Refrigeration cycle device

Abstract

A refrigeration cycle device (1) comprises a refrigerant circuit (2) and a control device (100). The refrigerant circuit (2) includes a compressor (10), a condenser (20), an expansion valve (30), and an evaporator (40). The refrigerant circuit (2) further comprises: an injection passage (50) connecting a branch portion (53), which is provided in a passage (P2) between the condenser (20) and the expansion valve (30), and the compressor (10); and an inner heat exchanger (51) configured to cool a refrigerant flowing between the condenser (20) and the branch portion (53) by using a refrigerant flowing through the injection passage (50). The refrigerant is a flammable refrigerant that has a higher boiling point than that of R32. The evaporator (40) is a flat tube heat exchanger.

Description

Refrigeration cycle equipment

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

[0002] International Publication No. 2021 / 240615 (Patent Document 1) discloses a refrigeration cycle device including a refrigerant circuit configured so that a flammable refrigerant circulates through a compressor, a condenser, an expansion valve, and an evaporator in that order.

[0003] International Publication No. 2021 / 240615

[0004] Generally, when a flammable refrigerant is used in a refrigeration cycle device, there is a limit to the amount of refrigerant that can be charged, which makes it difficult to achieve subcooling (SC) at the condenser outlet. As a countermeasure, in the past, there have been cases where the capacity of the compressor (the product of the volume and the rotation speed) was increased to increase the volumetric flow rate of the refrigerant output from the compressor, thereby improving the capacity of the refrigeration cycle device.

[0005] However, when a flammable refrigerant with a higher boiling point than R32 is used, there is a concern that the performance of the refrigeration cycle device will decrease even if the compressor capacity is increased. Specifically, refrigerants with a higher boiling point than R32 have large changes in their physical properties (saturation temperature, density, etc.) in response to pressure changes in the low-pressure region. As a result, if the density of the refrigerant drawn into the compressor decreases significantly due to pressure loss in the evaporator, even if the compressor capacity is increased, the mass flow rate of the refrigerant output from the compressor will not increase sufficiently, and there is a concern that the performance of the refrigeration cycle device will decrease.

[0006] In particular, when a flat tube heat exchanger is used as the evaporator, the pressure loss in the evaporator is greater than when the evaporator is a circular tube heat exchanger, which raises concerns that the mass flow rate of the refrigerant output from the compressor 10 will further decrease, further reducing the capacity of the refrigeration cycle device.

[0007] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to improve the capacity of a refrigeration cycle device that uses a flammable refrigerant with a higher boiling point than R32 and that uses a flat tube heat exchanger as an evaporator.

[0008] The refrigeration cycle device according to the present disclosure includes a refrigerant circuit including a compressor, a condenser, an expansion valve, and an evaporator, configured to circulate a refrigerant in this order by operation of the compressor, and a control device for controlling the compressor. The refrigerant circuit further includes an injection flow path that connects the compressor to a branching portion provided in a flow path between the condenser and the expansion valve and supplies refrigerant from the branching portion to the compressor, and an internal heat exchanger that is provided between the condenser and the branching portion and configured to cool the refrigerant flowing between the condenser and the branching portion with the refrigerant flowing through the injection flow path. The refrigerant is a flammable refrigerant with a boiling point higher than that of R32. The evaporator is a flat-tube heat exchanger.

[0009] According to the present disclosure, it is possible to improve the capacity of a refrigeration cycle device that uses a flammable refrigerant with a higher boiling point than R32 and that uses a flat tube heat exchanger as an evaporator.

[0010] It is a diagram (part 1) showing an example of the overall configuration of a refrigeration cycle device. It is a diagram showing a correspondence relationship between the rotation speed of a compressor and a refrigerant mass flow rate. It is a flowchart showing an example of a processing procedure of a control device. It is a diagram (part 2) showing an example of the overall configuration of a refrigeration cycle device.

[0011] 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.

[0012] 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.

[0013] The refrigerant circuit 2 includes a compressor 10, a condenser 20, an expansion valve 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, expansion valve 30, flow path P3, evaporator 40, and flow path P4 in this order.

