Refrigeration cycle device

Abstract

A refrigeration cycle device (1) is provided with: a refrigerant circuit (2) through which a hydrocarbon-based refrigerant circulates; and a control device (100). The refrigerant circuit (2) includes a compressor (10), a natural convection-type condenser (20), a pressure-reducing device (30), and an evaporator (40). The control device (100) controls the pressure-reducing device (30) such that a degree of suction superheat, which is a degree of superheat of the refrigerant that is sucked into the compressor (10), becomes a target degree of superheat. The target degree of superheat is set to the degree of suction superheat when a coefficient of performance, which is a ratio of the cooling capacity of the refrigeration cycle device (1) to the power consumption of the compressor (10), is maximized.

Description

Refrigeration Cycle Equipment

[0001] The present disclosure relates to a refrigeration cycle device.

[0002] Hydrocarbon (HC)-based refrigerants such as propane and isobutane have low global warming potential (GWP), and therefore, refrigeration cycle devices using hydrocarbon-based refrigerants have rapidly become popular in recent years.

[0003] For example, International Publication No. 2020 / 144764 (Patent Document 1) describes a refrigeration cycle device that uses a hydrocarbon-based refrigerant. This refrigeration cycle device includes a refrigerant circuit including a compressor, a condenser, an expansion device, and an evaporator, and is configured to circulate the hydrocarbon-based refrigerant in this order by operation of the compressor, and a control device. This refrigeration cycle device is also intended to be an air conditioner and includes a forced convection condenser. That is, a condenser fan that forcibly blows air to the condenser is provided near the condenser.

[0004] International Publication No. 2020 / 144764

[0005] As described above, the refrigeration cycle device disclosed in WO 2020 / 144764 (Patent Document 1) includes a forced convection condenser.

[0006] However, some refrigeration cycle devices are equipped with condensers that are not forced convection condensers, but rather condensers that cool the internal refrigerant by natural convection of an external fluid (hereinafter also referred to as "natural convection condensers").

[0007] Natural convection heat exchangers generally have a lower heat transfer coefficient than forced convection heat exchangers, so to ensure the performance of natural convection condensers, it is desirable to increase the size of the heat exchange section. However, hydrocarbon refrigerants are flammable, so there is a limit to the amount of refrigerant they can contain. Simply increasing the condenser size raises concerns that a shortage of refrigerant will occur in the condenser. If the condenser does not have enough refrigerant, the condensing temperature cannot be raised and the refrigerant will not be able to be condensed completely, which could result in insufficient cooling capacity and energy saving performance.

[0008] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to improve condenser performance and ensure cooling capacity in a refrigeration cycle device that uses a hydrocarbon refrigerant and is equipped with a natural convection condenser while suppressing a decrease in energy-saving performance.

[0009] The refrigeration cycle apparatus according to the present disclosure uses a hydrocarbon refrigerant and includes a refrigerant circuit including a compressor, a condenser, a pressure reducing device, and an evaporator, configured to circulate the refrigerant in this order by operation of the compressor, and a control device. The condenser is a natural convection heat exchanger configured to cool the refrigerant inside the condenser by natural convection of an external fluid. The control device controls the pressure reducing device so that the suction superheat, which is the degree of superheat of the refrigerant drawn into the compressor, reaches a target superheat. The target superheat is set to the suction superheat that maximizes the coefficient of performance, which is the ratio of the cooling capacity of the refrigeration cycle apparatus to the power consumption of the compressor.

[0010] According to the present disclosure, in a refrigeration cycle device that uses a hydrocarbon-based refrigerant and is equipped with a natural convection condenser, it is possible to improve condenser performance and ensure cooling capacity while suppressing a decrease in energy-saving performance.

[0011] FIG. 1 is a diagram (part 1) schematically showing an example of the overall configuration of a refrigeration cycle device. FIG. 2 is a flowchart showing an example of a processing procedure of a control device. FIG. 3 is a diagram (part 4) schematically showing an example of the overall configuration of a refrigeration cycle device.

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0013] 1 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1 according to this embodiment. The refrigeration cycle apparatus 1 includes a refrigerant circuit 2 through which a refrigerant circulates, and a control device 100.

[0014] The refrigerant circuit 2 includes a compressor 10, a condenser 20, a pressure reducing device 30, an evaporator 40, and flow paths P1 to P4. The refrigerant circuit 2 is configured such that, when the compressor 10 is operated, the refrigerant circulates through the compressor 10, flow path P1, condenser 20, flow path P2, pressure reducing device 30, flow path P3, evaporator 40, and flow path P4 in this order.

