Refrigeration cycle device

Abstract

Provided is a refrigeration cycle device (1) comprising a refrigerant circuit (10) and a control unit (4). The refrigerant circuit (10) is connected to a compressor (11), a first heat exchanger (13), a first expansion mechanism (14), and a second heat exchanger (15). The refrigerant circuit (10) circulates a refrigerant including R290. The control unit 4 performs first control for reducing the amount of fluid that exchanges heat with the refrigerant in at least one of the first heat exchanger (13) and the second heat exchanger (15) when the height differential pressure of the compressor (11) is not sufficient.

Description

Refrigeration Cycle Equipment

[0001] This relates to a refrigeration cycle device.

[0002] Patent Document 1 (WO 2020 / 100228) discloses that the discharge superheat degree of R290 is smaller than that of R32 (paragraph

[0079] ).

[0003] The inventors noticed that when R290 is used as the refrigerant in a refrigeration cycle system, the pressure difference between the low pressure on the suction side of the compressor and the high pressure on the discharge side is likely to be insufficient.If the pressure difference between the high and low sides of the compressor is insufficient, chattering (overturning) occurs inside the compressor, reducing the reliability of the compressor.

[0004] A refrigeration cycle apparatus according to a first aspect includes a refrigerant circuit and a control unit. The refrigerant circuit is connected to a compressor, a first heat exchanger, a first expansion mechanism, and a second heat exchanger. A refrigerant containing R290 circulates through the refrigerant circuit. When a condition occurs in which the differential pressure between the compressor and the first heat exchanger is insufficient, the control unit performs a first control to reduce the amount of fluid exchanging heat with the refrigerant in at least one of the first heat exchanger and the second heat exchanger.

[0005] According to the refrigeration cycle apparatus of the first aspect, when the differential pressure of the compressor is insufficient, a first control is performed to reduce the amount of fluid exchanging heat with the refrigerant containing R290 in at least one of the first heat exchanger and the second heat exchanger. The first control can reduce the capacity of at least one of the first heat exchanger and the second heat exchanger, in which the amount of fluid exchanging heat with the refrigerant containing R290 has been reduced. This can increase the differential pressure of the compressor, thereby improving the reliability of the compressor.

[0006] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, further comprising a first fan. The first fan sends outdoor air as a fluid to the first heat exchanger. When the above condition is met, the control unit reduces the airflow rate of the first fan.

[0007] In the refrigeration cycle apparatus of the second aspect, in the first control, the capacity of the first heat exchanger can be reduced by reducing the air volume of the first fan.

[0008] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the second aspect, wherein the control unit reduces the settable minimum rotation speed of the first fan when the above condition is met.

[0009] In the refrigeration cycle apparatus of the third aspect, in the first control, the air volume is reduced by lowering the minimum rotation speed of the first fan, so that a refrigeration cycle apparatus in which the capacity of the first heat exchanger is reduced can be easily realized.

[0010] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to the second or third aspect, wherein when the above condition is met, the control unit drives the first fan under duty control or in an operation including a zero rotation step.

[0011] In the refrigeration cycle device of the fourth aspect, in the first control, the air volume is reduced by driving the first fan using duty control or an operation including a 0 rotation step, so that a refrigeration cycle device in which the capacity of the first heat exchanger is reduced can be easily realized.

[0012] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the second aspect to the fourth aspect, wherein the control unit changes the content of control of the first fan in a stepwise manner during the first control.

[0013] In the refrigeration cycle apparatus according to the fifth aspect, the content of control of the first fan is changed in stages according to the state of the pressure difference between high and low, thereby making it possible to reduce the reduction in the airflow rate of the first fan according to the state of the pressure difference between high and low.

[0014] A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to the fifth aspect, wherein the conditions include a first condition and a second condition. The first condition is that a differential pressure between high and low in the compressor is greater than a predetermined value. The second condition is that the differential pressure between high and low in the compressor is equal to or less than a predetermined value. When the first condition is met, the control unit lowers the settable minimum rotation speed of the first fan, and when the second condition is met, the control unit drives the first fan by duty control or by an operation including a zero rotation step.

[0015] Duty control and control to drive the first heat exchanger in an operation including a 0-rotation step can reduce the capacity of the first heat exchanger more than control to lower the minimum rotation speed. Therefore, in the refrigeration cycle apparatus of the sixth aspect, control to lower the minimum rotation speed is performed when the high-low differential pressure is relatively large, and duty control or control to drive the first fan in an operation including a 0-rotation step is performed when the high-low differential pressure is relatively small. This makes it possible to reduce the reduction in the airflow rate of the first fan depending on the high-low differential pressure conditions.

[0016] A seventh aspect of the present invention is a refrigeration cycle apparatus according to any one of the first to sixth aspects, further comprising a water circuit. Water circulates through the water circuit. A second heat exchanger and a pump are connected to the water circuit. The second heat exchanger exchanges heat between the water as a fluid and the refrigerant. When the above condition is met, the control unit reduces the flow rate of the pump.

[0017] In the refrigeration cycle apparatus of the seventh aspect, in the first control, the capacity of the second heat exchanger can be reduced by reducing the flow rate of the pump.

[0018] An eighth aspect of the present invention is a refrigeration cycle apparatus according to any one of the first to sixth aspects, further comprising a second fan. The second fan sends indoor air as a fluid to the second heat exchanger. When the above condition is met, the control unit reduces the airflow rate of the second fan.

[0019] In the refrigeration cycle apparatus of the eighth aspect, in the first control, the capacity of the second heat exchanger can be reduced by reducing the air volume of the second fan.

[0020] A ninth aspect of the present invention is the refrigeration cycle apparatus of any one of the first to eighth aspects, wherein the control unit performs a heating operation. The refrigeration cycle apparatus further includes a liquid-gas heat exchanger. During the heating operation, the liquid-gas heat exchanger exchanges heat between the refrigerant flowing from the second heat exchanger to the first heat exchanger and the refrigerant flowing from the first heat exchanger to the compressor.

[0021] In the refrigeration cycle apparatus of the ninth aspect, the efficiency of the liquid-gas heat exchanger can be improved by performing the first control to ensure the high-low differential pressure of the compressor.

[0022] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to any one of the first to ninth aspects, wherein the control unit performs a heating operation and a cooling operation. The control unit performs a first control during the heating operation and the cooling operation.

[0023] In the refrigeration cycle apparatus of the tenth aspect, a refrigerant containing R290, which has a small differential pressure, is used, and therefore a problem of reduced compressor reliability occurs during heating operation in addition to cooling operation. Here, the first control is performed during heating operation and cooling operation, where the problem occurs, and therefore the reliability of the compressor can be improved during both heating operation and cooling operation.

[0024] A refrigeration cycle apparatus according to an eleventh aspect is the refrigeration cycle apparatus according to any one of the first to tenth aspects, wherein the control unit performs a heating operation. The condition is that during the heating operation, the temperature of the outdoor air is equal to or higher than a first temperature.

[0025] In the refrigeration cycle apparatus of the eleventh aspect, when the temperature of the outdoor air is equal to or higher than a first temperature during heating operation, the control unit determines that the pressure difference is insufficient and performs the first control. Thus, the first control can be performed even when the pressure difference is not detected.

[0026] A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the first to eleventh aspects, wherein the control unit performs a cooling operation under the condition that the temperature of the outdoor air is equal to or lower than a second temperature during the cooling operation.

[0027] In the refrigeration cycle apparatus of the twelfth aspect, when the outdoor air temperature is equal to or lower than the second temperature during cooling operation, the control unit determines that the pressure difference is insufficient and performs the first control. Therefore, the first control can be performed even when the pressure difference is not detected.

[0028] A thirteenth aspect of the present invention is a refrigeration cycle apparatus according to any one of the first to twelfth aspects, wherein the control unit performs a heating operation. The refrigeration cycle apparatus further includes a liquid pipe, an injection pipe, a second expansion mechanism, and an economizer heat exchanger. The liquid pipe connects the first heat exchanger and the second heat exchanger. The injection pipe branches off from the liquid pipe and is connected to the compressor. The second expansion mechanism decompresses the refrigerant passing through the injection pipe. During heating operation, the economizer heat exchanger exchanges heat between the refrigerant decompressed by the second expansion mechanism and the refrigerant flowing from the second heat exchanger to the first heat exchanger. The volume of the first heat exchanger is set to V1 (m ３ ), the volume of the economizer heat exchanger is V2 (m ３ ), the volume of the components in which the refrigerant is sealed other than the first heat exchanger and the economizer heat exchanger is V3 (m ３ ), the density of the refrigerant is D (g / m ３ ), the refrigerant filled in the refrigerant circuit is 0.5×(V1+V2)×D+0.1×V3×D or less.

[0029] In the refrigeration cycle apparatus of the thirteenth aspect, because R290 is flammable, the refrigerant charge amount is reduced for safety reasons. However, if the refrigerant charge amount is low, it is likely that the compressor will not have a high-low differential pressure, which poses a significant problem. To address this problem, the first control is performed when the high-low differential pressure is insufficient, thereby achieving both increased safety and improved compressor reliability.

[0030] A refrigeration cycle apparatus according to a fourteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the thirteenth aspect, wherein the first heat exchanger is a microchannel heat exchanger.

[0031] In the refrigeration cycle apparatus of the fourteenth aspect, the first heat exchanger is a microchannel heat exchanger, so the amount of refrigerant is small. However, if the refrigerant charge amount is small, the compressor is likely to be insufficiently pressurized, which poses a significant problem. To address this problem, the first control is performed when the pressure difference is insufficient, thereby improving the reliability of the compressor even when a microchannel heat exchanger is used.

[0032] 1 is a schematic configuration diagram of a refrigeration cycle device of a first embodiment; FIG. 2 is a control block diagram of the refrigeration cycle device of the first embodiment; FIG. 3 is a diagram showing the operation (refrigerant flow) of the refrigeration cycle device of the first embodiment in cooling operation; FIG. 4 is a diagram showing the operation (refrigerant flow) of the refrigeration cycle device of the first embodiment in heating operation; FIG. 5 is a diagram showing the control flow of first control of the refrigeration cycle device of the first embodiment; FIG. 6 is a diagram showing tipping lines of R290 and R32; FIG. 7 is a diagram showing the control flow of first control of the second embodiment; FIG. 8 is a schematic configuration diagram of a refrigeration cycle device of a third embodiment; FIG. 9 is a control block diagram of the refrigeration cycle device of the third embodiment; FIG. 10 is a diagram showing the operation (refrigerant flow) of the refrigeration cycle device of the third embodiment in cooling operation; FIG. 11 is a diagram showing the operation (refrigerant flow) of the refrigeration cycle device of the third embodiment in heating operation; FIG. 12 is a diagram showing the control flow of first control of the refrigeration cycle device of the third embodiment.

[0033] <First embodiment> (1) Overall configuration A refrigeration cycle device 1 according to one embodiment of the present disclosure shown in FIG. 1 is a device that cools or heats water circulating in a water circuit 30 by causing a refrigerant circuit 10 to perform a vapor compression refrigeration cycle, and uses this water to cool or heat a target space.

