Cooling device

Abstract

To provide a cooling device which can maintain a temperature in a freezer to a substantially constant low temperature state while inhibiting phase change of carbon dioxide in a refrigeration cycle to a solid.SOLUTION: A cooling device 1 comprises a refrigeration cycle 10, a freezer 2, a heating unit, and a temperature detection unit. The refrigeration cycle 10 uses carbon dioxide as a refrigerant. The inside of the freezer 2 is cooled by the refrigeration cycle 10. The heating unit is disposed in the freezer 2. The temperature detection unit detects a temperature in the freezer 2. The heating unit executes heating on the basis of the temperature detected by the temperature detection unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cooling device that cools products using a refrigeration cycle and a freezer that uses carbon dioxide (CO2) as a refrigerant. [Background technology]

[0002] In frozen food and refrigerated food manufacturing plants, products are moved into a freezer by a conveyor or the like, and the products are frozen or cooled. The cooling device used here is equipped with a refrigeration cycle having a compressor, gas cooler, expansion valve, evaporator, etc., and the evaporator of the refrigeration cycle is installed in the freezer. In the refrigeration cycle, the refrigerant in the refrigeration cycle is compressed by the compressor, and the compressed refrigerant flows inside the evaporator in the freezer after passing through the gas cooler and expansion valve. The evaporator cools the air in the freezer by the latent heat generated when the refrigerant flowing inside changes from liquid phase to gas phase. The refrigerant that has passed through the evaporator is returned to the suction side of the compressor.

[0003] In recent years, from the viewpoint of protecting the global environment, the refrigerants used in the refrigeration cycle of this type of cooling device are being switched from fluorocarbon-based refrigerants to natural refrigerants such as carbon dioxide (CO2) and ammonia (NH3). These natural refrigerants are preferable from the viewpoint of protecting the global environment, but some of them are pressurized, and care must be taken when using them in cooling devices.

[0004] In particular, when carbon dioxide (CO2) is used as a refrigerant for a cooling device, the triple point temperature of carbon dioxide is -56.6°C, which is a temperature that may interfere with the refrigeration cycle, so when the thermal load in the freezer is small, there is a risk that the carbon dioxide in the refrigeration cycle will change phase to a solid (become dry ice).If carbon dioxide becomes dry ice in the refrigeration cycle, it will hinder smooth circulation of the refrigerant in the refrigeration cycle and there is a risk of damaging the cooling device.

[0005] In factories that manufacture frozen and refrigerated foods, the freezer is cooled before products are put into it, and when the temperature inside the freezer reaches a specified level, the cooling system goes into standby mode. During standby mode, the compressor runs at partial load (unloaded). Also, if the addition of products is stopped due to a problem on the production line upstream of the freezer, the cooling system will go into standby mode in the same way as above.

[0006] When a fluorocarbon-based refrigerant or ammonia-based refrigerant is used as the refrigerant of the cooling device, even if the expansion valve is narrowed and the suction pressure drops significantly when the compressor is at a minimum partial load, the temperature inside the freezer can be maintained at a constant temperature without any problems. However, when carbon dioxide is used as the refrigerant of the cooling device, if the suction pressure of the compressor drops significantly, the temperature of carbon dioxide in the low pressure section of the refrigeration cycle may reach the triple point temperature. In this case, as described above, the carbon dioxide turns into dry ice, which hinders the smooth circulation of the refrigerant in the refrigeration cycle and may damage the cooling device.

[0007] As a countermeasure to this problem, a cooling device has been proposed in which, during standby operation, the compressor is stopped and restarted at appropriate times to prevent carbon dioxide from turning into dry ice (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2008-164227 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, once the compressor is stopped during standby, it takes a long time for the compressor to restart and for the compressor's rotation speed to reach a specified value. Therefore, if the compressor is repeatedly stopped and restarted during standby, the temperature inside the freezer will fluctuate significantly, making it difficult to keep the temperature inside the freezer and the temperature of the product constant.

[0010] Furthermore, if the compressor is repeatedly stopped and restarted during standby operation, a large load is placed on the compressor motor and starter, which is likely to shorten the lifespan of the compressor, motor, and starter.

[0011] SUMMARY OF THE PRESENT EMBODIMENTS The present invention aims to provide a cooling device that can maintain the temperature inside the freezer during standby operation at a substantially constant low temperature while suppressing the conversion of carbon dioxide into dry ice in the refrigeration cycle. [Means for solving the problem]

[0012] In order to solve the above problems, the cooling device according to the present invention employs the following configuration. That is, a cooling device according to one aspect of the present invention comprises a refrigeration cycle that uses carbon dioxide as a refrigerant, a freezer whose inside is cooled by the refrigeration cycle, a heating unit disposed within the freezer, and a temperature detection unit that detects the temperature within the freezer, and the heating unit performs heating based on the temperature detected by the temperature detection unit.