[0015] In this embodiment, a hydrocarbon refrigerant (hereinafter also referred to as "HC refrigerant") such as R290 or R600a is used as the refrigerant circulating through the refrigerant circuit 2. Note that, because HC refrigerants are flammable, there is a limit to the amount of refrigerant that can be charged into the refrigerant circuit 2.

[0016] The compressor 10 draws in refrigerant from the flow path P4, compresses it, and discharges it as high-temperature, high-pressure gas refrigerant to the flow path P1. The compressor 10 discharges the refrigerant at a flow rate corresponding to the rotation frequency (rotation speed). The compressor 10 is controlled by the control device 100.

[0017] The condenser 20 is a natural convection heat exchanger having a flow path through which a refrigerant flows. That is, in the condenser 20, the refrigerant flowing inside the flow path is cooled by the natural convection of a fluid (e.g., air) outside the flow path. For example, when the refrigeration cycle apparatus 1 is installed in a household refrigerator, the condenser 20 is disposed near a side panel of the refrigerator and is configured to cool the refrigerant inside the condenser 20 by the natural convection of external air in contact with the side panel. Therefore, no fan is disposed near the condenser 20.

[0018] The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 is supplied to the condenser 20, where it is cooled by heat exchange to become a liquid refrigerant.

[0019] The condenser 20 according to this embodiment is a flat-tube heat exchanger. The flat-tube heat exchanger has flat tubes with a cross-sectional shape resembling a rectangle with rounded corners and a large aspect ratio, which serve as flow paths for the refrigerant. The interior of the flat tube is divided by a plurality of slits, which results in a plurality of narrow-diameter tubes formed inside the flat tube. Compared to a typical circular-tube heat exchanger, the flat-tube heat exchanger can have a smaller internal volume because it exchanges more heat with the fluid outside the flow path.

[0020] The pressure reducing device 30 is a device that reduces the pressure of a high-pressure refrigerant. The pressure reducing device 30 is, for example, an electronically controlled expansion valve equipped with a valve element whose opening degree is adjustable. Note that the pressure reducing device 30 is not limited to an electronically controlled expansion valve, and may be, for example, a device configured to adjust the amount of pressure reduction by switching between multiple thin tubes (capillary tubes) of different lengths, as is used in general household refrigerators. The amount of pressure reduction (throttling amount) by the pressure reducing device 30 is controlled by the control device 100. The liquid refrigerant reduced in pressure by the pressure reducing device 30 is supplied to the evaporator 40 via a flow path P3.

[0021] The evaporator 40 is a forced convection heat exchanger having a flow path through which the refrigerant flows. In the evaporator 40, the liquid refrigerant flowing inside the flow path absorbs heat from the fluid (e.g., air) outside the flow path and becomes gas refrigerant. At this time, the fluid outside the evaporator 40 is cooled by the latent heat and sensible heat of the refrigerant. An evaporator fan 41 that forcibly blows air into the evaporator 40 is provided near the evaporator 40. The refrigerant inside the evaporator 40 and the air from the evaporator fan 41 are configured to flow in directions opposite to each other. In other words, the evaporator 40 in this embodiment is a counterflow heat exchanger. The gas refrigerant output from the evaporator 40 to flow path P4 is drawn into the compressor 10.

[0022] Furthermore, the refrigerant circuit 2 according to this embodiment includes an internal heat exchanger 50. The internal heat exchanger 50 is configured to exchange heat between the refrigerant flowing through a flow path P2 connecting the condenser 20 and the pressure reducing device 30 and the refrigerant flowing through a flow path P4 connecting the evaporator 40 and the compressor 10. By providing the internal heat exchanger 50, the refrigerant cooled by the condenser 20 can be further cooled by the internal heat exchanger 50.

[0023] 1, a plurality of sensors are arranged in the refrigerant circuit 2 to detect the operating state of the refrigerant circuit 2 (for example, the pressure and temperature of the refrigerant at each location). These sensors output the detection results to the control device 100.

[0024] The control device 100 includes a CPU (Central Processing Unit) 101, a memory 102, and an input / output port (not shown) for inputting and outputting various signals. The control device 100 controls the devices (such as the compressor 10, the pressure reducing device 30, and the evaporator fan 41) of the refrigeration cycle device 1 based on signals from the sensors and devices, and programs stored in the memory 102. Note that the control performed by the control device 100 is not limited to software processing, and can also be processed by dedicated hardware (electronic circuits).