[0034] The refrigeration cycle device 1 includes a heat source unit 2 and a utilization unit 3. The heat source unit 2 and the utilization unit 3 are connected to each other. In this embodiment, there is one heat source unit 2 and one utilization unit 3.

[0035] The refrigeration cycle apparatus 1 also includes a refrigerant circuit 10, a water circuit 30, and a control unit 4. Refrigerant circulates in the refrigerant circuit 10. Water circulates in the water circuit 30. The refrigerant circuit 10 and the water circuit 30 are connected to each other. The control unit 4 performs heating operation and cooling operation.

[0036] (2) Detailed Configuration (2-1) Refrigerant Circuit The refrigerant circuit 10 is a circuit through which a refrigerant circulates during heating operation and cooling operation. The refrigerant circuit 10 is filled with a refrigerant containing R290 (propane). The refrigerant may be a single refrigerant of R290 or a mixed refrigerant of R290 and another refrigerant. The refrigerant also contains refrigerant oil. The refrigerant oil is, for example, PAG (polyalkylene glycol).

[0037] The refrigerant circuit 10 mainly includes a compressor 11, a switching mechanism 12, a first heat exchanger 13, a first expansion mechanism 14, a second heat exchanger 15, a liquid pipe 16, a liquid-gas heat exchanger 17, a branch pipe 18, an injection pipe 19, a second expansion mechanism 20, an economizer heat exchanger 21, a first valve 22, a second valve 23, a third valve 24, a fourth valve 25, and an accumulator 26.

[0038] (2-1-1) Compressor The compressor 11 compresses a low-pressure refrigerant in the refrigeration cycle to a high pressure. Here, the compressor 11 is a two-stage compressor that draws in the low-pressure refrigerant in the refrigeration cycle, compresses it to an intermediate pressure in the refrigeration cycle, and then further compresses the intermediate-pressure refrigerant to a high pressure and discharges it. Here, a scroll compressor is used as the compressor 11.

[0039] The compressor 11 includes a casing 11a, a first compression element 11b, a second compression element 11c, a drive motor 11d, a first suction portion 11e, a second suction portion 11f, and a discharge portion 11g.

[0040] The casing 11a accommodates a first compression element 11b and a second compression element 11c. The first compression element 11b and the second compression element 11c are connected to a single drive shaft (not shown). When the compressor 11 is in operation, a drive motor 11d rotationally drives the first compression element 11b and the second compression element 11c via the drive shaft. In other words, the compressor 11 has a single-shaft, two-stage compression structure.

[0041] The first suction section 11e draws low-pressure refrigerant from the refrigerant circuit 10. The second suction section 11f draws intermediate-pressure refrigerant from the refrigerant circuit 10. The discharge section 11g discharges high-pressure refrigerant to the refrigerant circuit 10. The second suction section 11f is an example of a suction section.

[0042] The second suction section 11f has a check valve (not shown) that allows the refrigerant to flow from the outside to the inside of the casing 11a and restricts the refrigerant from flowing from the inside to the outside of the casing 11a.

[0043] The first compression element 11b compresses the refrigerant drawn by the first suction port 11e to an intermediate pressure and discharges it to the second compression element 11c. The second compression element 11c compresses both the intermediate-pressure refrigerant drawn by the first compression element 11b and the intermediate-pressure refrigerant drawn by the second suction port 11f to a high pressure and discharges it to the discharge port 11g.

[0044] The structure of the compressor 11 is not limited to the single-shaft two-stage compression structure, and may be configured with a compression element driven by a separate drive motor, for example.

[0045] (2-1-2) Switching Mechanism The switching mechanism 12 switches the direction of refrigerant flow in the refrigerant circuit 10 between two states. The switching mechanism 12 is a four-way switching valve. The switching mechanism 12 has a first port P1, a second port P2, a third port P3, and a fourth port P4.

[0046] The switching mechanism 12 switches between a first state (a state indicated by a solid line in FIG. 1 ) and a second state (a state indicated by a dashed line in FIG. 1 ). In the first state, the switching mechanism 12 connects the first port P1 to the second port P2 and connects the third port P3 to the fourth port P4. In the second state, the switching mechanism 12 connects the first port P1 to the fourth port P4 and connects the second port P2 to the third port P3.

[0047] The switching mechanism 12 is not limited to a four-way switching valve, and may be configured, for example, by combining a plurality of electromagnetic valves and refrigerant flow paths.

[0048] (2-1-3) First Heat Exchanger The first heat exchanger 13 is an air heat exchanger. The first heat exchanger 13 exchanges heat between the refrigerant flowing inside and the outside air (outdoor air) sent from the first fan 13a. The first heat exchanger 13 functions as a refrigerant radiator during cooling operation and as a refrigerant evaporator during heating operation. The first heat exchanger 13 may be a cross-fin heat exchanger, a microchannel heat exchanger, or any other heat exchanger suitable for the application. In this embodiment, the first heat exchanger 13 is a microchannel heat exchanger.

[0049] The first heat exchanger 13 has a refrigerant flow path (not shown). The refrigerant flow path of the first heat exchanger 13 is provided in the refrigerant circuit 10.

[0050] In the following, for ease of explanation, during heating operation, the end of the refrigerant flow path of the first heat exchanger 13 into which the refrigerant flows will be referred to as the first end 13aa, and the end of the refrigerant flow path from which the refrigerant flows out will be referred to as the second end 13ab.

[0051] (2-1-4) First Expansion Mechanism The first expansion mechanism 14 reduces the pressure of the refrigerant passing through it to a low pressure. The first expansion mechanism 14 is provided in the liquid pipe 16. The first expansion mechanism 14 is, for example, an electric expansion valve.

[0052] (2-1-5) Second Heat Exchanger The second heat exchanger 15 is a water heat exchanger. In this embodiment, the second heat exchanger 15 exchanges heat between the refrigerant flowing through the refrigerant circuit 10 and the water flowing through the water circuit 30. The second heat exchanger 15 functions as a refrigerant evaporator during cooling operation and as a refrigerant radiator during heating operation. A heat exchanger suitable for the application, such as a plate heat exchanger, is used as the second heat exchanger 15.

[0053] The second heat exchanger 15 has a refrigerant flow path 15a and a water flow path 15b. The refrigerant flow path 15a is provided in the refrigerant circuit 10. The water flow path 15b is provided in the water circuit 30. The refrigerant flowing through the refrigerant flow path 15a exchanges heat with the water flowing through the water flow path 15b. The water that has exchanged heat with the refrigerant circulates through the water circuit 30 and heats or cools the air in the target space.

[0054] For ease of explanation, in the heating operation, the end of the refrigerant flow path 15a into which the refrigerant flows will be referred to as a first end 15aa, and the end of the refrigerant flow path 15a from which the refrigerant flows out will be referred to as a second end 15ab.

[0055] (2-1-6) Liquid Pipe The liquid pipe 16 connects the radiator (the first heat exchanger 13 during cooling operation and the second heat exchanger 15 during heating operation) and the evaporator (the second heat exchanger 15 during cooling operation and the first heat exchanger 13 during heating operation). Here, the liquid pipe 16 connects the first end 13aa of the refrigerant flow path of the first heat exchanger 13 to the second end 15ab of the refrigerant flow path 15a of the second heat exchanger 15.

[0056] (2-1-7) Liquid-to-Gas Heat Exchanger The liquid-to-gas heat exchanger 17 exchanges heat between the refrigerant flowing from the radiator (second heat exchanger 15 during heating operation) to the evaporator (first heat exchanger 13 during heating operation) and the refrigerant flowing from the evaporator to the compressor 11. The liquid-to-gas heat exchanger 17 is a pre-cooling heat exchanger that cools the refrigerant flowing from the radiator to the evaporator. The liquid-to-gas heat exchanger 17 has a first heat transfer pipe 17a and a second heat transfer pipe 17b.

[0057] The first heat transfer pipe 17a is connected to the third port P3 of the switching mechanism 12. The other end of the first heat transfer pipe 17a is connected to the first suction section 11e of the compressor 11 via the accumulator 26.

[0058] The second heat transfer pipe 17b is connected to the branch pipe 18 at both ends thereof, and the refrigerant flows from the radiator to the evaporator through the second heat transfer pipe 17b.

[0059] In this embodiment, during heating operation, the liquid-gas heat exchanger 17 exchanges heat between the refrigerant passing through the first heat transfer pipe 17a and the refrigerant passing through the second heat transfer pipe 17b. On the other hand, during cooling operation, the liquid-gas heat exchanger 17 does not exchange heat between the refrigerant passing through the first heat transfer pipe 17a and the refrigerant passing through the second heat transfer pipe 17b. Specifically, the refrigerant flows through the first heat transfer pipe 17a and the second heat transfer pipe 17b during heating operation, but does not flow through the second heat transfer pipe 17b during cooling operation.

[0060] (2-1-8) Branch Pipe The branch pipe 18 is a refrigerant flow path that branches off from the liquid pipe 16 between the second heat exchanger 15 and the first expansion mechanism 14 and connects to the second heat transfer pipe 17b of the liquid-gas heat exchanger 17. In other words, the second heat transfer pipe 17b is provided midway through the branch pipe 18.

[0061] One end of the second heat transfer pipe 17b is connected to a branch pipe 18 branching from the second heat exchanger 15 side. The other end of the second heat transfer pipe 17b is connected to a branch pipe 18 branching from the first expansion mechanism 14 side.

[0062] In the following, for ease of explanation, the point where the branch pipe 18 branches off from the second heat exchanger 15 side of the liquid pipe 16 may be referred to as the first branch section 18a, and the point where the branch pipe 18 branches off from the first expansion mechanism 14 side of the liquid pipe 16 may be referred to as the second branch section 18b.

[0063] (2-1-9) Injection Pipe The injection pipe 19 branches off a portion of the refrigerant flowing from the radiator (the second heat exchanger 15 in FIG. 1 ) to the evaporator (the first heat exchanger 13 in FIG. 1 ) and sends it to the compressor 11. Here, the injection pipe 19 branches off from the liquid pipe 16 and connects to the first suction section 11e and the second suction section 11f of the compressor 11. Therefore, the injection pipe 19 can merge with the low-pressure refrigerant of the compressor 11 and with the refrigerant of an intermediate pressure between the high pressure and low pressure of the compressor 11.

[0064] The injection pipe 19 branches off between the radiator and the economizer heat exchanger 21. In this embodiment, the injection pipe 19 branches off between the second heat exchanger 15 and the economizer heat exchanger 21 in the refrigerant flow during heating operation. In other words, the injection pipe 19 branches off downstream of the radiator and upstream of the economizer heat exchanger 21 during heating operation.

[0065] In FIG. 1, the injection tube 19 has a first portion 19a, a second portion 19b, a third portion 19c, and a fourth portion 19d.

[0066] The first portion 19a branches off from the liquid pipe 16 and is shared with the branch pipe 18. Here, the first portion 19a branches off from a first branch portion 18a in the liquid pipe 16.

