Refrigeration device, environment formation device and refrigeration method

Abstract

To enable a more flexible operation while suppressing frost formation on an evaporator.SOLUTION: A refrigeration device 10 includes: a refrigeration circuit 15 in which a compressor 1, a condenser 2, an expansion valve 3, an evaporator 4 and a flow regulating valve 22 are disposed in this order and a refrigerant circulates; a valve control section 103 that controls the expansion valve 3 and the flow regulating valve 22; and a target value change section 102 for changing a target value of an evaporation temperature or evaporation pressure in the evaporator 4. The valve control section 103 controls one of the expansion valve 3 and the flow regulating valve 22 on the basis of the target value changed by the target value change section 102, and controls the other of the expansion valve 3 and the flow regulating valve 22 in accordance with a refrigeration request level or a temperature of a cooling object.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a refrigeration device, an environment forming device, and a refrigeration method.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1 below, there is known a refrigeration device in which a pressure regulating valve is provided on the downstream side of an evaporator in a refrigeration circuit. The pressure regulating valve is a spring-type pressure regulating valve and can keep the refrigerant pressure in the evaporator at a certain value or more. Thereby, it is possible to suppress the occurrence of icing (frost) in the fin portion of the evaporator.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The pressure regulating valve disclosed in Patent Document 1 is of a spring type and is provided to keep the refrigerant pressure in the evaporator at a certain value or more. By providing such a spring-type pressure regulating valve on the downstream side of the evaporator, frosting in the evaporator can be suppressed. On the other hand, since the refrigerant pressure in the evaporator is fixed at a certain value or more by the pressure regulating valve, there is a problem that the refrigeration device of Patent Document 1 cannot operate flexibly. For example, when the temperature of the indoor air flowing through the evaporator is high, the problem of frosting is less likely to occur, so there is no need to keep the refrigerant pressure in the evaporator at a certain value or more.

[0005] Therefore, the present invention has been made in view of the above prior art, and an object thereof is to enable more flexible operation while suppressing frosting in the evaporator.

Means for Solving the Problems

[0006] To achieve the above object, a refrigeration apparatus according to the present invention includes a refrigeration circuit in which a compressor, a condenser, an expansion valve, an evaporator, and a flow rate adjustment valve are arranged in this order to circulate a refrigerant, a valve control unit that controls the expansion valve and the flow rate adjustment valve, and a target value change unit for changing a target value of an evaporation temperature or an evaporation pressure in the evaporator. The valve control unit controls one of the expansion valve and the flow rate adjustment valve based on the target value changed by the target value change unit, and controls the other of the expansion valve and the flow rate adjustment valve according to a refrigeration demand level or a temperature of a cooling target.

[0007] In the refrigeration apparatus according to the present invention, the valve control unit controls one of the expansion valve and the flow rate adjustment valve based on a target value of an evaporation temperature or an evaporation pressure in the evaporator. At this time, as the opening degree of the flow rate adjustment valve is throttled to be smaller, the evaporation temperature or the evaporation pressure in the evaporator tends to be higher. Therefore, compared with a refrigeration circuit not provided with the flow rate adjustment valve, the evaporation temperature (or evaporation pressure) can be increased. Thereby, for example, even when control is performed so that the temperature of the cooling target becomes lower, it is possible to make the state where frost does not adhere to the evaporator or the state where frost hardly adheres. In other words, it becomes possible to control so that the temperature of the cooling target becomes lower in a state where frost hardly adheres. In the refrigeration circuit, the degree of pressure reduction corresponding to the differential pressure between the high pressure and the low pressure of the refrigeration circuit obtained by the compressor is obtained by the expansion valve and the flow rate adjustment valve.

[0008] In addition, since the target value of the evaporation temperature or evaporation pressure can be changed by the target value changing unit, a more flexible operation becomes possible compared to the case where the target value of the evaporation temperature or evaporation pressure is fixed. For example, in the case of a configuration in which an expansion valve is controlled based on the evaporation temperature or evaporation pressure, when the target value of the evaporation temperature or evaporation pressure is changed to a higher value, for example, the opening degree of the expansion valve is controlled to become larger. On the other hand, since the flow rate adjustment valve is controlled according to the degree of refrigeration demand or the temperature of the cooling target, the evaporation temperature or evaporation pressure will change according to the change amount of the opening degree of the flow rate adjustment valve. For this reason, since the opening degree of the expansion valve is further adjusted according to this changed evaporation temperature or evaporation pressure, the change in the evaporation temperature or evaporation pressure is suppressed. Therefore, with the expansion valve and the flow rate adjustment valve, while adjusting the evaporation temperature or evaporation pressure to the target value, it is possible to exhibit a desired refrigeration capacity according to the degree of refrigeration demand or the temperature of the cooling target.

[0009] On the other hand, for example, in the case of a configuration in which a flow rate adjustment valve is controlled based on the evaporation temperature or evaporation pressure, when the target value of the evaporation temperature or evaporation pressure is changed to a higher value, for example, the opening degree of the flow rate adjustment valve is controlled to become smaller. At this time, since the expansion valve is controlled according to the degree of refrigeration demand or the temperature of the cooling target, the evaporation temperature or evaporation pressure will change according to the change amount of the opening degree of the expansion valve. For this reason, since the opening degree of the flow rate adjustment valve is further adjusted according to this changed evaporation temperature or evaporation pressure, the change in the evaporation temperature or evaporation pressure is suppressed. Therefore, with the expansion valve and the flow rate adjustment valve, while adjusting the evaporation temperature or evaporation pressure to the target value, it is possible to exhibit a desired refrigeration capacity according to the degree of refrigeration demand or the temperature of the cooling target. Also, since the sensible heat ratio can be changed by the evaporation temperature (the temperature of the evaporator), for example, when adjusting the humidity of the air to be cooled, it is possible to exhibit a desired dehumidifying capacity.

[0010] The target value changing unit may be configured to set the target value to a first target value when the temperature of the cooling target is a first temperature, and set the target value to a second target value lower than the first target value when the temperature of the cooling target is a second temperature lower than the first temperature.

