Refrigeration cycle device

Abstract

[Problem] To improve the operating efficiency of a refrigeration cycle device. [Solution] This refrigeration cycle device comprises an economizer circuit that reduces the pressure of a refrigerant branched from a refrigerant path between a condenser and an evaporator by means of an economizer expansion valve, and causes the refrigerant to merge with a refrigerant of which the pressure has been reduced to an intermediate pressure in a compressor, a supercooling circuit that reduces the pressure of the refrigerant branched from the refrigerant path between the condenser and the evaporator by means of a supercooling expansion valve and causes the refrigerant to merge with a refrigerant on a suction side of the compressor, a first temperature sensor that detects a first refrigerant temperature of the refrigerant discharged from the compressor, and a control unit for adjusting the opening degree of the economizer expansion valve and the opening degree of the supercooling expansion valve, wherein the control unit sets the opening degree of the supercooling expansion valve to a first opening degree when the rotational speed of the compressor is a first rotational speed, sets the opening degree of the supercooling expansion valve to a second opening degree greater than the first opening degree when the rotational speed is a second rotational speed greater than the first rotational speed, and controls the opening degree of the economizer expansion valve in accordance with the first refrigerant temperature.

Description

Refrigeration cycle equipment

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

[0002] In recent years, issues of energy depletion and global warming have been attracting attention, and refrigerants used in refrigerators and air conditioners are desired to have a high COP (Coefficient of Performance) and a low environmental impact. In particular, the issue of global warming has attracted a lot of attention, and refrigerants that have a low direct impact, i.e., a low GWP (Global Warming Potential), and a low indirect impact, i.e., energy consumption, due to leakage are required.

[0003] Known means for improving the performance of refrigerators and the like include economizers, which can reduce the input power of the compressor, and subcooling bypass technologies, which can reduce the pressure loss mainly on the low-pressure side.

[0004] JP 2009-204244 A

[0005] There has been a desire to improve operational efficiency by using an economizer and subcooling bypass.

[0006] The present invention has been made in view of the above problems, and has as its object to improve the operating efficiency of a refrigeration cycle device.

[0007] The present invention is a refrigeration cycle device comprising: an economizer circuit in which refrigerant branched from a refrigerant path between a condenser and an evaporator is decompressed by an economizer expansion valve and merged with refrigerant decompressed to an intermediate pressure in a compressor; a subcooling circuit in which refrigerant branched from the refrigerant path between the condenser and the evaporator is decompressed by a subcooling expansion valve and merged with refrigerant on the suction side of the compressor; a first temperature sensor that detects a first refrigerant temperature of the refrigerant discharged from the compressor; and a control unit that adjusts the opening of the economizer expansion valve and the opening of the subcooling expansion valve, wherein the control unit sets the opening of the subcooling expansion valve to a first opening when the rotation speed of the compressor is a first rotation speed, and sets the opening of the subcooling expansion valve to a second opening greater than the first opening when the rotation speed is a second rotation speed greater than the first rotation speed, and controls the opening of the economizer expansion valve in accordance with the first refrigerant temperature.

[0008] Another aspect of the present invention is a refrigeration cycle apparatus including: an economizer circuit that reduces the pressure of refrigerant branched from a refrigerant path between a condenser and an evaporator using an economizer expansion valve and merges the refrigerant with refrigerant that has been reduced to an intermediate pressure in a compressor; a subcooling circuit that reduces the pressure of refrigerant branched from the refrigerant path between the condenser and the evaporator using a subcooling expansion valve and merges the refrigerant with refrigerant on the suction side of the compressor; a first temperature sensor that detects a first refrigerant temperature of refrigerant discharged from the compressor; a second temperature sensor that detects a second refrigerant temperature of refrigerant between the subcooling circuit and the evaporator; and a control unit that adjusts the aperture of the economizer expansion valve and the subcooling expansion valve, wherein the control unit controls the aperture of the subcooling expansion valve based on the second refrigerant temperature and controls the aperture of the economizer expansion valve based on the first refrigerant temperature, and a mixed refrigerant having a temperature gradient is used as the refrigerant.

[0009] According to the present invention, the operating efficiency of a refrigeration cycle device can be improved.

[0010] 1 is a diagram showing a refrigeration cycle device according to a first embodiment. 2 is a flowchart showing control according to the first embodiment. 3 is a diagram showing a refrigeration cycle device according to a second embodiment. 4 is a flowchart showing control according to the second embodiment. 5 is a ph diagram. 6 is a diagram showing an economizer circuit, a subcooling circuit, and a common heat exchanger according to a third embodiment. 7 is a diagram showing an economizer circuit, a subcooling circuit, and a common heat exchanger in a case where bypass is dominant. 8 is a diagram showing an economizer circuit, a subcooling circuit, and a common heat exchanger according to a fourth embodiment. 9 is a diagram showing an economizer circuit, a subcooling circuit, and a common heat exchanger in a case where bypass is dominant.

