A CO2 refrigeration system for an ice-playing surface comprises an evaporation stage in which heat is absorbed from an ice-playing surface. CO2 compressors in a compression stage compress CO2 refrigerant subcritically and transcritically. A gas cooling stage has a plurality of heat-reclaim units reclaiming heat from the CO2 refrigerant. A pressure-regulating device is downstream of the gas cooling stage, to control a pressure of the CO2 refrigerant in the gas cooling stage. A reservoir is downstream of the pressure-regulating device for receiving CO2 refrigerant in a liquid state. A controller operates the pressure-regulating device to control the pressure of the CO2 refrigerant in the gas cooling stage as a function of the heat demand of the plurality of heat-reclaim units, the controller causing the pressure of the CO2 refrigerant to reach a transcritical level as a function of a heat demand of the plurality of heat-reclaim units.