[0011] In this mode, when the temperature of the object to be cooled is a second temperature lower than the first temperature, the target value of the evaporation temperature or the evaporation pressure is set to a second target value lower than the first target value. As a result, when the temperature of the object to be cooled is the second temperature (lower temperature), in one of the expansion valve and the flow rate adjustment valve, if it is the expansion valve, the opening degree is controlled to be smaller, and if it is the flow rate adjustment valve, the opening degree is controlled to be larger. And for the other of the expansion valve and the flow rate adjustment valve, it is controlled according to the refrigeration demand degree or the temperature of the object to be cooled. Therefore, the evaporation temperature or the evaporation pressure in the evaporator is adjusted according to the temperature of the object to be cooled, and the refrigeration capacity corresponding to the refrigeration demand degree or the temperature of the object to be cooled is exerted. For example, when the temperature of the object to be cooled is higher, since the target value of the evaporation temperature or the evaporation pressure is set to a higher value, it is possible to operate with a lower refrigeration capacity compared to the control with a constant target value of the evaporation temperature or the evaporation pressure. On the other hand, when the temperature of the object to be cooled is lower, since the target value of the evaporation temperature or the evaporation pressure is set to a lower value, the refrigeration capacity can be appropriately exerted.

[0012] The valve control unit may have a control mode in which, with the flow rate adjustment valve in a fully open state, the expansion valve is controlled so that the evaporation temperature or the evaporation pressure becomes the target value changed by the target value changing unit.

[0013] In this mode, since the valve control unit has a control mode in which the expansion valve is controlled with the flow rate adjustment valve in a fully open state, control other than the control of the flow rate adjustment valve according to the refrigeration demand degree or the temperature of the object to be cooled becomes possible. Therefore, more flexible operation as a refrigeration device becomes possible.

[0014] The refrigeration device may include a pressure detector that detects the suction pressure of the compressor. In this case, the valve control unit may control the other of the expansion valve and the flow rate adjustment valve so that the detection value of the pressure detector becomes the suction pressure target value set according to the refrigeration demand degree.

[0015] In this mode, one of the expansion valve and the flow control valve is controlled so that the evaporation temperature or evaporation pressure in the evaporator reaches the target value. On the other hand, the other of the expansion valve and the flow control valve is controlled so that the detected value of the pressure detector reaches the suction pressure target value set according to the refrigeration demand degree. Therefore, not only the evaporation temperature is adjusted to the target value, but also the suction pressure is adjusted to the target value. That is, by adjusting the suction pressure, the refrigeration capacity is adjusted, so that the refrigeration capacity can be made variable with respect to the adjusted evaporation temperature. In addition, when adjusting the evaporation temperature to the target value, it is possible to prevent the suction pressure from excessively decreasing. Therefore, it contributes to the stable operation of the compressor.

[0016] The environment forming apparatus according to the present invention includes an environmental chamber and the refrigeration apparatus for cooling the inside of the environmental chamber.

[0017] The refrigeration method according to the present invention is a refrigeration method using a refrigeration apparatus including a refrigeration circuit in which a compressor, a condenser, an expansion valve, an evaporator, and a flow control valve are arranged in this order and a refrigerant is circulated. The method changes the target value of the evaporation temperature or evaporation pressure in the evaporator, controls one of the expansion valve and the flow control valve based on the changed target value, a reception unit receives information regarding the refrigeration demand degree or the temperature of the cooling target, and controls the other of the expansion valve and the flow control valve according to the refrigeration demand degree or the temperature of the cooling target received by the reception unit.

Effect of the Invention

[0018] As described above, according to the present invention, it is possible to perform more flexible operation while suppressing frosting in the evaporator.

Brief Description of the Drawings

[0019]

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Mode for Carrying Out the Invention

[0020] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[0021] (First Embodiment) As shown in FIG. 1, a refrigeration device 10 according to the first embodiment includes a refrigeration circuit 15 filled with a refrigerant. The refrigerant may be a low-boiling refrigerant such as R404A. Therefore, the evaporation temperature can be lowered to, for example, about -40°C.

[0022] In the refrigeration circuit 15, a compressor 1, a condenser 2, an expansion valve 3, an evaporator 4, and a flow rate adjustment valve 22 are provided in this order. When the compressor 1 operates, the refrigerant circulates within the refrigeration circuit 15, thereby performing a vapor compression refrigeration cycle. The refrigeration device 10 may be used to cool the indoor air of a refrigerator or a freezer, or may be used to generate chilled water with a chiller. Alternatively, the refrigeration device 10 may be used in an environmental forming device such as an environmental test device for providing an environment with a predetermined temperature and humidity. Alternatively, the refrigeration device 10 may be used in an air conditioner for adjusting the temperature and humidity environment of the interior of a house or the like. In this embodiment, it is assumed that the refrigeration device 10 is used in a refrigerator-freezer.

[0023] The compressor 1 is responsible for the compression process of the refrigeration cycle and is configured to suck and compress the refrigerant. The compressor 1 includes, for example, a compression mechanism such as a reciprocating type, a scroll type, or a screw type, and is configured to drive the compression mechanism by a motor with a constant rotational speed. Note that the compressor 1 may be configured such that the rotational speed of the motor can be adjusted by an inverter. Also, the compressor 1 may have a configuration in which two compressors 1 with different capacities are connected in parallel.

[0024] The condenser 2 is responsible for the condensation process of the refrigeration cycle and is configured to exchange heat between the refrigerant discharged from the compressor 1 and a cooling medium such as air, water, or refrigerant to condense the refrigerant.

[0025] The expansion valve 3 is responsible for the expansion process of the refrigeration cycle and is configured to expand the liquid refrigerant condensed in the condenser 2. The expansion valve 3 is constituted by, for example, an electronic expansion valve. Therefore, by adjusting the valve opening degree, the evaporation temperature, which is the temperature of the refrigerant flowing through the evaporator 4 in the refrigeration circuit 15, and the evaporation pressure, which is the pressure of the refrigerant in the evaporator 4, can be changed.

[0026] The evaporator 4 is responsible for the evaporation process in the refrigeration cycle. It is configured to exchange heat between the liquid refrigerant depressurized by the expansion valve 3 and air to evaporate the liquid refrigerant. The evaporator 4 cools the air supplied to the refrigerator. When the refrigeration device 10 is provided in a chiller that generates cooling water, the evaporator 4 is configured to evaporate the liquid refrigerant to cool the cooling water.

[0027] The flow rate adjustment valve 22 is provided to adjust the flow rate of the refrigerant flowing through the evaporator 4. The flow rate adjustment valve 22 is constituted by, for example, an electronic expansion valve. When the opening degree of the flow rate adjustment valve 22 is adjusted, the low pressure in the refrigeration cycle and the pressure of the refrigerant flowing in the evaporator 4 also change.

