JP2013108646A - Container refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a designed pressure of an evaporator to be disposed on a low pressure side by preventing an increase in equalized pressure on a low pressure side of a refrigerant circuit, in employing a supercritical refrigeration cycle that uses carbon dioxide as a refrigerant, in a container refrigerator.SOLUTION: This refrigeration device 1 for container includes a refrigerant circuit 10 formed by sequentially connecting a compressor 21, a gas cooler 22, an expanding mechanism 23 and an evaporator 24, to perform supercritical refrigeration cycle that uses carbon dioxide as a refrigerant. A receiver 27 is disposed between the gas cooler 22 and the first expanding mechanism 26. The receiver 27 is provided with a supercooling heat exchanger 28 for cooling the refrigerant located in the receiver 27 by the refrigerant moving toward the suction of the compressor 21 from an outlet of the evaporator 24. Pump-down operation is executed while slightly opening the first expanding mechanism 26, when normal operation is suspended.

Description

  The present invention relates to a container refrigeration apparatus.

  As described in Patent Document 1 (Japanese Patent Laid-Open No. 2011-112270), a conventional container refrigeration apparatus mainly includes a compressor, a condenser, an expansion mechanism, and an evaporator that are sequentially connected. It has a refrigerant circuit.

  In this container refrigeration apparatus, the inside of the container is cooled by the operation of the refrigerant circuit as described below. First, the low-pressure refrigerant is compressed in the compressor to become a high-pressure refrigerant. The high-pressure refrigerant is cooled and condensed in the condenser. The high-pressure refrigerant is depressurized in the expansion mechanism until the pressure becomes low. The low-pressure refrigerant is heated and evaporated in the evaporator to cool the internal air.

  In the container refrigeration apparatus, a chlorofluorocarbon refrigerant has been conventionally used. However, in recent years, it has been considered to change the chlorofluorocarbon refrigerant to a natural refrigerant such as carbon dioxide from the viewpoint of environmental problems.

  However, when carbon dioxide is used as the refrigerant in the container refrigeration apparatus, a supercritical refrigeration cycle is achieved in which the pressure of the refrigerant discharged from the compressor exceeds the critical pressure of the refrigerant. For this reason, compared with the case where a CFC-based refrigerant is used, the operating pressure is increased, and it is necessary to lower the design pressure of the equipment constituting the refrigerant circuit. In addition, when the normal operation is stopped, the refrigerant circuit is in a state where the pressure is equalized. However, under the condition where the outside air temperature is high, this pressure equalization pressure also increases, and in particular, the evaporation provided on the low pressure side of the refrigerant circuit. It becomes difficult to keep the design pressure of the vessel low.

  An object of the present invention is to provide an evaporator provided on a low-pressure side in a container refrigeration apparatus by suppressing an increase in pressure equalization on the low-pressure side of a refrigerant circuit when adopting a supercritical refrigeration cycle using carbon dioxide as a refrigerant. The design pressure is to be kept low.

  A container refrigeration apparatus according to a first aspect includes a refrigerant circuit in which a compressor, a gas cooler, a first expansion mechanism, and an evaporator are sequentially connected. The refrigerant circuit uses carbon dioxide as the refrigerant, and performs a supercritical refrigeration cycle in which the pressure of the refrigerant discharged from the compressor exceeds the critical pressure of the refrigerant. A receiver for storing the refrigerant is provided between the gas cooler and the first expansion mechanism. The receiver is provided with a supercooling heat exchanger that cools the refrigerant present in the receiver by the refrigerant from the outlet of the evaporator toward the suction of the compressor. When the normal operation is stopped, the first expansion mechanism is provided. With the pump open slightly, the pump-down operation is performed to store the refrigerant in the gas cooler and receiver.

  In this container refrigeration apparatus, since carbon dioxide is used as a refrigerant, the cycle performance tends to be lower than when a fluorocarbon refrigerant is used. For this reason, in this container refrigeration apparatus, in order to improve cycle performance, a supercooling heat exchanger for further cooling the refrigerant cooled by the gas cooler is provided.

  Here, considering only the viewpoint of improving the cycle performance, the supercooling heat exchanger may be connected anywhere between the gas cooler and the evaporator, and the cooling source of the supercooling heat exchanger Is not limited.

  Further, in this container refrigeration apparatus, carbon dioxide is used as the refrigerant, and there is no need for recovery. Therefore, there is no need to perform a pump-down operation in which the refrigerant is stored in the gas cooler and the receiver.

  However, in this container refrigeration apparatus, as described above, when a supercritical refrigeration cycle using carbon dioxide as a refrigerant is employed, an increase in the equal pressure on the low pressure side of the refrigerant circuit is suppressed, and the container is provided on the low pressure side. There is a problem of keeping the design pressure of the evaporator low.

  For this reason, in this container refrigeration system, the rise in the equal pressure on the low pressure side of the refrigerant circuit is suppressed to the low pressure side with respect to the connection position of the supercooling heat exchanger, the cooling source, and the necessity of pump down operation. It is preferable to determine in consideration of the viewpoint of keeping the design pressure of the provided evaporator low. Here, the degree of suppression of the design pressure of the evaporator provided on the low pressure side is determined by the amount of refrigerant stored in the gas cooler and the receiver when the normal operation for cooling the inside of the warehouse and the amount of refrigerant stored in the receiver (that is, the amount of refrigerant stored) It is determined by the balance. In addition, since carbon dioxide is used as the refrigerant, the refrigerant stored in the gas cooler and the receiver is stored in a supercritical state. For this reason, since the refrigerant | coolant storage amount in a gas cooler and a receiver changes greatly with the temperature of a refrigerant | coolant, it is preferable to store a refrigerant | coolant at the lowest possible temperature.

  Therefore, in this container refrigeration apparatus, first, when the normal operation is stopped, a pump-down operation in which the refrigerant is stored in the gas cooler and the receiver is performed. Thereby, although the refrigerant in the refrigerant circuit is in a supercritical state, it is stored in the gas cooler and the receiver. Moreover, in this container refrigeration apparatus, a supercooling heat exchanger is provided in the receiver. Thereby, in the pump down operation, the refrigerant stored in the receiver is cooled, so that the refrigerant can be stored in the receiver at a low temperature. In addition, the normal pump-down operation is performed in a state where the downstream of the receiver of the refrigerant circuit is closed and the refrigerant is not circulated. Here, the first expansion mechanism located downstream of the receiver is opened a little. ing. That is, the pump-down operation is performed in a state in which the refrigerant flow from the outlet of the evaporator, which is the cooling source of the supercooling heat exchanger, toward the intake of the compressor is secured. For this reason, in the pump-down operation, cooling of the refrigerant stored in the receiver is promoted, and the amount of refrigerant stored in the receiver can be increased. Thereby, the rise in the pressure equalization pressure on the low pressure side of the refrigerant circuit is suppressed, and the design pressure of the evaporator provided on the low pressure side can be suppressed low.

  As described above, in this container refrigeration apparatus, the above-described connection position and cooling source are adopted for the supercooling heat exchanger for improving the cycle performance, and the first expansion mechanism is installed when the normal operation is stopped. The pump down operation is performed with the door slightly open. As a result, in this container refrigeration system, when adopting a supercritical refrigeration cycle using carbon dioxide as a refrigerant, the rise of the equal pressure on the low pressure side of the refrigerant circuit is suppressed, and the design of the evaporator provided on the low pressure side The pressure can be kept low.

  The container refrigeration apparatus according to the second aspect is the container refrigeration apparatus according to the first aspect, wherein the first expansion mechanism has an opening at which the high pressure of the refrigerant circuit becomes a predetermined high pressure value during pump down operation. And / or the opening degree at which the low pressure of the refrigerant circuit becomes a predetermined low pressure value.

  In this container refrigeration apparatus, since the opening degree of the first expansion mechanism is set based on the high pressure and low pressure of the refrigerant circuit during the pump down operation, the first expansion mechanism is slightly opened during the pump down operation. Can be maintained. Thereby, in this container refrigeration apparatus, the pump-down operation can be performed while cooling the refrigerant in the receiver.

  The container refrigeration apparatus according to the third aspect further includes an internal fan for sending air to the evaporator in the container refrigeration apparatus according to the first or second aspect, Stopped during pump down operation.