[0025] As described above, the refrigeration cycle device 1 according to this embodiment uses an HC refrigerant and includes the natural convection type condenser 20 .

[0026] Natural convection heat exchangers generally have a lower heat transfer coefficient than forced convection heat exchangers. Therefore, to ensure the performance of the natural convection condenser 20, it is desirable to increase the size of the heat exchange portion of the condenser 20. However, because HC refrigerants are flammable, there is a limit to the amount of refrigerant that can be charged. Therefore, simply increasing the size of the heat exchange portion of the condenser 20 raises concerns that the refrigerant in the condenser 20 may result in a shortage of refrigerant.

[0027] If the refrigerant in the condenser 20 is insufficient, it becomes difficult to increase the refrigerant pressure in the condenser 20, and the condensing temperature cannot be increased, making it impossible to condense the refrigerant in the condenser 20. As a result, the amount of refrigerant liquid supplied to the evaporator 40 becomes insufficient, and the evaporator 40 cannot obtain sufficient latent heat, which may result in insufficient cooling capacity. Because cooling capacity depends on the amount of refrigerant circulating, it is possible to increase the amount of refrigerant circulating by increasing the power of the compressor 10 to compensate for the insufficient cooling capacity, but in this case, the power consumption of the compressor 10 increases, thereby reducing energy-saving performance.

[0028] In view of the above problems, the control device 100 according to this embodiment controls the pressure reducing device 30 to control the degree of superheat of the refrigerant sucked into the compressor 10 (hereinafter also referred to as the "suction superheat degree SH") as follows.

[0029] First, the control device 100 calculates the suction superheat SH when the coefficient of performance (COP) of the refrigeration cycle device 1 is maximized based on the operating state of the refrigerant circuit 2 (for example, the pressure and temperature of the refrigerant at each location), and sets the calculated result as the "target superheat SHt." The coefficient of performance COP is the ratio of the cooling capacity of the refrigeration cycle device 1 to the power consumption of the compressor 10 (=cooling capacity / power consumption), and a larger value of the coefficient of performance indicates higher energy-saving performance.

[0030] The correspondence relationship between the operating state of the refrigerant circuit 2 and the target degree of superheat SHt (= the suction superheat SH when the coefficient of performance COP is maximized) can be determined by experiment, etc. Therefore, for example, the correspondence relationship between the operating state of the refrigerant circuit 2 and the target degree of superheat SHt can be determined in advance by experiment, etc. and stored in the memory 102, and the control device 100 can refer to the correspondence relationship stored in the memory 102 and set the target degree of superheat SHt that corresponds to the actual operating state detected by the sensor.

[0031] The control device 100 then controls the pressure reducing device 30 so that the suction superheat degree SH of the compressor 10 is equal to the target superheat degree SHt. This control, compared to the control of a typical air conditioner, throttles the pressure reducing device 30 to increase the suction superheat degree SH, thereby increasing the amount of gas in the low-pressure evaporator 40 and the amount of liquid in the high-pressure condenser 20. As a result, the refrigerant distribution amount in the high-pressure condenser 20 can be increased, thereby raising the condensing temperature. Furthermore, because the target superheat degree SHt is set to a value that maximizes the coefficient of performance (COP), a decrease in energy-saving performance is also suppressed. As a result, in a refrigeration cycle system 1 using an HC refrigerant and including a natural convection condenser 20, the performance of the condenser 20 can be improved and cooling capacity can be ensured while a decrease in energy-saving performance is suppressed.

[0032] Furthermore, by increasing the suction superheat SH as described above, it becomes easier to utilize not only the latent heat of the refrigerant but also its sensible heat as cooling capacity. That is, although the latent heat of HC refrigerants (such as R290 and R600a) is smaller than that of general air conditioner refrigerants (such as R410a and R32), in the refrigeration cycle system 1 according to this embodiment, increasing the suction superheat SH expands the gas region within the evaporator 40, making it possible to utilize not only the latent heat of the HC refrigerant but also its sensible heat as cooling capacity. As a result, energy saving performance can be improved.

[0033] Furthermore, in the refrigeration cycle apparatus 1 according to this embodiment, the internal heat exchanger 50 is provided, so that the sensible heat of the gas refrigerant flowing through the flow path P4 can be used to cool the liquid refrigerant on the outlet side of the condenser 20 (the inlet side of the evaporator 40), thereby further improving the cooling capacity.

[0034] 2 is a flowchart showing an example of a processing procedure executed by the control device 100 when controlling the pressure reducing device 30. This flowchart is repeatedly executed during operation of the refrigeration cycle apparatus 1.