[0028] The refrigeration circuit 15 is provided with an evaporation temperature detector 21. The evaporation temperature detector 21 is a detector for detecting the temperature of the refrigerant in the evaporator 4, that is, the evaporation temperature of the refrigerant in the evaporation process of the refrigeration cycle or a temperature corresponding thereto. For this reason, the evaporation temperature detector 21 may be arranged at a position between the expansion valve 3 and the evaporator 4 in the refrigeration circuit 15, or may be provided to detect the temperature of the refrigerant in the evaporator 4. The evaporation temperature detector 21 outputs a signal indicating the detected temperature.

[0029] The signal output from the evaporation temperature detector 21 is input to the controller 100. The controller 100 is constituted by a microcomputer including a CPU that executes arithmetic processing, a ROM that stores a processing program, data, etc., and a RAM that temporarily stores data. By executing the processing program stored in the controller 100, as shown in FIG. 2, the controller 100 can function as a reception unit 101, a target value change unit 102, and a valve control unit 103.

[0030] The reception unit 101 is configured to repeatedly receive the refrigeration demand degree every predetermined time and temporarily store the received refrigeration demand degree. The refrigeration demand degree is generated by the generator 120, and the refrigeration demand degree generated by this generator 120 is input to the reception unit 101. In the illustrated example, an example in which the generator 120 is configured separately from the controller 100 is shown, but the generator 120 for generating the refrigeration demand degree may be a function of the controller 100.

[0031] The generator 120 repeatedly receives signals from, for example, a sensor 121 that detects the temperature of the object to be cooled (the temperature inside the refrigerator-freezer), an input device 122 that inputs a set value of the temperature of the object to be cooled (the temperature inside the refrigerator-freezer), etc. every predetermined time, and calculates the refrigeration demand degree each time. The refrigeration demand degree is represented by a dimensionless numerical value of the refrigeration load in the refrigerator-freezer that is the object to be cooled. For example, it is calculated by a difference value between the detected value (the detected temperature of the sensor 121) of the temperature of the object to be cooled (the temperature inside the refrigerator-freezer) and the set value. Therefore, the greater the difference between the detected value of the temperature of the object to be cooled (the temperature inside the refrigerator-freezer) and the set value, the greater the refrigeration demand degree. Since the refrigeration demand degree can change every moment, the generator 120 outputs the refrigeration demand degree every predetermined time.

[0032] The target value changing unit 102 is configured to change the target value of the evaporation temperature according to the refrigeration demand degree received by the reception unit 101 and the temperature of the object to be cooled (the temperature inside the refrigerated freezer), which is the detected temperature of the sensor 121. When the target value changing unit 102 sets the target value of the evaporation temperature to the first value when the received refrigeration demand degree is the first refrigeration demand degree, when the received refrigeration demand degree is the second refrigeration demand degree, which is lower than the first refrigeration demand degree, the target value of the evaporation temperature is changed to the second value, which is lower than the first value. Also, in the low-temperature region described later, when the target value changing unit 102 sets the target value of the evaporation temperature to the first value when the temperature of the object to be cooled (the temperature inside the refrigerated freezer) is the first temperature, when the temperature of the object to be cooled (the temperature inside the refrigerated freezer) is the second temperature, which is lower than the first temperature, the target value of the evaporation temperature is changed to the second value, which is lower than the first value. Further, in the high-temperature region described later, the target value changing unit 102 sets the target value of the evaporation temperature to the same value regardless of the temperature of the object to be cooled (the temperature inside the refrigerated freezer).

[0033] As shown in FIG. 3, the target value of the evaporation temperature includes a low-temperature region that changes according to the temperature of the object to be cooled (the temperature inside the refrigerated freezer) and a high-temperature region that is constant regardless of the temperature of the object to be cooled. The threshold temperature TS, which is the boundary between the low-temperature region and the high-temperature region, is set to a temperature of, for example, 0°C or higher and 60°C or lower, or 10°C or higher and 50°C or lower, or 20°C or higher and 40°C or lower. In the low-temperature region, the target value of the evaporation temperature is set to decrease as the temperature of the object to be cooled decreases. On the other hand, in the high-temperature region, the target value of the evaporation temperature is set to be the same value regardless of the temperature of the object to be cooled.

[0034] Note that the target value of the evaporation temperature does not necessarily have to be set in this way. For example, the target value of the evaporation temperature may be set such that it increases as the temperature of the object to be cooled increases over the entire temperature range that the temperature of the object to be cooled can take. Specifically, in the low-temperature region (the region where the temperature inside the storage is lower than the threshold temperature TS), as shown in FIG. 3, the target value of the evaporation temperature may change linearly as the temperature of the object to be cooled (the temperature inside the storage) changes. Alternatively, it may change curvilinearly, or may change stepwise (in a staircase shape). Also, as shown in FIG. 3, it is not necessary to set the manner of change of the target value of the evaporation temperature to be different between the low-temperature region and the high-temperature region. For example, over the entire region of the temperature of the object to be cooled (the temperature inside the storage), the target value of the evaporation temperature may change as the temperature of the object to be cooled (the temperature inside the storage) changes. In that case, it may change linearly, curvilinearly, or stepwise (in a staircase shape). At this time, when the target value changing unit 102 sets the target value of the evaporation temperature to be the first value when the temperature of the object to be cooled (the temperature inside the refrigerating and freezing cabinet) is the first temperature, when the temperature of the object to be cooled (the temperature inside the refrigerating and freezing cabinet) is the second temperature, which is lower than the first temperature, the target value of the evaporation temperature is changed to the second value, which is lower than the first value. Note that when the refrigeration device 10 is configured as a chiller, the temperature of the object to be cooled is the temperature of the cooling water introduced into the evaporator 4.

[0035] The target value of the evaporation temperature may have a width with respect to the temperature of the object to be cooled (the temperature inside the storage). For example, the target value of the evaporation temperature may not only be changed according to the temperature of the object to be cooled (the temperature inside the storage), but may also be changed according to the degree of refrigeration required. That is, when the temperature of the object to be cooled (the temperature inside the storage) is a certain temperature, the target value of the evaporation temperature may be further changed according to the degree of refrigeration required. In that case, the target value of the evaporation temperature is set to be higher as the degree of refrigeration required is greater, and lower as the degree of refrigeration required is smaller. The upper limit value and the lower limit value of the evaporation temperature in that case may include a low-temperature region that changes according to the temperature of the object to be cooled and a region that is at a temperature higher than the low-temperature region and is constant regardless of the temperature of the object to be cooled, but is not limited to this. The upper limit value and the lower limit value of the target value of the evaporation temperature may be set such that they increase as the temperature of the object to be cooled increases over the entire temperature range that the temperature of the object to be cooled can take.

[0036] The valve control unit 103 is configured to control the expansion valve 3 based on the target value of the evaporation temperature changed by the target value changing unit 102, and to control the flow rate adjustment valve 22 according to the degree of refrigeration demand.

