Comparative Life Cycle Assessment of Commonly Used Refrigerants in Commercial Refrigeration Systems

摘要

Background, Aim and Scope. In accordance with the Montreal Protocol and Kyoto Protocols, the refrigeration industry is currently evaluating the environmental performance of using HFCs and the so-called natural refrigerants, such as NH_3 or CO_2, as a long-term substitute for CFCs and HCFCs. The objective of this study is to quantify and compare the environmental impact throughout the life cycle of commercial refrigeration systems using HCFCs, HFCs and natural refrigerants. The function of the system under study is the refrigeration of a standard European supermarket with an average surface area of 2000 m~2, with a cooling duty of 130 kW over a period of 15 years. Different scenarios have been created involving a combination of the most common refrigerants (HCFCs (R-22), HFCs (R-134a, R-404A, R-407A, R-407C, R-410A, R-507A) and natural ones (R-744 and R-717)), with different commercial refrigeration systems (direct expansion, secondary loop and distributed), for medium and low temperature. For each scenario, an environmental evaluation was carried out, using the Life Cycle Assessment (LCA) methodology, to compare the influence of both the refrigerant and refrigeration system on the overall contribution to impact.rnMaterials and Methods. According to ISO 1404X standards, the analysis is performed at the following two levels. 1) Firstly, the emissions accounted for in the inventory stage are sorted into impact categories according to CML to obtain an indicator for each category (mandatory elements). 2) Secondly, the weighting of environmental data to a single unit is applied (optional elements). In compliance with ISO 14042, a sensitivity analysis is performed and three different impact assessment methods (Eco-Indicator'95, Eco-Indicator'99 and EPS'00) are applied in order to analyse their influence on the results.rnResults. The use of natural refrigerants such as R-744 and R-717 in direct expansion and secondary loop systems, respectively, is completely justified from the environmental point of view, taking into account that it offers better results for most impact categories and for all impact assessment methods. The need to promote the use of R-744 has to be stressed, despite the fact that it is presently in an experimental phase, and that its current installation outputs are low, since it has been demonstrated that it will perform better in direct expansion systems from an environmental point of view in a future scenario in which its efficiency equals that of R-404A, in the same way as what occurs with R-717 for secondary loop systems.The needrnto replace HCFCs by HFCs or natural refrigerants is clearly shown by the contribution to the ozone depletion category.rnDiscussion. Energy efficiency of a refrigeration installation is a determinant parameter to assess pollutant emissions to the environment. If we assume a future scenario in which R-744 has an efficiency similar to that of R-404A, then R-744 is seen as the refrigerant which offers a better environmental behaviour in the direct expansion system.rnConclusions. It can be concluded that this study demonstrates how using the so-called natural refrigerants as a long-term substitute for CFCs and HCFCs, even better than the use of HFCs, is environmentally feasible.