  In the container refrigeration apparatus, heating of the refrigerant in the evaporator can be suppressed as much as possible during the pump-down operation. Thereby, in this container refrigeration apparatus, the temperature of the refrigerant from the outlet of the evaporator, which is the cooling source of the supercooling heat exchanger, toward the suction of the compressor is maintained as low as possible, and the refrigerant in the receiver is as low as possible. Can be cooled to temperature.

  A container refrigeration apparatus according to a fourth aspect is the container refrigeration apparatus according to any one of the first to third aspects, further including a second expansion mechanism between the gas cooler and the receiver. The down operation is performed with the second expansion mechanism opened.

  In this container refrigeration apparatus, during normal operation, the receiver functions as an intermediate pressure receiver for storing intermediate pressure refrigerant in the refrigeration cycle, and during pump down operation, the receiver stores high pressure refrigerant in the refrigeration cycle. It will function as a high-pressure receiver. For this reason, in this container refrigeration apparatus, the refrigerant can be stored in a liquid state in the receiver during normal operation. Thereby, in this container refrigeration apparatus, the refrigerant storage amount difference between the refrigerant storage amount in the receiver during the pump-down operation and the refrigerant storage amount in the receiver during the normal operation tends to increase.

  However, in the container refrigeration apparatus, as described above, during the pump-down operation, the first expansion mechanism is slightly opened and the refrigerant in the receiver is cooled by the supercooling heat exchanger. The difference in the refrigerant storage amount between the pump-down operation and the normal operation can be made as small as possible. Thereby, in this container refrigeration apparatus, since the receiver which has a volume close | similar to the refrigerant | coolant storage amount of the receiver at the time of normal operation can be selected, the cost increase by a receiver can be suppressed.

  The container refrigeration apparatus according to the fifth aspect is the container refrigeration apparatus according to any one of the first to fourth aspects. When the pump down operation is stopped during the normal operation, the refrigerant circuit has a predetermined pressure condition. It is done when you meet.

  In this container refrigeration system, the pump down operation is performed only when the rise in the equal pressure on the low pressure side of the refrigerant circuit is large, such as when the outside temperature is high or the pressure on the low pressure side of the refrigerant circuit is high. It can be carried out. As a result, in this container refrigeration system, when the rise in the equal pressure on the low pressure side of the refrigerant circuit is small, such as when the outside temperature is low or the pressure on the low pressure side of the refrigerant circuit is low, the pump It is possible to do without down operation.

  In the container refrigeration apparatus according to the sixth aspect, in the container refrigeration apparatus according to any one of the first to fifth aspects, the receiver and the supercooling heat exchanger are arranged in the interior space.

  In this container refrigeration apparatus, the temperature rise of the receiver and the supercooling heat exchanger can be suppressed as much as possible when the normal operation including the pump down operation is stopped. Thereby, in this container refrigeration apparatus, the temperature of the refrigerant stored in the receiver can be kept as low as possible during the pump-down operation, and the thickness of the cooling material covering the supercooling heat exchanger and the receiver can be reduced. It can be made smaller or the cold insulation material can be omitted.

  As described above, according to the present invention, the following effects can be obtained.

  In the container refrigeration apparatus according to the first aspect, when the normal operation is stopped, the first expansion mechanism is slightly opened and the refrigerant in the receiver is cooled by the supercooling heat exchanger and the pump down operation is performed. Thus, in adopting a supercritical refrigeration cycle using carbon dioxide as a refrigerant, it is possible to suppress an increase in the pressure equalization pressure on the low pressure side of the refrigerant circuit and to keep the design pressure of the evaporator provided on the low pressure side low. .

  In the container refrigeration apparatus according to the second aspect, since the opening degree of the first expansion mechanism is set based on the high pressure and low pressure of the refrigerant circuit during the pump down operation, the first expansion mechanism is installed during the pump down operation. The pump-down operation can be performed while maintaining a slightly opened state and cooling the refrigerant in the receiver.

  In the container refrigeration apparatus according to the third aspect, heating of the refrigerant in the evaporator can be suppressed as much as possible during the pump-down operation, so that the suction of the compressor from the outlet of the evaporator that is the cooling source of the supercooling heat exchanger The refrigerant in the receiver can be kept as low as possible to cool the refrigerant in the receiver to the lowest possible temperature.

  In the container refrigeration apparatus according to the fourth aspect, during normal operation, the receiver functions as an intermediate pressure receiver for storing intermediate-pressure refrigerant in the refrigeration cycle. Since the refrigerant in the receiver is cooled by the supercooling heat exchanger with a little open, the difference in refrigerant storage amount between the pump down operation and the normal operation is made as small as possible. A receiver having a volume close to the amount of refrigerant stored in the receiver during operation can be selected, and the cost increase due to the receiver can be suppressed.

  In the container refrigeration apparatus according to the fifth aspect, only when the rise in the equal pressure on the low pressure side of the refrigerant circuit is large, such as when the outside temperature is high or the pressure on the low pressure side of the refrigerant circuit is low. Since the pump down operation can be performed, such as when the outside temperature is low or when the pressure on the low pressure side of the refrigerant circuit is low, etc. The pump-down operation can be omitted.

  In the container refrigeration apparatus according to the sixth aspect, the temperature rise of the receiver and the supercooling heat exchanger can be suppressed as much as possible when the normal operation including the pump down operation is stopped. The temperature of the stored refrigerant can be kept as low as possible, the thickness of the cold insulation material covering the supercooling heat exchanger and the receiver can be reduced, or the cold insulation material can be omitted.

It is a disassembled perspective view which shows the external appearance of the container provided with the container refrigeration apparatus concerning one Embodiment of this invention. It is a schematic front view of the container refrigeration apparatus concerning one Embodiment of this invention. It is a schematic side view of the container refrigeration apparatus concerning one Embodiment of this invention. 1 is a schematic refrigerant circuit diagram of a container refrigeration apparatus according to an embodiment of the present invention. It is a schematic block diagram of an intermediate pressure receiver and a supercooling heat exchanger. It is a schematic block diagram of an intermediate pressure receiver and a supercooling heat exchanger. It is a control block diagram of the refrigeration apparatus for containers. It is the pressure-enthalpy diagram in which the refrigerating cycle at the time of normal operation was illustrated. It is a flowchart of the pump down operation performed at the time of a stop of normal operation. It is a schematic refrigerant circuit diagram of the container refrigeration apparatus showing the flow of the refrigerant during the pump-down operation. It is the pressure-enthalpy diagram in which the refrigerating cycle at the time of pump down operation was illustrated. It is a schematic refrigerant circuit figure of the refrigeration equipment for containers concerning a modification.

  Hereinafter, embodiments of a container refrigeration apparatus according to the present invention will be described with reference to the drawings. In addition, the specific structure of the container refrigeration apparatus according to the present invention is not limited to the following embodiments and modifications thereof, and can be changed without departing from the scope of the invention.

(1) Configuration of container refrigeration apparatus FIGS. 1 to 7 show a container refrigeration apparatus 1 according to an embodiment of the present invention. Here, FIG. 1 is an exploded perspective view showing an appearance of the container 2 provided with the container refrigeration apparatus 1 of the present invention. FIG. 2 is a schematic front view of the container refrigeration apparatus 1. FIG. 3 is a schematic side view of the container refrigeration apparatus 1. FIG. 4 is a schematic refrigerant circuit diagram of the container refrigeration apparatus 1. 5 and 6 are schematic configuration diagrams of the intermediate pressure receiver 27 and the subcooling heat exchanger 28. FIG. FIG. 7 is a control block diagram of the container refrigeration apparatus 1.

  The container refrigeration apparatus 1 is mounted on an opening surface 2a of a container 2 that is handled as a marine container or an onshore container, and is an apparatus that cools the internal IS of the container 2 by performing a vapor compression refrigeration cycle operation. is there. The container refrigeration apparatus 1 mainly includes a frame 3 that covers the opening surface 2 a of the container 2, a refrigerant circuit 10, an external fan 36, and an internal fan 37.

