Refrigeration system and heat source unit

A heat source unit constituting, together with a plurality of utilization units each including a utilization circuit, a refrigeration system including a refrigerant circuit in which carbon dioxide circulates as a refrigerant,

• the refrigerant circuit including a plurality of heat exchangers, a receiver, a degassing passage through which the refrigerant in a gas state is discharged from the receiver, and a degassing valve disposed on the degassing passage,
• the refrigeration system implementing a first operation during which one of the plurality of heat exchangers functions as a radiator while two of the plurality of heat exchangers function as evaporators, and the refrigerant flows from the heat exchanger functioning as a radiator into the receiver and then flows from the receiver into each of the two heat exchangers functioning as evaporators,
• the heat source unit comprising:
• a heat source circuit connected to the utilization circuits of the utilization units to constitute the refrigerant circuit;
• and
• a heat source control unit configured to change the degassing valve from a closed state to an open state on a condition that a pressure in the receiver exceeds a first pressure set in advance, in the first operation.