount of energy required to heat the building by one litre of oil per year during the insulation material’s lifetime (30 years). The energy payback time is, in this case, one year, the energy yield factor is 30. In a second step, the envelope surface area must or can be improved in terms of its structural configuration. The aim is to achieve a solution using materials appropriate to the task, i.e. materials with the least environmental impact.
foamglass
CO2 eq. [kg CO2 /m2]
Insulation material
WLG
¬ value [W/mK]
density [kg/m3]
thickness [cm]
mineral rockwool glass wool mineral foam
035 032 045
0.035 0.032 0.045
180 100 115
9 8 12
18.9 5.0
polyurethane PUR- hardfoam
024
0.024
30
6
9.7
polystyrene expanded extruded
032 035
0.032 0.035
15 40
8 9
3.7 8.4
038
0.038
100
10
10.9
replenishable raw materials wood fibre 051 cellulose 040
0.051 0.040
280 60
13 11
-23.7 3.26 1.31
Environmental assessment of exterior wall insulation with different thicknesses Material thickness U value CO2 eq. [W/m2K] production 1) [kg CO2 /m2]
CO2 eq. heating [kg CO2 /m2a] actual value
saving
environmental assessment energy yield amortisation [a]
existing building
1.35
+ 6 cm
0.33
4.13
6.7
20.8
150
0.2
+ 12 cm
0.21
4.13
3.3
3.4
25
1.2
+ 18 cm
0.15
4.13
2.4
0.9
25
4.7
+ 24 cm 2)
0.12
4.13
1.9
0.5
3.7
8.1
+ 30 cm
0.10
4.13
1.6
0.3
2.4
12.5
1) 2)
27.5
for each increase of 6 cm the increase of insulation from 18 to 24 cm (additional emissions due to production: 4.13 kg CO2 /m2) reduces the annual CO2 emissions by 0.5 (from 2.4 to 1.9 kg CO2 /m2)
1.32
Sustainable building
The DGNB assessment scheme uses a holistic approach to determine and evaluate the quality of buildings. The quality in terms of energy is considered in the subitem “Life cycle assessment”. Aspects considered include the environmental load created by producing the selected building materials and the input of resources to heat, cool and ventilate the building, which is rated according to the consumption of primary energy. However, some aspects that are associated with the assessment system, such as the weighting of individual criteria or the lack of parameters to evaluate the compactness and appropriateness of buildings, require further review. In particular, the relatively little significance paid to the subitem “Ecology” within the overall assessment is questionable. Because it is fairly easy to accumulate the necessary points for a green label in other sections, these important measures are simply not carried out. The method used to assess a property is presented in figure 1.34. 28
a
b
c
d
1.33