Life cycle GHG assessment of magnetic bearing and oil lubricated bearing water cooled chillers

Abstract

AbstractChillers are an important component of the heating ventilation, and air conditioning industry which is one of the largest energy consuming sectors. Magnetic bearing systems have been adopted in the chiller industry to improve compressor efficiency. A life cycle assessment (LCA) of greenhouse gas emissions of magnetic bearing chillers, with a particular focus on the manufacturing stage, has not previously been conducted. This study evaluated global warming potentials of two water chiller systems, an oil lubricated bearing system, and a magnetic bearing system, over their life cycle stages including raw material extraction, manufacturing, transportation, use, and the end of life. The standard ISO 14044 LCA framework was employed to assess the two 500‐ton cooling capacity chillers from a US chiller manufacturing company. Uncertainty analysis was conducted on carbon emission factors from the research literature and sensitivity analysis was conducted on key variables including power mix emission factor, chiller efficiency, and transportation method. The results show that magnetic bearing systems perform better with respect to life cycle GHG emissions. For a general water chiller system life cycle, over 90% of the emissions result from electricity consumption during the use stage with the next largest emissions arising from material extraction and manufacturing. While the material use and manufacturing GHG emissions are similar in the two systems, due to its higher compressor efficiency the magnetic bearing system generates fewer GHG emissions in the use stage. Sensitivity analysis was conducted on electricity mix, non‐standard part load value (NPLV), and transportation method. When the factor values were varied with 5% steps to ±25%, the chiller efficiency and power mix emission factors behaved in similar ways in improving life cycle GHG emissions. NPLV, however, becomes more challenging to improve despite the long history of research on compressor efficiency. This study not only provides analytical data at the product level as to how much GHG emissions can be reduced by improving compressor efficiency and incorporating clean energy, but also provides life cycle GHG inventory data for different end of life and transportation strategies.