[0035] First, the control device 100 acquires detection results of the operating state of the refrigerant circuit 2 from each sensor (step S10). The operating state acquired in this process may be, for example, the inlet pressure of the compressor 10 and the outlet pressure of the compressor 10. Since pressure sensors for detecting these pressures are relatively expensive, for example, a temperature sensor for detecting the temperature (evaporation temperature) of the two-phase region of the evaporator 40 and a temperature sensor for detecting the temperature (condensation temperature) of the two-phase region of the condenser 20 may be provided instead of these pressure sensors, and the inlet pressure of the compressor 10 and the outlet pressure of the compressor 10 may be estimated from the detection results of these temperature sensors.

[0036] Next, the control device 100 calculates the suction superheat degree when the coefficient of performance COP is maximized based on the operating state acquired in step S10, and sets the calculated suction superheat degree as the target superheat degree SHt (step S20). An example of the method for setting the target superheat degree SHt is as described above.

[0037] Next, the control device 100 controls the pressure reducing device 30 so that the suction superheat degree SH of the compressor 10 becomes the target superheat degree SHt set in step S20 (step S30).

[0038] As described above, the refrigeration cycle device 1 of this embodiment uses an HC refrigerant, which has a limited amount that can be enclosed, and is equipped with a natural convection condenser 20 with a low heat transfer coefficient, so there is a concern that it may run out of refrigerant, causing insufficient cooling capacity and reduced energy-saving performance.

[0039] However, in the refrigeration cycle system 1 according to this embodiment, the control device 100 sets a target superheat degree SHt at which the coefficient of performance COP is maximized, and controls the pressure reducing device 30 so that the suction superheat degree SH becomes the target superheat degree SHt. This throttles the pressure reducing device 30, increasing the suction superheat degree SH, thereby increasing the amount of refrigerant distributed in the high-pressure side condenser 20 and raising the condensing temperature. Furthermore, the coefficient of performance COP is maximized, suppressing a decrease in energy-saving performance. As a result, the performance of the condenser 20 is improved and cooling capacity is ensured while suppressing a decrease in energy-saving performance.

[0040] Furthermore, the refrigeration cycle apparatus 1 according to this embodiment is provided with an internal heat exchanger 50 that cools the liquid refrigerant on the outlet side of the condenser 20 (the inlet side of the evaporator 40) by utilizing the sensible heat of the gas refrigerant flowing through the flow path P4, thereby further improving the cooling capacity.

[0041] Furthermore, the condenser 20 according to this embodiment is a flat-tube heat exchanger. The flat-tube heat exchanger has a smaller internal volume than a typical circular-tube heat exchanger, which reduces the amount of refrigerant required. Therefore, even if the amount of refrigerant charged is limited, it is possible to reduce the risk of refrigerant shortage.

[0042] Furthermore, the evaporator 40 according to this embodiment is a counterflow heat exchanger. This increases the heat exchange rate of the evaporator 40, making it easier to increase the suction superheat SH. [Modification 1] FIG. 3 is a diagram schematically showing an example of the overall configuration of a refrigeration cycle apparatus 1A according to this modification 1. The refrigeration cycle apparatus 1A is configured by replacing the refrigerant circuit 2 of the refrigeration cycle apparatus 1 according to the above-described embodiment with a refrigerant circuit 2A. The refrigerant circuit 2A is configured by adding an injection flow path 61 and an injection expansion valve 62 to the refrigerant circuit 2, and by changing the internal heat exchanger 50 to an internal heat exchanger 60. The other configurations of the refrigeration cycle apparatus 1A are the same as those of the refrigeration cycle apparatus 1 described above.

[0043] The injection flow path 61 connects a branch portion 63 provided in the flow path P2 (a flow path between the condenser 20 and the pressure reducing device 30) with the intermediate pressure section 10a of the compressor 10, and supplies liquid refrigerant from the branch portion 63 to the intermediate pressure section 10a of the compressor 10. This cools the compressor 10, and prevents the discharge temperature of the compressor 10 from rising excessively.

[0044] The internal heat exchanger 60 is provided in a portion of the flow path P2 between the condenser 20 and the branching portion 63, and is configured to cool the refrigerant flowing between the condenser 20 and the branching portion 63 with the refrigerant flowing through the injection flow path 61. With this configuration, the refrigerant cooled by the condenser 20 can be further cooled by the internal heat exchanger 60.