[0067] The second section 19b allows the refrigerant that has flowed through the first section 19a to flow into a first heat transfer tube 21a (described later) of the economizer heat exchanger 21. The second section 19b is connected to the end of the first section 19a opposite to the branch section (first branch section 18a in this example) from the liquid pipe 16. The first heat transfer tube 21a of the economizer heat exchanger 21 is provided midway through the second section 19b.

[0068] The third section 19c allows the refrigerant that has flowed through the first heat transfer tube 21a of the economizer heat exchanger 21 to flow into the first suction section 11e of the compressor 11. The third section 19c connects the end of the second section 19b opposite to the first section 19a to the first suction section 11e of the compressor 11.

[0069] The fourth section 19d allows the refrigerant that has flowed through the first heat transfer tube 21a of the economizer heat exchanger 21 to flow into the second suction section 11f of the compressor 11. The fourth section 19d connects the end of the second section 19b opposite to the first section 19a to the second suction section 11f of the compressor 11.

[0070] (2-1-10) Second Expansion Mechanism The second expansion mechanism 20 reduces the pressure of the refrigerant passing through the injection pipe 19 to an intermediate pressure. The second expansion mechanism 20 is provided in the second section 19b of the injection pipe 19, between the connection section with the first section 19a and the economizer heat exchanger 21.

[0071] The second expansion mechanism 20 is, for example, an on / off valve such as a solenoid valve, or a flow control valve such as an electrically operated expansion valve. In this embodiment, the second expansion mechanism 20 is an electrically operated expansion valve.

[0072] (2-1-11) Economizer Heat Exchanger The economizer heat exchanger 21 exchanges heat between the refrigerant that passes through the injection pipe 19 and is decompressed by the second expansion mechanism 20, and the refrigerant that flows from the radiator to the evaporator. The economizer heat exchanger 21 has a first heat transfer pipe 21a and a second heat transfer pipe 21b. The economizer heat exchanger 21 exchanges heat between the refrigerant that passes through the first heat transfer pipe 21a and the refrigerant that passes through the second heat transfer pipe 21b.

[0073] The first heat transfer pipe 21a is connected to the injection pipe 19 through which the refrigerant flows. The first heat transfer pipe 21a is provided in the injection pipe 19. One end of the first heat transfer pipe 21a is connected to the second expansion mechanism 20 via the injection pipe 19. The other end of the first heat transfer pipe 21a is connected to the first suction section 11e and the second suction section 11f of the compressor 11 via the injection pipe 19.

[0074] The refrigerant flowing through the branch pipe 18 passes through the second heat transfer pipe 21b. The second heat transfer pipe 21b is provided on the branch pipe 18. One end of the second heat transfer pipe 21b is connected to the first valve 22 via the branch pipe 18. The other end of the second heat transfer pipe 21b is connected to the second heat transfer pipe 17b of the liquid-gas heat exchanger 17 via the branch pipe 18.

[0075] In this embodiment, during heating operation, the economizer heat exchanger 21 exchanges heat between the refrigerant passing through the first heat transfer tube 21a and the refrigerant passing through the second heat transfer tube 21b. On the other hand, during cooling operation, the economizer heat exchanger 21 does not exchange heat between the refrigerant passing through the first heat transfer tube 21a and the refrigerant passing through the second heat transfer tube 21b. Specifically, the refrigerant flows through the first heat transfer tube 21a and the second heat transfer tube 21b during heating operation, but does not flow through the first heat transfer tube 21a and the second heat transfer tube 21b during cooling operation.

[0076] (2-1-12) First Valve The first valve 22 regulates the flow of refrigerant from the liquid pipe 16 to the economizer heat exchanger 21 in the first portion 19a of the injection pipe 19. The first valve 22 is an on-off valve that switches between an open state and a closed state.

[0077] The first valve 22 is in an open state during heating operation and in a closed state during cooling operation.

[0078] (2-1-13) Second Valve The second valve 23 regulates the refrigerant flowing through the injection pipe 19 in the third portion 19c of the injection pipe 19 from flowing into the first suction section 11e of the compressor 11. The second valve 23 is an on-off valve that switches between an open state and a closed state.

[0079] The second valve 23 is closed in heating operation and is open in cooling operation.

[0080] (2-1-14) Third Valve The third valve 24 regulates the flow of refrigerant from the second branch portion 18b to the second heat transfer tube 17b in the branch pipe 18. The third valve 24 is provided in the branch pipe 18. The third valve 24 is a check valve that regulates the flow of refrigerant from the second branch portion 18b to the second heat transfer tube 17b and allows the flow of refrigerant from the second heat transfer tube 17b to the second branch portion 18b.

[0081] (2-1-15) Fourth Valve The fourth valve 25 regulates the flow of refrigerant from the first branch portion 18a to the second branch portion 18b in the liquid pipe 16. The fourth valve 25 is provided between the first branch portion 18a and the second branch portion 18b in the liquid pipe 16. The fourth valve 25 is a check valve that regulates the flow of refrigerant from the first branch portion 18a to the second branch portion 18b and allows the flow of refrigerant from the second branch portion 18b to the first branch portion 18a.

[0082] (2-1-16) Accumulator The accumulator 26 is connected between the switching mechanism 12 and the first suction section 11e of the compressor 11. Here, the accumulator 26 is provided in a refrigerant flow path that connects the other end of the first heat transfer tube 17a of the liquid-gas heat exchanger 17 and the first suction section 11e of the compressor 11. The accumulator 26 separates the refrigerant that flows out of the first heat transfer tube 17a of the liquid-gas heat exchanger 17 and flows into the first suction section 11e of the compressor 11 into gas refrigerant and liquid refrigerant.

[0083] (2-1-17) Refrigerant Charge Amount The charge amount of the refrigerant containing R290 charged into the refrigerant circuit 10 of this embodiment is smaller than when a refrigerant such as R32 is charged. Specifically, when the evaporator or radiator is an outdoor heat exchanger (here, the first heat exchanger 13), the volume of the outdoor heat exchanger is defined as V1 (m ３ ), the volume of the economizer heat exchanger 21 is V2 (m ３ ), the volume of the components in which the refrigerant is sealed other than the outdoor heat exchanger and the economizer heat exchanger 21 is V3 (m ３ ), the density of the refrigerant is D (g / m ３ ), the refrigerant filled into the refrigerant circuit 10 is equal to or less than 0.5×(V1+V2)×D+0.1×V3×D.

[0084] (2-2) Water Circuit The water circuit 30 is a circuit through which water circulates during heating and cooling operations. The water circuit 30 includes the second heat exchanger 15, a pump 31, a gas-liquid separator 32, and a third heat exchanger 33.

[0085] (2-2-1) Second Heat Exchanger The water flow path 15 b of the second heat exchanger 15 described above constitutes the water circuit 30 .

[0086] (2-2-2) Pump The pump 31 applies a predetermined pressure to the sucked water and discharges it. The pump 31 circulates the water filled in the water circuit 30 in a certain direction through the water circuit 30.

[0087] (2-2-3) Gas-Liquid Separator The gas-liquid separator 32 separates the refrigerant mixed in the water pipe connected to the second heat exchanger 15. The gas-liquid separator 32 is disposed downstream of the second heat exchanger 15. Here, the gas-liquid separator 32 is disposed between the outlet of the water flow path 15b of the second heat exchanger 15 and the inlet of the third heat exchanger 33.

[0088] (2-2-4) Third Heat Exchanger The third heat exchanger 33 exchanges heat between the water flowing inside and the indoor air sent from the third fan 33 a. The third heat exchanger 33 may be a heat exchanger suitable for the application, such as a radiator.

[0089] The third heat exchanger 33 has a water flow path (not shown). The water flow path of the third heat exchanger 33 is provided in the water circuit 30.

[0090] (2-3) Heat Source Unit The heat source unit 2 is placed in a space different from the space to be heated or cooled. Here, the heat source unit 2 is installed outdoors (on the roof of a building, near the exterior wall of a building, etc.). The heat source unit 2 includes the above-mentioned refrigerant circuit 10, the first fan 13a, part of the above-mentioned water circuit 30, and various sensors. Here, the heat source unit 2 includes a pump 31 and a gas-liquid separator 32 as part of the water circuit 30.

[0091] (2-3-1) First Fan The first fan 13a sends outdoor air to the first heat exchanger 13. The first fan 13a is driven by a fan motor.

[0092] (2-3-2) Sensors The heat source unit 2 is provided with various sensors. Specifically, the heat source unit 2 is provided with an outdoor temperature sensor 41, a discharge pressure sensor 42, a discharge temperature sensor 43, a suction pressure sensor 44, a suction temperature sensor 45, and an outlet hot water temperature sensor 47. The outdoor temperature sensor 41 detects the temperature of the outdoor air before passing through the first heat exchanger 13. The discharge pressure sensor 42 detects the pressure of the refrigerant discharged from the compressor 11. The discharge temperature sensor 43 detects the temperature of the refrigerant discharged from the compressor 11. The suction pressure sensor 44 detects the pressure of the refrigerant drawn into the compressor 11. The suction temperature sensor 45 detects the temperature of the refrigerant drawn into the compressor 11. The outlet hot water temperature sensor 47 detects the temperature of water after passing through the second heat exchanger 15.

[0093] (2-4) User Machine The user machine 3 is installed in a building. The heat source machine 2 and the user machine 3 are thermally connected via the second heat exchanger 15. Here, the water circuit 30 of the user machine 3 is connected to the water flow path 15b of the second heat exchanger 15. The user machine 3 includes a part of the water circuit 30 described above, a third fan 33a, and various sensors. Here, the user machine 3 includes the third heat exchanger 33 as part of the water circuit 30.

[0094] (2-4-1) Third Fan The third fan 33a sends indoor air to the third heat exchanger 33. The third fan 33a is driven by a fan motor.

[0095] (2-4-2) Sensor The utilization device 3 is provided with an indoor temperature sensor 46 that detects the indoor temperature, which is the temperature of the air taken in from the room before passing through the third heat exchanger 33.

[0096] (2-5) Control Unit (2-5-1) Overview The control unit 4 controls the components of the refrigeration cycle apparatus 1. As shown in FIG. 2 , the control unit 4 is electrically connected to the compressor 11, the switching mechanism 12, the first expansion mechanism 14, the second expansion mechanism 20, the first fan 13a, the third fan 33a, the first valve 22, the second valve 23, the pump 31, the outdoor temperature sensor 41, the discharge pressure sensor 42, the discharge temperature sensor 43, the suction pressure sensor 44, the suction temperature sensor 45, the indoor temperature sensor 46, and the outlet hot water temperature sensor 47 so as to be able to send and receive signals. The control unit 4 acquires information such as the operating status of each device and the measured values ​​of each sensor. Based on the acquired information, the control unit 4 controls each device of the refrigeration cycle apparatus 1 to perform cooling operation, heating operation, defrosting operation, reduced capacity operation, and the like.

[0097] The control unit 4 is realized by a computer. The control unit 4 includes a control and arithmetic device and a storage device (both not shown). A processor such as a CPU or a GPU can be used as the control and arithmetic device. The control and arithmetic device reads a program stored in the storage device and performs predetermined arithmetic processing in accordance with this program. Furthermore, the control and arithmetic device can write the results of calculations to the storage device and read information stored in the storage device in accordance with the program.