[0011] (First embodiment) Fig. 1 is a diagram showing a refrigeration cycle apparatus 1 according to a first embodiment. The refrigeration cycle apparatus 1 is used in a refrigerator or an air conditioner. In the refrigeration cycle apparatus 1 according to this embodiment, the refrigerant is a mixed refrigerant having a temperature gradient. An example of such a mixed refrigerant is R448A. However, the refrigerant may be a single refrigerant.

[0012] The refrigeration cycle apparatus 1 includes a condenser (heat source side heat exchanger) 11, an expansion valve 12, an evaporator (load side heat exchanger) 13, a compressor 14, an economizer circuit 20, and a subcooling circuit 30. The refrigerant exchanges heat with the surroundings in the condenser 11 and changes from a high-temperature gas to a liquid. The refrigerant then passes through the economizer circuit 20 and the subcooling circuit 30, is decompressed in the expansion valve 12, and exchanges heat with the surroundings in the evaporator 13 and changes from the liquid to a low-temperature, low-pressure gas. The refrigerant is then compressed in the compressor 14 and discharged from the compressor 14 as a high-temperature, high-pressure gas.

[0013] In the economizer circuit 20, an economizer heat exchanger 21 is provided in the mainstream path 101, and an economizer expansion valve 22 is provided in the first branch path 102. A portion of the liquid refrigerant that has undergone heat exchange in the condenser 11 flows through the first branch path 102 and is reduced in pressure to the intermediate pressure of the compressor 14 by the economizer expansion valve 22. The reduced-pressure liquid refrigerant is vaporized by heat exchange with mainstream refrigerant in the economizer heat exchanger 21, and flows into the intermediate portion of the compressor 14 via the injection path 103. In the compressor 14, the gas refrigerant flowing through the mainstream path 101 and the gas refrigerant that has been reduced in pressure to the intermediate pressure and that has flowed in from the injection path 103 are merged. This reduces the amount of refrigerant drawn into the mainstream of the compressor 14, thereby reducing the input (power) of the compressor 14.

[0014] In the subcooling circuit 30, a subcooling heat exchanger 31 is provided in the mainstream path 101, and a subcooling expansion valve 32 is provided in the second branch path 104. A portion of the refrigerant that has exchanged heat in the condenser 11 and passed through the mainstream path 101 of the economizer circuit 20 flows through the second branch path 104 and is decompressed to the suction pressure of the compressor 14 by the subcooling expansion valve 32. The decompressed refrigerant vaporizes by heat exchange with mainstream refrigerant in the subcooling heat exchanger 31 and flows into the piping on the suction side of the compressor 14 (the piping of the mainstream path 101) via the subcooling bypass 105. The gas refrigerant in the subcooling bypass 105 merges with the refrigerant flowing through the mainstream path 101 at the suction side of the compressor 14. This reduces the refrigerant flow rate flowing through the mainstream via the expansion valve 12 and the load-side heat exchanger 13, thereby reducing pressure loss.

[0015] The refrigeration cycle apparatus 1 of this embodiment uses both the economizer circuit 20 and the subcooling circuit 30. The refrigeration cycle apparatus 1 of this embodiment includes a control unit 40 that controls the aperture of the economizer expansion valve 22 to control the economizer circuit 20, and further controls the aperture of the subcooling expansion valve 32 to control the subcooling circuit 30. Furthermore, in the refrigeration cycle apparatus 1, a first temperature sensor 51 is provided in the piping between the compressor 14 and the condenser 11 on the discharge side of the compressor 14. The control unit 40 acquires a first refrigerant temperature, which is the temperature of the refrigerant discharged from the compressor 14, detected by the first temperature sensor 51, and performs control based on the first refrigerant temperature.

[0016] 2 is a flowchart showing control by the control unit 40. When control starts, first, in step S100, the control unit 40 acquires the rotation speed of the compressor 14. Next, in step S102, the control unit 40 sets the opening degree of the subcooling expansion valve 32 based on the rotation speed. Specifically, the control unit 40 controls the opening degree of the subcooling expansion valve 32 so that it increases as the rotation speed increases. For example, the control unit 40 increases the opening degree of the subcooling expansion valve 32 by a fixed amount each time the rotation speed increases by a fixed amount.

