ABSTRACT
One of the deficiencies of the conventional Life Cycle Assessment (LCA) method is that it does not consider time explicitly. In addition, there are problems associated with the temporal boundary in the normalization step of LCA. The purpose of this research is to propose a new life cycle assessment method termed “rate load LCA method” that incorporated time dimension into the life cycle inventory analysis and thus life cycle impact assessment phases and rectifies the inconsistency problem in temporal boundary in the normalization step.
Basic premise of the rate load LCA method is that same amount of load over a shorter time period would affect more seriously on the environmental than that over a longer time period. In this work, the manufacturing throughput time and the critical path time concept were used as parameters for consideration of time dimension in the inventory data collection step. Time duration of each life cycle stage was used in order to calculate both the inventory rate load and the characterized impact rate load. Next, the difference between the conventional (cumulative load) LCA method and the rate load LCA method was analyzed. A modified definition of normalized impact was made to solve inconsistency problem in the temporal boundary between the characterized impact and the normalization reference. In the case study, LCA data of a refrigerator were used to compare the cumulative load LCA method with the rate load LCA method. The considered impact categories in this case study were acidification and global warming.
Comparison between the cumulative load LCA method and the rate load LCA method results in different pictures about the distribution of the environmental loads among different life cycle stages. This leads to identification of different significant issues of a product system. The time adjustment to the normalized impact calculation also eliminates inconsistency problem in the temporal boundary between the characterized impact and the normalization reference. In the case study, the significant issues of a refrigerator product system was the use stage if the cumulative load LCA method was used, and the manufacturing stage if the rate load LCA method was used. The different significant issues of the refrigerator from the two different LCA methods are the direct result of considering time duration in the inventory data collection step.
Time consideration in the rate load LCA method indicated that the proposed method not only renders new perspective on the environmental impacts of a product system but also rectifies inconsistency in temporal dimension of the normalization step. Thus, it can be stated that the rate load LCA method is complementary to the cumulative load LCA method.
Next, the carrying capacity concept can be considered into the rate load LCA method. The fractional depletion of carrying capacity was defined and the calculation procedure of the fractional depletion of carrying capacity was proposed. In the case study, the critical loads in ten areas of Korea were chosen in order to demonstrate the effect of critical load on the environmental impact caused by characterized impact rate load (CIRL). The fractional depletion of carrying capacity can provide new insight as to the nature of the resource consumption and environmental emissions of a product system by considering the carrying capacity in the area of interest.