[0098] (2-5-2) First Control The following describes the first control performed by the control unit 4. The first control reduces the amount of fluid exchanging heat with the refrigerant in at least one of the first heat exchanger 13 and the second heat exchanger 15 when the differential pressure between the compressor 11 and the high and low pressures is insufficient. In other words, the first control reduces the amount of fluid exchanging heat with the refrigerant in at least one of the first heat exchanger 13 and the second heat exchanger 15, depending on the differential pressure between the compressor 11. The control unit 4 performs the first control during both heating operation and cooling operation.

[0099] A condition in which the differential pressure of the compressor 11 is insufficient is a condition in which the differential pressure value is such that chattering occurs within the compressor 11. This condition is, for example, a condition in which the differential pressure value of the compressor 11 is equal to or less than a threshold value. The differential pressure value is the difference between the low pressure on the suction side of the compressor 11 and the high pressure on the discharge side. In other words, the differential pressure is the difference between the high pressure and the low pressure of the refrigeration cycle. More specifically, the low pressure is the pressure of the refrigerant drawn from the first suction section 11e of the compressor 11. The high pressure is the pressure discharged from the discharge section 11g of the compressor 11. The differential pressure value can be calculated, for example, from the difference between the high pressure detected by the discharge pressure sensor 42 and the high pressure measured by the suction pressure sensor 44.

[0100] Here, the conditions include a first condition and a second condition. The first condition is that the differential pressure between the high and low pressures of the compressor 11 is greater than a predetermined value. The second condition is that the differential pressure between the high and low pressures of the compressor 11 is equal to or less than a predetermined value.

[0101] In this embodiment, as a first control, the control unit 4 reduces the amount of outdoor air as a fluid that exchanges heat with the refrigerant in the first heat exchanger 13 when the pressure difference between the high and low pressures of the compressor 11 is insufficient.

[0102] Specifically, when the conditions are met, the control unit 4 reduces the airflow rate of the first fan 13a. In this manner, in this embodiment, the fluid is outdoor air, and the airflow rate is reduced by fan control. Here, the control unit 4 controls only the first fan 13a as the first control.

[0103] More specifically, when the conditions are met, the control unit 4 lowers the settable minimum rotation speed of the first fan 13a. Furthermore, when the conditions are met, the control unit 4 drives the first fan 13a using duty control or an operation that includes a zero rotation step. As such, in the first control of this embodiment, the performance of the first fan 13a is reduced by performing at least one of lowering the minimum rotation speed of the first fan 13a, driving the first fan 13a using duty control, and driving the first fan 13a using an operation that includes a zero rotation step.

[0104] The control unit 4 may change the control of the first fan 13a in stages during the first control. In other words, there are multiple fan controls, and the control changes the fan control in stages during the first control. Here, the control unit 4 changes the fan control depending on a first condition in which the differential pressure is relatively high and a second condition in which the differential pressure is relatively low. Control of driving the first fan 13a using duty control and an operation including a zero rotation step reduces the performance of the first fan 13a more than control of lowering the settable minimum rotation speed of the first fan 13a. Therefore, in this embodiment, when the first condition is met, the settable minimum rotation speed of the first fan 13a is lowered. When the second condition is met, the first fan 13a is driven using duty control or an operation including a zero rotation step.

[0105] When the restoration condition is met, the control unit 4 ends the first control and performs the second control during normal cooling operation or heating operation. The restoration condition may be different from the condition in which the differential pressure of the compressor 11 is insufficient, but in this embodiment, it is the same.

[0106] (3) Operation The operation of the refrigeration cycle apparatus 1 will be described with reference to Fig. 1 to Fig. 6. The refrigeration cycle apparatus 1 performs cooling operation and heating operation. The operation of the refrigeration cycle apparatus 1, including these operations, is controlled by the control unit 4.

[0107] (3-1) Cooling Operation Hereinafter, the operation of the refrigeration cycle apparatus 1 during cooling operation will be described with reference to Fig. 3. The cooling operation shown in Fig. 3 is performed by the control unit 4, upon receiving a command for cooling operation, controlling the operation of the compressor 11, the switching mechanism 12, the first expansion mechanism 14, the second expansion mechanism 20, the first fan 13a, the first valve 22, the second valve 23, the pump 31, the third fan 33a, etc.

[0108] Specifically, the control unit 4 starts the compressor 11 and controls the rotation speed of the drive motor 11d of the compressor 11. The switching mechanism 12 is controlled to be in the second state. The opening of the first expansion mechanism 14 is controlled. The control unit 4 controls the opening of the first expansion mechanism 14, for example, so that the superheat degree of the refrigerant flowing out of the second heat exchanger 15 approaches a predetermined target superheat degree. The control unit 4 sets the target superheat degree of the refrigerant flowing out of the first end 15aa of the second heat exchanger 15, for example, based on a target outlet temperature of water flowing out of the water flow path 15b of the second heat exchanger 15. Then, the control unit 4 controls the opening of the first expansion mechanism 14 so that the superheat degree of the refrigerant flowing out of the second heat exchanger 15 approaches the target superheat degree. The second expansion mechanism 20 is controlled to be fully open or approximately fully open (hereinafter simply referred to as fully open). The first valve 22 is controlled to be in a closed state, the second valve 23 is controlled to be in an open state, and the control unit 4 causes the pump 31 to start operating.

[0109] (3-1-1) Refrigerant Circuit When the compressor 11 starts operating, low-pressure gas refrigerant in the refrigeration cycle is drawn in through the first suction port 11e. The first compression element 11b compresses the low-pressure refrigerant drawn in through the first suction port 11e to an intermediate pressure and discharges it to the second compression element 11c. The second compression element 11c compresses the intermediate-pressure refrigerant discharged from the first compression element 11b to a high pressure in the refrigeration cycle and discharges it as gas refrigerant to the discharge port 11g.

[0110] As will be described in detail later, during cooling operation, a portion of the injection pipe 19 becomes low pressure. Therefore, the check valve of the second suction part 11f restricts the outflow of intermediate-pressure refrigerant from the inside to the outside of the casing 11a.

[0111] The high-pressure gas refrigerant flowing out from the discharge port 11g passes through the switching mechanism 12, in this order, via the first port P1 and the fourth port P4, and flows into the refrigerant flow path of the first heat exchanger 13 from the second end 13ab. The refrigerant that flows into the first heat exchanger 13 exchanges heat with the outdoor air sent from the first fan 13a, dissipating heat, becoming high-pressure liquid refrigerant and flowing out from the first end 13aa. In this way, the first heat exchanger 13 functions as a radiator.

[0112] The high-pressure refrigerant flowing out of the first heat exchanger 13 flows through the liquid pipe 16, and is reduced in pressure to a low level when passing through the first expansion mechanism 14, becoming a gas-liquid two-phase refrigerant. Because the branch pipe 18 is provided with the third valve 24, the refrigerant flowing through the liquid pipe 16 passes through the fourth valve 25 without flowing into the branch pipe 18.

[0113] Because the first valve 22 is closed, the refrigerant that has passed through the fourth valve 25 flows into the second heat exchanger 15 from the second end 15ab without flowing into the branch pipe 18 or the injection pipe 19. The refrigerant that has flowed into the second heat exchanger 15 exchanges heat with the water flowing through the water flow path 15b and evaporates, becoming a low-pressure gas refrigerant that flows out from the first end 15aa. In this way, the second heat exchanger 15 functions as an evaporator.

[0114] The low-pressure refrigerant flowing out of the second heat exchanger 15 passes through the switching mechanism 12, in this order, via the second port P2 and the third port P3, and flows into the first heat transfer tube 17a of the liquid-gas heat exchanger 17. As will be described later, in cooling operation, the refrigerant in the second heat transfer tube 17b is recovered by the compressor 11. Therefore, the refrigerant that flowed into the first heat transfer tube 17a flows out of the first heat transfer tube 17a without undergoing heat exchange. The refrigerant that flowed out of the first heat transfer tube 17a passes through the accumulator 26 and is again drawn into the compressor 11 from the first suction port 11e.

[0115] During cooling operation, the first valve 22 is closed, and therefore the refrigerant flowing through the liquid pipe 16 does not flow into the injection pipe 19. Furthermore, during cooling operation, the first valve 22 is closed, the second valve 23 is open, and the second expansion mechanism 20 is fully open. Therefore, when the compressor 11 operates, a portion of the injection pipe 19, the first heat transfer pipe 21 a and the second heat transfer pipe 21 b of the economizer heat exchanger 21, the second heat transfer pipe 17 b of the liquid-gas heat exchanger 17, and a portion of the branch pipe 18 are at low pressure. Specifically, the portion of the injection pipe 19 is the portion between the first valve 22 and the first suction section 11 e of the compressor 11. Specifically, the portion of the branch pipe 18 is the portion between the first valve 22 and the third valve 24.

[0116] As a result, when switching from heating operation to cooling operation, the refrigerant remaining in part of the injection pipe 19, the first heat transfer pipe 21a and the second heat transfer pipe 21b of the economizer heat exchanger 21, the second heat transfer pipe 17b of the liquid-gas heat exchanger 17, and part of the branch pipe 18 flows into the compressor 11 through the first suction section 11e and is recovered.

[0117] In this way, the liquid-gas heat exchanger 17 is configured so that the refrigerant does not flow through the second heat transfer pipe 17b during cooling operation. Also, the economizer heat exchanger 21 is configured so that the refrigerant does not flow through the second heat transfer pipe 17b during cooling operation.

[0118] (3-1-2) Water Circuit When the pump 31 starts operating, the water filled in the water circuit 30 is sucked in through the suction port of the pump 31 and then discharged from the discharge port of the pump 31.

[0119] The water flowing out of the pump 31 flows into the water flow path 15b of the second heat exchanger 15. The water that has flowed into the water flow path 15b exchanges heat with (is cooled by) the low-pressure refrigerant flowing through the refrigerant flow path 15a, and then flows out.

[0120] The water flowing out of the second heat exchanger 15 flows into the gas-liquid separator 32. In the gas-liquid separator 32, when the refrigerant leaks into the water side in the second heat exchanger 15, the refrigerant is recovered.

[0121] The water flowing out of the gas-liquid separator 32 flows into the third heat exchanger 33. The water that flows into the third heat exchanger 33 exchanges heat with the indoor air sent from the third fan 33a, thereby cooling the air in the space to be air-conditioned.

[0122] The water that has exchanged heat with the air in the location where the third heat exchanger 33 is installed is sucked back into the pump 31 .

[0123] (3-2) Heating Operation Hereinafter, with reference to Fig. 4, a description will be given of the operation during heating operation of the refrigeration cycle apparatus 1. The heating operation shown in Fig. 4 is performed by the control unit 4, which has received a command for heating operation, controlling the operation of the compressor 11, the switching mechanism 12, the first expansion mechanism 14, the second expansion mechanism 20, the first fan 13a, the first valve 22, the second valve 23, the pump 31, the third fan 33a, etc.