[0017] The higher the rotation speed of the compressor 14, the greater the pressure loss. Therefore, in this embodiment, the higher the rotation speed, the greater the opening of the subcooling expansion valve 32 in the subcooling circuit 30, and the amount of refrigerant passing through the subcooling bypass 105, thereby reducing the refrigerant flow rate passing through the load-side heat exchanger 13. This reduces the pressure loss.

[0018] In addition, the control unit 40 sets the opening of the subcooling expansion valve 32 to a first opening when the rotation speed is a first rotation speed, and sets the opening of the subcooling expansion valve 32 to a second opening that is greater than the first opening when the rotation speed is a second rotation speed that is greater than the first rotation speed, and the specific control for this is not limited to the embodiment.

[0019] Next, in step S104, the control unit 40 acquires the first refrigerant temperature from the first temperature sensor 51. Next, in step S106, the control unit 40 compares the first refrigerant temperature with a first temperature threshold. The first temperature threshold is assumed to be set in advance. When liquid refrigerant flows into the subcooling bypass 105, the discharge temperature of the compressor 14 decreases. This first temperature threshold is a temperature for detecting such a state.

[0020] If the first refrigerant temperature is lower than the first temperature threshold (Y in step S106), the control unit 40 reduces the opening of the economizer expansion valve 22 (step S108), and then the process proceeds to step S112. In step S108, the control unit 40 reduces the opening of the economizer expansion valve 22 by, for example, a certain amount.

[0021] On the other hand, if the first refrigerant temperature is equal to or higher than the first temperature (N in step S106), the control unit 40 sets the aperture of the economizer expansion valve 22 in accordance with the aperture of the subcooling expansion valve 32 (step S110), and then proceeds to step S112. As the rotation speed of the compressor 14 decreases, the aperture of the subcooling expansion valve 32 is set to a smaller value, and accordingly, the aperture of the economizer expansion valve 22 is set to a larger value. In this way, the aperture of the economizer expansion valve 22 is controlled based on the aperture of the subcooling expansion valve 32.

[0022] In step S112, the control unit 40 determines whether or not to end the control. If the air conditioning operation has ended, the control unit 40 determines to end the control. If the control unit 40 determines to end the control (Y in step S112), the control unit 40 ends the control. If the control unit 40 determines not to end the control (N in step S112), the control unit 40 proceeds to step S100 and continues the control.

[0023] As described above, to reduce pressure loss, the aperture of the subcooling expansion valve 32 of the subcooling circuit 30 is adjusted according to the rotation speed of the compressor 14. However, if the aperture of the subcooling expansion valve 32 becomes too large as the rotation speed of the compressor 14 increases, liquid refrigerant flows into the subcooling bypass 105, leading to a decrease in performance of the subcooling circuit 30. To prevent a decrease in performance of the subcooling circuit 30, it is necessary to reduce the aperture of the economizer expansion valve 22. This reduces the amount of refrigerant flowing through the injection flow path 103, reduces the cooling of the refrigerant flowing through the mainstream path 101 of the economizer circuit 20, raises the temperature of the mainstream path 101 flowing into the subcooling heat exchanger 31, and increases the heat exchange amount in the subcooling heat exchanger 31.

[0024] Liquid return in the subcooling bypass 105 manifests as a decrease in the discharge temperature from the compressor 14. Therefore, in this embodiment, the control unit 40 monitors the first refrigerant temperature, which corresponds to the discharge temperature, and reduces the opening of the economizer expansion valve 22 when the first refrigerant temperature is equal to or lower than the first temperature threshold. This reduces the cooling of the refrigerant in the mainstream path 101 of the economizer circuit 20, and increases the temperature of the refrigerant flowing into the subcooling circuit 30. This increases the heat exchange amount in the subcooling heat exchanger 31.

[0025] Furthermore, when the rotation speed of the compressor 14 is relatively low, the pressure loss reduction effect is small. Therefore, in this case, the control unit 40 controls the subcooling expansion valve 32 to be opened less, while at the same time increasing the opening of the economizer expansion valve 22. In other words, when the rotation speed of the compressor 14 is relatively low, the injection amount is increased. This makes it possible to increase the effect of reducing the input of the compressor 14 by the economizer circuit 20.

[0026] As described above, the refrigeration cycle apparatus 1 of the first embodiment adjusts the opening degree of the economizer expansion valve 22 and the opening degree of the subcooling expansion valve 32. This optimizes the effect of reducing pressure loss by the subcooling circuit 30 and the effect of reducing the input power of the compressor 14 by the economizer circuit 20, thereby improving the operating efficiency of the refrigeration cycle apparatus 1.