[0037] The control of the expansion valve 3 is performed each time the target value of the evaporation temperature is adjusted. The target value of the evaporation temperature is set by the target value changing unit 102 to a value corresponding to the temperature of the object to be cooled (for example, the temperature inside the storage) which is the detected temperature of the sensor 121. Then, the valve control unit 103 controls the expansion valve 3 so that the detected temperature by the evaporation temperature detector 21 approaches the target value of the evaporation temperature set by the target value changing unit 102. The expansion valve 3 has a smaller opening degree when the target value of the evaporation temperature is low, and a larger opening degree when the target value of the evaporation temperature is high.

[0038] Also, each time the reception unit 101 receives the degree of refrigeration demand, the valve control unit 103 adjusts the opening degree of the flow rate adjustment valve 22 according to the received degree of refrigeration demand. That is, in the controller 100, information in which the opening degree of the flow rate adjustment valve 22 is assigned to the degree of refrigeration demand is stored, and the valve control unit 103 controls the flow rate adjustment valve 22 using this information.

[0039] Note that, in the controller 100, instead of storing information in which the opening degree of the flow rate adjustment valve 22 is assigned to the degree of refrigeration demand, information in which the suction pressure is assigned to the degree of refrigeration demand may be stored. In this case, the valve control unit 103 will control the flow rate adjustment valve 22 using this information. However, even in this case, there is no change in that the flow rate adjustment valve 22 is controlled based on the degree of refrigeration demand. For example, when the degree of refrigeration demand is large, the suction pressure is set to a high value. In that case, the flow rate adjustment valve 22 is controlled so that the opening degree of the flow rate adjustment valve 22 becomes large. Also, when the degree of refrigeration demand is small, the suction pressure is set to a low value. In that case, the flow rate adjustment valve 22 is controlled so that the opening degree of the flow rate adjustment valve 22 becomes small.

[0040] As shown in FIG. 4, the flow rate control valve 22 is controlled such that its opening degree increases when the refrigeration demand is high and decreases when the refrigeration demand is low. Note that the flow rate control valve 22 may maintain a constant opening degree within a range where the refrigeration demand is equal to or higher than a predetermined value, within a range where the refrigeration demand is equal to or lower than a predetermined value, or in both ranges.

[0041] When the temperature of the object to be cooled (for example, the temperature inside the storage) is lower than the threshold temperature TS, the lower the temperature of the object to be cooled, the lower the target value of the evaporation temperature is set. Therefore, the valve control unit 103 controls the expansion valve 3 so that the opening degree of the expansion valve 3 becomes smaller as the temperature of the object to be cooled decreases. At this time, the valve control unit 103 controls the flow rate control valve 22 to an opening degree based on the refrigeration demand. That is, the flow rate control valve 22 is controlled without being based on the evaporation temperature (evaporation pressure). Further, when the temperature of the object to be cooled is lower than the threshold temperature TS, the higher the temperature of the object to be cooled, the higher the target value of the evaporation temperature is set. Therefore, the valve control unit 103 controls the expansion valve 3 so that the opening degree of the expansion valve 3 becomes larger as the temperature of the object to be cooled increases. Even in this case, the valve control unit 103 controls the flow rate control valve 22 to an opening degree based on the refrigeration demand.

[0042] On the other hand, when the temperature of the object to be cooled (for example, the temperature inside the storage) is higher than the threshold temperature TS, the target value of the evaporation temperature is set to a constant value regardless of the temperature of the object to be cooled. Therefore, the valve control unit 103 controls the expansion valve 3 to reach the set target value of the evaporation temperature. Also in this case, the valve control unit 103 adjusts the opening degree of the flow rate control valve 22 based on the refrigeration demand. That is, the flow rate control valve 22 is controlled such that its opening degree becomes smaller as the refrigeration demand decreases and becomes larger as the refrigeration demand increases. Therefore, the refrigerating capacity can be varied while maintaining a high evaporation temperature.

[0043] Here, a refrigeration method using the refrigeration device 10 having the above configuration will be described.

[0044] When the target temperature of the temperature inside the storage is set and the operation of the refrigeration device 10 is started, as shown in FIG. 5, the controller 100 receives the refrigeration demand degree generated by the generator 120 and the detected temperature of the sensor 121 (the temperature of the object to be cooled) (steps ST11, ST12). The refrigeration demand degree and the detected temperature of the sensor 121 are repeatedly received by the controller 100 every predetermined time.

[0045] Subsequently, the target value changing unit 102 of the controller 100 changes the target value of the evaporation temperature according to the refrigeration demand degree received by the reception unit 101 and the detected temperature of the sensor 121 (step ST13).

[0046] At this time, when the detected temperature of the sensor 121 is in the low temperature region where it is equal to or lower than the preset threshold temperature TS, the target value changing unit 102 sets a lower target value as the target value of the evaporation temperature as the received detected temperature becomes lower, while setting a higher target value as the target value of the evaporation temperature as the received detected temperature of the sensor 121 becomes higher. That is, in the case of the low temperature region, even when the refrigeration demand degrees are the same, the lower the detected temperature, the lower the target value of the evaporation temperature is set.

[0047] In addition, when the detected temperature of the sensor 121 is in the high temperature region higher than the preset threshold temperature TS, the target value changing unit 102 sets the target value of the evaporation temperature to a constant value regardless of the detected temperature of the sensor 121.

[0048] Subsequently, the valve control unit 103 controls the expansion valve 3 based on the target value of the evaporation temperature changed by the target value changing unit 102, and controls the flow rate adjustment valve 22 according to the refrigeration demand degree (step ST14).

[0049] Specifically, the valve control unit 103 sets the opening degree of the flow rate adjustment valve 22 to a predetermined opening degree according to the refrigeration demand degree (for example, the maximum opening degree when the refrigeration demand degree is 100%), and in this state, controls the expansion valve 3 so that the detected temperature by the evaporation temperature detector 21 approaches the target value of the evaporation temperature set by the target value changing unit 102. At this time, the lower the target value of the evaporation temperature, the smaller the opening degree of the expansion valve 3, and the higher the target value of the evaporation temperature, the larger the opening degree of the expansion valve 3.

[0050] When the refrigeration demand degree received by the reception unit 101 changes from the previously received refrigeration demand degree, the valve control unit 103 adjusts the opening degree of the flow rate adjustment valve 22 according to the change amount of the refrigeration demand degree. Since the evaporation temperature changes accordingly, the valve control unit 103 further adjusts the opening degree of the expansion valve 3 so that the evaporation temperature approaches the target value.