[0124] Specifically, the control unit 4 starts the compressor 11 and controls the rotation speed of the drive motor 11d of the compressor 11. The switching mechanism 12 is controlled to be in the first state. The opening of the first expansion mechanism 14 is controlled. The control unit 4 controls the opening of the first expansion mechanism 14, for example, so that the degree of subcooling of the refrigerant flowing out of the second heat exchanger 15 approaches a predetermined target degree of subcooling. The control unit 4 sets a target degree of superheat of the refrigerant flowing out of the first end 15aa of the second heat exchanger 15 based on, for example, a target outlet temperature of water flowing out of the water flow path 15b of the second heat exchanger 15. The control unit 4 then controls the opening of the first expansion mechanism 14 so that the degree of superheat of the refrigerant flowing out of the second heat exchanger 15 approaches the target degree of superheat. The control unit 4 also controls the opening of the second expansion mechanism 20, for example, so that the degree of superheat of the refrigerant flowing out of the second expansion mechanism 20 approaches the predetermined target degree of superheat. The first valve 22 is controlled to be in an open state, the second valve 23 is controlled to be in a closed state, and the control unit 4 causes the pump 31 to start operating.

[0125] (3-2-1) Refrigerant Circuit When the compressor 11 starts operating, low-pressure gas refrigerant in the refrigeration cycle is drawn through the first suction port 11e, and intermediate-pressure gas refrigerant in the refrigeration cycle is drawn through the second suction port 11f. The first compression element 11b compresses the low-pressure refrigerant drawn through the first suction port 11e to an intermediate pressure and discharges it to the second compression element 11c. The second compression element 11c compresses both the intermediate-pressure refrigerant discharged from the first compression element 11b and the intermediate-pressure refrigerant drawn through the second suction port 11f to a high pressure in the refrigeration cycle and discharges it as gas refrigerant to the discharge port 11g.

[0126] The high-pressure gas refrigerant flowing out from the discharge port 11g passes through the switching mechanism 12, in this order, via the first port P1 and the second port P2, and flows into the refrigerant flow path 15a of the second heat exchanger 15 from the first end 15aa. The refrigerant that flows into the second heat exchanger 15 exchanges heat with water flowing through the water flow path 15b, dissipating heat, becoming high-pressure liquid refrigerant and flowing out from the second end 15ab. In other words, the second heat exchanger 15 functions as a radiator.

[0127] The high-pressure refrigerant flowing out of the second heat exchanger 15 flows through the liquid pipe 16. Because the first valve 22 is open and the fourth valve 25 is provided downstream of the first branch portion 18a, the refrigerant flowing through the liquid pipe 16 flows into the injection pipe 19 at the first branch portion 18a without passing through the fourth valve 25. The refrigerant that has flowed into the injection pipe 19 passes through the first valve 22 at the first portion 19a, and then is divided into the second portion 19b of the injection pipe 19 and the branch pipe 18.

[0128] The refrigerant that has flowed into the second portion 19b of the injection pipe 19 is reduced in pressure to an intermediate pressure as it flows through the second expansion mechanism 20. The intermediate-pressure refrigerant flows into the first heat transfer pipe 21a of the economizer heat exchanger 21, exchanges heat with the refrigerant passing through the second heat transfer pipe 21b of the economizer heat exchanger 21, and then flows out of the first heat transfer pipe 21a.

[0129] Because the second valve 23 is closed, the refrigerant that flows out of the first heat transfer tube 21a flows into the fourth section 19d of the injection tube 19 without flowing into the third section 19c of the injection tube 19. The refrigerant that flows into the fourth section 19d is again drawn into the compressor 11 from the second suction section 11f.

[0130] The refrigerant that flows into the branch pipe 18 flows into the second heat transfer pipe 21b of the economizer heat exchanger 21, exchanges heat with the refrigerant passing through the first heat transfer pipe 21a of the economizer heat exchanger 21, and flows out from the second heat transfer pipe 21b.

[0131] The refrigerant flowing out of the second heat transfer pipe 21b passes through the branch pipe 18 and flows into the second heat transfer pipe 17b of the liquid-gas heat exchanger 17. The refrigerant flowing into the second heat transfer pipe 17b exchanges heat with the refrigerant flowing through the first heat transfer pipe 17a of the liquid-gas heat exchanger 17, passes through the third valve 24, and flows into the liquid pipe 16 from the second branch part 18b.

[0132] The refrigerant that has flowed into the liquid pipe 16 is reduced in pressure to a low level as it passes through the first expansion mechanism 14, becoming a gas-liquid two-phase refrigerant and flowing into the first heat exchanger 13 from the first end 13aa. The refrigerant that has flowed into the first heat exchanger 13 exchanges heat with the outdoor air sent from the first fan 13a and evaporates, becoming a low-pressure gas refrigerant and flowing out from the second end 13ab. In other words, the first heat exchanger 13 functions as an evaporator.

[0133] The low-pressure refrigerant flowing out of the first heat exchanger 13 passes through the switching mechanism 12, in this order, via the fourth port P4 and the third port P3, and flows into the first heat transfer tube 17a of the liquid-gas heat exchanger 17. The refrigerant that has flowed into the first heat transfer tube 17a exchanges heat with the refrigerant passing through the second heat transfer tube 17b of the liquid-gas heat exchanger 17, and then flows out of the first heat transfer tube 17a. The refrigerant that has flowed out of the first heat transfer tube 17a passes through the accumulator 26 and is again drawn into the compressor 11 through the first suction port 11e.

[0134] In this way, the liquid-gas heat exchanger 17 and the economizer heat exchanger 21 are configured so that the refrigerant flows through them during heating operation.

[0135] (3-2-2) Water Circuit When the pump 31 starts operating, the water filled in the water circuit 30 is sucked in through the suction port of the pump 31 and then discharged from the discharge port of the pump 31.

[0136] The water flowing out of the pump 31 flows into the water flow path 15b of the second heat exchanger 15. The water that has flowed into the water flow path 15b exchanges heat with the low-pressure refrigerant flowing through the refrigerant flow path 15a (is heated), and then flows out.

[0137] The water flowing out of the second heat exchanger 15 flows into the gas-liquid separator 32. In the gas-liquid separator 32, when the refrigerant leaks into the water side in the second heat exchanger 15, the refrigerant is recovered.

[0138] The water flowing out of the gas-liquid separator 32 flows into the third heat exchanger 33. The water that has flowed into the third heat exchanger 33 exchanges heat with the indoor air sent from the third fan 33a, thereby heating the air in the space to be air-conditioned.

[0139] The water that has exchanged heat with the air in the location where the third heat exchanger 33 is installed is sucked back into the pump 31 .

[0140] (3-3) First Control During Cooling Operation and Heating Operation When the differential pressure of the compressor 11 is insufficient during heating operation and cooling operation, the control unit 4 performs the first control. Hereinafter, the operation of performing the first control during heating operation and cooling operation will be described with reference to FIG. 5 .

[0141] 5, the control unit 4 determines whether the differential pressure of the compressor 11 is insufficient during heating operation and cooling operation (step S1). Here, the control unit 4 obtains the suction pressure detected by the suction pressure sensor 44 and the discharge pressure detected by the discharge pressure sensor 42 to calculate the differential pressure. Then, it determines whether the calculated differential pressure is equal to or less than a threshold value.

[0142] In step S1, if the control unit 4 determines that the conditions are not satisfied, it continues the normal second control during the cooling operation (3-1) or the heating operation (3-2) (step S2).On the other hand, in step S1, if the control unit 4 determines that the conditions are satisfied, it determines that the high-low differential pressure of the compressor 11 is insufficient, and performs the first control (step S3).

[0143] In the first control of step S3, the air volume of the first fan 13a is reduced. Here, the first control reduces the settable minimum rotation speed of the first fan 13a. In this embodiment, the outlet hot water temperature detected by the outlet hot water temperature sensor 47 in the water circuit 30 is controlled based on the required indoor temperature.

[0144] In this embodiment, the control unit 4 changes the control of the first fan 13a in a stepwise manner during the first control.

[0145] Specifically, the control unit 4 determines whether the calculated differential pressure is greater than a predetermined value, which satisfies a first condition (step S31). If the control unit 4 determines that the first condition is satisfied in step S31, it reduces the settable minimum rotation speed of the first fan 13a (step S32). If the control unit 4 determines that the first condition is not satisfied in step S31, it satisfies a second condition, and therefore drives the first fan 13a under duty control or in an operation including a zero rotation step (step S33).

[0146] While the first control is being performed, the control unit 4 determines at a predetermined timing whether the condition that the high-low differential pressure of the compressor 11 is insufficient has been canceled by performing the first control (step S4). In this embodiment, the condition for performing the first control is the same as the condition for canceling the first control.

[0147] In step S4, if the control unit 4 determines that the condition of insufficient high-low differential pressure has been resolved, it terminates the first control and returns to the normal second control during heating or cooling operation (step S2).

[0148] On the other hand, if the control unit 4 determines in step S4 that the condition of insufficient high-low differential pressure is maintained, it continues the first control (step S3). Here, the process returns to the step of determining whether the first condition is satisfied (step S31).

[0149] (4) Characteristics of R290 Referring to FIG. 6 , a problem specific to R290 will be described. FIG. 6 is a diagram illustrating the respective tipping lines when the same scroll compressor is used in the same refrigerant circuit with the refrigerant R290 and the refrigerant R32. In FIG. 6 , the outer frames for R290 and R32 indicate the operable ranges of the compressor. The areas to the right of the tipping line L1 for R290 and the tipping line L2 for R32 (areas in the directions indicated by multiple arrows) are areas where tipping occurs (tipping areas). Note that tipping is a phenomenon in which the movable scroll moves downward relative to the fixed scroll, reducing the reliability of the compressor.

[0150] As shown in Figure 6, the chipping region is wider for R290 than for R32. For example, point A is a condensation temperature and evaporation temperature state where R32 does not chip, but R290 does. For this reason, R290 is prone to entering the chipping region, which poses the problem of chattering occurring in the compressor.

[0151] To address this issue, in this embodiment, when the differential pressure is insufficient, the first control is performed, and by increasing the high pressure, it is possible to prevent the tipping area from being reached.

[0152] Furthermore, in this embodiment, by performing the first control during both cooling operation and heating operation, it is possible to prevent the air conditioner from entering the chipping region during cooling operation and also to prevent the air conditioner from entering the chipping area during heating operation.

[0153] (5) Features (5-1) The refrigeration cycle apparatus 1 of this embodiment includes a refrigerant circuit 10 and a control unit 4. The refrigerant circuit 10 is connected to a compressor 11, a first heat exchanger 13, a first expansion mechanism 14, and a second heat exchanger 15. A refrigerant containing R290 circulates through the refrigerant circuit 10. When a condition occurs in which the high-low pressure differential of the compressor 11 is insufficient, the control unit 4 performs a first control to reduce the amount of fluid exchanging heat with the refrigerant in at least one of the first heat exchanger 13 and the second heat exchanger 15.