  The frame 3 has a shape in which the lower part protrudes toward the in-compartment IS side of the container 2, and the lower part of the frame 3 on the out-compartment OS side has a compression that configures the outside fan 36 and the refrigerant circuit 10. The outside space S1 in which the machine 21, the gas cooler 22, and the like are arranged is formed. Further, a partition plate 4 is disposed on the interior IS side of the frame 3 so as to be spaced from the frame 3. The partition plate 4 is attached to the frame 3 via a support (not shown). Between the frame 3 and the partition plate 4, an internal space S <b> 2 in which the internal fan 37, the evaporator 23 configuring the refrigerant circuit 10, and the like are disposed is formed. In addition, a suction port 4a for sucking the air in the interior IS of the container 2 into the interior space S2 is formed in the upper part of the partition plate 4, and in the lower part of the partition plate 4, the interior space S2 of the interior space S2 is formed. An air outlet 4b is formed for blowing air to the internal space IS.

  The refrigerant circuit 10 mainly includes a compressor 21, a gas cooler 22, an expansion mechanism 23, and an evaporator 24, and is configured by sequentially connecting these devices 21 to 24 and the like. The refrigerant circuit 10 uses carbon dioxide as the refrigerant, and the supercritical refrigeration cycle in which the pressure of the refrigerant discharged from the compressor 21 (that is, the high pressure in the refrigeration cycle) exceeds the critical pressure of the refrigerant. Is what you do.

  The compressor 21 is a device that compresses the refrigerant (in this case, compresses until the pressure exceeds the critical pressure of the refrigerant), and is disposed in the outer space S1. The compressor 21 mainly includes a low-stage compressor 21a and a high-stage compressor 21b. The low-stage compressor 21a has a hermetic structure in which a rotary-type or scroll-type displacement type compression element (not shown) is rotated by a low-stage compressor motor 31a. The high-stage compressor 21b has a hermetic structure in which a rotary-type or scroll-type volumetric compression element (not shown) is rotationally driven by a high-stage compressor motor 31b. Here, as the compressor motors 31a and 31b, motors of variable rotation speed (frequency) controlled by an inverter are used. The low-stage compressor 21a has a suction refrigerant pipe 32 connected to the suction side and an intermediate refrigerant pipe 33 connected to the discharge side. The high-stage compressor 21b has an intermediate refrigerant pipe 33 connected to the suction side and a discharge refrigerant pipe 34 connected to the discharge side. Thereby, the low stage side compressor 21a and the high stage side compressor 21b are connected in series, and comprise the multistage (here 2 stage) compressor which compresses a refrigerant | coolant sequentially. The intermediate refrigerant pipe 33 is provided with a low-stage check mechanism 33a, and the discharge refrigerant pipe 34 is provided with a high-stage check mechanism 34a. The low-stage check mechanism 33a allows the refrigerant to flow from the discharge side of the low-stage compressor 21a to the suction side of the high-stage compressor 21b, and is low from the suction side of the high-stage compressor 21b. This is a mechanism for blocking the reverse flow of the refrigerant to the discharge side of the stage side compressor 21a. The high-stage check mechanism 34a allows the refrigerant to flow from the discharge side of the high-stage compressor 21b to the inlet side of the gas cooler 22, and from the inlet side of the gas cooler 22 to the discharge side of the high-stage compressor 21a. It is a mechanism for interrupting the reverse flow of the refrigerant. Here, check valves are used as the check mechanisms 33a and 34a. Here, a two-stage compressor is adopted as the compressor 21, but a multi-stage compressor having three or more stages may be used, or a single-stage compressor may be used. In addition, here, a multistage compressor is configured by connecting in series two compressors 21a and 21b in which one drive motor is connected to one compression element. However, a plurality of compression elements are connected to a common drive motor. A multi-stage compressor may be configured by connecting together.

  The gas cooler 22 is a device that radiates heat of the high-pressure refrigerant compressed in the compressor 21, and is disposed in the outer space S1. Here, the gas cooler 22 is a cross-fin type fin-and-tube heat exchanger composed of heat transfer tubes and a large number of fins, and radiates high-pressure refrigerant using outside air as a cooling source. It has become. The gas cooler 22 has an inlet connected to the discharge refrigerant pipe 34 and an outlet connected to the liquid refrigerant pipe 35. The outside air as a cooling source of the gas cooler 22 is supplied by the outside fan 36. The outside fan 36 is arranged in the outside space S1, and a propeller fan is used here. The outside fan 36 is rotationally driven by the outside fan motor 36a. Here, a cross fin type fin-and-tube heat exchanger is employed as the gas cooler 22, but other types of heat exchangers may be used.

  The expansion mechanism 23 is a mechanism for reducing the pressure of the high-pressure refrigerant that has dissipated heat in the gas cooler 22 until it reaches a low pressure in the refrigeration cycle, and is disposed in the interior space S2. The expansion mechanism 23 is provided in the liquid refrigerant pipe 35 and mainly includes an upstream expansion mechanism 25 (second expansion mechanism) that depressurizes the refrigerant and a downstream expansion that depressurizes the refrigerant depressurized in the upstream expansion mechanism 25. And a mechanism 26 (first expansion mechanism). Specifically, the upstream side expansion mechanism 25 is a mechanism for reducing the pressure of the high-pressure refrigerant after radiating heat in the gas cooler 22 until it reaches an intermediate pressure in the refrigeration cycle. The downstream side expansion mechanism 26 is a mechanism for reducing the pressure of the intermediate-pressure refrigerant that has been reduced in pressure by the upstream side expansion mechanism 25 until it reaches a low pressure. Here, electric expansion valves are used as the expansion mechanisms 25 and 26.

  The liquid refrigerant pipe 35 is provided with an intermediate pressure receiver 27 that stores the refrigerant decompressed in the upstream expansion mechanism 25 at a portion between the upstream expansion mechanism 25 and the downstream expansion mechanism 26. Here, the intermediate pressure receiver 27 is a cylindrical container and is disposed in the internal space S2. The intermediate-pressure refrigerant flowing into the intermediate-pressure receiver 27 is reduced to a pressure equal to or lower than the critical pressure of the refrigerant in the upstream expansion mechanism 25 and is in a saturated state or a gas-liquid two-phase state. 27 will be stored.

  In addition, the intermediate pressure receiver 27 receives the refrigerant (that is, the intermediate pressure receiver side refrigerant) present in the intermediate pressure receiver 27 by the refrigerant (that is, the intake side refrigerant) that goes from the outlet of the evaporator 24 toward the intake of the compressor 21. A supercooling heat exchanger 28 for cooling is provided. Here, the supercooling heat exchanger 28 is provided in and integrated with the intermediate pressure receiver 27, and is disposed in the interior space S2. Specifically, the supercooling heat exchanger 28 is provided such that a straight tubular heat transfer pipe 28 a provided in the suction refrigerant pipe 31 is in contact with the cylindrical portion of the intermediate pressure receiver 27, and thereby the suction side refrigerant Constitutes a heat exchanger for cooling the intermediate pressure receiver side refrigerant. The structure in which the supercooling heat exchanger 28 is provided in the intermediate pressure receiver 27 and integrated is not limited to that shown in FIG. For example, as shown in FIG. 6, even in a supercooling heat exchanger 28 having a structure in which a coiled heat transfer tube 28 b is provided so as to surround a cylindrical portion of the intermediate pressure receiver 27 and integrated with the intermediate pressure receiver 27. Good.

  The evaporator 24 is a device that evaporates the low-pressure refrigerant decompressed by the expansion mechanism 23, and is disposed in the interior space S2. Here, the evaporator 24 is a cross-fin type fin-and-tube heat exchanger composed of heat transfer tubes and a large number of fins. The evaporator 24 evaporates low-pressure refrigerant using the inside air as a heating source, Thereby, the air in a store | warehouse | chamber is cooled. The evaporator 24 has an inlet connected to the liquid refrigerant pipe 35 and an outlet connected to the suction refrigerant pipe 32. The internal air as a heating source of the evaporator 24 is supplied by the internal fan 37. The inside fan 37 is arranged in the inside space S2, and here, two propeller fans are used. The internal fan 37 is rotationally driven by an internal fan motor 37a. Here, as the evaporator 24, a cross fin type fin-and-tube heat exchanger is adopted, but other types of heat exchangers may be used.

