This case study documents one year of operating experience with a transcritical carbon dioxide (TC CO2) booster refrigeration system at Delhaize America’s Hannaford supermarket location in Turner, Maine.  This supermarket, which began operation in June 2013, is the first supermarket installation in the U.S. of a TC CO2 booster refrigeration system.  We compare refrigeration system performance to that for a supermarket having nearly identical layout and refrigeration loads, in a similar climate and of similar vintage, that uses a conventional hydrofluorocarbon (HFC) refrigerant.  Delhaize provided the submetered and utility data used to generate the performance summaries herein.