[0154] According to the refrigeration cycle apparatus 1 of this embodiment, when the differential pressure of the compressor 11 becomes insufficient, a first control is performed to reduce the amount of fluid exchanging heat with the refrigerant containing R290 in at least one of the first heat exchanger 13 and the second heat exchanger 15. The first control can reduce the capacity of at least one of the first heat exchanger 13 and the second heat exchanger 15, which has reduced the amount of fluid exchanging heat with the refrigerant containing R290. This can increase the differential pressure of the compressor 11. This can prevent the compressor 11 from operating under conditions where the differential pressure is insufficient, thereby improving the reliability of the compressor 11.

[0155] Therefore, the refrigeration cycle device 1 is preferably used in an environment where low load operation is performed at a predetermined load or less during cooling operation and heating operation.

[0156] (5-2) The refrigeration cycle apparatus 1 of this embodiment preferably further includes a first fan 13a. The first fan 13a sends outdoor air as a fluid to the first heat exchanger 13. When the above conditions are met, the control unit 4 reduces the airflow rate of the first fan 13a.

[0157] Here, in the first control, the capacity of the first heat exchanger 13 can be reduced by reducing the air volume of the first fan 13a.

[0158] (5-3) In the refrigeration cycle apparatus 1 of this embodiment, preferably, when the above conditions are met, the control unit 4 lowers the settable minimum rotation speed of the first fan 13a.

[0159] Here, in the first control, the air volume is reduced by lowering the minimum rotation speed of the first fan 13a, so that a refrigeration cycle apparatus 1 in which the capacity of the first heat exchanger 13 is reduced can be easily realized.

[0160] (5-4) In the refrigeration cycle apparatus 1 of this embodiment, preferably, when the above conditions are met, the control unit 4 drives the first fan 13a under duty control or in an operation including a 0 rotation step.

[0161] Here, in the first control, the air volume is reduced by driving the first fan 13a using duty control or an operation including a 0 rotation step, so that a refrigeration cycle device 1 that reduces the capacity of the first heat exchanger 13 can be easily realized.

[0162] (5-5) In the refrigeration cycle apparatus 1 of this embodiment, the control unit 4 preferably changes the control of the first fan 13a in a stepwise manner in the first control.

[0163] Here, the control of the first fan 13a is changed in stages depending on the pressure difference, thereby reducing the reduction in the airflow rate of the first fan 13a depending on the pressure difference.

[0164] (5-6) In the refrigeration cycle apparatus 1 of this embodiment, the above conditions preferably include a first condition and a second condition. The first condition is that the differential pressure between high and low in the compressor 11 is greater than a predetermined value. The second condition is that the differential pressure between high and low in the compressor 11 is equal to or less than a predetermined value. When the first condition is met, the control unit 4 lowers the settable minimum rotation speed of the first fan 13a, and when the second condition is met, the control unit 4 drives the first fan 13a by duty control or by an operation including a zero rotation step.

[0165] Duty control and control to drive the first heat exchanger 13 in an operation including a 0-rotation step can reduce the capacity of the first heat exchanger 13 more than control to lower the minimum rotation speed. Therefore, here, when the differential pressure is relatively large, control to lower the minimum rotation speed is performed, and when the differential pressure is relatively small, duty control or control to drive the first fan 13a in an operation including a 0-rotation step is performed. This makes it possible to reduce the reduction in the airflow rate of the first fan 13a depending on the differential pressure conditions.

[0166] (5-7) In the refrigeration cycle apparatus 1 of this embodiment, preferably, the control unit 4 executes a heating operation. The refrigeration cycle apparatus 1 further includes a liquid-gas heat exchanger 17. During the heating operation, the liquid-gas heat exchanger 17 exchanges heat between the refrigerant flowing from the second heat exchanger 15 to the first heat exchanger 13 and the refrigerant flowing from the first heat exchanger 13 to the compressor 11.

[0167] Here, the efficiency of the liquid-gas heat exchanger 17 can be improved by performing the first control and ensuring the high-low pressure differential of the compressor 11. Furthermore, even if the amount of refrigerant charged in the refrigerant circuit 10 is reduced, the liquid-gas heat exchanger 17 can compensate for the lack of capacity.

[0168] (5-8) In the refrigeration cycle device 1 of this embodiment, the control unit 4 preferably executes the heating operation and the cooling operation. The control unit 4 performs the first control during the heating operation and the cooling operation.

[0169] Here, since a refrigerant containing R290, which has a small differential pressure, is used, a unique problem occurs in that the reliability of the compressor decreases not only during cooling operation but also during heating operation. Here, the first control is performed during both heating operation and cooling operation, when the problem occurs, and therefore the reliability of the compressor can be improved during both heating operation and cooling operation.

[0170] (5-9) In the refrigeration cycle apparatus 1 of this embodiment, preferably, the control unit 4 executes a heating operation. The refrigeration cycle apparatus 1 further includes a liquid pipe 16, an injection pipe 19, a second expansion mechanism 20, and an economizer heat exchanger 21. The liquid pipe 16 connects the first heat exchanger 13 and the second heat exchanger 15. The injection pipe 19 branches off from the liquid pipe 16 and is connected to the compressor 11. The second expansion mechanism 20 decompresses the refrigerant passing through the injection pipe 19. During heating operation, the economizer heat exchanger 21 exchanges heat between the refrigerant decompressed by the second expansion mechanism 20 and the refrigerant flowing from the second heat exchanger 15 to the first heat exchanger 13. The volume of the first heat exchanger 13 is set to V1 (m ３ ), the volume of the economizer heat exchanger 21 is V2 (m ３), the volume of the components in which the refrigerant is sealed other than the first heat exchanger 13 and the economizer heat exchanger 21 is V3 (m ３ ), the density of the refrigerant is D (g / m ３ ), the refrigerant filled into the refrigerant circuit 10 is equal to or less than 0.5×(V1+V2)×D+0.1×V3×D.

[0171] Here, because R290 is flammable, the amount of refrigerant charged is kept low for safety reasons. However, if the amount of refrigerant charged is low, it is likely that the differential pressure across the compressor 11 will not be sufficient, which poses a significant problem. To address this problem, the first control is performed when the differential pressure is insufficient, thereby achieving both increased safety and improved reliability of the compressor 11.

[0172] (5-10) In the refrigeration cycle apparatus 1 of this embodiment, the first heat exchanger 13 is preferably a microchannel heat exchanger.

[0173] Here, the first heat exchanger 13 is a microchannel heat exchanger, so the amount of refrigerant is small. However, if the amount of refrigerant charged is small, the compressor 11 is likely to be in a state where the differential pressure between high and low is not established, which poses a major problem. To address this problem, the first control is performed when the differential pressure between high and low is insufficient, so the reliability of the compressor 11 can be improved even when a microchannel heat exchanger is used.

[0174] (6) Modifications (6-1) Modification 1 In the first embodiment, the condition for the high-low differential pressure to be insufficient is the pressure difference between the high pressure and the low pressure, but this is not limited to this. In this modification, the condition is the temperature of the outdoor air. Specifically, the condition is that the temperature of the outdoor air is equal to or higher than a first temperature during heating operation. Also, the condition is that the temperature of the outdoor air is equal to or lower than a second temperature during cooling operation.

[0175] (6-2) Modification 2 In the first embodiment, the refrigeration cycle apparatus 1 is described as including one third heat exchanger 33. However, the present invention is not limited to this. The refrigeration cycle apparatus 1 may include a plurality of third heat exchangers 33.

[0176] In this modification, the multiple third heat exchangers 33 are connected in parallel to each other with respect to the second heat exchanger 15. There are also multiple utilization units 3 that include the third heat exchangers 33. The multiple utilization units 3 may or may not be capable of individually performing cooling or heating operation.

[0177] Second Embodiment (1) Overall Configuration The refrigeration cycle apparatus of the second embodiment basically has the same configuration as the refrigeration cycle apparatus 1 of the first embodiment, but differs in the first control.

[0178] The refrigerant circuit 10 and the water circuit 30 of the second embodiment are the same as those of the first embodiment. The heat source unit 2 and the user unit 3 of the second embodiment are the same as those of the first embodiment. The control unit 4 will be described below.

[0179] (2) Detailed Configuration When the condition of the high-low pressure differential of the compressor 11 is insufficient, the control unit 4 of this embodiment performs a first control to reduce the amount of fluid exchanging heat with the refrigerant in the first heat exchanger 13 and the second heat exchanger 15. The first control of this embodiment is similar to the first embodiment in that the amount of fluid exchanging heat with the refrigerant in the first heat exchanger 13 is reduced. The first control of this embodiment reduces the amount of fluid exchanging heat with the refrigerant in the second heat exchanger 15. Specifically, the control unit reduces the flow rate of the pump 31 in the first control. In this way, the first control of this embodiment includes control to reduce the flow rate of water by pump control.

[0180] In detail, when the condition of the high-low differential pressure of the compressor 11 becomes insufficient, the control unit 4 first reduces the airflow rate of the first fan 13a, as in the first embodiment. If the condition of the high-low differential pressure being insufficient is not resolved even after reducing the airflow rate of the first fan 13a, the control unit 4 reduces the flow rate of the pump 31.

[0181] (3) Operation The normal cooling operation and heating operation of the refrigeration cycle device of the second embodiment are the same as those of the first embodiment shown in Figures 3 and 4. Hereinafter, the first control during the cooling operation and heating operation will be described with reference to Figure 7.

[0182] 7, the control unit 4 determines whether the pressure difference between the high and low pressures of the compressor 11 is insufficient during heating operation and cooling operation (step S1), as in the first embodiment. If the condition is not met in step S1, the control unit 4 continues the normal second control during heating operation or cooling operation (step S2). On the other hand, if the condition is met in step S1, the control unit 4 performs the first control (step S3).

[0183] In the first control of step S3, the controller 4 first reduces the airflow rate of the first fan 13a. Specifically, as in the first embodiment, the controller 4 determines whether the first condition is met (step S31). If the first condition is met in step S31, the controller 4 reduces the minimum settable rotation speed of the first fan 13a (step S32). If the first condition is not met but the second condition is met in step S31, the controller 4 drives the first fan 13a under duty control or in an operation that includes a zero rotation step (step S33). In steps S32 and S33, the outlet hot water temperature detected by the outlet hot water temperature sensor 47 in the water circuit 30 is controlled based on the required indoor temperature.

[0184] While the control to reduce the airflow rate of the first fan 13a is being performed, the control unit 4 determines at a predetermined timing whether the condition that the pressure difference between the high and low levels of the compressor 11 is insufficient has been lifted (step S4). If the control unit 4 determines in step S4 that the condition that the pressure difference between the high and low levels is insufficient has been lifted, the control unit 4 ends the first control and returns to the normal second control during heating operation or cooling operation (step S2).

[0185] On the other hand, if the control unit 4 determines in step S4 that the condition of insufficient differential pressure is maintained, it continues the first control. Here, the flow rate of the pump 31 is reduced (step S35). In step S35, the flow rate of the pump is reduced in the water circuit 30 regardless of the required room temperature. Thus, in this embodiment, if the differential pressure is still insufficient after the control to reduce the airflow rate of the first fan 13a is performed, further pump control is performed.

