Abstract: A CO2 based system, such as a heat pump system or a refrigeration system, is disclosed. The system comprises a plurality of ejectors arranged in parallel. Each of the ejectors comprises a motive port and a suction port. Each of the ejectors has a fixed geometry. A first actuated ball valve is arranged in front of the motive port. A second actuated ball valve is arranged in front of the suction port. The system comprises a control unit arranged and configured to control the activity of the ball valves on the basis of one or more predefined criteria.