[0013] The cooling device with the above configuration cools the inside of the freezer by the latent heat generated when the refrigerant flowing through the refrigeration cycle evaporates. In a situation where the thermal load inside the freezer is extremely small, such as during standby operation, if the compressor of the refrigeration cycle continues to operate, the amount of heat absorbed by the refrigerant in the evaporator decreases as the temperature inside the freezer drops. When the amount of heat absorbed by the refrigerant in the evaporator decreases, the temperature of the refrigerant on the suction side of the compressor drops, and the temperature of the refrigerant approaches the temperature of the triple point of carbon dioxide. At this time, if the heating unit in the freezer performs heating based on the detection result of the temperature detection unit, the heat functions as a pseudo thermal load in the freezer. In other words, the amount of heat absorbed by the refrigerant in the evaporator increases due to the heating performed by the heating unit. As a result, an excessive temperature drop of the refrigerant on the suction side of the compressor is suppressed, and the carbon dioxide refrigerant does not turn into dry ice.

[0014] The heating section may be configured to perform heating when the temperature detected by the temperature detection section becomes equal to or lower than a specified threshold temperature that is lower than a set temperature inside the freezer.

[0015] In this case, when the temperature inside the freezer detected by the temperature detection unit falls below a specified threshold temperature, the heating unit in the freezer starts heating. This causes the heating by the heating unit to act as a pseudo heat load, increasing the amount of heat absorbed by the refrigerant in the evaporator. As a result, excessive temperature drops in the refrigerant on the suction side of the compressor are suppressed, and the carbon dioxide refrigerant does not turn into dry ice.

[0016] The heating units may be provided in plurality, and the threshold temperatures may be set in plurality so that the temperature decreases in stages, and the heating units and the threshold temperatures may be associated with each of the threshold temperatures such that the lower the threshold temperature, the greater the total amount of heat is.

[0017] In this case, when the temperature detected by the temperature detection unit drops further below the freezer internal set temperature, the heating unit corresponding to the first threshold temperature starts heating when the detected temperature first drops below the first threshold temperature. Then, when the detected temperature drops further and drops below the second threshold temperature, the heating unit corresponding to the second threshold temperature starts heating. At this time, the heating unit corresponding to the second threshold temperature starts heating in addition to the heating unit corresponding to the first threshold temperature, so the total amount of heat in the heating units increases. When the threshold temperature is set to the third or higher stage, the number of heating parts that perform heating increases in accordance with the increase in the number of stages. Therefore, when this configuration is adopted, the total heat amount of all the heating parts that perform heating in response to a temperature drop (a drop in the detected temperature) in the freezer increases, and the amount of heat absorbed by the refrigerant in the evaporator increases rapidly. Also, in this configuration, the number of heating parts that perform heating in response to a temperature drop (a drop in the detected temperature) in the freezer increases stepwise, so that it is possible to quickly suppress an excessive drop in temperature of the refrigerant on the suction side of the compressor while suppressing energy consumption in the heating parts.

[0018] When the temperature detected by the temperature detection unit becomes equal to or lower than the threshold temperature, the heating unit may perform heating with an amount of heat corresponding to a temperature difference between the detected temperature and the threshold temperature.

[0019] In this case, the heating section inside the freezer performs heating using an amount of heat corresponding to the temperature difference between the detected temperature of the temperature detection section and the threshold temperature, thereby quickly suppressing excessive temperature drops of the refrigerant on the suction side of the compressor while limiting heating more than necessary.

[0020] The refrigeration cycle may be a direct expansion type refrigeration cycle in which an evaporator of the refrigeration cycle is disposed inside the freezer, and the cold energy of the refrigerant that has passed through an expansion valve of the refrigeration cycle is directly exchanged with the air in the freezer by the evaporator.

[0021] In the case of a direct expansion type refrigeration cycle, unlike the secondary refrigerant type refrigeration cycle, there is no function capable of absorbing sudden changes in heat load, such as a buffer tank, etc. Therefore, in a cooling device having a direct expansion type refrigeration cycle, the above-mentioned configurations that can suppress an excessive temperature drop of the refrigerant on the suction side of the compressor by heating with the heating unit are particularly effective.

