An annual energy performance evaluation method for open refrigerated display cabinets (ORDC) driven by CO2 heat pumps in supermarkets is established to predict the annual heat load, energy consumption, COP and total CO2 emissions. Significant condition variations that affect the system performance are considered. The system is thermodynamically modelled with reference to the actual equipment. Experimental data at a comprehensive range of operative conditions are fitted then the characteristic equations for both the heat load of the ORDC and energy consumption of the condensing unit are obtained. The seasonal and climatic condition changes are accounted by integrating the available annual outdoor temperature data of the store location on the performance calculation. Relative error between the estimated energy consumption and experiment stays within ±20%. The constructed tool is capable of predicting the performance of multiple combinations of different ORDC types and can therefore be used for benchmarking, identifying energy conservation opportunities, and assessment of GHG emission.