  The intermediate refrigerant pipe 33 is provided with an intercooler 38 that radiates the refrigerant discharged from the low-stage compressor 21a. The intercooler 38 is disposed in the outer space S1. Here, the intercooler 38 is a cross-fin type fin-and-tube heat exchanger composed of heat transfer tubes and a large number of fins, and is discharged from the low-stage compressor 21a using outside air as a cooling source. The discharged refrigerant is radiated. Here, the intercooler 38 is integrated with the gas cooler 22. The outside air as a cooling source for the intercooler 38 is supplied by the outside fan 36 in the same manner as the gas cooler 22. Here, as the intercooler 38, a cross-fin type fin-and-tube heat exchanger is adopted, but other types of heat exchangers may be used. Here, in order to improve the cycle performance, the intercooler 38 is provided in the refrigerant circuit 10. However, if the desired cycle performance can be obtained without the intercooler 38, the refrigerant circuit 10 It may be omitted.

  The liquid refrigerant pipe 35 is an economizer heat exchanger that cools the refrigerant flowing between the outlet of the gas cooler 22 and the upstream expansion mechanism 25 at a portion between the outlet of the gas cooler 22 and the upstream expansion mechanism 25. A container 39 is provided. The economizer heat exchanger 39 is disposed in the outer space S1. Here, the economizer heat exchanger 39 is a plate-type heat exchanger, and heat exchange is performed between the refrigerant flowing through the high-pressure side flow path 39a and the refrigerant flowing through the intermediate pressure-side flow path 39b. A high-pressure refrigerant that flows through a portion between the outlet side of the gas cooler 22 of the liquid refrigerant pipe 35 and the upstream-side expansion mechanism 25 flows through the high-pressure side flow path 39a. An intermediate pressure refrigerant flowing through the intermediate pressure injection pipe 40 branched from a portion between the outlet side of the gas cooler 22 of the liquid refrigerant pipe 35 and the upstream side expansion mechanism 25 flows in the intermediate pressure side flow path 39b. Yes. Here, the intermediate pressure injection pipe 40 is branched from a portion between the outlet side of the gas cooler 22 of the liquid refrigerant pipe 35 and the high pressure side passage 39 a of the economizer heat exchanger 39. The intermediate pressure injection pipe 40 may be branched from a portion between the outlet of the high pressure side passage 39a of the economizer heat exchanger 39 and the upstream side expansion mechanism 25. Further, the intermediate pressure injection pipe 40 joins a portion between the outlet side of the intercooler 38 of the intermediate refrigerant pipe 33 and the suction of the high stage compressor 21b. The intermediate pressure injection pipe 40 is provided with an intermediate pressure return expansion mechanism 41 at the inlet side portion of the intermediate pressure side flow path 39b. The intermediate pressure return expansion mechanism 41 is a mechanism for reducing the pressure of the high-pressure refrigerant branched to the intermediate pressure injection pipe 40 until the intermediate pressure is reached, and is disposed in the outer space S1. Here, an electric expansion valve is used as the intermediate pressure return expansion mechanism 41. Here, in order to improve cycle performance, the economizer heat exchanger 39 and the intermediate pressure injection pipe 40 are provided in the refrigerant circuit 10. However, if desired cycle performance can be obtained without the economizer heat exchanger 39 and the intermediate pressure injection pipe 40, the refrigerant circuit 10 may be omitted.

  Further, the discharge refrigerant pipe 34 is a discharge that is opened / closed or adjusted in opening degree during the defrosting operation or reheating operation of the evaporator 24 in a portion between the high-stage check mechanism 34a and the inlet of the gas cooler 22. A flow rate adjusting mechanism 42 is provided. The discharge flow rate adjusting mechanism 42 is disposed in the outer space S1. Here, an electric expansion valve is used as the discharge flow rate adjustment mechanism 42. In addition, a heating refrigerant pipe 43 is branched into the discharge refrigerant pipe 34 from a portion between the high-stage check mechanism 34 a and the discharge flow rate adjustment mechanism 42. The heating refrigerant pipe 43 joins the portion between the downstream expansion mechanism 26 and the evaporator 24 of the liquid refrigerant pipe 35. The heating refrigerant pipe 43 mainly has a reheating refrigerant pipe 44 and a defrosting refrigerant pipe 45. The reheating refrigerant pipe 44 is provided with a reheating side opening / closing mechanism 46 made of an electromagnetic valve, a reheating coil 47 disposed on the leeward side of the evaporator 24, and a reheating side pressure reducing mechanism 48 made of a capillary tube. It has been. Thereby, by adjusting the opening degree of the discharge flow rate adjusting mechanism 42 and opening the reheat side opening / closing mechanism 46, a part of the high-pressure refrigerant discharged from the compressor 21 is supplied to the reheat coil 47. The reheating operation of reheating the internal air cooled by the evaporator 24 can be performed. The defrosting refrigerant pipe 45 branches into a drain pan heating refrigerant pipe 49 and an evaporator heating refrigerant pipe 50. The defrosting refrigerant pipe 45 is provided with a defrosting side opening / closing mechanism 51 including an electromagnetic valve at a branch portion between the drain pan heating refrigerant pipe 49 and the evaporator heating refrigerant pipe 50. The drain pan heating refrigerant pipe 49 is provided with a drain pan heater 52 disposed on a drain pan (not shown) provided below the evaporator 24 and the reheating coil 47. As a result, the discharge flow rate adjusting mechanism 42 is closed and the defrosting side opening / closing mechanism 51 is opened, so that the high-pressure refrigerant discharged from the compressor 21 is supplied directly to the evaporator 24 while being supplied to the drain pan heater 52. And the defrosting operation of the evaporator 24 can be performed. Here, for the defrosting operation and the reheating operation of the evaporator 24, the refrigerant pipe 43 for heating and the discharge flow rate adjusting mechanism 42 are provided in the refrigerant circuit 10, but the defrosting operation and the reheating operation are performed. The configuration for the above is not limited to this, and the defrosting operation and the reheating operation may be performed by another configuration.

  The container refrigeration apparatus 1 is provided with various sensors and switches. Specifically, the suction refrigerant pipe 32 is provided with a suction pressure sensor 53 that detects the pressure Ps of the low-pressure refrigerant sucked into the compressor 21 (low stage compressor 21a). Here, the evaporation temperature Te of the refrigerant circuit 10 is obtained by converting the pressure Ps of the low-pressure refrigerant detected by the suction pressure sensor 53 into the saturation temperature of the refrigerant. The suction refrigerant pipe 32 is provided with a suction temperature sensor 54 that detects the temperature Ts of the low-pressure refrigerant sucked into the compressor 21 (low stage compressor 21a). Further, the suction refrigerant pipe 32 is provided with an evaporator outlet temperature sensor 55 that detects the temperature Teo of the low-pressure refrigerant at the outlet of the evaporator 24. Here, the superheat degree SH of the refrigerant at the outlet of the evaporator 24 is obtained by subtracting the evaporation temperature Te from the temperature Teo. The discharge refrigerant pipe 34 is provided with a discharge pressure sensor 56 that detects the pressure Td of the high-pressure refrigerant discharged from the compressor 21 (the high-stage compressor 21b). Further, the discharge refrigerant pipe 34 is provided with a discharge temperature sensor 57 that detects the temperature of the high-pressure refrigerant discharged from the compressor 21 (the high-stage compressor 21b). Further, the discharge refrigerant pipe 34 is provided with a discharge pressure switch 58 for detecting an abnormal high pressure of the high-pressure refrigerant discharged from the compressor 21 (the high-stage compressor 21b) and stopping the compressor 21. Further, an outside temperature sensor 59 for detecting the outside temperature Ta is provided in the vicinity of the outside fan 36, and in the vicinity of the inside fan 37 (in the vicinity of the suction port 4a of the partition plate 4), a warehouse is provided. An internal temperature sensor 60 for detecting the internal temperature Tr is provided.

  In addition, the container refrigeration apparatus 1 includes a control unit 7 for controlling the operation of each part such as the compressor 21, the fans 36 and 37, and the expansion mechanism 23 that constitute the container refrigeration apparatus 1. The control unit 6 includes a microcomputer, a memory, and the like, and controls the operation of each unit constituting the container refrigeration apparatus 1 based on various operation settings, detection values of various sensors, and the like.

(2) Operation of container refrigeration apparatus Next, the operation of the normal operation of the container refrigeration apparatus 1 and the operation of the pump-down operation performed when the normal operation is stopped will be described with reference to FIGS. 4 and 8 to 11. To do. Here, FIG. 8 is a pressure-enthalpy diagram illustrating the refrigeration cycle during normal operation. FIG. 9 is a flowchart of the pump-down operation performed when normal operation is stopped. FIG. 10 is a schematic refrigerant circuit diagram of the container refrigeration apparatus 1 showing the refrigerant flow during the pump-down operation. FIG. 11 is a pressure-enthalpy diagram illustrating a refrigeration cycle during pump-down operation.