[0022] The heating section may be arranged on the inlet side of the evaporator into which air enters the freezer.

[0023] In this case, the heat from the heating section can be efficiently absorbed by the refrigerant in the evaporator, so that when the temperature of the refrigerant on the suction side of the compressor drops excessively, the amount of heat absorbed by the refrigerant in the evaporator can be rapidly increased.

[0024] The heating portion is preferably an electric heater.

[0025] In this case, the inside of the freezer can be heated quickly with a simple configuration that does not require complicated piping or the like. Effect of the Invention

[0026] The cooling device according to the present invention can suppress an excessive drop in the temperature of the refrigerant on the intake side of the compressor by applying a pseudo heat load by the heating unit. Therefore, when the cooling device according to the present invention is adopted, the temperature inside the freezer can be maintained at a substantially constant low temperature while suppressing the carbon dioxide in the refrigeration cycle from turning into dry ice. [Brief description of the drawings]

[0027] [Figure 1] 1 is an overall configuration diagram of a cooling device according to a first embodiment. [Diagram 2] 5 is a flowchart showing an example of control of the cooling device of the first embodiment. [Diagram 3] FIG. 11 is a diagram showing an operating state of an electric heater of a cooling device according to a second embodiment. [Figure 4] 10 is a flowchart showing an example of control of a cooling device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

[0029] First Embodiment FIG. 1 is a diagram showing the overall configuration of a cooling device 1 according to the present embodiment. The cooling device 1 is used, for example, in a manufacturing factory for frozen foods, refrigerated foods, etc. Reference numeral 2 in Fig. 1 denotes a freezer. Products 5 are transported to the freezer 2 from an upstream manufacturing line by a transport device 6 such as a belt conveyor. The freezer 2 constitutes a part of the cooling device 1.

[0030] The cooling device 1 includes a refrigeration cycle 10 that uses carbon dioxide (CO2) as a refrigerant, and a freezer 2 whose inside is cooled by the refrigeration cycle 10. The refrigeration cycle 10 includes a compressor 11, a gas cooler 12, a first expansion valve 13, and an evaporator 14, which are connected by a refrigerant pipe. The compressor 11 and the gas cooler 12, together with a second expansion valve 15 and a receiver 16, constitute a condensing unit 20, which is installed outside the freezer 2.

[0031] The compressor 11 is driven by a motor 17. The motor 17 is controlled by a control device 30. The compressor 11 draws in refrigerant from the evaporator 14 side of the piping, compresses the drawn refrigerant, and discharges it to the gas cooler 12 side.

[0032] The gas cooler 12 is connected by a pipe to the downstream side of the compressor 11. The gas cooler 12 exchanges heat between the refrigerant fed from the compressor 11 and the outside air, and exhausts the heat of the refrigerant. The gas cooler 12 is provided with a blower fan 32 for blowing outside air to the heat exchange section.

[0033] The receiver 16 is connected to the downstream side of the gas cooler 12 by piping, and a second expansion valve 15 is provided in the piping between the gas cooler 12 and the receiver 16. The opening degree of the second expansion valve 15 is adjusted by control of the control device 30. The second expansion valve 15 reduces the pressure of the high-pressure refrigerant whose heat has been removed by the gas cooler 12. The reduced-pressure liquefied refrigerant is stored in the receiver 16.

[0034] The first expansion valve 13 is provided in the piping downstream of the receiver 16. The first expansion valve 13 is configured by an electronic expansion valve or the like that is capable of adjusting the opening degree. The opening degree of the first expansion valve 13 is adjusted by the control of the control device 30. The first expansion valve 13 further reduces the pressure of the refrigerant supplied from the receiver 16 to a pressure that corresponds to the opening degree.

[0035] The evaporator 14 is connected by piping to the downstream side of the first expansion valve 13. The evaporator 14 is installed inside the freezer 2. The evaporator 14 vaporizes (evaporates) the refrigerant that has passed through the first expansion valve 13. The refrigerant flowing inside the evaporator 14 exchanges heat with the air inside the freezer 2, and absorbs heat inside the freezer 2. This cools the inside of the freezer 2. The evaporator 14 is provided with a blower fan 31 for blowing air inside the freezer 2 to the heat exchange section.

