Refrigeration cycling device

Abstract

A refrigeration cycle apparatus (1) is a refrigeration cycle apparatus including a refrigerant circuit (10) in which a refrigerant containing R290 circulates, and includes a compressor (11), a radiator, an evaporator, an injection pipe (19), a second expansion mechanism (20), and an economizer heat exchanger (21). The compressor (11) sucks the low-pressure refrigerant from the refrigerant circuit (10), compresses the refrigerant, and discharges the high-pressure refrigerant. The high-pressure refrigerant radiates heat in the radiator. The low-pressure refrigerant evaporates in the evaporator. The injection pipe (19) causes a part of the refrigerant flowing from the radiator to the evaporator to branch and sends the refrigerant to the compressor (11). The second expansion mechanism (20) decompresses the refrigerant passing through the injection pipe (19). The economizer heat exchanger (21) exchanges heat between the refrigerant decompressed by the second expansion mechanism (20) and the refrigerant flowing from the radiator to the evaporator. The injection pipe (19) branches from between the radiator and the economizer heat exchanger (21).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a refrigeration cycle apparatus.BACKGROUND ART

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

[0079] and the like).SUMMARY OF THE INVENTION <Technical Problem>

[0003] The inventor of the present invention has focused on the problem that the temperature of a refrigerant discharged from a compressor decreases when the R290 refrigerant is used as a refrigerant of a refrigeration cycle apparatus including an economizer heat exchanger.<Solution to Problem>

[0004] A refrigeration cycle apparatus according to a first aspect is a refrigeration cycle apparatus including a refrigerant circuit through which a refrigerant containing R290 circulates, and includes a compressor, a radiator, an evaporator, an injection pipe, an expansion mechanism, and an economizer heat exchanger. The compressor sucks a low-pressure refrigerant from the refrigerant circuit, compresses the refrigerant, and discharges the high-pressure refrigerant. The high-pressure refrigerant radiates heat in the radiator. The low-pressure refrigerant evaporates in the evaporator. The injection pipe causes a part of the refrigerant flowing from the radiator to the evaporator to branch and sends the branched refrigerant to the compressor. The expansion mechanism decompresses the refrigerant passing through the injection pipe. The economizer heat exchanger performs heat exchange between the refrigerant having been decompressed by the expansion mechanism and the refrigerant flowing from the radiator to the evaporator. The injection pipe branches from between the radiator and the economizer heat exchanger.

[0005] In the refrigeration cycle apparatus according to the first aspect, the refrigerant containing R290 passing through the injection pipe branching from between the radiator and the economizer heat exchanger is sent to the compressor. Therefore, even when the economizer heat exchanger is provided, it is possible to suppress excessive decrease in the temperature of the refrigerant containing R290 returning to the compressor. Therefore, it is possible to suppress a decrease in the discharge temperature of the compressor.

[0006] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, in which the injection pipe joins a refrigerant having an intermediate pressure between a high pressure and a low pressure of the compressor.

[0007] In the refrigeration cycle apparatus according to the second aspect, the refrigerant branching from between the radiator and the economizer heat exchanger can be sent to an intermediate portion of the compression stroke of the compressor. Therefore, it is possible to suppress an excessive decrease in temperature of the refrigerant compressed to the intermediate pressure in the compressor.

[0008] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the second aspect, in which the intermediate-pressure refrigerant has a pressure of 0.7 MPa or more and 0.9 MPa or less.

[0009] In the refrigeration cycle apparatus according to the third aspect, the discharge degree of superheating can be increased by setting the pressure of the intermediate-pressure refrigerant as described above.

[0010] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to the second or third aspect, in which the refrigerant after joining rises by 1.2°C or more with respect to the refrigerant before joining in the compressor.

[0011] In the refrigeration cycle apparatus according to the fourth aspect, the discharge degree of superheating can be increased by setting the temperature of the intermediate-pressure refrigerant after joining as described above.

[0012] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the first to fourth aspects, and further includes a liquid-gas heat exchanger. The liquid-gas heat exchanger exchanges heat between the refrigerant flowing from the radiator to the evaporator and the refrigerant flowing from the evaporator to the compressor.

[0013] In the refrigeration cycle apparatus according to the fifth aspect, the liquid-gas heat exchanger can further suppress decrease in discharge temperature of the compressor.

[0014] A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to any one of the first to fifth aspects, in which the radiator or the evaporator is a water heat exchanger that exchanges heat between the refrigerant and water. The refrigeration cycle apparatus further includes a water circuit through which water flowing through the water heat exchanger circulates.

[0015] Even when the water heat exchanger is used as in the refrigeration cycle apparatus according to the sixth aspect, it is possible to suppress a decrease in discharge temperature.

[0016] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to the sixth aspect, in which the water circuit includes a gas-liquid separator disposed downstream of the water heat exchanger.

[0017] In the refrigeration cycle apparatus according to the seventh aspect, in a case where the refrigerant containing R290 leaks to the water side in the water heat exchanger, the refrigerant can be recovered by the gas-liquid separator.

[0018] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to any one of the first to seventh aspects, in which in a case where the evaporator or the radiator is an outdoor heat exchanger, volume of the outdoor heat exchanger is V1 (m 3< ), volume of the economizer heat exchanger is V2 (m 3< ), volume of a member in which the refrigerant is sealed other than the outdoor heat exchanger and the economizer heat exchanger is V3 (m 3< ), and density of the refrigerant is D (g / m 3< ), the refrigerant charged in the refrigerant circuit is 0.5 × (V1 + V2) × D + 0.1 × V3 × D or less.

