Container refrigeration device

Abstract

A container refrigeration device (10) is provided with a control unit (100) which, if the pressure detected by a pressure detecting unit (P) during a cooling operation for cooling the inside of a container (1) is lower than a predetermined first pressure that is less than atmospheric pressure, controls a pressure equalization mechanism (40, 80) to perform a pressure equalization operation for equalizing the pressure inside and outside the container (1).

Description

Container refrigeration equipment

[0001] The present disclosure relates to a container refrigeration system.

[0002] Conventionally, container refrigeration systems that cool the interior of a container are known. The container stores objects such as food. The container refrigeration system cools the air inside the container using an evaporator. As a result, the temperature around the object is maintained at or below a predetermined temperature.

[0003] Patent No. 5625582

[0004] When the air inside the container is suddenly cooled by the container refrigeration unit, the pressure inside the container drops, causing the pressure inside the container to become negative (lower than atmospheric pressure), which could lead to damage to the container.

[0005] The present disclosure aims to prevent damage to a container due to a drop in pressure within the container.

[0006] The first aspect is directed to a container refrigeration system, and includes a pressure detection unit (P) that detects the pressure inside a container (1), a pressure equalization mechanism (40, 80) that equalizes the pressure inside and outside the container (1), and a control unit (100) that controls the pressure equalization mechanism (40, 80) to perform a pressure equalization operation to equalize the pressure inside and outside the container (1) when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure during a cooling operation for cooling the inside of the container (1). Here, the "pressure detection unit" includes not only means for directly detecting pressure using a sensor, but also means for indirectly detecting pressure using an index for estimating pressure.

[0007] In the first aspect, in a cooling operation for cooling the inside of the container (1), when the pressure inside the container (1) is lower than a predetermined first pressure, the control unit (100) causes the pressure equalizing mechanism (40, 80) to perform a pressure equalization operation. In the pressure equalization operation, the pressure equalizing mechanism (40, 80) equalizes the pressure inside and outside the container (1), thereby preventing the internal pressure of the container (1) from becoming negative. As a result, damage to the container (1) can be prevented.

[0008] In a second aspect, in the first aspect, the pressure equalization mechanism (40, 80) is a ventilation device (40) that ventilates the container (1), and the ventilation device (40) introduces air outside the container (1) into the container (1) during the pressure equalization operation.

[0009] In the pressure equalization operation of the second aspect, the ventilation device (40) serving as a pressure equalization mechanism introduces air outside the container (1) into the container (1), thereby preventing the internal pressure of the container (1) from becoming negative, and thus preventing damage to the container (1).

[0010] In a third aspect, in the first aspect, the pressure equalization mechanism (40, 80) is a regulator (80) that regulates the composition of air inside the container (1), and the regulator (80) introduces air outside the container (1) into the container (1) during the pressure equalization operation.

[0011] In the pressure equalization operation of the third aspect, the adjusting device (80) serving as a pressure equalization mechanism introduces air outside the container (1) into the container (1), thereby preventing the internal pressure of the container (1) from becoming negative, and thus preventing damage to the container (1).

[0012] In a fourth aspect, in any one of the first to third aspects, the control unit (100) terminates the pressure equalization operation when the pressure detected by the pressure detection unit (P) during the pressure equalization operation is higher than a predetermined second pressure that is lower than atmospheric pressure.

[0013] In the fourth aspect, when the pressure inside the container (1) is higher than a predetermined first pressure during the pressure equalization operation, the control unit (100) terminates the pressure equalization operation, thereby quickly preventing the temperature of the air inside the container (1) from increasing due to the pressure equalization operation.

[0014] In a fifth aspect, in the fourth aspect, the control unit (100) terminates the pressure equalization operation when the pressure in the container (1) is higher than a predetermined first pressure and the temperature of the air in the container (1) is lower than a predetermined temperature.

[0015] In the fifth aspect, the pressure equalization operation is terminated when the pressure inside the container (1) is higher than a predetermined first pressure and the temperature of the air inside the container (1) is lower than a predetermined temperature. If the pressure equalization operation is terminated under conditions where the temperature of the air inside the container (1) is relatively high, the air temperature may further decrease as the cooling operation is performed, which may cause the negative pressure inside the container (1) to increase again. In contrast, in the present invention, the pressure equalization operation is terminated after the temperature of the air inside the container (1) becomes relatively low, which prevents the negative pressure inside the container (1) from increasing again during the subsequent cooling operation. As a result, damage to the container (1) can be prevented.

[0016] A sixth aspect is any one of the first to fifth aspects, wherein the control unit (100) controls the pressure equalizing mechanism (40, 80) to perform a first pressure equalizing operation as the pressure equalizing operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure during the first cooling operation after the container refrigeration unit is started up.

[0017] In the sixth aspect, during the first cooling operation after start-up of the container refrigeration unit, if the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure, the first pressure equalization operation is executed. Therefore, even if the temperature of the air in the container (1) is rapidly cooled by the first cooling operation, damage to the container (1) can be suppressed.

[0018] In a seventh aspect, in any one of the first to fifth aspects, the control unit (100) executes a second pressure equalization operation as the pressure equalization operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure after the door (D) of the container (1) is opened or closed during the cooling operation.

[0019] In the seventh aspect, after the door (D) is temporarily opened during the cooling operation, if the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure, the second pressure equalization operation is performed. Therefore, even if relatively high-temperature air enters the container (1) when the door (D) is opened and this air is suddenly cooled, damage to the container (1) can be suppressed.

[0020] In an eighth aspect, in the seventh aspect, when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure during the first cooling operation after the container refrigeration system is started up, the control unit (100) controls the pressure equalizing mechanism (40, 80) to perform a first pressure equalizing operation as the pressure equalizing operation, and in the second pressure equalizing operation, the pressure equalizing mechanism (40, 80) introduces air outside the container (1) into the container (1) at a flow rate greater than that in the first pressure equalizing operation.

[0021] In the eighth aspect, in the second pressure equalization operation, the pressure equalization mechanism (40, 80) introduces a larger flow rate of outside air into the container (1) than in the first pressure equalization operation. This is because, when relatively high-temperature air is cooled inside the container (1) after the door (D) is temporarily opened, the internal pressure of the container (1) is likely to decrease more quickly than during the initial cooling operation after the container refrigeration unit is started up.

[0022] In a ninth aspect, in any one of the first to eighth aspects, the control unit (100) controls the pressure equalization mechanism (40, 80) in the cooling operation so that the flow rate of air introduced from the outside to the inside of the container (1) decreases as the temperature of the air inside the container (1) decreases.

[0023] In the ninth aspect, when the temperature of the air in the container (1) is high and the negative pressure in the container (1) is likely to increase, the amount of outside air introduced is increased. When the temperature of the air in the container (1) is low and the cooling load due to the introduction of outside air is likely to increase, the amount of outside air introduced is decreased.

[0024] A tenth aspect is any one of the first to ninth aspects, wherein the pressure detection part (P) is a pressure sensor (53).

[0025] In the tenth aspect, the internal pressure of the container (1) is detected by a pressure sensor (53).

[0026] An eleventh aspect is any one of the first to ninth aspects, further comprising a drain pipe (60) that discharges condensed water generated inside the container (1) to the outside of the container (1) and has a trap section (61) in which the condensed water accumulates, and the pressure detection section (P) detects the pressure inside the container (1) based on the water level in the trap section (61).

[0027] In the eleventh aspect, the pressure inside the container (1) is detected based on the water level in the trap portion (61) of the drain pipe (60), because a change in the pressure inside the container (1) causes a change in the water level in the trap portion (61).

[0028] A twelfth aspect is any one of the first to ninth aspects, wherein the pressure detection unit (P) detects the pressure inside the container (1) based on the temperature of the air inside the container (1) before or at the start of the cooling operation and the temperature of the air inside the container (1) during the cooling operation.

[0029] In the twelfth aspect, the pressure inside the container (1) is detected based on the temperature of the air inside the container (1) before and after the start of the cooling operation, because when the temperature of the air inside the container (1) decreases due to the cooling operation, the pressure inside the container (1) changes.

[0030] In a thirteenth aspect, in any one of the first to ninth aspects, the container (1) is provided with gas sensors (71, 72) that detect the concentration of gas components in the air inside the container (1), and the pressure detection unit (P) detects the pressure inside the container (1) based on the concentrations detected by the gas sensors (71, 72) before or at the start of the cooling operation and the concentrations detected by the gas sensors (71, 72) during the cooling operation.