[0014] In this embodiment, R290, a flammable refrigerant having a boiling point higher than that of R32, is used as the refrigerant circulating through the refrigerant circuit 2. Note that the flammable refrigerant having a boiling point higher than that of R32 is not limited to R290, and may be, for example, R600a, R454A, R454B, R454C, R474A, R479A, or R1234yf.

[0015] 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 that corresponds to the rotational frequency (rotational speed). The rotational frequency of the compressor 10 is controlled by the control device 100.

[0016] The condenser 20 is a heat exchanger having a flow path through which the refrigerant flows. In the condenser 20, heat exchange occurs between the refrigerant flowing inside the flow path and the air outside the flow path. A part or all of the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 is cooled by heat exchange in the condenser 20 and becomes a liquid refrigerant.

[0017] The expansion valve 30 is a pressure reducing device that reduces the pressure of the high-pressure refrigerant. For example, an electronically controlled expansion valve having a valve element with an adjustable opening degree can be used as the expansion valve 30. The opening degree of the expansion valve 30 is controlled by the control device 100.

[0018] The evaporator 40 is a heat exchanger having a flow path through which the refrigerant flows. In the evaporator 40, heat exchange occurs between the refrigerant flowing inside the flow path and the air outside the flow path. The refrigerant decompressed by the expansion valve 30 becomes a gas refrigerant through heat exchange in the evaporator 40. The gas refrigerant output from the evaporator 40 to the flow path P5 is drawn into the compressor 10.

[0019] The evaporator 40 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 the flow path for the refrigerant. The interior of the flat tube is divided by a plurality of slits, which form a plurality of tubes with small diameters inside the flat tube. Compared to a typical circular-tube heat exchanger, the flat-tube heat exchanger has a higher heat exchange rate with the air outside the flow path, but the diameter of each tube is small, which tends to result in a larger pressure loss.

[0020] Furthermore, the refrigerant circuit 2 includes an injection flow path 50 , an internal heat exchanger 51 , and an injection expansion valve 52 .

[0021] The injection flow path 50 connects a branching portion 53 provided in the flow path P2 (a flow path between the condenser 20 and the expansion valve 30) with the intermediate pressure section 10a of the compressor 10, and supplies refrigerant including liquid refrigerant from the branching portion 53 to the intermediate pressure section 10a of the compressor 10. The supply of liquid refrigerant from the injection flow path 50 to the intermediate pressure section 10a of the compressor 10 cools the compressor 10. This prevents the discharge temperature of the compressor 10 from rising excessively.

[0022] The internal heat exchanger 51 is provided in a portion of the flow path P2 between the condenser 20 and the branching portion 53, and is configured to cool the refrigerant flowing between the condenser 20 and the branching portion 53 with the refrigerant flowing through the injection flow path 50. With this configuration, the refrigerant cooled by the condenser 20 can be further cooled by the internal heat exchanger 51.

[0023] The injection expansion valve 52 is provided in a portion of the injection flow path 50 between the branching portion 53 and the internal heat exchanger 51. The injection expansion valve 52 adjusts the flow rate of the refrigerant flowing through the injection flow path 50. 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 52. The opening degree of the injection expansion valve 52 is controlled by the control device 100.

[0024] 1, a plurality of sensors are arranged in the refrigerant circuit 2 to detect the refrigerant state (pressure, temperature, etc.) at various locations in the refrigerant circuit 2. These sensors output the detection results to the control device 100.

[0025] 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 (compressor 10, expansion valve 30, injection expansion valve 52, etc.) 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 circuitry).

[0026] When the refrigeration cycle device 1 is used as an air conditioner for indoor cooling, it is assumed that the condenser 20 is disposed outdoors and the evaporator 40 is disposed indoors.