[0036] In this embodiment, two evaporators 14 are provided in the freezer 2. The refrigeration cycle 10 includes a feed pipe 18d connected to the receiver 16 in the condensing unit 20, and a return pipe 18s connected to the compressor 11 in the condensing unit 20. The feed pipe 18d branches into two branch pipes 19d, each of which is connected to a corresponding evaporator 14. A first expansion valve 13 is provided in each branch pipe 19d. A branch pipe 19s is connected to the downstream side of each evaporator 14. Each branch pipe 19s is connected to a return pipe 18s. In the cooling device 1 of this embodiment, two pairs of the first expansion valve 13 and the evaporator 14 are connected in parallel to the feed pipe 18d and the return pipe 18s connected to the condensing unit 20. The number of pairs of the first expansion valve 13 and the evaporator 14 connected in parallel to the feed pipe 18d and the return pipe 18s may be three or more. Also, only one pair of the first expansion valve 13 and the evaporator 14 may be connected to the feed pipe 18d and the return pipe 18s.

[0037] The freezer 2 is also provided with a temperature sensor 21 (temperature detection unit) for detecting the temperature inside the freezer 2. In this embodiment, the temperature sensor 21 is disposed downstream of the air blowing direction of each of the two evaporators 14 inside the freezer 2 (the side where the air that has passed through the evaporators 14 flows out). A signal line of the temperature sensor 21 is connected to an input unit of the control device 30. The detected temperature detected by the temperature sensor 21 is used by the control device 30 to control each unit, which will be described in detail later.

[0038] Furthermore, the freezer 2 is provided with an electric heater 22 which is a heating section. In this embodiment, the electric heater 22 is disposed upstream of the air blowing direction of each of the two evaporators 14 in the freezer 2 (near the air inlet of each evaporator 14). The electric heater 22 is controlled by the control device 30. The electric heater 22 performs heating under the control of the control device 30 based on the temperature detected by the temperature sensor 21. Heating in the freezer 2 by the electric heater 22 (heating of the air inlet of the evaporator 14) is performed to prevent the temperature of carbon dioxide (refrigerant) in the refrigeration cycle 10 from becoming equal to or lower than the triple point due to a decrease in the thermal load in the freezer 2.

[0039] If the temperature inside the freezer 2 when the refrigerant carbon dioxide reaches the triple point temperature in the refrigeration cycle 10 is defined as the "dry ice temperature," the electric heater 22 performs heating before the temperature inside the freezer 2 reaches the dry ice temperature. In this embodiment, when the set temperature in the freezer (the target cooling temperature in the freezer 2) is -35°C, for example, a temperature 1°C lower than the set temperature in the freezer is set as the first threshold temperature (prescribed threshold temperature). The first threshold temperature is a temperature higher than the dry ice temperature. The electric heater 22 performs heating when the temperature in the freezer 2 (the temperature detected by the temperature sensor 21) becomes equal to or lower than the first threshold temperature. That is, the control device 30 constantly monitors the temperature in the freezer 2 through the temperature sensor 21, and performs heating by the electric heater 22 (activates the electric heater 22) when the temperature detected by the temperature sensor 21 becomes equal to or lower than the first threshold temperature. As a result, the refrigerant (carbon dioxide) flowing in the evaporator 14 absorbs the heat of the air heated by the electric heater 22, and is prevented from becoming equal to or lower than the triple point.

[0040] Furthermore, when the temperature detected by the temperature sensor 21 becomes equal to or lower than the first threshold temperature (after the electric heater 22 is activated) and then becomes equal to or higher than a second threshold temperature that is a predetermined temperature higher than the first threshold temperature (for example, 0.5°C higher), the control device 30 stops heating by the electric heater 22. This prevents the electric heater 22 from heating the inside of the freezer 2 more than necessary.

[0041] Next, an example of control by the control device 30 of the cooling device 1 will be described with reference to the flowchart shown in FIG.

[0042] As shown in FIG. 2, when control by the controller 30 is started, the controller 30 reads various instruction values ​​such as the actual temperature in the freezer 2 and the target cooling temperature (step S1). Thereafter, the control device 30 controls the output of the compressor 11 and the opening degree of the first expansion valve 13 so that the temperature inside the freezer 2 becomes the target cooling temperature (step S2). As a result, the inside of the freezer 2 is cooled so as to approach the target cooling temperature.

[0043] In step S3, the control device 30 determines whether the temperature T detected by the temperature sensor 21 is equal to or lower than the first threshold temperature Ta, and if the detected temperature T is equal to or lower than the first threshold temperature Ta, the control device 30 proceeds to step S4. If the detected temperature T is not equal to or lower than the first threshold temperature Ta, the control device 30 proceeds to step S5. When the process proceeds to step S4, the electric heater 22 is operated to apply a pseudo heat load to the refrigerant (carbon dioxide) in the evaporator 14. As a result, the temperature of the refrigerant (carbon dioxide) flowing in the refrigeration cycle 10 is prevented from becoming equal to or lower than the triple point.