[0031] In the thirteenth aspect, the pressure inside the container (1) is detected based on the concentrations detected by the gas sensors (71, 72) before and after the start of the cooling operation, because there is a correlation between the concentrations detected by the gas sensors (71, 72) and the pressure inside the container (1).

[0032] FIG. 1 is a front perspective view of a container refrigeration unit according to an embodiment. FIG. 2 is a longitudinal cross-sectional view of the container refrigeration unit. FIG. 3 is a block diagram of the main components of the container refrigeration unit. FIG. 4 is a piping diagram of the container refrigeration unit. FIG. 5 is a schematic front view of a ventilation system. FIG. 5(A) shows the lid in the closed position, FIG. 5(B) shows the lid in the intermediate position, and FIG. 5(C) shows the lid in the fully open position. FIG. 6 is a perspective view of the container as seen from the rear (door side). FIG. 7 is a flowchart illustrating the control operation of the pressure equalizing mechanism. FIG. 8 is a flowchart illustrating the control of the pressure equalizing mechanism in the first mode. FIG. 9 is a flowchart illustrating the control of the pressure equalizing mechanism in the second mode. FIG. 10 is a schematic diagram illustrating the drain piping and pressure detection unit of Modification 1A, showing a state in which the pressure inside the container is equal to the pressure outside the container. Fig. 11 is a schematic diagram showing the drain pipe and pressure detection unit of Modification 1A, illustrating a state in which the pressure inside the container is lower than the pressure outside. Fig. 12 is a diagram corresponding to Fig. 3 of Modification 1C. Fig. 13 is a diagram corresponding to Fig. 3 of Modification 1D. Fig. 14 is a diagram corresponding to Fig. 2 of Modification 2A. Fig. 15 is a diagram corresponding to Fig. 3 of Modification 2B.

[0033] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below, and various modifications are possible within the scope of the technical concept of the present disclosure. Since the drawings are intended to conceptually explain the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary to facilitate understanding.

[0034] (1) Overall Configuration of the Container Refrigeration Unit The container refrigeration unit (10) will be described. In the following description, terms such as "front," "rear," "up," "down," "right," and "left" are based on the directions indicated by the arrows in FIG. 1 .

[0035] As shown in Figures 1 and 2, a container refrigeration unit (10) is provided in a container (1). The container (1) is used for marine transportation. The container (1) is a refrigerated container that cools the air inside the container (1). The container (1) has a container body (2) and a container refrigeration unit (10). The container body (2) stores objects such as food and plants. The container refrigeration unit (10) cools the air in an interior space (3) of the container body (2). As shown in Figure 2, a front opening (4) is formed in the front of the container body (2). The container refrigeration unit (10) is attached to the container body (2) so as to close the front opening (4) of the container body (2).

[0036] As shown in FIG. 3, the container refrigeration system (10) includes a cooling unit (10A) for cooling the interior space (3), and a ventilation device (40) for ventilating the interior space (3).

[0037] (2) Cooling Unit As shown in Figures 1 and 2, the cooling unit (10A) has a casing (11). The casing (11) forms a lid for the front opening (4) of the container body (2). The casing (11) has a casing body (12) and a partition plate (13). The casing body (12) separates the container body (2) into an external space (5), which is the external space, and the internal space (3). The partition plate (13) is located on the back side (rear side) of the casing (11).

[0038] The cooling unit (10A) has, as components arranged outside the compartment, a compressor (25), an external heat exchanger (26), and an external fan (27). The cooling unit (10A) has, as components arranged inside the compartment, an internal heat exchanger (29) and an internal fan (30).

[0039] (2-1) Casing Body As shown in FIG. 2, the casing body (12) has a flat plate portion (12a) and a recessed portion (12b). The flat plate portion (12a) is formed on the upper part of the casing body (12) so as to be substantially flush with the front opening (4) of the casing (11). As shown in FIG. 1, an inspection window (22) is provided in the flat plate portion (12a). The inspection window (22) is located on the right side of the flat plate portion (12a). The inspection window (22) is a transparent window through which the inside of the casing body (12) can be seen.

[0040] The recess (12b) is formed in the lower part of the casing (11). The recess (12b) is recessed rearward from the lower end of the flat plate portion (12a). An external storage space (14) is formed in front of the recess (12b). An internal storage space (15) is formed above the recess (12b) and between the flat plate portion (12a) and the partition plate (13). The lower end of the recess (12b) forms a bottom plate (12c). The bottom plate (12c) extends to both the left and right ends of the casing body (12).

[0041] The casing body (12) is formed by laminating an external casing (16), a heat insulating layer (17), and an internal casing (18) in the thickness direction (front-rear direction). The external casing (16) faces the external space (5). The internal casing (18) faces the interior of the refrigerator. The heat insulating layer (17) is provided between the external casing (16) and the internal casing (18). The external casing (16) is made of aluminum material. The internal casing (18) is made of fiber-reinforced plastic (FRP). The heat insulating layer (17) is made of foamed resin.

[0042] (2-2) Partition Plate and Air Passageway As shown in FIG. 2, the partition plate (13) is a plate-like member located on the rear side of the recessed portion (12b). The partition plate (13) extends in the vertical direction so as to be spaced a predetermined distance from the rear surface of the recessed portion (12b). An internal passageway (19), through which internal air flows, is formed between the casing body (12) and the partition plate (13). An inlet port (20) is formed between the upper end of the partition plate (13) and the upper wall (2a) of the container body (2). The inlet port (20) connects the internal space (3) to the inlet end of the internal passageway (19). An outlet port (21) is formed between the lower end of the partition plate (13) and the lower wall (2b) of the container body (2). The outlet port (21) connects the internal space (3) to the outlet end of the internal passageway (19).

[0043] (2-3) Equipment in the External Space The external storage space (14) is provided with a compressor (25), an external heat exchanger (26), and an external fan (27). The compressor (25) is installed on the bottom plate (12c) of the casing (11). The compressor (25) is disposed near the bottom of the external storage space (14). The compressor (25) is disposed near the right of the external storage space (14).

[0044] The external fan (27) is located near the upper part of the external storage space (14). The external fan (27) is a propeller fan. As shown in Figure 2, an external passage (28) through which external air flows is formed behind the external fan (27).

[0045] The external heat exchanger (26) is provided in the external storage space (14) at a height position between the external fan (27) and the compressor (25). The external heat exchanger (26) is located in the external passage (28). The external heat exchanger (26) is a fin-and-tube type heat exchanger.

[0046] (2-4) Equipment in the Internal Space An internal heat exchanger (29) and an internal fan (30) are provided in the internal storage space (15). The internal heat exchanger (29) is supported by the casing (11) so as to span the casing body (12) and the partition plate (13). The internal heat exchanger (29) is a fin-and-tube heat exchanger.

[0047] (2-5) Refrigerant Circuit As shown in FIG. 4, the cooling unit (10A) has a refrigerant circuit (R). The refrigerant circuit (R) is filled with a refrigerant. The refrigerant circuit (R) performs a vapor compression refrigeration cycle by circulating the refrigerant. The refrigerant used in the refrigerant circuit (R) is, for example, a natural refrigerant such as propane or carbon dioxide.

[0048] The refrigerant circuit (R) mainly includes a compressor (25), an external heat exchanger (26), an expansion valve (31), and an internal heat exchanger (29).

[0049] The compressor (25) compresses the sucked refrigerant. The compressor (25) discharges the compressed refrigerant. A discharge pipe (32) is connected to a discharge portion of the compressor (25). A suction pipe (33) is connected to a suction portion of the compressor (25). An accumulator (34) is provided in the suction pipe (33). The accumulator (34) is a container for storing liquid refrigerant.

[0050] The external heat exchanger (26) exchanges heat between the refrigerant flowing therethrough and the external air. The gas end of the external heat exchanger (26) communicates with the discharge pipe (32). The liquid end of the external heat exchanger (26) is connected to the liquid end of the internal heat exchanger (29) via a liquid pipe (35). The external heat exchanger (26) functions as a radiator (condenser) that radiates heat from the refrigerant to the air.

[0051] The expansion valve (31) is provided in the liquid pipe (35). The expansion valve (31) is an expansion mechanism that reduces the pressure of high-pressure refrigerant to low-pressure refrigerant. The expansion valve (31) is an electronic expansion valve with an adjustable opening. The expansion mechanism may be a capillary tube or an expander. A receiver (36) is provided in the liquid pipe (35) between the external heat exchanger (26) and the expansion valve (31). The receiver (36) is a container that stores excess refrigerant in the refrigerant circuit (R).

