M. Cˇ ekon et al.: Cardboard-Based Packaging Materials as Renewable Thermal Insulation of Buildings
DOI: 10.7569/JRM.2017.634135
related with the production of the assessed materi- als are included in the LCA; for example, extraction of raw materials, transport of the raw materials to the production facilities and the production process. The results of individual materials should be com- pared on the basis of a “functional unit.” This reference unit should be common to all assessed samples. The functional unit for evaluation of the environmental impacts of thermal insulations is defined in the PCR as the mass (weight) of the insulation necessary to pro- vide thermal resistance R = 1 m 2 ·K·W –1 [17]. Asdrubali et al. [9] also used this approach in their work. This approach is suitable for comparison of homogenous thermal insulations with small air cavities like PIR, EPS, MW or foam glass. However, it is not suitable for the calculation of the environmental impacts of the described CBM samples. None of these samples has the thermal resistance R = 1 m 2 ·K·W –1 . It would be necessary to either stack several layers together or to increase the thickness of the samples. Either solu- tion would distort the results. Stacking up several layers of the described CBMs is a simple solution for increasing the thermal resistance. However, the ther- mal resistance of the stacked CBM layers would still not be equal to 1 m 2 ·K·W –1 . Increasing the thickness of one layer would increase the thermal resistance as well as mass, but the increase will not be linear. The thermal resistance of the described CBM samples is related to their shape, especially to the dimensions of the air cavities. Increasing the thickness would reduce the ratio between the samples’ thermal resistance and mass. Therefore, we decided to use mass of 1 m 2 of a cardboard sample as a functional unit in this work. Secchi et al. used a similar approach [10]. However, they did not sufficiently address the fact that indi- vidual samples have different physical properties. According to the measurements presented in the pre- vious sections, each CBM sample has different mass and thermal resistance. Therefore, direct comparison of the environmental impacts of the samples is impos- sible with the specified functional unit. Still, each CBM sample can be separately compared with the mass of the PIR, EPS and MW necessary to reach the same thermal resistance at 20 °C (see Table 2). The results of such partial LCAs should still be sufficient to indi- rectly identify the most environmentally friendly CBM sample. 4.2 Life-Cycle Inventory and Impact Assessment Individual materials are represented by generic data from ecoinvent 2.0 database [19] in this LCA. These generic data describe production of PIR, EPS and MW from primary raw materials. It should be noted that
Table 2 Thermal resistance at mean temperature.
Equivalent thermal resistance at specific mean temperature [m 2 ·K·W –1 ]
Thickness [mm]
Sample
10 °C 20 °C 30 °C
M1 M2 M3 M4 M5 M6 M7 M8 M9
69.662 34.007 30.400 26.810 13.268 18.130 28.625 20.084 19.736 25.808
0.5969 0.5195 0.6997 0.6870 0.3382 0.3177 0.3688 0.3505 0.1879 0.1781 0.2345 0.2222 0.4587 0.4438 1.0856 1.0571 0.5194 0.5048 0.6938 0.6738
0.4544 0.6309 0.2892 0.3246 0.1646 0.2056 0.4222 0.9943 0.4837 0.6452
M10
Table 3 Thermal resistance at mean temperature.
Equivalent thermal conductivity coefficient at specific mean temperature [W·m· 1 ·K· –1 ]
Thickness [mm]
10 °C 20 °C 30 °C
Sample
M1 M2 M3 M4 M5 M6 M7 M8 M9
69.662 34.007 30.400 26.810 13.268 18.130 28.625 20.084 19.736 25.808
0.1167 0.1341 0.1533 0.0486 0.0495 0.0539 0.0899 0.0957 0.1051 0.0727 0.0765 0.0826 0.0706 0.0745 0.0806 0.0773 0.0816 0.0882 0.0624 0.0645 0.0678 0.0185 0.0190 0.0202 0.0380 0.0391 0.0408 0.0372 0.0383 0.0400
M10
the description of the cardboard in the used dataset mentions the use of recycled secondary raw materials, but with no specifications. The assessment itself is con- ducted by a GaBi software tool. The assessed mass of the materials considered in the LCAs is specified in Table 4. It is calculated based on the samples’ densities specified in Table 1 and ther- mal resistances at 20 °C specified in Table 2. The first column in the table specifies mass of the CBM samples according to data from the aforementioned tables. The other columns in each row specify the equivalent mass of the PIR, EPS and MW necessary to provide the same thermal resistance as the CBMs in the first column.
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J. Renew. Mater. Supplement June 2017
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