The Effect of Revised Characterization Indices for N₂O and CO₂ in Life Cycle Assessment of Optical Fiber Networks – The Case of Ozone Depletion and Aquatic Acidification

摘要

The general trend for fixed broadband is that FTTx will overtake ADSL platforms and the number of FTTx subscribers is increasing exponentially. Moreover, it is likely that the ozone depletion potential (ODP) of dinitrogen oxide (N2O) and the aquatic acidification potential (AAP) of CO2 have been underestimated in LCA studies. The aim of this study is for the first time to assess the ODP and AAP of different FTTx network deployments in Italy adding the most recent characterization factors for N2O and CO2. An LCA case study was conducted covering three FTTx deployments (FTTC is compared to FTTB and FTTH) for 10,000 homes during one year in Italy. The focus is primarily on ODP and AP results in different life cycle phases. The ODP results suggest, using 0.017 kg/kg instead of 0 kg/kg as CFC-11e factor for N2O, for the greenfield/high power customer premise equipment (CPE) scenario, that FTTB, FTTC, and FTTH all rises from around 80–100 gram to around 600–700 gram CFC-11e/year dominated by the use and deployment stages. For AAP, with 1.752 kg/kg as SO2e factor for CO2 instead of 0 kg/kg, the rise is from 5–6 tons to 1,500–1,800 tons SO2e/year. The weight of the use stage is increasing with these new characterization indices. For FTTC controlling the power of the CPE is more important than the technique used for deployment. However, for FTTB and FTTH the deployment technique becomes almost as important as the power mode. Concerning FTTH, the main drivers for CFC-11e footprint are the electricity usage of the home gateways (HGWs), their manufacturing, and the use of diesel trucks in traditional civil works and mini-trench deployment. The inclusion of “average” bandwidth gives an advantage for FTTH as more data can be transferred more efficient and faster. For brownfield deployment in Italy (low power CPEs), FTTH architecture has the lowest amount of total CFC-11e emissions (appr. 130 grams). One of the most important criteria, from ozone depletion point of view, when choosing an FTTx network, is whether fiber has been deployed or not. Including the ODP factor for N2O increases the ODP score by 430–660% for the present systems. The increase for AAP is dramatic and shall be interpreted as a suggestion to include CO2 acidification in further LCIA research.