[0052] The internal heat exchanger (29) exchanges heat between the refrigerant flowing therethrough and the internal air. The gas end of the internal heat exchanger (29) communicates with the suction pipe (33). The internal heat exchanger (29) functions as an evaporator in which the refrigerant absorbs heat from the air.

[0053] The refrigerant circuit (R) has a bypass pipe (37). An inflow end of the bypass pipe (37) communicates with the discharge pipe (32), and an outflow end of the bypass pipe (37) communicates with the liquid pipe (35). The bypass pipe (37) sends the refrigerant discharged from the compressor (25) to the internal heat exchanger (29), bypassing the external heat exchanger (26).

[0054] The refrigerant circuit (R) is provided with a first valve (38) and a second valve (39). The first valve (38) is provided between the discharge side of the compressor (25) and the gas end of the external heat exchanger (26), and downstream of the connection portion of the bypass pipe (37). The second valve (39) is provided in the bypass pipe (37). The first valve (38) and the second valve (39) are formed by solenoid on-off valves. The first valve (38) and the second valve (39) may be flow control valves whose opening degrees are adjustable.

[0055] (3) Ventilation Device The configuration of the ventilation device (40) will be described with reference to Figures 1, 2, and 5. The ventilation device (40) ventilates the internal space (3) of the container body (2). The ventilation device (40) of this embodiment has an air supply function of supplying outside air, i.e., outdoor air, to the internal space (3) and an exhaust function of discharging the internal air to the external space (5). In this embodiment, the ventilation device (40) also serves as a pressure equalization mechanism.

[0056] As shown in Fig. 1, the ventilation device (40) is disposed in a left-side portion of the flat plate portion (12a) of the casing body (12). As shown in Fig. 2, the ventilation device (40) is provided in a ventilation mounting opening (6) formed in the front surface of the casing body (12). The ventilation mounting opening (6) penetrates the casing body (12) from front to rear. The ventilation mounting opening (6) is formed across the exterior casing (16), the heat insulating layer (17), and the interior casing (18).

[0057] An air supply passage (41) and an exhaust passage (42) are formed inside the ventilation device (40). The air supply passage (41) and the exhaust passage (42) communicate between the internal space (3) and the external space (5). Specifically, the inflow end of the air supply passage (41) communicates with the external space (5). The outflow end of the air supply passage (41) communicates with the primary side (upstream side) of the internal fan (30) in the internal passage (19). The inflow end of the exhaust passage (42) communicates with the secondary side (downstream side) of the internal fan (30) in the internal passage (19). The outflow end of the exhaust passage (42) communicates with the external space (5).

[0058] The ventilation device (40) has a ventilation fan. The ventilation fan is configured by the above-described internal fan (30). In this embodiment, the internal fan (30) is used both as the ventilation device (40) and the cooling unit (10A). When the internal fan (30) is driven, outside air from the external space (5) is supplied to the internal space (3) through the air supply passage (41). At the same time, inside air from the internal space (3) is discharged to the external space (5) through the exhaust passage (42).

[0059] 2 and 5, an air supply communication port (41a) is formed at an end of the air supply passage (41) facing the external space (5), and an exhaust communication port (42a) is formed at an end of the exhaust passage (42) facing the external space (5).

[0060] As shown in FIG. 2 , the ventilation device (40) includes a motor (43), a drive shaft (44) that is rotationally driven by the motor (43), and an open / close lid (45) that is connected to the drive shaft (44). The motor (43) and the drive shaft (44) are housed in a casing of the ventilation device (40). The motor (43) is configured as a stepping motor. The drive shaft (44) is directly connected to the motor (43). The drive shaft (44) may also be indirectly connected to the motor (43) via a pinion or gear.

[0061] The open-close lid (45) is provided in front of the drive shaft (44). The open-close lid (45) is configured to be rotatable about the axis of the drive shaft (44). The open-close lid (45) opens and closes the air supply passage (41) and the exhaust passage (42) depending on the angle of rotation of the open-close lid (45). The open-close lid (45) constitutes an opening adjustment mechanism that adjusts the opening degrees of the air supply passage (41) and the exhaust passage (42).

[0062] 5, the open / close lid (45) is formed with an air intake opening (46) and an exhaust opening (47). The air intake opening (46) is configured to be able to communicate with the air intake communication port (41 a). The exhaust opening (47) is configured to be able to communicate with the exhaust communication port (42 a).

[0063] Specifically, when the open-close lid (45) is at the first rotation angle (closed position) shown in Fig. 5(A), the entire air supply communication opening (41a) is covered by the open-close lid (45), and the entire air exhaust communication opening (42a) is covered by the open-close lid (45). As a result, the air supply passage (41) and the air exhaust passage (42) are fully closed.

[0064] When the open-close cover (45) is at the second rotation angle (fully open position) shown in Figure 5(C), the entire air supply communication port (41a) overlaps with the air supply opening (46), and the entire air exhaust communication port (42a) overlaps with the air exhaust opening (47). As a result, the air supply passage (41) and the air exhaust passage (42) are fully open.

[0065] When the open-close cover (45) is at the third rotation angle (intermediate position) shown in Fig. 5(B), a portion of the air supply communication port (41a) overlaps with the air supply opening (46) in the axial direction, and a portion of the exhaust communication port (42a) overlaps with the exhaust opening (47) in the axial direction. The intermediate position is a position between the closed position and the fully open position. Therefore, the opening degrees of the air supply passage (41) and the exhaust passage (42) are smaller than those in the fully open state.

[0066] The rotation angle of the opening / closing lid (45) is adjusted between the closed position and the fully open position, thereby adjusting the opening degree of the air supply passage (41) and the air exhaust passage (42), and further adjusting the ventilation volume of the ventilation device (40).

[0067] (4) Sensors The container refrigeration system (10) has a plurality of sensors. As shown in Figures 2 and 3, the plurality of sensors include an inside temperature sensor (51), an outside temperature sensor (52), and a pressure sensor (53).

[0068] The internal temperature sensor (51) detects the temperature of the internal air in the container (1). The internal temperature sensor (51) is arranged in the internal passage (19) upstream of the internal fan (30) in the air flow direction. The internal temperature sensor (51) is arranged near the inlet (20) of the internal passage (19).

[0069] The outside-compartment temperature sensor (52) detects the temperature of the outside air outside the container (1). The outside-compartment temperature sensor (52) is arranged in the external passage (28) upstream of the external heat exchanger (26) in the air flow direction. The outside-compartment temperature sensor (52) is arranged near the inlet of the external passage (28).

[0070] The pressure sensor (53) is an example of a pressure detection unit (P). The pressure sensor (53) detects the pressure inside the container (1). The pressure sensor (53) is arranged in the internal passage (19). For example, the pressure sensor (53) is arranged upstream of the internal fan (30) in the air flow direction in the internal passage (19). However, the pressure sensor (53) may be arranged downstream of the internal fan (30) in the air flow direction in the internal passage (19).

[0071] (5) Control Unit and Operation Unit As shown in FIG. 3 , the container refrigeration system (10) has a control unit (100). The control unit (100) controls the cooling unit (10A) and the ventilation system (40). The control unit (100) includes a microprocessor, an electric circuit, and an electronic circuit. The microprocessor includes a CPU (Central Processing Unit), a memory, a communication interface, an analog input / output, and a contact input / output interface. The memory stores various programs to be executed by the CPU and data used by the programs.

[0072] The control unit (100) controls each device of the cooling unit (10A). Specifically, the control unit (100) controls the rotation speed of the compressor (25), the rotation speed of the internal fan (30), the rotation speed of the external fan (27), the opening of the expansion valve (31), etc. The control unit (100) controls the motor (43) of the ventilation device (40). The control unit (100) adjusts the opening of the air supply passage (41) and the air exhaust passage (42) of the ventilation device (40), and further adjusts the ventilation volume of the ventilation device (40).

[0073] As shown in FIG. 3 , the container refrigeration unit (10) has an operation unit (110). The operation unit (110) is configured with, for example, a touch panel, a remote controller, a switch, or the like provided on the container refrigeration unit (10). The operation unit (110) may be a communication terminal connected to the container refrigeration unit (10) via a network. A user can operate the operation unit (110) to switch the operation mode of the container refrigeration unit (10) or change the set values ​​of each operation mode. The set values ​​include a target temperature of the interior space (3).