[0045] The injection expansion valve 62 is provided in a portion of the injection flow path 61 between the branching portion 63 and the internal heat exchanger 60. The injection expansion valve 62 adjusts the flow rate of the refrigerant flowing through the injection flow path 61. For example, an electronically controlled expansion valve equipped with a valve element whose opening degree can be adjusted can be used as the injection expansion valve 62. The opening degree of the injection expansion valve 62 is controlled by the control device 100.

[0046] In this way, the refrigerant circuit 2 according to the above-described embodiment may be replaced with the refrigerant circuit 2A according to Modification 1. [Modification 2] The injection flow path 61 according to Modification 1 supplies liquid refrigerant to the intermediate pressure section 10a of the compressor 10, but the injection flow path 61 may supply liquid refrigerant to the inlet pipe of the compressor 10.

[0047] 4 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1B according to Modification 2. The refrigeration cycle apparatus 1B is configured by replacing the refrigerant circuit 2A of the refrigeration cycle apparatus 1A according to Modification 1 with a refrigerant circuit 2B. The refrigerant circuit 2B is configured by replacing the injection flow path 61 of the refrigerant circuit 2A with an injection flow path 61B.

[0048] The injection flow path 61B connects the branching portion 63 with the flow path P4 on the inlet side of the compressor 10, and supplies liquid refrigerant from the branching portion 63 to the flow path P4 on the inlet side of the compressor 10.

[0049] In this way, the refrigerant circuit 2A according to Modification 1 may be replaced with the refrigerant circuit 2B according to Modification 2. [Modification 3] Although the refrigerant circuit 2 according to the present embodiment described above includes the internal heat exchanger 50, the refrigerant circuit 2 may not include the internal heat exchanger 50.

[0050] 5 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1C according to Modification 3. The refrigeration cycle apparatus 1C is obtained by replacing the refrigerant circuit 2 of the refrigeration cycle apparatus 1 according to the above-described embodiment with a refrigerant circuit 2C. The refrigerant circuit 2C is obtained by removing the internal heat exchanger 50 from the above-described refrigerant circuit 2.

[0051] In this way, the refrigerant circuit 2 according to the above-described embodiment may be replaced with the refrigerant circuit 2C according to the third modified example.

[0052] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0053] 1, 1A to 1C refrigeration cycle device, 2, 2A to 2C refrigerant circuit, 10 compressor, 10a intermediate pressure section, 20 condenser, 30 pressure reducing device, 40 evaporator, 41 evaporator fan, 50, 60 internal heat exchanger, 61, 61B injection flow path, 62 injection expansion valve, 63 branching section, 100 control device, 101 CPU, 102 memory, P1 to P4 flow path.

Claims

1. A refrigeration cycle device that uses a hydrocarbon refrigerant, comprising: a refrigerant circuit including a compressor, a condenser, a pressure reducing device, and an evaporator, and configured to circulate the refrigerant in this order by operation of the compressor; and a control device, wherein the condenser is a natural convection heat exchanger configured to cool the refrigerant inside the condenser by natural convection of an external fluid, and the control device controls the pressure reducing device so that an intake superheat, which is the degree of superheat of the refrigerant sucked into the compressor, becomes a target superheat, and the target superheat is set to the intake superheat when a coefficient of performance, which is the ratio of the cooling capacity of the refrigeration cycle device to the power consumption of the compressor, is maximized.

2. The refrigeration cycle device according to claim 1, wherein the control device sets the target degree of superheat depending on an operating state of the refrigerant circuit.

3. The refrigeration cycle device according to claim 1, wherein the evaporator is a counterflow heat exchanger configured so that the refrigerant inside the evaporator and the fluid outside the evaporator flow in directions opposite to each other.

4. The refrigeration cycle device according to claim 1, wherein the condenser is a flat tube heat exchanger.

5. A refrigeration cycle device according to any one of claims 1 to 4, wherein the refrigerant circuit further comprises an internal heat exchanger configured to cool the refrigerant flowing between the condenser and the pressure reducing device with the refrigerant flowing between the evaporator and the compressor.

6. A refrigeration cycle device according to any one of claims 1 to 4, wherein the refrigerant circuit further comprises: an injection flow path that connects a branch section provided in a flow path between the condenser and the pressure reducing device with an intermediate pressure section or an inlet side flow path of the compressor, and supplies refrigerant from the branch section to the intermediate pressure section or the inlet side flow path of the compressor; and an internal heat exchanger configured to cool the refrigerant flowing between the condenser and the branch section with the refrigerant flowing through the injection flow path.

Images