[0027] Second Embodiment Next, with reference to FIG. 3 , a refrigeration cycle apparatus 2 according to a second embodiment will be described, focusing on differences from the refrigeration cycle apparatus 1 according to the first embodiment. The refrigeration cycle apparatus 2 according to the second embodiment includes a second temperature sensor 52 in addition to a first temperature sensor 51. The second temperature sensor 52 is installed in a pipe between the subcooling circuit 30 and the expansion valve 12 and detects a second refrigerant temperature, which is the temperature of the refrigerant flowing between the subcooling circuit 30 and the expansion valve 12. In addition, in the refrigeration cycle apparatus 2 according to the second embodiment, the refrigerant is a mixed refrigerant with a temperature gradient. An example of such a mixed refrigerant is R448A.

[0028] In the refrigeration cycle device 2 of this embodiment, the control unit 40 controls the opening degree of the subcooling expansion valve 32 based on the second refrigerant temperature detected by the second temperature sensor 52, and further controls the opening degree of the economizer expansion valve 22 based on the first refrigerant temperature.

[0029] FIG. 4 is a flowchart showing control by the control unit 41 of the refrigeration cycle apparatus 2 according to the second embodiment. When control is initiated, first, in step S200, the control unit 41 acquires the second refrigerant temperature from the second temperature sensor 52. Next, in step S202, the control unit 41 sets the aperture of the subcooling expansion valve 32 based on the second refrigerant temperature. Specifically, when the second refrigerant temperature is higher than a target refrigerant temperature, the control unit 41 increases the aperture of the subcooling expansion valve 32. For example, the control unit 41 increases the aperture of the subcooling expansion valve 32 by a certain amount. Here, the target refrigerant temperature is set by the control unit 41 according to the operating state, etc. The control unit 41 may also adjust the aperture of the subcooling expansion valve 32 according to the difference between the target refrigerant temperature and the second refrigerant temperature.

[0030] Next, in step S204, the control unit 41 acquires the first refrigerant temperature from the first temperature sensor 51. Next, in step S206, the control unit 41 compares the first refrigerant temperature with a first temperature threshold. The first temperature threshold is assumed to be set in advance. If the first refrigerant temperature is lower than the first temperature threshold (Y in step S206), the control unit 41 reduces the opening of the economizer expansion valve 22 (step S208), and then proceeds to step S212. In step S208, the control unit 41 reduces the opening of the economizer expansion valve 22 by, for example, a certain amount.

[0031] On the other hand, if the first refrigerant temperature is equal to or higher than the first temperature threshold value (N in step S206), the control unit 41 sets the aperture of the economizer expansion valve 22 in accordance with the aperture of the subcooling expansion valve 32 (step S210), and then proceeds to step S212. As the rotation speed of the compressor 14 decreases, a smaller value is set as the aperture of the subcooling expansion valve 32, and in response, a larger value is set as the aperture of the economizer expansion valve 22.

[0032] In step S212, the control unit 41 determines whether or not to end the control. If the air conditioning operation has ended, the control unit 41 determines to end the control. If the control unit 41 determines to end the control (Y in step S212), the control unit 41 ends the control. If the control unit 41 determines not to end the control (N in step S212), the control unit 41 proceeds to step S100 and continues the control.

[0033] In the refrigeration cycle device 2 of this embodiment, a mixed refrigerant with a temperature gradient is used as the refrigerant. By lowering the liquid temperature of such a non-azeotropic mixed refrigerant, the temperature of the refrigerant flowing into the evaporator 13 can be lowered, and the temperature difference with the air that is the target of heat exchange can be increased, thereby increasing the amount of heat exchange.

[0034] FIG. 5 is a pH diagram for R448A. With R448A, the refrigerant temperature flowing into the evaporator 13 is −42°C, but can be lowered to −46°C. Thus, with a mixed refrigerant, the evaporation temperature can be lowered even if the evaporation pressure remains unchanged, improving the performance of the refrigeration cycle device 2. On the other hand, for example, when adjusting the heat exchange amount to the same as that at an evaporation temperature of −42°C, the inflow refrigerant temperature is lowered to −46°C, but the average refrigerant temperature is set to −42°C, allowing the evaporation pressure to be increased. In other words, the pressure difference during the compression process can be reduced, thereby reducing the input power of the compressor 14.

