A refrigeration apparatus for refrigerating a fluid comprising: a refrigerant; a compressor, a condenser, an expansion device, and an evaporator, fluidly connected to form a refrigeration cycle; a controllable valve configured to control a flow of the refrigerant from the condenser to the evaporator; at least one sensor configured to measure a property of the refrigerant; a controller configured to receive from said at least one sensor information about the measured property and use said information to determine an amount of the refrigerant stored in a portion of the refrigeration cycle between an outlet of the compressor and an inlet of the controllable valve including the condenser or in a portion of the refrigeration cycle including the condenser and the output line of the condenser up to the controllable valve or up to the expansion device, the controller being further configured to receive information about a capacity at which the compressor is working and to determine said amount of the refrigerant further based on said information about the capacity at which the compressor is working, the controllable valve being controlled based on the determined amount of the refrigerant, characterized in that the controller is configured to compute a displacement of refrigerant by the compressor and a throughput of refrigerant through the expansion device, and to compute the amount of refrigerant in the portion of the refrigeration cycle between the outlet of the compressor and the inlet of the controllable valve including the condenser or in the portion of the refrigeration cycle including the condenser and the output line of the condenser up to the controllable based on the displacement and the throughput. valve or up to the expansion device a refrigerant; a compressor, a condenser, an expansion device, and an evaporator, fluidly connected to form a refrigeration cycle; a controllable valve configured to control a flow of the refrigerant from the condenser to the evaporator; at least one sensor configured to measure a property of the refrigerant; a controller configured to receive from said at least one sensor information about the measured property and use said information to determine an amount of the refrigerant stored in a portion of the refrigeration cycle between an outlet of the compressor and an inlet of the controllable valve including the condenser or in a portion of the refrigeration cycle including the condenser and the output line of the condenser up to the controllable valve or up to the expansion device, the controller being further configured to receive information about a capacity at which the compressor is working and to determine said amount of the refrigerant further based on said information about the capacity at which the compressor is working, the controllable valve being controlled based on the determined amount of the refrigerant, characterized in that the controller is configured to compute a displacement of refrigerant by the compressor and a throughput of refrigerant through the expansion device, and to compute the amount of refrigerant in the portion of the refrigeration cycle between the outlet of the compressor and the inlet of the controllable valve including the condenser or in the portion of the refrigeration cycle including the condenser and the output line of the condenser up to the controllable based on the displacement and the throughput. valve or up to the expansion device