[0074] (6) Overview of Cooling Operation The container refrigeration system (10) performs cooling operation, which is an operation mode that is executed by a user or the like operating the operation unit (110).

[0075] During the cooling operation, a refrigeration cycle is performed in which refrigerant compressed by the compressor (25) is condensed in the external heat exchanger (26), decompressed by the expansion valve (31), and evaporated in the internal heat exchanger (29). Air flowing out from the internal space (3) into the internal passage (19) is cooled by the internal heat exchanger (29) functioning as an evaporator. The cooled air is sent to the internal space (3). During the cooling operation, the control unit (100) controls the rotation speed of the compressor (25) based on the difference between the temperature of the internal air in the internal space (3) and the target temperature.

[0076] In the cooling operation, the control unit (100) controls the compressor (25) so that the temperature of the internal air reaches a target temperature. When the temperature of the internal air reaches the target temperature (thermo-off temperature, e.g., −18°C), the control unit (100) stops the compressor (25). As a result, the internal heat exchanger (29) is essentially in a stopped state (thermo-off state). Thereafter, when the temperature of the internal air reaches a predetermined temperature (thermo-on temperature, e.g., −16°C) higher than the target temperature, the control unit (100) operates the compressor (25) to cause the internal heat exchanger (29) to function as an evaporator. The control unit (100) controls the rotation speed of the compressor (25) to adjust the evaporation temperature of the internal heat exchanger (29). As a result, the temperature of the internal air is maintained within a predetermined target range. The thermo-off temperature corresponds to the set temperature input via the operation unit (110). The thermo-on temperature is the set temperature plus a predetermined temperature (e.g., 2°C).

[0077] (7) Measures to prevent container damage during cooling operation (7-1) Issues During the cooling operation described above, the temperature of the air inside the container decreases as the air inside the container is cooled. When the temperature of the air inside the container decreases during cooling operation, the volume of the air inside the container decreases, causing the pressure inside the container (1) to decrease, and this pressure may become a negative pressure that is lower than atmospheric pressure. As a result, the negative pressure inside the container (1) exceeds the pressure resistance of the container (1), causing a problem of damage to the container (1). Damage to the container (1) may occur, for example, when the container body (2) is deformed due to the negative pressure inside the container (1).

[0078] In particular, during the cooling operation, the pressure in the container (1) drops sharply in the following two periods:

[0079] The first period is a pull-down operation period. The pull-down operation is the first cooling operation after the container refrigeration system (10) is started. In other words, the pull-down operation is the first cooling operation after the container refrigeration system (10) is turned on. At the start of the pull-down operation, the temperature of the inside air is relatively high, close to the outside air temperature. In the pull-down operation, the relatively high temperature inside air is cooled to a temperature for refrigerating or freezing objects. For example, if the temperature of the inside air at the start of the pull-down operation is 30°C, this air may be cooled to a target temperature of -12°C. In this way, when the relatively high temperature inside air is cooled by a large temperature difference, the pressure inside the container (1) decreases, and the negative pressure increases.

[0080] The second period is a period after the door (D) of the container (1) is temporarily opened during the cooling operation. As shown in FIG. 6 , the container (1) has a door (D) for loading and unloading objects. The door (D) is provided, for example, on the rear surface (7) of the rear side of the container (1). The door (D) opens and closes an opening formed on the rear surface that communicates with the interior space (3). During the cooling operation, the temperature of the interior air is maintained within a target range, i.e., a range between the thermo-off temperature (−18°C) and the thermo-on temperature (−16°C) described above. Assume that, when the interior heat exchanger (29) is in the thermo-off state, an operator temporarily opens the door (D) of the container (1) for some purpose and then closes it. When the door (D) is opened, air from outside the container (1) enters the interior of the container (1). The air that enters from outside the container (1) is at a relatively high temperature (e.g., 30°C) compared to the temperature of the interior air (e.g., −18°C). As a result, the infiltrated air is rapidly cooled by the surrounding in-compartment air. Furthermore, when the temperature of the in-compartment air rises above the thermo-on temperature due to the infiltration of outside air, the compressor (25) is operated and the in-compartment heat exchanger (29) is brought into the thermo-on state. As a result, the infiltrated air is rapidly cooled by the in-compartment heat exchanger (29). For the above reasons, when the door (D) is opened or closed during the cooling operation, the pressure inside the container (1) drops rapidly and the negative pressure increases. This problem becomes particularly noticeable when the door (D) is opened or closed when the in-compartment heat exchanger (29) is in the thermo-off state.

[0081] Furthermore, the problem of damage to the container (1) is caused by the following. From the viewpoint of quality control of the container (1), improved airtightness is required. The more airtight the container (1) is, the less air leaks through gaps in the container (1). As a result, the energy saving performance of the container refrigeration system (10) is improved. On the other hand, if the airtightness of the container (1) is increased, when the inside of the container (1) becomes negative pressure during cooling operation, it becomes difficult for air outside the container (1) to enter the inside of the container (1) through gaps. Therefore, the negative pressure inside the container (1) increases further during cooling operation, and this negative pressure exceeds the withstand pressure of the container (1).

[0082] (7-2) Control of Pressure Equalization Mechanism To solve the above-described problems, the container refrigeration system (10) performs a pressure equalization operation. The pressure equalization operation is an operation of equalizing the pressure between the outside and the inside of the container (1) when the negative pressure inside the container (1) increases during the cooling operation. In other words, the pressure equalization operation is an operation of introducing air outside the container (1) into the inside of the container (1) when the negative pressure inside the container (1) increases during the cooling operation. The pressure equalization operation of this embodiment is performed by the ventilation device (40), which is a pressure equalization mechanism. The pressure equalization operation includes a first pressure equalization operation and a second pressure equalization operation. The first pressure equalization operation is an operation of equalizing the pressure between the outside and the inside of the container (1) during the pull-down operation described above. The second pressure equalization operation is an operation of equalizing the pressure between the outside and the inside of the container (1) after the door (D) is opened or closed during the cooling operation. The first pressure equalization operation is performed in the first mode. The first mode is a control mode for controlling the pressure equalization mechanism during pull-down operation. The second pressure equalization operation is performed in the second mode. The second mode is a control mode for controlling the pressure equalization mechanism after the door (D) is opened or closed.

[0083] The control of the pressure equalization mechanism will be described in detail with reference to the flowcharts of FIGS.

[0084] (7-2-1) Basic Control As shown in FIG. 7, when a command to start the cooling operation is received in step S11, the control unit (100) starts the cooling operation in step S12. The command to start the cooling operation is input to the control unit (100) by a user operating the operation unit (110). Note that, at the start of the cooling operation, the ventilation device (40) does not equalize the pressure inside and outside the container (1). Specifically, the opening / closing lid (45) of the ventilation device (40) is in the fully closed position.

[0085] The control unit (100) determines whether to perform a pressure equalization operation based on the pressure detected by the pressure sensor (53). The pressure detected by the pressure sensor (53) corresponds to the pressure inside the container (1). The control unit (100) determines whether to transition to the first mode or the second mode depending on the rate of change of the detected pressure until the detected pressure becomes equal to or lower than the first pressure. If the rate of change is slow, the control unit (100) transitions to the first mode, and if the rate of change is fast, the control unit (100) transitions to the second mode.

[0086] Specifically, in step S13, if the first condition is satisfied, that is, the pressure detected by the pressure sensor (53) is equal to or less than the first pressure, and the time Δt required for the detected pressure to reach the first pressure is equal to or greater than the predetermined time t1, the control unit (100) performs the first mode process in step S17. The first pressure is a predetermined pressure lower than atmospheric pressure. The detected pressure being equal to or less than the first pressure, in other words, means that the negative pressure is equal to or greater than a predetermined value. The first pressure is, for example, a pressure equivalent to a negative pressure of 2 [KPa]. The negative pressure equivalent to the first pressure is set to a predetermined value lower than the withstand pressure of the container (1). The time Δt required for the detected pressure to reach the first pressure is the time from the time ta when the detected pressure starts to decrease to the time tb when the detected pressure reaches the first pressure. The control unit (100) determines, for example, the time ta when the detected pressure starts to decrease at a predetermined rate of change (gradient).