[0027] As described above, the refrigeration cycle apparatus 1 according to this embodiment uses R290, a flammable refrigerant with a higher boiling point than R32. The amount of flammable refrigerant that can be charged is limited, which makes it difficult to achieve supercooling at the outlet of the condenser 20. Furthermore, refrigerants with higher boiling points than R32 exhibit large changes in their physical properties (saturation temperature, density, etc.) in response to pressure changes in the low-pressure region. This significantly reduces the density of the refrigerant drawn into the compressor 10 due to pressure loss in the evaporator 40. This reduces the mass flow rate of the refrigerant output from the compressor 10, potentially reducing the capacity of the refrigeration cycle apparatus 1.

[0028] In particular, in the refrigeration cycle device 1 according to this embodiment, since the evaporator 40 is a flat tube heat exchanger, the pressure loss in the evaporator 40 is greater than when the evaporator 40 is a circular tube heat exchanger, and there is a concern that the mass flow rate of the refrigerant output from the compressor 10 will further decrease.

[0029] In consideration of the above-described problems, the refrigeration cycle apparatus 1 according to the present embodiment is provided with an internal heat exchanger 51 and an injection flow path 50. This allows for improved performance of the refrigeration cycle apparatus 1, which uses a flammable refrigerant (R290) having a higher boiling point than R32 as the refrigerant and a flat-tube heat exchanger as the evaporator 40. Specifically, for example, when the refrigeration cycle apparatus 1 is used as an air conditioner for indoor cooling, the cooling by the internal heat exchanger 51 increases the subcooling at the outlet of the condenser 20, and the mass flow rate of the refrigerant output from the compressor 10 can be increased by supplying the refrigerant to the compressor 10 from the injection flow path 50. As a result, the cooling performance of the refrigeration cycle apparatus 1 can be improved.

[0030] Furthermore, in order to further improve performance, the control device 100 controls the rotation speed of the compressor 10 so as to maximize the mass flow rate of the refrigerant output from the compressor 10 .

[0031] Fig. 2 is a diagram schematically showing the correspondence relationship between the rotation speed of the compressor 10 and the mass flow rate of the refrigerant output from the compressor 10 (hereinafter also simply referred to as "refrigerant mass flow rate"). In Fig. 2, the horizontal axis represents the rotation speed of the compressor 10 (unit: Hz), and the vertical axis represents the refrigerant mass flow rate.

[0032] As shown in Figure 2, the refrigerant mass flow rate increases as the rotational speed of the compressor 10 increases when the rotational speed of the compressor 10 is below a certain value. However, it reaches a maximum value when the rotational speed of the compressor 10 is a certain value, and decreases even when the rotational speed of the compressor 10 increases when the rotational speed of the compressor 10 exceeds the certain value. That is, if the rotational speed of the compressor 10 at which the refrigerant mass flow rate reaches a maximum value is defined as a "threshold value," the refrigerant mass flow rate monotonically increases as the rotational speed of the compressor 10 increases in a region where the rotational speed of the compressor 10 is below the threshold value (hereinafter also referred to as a "monotonically increasing region"), but monotonically decreases as the rotational speed of the compressor 10 increases in a region where the rotational speed of the compressor 10 exceeds the threshold value (hereinafter also referred to as a "monotonically decreasing region"). Note that the "threshold value" can change depending on the operating state and environmental conditions of the refrigeration cycle apparatus 1, so it is difficult to determine a single value in advance.

[0033] In consideration of these characteristics, the control device 100 according to this embodiment repeatedly changes the rotation speed of the compressor 10 by a predetermined amount in a direction in which the refrigerant mass flow rate approaches the maximum value. Specifically, when the operating point of the compressor 10 is within the above-described monotonically increasing region, the control device 10 sets the change direction of the rotation speed of the compressor 10 to a positive direction (increasing direction), and when the operating point of the compressor 10 is within the above-described monotonically decreasing region, the control device 10 sets the change direction of the rotation speed of the compressor 10 to a negative direction (decreasing direction), and changes the rotation speed of the compressor 10 by a predetermined amount in the set change direction. By repeating this process, the refrigerant mass flow rate can approach the maximum value.

[0034] 3 is a flowchart showing an example of a processing procedure of the control device 100. This flowchart is repeatedly executed at predetermined calculation intervals while the compressor 10 is in operation.