[0035] The subcooling heat exchanger 31 has a greater effect in lowering the temperature of the liquid refrigerant than the economizer heat exchanger 21. Therefore, as described above, the refrigeration cycle apparatus 2 of this embodiment adjusts the aperture of the subcooling expansion valve 32 in accordance with the second refrigerant temperature, which is the temperature of the liquid refrigerant. Meanwhile, also in this embodiment, if the aperture of the subcooling expansion valve 32 becomes too large, liquid refrigerant flows into the subcooling bypass 105, resulting in a decrease in the discharge temperature from the compressor 14. Therefore, similar to the control in the first embodiment, the control unit 41 reduces the aperture of the economizer expansion valve 22 when the first refrigerant temperature, which corresponds to the discharge temperature, is equal to or lower than the first temperature threshold.

[0036] As described above, the refrigeration cycle apparatus 2 of the second embodiment adjusts the opening degree of the economizer expansion valve 22 and the opening degree of the subcooling expansion valve 32. This optimizes the effect of reducing pressure loss by the subcooling circuit 30 and the effect of reducing power consumption of the compressor 14 by the economizer circuit 20, thereby improving the operating efficiency of the refrigeration cycle apparatus 2.

[0037] Third Embodiment Next, a refrigeration cycle apparatus 3 according to a third embodiment will be described, focusing on differences from the other embodiments. The refrigeration cycle apparatus 3 according to the third embodiment further includes a common heat exchanger that is shared by the economizer circuit and the subcooling circuit. Simply adjusting the opening degrees of the economizer heat exchanger 21 and the subcooling heat exchanger 31 limits the flow rate. On the other hand, increasing the size of these heat exchangers 21 and 31 undesirably increases the overall size of the refrigeration cycle apparatus 3. Therefore, the refrigeration cycle apparatus 3 according to this embodiment includes a common heat exchanger 400 that can be used as both the economizer heat exchanger and the subcooling heat exchanger.

[0038] 6 is a diagram illustrating an economizer circuit 200, a subcooling circuit 300, and a common heat exchanger 400 in a refrigeration cycle apparatus 3 according to a third embodiment. A first branch point 121, a second branch point 122, and a third branch point 123 are provided in this order in the main path 101.

[0039] An economizer circuit 200 is provided in the mainstream path 101 downstream of the third branch point 123. The third branch path 133 branched at the third branch point 123 further branches. As a result, the mainstream refrigerant passes through the economizer heat exchanger 21, the common heat exchanger 400, and the subcooling heat exchanger 31. The refrigerant that has passed through these heat exchangers then merges and flows to the load-side heat exchanger 13.

[0040] The first branch path 131, which branches off at the first branch point 121, is provided with a subcooling expansion valve 32, and a fourth branch point 124 is provided downstream thereof. One of the paths branching off at the fourth branch point 124 connects to the subcooling bypass 105 via the subcooling heat exchanger 31. The other path is provided with a first check valve 401, then passes through the common heat exchanger 400, and further branches off at a fifth branch point 125. One of the paths is provided with a second on-off valve 412, which connects between the subcooling heat exchanger 31 and the subcooling bypass 105 downstream thereof. The other path is provided with a second check valve 402, which connects between the economizer heat exchanger 21 and the injection path 103 downstream thereof.

[0041] The second branch path 132 branching off at the second branch point 122 is provided with an economizer expansion valve 22, and downstream of that is provided a sixth branch point 126. One path branching off at the sixth branch point 126 is connected to the injection path 103 via the economizer heat exchanger 21. The other path is provided with a first on-off valve 411, and downstream of that is connected between the first check valve 401 and the common heat exchanger 400.

[0042] When the rotation speed of the compressor 14 is equal to or lower than a preset rotation speed threshold, the control unit 40 determines that the economizer is dominant and uses the common heat exchanger 400 as an economizer heat exchanger. Here, it is assumed that the rotation speed threshold is set in advance. As shown in FIG. 6 , the control unit 40 closes the first check valve 401 and opens the first on-off valve 411. In addition, the control unit 40 closes the second on-off valve 412 and opens the second check valve 402.

[0043] In this case, the refrigerant on the mainstream path 101 side flows in parallel into the economizer heat exchanger 21, the subcooling heat exchanger 31, and the common heat exchanger 400 that functions as an economizer heat exchanger. The refrigerant on the mainstream path 101 side that has passed through these heat exchangers is cooled in the heat exchangers 21, 31, and 400, and after joining together, flows toward the load-side heat exchanger 13 side, i.e., toward the expansion valve 12.