[0087] In this way, if the time Δt required for the detected pressure to reach the first pressure is relatively long in step S13, it can be determined that the pressure inside the container (1) is decreasing due to the pull-down operation. Therefore, the process proceeds to the first mode in step S17, and the control of the ventilation device (40) corresponding to the pull-down operation shown in FIG. 8 is executed.

[0088] If the condition of step S13 is not satisfied, the process proceeds to step S14. In step S14, if the first condition is satisfied, that is, the detected pressure is equal to or less than the first pressure, and if the time Δt required for the detected pressure to reach the first pressure is shorter than the predetermined time t1, the control unit (100) performs the second mode process of step S18. When the air inside the container (1) is cooled due to the opening and closing of the door (D) during the cooling operation, the rate at which the pressure inside the container (1) decreases becomes faster than in the pull-down operation. Therefore, if the time Δt required for the detected pressure to reach the first pressure is relatively short, it can be determined that the pressure inside the container (1) is decreasing due to the opening and closing of the door (D). Therefore, the process proceeds to the second mode of step S18, and the control of the ventilation device (40) after the opening and closing of the door (D) shown in FIG. 9 is executed.

[0089] If the conditions of steps S13 and S14 are not satisfied, the process proceeds to step S15. If a command to terminate the cooling operation is received in step S15, the control unit (100) terminates the cooling operation in step S16. The command to terminate the cooling operation is input to the control unit (100) by a user operating the operation unit (110).

[0090] (7-2-2) First Mode The first mode is a control mode of the ventilation device (40) during pull-down operation. As shown in Fig. 8 , upon transition to the first mode, in step S21, the control unit (100) controls the ventilation device (40) to perform a pressure equalization operation to equalize the pressure inside and outside the container (1). In other words, when the first condition in step S13 is satisfied during the first cooling operation (pull-down operation) after the start-up of the container refrigeration system (10), the control unit (100) controls the ventilation device (40) to perform a first pressure equalization operation as a pressure equalization operation.

[0091] In step S21, the control unit (100) controls the ventilation device (40) to introduce a first flow rate of outside air into the container (1). Specifically, the control unit (100) adjusts the rotation angle of the open / close lid (45) of the ventilation device (40), i.e., the opening degrees of the air supply passage (41) and the exhaust passage (42), so that the flow rate of air introduced into the container (1) becomes the first flow rate. By introducing outside air into the container (1), the pressure inside and outside the container (1) is equalized. As a result, the pressure inside the container (1) increases rapidly. In other words, the negative pressure inside the container (1) decreases.

[0092] Next, in step S22, if the detected pressure is higher than the second pressure and the inside temperature is equal to or lower than the first temperature, the process proceeds to step S23. In step S23, the control unit (100) controls the ventilation device (40) so that a second flow rate of outside air is introduced into the container (1). The second pressure has the same value as the first pressure and corresponds to a negative pressure of 2 [Kpa]. The second pressure may be higher or lower than the first pressure. The second flow rate is a predetermined flow rate that is smaller than the first flow rate. The first flow rate is, for example, 5 [m 3 / h], and the second flow rate is, for example, 3 [m 3 / h]. The first temperature is, for example, 10° C. The internal temperature is a value detected by the internal temperature sensor (51).

[0093] As described above, in this embodiment, when the temperature of the inside air falls below a predetermined temperature during the pressure equalization operation, the control unit (100) reduces the amount of air introduced into the container (1). This is because when the temperature of the inside air falls, the pressure inside the container (1) does not drop significantly, and the risk of damage to the container (1) is reduced. By reducing the amount of outside air introduced, the inside air can be cooled quickly during the pull-down operation. By reducing the amount of outside air introduced, the cooling load inside the container (1) can be reduced, and the pull-down operation can be completed quickly.

[0094] Next, in step S24, if the second condition that the detected pressure is higher than the second pressure is satisfied and the third condition that the internal temperature is equal to or lower than the second temperature is satisfied, the process proceeds to step S25. In step S25, the control unit (100) terminates the pressure equalization control of the ventilation device (40). Specifically, the control unit (100) places the opening / closing cover (45) of the ventilation device (40) in the fully closed position. The second temperature is a predetermined temperature lower than the first temperature. The second temperature is, for example, 0°C.

[0095] When the temperature of the air inside the container (1) reaches the second temperature (e.g., 0°C), even if the temperature of the air inside the container (1) is further reduced by the pull-down operation, the internal pressure of the container (1) does not decrease significantly, and the possibility of negative pressure occurring inside the container (1) is reduced. Therefore, in step S24, when the second and third conditions are satisfied, the control unit (100) terminates the pressure equalization operation of the ventilation device (40).

[0096] By the above control, even if the pressure inside the container (1) drops during the pull-down operation, the negative pressure inside the container (1) can be prevented from exceeding the withstand pressure of the container (1), thereby preventing damage to the container (1) due to the pull-down operation.

[0097] (7-2-3) Second Mode The second mode is a control mode of the ventilation device (40) after the door (D) is temporarily opened or closed during cooling operation. As described above, the transition condition to the second mode (step S14) is likely to be met when the door (D) is temporarily opened or closed while the internal heat exchanger (29) is in the thermo-off state, in other words, when the internal temperature is within the target range.

[0098] 9 , upon transition to the second mode, in step S31, the control unit (100) controls the ventilation device (40) to perform a pressure equalization operation to equalize the pressure inside and outside the container (1). In other words, when the first condition of step S14 is satisfied after the door (D) is opened or closed during the cooling operation, the control unit (100) controls the ventilation device (40) to perform a second pressure equalization operation as the pressure equalization operation.

[0099] In step S31, the control unit (100) controls the ventilation device (40) to introduce a third flow rate of outside air into the container (1). Specifically, the control unit (100) adjusts the rotation angle of the open / close lid (45) of the ventilation device (40), i.e., the opening degrees of the air supply passage (41) and the exhaust passage (42), so that the flow rate of air introduced into the container (1) becomes the third flow rate. By introducing the outside air into the container (1), the pressure inside and outside the container (1) is equalized. As a result, the pressure inside the container (1) increases rapidly. In other words, the negative pressure inside the container (1) decreases.

[0100] Here, the third flow rate is greater than the first and second flow rates in the first mode. The third flow rate is, for example, 10 m 3 / h]. That is, in the second pressure equalization operation, the ventilation device (40) introduces air from outside the container (1) into the container (1) at a flow rate greater than that in the first pressure equalization operation. As described above, after the door (D) is opened and closed, the pressure inside the container (1) decreases more quickly than in the pull-down operation. In contrast, the ventilation device (40) introduces outside air at a relatively large flow rate, and therefore, it is possible to prevent the negative pressure inside the container (1) from reaching the withstand pressure of the container (1).

[0101] Next, in step S32, if a second condition is met, that is, the detected pressure is higher than the second pressure, the process proceeds to step S33. In step S33, the control unit (100) terminates the pressure equalization control of the ventilation device (40). Specifically, the control unit (100) sets the opening / closing lid (45) of the ventilation device (40) to the fully closed position.

[0102] By the above control, even if the pressure inside the container (1) decreases due to the opening and closing of the door (D), the negative pressure inside the container (1) can be prevented from exceeding the withstand pressure of the container (1), thereby preventing damage to the container (1) due to the opening and closing of the door (D).

[0103] (8) Effects of the Embodiment (8-1) The control unit (100) of the present embodiment controls the ventilation device (40) to perform a pressure equalization operation to equalize the pressure inside and outside the container (1) when a first condition is met in which the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure during the cooling operation for cooling the inside of the container (1).

[0104] Therefore, even if the pressure inside the container (1) decreases due to cooling of the air inside the container (1), the pressure inside the container (1) can be quickly increased by the pressure equalization operation. As a result, the negative pressure inside the container (1) can be prevented from increasing, and damage to the container (1) can be prevented.

[0105] In addition, by performing such control, even if a highly airtight container (1) is used, damage to the container (1) can be suppressed, and as a result, the energy saving performance of the container refrigeration system (10) can be prevented from being impaired due to the intrusion of outside air through gaps in the container (1).

[0106] (8-2) In this embodiment, the pressure equalization mechanism is a ventilation device (40) that ventilates the container (1). Therefore, the ventilation device (40) can be used as a pressure equalization mechanism, thereby reducing the number of parts. The ventilation device (40) can introduce a relatively large flow rate of outside air into the container (1). Therefore, even if the pressure inside the container (1) suddenly drops, outside air that can compensate for this can be quickly introduced into the container (1).