<Normal operation>
The normal operation is performed in a state where the refrigerant circuit 10 is fully opened and the reheating side opening / closing mechanism 46 and the defrosting side opening / closing mechanism 51 are fully closed.

  In such a state of the refrigerant circuit 10, low-pressure refrigerant (see point A in FIGS. 4 and 8) is sucked into the compressor 21 from the suction refrigerant pipe 32, and first, the intermediate pressure is reduced to the intermediate pressure by the low-stage compressor 21a. After being compressed, the refrigerant is discharged into the intermediate refrigerant pipe 33 (see point B in FIGS. 4 and 8).

  The intermediate-pressure refrigerant discharged from the low-stage compressor 21a is sent to the intercooler 38 through the low-stage check mechanism 33a. The intermediate pressure refrigerant sent to the intercooler 38 performs heat exchange with outside air supplied by the outside fan 36 in the intercooler 38 and dissipates heat (see point C in FIGS. 4 and 8).

  The intermediate-pressure refrigerant radiated in the intercooler 38 is further cooled by joining with the refrigerant (see point M in FIGS. 4 and 8) returned from the intermediate-pressure injection pipe 40 to the intermediate refrigerant pipe 33 (see FIG. 4). 4 and point D in FIG. 8).

  The intermediate pressure refrigerant combined with the refrigerant returning from the intermediate pressure injection pipe 40 is sucked into the high stage compressor 21b, further compressed, and discharged from the compressor 21 to the discharge refrigerant pipe 34 (FIGS. 4 and 4). (See point E in 8). Here, the high-pressure refrigerant discharged from the compressor 21 is compressed to a pressure exceeding the critical pressure of the refrigerant (see the pressure Pcp in FIG. 8) by the two-stage compression operation by the compressors 21a and 21b.

  The high-pressure refrigerant discharged from the compressor 21 is sent to the gas cooler 22 through the discharge flow rate adjusting mechanism 42.

  The high-pressure refrigerant sent to the gas cooler 22 radiates heat by exchanging heat with outside air supplied by the outside fan 36 in the gas cooler 22, and is sent to the liquid refrigerant pipe 35 (see FIGS. 4 and 8). (See point F).

  A part of the high-pressure refrigerant radiated in the gas cooler 22 is branched to the intermediate-pressure injection pipe 40, and the rest is sent to the high-pressure side flow path 39 a of the economizer heat exchanger 39. Then, the high-pressure refrigerant flowing through the intermediate pressure injection pipe 40 is reduced in the intermediate pressure return expansion mechanism 41 until the intermediate pressure is reached (see point L in FIGS. 4 and 8). The intermediate pressure refrigerant decompressed by the intermediate pressure return expansion mechanism 41 is sent to the intermediate pressure side flow path 39 b of the economizer heat exchanger 39. The high-pressure refrigerant sent to the high-pressure side passage 39a of the economizer heat exchanger 39 is cooled by performing heat exchange with the intermediate-pressure refrigerant sent to the intermediate-pressure side passage 39b of the economizer heat exchanger 39. (Refer to point G in FIGS. 4 and 8) and sent to the upstream expansion mechanism 25. At this time, the intermediate pressure refrigerant sent to the intermediate pressure side flow path 39b of the economizer heat exchanger 39 is heated by heat exchange with the high pressure refrigerant sent to the high pressure side flow path 39a of the economizer heat exchanger 39 ( 4 and FIG. 8), the refrigerant flows through the intermediate refrigerant pipe 33.

  The high-pressure refrigerant cooled in the economizer heat exchanger 39 is depressurized to an intermediate pressure in the upstream side expansion mechanism 25 to become a saturated state or a gas-liquid two-phase state (see point H in FIGS. 4 and 8). ).

  The intermediate pressure refrigerant depressurized in the upstream expansion mechanism 25 flows into the intermediate pressure receiver 27 and is temporarily stored in the intermediate pressure receiver 27 in a liquid state. The intermediate-pressure refrigerant temporarily stored in the intermediate-pressure receiver 27 is a low-pressure refrigerant that flows through the heat transfer tube 28a (or 28b) of the supercooling heat exchanger 28 provided in the intermediate-pressure receiver 27 in the intermediate-pressure receiver 27. It is further cooled by exchanging heat with the refrigerant. (See point I in FIGS. 4 and 8). Here, the low-pressure refrigerant that flows through the heat transfer tube 28a (or 28b) of the supercooling heat exchanger 28 is low-pressure refrigerant that flows through the intake refrigerant tube 32 from the outlet of the evaporator 24 toward the intake of the compressor 21, A low-pressure refrigerant is a cooling source for the supercooling heat exchanger 28. Then, the intermediate-pressure refrigerant that is cooled in the supercooling heat exchanger 28 and temporarily stored in the intermediate-pressure receiver 27 is sent to the downstream expansion mechanism 26 and depressurized until the pressure becomes low (FIG. 4 and point J in FIG. 8).

  The low-pressure refrigerant decompressed in the downstream side expansion mechanism 26 is sent to the evaporator 24, evaporates by exchanging heat with the internal air supplied by the internal fan 37, and sent to the suction refrigerant pipe 32. (See point K in FIGS. 4 and 8).

  As described above, the low-pressure refrigerant sent to the suction refrigerant pipe 32 is sent to the heat transfer pipe 28a (or 28b) of the supercooling heat exchanger 28 to exchange heat with the refrigerant present in the intermediate pressure receiver 27. Then, it is heated and again sucked into the compressor 21 (see point A in FIGS. 4 and 8).

  In such normal operation, the control unit 7 controls the operation of each unit so that the internal temperature Tr approaches the set target temperature Trs. Here, the control unit 7 mainly controls the operation of each unit based on the temperature difference between the internal temperature Tr and the target temperature Trs (that is, the refrigeration load required in the evaporator 24).

  Specifically, first, the control unit 7 calculates the target value Pss of the low pressure Ps of the refrigerant circuit 10 from the temperature difference between the internal temperature Tr and the target temperature Trs (when converting the low pressure Ps to the evaporation temperature Te, The target value Tes) is determined.

  And the control part 7 is the rotation speed (frequency) of the compressor motors 31a and 31b of the compressor 21 so that the evaporation temperature Te or the low pressure Ps of the refrigerant circuit 10 becomes constant at the target evaporation temperature value Tes or the target low pressure value Pss. ) Is controlled (low pressure control). That is, when the evaporation temperature Te or the low pressure Ps is higher than the target evaporation temperature value Tes or the target low pressure value Pss, control is performed to increase the rotation speed (frequency) of the compressor motors 31a and 31b of the compressor 21. . Conversely, when the evaporation temperature Te or the low pressure Ps is lower than the target evaporation temperature value Tes or the target low pressure value Pss, control is performed to reduce the rotation speed (frequency) of the compressor motors 31a and 31b of the compressor 21. Yes.

  Here, the control unit 7 controls the opening degree of the upstream expansion mechanism 25 so that the high pressure Pd of the refrigerant circuit 10 becomes constant at the high pressure target value Pds (high pressure control). That is, when the high pressure Pd is higher than the high pressure target value Pds, control is performed to increase the opening degree of the upstream expansion mechanism 25. Conversely, when the high pressure Pd is lower than the high pressure target value Pds, control is performed to reduce the opening degree of the upstream side expansion mechanism 25.

  Here, the control unit 7 controls the opening degree of the downstream side expansion mechanism 26 so that the superheat degree SH of the refrigerant at the outlet of the evaporator 24 becomes constant at the superheat degree target value SHs (superheat degree). control). That is, when the superheat degree SH is higher than the superheat degree target value SHs, control is performed to increase the opening degree of the downstream side expansion mechanism 26. Conversely, when the superheat degree SH is smaller than the superheat degree target value SHs, control is performed to reduce the opening degree of the downstream side expansion mechanism 26.

<Pump down operation>
The pump-down operation is an operation in which refrigerant is stored in the gas cooler 22 and the intermediate pressure receiver 27 when the normal operation is stopped in order to suppress an increase in the pressure equalization pressure on the low pressure side of the refrigerant circuit 10 when the normal operation is stopped. Unlike the normal pump-down operation, this pump-down operation is performed with the downstream expansion mechanism 26 slightly opened. This pump down operation will be described along steps ST1 to ST5 in the flowchart of FIG.