[0044] Meanwhile, the refrigerant decompressed by the economizer expansion valve 22 branches at a sixth branch point 126 and flows in parallel into the economizer heat exchanger 21 and the common heat exchanger 400, which also functions as an economizer heat exchanger. The flowing refrigerant is heated in each heat exchanger 21, 400, and then injected. The refrigerant decompressed by the subcooling expansion valve 32 evaporates in the subcooling heat exchanger 31 and is bypassed to the suction side of the compressor 14 via the subcooling bypass 105. In this way, even when a large amount of refrigerant flows through the economizer circuit 200, the common heat exchanger 400 functions as an economizer heat exchanger in addition to the economizer heat exchanger 21, thereby preventing insufficient evaporation.

[0045] Furthermore, when the rotation speed of the compressor 14 is greater than the rotation speed threshold, the control unit 40 determines that the bypass is dominant and uses the common heat exchanger 400 as a subcooling heat exchanger. Specifically, as shown in Fig. 7 , the control unit 40 opens the first check valve 401 and closes the first on-off valve 411. Furthermore, the control unit 40 opens the second on-off valve 412 and closes the second check valve 402.

[0046] In this case, a portion of the high-pressure refrigerant flowing out of the condenser 11 flows toward the economizer expansion valve 22 and the subcooling expansion valve 32. The remaining refrigerant on the main path 101 side flows in parallel into the economizer heat exchanger 21, the subcooling heat exchanger 31, and the common heat exchanger 400 that functions as a subcooling heat exchanger. The refrigerant that has passed through these heat exchangers is cooled in the heat exchangers 21, 31, and 400, merges, and then flows toward the load-side heat exchanger 13, i.e., toward the expansion valve 12.

[0047] Meanwhile, the refrigerant decompressed by the economizer expansion valve 22 flows into the economizer heat exchanger 21, where it is heated, evaporated, and injected. The refrigerant decompressed by the subcooling expansion valve 32 branches at the fourth branch point 124 and flows in parallel into the subcooling heat exchanger 31 and the common heat exchanger 400, which functions as a subcooling heat exchanger. The flowing refrigerant is heated and evaporated in these heat exchangers 31 and 400, and bypassed to the suction side of the compressor 14 via the subcooling bypass 105. In this way, even when a large amount of refrigerant flows through the subcooling circuit 300, the common heat exchanger 400 functions as a subcooling heat exchanger in addition to the subcooling heat exchanger 31, preventing liquid refrigerant from flowing through the subcooling bypass 105.

[0048] As described above, the common heat exchanger 400 can be switched for use, and therefore the operating efficiency of the refrigeration cycle device 3 can be improved.

[0049] (Fourth embodiment) Next, a refrigeration cycle apparatus 4 according to a fourth embodiment will be described, focusing on differences from the other embodiments. The refrigeration cycle apparatus 4 according to the fourth embodiment includes a common heat exchanger, similar to the refrigeration cycle apparatus 3 according to the third embodiment. The refrigeration cycle apparatus 3 according to the third embodiment is configured to switch the low-pressure side circuit between an injection flow path and a subcooling bypass. In contrast, the refrigeration cycle apparatus 4 according to the fourth embodiment also switches the high-pressure side circuit between an injection flow path and a subcooling bypass.

[0050] 8 is a diagram illustrating the economizer circuit 210, the subcooling circuit 310, and the common heat exchanger 410 in the refrigeration cycle apparatus 4 according to the fourth embodiment. An eleventh branch point 521 and a twelfth branch point 522 are provided in this order in the main path 501.

[0051] The economizer circuit 210 is provided in the mainstream path 501 downstream of the twelfth branch point 522. The twelfth branch path 532 branching off at the twelfth branch point 522 passes through the common heat exchanger 410 and then merges with the mainstream path 501 at a position between the economizer circuit 210 and the subcooling circuit 310. In this path, an eleventh on-off valve 611 is provided between the twelfth branch point 522 and the common heat exchanger 410. In addition, in this path, a thirteenth branch path 523 is provided on the path on the outlet side of the common heat exchanger 410. One of the paths branching off at the thirteenth branch path 523 is provided with a twelfth check valve 602, which connects downstream to the mainstream path 501 on the outlet side of the economizer heat exchanger 21. The other path is provided with a twelfth on-off valve 612, which connects downstream to the mainstream path 501 on the outlet side of the subcooling heat exchanger 31.