[0107] Furthermore, the ventilation device (40) can adjust the ventilation rate, i.e., the amount of outside air introduced. Therefore, outside air can be introduced into the container (1) in accordance with the pressure drop inside the container (1). As a result, it is possible to prevent the energy-saving performance of the container refrigeration unit (10) from being impaired by excessive introduction of outside air.

[0108] (8-3) The control section (100) terminates the pressure equalization operation when the pressure detected by the pressure detection section (P) during the pressure equalization operation is higher than a predetermined second pressure that is lower than atmospheric pressure.

[0109] This makes it possible to avoid the pressure equalization operation from continuing even when the pressure inside the container (1) is high, thereby preventing the introduction of excessive outside air from impairing the energy saving performance of the container refrigeration system (10).

[0110] (8-4) The control unit (100) terminates the pressure equalization operation when the pressure detected by the pressure detection unit (P) is higher than a predetermined second pressure that is lower than atmospheric pressure and the temperature of the air in the container (1) is lower than a predetermined temperature. In other words, even if the pressure detected by the pressure detection unit (P) is higher than the predetermined second pressure that is lower than atmospheric pressure, the control unit (100) does not terminate the pressure equalization operation when the temperature of the air in the container (1) is equal to or higher than a predetermined temperature.

[0111] If the temperature of the air inside the container (1) is low (for example, 0°C), there is little risk that the air will be further cooled and the negative pressure inside the container (1) will increase. Therefore, it is possible to prevent the negative pressure inside the container (1) from increasing again after the pressure equalization operation is completed, which could result in damage to the container (1).

[0112] (8-5) The control unit (100) controls the ventilation device (40) to perform a first pressure equalization operation as a pressure equalization operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure during the first cooling operation (pull-down operation) after the container refrigeration system (10) is started up.

[0113] During the pull-down operation, the negative pressure inside the container (1) is likely to increase, increasing the risk of damage to the container (1). By performing the first pressure equalization operation at this timing, damage to the container (1) can be avoided.

[0114] (8-6) The control unit (100) controls the ventilation device (40) to perform a second pressure equalization operation as a pressure equalization operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure after the door (D) of the container (1) is opened or closed during the cooling operation.

[0115] When the door of the container (1) is temporarily opened and closed, the negative pressure inside the container (1) is likely to increase, increasing the risk of damage to the container (1). By performing the second pressure equalization operation at this timing, damage to the container (1) can be avoided.

[0116] (8-7) During the cooling operation (strictly speaking, the pull-down operation), the control unit (100) controls the pressure equalization mechanism (40, 80) so that the flow rate of air introduced from the outside to the inside of the container (1) decreases as the temperature of the air inside the container decreases.

[0117] When the temperature of the air inside the container is high, the negative pressure in the container (1) is likely to increase due to cooling of the air inside the container. In this case, the amount of outside air introduced increases, so damage to the container (1) can be reliably prevented.

[0118] When the temperature of the air inside the container is low, the negative pressure in the container (1) is unlikely to increase due to cooling of the air inside the container. At this time, the amount of outside air introduced is small, so the amount of outside air introduced does not become excessively large. As a result, it is possible to prevent the reliability of the container refrigeration system (10) from being impaired due to the introduction of outside air. In particular, when the temperature of the air inside the container is low, the temperature difference between the outside air and the inside air is large, and the cooling load of the container (1) is likely to increase due to the introduction of outside air. At this time, by reducing the amount of outside air introduced, it is possible to avoid impairment of the energy-saving properties of the container refrigeration system (10).

[0119] (8-8) The pressure detection part (P) is a pressure sensor (53), which can accurately detect the pressure inside the container (1).

[0120] (9) Modifications The above-described embodiment may be modified as follows: The following describes the differences from the above-described embodiment in particular.

[0121] (9-1) Modification 1: Modification of Pressure Detector The pressure detector (P) of the above embodiment may have the following modified configuration.

[0122] (9-1-1) Modification 1A As shown schematically in FIG. 10 , the container refrigeration system (10) of Modification 1A includes a drain pipe (60). The inflow end (60a) of the drain pipe (60) communicates with the internal space (3) inside the container (1). The outflow end (60b) of the drain pipe (60) communicates with the external space (5) outside the container (1). The inflow end (60a) of the drain pipe (60) forms a flow path for discharging water received in a drain pan inside the container (1) to the outside of the container (1). The drain pan is disposed below the internal heat exchanger (29) and receives condensed water generated from air cooled by the internal heat exchanger (29). The drain pipe (60) may be a flexible resin hose or a hard metal pipe.

[0123] The drain pipe (60) has a trap portion (61) curved downward. The trap portion (61) has a first straight portion (62) closer to the inside of the container (1), a second straight portion (63) closer to the outside of the container (1), and a U-shaped U-portion (64) connecting the lower ends of the first straight portion (62) and the second straight portion (63). The first straight portion (62) and the second straight portion (63) extend in the vertical direction. The flow path cross-sectional area of ​​the first straight portion (62) is equal to the flow path cross-sectional area of ​​the second straight portion (63). Water collects in the trap portion (61), dividing the inside of the container (1) from the outside of the container (1) by this water.

[0124] The pressure detection unit (P) of Modification 1A includes a water level meter that measures the water level in the trap unit (61), and a control unit (100). The water level meter includes a first water level sensor (65) and a second water level sensor (66). The first water level sensor (65) and the second water level sensor (66) are of an ultrasonic type, a radio wave type, an electrode type, a float type, or the like. The first water level sensor (65) is disposed inside the first straight portion (62). The first water level sensor (65) measures the water level in the first straight portion (62). The second water level sensor (66) is disposed inside the second straight portion (63). The second water level sensor (66) measures the water level in the second straight portion (63).

[0125] The pressure detection section (P) detects the pressure based on the difference in water level between the first straight section (62) and the second straight section (63). When the pressure Pb inside the container (1) is equal to the pressure P0 (atmospheric pressure) outside the container (1), the water level h1 in the first straight section (62) and the water level h2 in the second straight section (63) are equal, as shown in FIG. 10. In contrast, when the pressure Pb inside the container (1) decreases during the cooling operation, the pressure Pb becomes smaller than the pressure P0 outside the container (1). As a result, as shown in FIG. 11, the water level h1 in the first straight section (62) becomes higher than the water level h2 in the second straight section (63). In the state shown in FIG. 11, the following relational expression (1) is established.

[0126] Pb×A1+ρ×g×H×A1=P0×A2 (1) where A1 is the flow path cross-sectional area of ​​the first straight section (62), and A2 is the flow path cross-sectional area of ​​the second straight section (63). In this example, A1 is equal to A2. ρ is the density of water, g is the acceleration of gravity, and H is the difference between the water level h1 and the water level h2 (H=h1−h2).

[0127] The control unit (100) calculates Pb inside the container (1) using the water levels measured by the first water level sensor (65) and the second water level sensor (66) and the relational expression (1). In this way, in the first modification, the pressure inside the container (1) can be detected.

[0128] (9-1-2) Modification 1B The pressure detection unit (P) of Modification 1B detects the pressure inside the container (1) based on the temperature of the air inside the container (1) and the temperature of the air inside the container (1) during the cooling operation. The pressure detection unit (P) includes an internal temperature sensor (51) and a control unit (100).

[0129] The internal temperature sensor (51) measures the temperature T0 of the air in the container (1) before or at the start of the cooling operation. Thereafter, the internal temperature sensor (51) measures the temperature Tb of the air in the container (1) during the cooling operation. The control unit (100) calculates the pressure Pb in the container (1) based on the following relational expression (2) based on Boyle's law:

[0130] P0 × V / T0 = Pb × V / Tb (2) Here, P0 is the pressure inside the container (1) before or at the start of the cooling operation, and corresponds to atmospheric pressure. V is the volume of the interior space (3) inside the container (1). As described above, in Modification 2, the pressure inside the container (1) can be detected.

[0131] The pressure detection part (P) may include an outside-compartment temperature sensor (52). The temperature detected by the outside-compartment temperature sensor (52) may be set as the temperature T0 of the air in the container (1) before or at the start of the cooling operation.