[0186] When performing the first control to reduce the air volume of the first fan 13a and the flow rate of the pump 31, the control unit 4 returns to step S1 at a predetermined timing and determines whether the condition of insufficient high-low pressure difference of the compressor 11 has been resolved by performing the first control.

[0187] (4) Features The refrigeration cycle apparatus of this embodiment further includes a water circuit 30. Water circulates through the water circuit 30. The water circuit 30 is connected to a second heat exchanger 15 and a pump 31. The second heat exchanger 15 exchanges heat between the water as a fluid and the refrigerant. The control unit 4 reduces the flow rate of the pump 31 when the above conditions are met.

[0188] Here, in the first control, the capacity of the second heat exchanger 15 can be reduced by reducing the flow rate of the pump 31 .

[0189] (5) Modifications (5-1) Modification 1 In the second embodiment described above, the first control is described as an example in which the flow rate of the pump 31 is reduced when the condition of an insufficient pressure difference across the compressor 11 cannot be resolved even when fan control for reducing the airflow rate of the first fan 13a is performed. However, this is not limiting. As the first control, the control unit 4 may simultaneously perform control for reducing the airflow rate of the first fan 13a and control for reducing the flow rate of the pump 31. In the first control of this modification, the airflow rate of the first fan 13a is reduced when the condition of an insufficient pressure difference across the compressor 11 cannot be resolved even when pump control for reducing the flow rate of the pump 31 is performed first.

[0190] (5-2) Modification 2 In the second embodiment and Modification 1, the air volume of the first fan 13a is reduced and the flow rate of the pump 31 is also reduced, but this is not limiting. In the first control of this modification, the flow rate of the pump 31 is reduced when certain conditions are met.

[0191] (5-3) Modification 3 In the second embodiment, the refrigeration cycle apparatus 1 is described as including one third heat exchanger 33. However, the present invention is not limited to this. The refrigeration cycle apparatus 1 may include a plurality of third heat exchangers 33.

[0192] <Third embodiment> (1) Overall configuration The refrigeration cycle device 5 of the third embodiment basically has the same configuration as the refrigeration cycle device 1 of the first embodiment, but differs in that it does not have a water circuit 30 and in the first control.

[0193] (2) Detailed Configuration (2-1) Second Heat Exchanger The refrigerant circuit 10 of the third embodiment differs in that the second heat exchanger 15 is an air heat exchanger. Specifically, the second heat exchanger 15 of the present embodiment is provided in the utilization device 3. Here, the second heat exchanger 15 is disposed in the target space.

[0194] The second heat exchanger 15 exchanges heat between the refrigerant flowing therein and the indoor air sent from the second fan 34. The second heat exchanger 15 in this embodiment is a heat exchanger suitable for the application, such as a cross-fin heat exchanger or a microchannel heat exchanger.

[0195] The second heat exchanger 15 has a refrigerant flow path (not shown). The refrigerant flow path of the second heat exchanger 15 is provided in the refrigerant circuit 10.

[0196] (2-2) Second Fan The second fan 34 sends outdoor air to the second heat exchanger 15. The second fan 34 is driven by a fan motor. The second fan 34 is provided in the utilization device 3.

[0197] (2-3) Control Unit As shown in FIG. 9, the control unit 4 is electrically connected to the compressor 11, the switching mechanism 12, the first expansion mechanism 14, the second expansion mechanism 20, the first fan 13a, the second fan 34, the first valve 22, the second valve 23, the pump 31, the outdoor temperature sensor 41, and the indoor temperature sensor 46 so as to be able to send and receive signals.

[0198] When the condition of insufficient high-low differential pressure of the compressor 11 is met, the control unit 4 reduces the airflow rate of the second fan 34. In this embodiment, when the above condition is met, the control unit 4 reduces the airflow rate of the first fan 13a and the second fan 34. The timing for reducing the airflow rate of the first fan 13a and the timing for reducing the airflow rate of the second fan 34 may be the same, or one of them may be reduced first. In this embodiment, the control unit 4 first reduces the airflow rate of the first fan 13a. When the condition of insufficient high-low differential pressure is not resolved even after reducing the airflow rate of the first fan 13a, the control unit 4 reduces the flow rate of the second fan 34.

[0199] The control for reducing the airflow rate of the first fan 13a is the same as in the first embodiment. The control for reducing the airflow rate of the second fan 34 may be the same as or different from that of the first fan 13a.

[0200] In this embodiment, since the discharge pressure sensor 42 and the suction pressure sensor 44 are not provided, the condition that the pressure difference between the compressor 11 is insufficient is the temperature of the outdoor air. Specifically, during heating operation, the temperature of the outdoor air is equal to or higher than a first temperature. Also, during cooling operation, the condition that the pressure difference between the compressor 11 is insufficient is equal to or lower than a second temperature.

[0201] (3) Operation The operation of the refrigeration cycle device 5 will be described with reference to Fig. 8 to Fig. 11. As in the first embodiment, the operation of the refrigeration cycle device 5, including the cooling operation and the heating operation, is performed by the control unit 4.

[0202] (3-1) Cooling Operation Hereinafter, the operation of the refrigeration cycle device 5 during cooling operation will be described with reference to Fig. 10. The cooling operation shown in Fig. 5 is performed by the control unit 4, upon receiving a command for cooling operation, controlling the operation of the compressor 11, the switching mechanism 12, the first expansion mechanism 14, the second expansion mechanism 20, the first fan 13a, the first valve 22, the second valve 23, the second fan 34, etc.

[0203] Specifically, the control unit 4 starts the compressor 11 and controls the rotation speed of the drive motor 11d of the compressor 11. The switching mechanism 12 is controlled to be in the second state. The opening degree of the first expansion mechanism 14 is controlled. The control unit 4 controls the opening degree of the first expansion mechanism 14, for example, so that the superheat degree of the refrigerant flowing out of the second heat exchanger 15 approaches a predetermined target superheat degree. The second expansion mechanism 20 is controlled to be fully open or almost fully open (hereinafter simply referred to as fully open). The first valve 22 is controlled to be in a closed state. The second valve 23 is controlled to be in an open state.

[0204] When the compressor 11 starts operating, low-pressure gas refrigerant in the refrigeration cycle is drawn in. The first compression element 11b compresses the low-pressure refrigerant drawn in by the first suction port 11e to an intermediate pressure and discharges it to the second compression element 11c. The second compression element 11c compresses the intermediate-pressure refrigerant discharged by the first compression element 11b to a high pressure in the refrigeration cycle and discharges it as gas refrigerant to the discharge port 11g.

[0205] The high-pressure gas refrigerant flowing out from the discharge port 11g passes through the switching mechanism 12 and flows into the refrigerant flow path of the first heat exchanger 13. The refrigerant that has flowed into the first heat exchanger 13 exchanges heat with the outdoor air sent from the first fan 13a, dissipating heat, and then flows out as high-pressure liquid refrigerant.

[0206] The high-pressure refrigerant flowing out of the first heat exchanger 13 flows through the liquid pipe 16, and is reduced in pressure to a low level and enters a gas-liquid two-phase state as it passes through the first expansion mechanism 14. The refrigerant flowing through the liquid pipe 16 passes through the fourth valve 25 without flowing into the branch pipe 18.

[0207] The refrigerant that has passed through the fourth valve 25 flows into the refrigerant flow path of the second heat exchanger 15 without flowing into the branch pipe 18. The refrigerant that has flowed into the second heat exchanger 15 exchanges heat with the indoor air sent from the second fan 34, evaporates, and flows out as low-pressure gas refrigerant. This cools the air in the space to be air-conditioned.

[0208] The low-pressure refrigerant that has exchanged heat with the air in the location where the second heat exchanger 15 is installed passes through the switching mechanism 12 and flows into the first heat transfer tube 17a of the liquid-gas heat exchanger 17. The refrigerant that has flowed into the first heat transfer tube 17a flows out of the first heat transfer tube 17a without undergoing heat exchange. The refrigerant that has flowed out of the first heat transfer tube 17a passes through the accumulator 26 and is again drawn into the compressor 11 through the first suction port 11e.

[0209] (3-2) Heating Operation Hereinafter, the operation of the refrigeration cycle apparatus 5 during heating operation will be described with reference to Fig. 11. The heating operation shown in Fig. 11 is performed by the control unit 4, upon receiving a command for heating operation, controlling the operation of the compressor 11, the switching mechanism 12, the first expansion mechanism 14, the second expansion mechanism 20, the first fan 13a, the first valve 22, the second valve 23, the second fan 34, etc.

[0210] Specifically, the control unit 4 starts the compressor 11 and controls the rotation speed of the drive motor 11d of the compressor 11. The switching mechanism 12 is controlled to be in the first state. The opening degree of the first expansion mechanism 14 is controlled. The control unit 4 controls the opening degree of the first expansion mechanism 14, for example, so that the degree of subcooling of the refrigerant flowing out of the second heat exchanger 15 approaches a predetermined target degree of subcooling. The control unit 4 also controls the opening degree of the second expansion mechanism 20, for example, so that the degree of superheat of the refrigerant flowing out of the second expansion mechanism 20 approaches a predetermined target degree of superheat. The first valve 22 is controlled to be in an open state. The second valve 23 is controlled to be in a closed state.

[0211] When the compressor 11 starts operating, low-pressure gas refrigerant in the refrigeration cycle is drawn through the first suction port 11e, and intermediate-pressure gas refrigerant in the refrigeration cycle is drawn through the second suction port 11f. The first compression element 11b compresses the low-pressure refrigerant drawn through the first suction port 11e to an intermediate pressure and discharges it to the second compression element 11c. The second compression element 11c compresses both the intermediate-pressure refrigerant discharged from the first compression element 11b and the intermediate-pressure refrigerant drawn through the second suction port 11f to a high pressure in the refrigeration cycle and discharges it as gas refrigerant to the discharge port 11g.

[0212] The high-pressure gas refrigerant flowing out from the discharge port 11g passes through the switching mechanism 12 and flows into the refrigerant flow path 15a of the second heat exchanger 15. The refrigerant that flows into the second heat exchanger 15 exchanges heat with the indoor air sent from the second fan 34, dissipating heat, and then flows out as high-pressure liquid refrigerant. This heats the air in the space to be air-conditioned.

[0213] The high-pressure refrigerant that has exchanged heat with the air in the location where the second heat exchanger 15 is installed flows through the liquid pipe 16. The refrigerant flowing through the liquid pipe 16 flows into the injection pipe 19 at the first branch section 18a without flowing through the fourth valve 25. The refrigerant that has flowed into the injection pipe 19 passes through the first valve 22 at the first section 19a, and then branches into the second section 19b of the injection pipe 19 and the branch pipe 18.

[0214] The refrigerant that has flowed into the second section 19b is reduced in pressure to an intermediate pressure while flowing through the second expansion mechanism 20. The intermediate-pressure refrigerant flows into the first heat transfer tube 21a of the economizer heat exchanger 21, exchanges heat with the refrigerant passing through the second heat transfer tube 21b of the economizer heat exchanger 21, and then flows out of the first heat transfer tube 21a.