[0035] First, the control device 100 calculates the refrigerant mass flow rate for the current calculation cycle (hereinafter also referred to as the "current refrigerant mass flow rate") based on the capacity of the compressor 10 and the density of the refrigerant drawn into the compressor 10 (step S10). The capacity of the compressor 10 can be calculated from the volume of the compressor 10 and the rotation speed of the compressor 10. The density of the refrigerant drawn into the compressor 10 can be calculated from the pressure and temperature of the refrigerant drawn into the compressor 10. Because the volume of the compressor 10 is a known fixed value determined by the hardware configuration of the compressor 10, the control device 100 can calculate the current refrigerant mass flow rate from the current rotation speed of the compressor 10 and the pressure and temperature of the refrigerant drawn into the compressor 10.

[0036] Next, the control device 100 reads from the memory 102 the refrigerant mass flow rate in the previous calculation cycle (hereinafter also referred to as the "previous refrigerant mass flow rate") and the rotation change direction of the compressor 10 in the previous calculation cycle (hereinafter also referred to as the "previous rotation change direction") (step S12).

[0037] Next, the control device 100 determines whether the current refrigerant mass flow rate is greater than the previous refrigerant mass flow rate (step S14).

[0038] If the current refrigerant mass flow rate is greater than the previous refrigerant mass flow rate (YES in step S14), the control device 100 sets the current rotation speed change direction to the same direction as the previous rotation speed change direction (step S16). That is, if the current refrigerant mass flow rate is greater than the previous refrigerant mass flow rate and the previous rotation speed change direction was positive (increasing), the operating point of the compressor 10 is estimated to be within the monotonically increasing region, and the control device 100 also sets the current rotation speed change direction to positive. On the other hand, if the current refrigerant mass flow rate is greater than the previous refrigerant mass flow rate and the previous rotation speed change direction was negative (decreasing), the operating point of the compressor 10 is estimated to be within the monotonically decreasing region, and the control device 100 also sets the current rotation speed change direction to negative.

[0039] On the other hand, if the current refrigerant mass flow rate is smaller than the previous refrigerant mass flow rate (NO in step S14), the control device 100 sets the current rotational speed change direction to the opposite direction of the previous rotational speed change direction (step S18). That is, if the current refrigerant mass flow rate is smaller than the previous refrigerant mass flow rate and the previous rotational speed change direction was positive, the current operating point of the compressor 10 is estimated to be within the monotonically decreasing region, and the control device 100 sets the current rotational speed change direction to the negative direction, opposite to the previous direction. On the other hand, if the current refrigerant mass flow rate is smaller than the previous refrigerant mass flow rate and the previous rotational speed change direction was negative, the current operating point of the compressor 10 is estimated to be within the monotonically increasing region, and the control device 100 sets the current rotational speed change direction to the positive direction, opposite to the previous direction.

[0040] Then, the control device 100 changes the rotation speed of the compressor 10 by a predetermined amount in the direction of the rotation speed change set in step S16 or step S18 (step S20).

[0041] By repeating the above series of processes, the rotation speed of the compressor 10 can be controlled so as to maximize the refrigerant mass flow rate output from the compressor 10.

[0042] As described above, the refrigeration cycle apparatus 1 according to this embodiment uses a flammable refrigerant (R290) with a higher boiling point than R32, making it difficult to subcool the refrigerant exiting the condenser 20. Furthermore, the evaporator 40 uses a flat-tube heat exchanger, which tends to increase pressure loss in the evaporator 40. However, the refrigeration cycle apparatus 1 according to this embodiment includes an internal heat exchanger 51 and an injection flow path 50. This increases the subcooling of the refrigerant exiting the condenser 20 through cooling by the internal heat exchanger 51, and increases the refrigerant mass flow rate output from the compressor 10 by supplying the refrigerant to the compressor 10 through the injection flow path 50. As a result, the cooling capacity of the refrigeration cycle apparatus 1 can be improved. [Variation 1] In the above-described embodiment, the evaporator 40 is a flat-tube heat exchanger. However, the condenser 20 may also be a flat-tube heat exchanger in addition to the evaporator 40. By using a flat-tube heat exchanger for the condenser 20, the volume of the refrigerant circuit 2 can be reduced, thereby further increasing subcooling. [Modification 2] In the above embodiment, the refrigeration cycle apparatus 1 is mainly used as an air conditioner for room cooling.