[0044] When the process proceeds to step S5, it is determined whether the temperature T detected by the temperature sensor 21 is equal to or higher than the second threshold temperature Tb, and when the detected temperature T is equal to or higher than the second threshold temperature Tb, the process proceeds to step S6. When the detected temperature T is not equal to or higher than the second threshold temperature Tb, the process returns to the process at the start of control. When the process proceeds to step S6, the operation of the electric heater 22 is stopped, and heating of the refrigerant (carbon dioxide) in the evaporator 14 is terminated. As a result, the electric heater 22 is prevented from heating the inside of the freezer 2 more than necessary. However, if the electric heater 22 is not heating at this time, the process returns to the process at the start of control.

[0045] As described above, in the cooling device 1 of this embodiment, the electric heater 22 (heating unit) is disposed in the freezer 2, and the electric heater 22 performs heating based on the temperature detected by the temperature sensor 21 (temperature detection unit) in the freezer 2. Therefore, even in a situation where the thermal load in the freezer 2 is extremely small, such as during standby operation, the application of a pseudo thermal load by the electric heater 22 can prevent the refrigerant (carbon dioxide) on the suction side of the compressor 11 from turning into dry ice. Therefore, when the cooling device 1 of this embodiment is employed, the temperature in the freezer 2 can be maintained at a substantially constant low temperature while preventing the carbon dioxide in the refrigeration cycle 10 from turning into dry ice.

[0046] Furthermore, in the cooling device 1 of this embodiment, heating is performed by the electric heater 22 (heating section) when the temperature detected by the temperature sensor 21 (temperature detection section) becomes equal to or lower than a specified threshold temperature (first threshold temperature) that is lower than the set temperature inside the freezer. As a result, heating by the electric heater 22 acts as a pseudo heat load before the temperature of carbon dioxide reaches the triple point in the refrigeration cycle 10, and the amount of heat absorbed by the refrigerant in the evaporator 14 increases. As a result, an excessive temperature drop of the refrigerant on the suction side of the compressor 11 is suppressed, and the carbon dioxide refrigerant does not turn into dry ice.

[0047] In addition, the cooling device 1 of this embodiment employs a direct expansion refrigeration cycle 10 in which the evaporator 14 is disposed directly inside the freezer 2, and the cold energy of the refrigerant that has passed through the first expansion valve 13 directly exchanges heat with the air in the freezer 2. The direct expansion refrigeration system does not have a function capable of absorbing sudden changes in heat load, such as a buffer tank, as in the case of the secondary refrigerant refrigeration system. For this reason, in a situation in which the heat load in the freezer 2 drops suddenly, such as during standby operation, the refrigerant carbon dioxide is likely to turn into dry ice. While employing such a direct expansion refrigeration system, the cooling device 1 of this embodiment can suppress an excessive temperature drop of the refrigerant on the suction side of the compressor 11 by heating with the electric heater 22 (heating section).

[0048] Furthermore, in the cooling device 1 of this embodiment, the electric heater 22, which is a heating unit, is disposed on the upstream side (near the suction unit) of the evaporator 14 in the air blowing direction, so that when the temperature of the refrigerant on the suction side of the compressor 11 drops excessively, the amount of heat absorbed by the refrigerant in the evaporator 14 can be rapidly increased. Therefore, when this configuration is adopted, it is possible to rapidly prevent carbon dioxide, which is the refrigerant, from turning into dry ice in the condensing unit 20. In addition, by adopting this configuration, it is possible to maintain the refrigerant in a gas state before being sucked into the compressor 11 even during standby operation, and liquid compression caused by the liquid refrigerant being sucked into the compressor 11 can be suitably suppressed.