  First, in step ST1, the control unit 7 determines whether normal operation is stopped. Here, in the refrigerant circuit 10 when the normal operation is stopped, the intermediate pressure return expansion mechanism 41, the reheating side opening / closing mechanism 46, and the defrosting side opening / closing mechanism 51 are fully closed, and the discharge flow rate adjusting mechanism 42 and the upstream side expansion are expanded. The mechanism 25 is in a fully open state, and the downstream side expansion mechanism 26 is in a fully open state or a fully closed state. If it is determined in step ST1 that the normal operation is stopped, the process proceeds to step ST2.

  Next, in step ST2, the control unit 7 determines whether or not the refrigerant circuit 10 satisfies a predetermined pressure condition. Here, such a determination is made when the outside temperature Ta is low, or when the pressure on the low pressure side of the refrigerant circuit 10 (for example, the constant pressure Ps) is low, or the like, on the low pressure side of the refrigerant circuit 10. This is because there is no need to perform pump-down operation when the increase in pressure and pressure is small. For this reason, the predetermined pressure condition is set, for example, as a condition where the pressure Ps is higher than a predetermined pump-down start pressure Psta. Alternatively, the condition is set such that the outside temperature Ta is higher than the outside temperature equivalent to the pump down start pressure Psta, that is, higher than a predetermined pump down start temperature Tsta. And when it determines with satisfy | filling a predetermined pressure condition in step ST2, it transfers to the process of step ST3.

  Next, in step ST3, the control unit 7 starts a pump-down operation. The pump-down operation is started by operating the compressor 21 and the outside fan 36 with the downstream expansion mechanism 26 slightly opened (see the arrow indicating the refrigerant flow in FIG. 10).

  Here, the opening degree of the downstream side expansion mechanism 26 is an opening degree at which the high pressure Pd of the refrigerant circuit 10 becomes a predetermined high pressure value and / or an opening degree at which the low pressure Ps of the refrigerant circuit 10 becomes a predetermined low pressure value. Is set. During the pump down operation, in order to increase the amount of refrigerant stored in the gas cooler 22 or the intermediate pressure receiver 27, it is preferable to set the high pressure Pd to a pressure higher than the high pressure value during the normal operation. Further, during the pump down operation, in order to increase the amount of refrigerant remaining in the evaporator 24, it is preferable to set the low pressure Ps to a pressure lower than the low pressure value during the normal operation. For this reason, here, the opening degree is set to be smaller than the opening degree range of the downstream side expansion mechanism 26 during the normal operation so that such high pressure Pd and low pressure Ps can be obtained. Here, the pump-down operation is performed in a state where the internal fan 37 is stopped.

  When the pump-down operation is started, the low-pressure refrigerant (see point A in FIGS. 10 and 11) is sucked into the compressor 21 from the suction refrigerant pipe 32 and is first compressed to an intermediate pressure by the low-stage compressor 21a. Then, the refrigerant is discharged into the intermediate refrigerant pipe 33 (see point B in FIGS. 10 and 11).

  The intermediate-pressure refrigerant discharged from the low-stage compressor 21a is sent to the intercooler 38 through the low-stage check mechanism 33a. The intermediate pressure refrigerant sent to the intercooler 38 performs heat exchange with the outside air supplied by the outside fan 36 in the intercooler 38 to dissipate heat (see point C in FIGS. 10 and 11). Here, unlike during normal operation, the refrigerant does not flow through the intermediate pressure injection pipe 40, so the refrigerant returned from the intermediate pressure injection pipe 40 to the intermediate refrigerant pipe 33 is transferred to the intermediate pressure refrigerant radiated by the intercooler 38. They do not join (see point D in FIGS. 10 and 11).

  The intermediate-pressure refrigerant that has radiated heat in the intercooler 38 is sucked into the high-stage compressor 21b, further compressed, and discharged from the compressor 21 to the discharge refrigerant pipe 34 (see point E in FIGS. 10 and 11). ). Here, the high-pressure refrigerant discharged from the compressor 21 is compressed to a pressure exceeding the critical pressure of the refrigerant (see the pressure Pcp in FIG. 11) by the two-stage compression operation by the compressors 21a and 21b. Here, since the downstream side expansion mechanism 26 is slightly opened as described above, the high pressure Pd during the pump-down operation is higher than the high pressure during the normal operation.

  The high-pressure refrigerant discharged from the compressor 21 is sent to the gas cooler 22 through the discharge flow rate adjusting mechanism 42.

  The high-pressure refrigerant sent to the gas cooler 22 radiates heat by exchanging heat with outside air supplied by the outside fan 36 in the gas cooler 22 and is sent to the liquid refrigerant pipe 35 (see FIGS. 10 and 11). (See point F). Here, unlike during normal operation, the refrigerant does not flow through the intermediate pressure injection pipe 40, so the high-pressure refrigerant radiated in the gas cooler 22 is not cooled in the economizer heat exchanger 39 (FIGS. 10 and 10). 11 point G).

  The high-pressure refrigerant that has passed through the economizer heat exchanger 39 is sent to the intermediate pressure receiver 27 without being reduced in pressure in the upstream side expansion mechanism 25 (see point H in FIGS. 10 and 11).

  The high-pressure refrigerant that has passed through the upstream-side expansion mechanism 25 flows into the intermediate-pressure receiver 27 and is stored in the intermediate-pressure receiver 27 in a high-pressure state (pressure exceeding the critical pressure), unlike during normal operation. The high-pressure refrigerant stored in the intermediate-pressure receiver 27 exchanges heat with the low-pressure refrigerant flowing in the heat transfer tube 28a (or 28b) of the supercooling heat exchanger 28 provided in the intermediate-pressure receiver 27. To cool further. (See point I in FIGS. 10 and 11). Here, the low-pressure refrigerant that flows through the heat transfer tube 28a (or 28b) of the supercooling heat exchanger 28 is low-pressure refrigerant that flows through the intake refrigerant tube 32 from the outlet of the evaporator 24 toward the intake of the compressor 21, A low-pressure refrigerant is a cooling source for the supercooling heat exchanger 28. A part of the high-pressure refrigerant that is cooled in the supercooling heat exchanger 28 and stored in the intermediate-pressure receiver 27 is sent to the downstream expansion mechanism 26 and decompressed until the pressure becomes low (FIG. 10). And see point J in FIG. 11). Here, since the downstream side expansion mechanism 26 is slightly opened as described above, the low pressure Ps during the pump-down operation is lower than the low pressure during the normal operation.

  The low-pressure refrigerant decompressed in the downstream side expansion mechanism 26 is sent to the evaporator 24. Here, unlike the normal operation, since the internal fan 37 is stopped, the refrigerant is sent to the suction refrigerant pipe 32 with little evaporation in the evaporator 24 (point K in FIGS. 10 and 11). reference).

  As described above, the low-pressure refrigerant sent to the suction refrigerant pipe 32 is sent to the heat transfer pipe 28a (or 28b) of the supercooling heat exchanger 28 to exchange heat with the refrigerant present in the intermediate pressure receiver 27. Then, it is heated and again sucked into the compressor 21 (see point A in FIGS. 10 and 11).

  Next, in step ST4, the control unit 7 determines whether the pump-down operation has been performed for a predetermined time. If it is determined in step ST4 that the pump-down operation has been performed for a predetermined time, the process proceeds to step ST5 and the pump-down operation is terminated. Here, after the end of the pump-down operation, the control unit 7 stops the compressor 21 and the external fan 36 and fully closes the downstream side expansion mechanism 26. Thereby, the refrigerant circuit 10 is divided into a low pressure side portion including the evaporator 24 and a high pressure side portion including the gas cooler 22 and the intermediate pressure receiver 27 according to the pressure level. Here, the low pressure side portion of the refrigerant circuit 10 is a portion between the downstream side expansion mechanism 26 and the low stage check mechanism 33a of the compressor 21, and the high pressure side portion of the refrigerant circuit 10 is the compressor. 21 is a portion on the high pressure side from the high stage side check mechanism 34 a to the downstream side expansion mechanism 26. Thereby, at the time of a stop of normal driving | operation, the raise of the equalization pressure of the low voltage | pressure side part of the refrigerant circuit 10 can be suppressed.