[0043] However, the refrigeration cycle apparatus 1 may also be used as an air conditioner for room heating. When the refrigeration cycle apparatus 1 is used as an air conditioner for room heating, it is assumed that the condenser 20 is disposed indoors and the evaporator 40 is disposed outdoors. In this case, the amount of refrigerant drawn into the compressor 10 can be increased by increasing the flow rate of the injection flow path 50, thereby improving the heating capacity. [Variation 3] In the above-described first embodiment, the refrigerant in the flow path P2 is cooled by the internal heat exchanger 51 to increase the degree of supercooling at the outlet of the condenser 20. However, the refrigerant in the flow path P2 may be further supercooled by adding an additional cooling device that cools the refrigerant in the flow path P2.

[0044] 4 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1A according to this modification. The refrigeration cycle apparatus 1A is configured by adding a cooling device 60 that cools the refrigerant in the flow path P2 to the above-described refrigeration cycle apparatus 1.

[0045] The cooling device 60 is a refrigerant circuit in which a refrigerant separate from the refrigerant flowing through the refrigerant circuit 2 circulates. The cooling device 60 includes a compressor 61, a condenser 62, an expansion valve 63, and a heat exchanger 64. The heat exchanger 64 is configured to exchange heat between the refrigerant in the flow path P2 of the refrigerant circuit 2 and the refrigerant in the cooling device 60. By adding such a cooling device 60, the refrigerant in the flow path P2 of the refrigerant circuit 2 can be further cooled by the cooling device 60. As a result, the subcooling of the refrigerant at the outlet of the condenser 20 can be further increased.

[0046] 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.

[0047] 1, 1A refrigeration cycle device, 2 refrigerant circuit, 10, 61 compressor, 10a intermediate pressure section, 20, 62 condenser, 30, 63 expansion valve, 40 evaporator, 50 injection flow path, 51 internal heat exchanger, 52 injection expansion valve, 53 branch section, 60 cooling device, 64 external heat exchanger, 100 control device, 101 CPU, 102 memory, P1 to P4 flow paths.

Claims

1. A refrigeration cycle device comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve, and an evaporator, and configured to circulate a refrigerant in this order by operation of the compressor; and a control device for controlling the compressor, wherein the refrigerant circuit further comprises: an injection flow path that connects the compressor to a branching portion provided in a flow path between the condenser and the expansion valve and supplies refrigerant from the branching portion to the compressor; and an internal heat exchanger that is provided between the condenser and the branching portion and is configured to cool the refrigerant flowing between the condenser and the branching portion with the refrigerant flowing through the injection flow path, wherein the refrigerant is a flammable refrigerant having a higher boiling point than R32, and the evaporator is a flat tube heat exchanger.

2. The refrigeration cycle device according to claim 1, wherein the control device changes the rotation speed of the compressor so as to maximize the output of the compressor.

3. A refrigeration cycle apparatus as described in claim 2, wherein the control device periodically calculates a refrigerant mass flow rate output by the compressor based on a capacity of the compressor and a density of the refrigerant sucked into the compressor, and changes the rotation speed of the compressor in a direction that increases the refrigerant mass flow rate.

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

5. The refrigeration cycle apparatus according to claim 1, further comprising a cooling device configured to cool the refrigerant flowing between the condenser and the expansion valve.

6. A refrigeration cycle device according to any one of claims 1 to 5, wherein the condenser is disposed outside the room, and the evaporator is disposed inside the room.

7. A refrigeration cycle device according to any one of claims 1 to 5, wherein the condenser is disposed indoors, and the evaporator is disposed outdoors.

Images