[0049] <Second embodiment> The cooling device of this embodiment has a basic configuration substantially similar to that of the first embodiment described above, and therefore, for the explanation of the configuration of the cooling device of this embodiment, refer to FIG. The cooling device of this embodiment differs from that of the first embodiment in the following points. (1) In the first embodiment, only one electric heater 22 is disposed upstream of each evaporator 14 in the air blowing direction, whereas in the present embodiment, three electric heaters 22 are provided for each evaporator 14. (2) The threshold temperature (hereinafter referred to as the “heating start threshold temperature”) at which each electric heater 22 (Heater 1, Heater 2, Heater 3) starts heating is set to a different value (Ta1, Ta2, Ta3) for each electric heater 22 (Heater 1, Heater 2, Heater 3). (3) The threshold temperature (hereinafter referred to as the “heating release threshold temperature”) for releasing the heating of each electric heater 22 (Heater 1, Heater 2, Heater 3) is set to a different value (Tb1, Tb2, Tb3) for each electric heater 22 (Heater 1, Heater 2, Heater 3). (4) The control device 30 compares the detected temperature of the temperature sensor 21 with the heating start threshold temperatures Ta1, Ta2, Ta3 and the heating release threshold temperatures Tb1, Tb2, Tb3, and controls the on / off of each electric heater 22 (Heater 1, Heater 2, Heater 3) based on the results.

[0050] 3 is a diagram showing the operating state of the electric heaters 22 (Heater 1, Heater 2, Heater 3) of the cooling device of this embodiment. The vertical axis in FIG. 3 represents the temperature inside the freezer 2, and the horizontal axis represents the elapsed time. The heating start threshold temperatures Ta1, Ta2, and Ta3 are specified threshold temperatures that are lower than the freezer internal temperature (e.g., -35°C) and higher than the triple point temperature of carbon dioxide, and the values ​​are set so that the temperature decreases stepwise in the order of Ta1, Ta2, and Ta3. The heating start threshold temperatures are set, for example, as Ta1=-36°C, Ta2=-37°C, and Ta3=-38°C. The heating release threshold temperatures Tb1, Tb2, and Tb3 are threshold temperatures that are higher than the heating start threshold temperatures Ta1, Ta2, and Ta3 by a set temperature (e.g., 0.5°C). The heating release threshold temperatures Tb1, Tb2, and Tb3 are set, for example, as Tb1=-35.5°C, Ta2=-36.5°C, and Ta3=-37.5°C.

[0051] 3, when the temperature detected by the temperature sensor 21 becomes equal to or lower than the first heating start threshold temperature Ta1, the control device 30 executes heating of the heater 1 (electric heater 22). When the temperature detected by the temperature sensor 21 becomes equal to or lower than the second heating start threshold temperature Ta2, the control device 30 executes heating of the heater 2 (electric heater 22), and when the temperature detected by the temperature sensor 21 becomes equal to or lower than the third heating start threshold temperature Ta3, the control device 30 executes heating of the heater 3 (electric heater 22). Therefore, as the temperature detected by the temperature sensor 21 decreases, the number of heaters (electric heaters 22) that execute heating increases in accordance with the progression of the decrease.

[0052] 3, when the temperature detected by the temperature sensor 21 becomes equal to or lower than the first-stage heating start threshold temperature Ta1 and then becomes equal to or higher than the first-stage heating release threshold temperature Tb1, the control device 30 stops the heating of the heater 1 (electric heater 22). When the temperature detected by the temperature sensor 21 becomes equal to or lower than the second-stage heating start threshold temperature Ta2 and then becomes equal to or higher than the second-stage heating release threshold temperature Tb2, the control device 30 stops the heating of the heater 2 (electric heater 22). Similarly, when the temperature detected by the temperature sensor 21 becomes equal to or lower than the third-stage heating start threshold temperature Ta3 and then becomes equal to or higher than the third-stage heating release threshold temperature Tb3, the control device 30 stops the heating of the heater 3 (electric heater 22).

[0053] Next, an example of control by the control device 30 of the second embodiment will be described with reference to the flowchart shown in FIG.

[0054] As shown in FIG. 4, when control by the controller 30 is started, the controller 30 reads various instruction values ​​such as the actual temperature in the freezer 2 and the target cooling temperature (step S101). Thereafter, the controller 30 controls the output of the compressor 11 and the opening degree of the first expansion valve 13 so that the temperature inside the freezer 2 becomes the target cooling temperature (step S102).

[0055] In step S103, the control device 30 determines whether the temperature T detected by the temperature sensor 21 is equal to or lower than the heating start threshold temperature Ta1, and if the detected temperature T is equal to or lower than the heating start threshold temperature Ta1, the process proceeds to step S104. If the detected temperature T is not equal to or lower than the heating start threshold temperature Ta1, the process proceeds to step S105. When the process proceeds to step S104, the heater 1 (electric heater 22) is operated to apply a pseudo heat load to the refrigerant (carbon dioxide) in the evaporator .