[0215] The refrigerant that flows out of the first heat transfer tube 21a flows into the fourth section 19d of the injection tube 19 without flowing into the third section 19c of the injection tube 19. The refrigerant that flows into the fourth section 19d is again drawn into the compressor 11 from the second suction section 11f.

[0216] The refrigerant that flows into the branch pipe 18 flows into the second heat transfer pipe 21b of the economizer heat exchanger 21, exchanges heat with the refrigerant passing through the first heat transfer pipe 21a of the economizer heat exchanger 21, and flows out from the second heat transfer pipe 21b.

[0217] The refrigerant flowing out of the second heat transfer pipe 21b passes through the branch pipe 18 and flows into the second heat transfer pipe 17b of the liquid-gas heat exchanger 17. The refrigerant flowing into the second heat transfer pipe 17b exchanges heat with the refrigerant flowing through the first heat transfer pipe 17a of the liquid-gas heat exchanger 17, passes through the third valve 24, and flows into the liquid pipe 16 from the second branch part 18b.

[0218] The refrigerant that has flowed into the liquid pipe 16 is reduced in pressure to a low level as it passes through the first expansion mechanism 14, and flows into the first heat exchanger 13 as a gas-liquid two-phase refrigerant. The refrigerant that has flowed into the first heat exchanger 13 exchanges heat with the outdoor air sent from the first fan 13a, evaporates, and flows out as a low-pressure gas refrigerant.

[0219] The low-pressure refrigerant flowing out of the first heat exchanger 13 passes through the switching mechanism 12 and flows into the first heat transfer tube 17a of the liquid-gas heat exchanger 17. The refrigerant that has flowed into the first heat transfer tube 17a exchanges heat with the refrigerant passing through the second heat transfer tube 17b of the liquid-gas heat exchanger 17, and then flows out of the first heat transfer tube 17a. The refrigerant that has flowed out of the first heat transfer tube 17a passes through the accumulator 26 and is again drawn into the compressor 11 through the first suction port 11e.

[0220] (3-3) First Control During Cooling Operation and Heating Operation Hereinafter, the operation of performing the first control during the heating operation and cooling operation of the refrigeration cycle device 5 will be described with reference to FIG.

[0221] 12 , the control unit 4 determines whether the high-low differential pressure of the compressor 11 is insufficient during heating operation and cooling operation (step S1). Here, the control unit 4 acquires the outdoor air temperature detected by the outdoor temperature sensor 41 and compares the acquired outdoor air temperature with the first temperature or the second temperature. Specifically, during heating operation, the control unit 4 determines whether the outdoor air temperature detected by the outdoor temperature sensor 41 is equal to or higher than the first temperature. Also, during cooling operation, the control unit 4 determines whether the outdoor air temperature detected by the outdoor temperature sensor 41 is equal to or lower than the second temperature.

[0222] In step S1, if the control unit 4 determines that the condition is not satisfied, the control unit 4 continues the normal second control during heating operation or cooling operation (step S2). On the other hand, in step S1, if the control unit 4 determines that the condition is satisfied, the control unit 4 determines that the high-low differential pressure of the compressor 11 is insufficient, and performs the first control (step S3).

[0223] In the first control in step S3, the airflow rate of the first fan 13a is first reduced. Specifically, as in the first embodiment, the control unit 4 determines whether a first condition is satisfied (step S31). If the first condition is satisfied in step S31, the control unit 4 reduces the settable minimum rotation speed of the first fan 13a (step S32). If the first condition is not satisfied in step S31, the first fan 13a is driven under duty control or in an operation including a zero rotation step (step S33).

[0224] While the control to reduce the airflow rate of the first fan 13a is being performed, the control unit 4 determines at a predetermined timing whether the condition that the pressure difference between the high and low levels of the compressor 11 is insufficient has been lifted (step S34). If the control unit 4 determines in step S34 that the condition that the pressure difference between the high and low levels is insufficient has been lifted, the control unit 4 ends the first control and returns to the normal second control during heating operation or cooling operation (step S2).

[0225] On the other hand, if the control unit 4 determines in step S34 that the condition of insufficient differential pressure is maintained, it continues the first control. Here, the airflow rate of the second fan 34 is reduced (step S36). In step S36, the airflow rate of the second fan 34 is reduced regardless of the required room temperature. In this way, in this embodiment, if the differential pressure is still insufficient after the control to reduce the airflow rate of the first fan 13a is performed, the control to further reduce the airflow rate of the second fan 34 is performed.

[0226] When performing the first control to reduce the air volume of the first fan 13a and the air volume of the second fan 34, the control unit 4 returns to step S1 at a predetermined timing and performs the first control to determine whether the condition that the high-low differential pressure of the compressor 11 is insufficient has been resolved.

[0227] (4) Features (4-1) The refrigeration cycle apparatus 5 of the third embodiment further includes a second fan 34. The second fan 34 sends indoor air as a fluid to the second heat exchanger 15. When the above conditions are met, the control unit 4 reduces the airflow rate of the second fan 34.

[0228] Here, in the first control, the capacity of the second heat exchanger 15 can be reduced by reducing the air volume of the second fan 34 .

[0229] (4-2) In the refrigeration cycle apparatus 5 of the third embodiment, the control unit 4 executes the heating operation under the condition that the temperature of the outdoor air is equal to or higher than the first temperature during the heating operation.

[0230] Here, when the temperature of the outdoor air is equal to or higher than the first temperature during heating operation, the control unit 4 determines that the differential pressure is insufficient and performs the first control. Therefore, the first control can be performed even when the differential pressure is not detected.

[0231] (4-3) In the refrigeration cycle apparatus 5 of the third embodiment, the control unit 4 executes the cooling operation under the condition that the temperature of the outdoor air is equal to or lower than the second temperature during the cooling operation.

[0232] Here, when the outdoor air temperature is equal to or lower than the second temperature during cooling operation, the control unit 4 determines that the differential pressure is insufficient and performs the first control. Therefore, the first control can be performed even when the differential pressure is not detected.

[0233] (5) Modifications (5-1) Modification 1 In the third embodiment, the air volume of the first fan 13a is reduced, and the air volume of the second fan 34 is also reduced, but this is not limiting. In the first control of this modification, the air volume of the second fan 34 is reduced when certain conditions are met.

[0234] (5-2) Modification 2 In the third embodiment, the above condition is based on the temperature of the outdoor air, but this is not limiting. In this modification, the pressure is estimated from a temperature sensor provided inside the first heat exchanger 13.

[0235] (5-3) Modification 3 In the third embodiment, the refrigeration cycle apparatus 1 is described as including one second heat exchanger 15. However, the present invention is not limited to this. The refrigeration cycle apparatus 1 may include a plurality of second heat exchangers 15.

[0236] Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure as defined in the claims.

[0237] 1, 5: Refrigeration cycle device 4: Control unit 10: Refrigerant circuit 11: Compressor 13: First heat exchanger 13a: First fan 15: Second heat exchanger 17: Liquid-gas heat exchanger 30: Water circuit 31: Pump 34: Second fan

[0238] International Publication No. 2020 / 100228

Claims

1. A refrigeration cycle device (1, 5) comprising: a refrigerant circuit (10) to which a compressor (11), a first heat exchanger (13), a first expansion mechanism (14), and a second heat exchanger (15) are connected, and in which a refrigerant containing R290 circulates; and a control unit (4) that performs a first control to reduce the amount of fluid exchanging heat with the refrigerant in at least one of the first heat exchanger and the second heat exchanger when a condition occurs in which the high-low differential pressure of the compressor is insufficient.

2. The refrigeration cycle apparatus according to claim 1, further comprising a first fan (13a) that sends outdoor air as the fluid to the first heat exchanger, and the control unit reduces the air volume of the first fan when the condition is met.

3. The refrigeration cycle apparatus according to claim 2, wherein the control unit reduces the settable minimum rotation speed of the first fan when the condition is met.

4. The refrigeration cycle apparatus according to claim 2 or 3, wherein when the condition is met, the control unit drives the first fan under duty control or in an operation including a zero rotation step.

5. The refrigeration cycle device according to any one of claims 2 to 4, wherein the control unit, in the first control, changes the content of the control of the first fan in a stepwise manner.

6. The refrigeration cycle apparatus of claim 5, wherein the conditions include a first condition that the pressure difference between the high and low of the compressor is greater than a predetermined value, and a second condition that the pressure difference between the high and low of the compressor is equal to or less than a predetermined value, and the control unit, when the first condition is met, lowers the settable minimum rotation speed of the first fan, and when the second condition is met, drives the first fan by duty control or in an operation including a 0 rotation step.

7. A refrigeration cycle device (1) as claimed in any one of claims 1 to 6, further comprising a water circuit (30) to which the second heat exchanger and a pump (31) are connected and through which water circulates, the second heat exchanger exchanges heat between the water as the fluid and the refrigerant, and the control unit reduces the flow rate of the pump when the condition is met.

8. A refrigeration cycle device (5) as claimed in any one of claims 1 to 6, further comprising a second fan (34) that sends indoor air as the fluid to the second heat exchanger, and wherein the control unit reduces the air volume of the second fan when the condition is met.

9. A refrigeration cycle device as described in any one of claims 1 to 8, further comprising a liquid-gas heat exchanger (17) that performs a heating operation and exchanges heat between the refrigerant flowing from the second heat exchanger to the first heat exchanger and the refrigerant flowing from the first heat exchanger to the compressor during the heating operation.

10. A refrigeration cycle device according to any one of claims 1 to 9, wherein the control unit executes a heating operation and a cooling operation, and the control unit performs the first control during the heating operation and the cooling operation.

11. The refrigeration cycle apparatus according to any one of claims 1 to 10, wherein the control unit executes a heating operation, and the condition is that the temperature of the outdoor air during the heating operation is equal to or higher than a first temperature.

12. The refrigeration cycle device according to any one of claims 1 to 11, wherein the control unit executes a cooling operation, and the condition is that the temperature of the outdoor air during the cooling operation is equal to or lower than a second temperature.

13. The control unit executes a heating operation, and further comprises a liquid pipe (16) connecting the first heat exchanger and the second heat exchanger, an injection pipe (19) branching from the liquid pipe and connected to the compressor, a second expansion mechanism (20) decompressing the refrigerant passing through the injection pipe, and an economizer heat exchanger (21) exchanging heat between the refrigerant decompressed by the second expansion mechanism and the refrigerant flowing from the second heat exchanger to the first heat exchanger during the heating operation, and the volume of the first heat exchanger is set to V1 (m ３ , the volume of the economizer heat exchanger is V2 (m ３ , the volume of the member in which the refrigerant is sealed other than the first heat exchanger and the economizer heat exchanger is V3 (m ３ , the density of the refrigerant is D (g / m ３ 13. The refrigeration cycle apparatus according to claim 1, wherein the refrigerant filled in the refrigerant circuit is equal to or less than 0.5×(V1+V2)×D+0.1×V3×D.

14. The refrigeration cycle device according to any one of claims 1 to 13, wherein the first heat exchanger is a microchannel heat exchanger.

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