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Refrigeration systems and heating/air conditioning units used in supermarkets are responsible for a great part of the annual electricity consumption of industrialized countries. Taking also into consideration the direct emissions of carbon dioxide to the environment due to leakage of refrigerants with high Global Warming Potential that are employed today for such applications, a step towards more environmentally friendly and less energy-consuming solutions should be made. In the current research, different topologies of an all-in-one R744 transcritical unit providing refrigeration, heating and air conditioning to a real Greek supermarket store (METRO S.A.) in Athens are studied, using the softwares Engineering Equation Solver and EnergyPlus. The different configurations include a state-of-the-art R744 system with parallel compression and multi-ejector block, the same system with the addition of a subcooling heat exchanger that utilizes available geothermal water, as well as the last described unit with the integration of adiabatic cooling configuration on the gas cooler. These solutions are investigated in terms of energy efficiency and environmental impact (total equivalent warming impact) and they are compared to an indirect arrangement employing R744 and R290, to conventional direct expansion solutions (with R448A or R404A) and to a heat pump employing R410A that covers the heating and air conditioning demands of the supermarket. The comparative energy analysis was separated into the refrigeration part, the heating and air conditioning part and the sum of them. The results indicated that for the climate of the store's location, the case including the subcooler and adiabatic cooling configuration, the case with only the subcooler and the case with neither the subcooler nor the adiabatic cooling configuration consume annually 20.9%, 17.6% and 8.7% less energy respectively than the combination of a refrigeration unit with R448A and a heat pump with R410A for the heating/cooling needs. • All-in-one CO 2 units for refrigeration, heating and air conditioning are studied. • Supermarket refrigeration units using CO 2 and conventional refrigerants are compared. • The use of adiabatic cooling and subcooler employing geothermal water is studied. • The most advanced CO 2 system consumes 20.9% less energy than the conventional system. • The most advanced CO 2 system emits 34.7% less eq.CO 2 tn than a conventional unit. [ABSTRACT FROM AUTHOR]