[0132] (9-1-3) Modification 1C As shown in FIG. 12 , the pressure detection unit (P) of modification 1C includes a humidity sensor (71) that is a gas sensor, and a control unit (100). The humidity sensor (71) measures the concentration of water vapor in the air in the container (1), i.e., the humidity of the air. The humidity sensor (71) is disposed inside the container (1). The humidity sensor (71) is disposed in the internal passage (19) upstream of the internal fan (30) in the air flow direction. The humidity sensor (71) is of a capacitive or resistive type. The humidity sensor (71) has a characteristic that its detection value changes depending on the ambient pressure.

[0133] The humidity sensor (71) measures the humidity R0 of the air in the container (1) before or at the start of the cooling operation. Thereafter, the humidity sensor (71) measures the humidity Rb of the air in the container (1) during the cooling operation. The humidity detected by the humidity sensor (71) varies depending on the pressure in the container (1). In other words, there is a correlation between the humidity detected by the humidity sensor (71) and the pressure in the container (1). The control unit (100) stores data correlating the humidity detected by the humidity sensor (71) and the pressure in the container (1). This data is a relational expression or a table. The control unit (100) calculates the pressure in the container (1) using this data, the humidity R0, and the humidity Rb. As described above, in Modification 1C, the pressure inside the container (1) can be detected using the humidity sensor (71).

[0134] The humidity sensor (71) is also used to adjust the humidity of the air in the container (1). The control section (100) controls the refrigerant circuit (R) based on the value detected by the humidity sensor (71).

[0135] (9-1-4) Modification 1D As shown in FIG. 13 , the pressure detection unit (P) of modification 1D includes a carbon dioxide sensor (72) that is a gas sensor, and a control unit (100). The carbon dioxide sensor (72) measures the concentration of carbon dioxide in the air inside the container (1). The carbon dioxide sensor (72) is disposed inside the container (1). The carbon dioxide sensor (72) is disposed in the internal passage (19) upstream of the air flow from the internal fan (30). The carbon dioxide sensor (72) is of a semiconductor type, an infrared type (NDIR type), or a thermal conductivity type. The carbon dioxide sensor (72) has a characteristic that its detection value changes depending on the ambient pressure.

[0136] The carbon dioxide sensor (72) measures the carbon dioxide concentration C0 in the air within the container (1) before or at the start of the cooling operation. Thereafter, the carbon dioxide sensor (72) measures the carbon dioxide concentration Cb in the air within the container (1) during the cooling operation. The carbon dioxide concentration detected by the carbon dioxide sensor (72) varies depending on the pressure within the container (1). In other words, there is a correlation between the concentration detected by the carbon dioxide sensor (72) and the pressure within the container (1). The control unit (100) stores data correlating the concentration detected by the carbon dioxide sensor (72) and the pressure within the container (1). This data is a relational expression or a table. The control unit (100) calculates the pressure within the container (1) using this data, the concentration C0, and the concentration Cb. As described above, in Modification 1D, the pressure within the container (1) can be detected using the carbon dioxide sensor (72). The gas sensor may be an oxygen sensor that measures the oxygen concentration in the air within the container (1) instead of the carbon dioxide sensor (72).

[0137] The carbon dioxide sensor (72) and the oxygen sensor are used to adjust the composition of the air in the container (1). The control unit (100) controls the regulator (80) based on the concentrations detected by the carbon dioxide sensor (72) and the oxygen sensor. The regulator (80) adjusts the composition of the air in the interior space (3) using, for example, a PSA (Pressure Swing Adsorption) device or a gas separation membrane. The regulator (80) will be described in detail later.

[0138] The control unit (100) may adjust the ventilation volume of the ventilation device (40) based on the concentrations detected by the carbon dioxide sensor (72) or the oxygen sensor.

[0139] (9-2) Modification 2: Modification of Pressure Equalizing Mechanism The pressure equalizing mechanism (40, 80) of the above embodiment may have the following modified configuration.

[0140] (9-2-1) Modification 2A As shown schematically in Fig. 14, the pressure equalization mechanism of Modification 2A is a regulator (80) that regulates the composition of air inside the container (1). The regulator (80) is disposed in the external storage space (14) of the casing (11). The regulator (80) has a supply path (81), an exhaust path (82), an air pump (83), and a PSA device (84).

[0141] The supply path (81) is a flow path for introducing outside air into the internal space (3). The inflow end of the supply path (81) opens to the external space (5). The outflow end of the supply path (81) communicates with the internal space (3). The exhaust path (82) is a flow path for discharging air from the PSA device (84) to the external space (5).

[0142] The supply path (81) is provided with an air pump (83) and a PSA unit (84). The air pump (83) is a transport unit that transports air. The air pump (83) has a pressurizing unit that pressurizes air and a decompressing unit that decompresses air. The PSA unit (84) has two adsorption units. The adsorption units are adsorption towers filled with an adsorbent that adsorbs nitrogen in the air. The adsorbent is, for example, zeolite.

[0143] The air pump (83) pressurizes one of the two adsorption sections and depressurizes the other. In the pressurized adsorption section, nitrogen in the air is adsorbed by the adsorbent, thereby generating oxygen-enriched air having a lower nitrogen concentration and a higher oxygen concentration than the outside air. In the depressurized adsorption section, nitrogen is desorbed from the adsorbent, thereby generating nitrogen-enriched air having a higher nitrogen concentration and a lower oxygen concentration than the outside air. The oxygen-enriched air is discharged to the external space (5) through the exhaust path (82). The nitrogen-enriched air is supplied to the internal space (3) through the supply path (81). This adjusts the oxygen concentration in the internal space (3).

[0144] In Modification 2A, when the pressure inside the container (1) falls below the first pressure during the cooling operation, the control unit (100) controls the adjusting device (80) to equalize the pressure inside and outside the container (1). Specifically, the control unit (100) operates the air pump (83) to perform a pressure equalization operation in which air outside the container (1) is introduced into the container (1) through the supply path (81). This makes it possible to prevent damage to the container (1) due to negative pressure.

[0145] The regulator (80) preferably has a bypass flow path through which air in the supply path (81) bypasses the PSA device (84) and is supplied to the interior space (3) during pressure equalization. This allows the outside air to be introduced into the container (1) with its composition unchanged. In addition, the flow resistance of the air flowing through the supply path (81) can be reduced, thereby reducing the power required for the air pump (83).

[0146] In the pressure equalization operation, the regulator (80) may introduce air pressurized to a pressure higher than atmospheric pressure by an air pump (83), thereby enabling the pressure inside the container (1) to be increased quickly.

[0147] When the pressure inside the container (1) becomes higher than the second pressure as a result of the pressure equalization operation, the control unit (100) causes the regulator (80) to terminate the pressure equalization operation. Specifically, the control unit (100) stops the air pump (83).

[0148] In the modification 2B, the adjusting device (80) functions not only to adjust the composition of the air but also as a pressure equalizing mechanism, thereby making it possible to reduce the number of parts.

[0149] (9-2-2) Modification 2B Modification 2B is directed to a refrigeration container (C) including a container refrigeration unit (10) and a container (1). The pressure equalization mechanism of Modification 2B is the door (D) of the container (1). As shown in FIG. 15 , the refrigeration container (1) has a drive mechanism (90) that automatically opens and closes the door (D). The drive mechanism (90) opens and closes the door (D) in response to a command from the control unit (100).

[0150] When the pressure inside the container (1) falls below the first pressure during the cooling operation, the control unit (100) controls the drive mechanism (90) to equalize the pressure inside and outside the container (1), thereby opening the door (D). This allows the pressure inside the container (1) to be quickly increased, and damage to the container (1) due to negative pressure to be suppressed.

[0151] When the pressure inside the container (1) becomes higher than the second pressure as a result of the pressure equalization operation, the control unit (100) causes the adjustment device (80) to terminate the pressure equalization operation. Specifically, the control unit (100) controls the drive mechanism (90) to close the door (D).

[0152] (9-3) Modification 3 When a first condition is met, that is, the cooling operation is the pull-down operation and the detected pressure is equal to or less than the first pressure, the control unit (100) may execute control in the first mode shown in Fig. 8. When a first command to start the cooling operation is issued after the container refrigeration system (10) is turned on, the control unit (100) determines that the cooling operation is the pull-down operation.

[0153] (9-4) Modification 4 The container refrigeration system (10) may have a detection unit that detects whether the door (D) is opened or closed. The control unit (100) may execute the control of the second mode shown in Figure 9 when the first condition that the detected pressure is equal to or less than the first pressure is satisfied after the fourth condition that the detection unit detects whether the door (D) is opened or closed during the cooling operation is satisfied.