[0056] When the process proceeds to step S105, it is determined whether or not the temperature T detected by the temperature sensor 21 is equal to or higher than the heating release threshold temperature Tb1, and when the detected temperature T is equal to or higher than the heating release threshold temperature Tb1, the process proceeds to step S106. When the detected temperature T is not equal to or higher than the heating release threshold temperature Tb1, the process returns to the process at the start of control. When the process proceeds to step S106, the operation of the heater 1 (electric heater 22) is stopped. This ends the heating of the refrigerant (carbon dioxide) in the evaporator 14 by the heater 1. However, if the heating of the heater 1 (electric heater 22) is not being performed at this time, the process returns directly to the process at the start of control.

[0057] After proceeding to step S104 to operate the heater 1 (electric heater 22), the process proceeds to step S107. In step S107, the control device 30 determines whether the temperature T detected by the temperature sensor 21 is equal to or lower than the heating-start threshold temperature Ta2, and if the detected temperature T is equal to or lower than the heating-start threshold temperature Ta2, the process proceeds to step S108. If the detected temperature T is not equal to or lower than the heating-start threshold temperature Ta2, the process proceeds to step S109. When the process proceeds to step S108, the heater 2 (electric heater 22) is operated. At this time, the heater 1 and the heater 2 both perform heating, and a large pseudo heat load is applied to the refrigerant (carbon dioxide) in the evaporator 14.

[0058] When the process proceeds to step S109, it is determined whether or not the temperature T detected by the temperature sensor 21 is equal to or higher than the heating release threshold temperature Tb2, and when the detected temperature T is equal to or higher than the heating release threshold temperature Tb2, the process proceeds to step S110. When the detected temperature T is not equal to or higher than the heating release threshold temperature Tb2, the process returns to the process at the start of control. When the process proceeds to step S110, the operation of the heater 2 (electric heater 22) is stopped. This ends the heating of the refrigerant (carbon dioxide) in the evaporator 14 by the heater 2. However, if the heating of the heater 2 (electric heater 22) is not being performed at this time, the process returns directly to the process at the start of control.

[0059] After proceeding to step S108 to operate the heater 2 (electric heater 22), the process proceeds to step S111. In step S111, the control device 30 determines whether the temperature T detected by the temperature sensor 21 is equal to or lower than the heating start threshold temperature Ta3, and proceeds to step S112 if the detected temperature T is equal to or lower than the heating start threshold temperature Ta3. If the detected temperature T is not equal to or lower than the heating start threshold temperature Ta3, the process proceeds to step S113. When the process proceeds to step S112, the heater 3 (electric heater 22) is operated. At this time, the heaters 1, 2, and 3 all perform heating, and a larger pseudo heat load is applied to the refrigerant (carbon dioxide) in the evaporator 14.

[0060] When the process proceeds to step S113, it is determined whether or not the temperature T detected by the temperature sensor 21 is equal to or higher than the heating release threshold temperature Tb3, and when the detected temperature T is equal to or higher than the heating release threshold temperature Tb3, the process proceeds to step S114. When the detected temperature T is not equal to or higher than the heating release threshold temperature Tb3, the process returns to the process at the start of control. When the process proceeds to step S114, the operation of the heater 3 (electric heater 22) is stopped. This ends the heating of the refrigerant (carbon dioxide) in the evaporator 14 by the heater 3. At this time, if the heating of the heater 3 (electric heater 22) is not being performed, the process returns directly to the process at the start of control. By carrying out the above-mentioned processing, the control device 30 prevents the temperature of the refrigerant (carbon dioxide) flowing in the refrigeration cycle 10 from becoming equal to or lower than the triple point.

[0061] As described above, the cooling device of this embodiment has the same basic configuration as the first embodiment, and therefore can obtain the same basic effects as the above-described first embodiment.

[0062] In addition, the cooling device of this embodiment is provided with a plurality of electric heaters 22 (heater 1, heater 2, heater 3) as heating units, and a plurality of heating start threshold temperatures Ta1, Ta2, and Ta3 are set so as to decrease stepwise. The electric heaters 22 (heater 1, heater 2, heater 3) and the heating start threshold temperatures Ta1, Ta2, and Ta3 are associated one-to-one with the electric heaters 22 (heater 1, heater 2, heater 3) that perform heating so that the total amount of heat of the electric heater 22 increases as the threshold value for each heating start threshold temperature Ta1, Ta2, and Ta3 decreases. Therefore, the total amount of heat of the electric heater 22 that performs heating increases in response to a decrease in temperature (decrease in detected temperature) in the freezer 2, and the amount of heat absorbed by the refrigerant in the evaporator 14 increases rapidly.