[0052] Meanwhile, an eleventh branch path 531 branching off at an eleventh branch point 521 is provided with an economizer expansion valve 22, and a fourteenth branch point 524 is provided downstream thereof. One of the paths branching off at the fourteenth branch point 524 passes through the economizer heat exchanger 21 and connects to the injection path 103. The other path is provided with a thirteenth on-off valve 613 and connects downstream thereof to the common heat exchanger 410. A fifteenth branch point 525 is provided on the path on the outlet side of the common heat exchanger 410. One of the paths branching off at the fifteenth branch point 525 is provided with a fourteenth check valve 604 and connects downstream thereof between the economizer heat exchanger 21 and the injection path 103. The other path is provided with a fourteenth on-off valve 614 and connects downstream thereof between the subcooling heat exchanger 31 and the subcooling bypass 105.

[0053] A sixteenth branch point 526 and a seventeenth branch point 527 are provided in this order in the mainstream path 501 on the outlet side of the economizer heat exchanger 21. The mainstream path 501 passing through the sixteenth branch point 526 and the seventeenth branch point 527 further passes through the subcooling heat exchanger 31 and is connected to the load-side heat exchanger 13, i.e., the expansion valve 12. A thirteenth branch path 533 branched off at the seventeenth branch point 527 is provided with an eleventh check valve 601, and is connected downstream thereof to the twelfth branch path 532.

[0054] A subcooling expansion valve 32 is provided in a 14th branch path 534 branching off at a 16th branch point 526, and an 18th branch point 528 is provided downstream thereof. One path branching off at the 18th branch point 528 passes through a subcooling heat exchanger 31 and connects to a subcooling bypass 105. A 13th check valve 603 is provided in the other path, and downstream thereof, it connects between a 13th on-off valve 613 and the common heat exchanger 410.

[0055] When the rotation speed of the compressor 14 is equal to or lower than a preset rotation speed threshold, the control unit 40 determines that the economizer is dominant and uses the common heat exchanger 410 as an economizer heat exchanger. Specifically, as shown in Fig. 8 , the control unit 40 closes the eleventh check valve 601 and the thirteenth check valve 603 and opens the twelfth check valve 602 and the fourteenth check valve 604. In addition, the control unit 40 opens the eleventh on-off valve 611 and the thirteenth on-off valve 613 and closes the twelfth on-off valve 612 and the fourteenth on-off valve 614.

[0056] In this case, a portion of the high-pressure refrigerant flowing out of the condenser 11 branches off at an eleventh branch point 521 to an eleventh branch path 531 as refrigerant for injection. The remaining refrigerant flows in parallel into the economizer heat exchanger 21 and the common heat exchanger 410, which also functions as an economizer heat exchanger. The refrigerants flowing into the economizer heat exchanger 21 and the common heat exchanger 410 merge after heat exchange and cooling. A portion of the merged refrigerant branches off at a sixteenth branch point 526 to a fourteenth branch path 534 as refrigerant for subcooling, is cooled in the subcooling heat exchanger 31, and flows to the load side.

[0057] Meanwhile, the refrigerant decompressed by the economizer expansion valve 22 flows in parallel into the economizer heat exchanger 21 and the common heat exchanger 410 that also functions as an economizer heat exchanger, where it is heated and evaporated in the heat exchangers and then injected. Also, the refrigerant decompressed by the subcooling expansion valve 32 evaporates in the subcooling heat exchanger 31 and is bypassed to the suction side of the compressor 14. With this configuration, the economizer circuit and the subcooling circuit can be switched even on the high-pressure side.

[0058] When the rotation speed of the compressor 14 is greater than the rotation speed threshold, the control unit 40 determines that the bypass is dominant and uses the common heat exchanger 400 as a subcooling heat exchanger. Specifically, as shown in Fig. 9 , the control unit 40 opens the eleventh check valve 601 and the thirteenth check valve 603 and closes the twelfth check valve 602 and the fourteenth check valve 604. In addition, the control unit 40 closes the eleventh on-off valve 611 and the thirteenth on-off valve 613 and opens the twelfth on-off valve 612 and the fourteenth on-off valve 614.

[0059] In this case, the high-pressure refrigerant flowing out of the condenser 11 flows only into the economizer heat exchanger 21. The refrigerant flowing out of the economizer heat exchanger 21 flows in parallel into the subcooling heat exchanger 31 and the common heat exchanger 410 functioning as a subcooling heat exchanger. The refrigerant decompressed by the economizer expansion valve 22 enters the economizer heat exchanger 21, where it is heated and evaporated in the heat exchanger, and then injected. On the other hand, the refrigerant decompressed by the subcooling expansion valve 32 flows into the subcooling heat exchanger 31 and the common heat exchanger 410 functioning as a subcooling heat exchanger, where it evaporates in the heat exchanger, and is bypassed to the suction side of the compressor 14.