[0154] The control unit (100) may execute the second mode control when the first condition is satisfied after the fifth condition is satisfied, that is, when the temperature of the inside air rises from within the target range to above the range. The control unit (100) may execute the second mode control when the fourth condition, the fifth condition, and the first condition are satisfied in this order.

[0155] (9-5) Modification 5 The first pressure (see step S14), which is the determination value for performing the second pressure equalization operation in the second mode, may be set higher than the first pressure (see step S13), which is the determination value for performing the first pressure equalization operation in the first mode. In this case, if the pressure inside the container (1) drops due to the door (D) being opened or closed during the cooling operation, the second pressure equalization operation in the second mode can be quickly performed. As described above, the pressure inside the container (1) drops suddenly after the door (D) is opened or closed, but by quickly responding to this pressure change, damage to the container (1) can be suppressed.

[0156] (9-6) Modification 6 The control unit (100) may control the pressure equalizing mechanism (40, 80) during the cooling operation so that the flow rate of air introduced from the outside to the inside of the container (1) decreases as the cooling operation time elapses. In particular, during the pull-down operation, the control unit (100) preferably controls the pressure equalizing mechanism (40, 80) so that the flow rate of air introduced from the outside to the inside of the container (1) decreases as the cooling operation time elapses.

[0157] As the cooling operation continues, the temperature of the air inside the container decreases. When the temperature of the air inside the container is low, the negative pressure in the container (1) is less likely to increase due to the cooling of the air inside the container. At this time, the amount of outside air introduced is reduced, and therefore the amount of outside air introduced does not become excessively large. As a result, it is possible to prevent the reliability of the container refrigeration system (10) from being impaired due to the introduction of outside air. When the temperature of the air inside the container is low, the cooling load of the container (1) is likely to increase due to the introduction of outside air. At this time, by reducing the amount of outside air introduced, it is possible to avoid impairment of the energy-saving properties of the container refrigeration system (10).

[0158] (9-7) Modification 7 The control unit (100) of Modification 7 controls the refrigerant circuit (R) to perform a dehumidifying operation to dehumidify the air inside the container before the cooling operation. In the dehumidifying operation, the compressor (25) is operated, and the internal heat exchanger (29) functions as an evaporator. The control unit (100) adjusts the rotation speed of the compressor (25) and, consequently, the evaporation temperature of the internal heat exchanger (29) so that the temperature of the air cooled by the internal heat exchanger (29) is equal to or lower than the dew point temperature. The evaporation temperature Te1 in the dehumidifying operation is higher than the evaporation temperature Te2 in the cooling operation. Therefore, in the dehumidifying operation, the air inside the container (1) can be dehumidified without significantly decreasing the temperature of the air.

[0159] When the cooling operation is performed after the dehumidifying operation, the temperature of the air in the container (1) decreases as described above. Here, the humidity of the air in the container has been reduced by the dehumidifying operation. Therefore, even if the air in the container (1) is cooled, a significant decrease in the pressure in the container (1) can be suppressed. As a result, damage to the container (1) due to negative pressure can be suppressed.

[0160] (10) Other Embodiments The above-described embodiment and each of the modifications may be configured as follows.

[0161] The container (1) does not have to be for marine transport, but may be for land transport carried by a vehicle such as a trailer or by rail.

[0162] The ventilation device (40) may have only an air supply function of supplying outside air from the external space (5) to the internal space (3), and may not have an exhaust function. In other words, the ventilation device (40) may have only an air supply passage (41), and exhaust air may be naturally discharged through an exhaust port provided in the container body (2).

[0163] The ventilation fan of the ventilation device (40) may be a fan dedicated to ventilation, separate from the internal fan.

[0164] The opening adjustment mechanism for adjusting the opening of the air supply passageway (41) or the exhaust passageway (42) does not necessarily have to be the open / close lid (45), but may be a damper or a valve mechanism provided in the air supply passageway (41) or the exhaust passageway (42).

[0165] Although the embodiments and modifications have been described above, it will be understood that various modifications in form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments, modifications, and other embodiments may be combined or substituted as appropriate as long as the functionality of the subject matter of the present disclosure is not impaired.

[0166] The above-mentioned descriptions such as "first," "second," "third," etc. are used to distinguish the words to which these descriptions are attached, and do not limit the number or order of the words.

[0167] As described above, the present disclosure is useful for container refrigeration systems.

[0168] 1 Container 10 Refrigeration unit for container 40 Ventilation unit (pressure equalization mechanism) 53 Pressure sensor 60 Drain piping 61 Trap unit 71, 72 Gas sensor 80 Regulating unit (pressure equalization mechanism) 100 Control unit D Door P Pressure detection unit

Claims

1. A container refrigeration system comprising: a pressure detection unit (P) that detects the pressure inside a container (1); a pressure equalization mechanism (40, 80) that equalizes the pressure inside and outside the container (1); and a control unit (100) that controls the pressure equalization mechanism (40, 80) to perform a pressure equalization operation to equalize the pressure inside and outside the container (1) when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure, during a cooling operation for cooling the inside of the container (1).

2. The container refrigeration system according to claim 1, wherein the pressure equalization mechanism (40, 80) is a ventilation device (40) that ventilates the container (1), and the ventilation device (40) introduces air outside the container (1) into the container (1) during the pressure equalization operation.

3. The container refrigeration system according to claim 1, wherein the pressure equalization mechanism (40, 80) is a regulator (80) that regulates the composition of the air inside the container (1), and the regulator (80) introduces air outside the container (1) into the container (1) during the pressure equalization operation.

4. A container refrigeration system as claimed in any one of claims 1 to 3, wherein the control unit (100) terminates the pressure equalization operation when the pressure detected by the pressure detection unit (P) during the pressure equalization operation is higher than a predetermined second pressure that is lower than atmospheric pressure.

5. The container refrigeration system according to claim 4, wherein the control unit (100) terminates the pressure equalization operation when the pressure detected by the pressure detection unit (P) is higher than a predetermined second pressure which is lower than atmospheric pressure and the temperature of the air inside the container (1) is lower than a predetermined temperature.

6. A container refrigeration system as described in any one of claims 1 to 5, wherein the control unit (100) controls the pressure equalizing mechanism (40, 80) to perform a first pressure equalizing operation as the pressure equalizing operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure, during an initial cooling operation after start-up of the container refrigeration system.

7. A container refrigeration system as claimed in any one of claims 1 to 5, wherein the control unit (100) controls the pressure equalization mechanism (40, 80) to perform a second pressure equalization operation as the pressure equalization operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure that is lower than atmospheric pressure after the door of the container (1) is opened or closed during cooling operation.

8. The container refrigeration system as set forth in claim 7, wherein the control unit (100) controls the pressure equalizing mechanism (40, 80) to perform a first pressure equalizing operation as the pressure equalizing operation when the pressure detected by the pressure detection unit (P) is lower than a predetermined first pressure lower than atmospheric pressure, and the pressure equalizing mechanism (40, 80) introduces air outside the container (1) into the container (1) at a flow rate greater than that of the first pressure equalizing operation, in the second pressure equalizing operation.

9. A container refrigeration system as described in any one of claims 1 to 8, wherein the control unit (100) controls the pressure equalization mechanism (40, 80) during cooling operation so that the flow rate of air introduced from the outside to the inside of the container (1) decreases as the temperature of the air inside the container (1) decreases.

10. A container refrigeration system as claimed in any one of claims 1 to 9, wherein the pressure detection section (P) is a pressure sensor (53).

11. A container refrigeration system as claimed in any one of claims 1 to 9, further comprising a drain pipe (60) for discharging condensed water generated inside the container (1) to the outside of the container (1) and having a trap section (61) in which the condensed water accumulates, and the pressure detection section (P) detects the pressure inside the container (1) based on the water level in the trap section (61).

12. A container refrigeration device as described in any one of claims 1 to 9, wherein the pressure detection unit (P) detects the pressure inside the container (1) based on the temperature of the air inside the container (1) before or at the start of the cooling operation and the temperature of the air inside the container (1) during the cooling operation.

13. A container refrigeration system as claimed in any one of claims 1 to 9, further comprising a gas sensor (71, 72) for detecting a concentration of a gas component in the air inside the container (1), wherein the pressure detection unit (P) detects the pressure inside the container (1) based on the concentration detected by the gas sensor (71, 72) before or at the start of the cooling operation and the concentration detected by the gas sensor (71, 72) during the cooling operation.

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