[0051] For example, when the refrigeration demand degree becomes smaller than the previous value, the valve control unit 103 makes the opening degree of the flow rate adjustment valve 22 smaller. Along with this, since the evaporation temperature rises, the valve control unit 103 makes the opening degree of the expansion valve 3 smaller along with this change in the evaporation temperature. Thereby, the evaporation temperature approaches the target value. At this time, since the opening degrees of the expansion valve 3 and the flow rate adjustment valve 22 become smaller, the flow rate of the refrigerant flowing through the evaporator 4 is restricted and the refrigeration capacity decreases.

[0052] At this time, in the low temperature region below the threshold temperature TS, the lower the detected temperature, the lower the target value of the evaporation temperature is adjusted. Therefore, even when the temperature of the object to be cooled is low and the temperature of the air returning to the evaporator 4 is low, the refrigerant can be easily evaporated. Also, since both the expansion valve 3 and the flow rate adjustment valve 22 are restricted, the flow rate of the refrigerant flowing through the evaporator 4 decreases, contributing to the reduction of the power of the compressor 1.

[0053] On the one hand, if the refrigeration requirement remains high, the opening degree of the flow rate adjustment valve 22 is maintained in a large state. Also, since the target value of the evaporation temperature is also maintained at a high value, the opening degree of the expansion valve 3 is maintained in a large state. Therefore, the flow rate of the refrigerant flowing through the evaporator 4 is ensured in a state where the evaporation temperature is high, and the refrigeration capacity is maintained in a state where a large refrigeration capacity is exhibited. Therefore, it is possible to exhibit a refrigeration capacity corresponding to a high refrigeration requirement degree.

[0054] Also, when the refrigeration requirement degree becomes larger than the previous value, the valve control unit 103 increases the opening degree of the flow rate adjustment valve 22. Along with this, since the evaporation temperature decreases, the valve control unit 103 increases the opening degree of the expansion valve 3 along with this change in the evaporation temperature. As a result, the evaporation temperature approaches the target value. At this time, as the opening degrees of the expansion valve 3 and the flow rate adjustment valve 22 increase, the flow rate of the evaporator 4 increases and the refrigeration capacity rises.

[0055] As described above, in this embodiment, the valve control unit 103 controls the expansion valve 3 based on the target value of the evaporation temperature in the evaporator 4. At this time, as the opening degree of the flow rate adjustment valve 22 is throttled to become smaller, the evaporation temperature (or evaporation pressure) in the evaporator 4 tends to become higher. Therefore, compared to a refrigeration circuit not provided with the flow rate adjustment valve 22, the evaporation temperature (or evaporation pressure) can be increased. As a result, for example, even when the temperature of the object to be cooled is lower, it is possible to make the state where frost does not adhere to the evaporator 4 or the state where frost hardly adheres. In other words, it becomes possible to control so that the temperature of the object to be cooled becomes lower. In the refrigeration circuit 15, the degree of pressure reduction corresponding to the differential pressure between the high pressure and the low pressure of the refrigeration circuit 15 obtained by the compressor 1 is obtained by the expansion valve 3 and the flow rate adjustment valve 22.

[0056] In addition, since the target value of the evaporation temperature can be changed by the target value changing unit 102, more flexible operation is possible compared to the case where the target value of the evaporation temperature is fixed. For example, when the target value of the evaporation temperature is changed to a higher value, the opening degree of the expansion valve 3 is controlled to be larger. At this time, since the flow rate adjustment valve 22 is controlled according to the degree of refrigeration demand, the evaporation temperature changes according to the change amount of the opening degree of the flow rate adjustment valve 22. For this reason, since the opening degree of the expansion valve 3 is further adjusted according to this changed evaporation temperature, the change in the evaporation temperature is suppressed. Therefore, by the expansion valve 3 and the flow rate adjustment valve 22, while adjusting the evaporation temperature to the target value, it is possible to exhibit a desired refrigeration capacity according to the degree of refrigeration demand. As a result, it is possible to widen the variable range of the refrigeration capacity while suppressing frosting, which can also contribute to the continuous operation and energy saving of the device. Further, the refrigeration device 10 may be configured as an air conditioner capable of adjusting humidity. In that case, since it becomes possible to control at an evaporation temperature (refrigerant temperature in the evaporator 4) suitable for the dew point temperature, a wide range of temperature and humidity operations become possible. Furthermore, since the sensible heat ratio can be changed by the evaporation temperature, it is possible to exhibit a desired dehumidifying capacity and contribute to energy saving.

[0057] Note that the valve control unit 103 is configured to control the flow rate adjustment valve 22 according to the degree of refrigeration demand. Alternatively, the flow rate adjustment valve 22 may be configured to be controlled according to the temperature of the object to be cooled. For example, when the temperature of the object to be cooled (temperature inside the storage) is lower than the freezing point, the valve control unit 103 may increase the opening degree of the flow rate adjustment valve 22 so that the evaporation temperature drops below the freezing point. Also, when the temperature of the object to be cooled is higher than the freezing point, the valve control unit 103 may control the flow rate adjustment valve 22 so that the opening degree becomes smaller in order to make the evaporation temperature higher than the freezing point. In this case, since the evaporation pressure in the evaporator 4 increases, the evaporation temperature rises, so frosting can be prevented. Note that depending on the temperature of the object to be cooled, the adjustment of the opening degree of the flow rate adjustment valve 22 may be the exact opposite of the above case.

[0058] (Second Embodiment) In the first embodiment, the expansion valve 3 is controlled based on the target value of the evaporation temperature, and the flow rate adjustment valve 22 is controlled according to the degree of refrigeration demand. On the other hand, in the second embodiment, the valve control unit 103 is configured to control the flow rate adjustment valve 22 based on the target value of the evaporation temperature changed by the target value changing unit 102, and to control the expansion valve 3 according to the degree of refrigeration demand.

[0059] In step ST14, the valve control unit 103 sets the opening degree of the expansion valve 3 to a predetermined opening degree according to the degree of refrigeration demand (for example, the maximum opening degree if the degree of refrigeration demand is 100%), and in this state, controls the flow rate adjustment valve 22 so that the detected temperature by the evaporation temperature detector 21 approaches the target value of the evaporation temperature set by the target value changing unit 102. At this time, if the target value of the evaporation temperature is lower than the current evaporation temperature, the opening degree of the flow rate adjustment valve 22 increases, and if the target value of the evaporation temperature is higher than the current evaporation temperature, the opening degree of the flow rate adjustment valve 22 decreases.

