Refrigerator and operation method during precooling of refrigerator

A refrigerator, comprising:

• a low-stage compressor for compressing a refrigerant;
• an expander-integrated compressor which includes a high-stage compressor for further compressing the refrigerant, and an expander for expanding the refrigerant compressed by the high-stage compressor, the expander being coupled to the high-stage compressor via a rotational shaft drivable by a motor;
• a cooling part for cooling a cooling object with the refrigerant expanded by the expander;
• a refrigerant circulation line for circulating the refrigerant, the refrigerant circulation line including a low-pressure line ranging from the expander to the low-stage compressor via the cooling part, an intermediate-pressure line ranging from the low-stage compressor to the high-stage compressor, and a high-pressure line ranging from the high-stage compressor to the expander;
• a bypass line which is connected at one end to a first connection portion disposed on the high-pressure line and is connected at another end to a second connection portion disposed on the low-pressure line;
• and
• a bypass valve disposed on the bypass line and capable of adjusting a flow rate of the refrigerant flowing through the bypass line by adjusting an opening degree.

An operation method in an initial operation period from startup to a completion of precooling of a refrigerator that includes:

• a low-stage compressor for compressing a refrigerant;
• an expander-integrated compressor which includes a high-stage compressor for further compressing the refrigerant, and an expander for expanding the refrigerant compressed by the high-stage compressor, the expander being coupled to the high-stage compressor via a rotational shaft drivable by a motor;
• a cooling part for cooling a cooling object with the refrigerant expanded by the expander;
• a refrigerant circulation line for circulating the refrigerant, the refrigerant circulation line including a low-pressure line ranging from the expander to the low-stage compressor via the cooling part, an intermediate-pressure line ranging from the low-stage compressor to the high-stage compressor, and a high-pressure line ranging from the high-stage compressor to the expander;
• a bypass line which is connected at one end to a first connection portion disposed on the high-pressure line and is connected at another end to a second connection portion disposed on the low-pressure line;
• a bypass valve disposed on the bypass line and capable of adjusting a flow rate of the refrigerant flowing through the bypass line by adjusting an opening degree;
• a temperature sensor for detecting a temperature of the refrigerant flowing between the cold recovery heat exchanger and the expander of the high-pressure line or a temperature of the refrigerant between the cooling part and the expander of the low-pressure line;
• and
• a controller for controlling the opening degree of the bypass valve and a rotation speed of the rotational shaft based on a detection result of the temperature sensor, the operation method during precooling of the refrigerator, comprising:
• a startup operation step of starting an operation by setting the rotation speed of the rotational shaft at a preset rotation speed lower than a rotation speed during a steady operation after the initial operation period and setting the opening degree of the bypass valve at a preset opening degree;
• a bypass control operation step of controlling, with the controller, such that the opening degree of the bypass valve is decreased until the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature;
• a non-bypass control operation step of cooling, at a stage when the temperature of the refrigerant reaches the first target temperature, the refrigerant until the temperature of the refrigerant reaches a preset second target temperature from the first target temperature, at a 0-percent opening degree of the bypass valve;
• and
• a cooling velocity control step of controlling, with the controller, the rotation speed such that a rate of decrease in the temperature of the refrigerant is maintained constant at least in the bypass control operation step among the bypass control operation step and the non-bypass control operation step.