- Hasse diagram technique (1) (remove)
- Comparative Life Cycle Assessment of CFC-replacement Compounds in Different Technical Applications (2008)
- Aim of the present project is to compare the results of the widely used concept of life cycle assessments (LCA) with those obtained by Discrete Mathematics. Mobile air conditioning (A/C) systems in passenger cars are chosen as an example for technical application of refrigerants. The environmental impacts due to life cycles of different possible substitute refrigerants are compared with the presently used 1,1,1,2-tetrafluoroethane (R134a). Additional refrigerants included in this study comprise dichloromethane (R30), propane (R290), isobutane (R600a), carbon dioxide (R744), pentafluorodimethyl ether (E125), 1,1,1’,1’-tetrafluorodimethyl ether (E134), hepta-fluoropropyl methyl ether (E7000), methyl nonafluorobutyl ether (E7100), ethyl nonafluorobutyl ether (E7200), and 1,1-difluoroethane (R152a). The data interpretation is carried out by means of independent methods such as the Dutch Handbook method (CML02), Eco-indicator 99 (EI99) and Total Equivalent Warming Impact (TEWI). According to the CML02 assessment method, R290, R600a, and R744 have a lower environmental impact compared with R134a in the impact categories “Stratospheric ozone depletion” (SOD), “Climate change” (CC), “Fresh water aquatic toxicity” (FAETP), and “Terrestrial ecotoxicity” (TETP). E125, E7000, E7100, and E7200 are the refrigerants with the lowest impacts in the categories “Acidification” (AP), “Eutrophication” (EP), “Photo-oxidant formation” (POCP), and “Human toxicity” (HTP). In the impact category “Depletion of abiotic resources” (ADP), R152a has a lower impact than R134a. The operation phase is the dominant phase within the life cycle. It accounts to > 79 % for impact category ADP, 71 – 99 % for CC, and > 50 % for FAETP. By means of EI 99 and TEWI, R152a, R290, R600a, R744, and E7200 have a smaller environmental impact than R134a under average operation scenario. According to EI99, the operation phase is with 43 – 63 % the dominating life cycle phase. Comparing the assessment of refrigerants by the three methods shows that each method ranked E134 higher than R134a. E7200, E7100, E7000, R152a, R600a, R290, and R744 are ranked lower than R134a. The fate of some persistent degradation products of the studied refrigerants is modelled. The concentrations of perfluorinated carboxylic acids in surface freshwater systems in Germany due to the annual direct refrigerant emissions of E7000, E7100, and E7200 from the A/C system of a passenger car are about the factor 107 to 109 smaller than the precautionary limit of 0.1 µg/L of the Federal Environment Agency for partly or non-assessable substances in drinking water (UBA 2003). Assuming that all 46 million German passenger cars (Destatis 2006a) are equipped with A/C systems using E7000, E7100, or E7200, the concentration of the degradation products in German surface waters will amount to 0.1 – 1 µg/L. That means even under the best-case scenario the above mentioned precautionary limit will be reached and under worst-case scenario exceeded. The ranking of refrigerants due to the aggregation of six substance-intrinsic properties by means of the mathematical model METEOR (METhod of Evaluation by ORder theory) was performed for 15 refrigerants i.e. chlorodifluoromethane (R22), difluoromethane (R32), pentafluoroethane (R125), 1,1,1-trifluoroethane (R143a), propene (R1270), ammonia (R717), R134a, R152a, R290, R30, R600a, R744, E7200, and the blends R407C and R410A. A high rank is accompanied with a high environmental impact. Considering a selection of possible aggregations, R22 is ranked to 87 % within the five highest ranks, followed by R143a with 85 %, and R32 with 71 %. Refrigerants which are ranked predominantly in the five lowest ranks include R717 (88 %), E7200 (81 %), and R290 (74 %). R744 has in ca. 40 % of the selected aggregations the highest rank and in 24 % the lowest rank. Two third of the refrigerants show a modification in their rank distribution pattern when putting an extreme low or high weight on the thermodynamic properties critical temperature and heat capacity. Additional to the results derived by the LCA conducted in this study, literature LCA results comprising different refrigeration processes and refrigerants were included in the comparison with results from METEOR. In general, METEOR does not agree with the results from LCA. In summary, ranking of refrigerants based on substance-intrinsic properties using METEOR can only give a rough estimation about general environmental impact of a certain refrigerant compared to others. Considering A/C systems in passenger cars, R152a, R290, R600a, and R744 appear as the most recommendable replacements of R134a in this application taking into account the results of the present LCA study derived by the three assessment methods and the fate modelling of some refrigerant degradation products.