[0063] Furthermore, in the cooling device of this embodiment, the number of electric heaters 22 (heater 1, heater 2, heater 3) that perform heating in response to a decrease in temperature (decrease in detected temperature) inside the freezer 2 is increased stepwise, so that excessive temperature decrease of the refrigerant on the suction side of the compressor 11 can be quickly suppressed while suppressing energy consumption in the electric heaters 22.

[0064] In this embodiment, three electric heaters 22 (Heater 1, Heater 2, Heater 3) are provided as heating parts, and the heating start threshold temperatures Ta1, Ta2, and Ta3 are set in three stages corresponding to the electric heaters 22. However, the number of heating parts and the number of setting stages of the heating start threshold temperature are not limited to this. The number of heating parts and the number of setting stages of the heating start threshold temperature may be two or less, or four or more. In addition, in this embodiment, the heating unit (electric heater 22) that performs heating is associated one-to-one with each heating start threshold temperature, but the heating unit (electric heater 22) that performs heating may also be associated one-to-many with the heating start threshold temperatures.

[0065] <Other embodiments> In each of the above embodiments, an electric heater 22 is used as the heating section disposed inside the freezer 2, but the heating section is not limited to the electric heater 22. For example, a section that uses a heat pump cycle separate from the refrigeration cycle 10 for heating, or a section that circulates a high-temperature fluid through piping, etc., can also be used. However, when the electric heater 22 is used as the heating section as in this embodiment, it becomes possible to heat the inside of the freezer 2 quickly with a simple configuration that does not require complicated piping, etc.

[0066] In each of the above embodiments, the control device 30 operates the electric heater 22 when the temperature detected by the temperature sensor 21 becomes equal to or lower than a specified threshold temperature. However, the control by the control device 30 is not limited to this. The control device 30 can also perform control as follows, for example.

[0067] In other words, when the detected temperature of the temperature sensor 21 (temperature detection unit) becomes lower than a threshold temperature (first threshold temperature), the control device 30 may control the heating temperature of the electric heater 22 (heating unit) so that the amount of heat is proportional to the temperature difference between the detected temperature and the threshold temperature (first threshold temperature). In this case, the electric heater 22 (heating unit) in the freezer 2 performs heating with an amount of heat according to the temperature difference between the temperature detected by the temperature sensor 21 and the threshold temperature (first threshold temperature). Therefore, when this configuration is adopted, excessive heating by the electric heater 22 can be restricted, while an excessive decrease in temperature of the refrigerant on the suction side of the compressor 11 can be quickly suppressed.

[0068] The present invention is not limited to the above-described embodiments, and various design modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiments, the cooling of food such as frozen food or refrigerated food is described as an example, but the use of the cooling device according to the present invention is not limited to cooling food. The cooling device according to the present invention can also be used to cool items other than food. [Explanation of symbols]

[0069] 1...Cooling device 2. Freezer 10...Refrigeration cycle 11...Compressor 21...Temperature sensor (temperature detection part) 22...Electric heater (heating part)

Claims

1. A refrigeration cycle using carbon dioxide as a refrigerant; a freezer whose inside is cooled by the refrigeration cycle; A heating section disposed within the freezer; A temperature detection unit that detects a temperature inside the freezer, The heating unit performs heating based on a temperature detected by the temperature detection unit.

2. 2. The cooling device according to claim 1, wherein the heating section performs heating when the temperature detected by the temperature detection section becomes equal to or lower than a specified threshold temperature that is lower than a set temperature inside the freezer.

3. A plurality of the heating units are provided, The threshold temperature is set in a plurality of steps so that the temperature is decreased stepwise, 3. The cooling device according to claim 2, wherein the heating units and the threshold temperatures are associated with each other such that the lower the threshold temperature, the greater the total amount of heat.

4. 3. The cooling device according to claim 2, wherein when a temperature detected by the temperature detection unit falls below the threshold temperature, the heating unit performs heating with an amount of heat corresponding to a temperature difference between the detected temperature and the threshold temperature.

5. The cooling device according to any one of claims 1 to 4, characterized in that the refrigeration cycle is a direct expansion type refrigeration cycle in which an evaporator of the refrigeration cycle is disposed inside the freezer, and cold energy of a refrigerant that has passed through an expansion valve of the refrigeration cycle is directly exchanged with air in the freezer by the evaporator.

6. The cooling device according to claim 5 , wherein the heating section is disposed on an inlet side of the evaporator into which air enters the freezer.

7. 5. The cooling device according to claim 1, wherein the heating section is an electric heater.

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