[0060] When the degree of refrigeration demand received by the reception unit 101 changes from the degree of refrigeration demand received last time, the valve control unit 103 adjusts the opening degree of the expansion valve 3 according to the change amount of the degree of refrigeration demand. Since the evaporation temperature changes accordingly, the valve control unit 103 further adjusts the opening degree of the flow rate adjustment valve 22 so that the evaporation temperature approaches the target value.

[0061] For example, when the degree of refrigeration demand becomes smaller than the previous value, the valve control unit 103 reduces the opening degree of the expansion valve 3. Along with this, the evaporation temperature drops. If the target evaporation temperature does not change, the valve control unit 103 reduces the opening degree of the flow rate adjustment valve 22 along with this change in the evaporation temperature. Thereby, the evaporation temperature approaches the target value. At this time, since the opening degrees of the expansion valve 3 and the flow rate adjustment valve 22 become smaller, the flow rate of the evaporator 4 is throttled and the refrigeration capacity decreases.

[0062] On the one hand, if the refrigeration requirement remains high, the opening degree of the expansion valve 3 is maintained in a large state. Also, since the target value of the evaporation temperature is also maintained at a high value, the opening degree of the flow rate adjustment valve 22 is maintained in a large state. Therefore, the flow rate of the refrigerant flowing through the evaporator 4 is ensured in a state where the evaporation temperature is high, and it is maintained in a state where a large refrigeration capacity is exerted. Therefore, it is possible to exert a refrigeration capacity corresponding to a high refrigeration requirement degree.

[0063] Also, when the refrigeration requirement degree becomes larger than the previous value, the valve control unit 103 increases the opening degree of the expansion valve 3. Along with this, since the evaporation temperature rises, the valve control unit 103 increases the opening degree of the flow rate adjustment valve 22 along with this change in the evaporation temperature. As a result, the evaporation temperature approaches the target value. Therefore, since the flow rate of the refrigerant flowing through the evaporator 4 increases, it is possible to exert a higher refrigeration capacity.

[0064] In the present embodiment, for example, when the target value of the evaporation temperature is changed to a higher value, the opening degree of the flow rate adjustment valve 22 is controlled to become smaller. At this time, since the expansion valve 3 is controlled according to the refrigeration requirement degree, the evaporation temperature changes according to the change amount of the opening degree of the expansion valve 3. For this reason, since the opening degree of the flow rate adjustment valve 22 is further adjusted according to this changed evaporation temperature, the change in the evaporation temperature is suppressed. For this reason, by the expansion valve 3 and the flow rate adjustment valve 22, it is possible to exert a desired refrigeration capacity according to the refrigeration requirement degree while adjusting the evaporation temperature to the target value. As a result, it is possible to widen the variable range of the refrigeration capacity while suppressing frosting, which can also contribute to the continuous operation and energy saving of the device. Also, when the refrigeration device 10 is configured as an air conditioner capable of adjusting humidity, since it becomes possible to control at an evaporation temperature (refrigerant temperature in the evaporator 4) suitable for the dew point temperature, a wide range of temperature and humidity operations become possible. Furthermore, since the sensible heat ratio can be changed by the evaporation temperature, it is possible to exert a desired dehumidification capacity, which can also contribute to energy saving.

[0065] Note that the valve control unit 103 may be configured to control the expansion valve 3 according to the temperature of the object to be cooled, instead of controlling the expansion valve 3 according to the degree of refrigeration demand. When the valve control unit 103 controls the expansion valve 3 according to the temperature of the object to be cooled, the expansion valve 3 is controlled such that its opening degree increases as the temperature of the object to be cooled rises, and its opening degree decreases as the temperature of the object to be cooled drops. That is, by controlling the expansion valve 3 such that its opening degree increases when the temperature of the object to be cooled is high, the evaporation temperature in the evaporator 4 rises. On the other hand, by controlling the expansion valve 3 such that its opening degree decreases when the temperature of the object to be cooled is low, the evaporation temperature in the evaporator 4 drops. Therefore, the object to be cooled can be efficiently cooled.

[0066] Note that the descriptions of other configurations, operations, and effects are omitted, but the description of the first embodiment can be incorporated into the description of the second embodiment.

[0067] (Third Embodiment) In the first and second embodiments, the target value changing unit 102 is configured to change the target value of the evaporation temperature. In contrast, in the third embodiment, the target value changing unit 102 is configured to change the target value of the evaporation pressure.

[0068] In the third embodiment, as shown in FIG. 6, an evaporation pressure detector 33 is provided instead of the evaporation temperature detector 21. The evaporation pressure detector 33 is disposed at a position between the expansion valve 3 and the evaporator 4 in the refrigeration circuit 15, and detects the evaporation pressure of the refrigerant in the evaporator 4.

[0069] Note that, instead of the evaporation pressure detector 33, as shown in FIG. 7, an evaporation pressure detector 32 disposed at a position between the evaporator 4 and the flow rate adjustment valve 22 in the refrigeration circuit 15 may be provided. Further, both the evaporation pressure detector 33 (see FIG. 6) and the evaporation pressure detector 32 may be provided, or the temperature detector 21 (see FIG. 1) and the evaporation pressure detector 32 may be provided. In the refrigeration circuit 15, there is a pressure difference due to the pressure loss in the evaporator 4 at the position between the expansion valve 3 and the flow rate adjustment valve 22. By considering the pressure difference, the evaporation pressure detector 32 can detect the refrigerant pressure (evaporation pressure) in the evaporator 4.

[0070] When the evaporation pressure detector 33 or the evaporation pressure detector 32 is provided, the target value of the evaporation temperature shown in FIG. 3 can be read as the target value of the evaporation pressure. The target value changing unit 102 sets the target value of the evaporation pressure to the first value when the temperature of the object to be cooled (the temperature inside the refrigerator-freezer) is the first temperature, while when the temperature of the object to be cooled (the temperature inside the refrigerator-freezer) is the second temperature which is lower than the first temperature, the target value of the evaporation pressure is set to the second value which is lower than the first value. Further, the target value changing unit 102 may be configured to provide a range for the target value of the evaporation pressure and change the target value of the evaporation pressure according to the received refrigeration demand degree.

[0071] In this case, the valve control unit 103 is configured to control the expansion valve 3 based on the target value of the evaporation pressure changed by the target value changing unit 102 and control the flow rate adjustment valve 22 according to the refrigeration demand degree. Alternatively, the valve control unit 103 may be configured to control the flow rate adjustment valve 22 based on the target value of the evaporation pressure changed by the target value changing unit 102 and control the expansion valve 3 according to the refrigeration demand degree. Note that the controller 100 may derive the temperature corresponding to the pressure of the evaporation pressure detector 32 and use it as the evaporation temperature.