  Thereafter, when the refrigerant circuit 10 is in a state where the predetermined pressure condition in step ST2 is satisfied again, such as when the outside temperature Ta becomes high, the processes of steps ST3 to ST5 are performed again. In addition, it is possible to suppress an increase in the uniform pressure at the low pressure side portion of the refrigerant circuit 10.

(3) Features of container refrigeration apparatus The container refrigeration apparatus 1 of the present embodiment has the following characteristics.

<A>
Since the container refrigeration apparatus 1 uses carbon dioxide as a refrigerant, the cycle performance tends to be lower than that in the case of using a chlorofluorocarbon refrigerant. Therefore, the container refrigeration apparatus 1 is provided with a supercooling heat exchanger 28 that further cools the refrigerant cooled by the gas cooler 22 in order to improve cycle performance.

  Here, considering only the viewpoint of improving the cycle performance, the supercooling heat exchanger 28 may be connected anywhere between the gas cooler 22 and the evaporator 24, and the supercooling heat exchanger The 28 cooling sources are not limited.

  Further, since the container refrigeration apparatus 1 uses carbon dioxide as a refrigerant and does not need to be recovered, there is no need to perform a pump-down operation in which the refrigerant is stored in the gas cooler 22 and the intermediate pressure receiver 27.

  However, in the container refrigeration apparatus 1, as described above, when the supercritical refrigeration cycle using carbon dioxide as the refrigerant is adopted, an increase in the equalizing pressure on the low pressure side of the refrigerant circuit 10 is suppressed, and the container is provided on the low pressure side. There is a problem of keeping the design pressure of the evaporator 24 to be low.

  For this reason, in the container refrigeration apparatus 1, regarding the connection position of the supercooling heat exchanger 28, the cooling source, and the necessity of the pump down operation, an increase in the pressure equalizing pressure on the low pressure side of the refrigerant circuit 10 is suppressed, and the low pressure It is preferable to determine in consideration of the viewpoint of keeping the design pressure of the evaporator 24 provided on the side low. Here, the degree of suppression of the design pressure of the evaporator 24 provided on the low-pressure side is determined by the amount of refrigerant stored in the gas cooler 22 and the intermediate pressure receiver 27 when the normal operation for cooling the interior is stopped (that is, the intermediate pressure receiver 27). It is determined by the balance with the refrigerant storage amount. Since carbon dioxide is used as the refrigerant, the refrigerant stored in the gas cooler 22 and the intermediate pressure receiver 27 is stored in a supercritical state. For this reason, since the refrigerant | coolant storage amount in the gas cooler 22 and the intermediate pressure receiver 27 changes greatly with the temperature of a refrigerant | coolant, it is preferable to store a refrigerant | coolant at the lowest possible temperature.

  Therefore, in the container refrigeration apparatus 1, first, when the normal operation is stopped, the pump-down operation in which the refrigerant is stored in the gas cooler 22 and the intermediate pressure receiver 27 is performed. Thereby, although the refrigerant in the refrigerant circuit 10 is in a supercritical state, it is stored in the gas cooler 22 and the intermediate pressure receiver 27. Moreover, in the container refrigeration apparatus 1, the supercooling heat exchanger 28 is provided in the intermediate pressure receiver 27. Thereby, in the pump down operation, the refrigerant stored in the intermediate pressure receiver 27 is cooled, so that the refrigerant can be stored in the intermediate pressure receiver 27 at a low temperature. Further, the normal pump-down operation is performed in a state where the downstream of the intermediate pressure receiver 27 of the refrigerant circuit 10 is closed and the refrigerant is not circulated. Here, the downstream side expansion mechanism 26 positioned downstream of the intermediate pressure receiver 27 is installed. I try to do it a little open. That is, the pump-down operation is performed in a state in which the refrigerant flow from the outlet of the evaporator 24 that is the cooling source of the supercooling heat exchanger 28 toward the suction of the compressor 21 is secured. For this reason, in the pump-down operation, cooling of the refrigerant stored in the intermediate pressure receiver 27 is promoted, and the refrigerant storage amount in the intermediate pressure receiver 27 can be increased. As a result, an increase in the pressure equalization pressure on the low pressure side of the refrigerant circuit 10 is suppressed, and the design pressure of the evaporator 24 provided on the low pressure side can be suppressed low.

  As described above, the container refrigeration apparatus 1 employs the connection position and the cooling source as described above for the supercooling heat exchanger 28 for improving the cycle performance, and at the time of stopping the normal operation, the downstream side expansion mechanism The pump down operation is performed with 26 slightly opened. Thereby, in the container refrigeration apparatus 1, when adopting the supercritical refrigeration cycle using carbon dioxide as the refrigerant, the evaporator 24 provided on the low pressure side is suppressed by suppressing an increase in the equal pressure on the low pressure side of the refrigerant circuit 10. The design pressure can be kept low.

<B>
Further, in the container refrigeration apparatus 1, since the opening degree of the downstream expansion mechanism 26 is set based on the high pressure Pd and the low pressure Ps of the refrigerant circuit 10 during the pump down operation, the downstream expansion mechanism is used during the pump down operation. 26 can be maintained in a slightly opened state. As a result, the container refrigeration apparatus 1 can perform a pump-down operation while cooling the refrigerant in the intermediate pressure receiver 27.

<C>
In the container refrigeration apparatus 1, the internal fan 37 is stopped during the pump-down operation, so that the heating of the refrigerant in the evaporator 24 can be suppressed as much as possible. Thereby, in the container refrigeration apparatus 1, the temperature of the refrigerant from the outlet of the evaporator 24 that is the cooling source of the supercooling heat exchanger 28 toward the suction of the compressor 21 is maintained as low as possible, and the inside of the intermediate receiver 27 Can be cooled to as low a temperature as possible.

<D>
Further, in the container refrigeration apparatus 1, the intermediate receiver 27 functions as an intermediate pressure receiver for storing refrigerant at an intermediate pressure in the refrigeration cycle during normal operation, and the intermediate pressure receiver 27 serves as a high pressure for the refrigeration cycle during pump down operation. It functions as a high-pressure receiver for storing the refrigerant. For this reason, in the container refrigeration apparatus 1, the refrigerant can be stored in the intermediate pressure receiver 27 in a liquid state during normal operation. Thereby, in the container refrigeration apparatus 1, the refrigerant storage amount difference between the refrigerant storage amount in the intermediate pressure receiver 27 during the pump-down operation and the refrigerant storage amount in the intermediate pressure receiver 27 during the normal operation increases. There is a tendency.

  However, in the container refrigeration apparatus 1, as described above, the refrigerant in the intermediate pressure receiver 27 is cooled by the supercooling heat exchanger 28 with the downstream expansion mechanism 26 slightly opened during the pump down operation. Therefore, the refrigerant storage amount difference between the pump-down operation and the normal operation can be made as small as possible. Thereby, in the container refrigeration apparatus 1, since the intermediate pressure receiver 27 having a volume close to the refrigerant storage amount of the intermediate pressure receiver 27 during normal operation can be selected, an increase in cost due to the intermediate pressure receiver 27 can be suppressed. it can.

<E>
Further, in the container refrigeration apparatus 1, when the rise in the equal pressure on the low pressure side of the refrigerant circuit 10 is large, such as when the outside temperature Ta is high or the pressure Ps on the low pressure side of the refrigerant circuit 10 is high ( That is, the pump-down operation can be performed only when the refrigerant circuit 10 satisfies a predetermined pressure condition. As a result, in the container refrigeration apparatus 1, when the rise in the equal pressure on the low pressure side of the refrigerant circuit 10 is small, such as when the outside temperature Ta is low or the pressure Ps on the low pressure side of the refrigerant circuit 10 is low. In this case, the pump-down operation can be omitted.

<F>
In the container refrigeration apparatus 1, the intermediate pressure receiver 27 and the supercooling heat exchanger 28 are arranged in the interior space S2. For this reason, the temperature rise of the intermediate pressure receiver 27 and the supercooling heat exchanger 28 can be suppressed as much as possible when the normal operation including the pump down operation is stopped. Thereby, in the container refrigeration apparatus 1, the temperature of the refrigerant stored in the intermediate pressure receiver 27 can be kept as low as possible during the pump down operation, and the supercooling heat exchanger 28 and the intermediate pressure receiver 27 can be The thickness of the cold insulating material to cover can be reduced, or the cold insulating material can be omitted.

