Refrigeration device for container

1. A container refrigeration apparatus provided in a container, having a refrigerant circuit where a refrigerant circulates to perform a refrigeration cycle, and allowing heat exchange in an evaporator connected to the refrigerant circuit between air in the container and the refrigerant to cool the air, the container refrigeration apparatus comprising:

a gas supply device including at least one adsorption column provided with an adsorbent for absorbing nitrogen in air, a first pumping mechanism supplying pressurized outside air to the at least one adsorption column, and a second pumping mechanism sucking air from the at least one adsorption column to produce nitrogen-enriched air having a higher nitrogen concentration than outside air and supplying the nitrogen-enriched air to the interior of the container via a supply passage;

an oxygen concentration sensor which measures an oxygen concentration of the air in the container;

a controller which controls the operation of the gas supply device so that the oxygen concentration measured by the oxygen concentration sensor reaches a target concentration;

a measurement passage which guides part of the nitrogen-enriched air passing through the supply passage to the oxygen concentration sensor so that the oxygen concentration sensor measures the oxygen concentration of the nitrogen-enriched air;

an on-off valve provided for the measurement passage,

the container houses a fan producing an air flow that passes the evaporator and circulates in the container, and an air passage having a one end opened on a blowout side of the fan and the other end opened on a suction side of the fan so that the air in the container flows from the one end to the other end of the air passage as the fan rotates,

the oxygen concentration sensor is provided for the air passage to measure the oxygen concentration of the air passing through the air passage,

the measurement passage is comprised of a branch pipe which connects the supply passage and the air passage, the branch pipe diverging, and guiding to the air passage, part of the nitrogen-enriched air passing through the supply passage, and

the controller is configured to perform, while the gas supply device is in operation and a rotation of the fan is stopped, a supply air measurement operation in which the on-off valve is opened and the oxygen concentration sensor is allowed to measure the oxygen concentration of the nitrogen-enriched air.

2. The container refrigeration apparatus of claim 1 , further comprising:

a connection joint; and

an introduction pipe, one end of which is connected to the connection joint,

wherein the other end of the introduction pipe is configured to introduce a calibration gas, which is supplied via an external supply pipe connected to the connection joint and is for use in calibration of the oxygen concentration sensor, into the measurement passage to be closer to the oxygen concentration sensor than the on-off valve.

3. The container refrigeration apparatus of claim 1 , wherein

the evaporator is provided on the blowout side of the fan,

the container refrigeration apparatus further comprises a unit controller which performs a cooling operation in which the fan is rotated and the refrigerant is circulated in the refrigerant circuit so that the air in the container is cooled in the evaporator through heat exchange with the refrigerant, and a defrosting operation in which the evaporator is defrosted by heating the evaporator with the rotation of the fan stopped, and

the controller is configured to perform, while the unit controller is performing the defrosting operation, the supply air measurement operation in which the on-off valve is opened and the oxygen concentration sensor is allowed to measure the oxygen concentration of the nitrogen-enriched air.