[0072] Also, as shown in FIG. 8, a temperature detector 34 may be used instead of the evaporation pressure detector 32. The temperature detector 34 is disposed in a bypass passage 16 connected to the refrigeration circuit 15. In this case, one end of the bypass passage 16 is connected between the condenser 2 and the expansion valve 3 in the refrigeration circuit 15, and the other end is connected between the evaporator 4 and the flow rate adjustment valve 22 in the refrigeration circuit 15. An electronic expansion valve 11 is provided in the bypass passage 16, and the temperature detector 34 is disposed at a position where the temperature in the evaporation process is detected downstream of the electronic expansion valve 11. In the bypass passage 16, the temperature downstream of the electronic expansion valve 11 becomes the evaporation temperature corresponding to the outlet pressure of the evaporator 4, so that the evaporation temperature considering the pressure loss of the evaporator 4 can be measured.

[0073] Although the description of other configurations, operations, and effects is omitted, the descriptions of the first and second embodiments can be incorporated into the description of the third embodiment.

[0074] (Fourth Embodiment) In the first embodiment, the valve control unit 103 always controls the flow rate adjustment valve 22 according to the degree of refrigeration demand. On the other hand, in the fourth embodiment, the valve control unit 103 has a first control mode in which the flow rate adjustment valve 22 is controlled according to the degree of refrigeration demand, and a second control mode in which the flow rate adjustment valve 22 is maintained fully open. The first control mode is executed when the temperature of the object to be cooled (the temperature inside the storage) is equal to or higher than a predetermined temperature, and is switched to the second control mode when the temperature inside the storage drops below the predetermined temperature. That is, in the second control mode, since the flow rate adjustment valve 22 is maintained fully open, the evaporation temperature decreases compared to the first control mode. Therefore, the second control mode is executed when the temperature of the object to be cooled is to be lowered to a low temperature such as below the freezing point or when it is desired to increase the refrigeration capacity. On the other hand, the first control mode is executed when suppressing frosting as in the first embodiment. The predetermined temperature for switching between the first control mode and the second control mode is set to a value less than 10°C, for example, 0°C or 5°C. Note that the second control mode may be executed not only when the temperature of the object to be cooled (the temperature inside the storage) is less than the predetermined temperature, but also when the temperature of the object to be cooled (the temperature inside the storage) is equal to or higher than the predetermined temperature and the evaporator 4 is in a situation where frosting is difficult to occur. For example, the second control mode is executed when it is desired to rapidly change the temperature of the object to be cooled (the temperature inside the storage) from a high temperature to a low temperature, or when it is desired to exhibit dehumidifying ability and achieve a low humidity in the temperature and humidity operation.

[0075] In the first control mode, the control described in step ST14 of the first embodiment is executed. On the other hand, in the second control mode, the flow rate adjustment valve 22 is maintained fully open. For this reason, in the second control mode, the control of the flow rate adjustment valve 22 based on the degree of refrigeration demand is not performed. However, in the second control mode, the expansion valve 3 is controlled so that the detected temperature of the evaporation temperature detector 21 becomes the target value of the evaporation temperature.

[0076] Note that in the first control mode, instead of controlling the flow rate adjustment valve 22, the expansion valve 3 may be controlled in the same manner as in the second embodiment (step ST14). Also, as in the third embodiment, the target value changing unit 102 is configured to change the target value of the evaporation pressure, and the valve control unit 103 controls the expansion valve 3 or the flow rate adjustment valve 22 based on the target value of the evaporation pressure changed by the target value changing unit 102, and may be configured to control the flow rate adjustment valve 22 or the expansion valve 3 according to the refrigeration demand degree. In this case, the evaporation pressure detector 33 shown in FIG. 6, the evaporation pressure detector 32 shown in FIG. 7, or the temperature detector 34 shown in FIG. 8 may be used.

[0077] Although the descriptions of other configurations, operations, and effects are omitted, the descriptions of the first to third embodiments can be incorporated into the fourth embodiment.

[0078] (Fifth Embodiment) In the first embodiment, the opening degree of the flow rate adjustment valve 22 is assigned to the refrigeration demand degree, whereas in the fifth embodiment, the target value of the suction pressure is assigned to the refrigeration demand degree, and the flow rate adjustment valve 22 is controlled to reach this target value of the suction pressure. Here, the same reference numerals are given to the same components as in the first embodiment, and the detailed description thereof is omitted.

[0079] As shown in FIG. 9, in the fifth embodiment, a pressure detector 31 for detecting the suction pressure of the compressor 1 is provided.

[0080] In the valve control unit 103, as shown in FIG. 10, the target value of the suction pressure is assigned to the refrigeration demand degree. The higher the refrigeration demand degree, the higher the target value of the suction pressure, and the lower the refrigeration demand degree, the lower the target value of the suction pressure. The maximum value and the minimum value of the target value of the suction pressure are set based on the specifications of the compressor 1.

[0081] That is, the lower the target value of the evaporation temperature, the smaller the opening degree of the expansion valve 3. Also, when the refrigeration requirement degree is low, the opening degree of the flow rate adjustment valve 22 also becomes smaller. For this reason, the suction pressure of the compressor 1 becomes low. However, the target value of the suction pressure assigned to the lowest value of the refrigeration requirement degree, that is, the lowest value in the target value, is set based on the specifications of the compressor 1. For this reason, even when the refrigeration requirement degree is the lowest, the compressor 1 can be stably operated.

[0082] The valve control unit 103 controls the flow rate adjustment valve 22 so that the detected pressure by the pressure detector 31 becomes the target value of the suction pressure set according to the refrigeration requirement degree. That is, also in this embodiment, the valve control unit 103 controls the flow rate adjustment valve 22 according to the refrigeration requirement degree.

[0083] Therefore, according to this embodiment, the expansion valve 3 is controlled so that the evaporation temperature in the evaporator 4 becomes the target value, while the flow rate adjustment valve 22 is controlled so that the detected value of the pressure detector 31 becomes the target value of the suction pressure set according to the refrigeration requirement degree. Therefore, not only is the evaporation temperature adjusted to the target value, but also the suction pressure is adjusted to the target value. For this reason, when adjusting the evaporation temperature to the target value, it is possible to prevent the suction pressure from excessively rising or falling. Therefore, it contributes to the stable operation of the compressor 1.