<G>
Further, in the container refrigeration apparatus 1, the above-described connection position and cooling are used for the supercooling heat exchanger 28 for improving the cycle performance from the viewpoint of keeping the design pressure of the evaporator 24 provided on the low pressure side low. However, this configuration also has an effect of easily maintaining the refrigerant storage amount in the intermediate pressure receiver 27 during normal operation in an optimum state.

  Here, the refrigerant storage amount in the intermediate pressure receiver 27 is determined by the balance with the flow rate of the refrigerant circulating through the refrigerant circuit 10 (that is, the refrigerant circulation flow rate). The refrigerant circulation flow rate varies depending on the refrigeration load required in the evaporator 24 (that is, the required refrigeration load). The change in the required refrigeration load appears as a change in the superheat degree SH of the refrigerant at the outlet of the evaporator 24 and the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10. For this reason, the refrigerant storage amount in the intermediate pressure receiver 27 can be appropriately changed according to the change in the superheat degree SH of the refrigerant at the outlet of the evaporator 24 and the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10. preferable.

  In contrast, in the container refrigeration apparatus 1, first, the supercooling heat exchanger 28 is provided in the intermediate pressure receiver 27. Thereby, in the supercooling heat exchanger 28, the refrigerant (that is, the intermediate pressure receiver side refrigerant) existing in the intermediate pressure receiver 27 is cooled. At this time, the refrigerant storage amount in the intermediate pressure receiver 27 changes according to the change in the temperature of the cooling source of the supercooling heat exchanger 28. Moreover, in the container refrigeration apparatus 1, a refrigerant (that is, a suction-side refrigerant) that goes from the outlet of the evaporator 24 toward the suction of the compressor 21 is used as a cooling source of the supercooling heat exchanger 28. As a result, in the supercooling heat exchanger 28, the intermediate pressure receiver side refrigerant is cooled by the suction side refrigerant. Therefore, the intermediate pressure receiver side refrigerant includes the superheat degree SH of the refrigerant at the outlet of the evaporator 24. And the change of the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10 is likely to appear. For this reason, the heat exchange amount in the supercooling heat exchanger 28 also changes in accordance with changes in the superheat degree SH of the refrigerant at the outlet of the evaporator 24 and the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10, and as a result, The refrigerant storage amount in the intermediate pressure receiver 27 also changes. Further, the suction-side refrigerant is a refrigerant in a low-pressure gas state of the refrigeration cycle, whereas the intermediate-pressure receiver-side refrigerant is a refrigerant in a saturated state or a gas-liquid two-phase state of the intermediate pressure of the refrigeration cycle. The temperature of the refrigerant is close. For this reason, changes in the degree of superheat SH of the refrigerant at the outlet of the evaporator 24 and the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10 are clearly apparent as changes in the temperature difference between the two refrigerants in the supercooling heat exchanger 28. It has become.

  Specifically, when the superheat degree SH of the refrigerant at the outlet of the evaporator 24 is large or when the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10 is high, the refrigerant circulation flow rate tends to be small with respect to the required refrigeration load. It is in. At this time, in the supercooling heat exchanger 28, the temperature difference between the intermediate pressure receiver side refrigerant and the suction side refrigerant becomes small, so that the cooling of the intermediate pressure receiver side refrigerant is suppressed, and the refrigerant storage amount in the intermediate pressure receiver is small. Become. As a result, the refrigerant circulation flow rate increases, and the optimum refrigerant circulation flow rate for the required refrigeration load, that is, the refrigerant storage amount in the intermediate pressure receiver 27 approaches the optimum state. Further, when the superheat degree SH of the refrigerant at the outlet of the evaporator 24 is small or when the evaporation temperature Te (or low pressure Ps) of the refrigerant circuit 10 is low, the refrigerant circulation flow rate tends to be large with respect to the required refrigeration load. At this time, in the subcooling heat exchanger 28, the temperature difference between the intermediate pressure receiver-side refrigerant and the suction-side refrigerant is increased, so that the cooling of the intermediate pressure receiver-side refrigerant is promoted and the refrigerant storage amount in the intermediate pressure receiver 27 is increased. Become more. Thereby, the refrigerant circulation flow rate becomes small, and the optimum refrigerant circulation flow rate for the required refrigeration load, that is, the refrigerant storage amount in the intermediate pressure receiver 27 approaches the optimum state.

  As described above, in the container refrigeration apparatus 1, the refrigerant storage amount in the intermediate pressure receiver 27 is adopted by adopting the connection position and the cooling source as described above for the supercooling heat exchanger 28 for improving the cycle performance. The self-adjusting function that brings the camera to the optimum state can also be demonstrated. In the container refrigeration apparatus 1, superheat control and low pressure control are performed, but superheat control and low pressure control are performed by the self-adjustment function of the refrigerant storage amount in the intermediate pressure receiver 27 by the supercooling heat exchanger 28. It also contributes to improving convergence.

(4) Modifications In the container refrigeration apparatus 1 of the above embodiment, not only the downstream expansion mechanism 26 on the downstream side of the receiver 27 is provided as the expansion mechanism 23, but also between the gas cooler 22 and the receiver 27. Although the upstream side expansion mechanism 25 is further provided, as shown in FIG. 12, the upstream side expansion mechanism 25 may be omitted and the receiver 27 may function as a high pressure receiver.

  Here, the receiver 27 functions as a high-pressure receiver not only during the pump-down operation but also during the normal operation. However, the increase in the pressure equalization pressure on the low-pressure side of the refrigerant circuit 10 is suppressed, and the design pressure of the evaporator 24 is suppressed. About the subject of restraining low, it is common with the said embodiment.

  Even in the configuration of the present modification, the same pump-down operation as in the above embodiment is performed, so that when the supercritical refrigeration cycle using carbon dioxide as the refrigerant is employed, the equalized pressure on the low pressure side of the refrigerant circuit 10 As a result, the design pressure of the evaporator 24 can be kept low.

  The present invention is widely applicable to container refrigeration apparatuses.

DESCRIPTION OF SYMBOLS 1 Refrigeration apparatus for containers 21 Compressor 22 Gas cooler 23 Expansion mechanism 24 Evaporator 10 Refrigerant circuit 25 Upstream expansion mechanism (second expansion mechanism)
26 Downstream expansion mechanism (first expansion mechanism)
27 Intermediate pressure receiver (receiver)
28 Supercooling heat exchanger 37 Inside fan

JP 2011-112270 A

Claims (6)

In a container refrigeration apparatus having a refrigerant circuit (10) in which a compressor (21), a gas cooler (22), a first expansion mechanism (26), and an evaporator (24) are sequentially connected.
The refrigerant circuit uses carbon dioxide as a refrigerant, and performs a supercritical refrigeration cycle in which the pressure of the refrigerant discharged from the compressor exceeds the critical pressure of the refrigerant,
Between the gas cooler and the first expansion mechanism, a receiver (27) for storing refrigerant is provided,
The receiver is provided with a supercooling heat exchanger (28) that cools the refrigerant present in the receiver by the refrigerant going from the outlet of the evaporator toward the suction of the compressor,
When the normal operation is stopped, a pump-down operation is performed in which the refrigerant is stored in the gas cooler and the receiver with the first expansion mechanism slightly opened.
Container refrigeration equipment (1). The first expansion mechanism (26) has an opening at which a high pressure of the refrigerant circuit (10) becomes a predetermined high pressure value and / or a low pressure of the refrigerant circuit at a predetermined low pressure value during the pump-down operation. Set to an opening
The container refrigeration apparatus (1) according to claim 1. An internal fan (37) for sending air to the evaporator (24);
The inside fan is stopped during the pump down operation.
The container refrigeration apparatus (1) according to claim 1 or 2. A second expansion mechanism (25) is further provided between the gas cooler (22) and the receiver (27),
The pump down operation is performed with the second expansion mechanism opened.
The container refrigeration apparatus (1) according to any one of claims 1 to 3. The pump-down operation is performed when the refrigerant circuit (10) satisfies a predetermined pressure condition when the normal operation is stopped.
The container refrigeration apparatus (1) according to any one of claims 1 to 4. The receiver (27) and the supercooling heat exchanger (28) are disposed in the interior space.
The container refrigeration apparatus (1) according to any one of claims 1 to 5.

Images