[0060] As described above, in the fourth embodiment as well, the common heat exchanger 400 can be switched and used, so that the operating efficiency of the refrigeration cycle device 4 can be improved.

[0061] It should be noted that the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims, such as applying a modified example of one embodiment to another embodiment.

[0062] In the first modified example, the timing of each process performed by the control unit is not limited to that described in the embodiment. For example, the process of acquiring the rotation speed of the compressor 14 and the process of acquiring the first refrigerant temperature (the compressor discharge temperature) may be performed simultaneously, or the first refrigerant temperature may be acquired first.

[0063] As a second modification, the configurations of the refrigeration cycle apparatuses including the common heat exchanger described in the third and fourth embodiments are merely examples. The refrigeration cycle apparatuses including the common heat exchanger may be configured to be able to switch between different common heat exchangers, and the specific configuration for this is not limited to the embodiments.

[0064] 1 to 4 Air conditioner 11 Heat source side heat exchanger 12 Expansion valve 13 Load side heat exchanger 14 Compressor 20, 200, 210 Economizer circuit 21 Economizer heat exchanger 22 Economizer expansion valve 30, 300, 310 Subcooling circuit 31 Subcooling heat exchanger 32 Subcooling expansion valve 40, 41 Control unit 51 First temperature sensor 52 Second temperature sensor 101 Main path 102 First branch path 103 Injection path 104 Second branch path 105 Subcooling bypass 400, 410 Common heat exchanger

Claims

1. A refrigeration cycle device comprising: an economizer circuit which reduces the pressure of refrigerant branched from a refrigerant path between a condenser and an evaporator using an economizer expansion valve, and merges the refrigerant with refrigerant reduced to an intermediate pressure in a compressor; a subcooling circuit which reduces the pressure of refrigerant branched from the refrigerant path between the condenser and the evaporator using a subcooling expansion valve, and merges the refrigerant with the refrigerant on the suction side of the compressor; a first temperature sensor which detects a first refrigerant temperature of the refrigerant discharged from the compressor; and a control unit which adjusts the opening of the economizer expansion valve and the opening of the subcooling expansion valve, wherein the control unit sets the opening of the subcooling expansion valve to a first opening when the rotation speed of the compressor is a first rotation speed, and sets the opening of the subcooling expansion valve to a second opening greater than the first opening when the rotation speed is a second rotation speed greater than the first rotation speed, and controls the opening of the economizer expansion valve in accordance with the first refrigerant temperature.

2. The refrigeration cycle device according to claim 1, wherein the control unit increases the opening degree of the subcooling expansion valve as the rotation speed increases.

3. The refrigeration cycle device according to claim 1, wherein the control unit reduces the opening of the economizer expansion valve when the first refrigerant temperature is lower than a first temperature threshold value.

4. The refrigeration cycle apparatus of claim 1, wherein the economizer circuit and the subcooling circuit are connected to a common heat exchanger, and the control unit causes the refrigerant flowing through the common heat exchanger to merge with the refrigerant on the suction side of the compressor when the rotational speed is a third rotational speed, and causes the refrigerant flowing through the common heat exchanger to merge with the intermediate-pressure refrigerant of the compressor when the rotational speed is a fourth rotational speed lower than the third rotational speed.

5. A refrigeration cycle device according to claim 1, wherein the refrigerant is a mixed refrigerant having a temperature gradient.

6. A refrigeration cycle device comprising: an economizer circuit which reduces the pressure of a refrigerant branched from a refrigerant path between a condenser and an evaporator using an economizer expansion valve, and merges the refrigerant with refrigerant reduced to an intermediate pressure in a compressor; a subcooling circuit which reduces the pressure of the refrigerant branched from the refrigerant path between the condenser and the evaporator using a subcooling expansion valve, and merges the refrigerant with the refrigerant on the suction side of the compressor; a first temperature sensor which detects a first refrigerant temperature of the refrigerant discharged from the compressor; a second temperature sensor which detects a second refrigerant temperature of the refrigerant between the subcooling circuit and the evaporator; and a control unit which adjusts the aperture of the economizer expansion valve and the aperture of the subcooling expansion valve, wherein the control unit controls the aperture of the subcooling expansion valve based on the second refrigerant temperature, and controls the aperture of the economizer expansion valve based on the first refrigerant temperature, and a mixed refrigerant with a temperature gradient is used as the refrigerant.

7. The refrigeration cycle device according to claim 6, wherein the control unit increases the opening degree of the subcooling expansion valve when the second refrigerant temperature is higher than a target refrigerant temperature.

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