[0084] In this embodiment, the flow rate adjustment valve 22 may be controlled so that the evaporation temperature in the evaporator 4 becomes the target value, while the expansion valve 3 may be controlled so that the detected value of the pressure detector 31 becomes the target value of the suction pressure set according to the refrigeration requirement degree. Although the description of other configurations, operations, and effects is omitted, the descriptions of the first to fourth embodiments can be incorporated into the fifth embodiment.

[0085] (Sixth Embodiment) FIG. 11 shows the sixth embodiment. Here, the same components as those in the first to fifth embodiments are denoted by the same reference numerals, and the detailed description thereof is omitted.

[0086] The sixth embodiment is an example in which the refrigeration device 10 is applied to an environmental forming device 50 such as an environmental test device. As shown in FIG. 11, the environmental forming device 50 has an environmental chamber 51 and adjusts the inside of this environmental chamber 51 to a predetermined temperature environment. The environmental forming device 50 further includes an air-conditioning chamber 52 for generating air with adjusted temperature, and the evaporator 4 of the refrigeration device 10 is disposed in this air-conditioning chamber 52.

[0087] In the air-conditioning chamber 52, a heater 54 for heating air and a blower 55 for blowing out the air with adjusted temperature into the environmental chamber 51 are disposed on the downstream side of the evaporator 4. In the environmental chamber 51, a sensor 121 for detecting the temperature of the object to be cooled (the indoor temperature of the environmental chamber 51) is installed. The input device 122 is used for inputting the set temperature of the temperature inside the environmental chamber 51. The environmental forming device 50 may be configured to be able to set a wide range of temperatures, such as a minus temperature range, a normal temperature range, or a high temperature range, and may have a program operation function for changing a plurality of temperatures stepwise or continuously.

[0088] Note that the environmental forming device 50 may be configured to obtain not only a predetermined temperature environment but also a predetermined humidity environment. In this case, a humidifier (not shown) is provided. In this case, the evaporator 4 can also function as a dehumidifier.

[0089] The generator 120 calculates the refrigeration requirement degree using the detected temperature by the sensor 121 and the set temperature from the input device 122.

[0090] The heater 54 is output-controlled based on the detected temperature by the sensor 121 and the set temperature from the input device 122. That is, a predetermined refrigerating capacity is exerted by controlling the expansion valve 3 and the flow rate adjustment valve 22 of the refrigerating device 10. However, since the detected temperature by the sensor 121 may be lower than the set temperature, the indoor temperature of the environmental chamber 51 is finely adjusted by the heater 54. Therefore, if overcooling by the refrigerating device 10 can be suppressed, not only can the power of the refrigerating device 10 be suppressed, but also the power of the heater 54 can be suppressed. In this regard, when the refrigeration requirement is small, the target value of the evaporation temperature is adjusted to a low value, so that the refrigerant circulation amount can be reduced by the expansion valve 3 and the flow rate adjustment valve 22, and thereby the reduction of the refrigerating capacity can be achieved. Therefore, the power of the heater 54 can also be suppressed, and further energy saving can be achieved. Also, since the target value of the evaporation temperature is changed by the target value changing unit 102, it is possible to set the evaporation temperature higher than the freezing point. Further, since the refrigerant flow rate flowing into the evaporator 4 can be adjusted by the flow rate adjustment valve 22, energy saving can be achieved while suppressing frosting. Particularly in the case of continuous operation in which the humidity is adjusted, it can greatly contribute to the effect. Thus, since the target value changing unit 102 controls the flow rate adjustment valve 22 while changing the target value of the evaporation temperature, both the followability to the set temperature and the energy saving after the temperature is reached can be obtained, which is particularly suitable when executing a program operation.

[0091] In addition, although the description of other configurations, operations, and effects is omitted, the descriptions of the first to fifth embodiments can be incorporated into the sixth embodiment.

[0092] (Other Embodiments) It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The present invention is not limited to the above embodiments, and various changes, improvements, etc. are possible without departing from the gist thereof. For example, as shown in FIG. 12, a bypass flow path 18 bypassing the flow rate adjustment valve 22 may be provided in the refrigeration circuit 15, and a solenoid valve 36 may be provided in this bypass flow path 18.

[0093] Also, in the above embodiment, one expansion valve 3 and one flow rate adjustment valve 22 are provided, but a plurality of expansion valves 3 and a plurality of flow rate adjustment valves 22 may be provided.

Explanation of Signs

[0094] 1: Compressor 2: Condenser 3: Expansion valve 4: Evaporator 10: Refrigeration device 15: Refrigeration circuit 22: Flow rate adjustment valve 31: Pressure detector 101: Reception unit 102: Target value change unit 103: Valve control unit

Claims

1. A refrigeration device comprising a refrigeration circuit in which a compressor, a condenser, an expansion valve, an evaporator, and a flow rate adjustment valve are arranged in this order to circulate a refrigerant, a valve control unit that controls the expansion valve and the flow rate adjustment valve, and a target value changing unit for changing a target value of an evaporation temperature or an evaporation pressure in the evaporator. The valve control unit controls one of the expansion valve and the flow rate adjustment valve based on the target value changed by the target value changing unit, and controls the other of the expansion valve and the flow rate adjustment valve according to a refrigeration demand level or a temperature of a cooling target.

2. The refrigeration device according to claim 1, wherein the target value changing unit is configured to set the target value to a first target value when the temperature of the cooling target is a first temperature, and set the target value to a second target value lower than the first target value when the temperature of the cooling target is a second temperature lower than the first temperature.

3. The refrigeration device according to claim 1, wherein the valve control unit has a control mode in which the expansion valve is controlled so that an evaporation temperature or an evaporation pressure becomes the target value changed by the target value changing unit with the flow rate adjustment valve fully open.

4. The refrigeration device according to claim 1, further comprising a pressure detector that detects a suction pressure of the compressor, wherein the valve control unit controls the other of the expansion valve and the flow rate adjustment valve so that a detection value of the pressure detector becomes a suction pressure target value set according to the refrigeration demand level.

5. An environment forming device comprising an environmental chamber, and the refrigeration device according to any one of claims 1 to 4 for cooling the inside of the environmental chamber.

6. A refrigeration method using a refrigeration device including a refrigeration circuit in which a compressor, a condenser, an expansion valve, an evaporator, and a flow rate adjustment valve are arranged in this order to circulate a refrigerant, the method comprising: changing a target value of an evaporation temperature or an evaporation pressure in the evaporator; controlling one of the expansion valve and the flow rate adjustment valve based on the changed target value; receiving, by a receiving unit, information regarding a refrigeration demand level or a temperature of a cooling target; and controlling the other of the expansion valve and the flow rate adjustment valve according to the refrigeration demand level or the temperature of the cooling target received by the receiving unit.

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