[0019] In the refrigeration cycle apparatus according to the eighth aspect, since R290 is flammable, the charging amount of the refrigerant is reduced from the viewpoint of safety. However, when the charging amount of the refrigerant is small, the discharge temperature of the compressor tends to be low, which causes a large problem. In order to solve this problem, the refrigerant branching from between the radiator and the economizer heat exchanger is sent to the compressor. This configuration therefore achieves both improvement in safety and suppression of decrease in discharge temperature.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Fig. 1 is a schematic configuration diagram of a refrigeration cycle apparatus according to one embodiment of the present disclosure. Fig. 2 is a control block diagram of the refrigeration cycle apparatus. Fig. 3 is a diagram illustrating operation (flow of refrigerant) in cooling operation of the refrigeration cycle apparatus. Fig. 4 is a diagram illustrating operation (flow of refrigerant) in heating operation of the refrigeration cycle apparatus. Fig. 5 is a pressure-enthalpy diagram of a refrigeration cycle during heating operation of the refrigeration cycle apparatus. Fig. 6 is a schematic configuration diagram of a refrigeration cycle apparatus according to a first modification. Fig. 7 is a diagram illustrating operation (flow of refrigerant) in cooling operation of the refrigeration cycle apparatus according to the first modification. Fig. 8 is a diagram illustrating operation (flow of refrigerant) in heating operation of the refrigeration cycle apparatus according to the first modification. DESCRIPTION OF EMBODIMENTS (1) Overall Configuration

[0021] A refrigeration cycle apparatus 1 according to one embodiment of the present disclosure illustrated in Fig. 1 is an apparatus that causes a refrigerant circuit 10 to perform a vapor compression refrigeration cycle to cool or heat water circulating through a water circuit 30, and is used for cooling and heating a target space using this water.

[0022] The refrigeration cycle apparatus 1 includes a heat source device 2 and a utilization device 3. The heat source device 2 and the utilization device 3 are connected to each other. In the present embodiment, the number of the heat source device 2 is one, and the number of the utilization device 3 is one.

[0023] In addition, the refrigeration cycle apparatus 1 includes the refrigerant circuit 10, the water circuit 30, and a control unit 4. The 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.(2) Detailed Configuration(2-1) Refrigerant Circuit

[0024] The refrigerant circuit 10 is a circuit in which a refrigerant circulates during heating operation and cooling operation. The refrigerant containing R290 (propane) is sealed in the refrigerant circuit 10. The refrigerant may be a single refrigerant of R290 or a mixed refrigerant of R290 and another refrigerant. In addition, the refrigerant includes refrigerator oil. The refrigerator oil is, for example, polyalkylene glycol (PAG).

[0025] 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 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.(2-1-1) Compressor

[0026] The compressor 11 compresses a low-pressure refrigerant in the refrigeration cycle to high pressure. Here, the compressor 11 is a two-stage compressor that sucks a low-pressure refrigerant in the refrigeration cycle, compresses the refrigerant to the intermediate pressure in the refrigeration cycle, further compresses the intermediate-pressure refrigerant to the high pressure, and discharges the refrigerant.

[0027] 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.

[0028] The casing 11a houses the first compression element 11b and the second compression element 11c. The first compression element 11b and the second compression element 11c are coupled to a single drive shaft (not illustrated). During operation of the compressor 11, the 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 uniaxial two-stage compression structure.

[0029] The first suction portion 11e sucks a low-pressure refrigerant from the refrigerant circuit 10. The second suction portion 11f sucks the intermediate-pressure refrigerant from the refrigerant circuit 10. The discharge portion 11g discharges the high-pressure refrigerant to the refrigerant circuit 10. The second suction portion 11f is an example of a suction portion.

[0030] The second suction portion 11f includes a check valve (not illustrated) that allows the inflow of the refrigerant from the outside to the inside of the casing 11a and regulates the outflow of the refrigerant from the inside to the outside of the casing 11a.

[0031] The first compression element 11b compresses the refrigerant sucked by the first suction portion 11e to the intermediate pressure and discharges the refrigerant 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 sucked by the second suction portion 11f to the high pressure, and discharges the compressed refrigerants to the discharge portion 11g.

[0032] Note that, the structure of the compressor 11 is not limited to the uniaxial two-stage compression structure. The structure of the compressor 11 may include, for example, a compression element driven by another drive motor.(2-1-2) Switching Mechanism

[0033] The switching mechanism 12 switches the refrigerant flow direction in the refrigerant circuit 10 between two states. The switching mechanism 12 is a four-way switching valve. The switching mechanism 12 includes a first port P1, a second port P2, a third port P3, and a fourth port P4.

[0034] The switching mechanism 12 is switched between a first state (state indicated by a solid line in Fig. 1) and a second state (state indicated by a broken line in Fig. 1). In the first state, the switching mechanism 12 causes the first port P1 and the second port P2 to communicate with each other, and causes the third port P3 and the fourth port P4 to communicate with each other. In the second state, the switching mechanism 12 causes the first port P 1 and the fourth port P4 to communicate with each other, and causes the second port P2 and the third port P3 to communicate with each other.

[0035] The switching mechanism 12 is not limited to the four-way switching valve, and may be configured by combining a plurality of electromagnetic valves and refrigerant flow paths, for example.(2-1-3) First Heat Exchanger

[0036] The first heat exchanger 13 is an air heat exchanger. The first heat exchanger 13 exchanges heat between the refrigerant flowing inside and outside air (outdoor air) sent from a first fan 13a. The first heat exchanger 13 is a heat exchanger that functions as a radiator for the refrigerant during cooling operation, and functions as an evaporator for the refrigerant during heating operation. As the first heat exchanger 13, a heat exchanger suitable for an application such as a cross-fin heat exchanger or a microchannel heat exchanger is employed. In the present embodiment, the first heat exchanger 13 is the microchannel heat exchanger.

[0037] The first heat exchanger 13 has a refrigerant flow path (not illustrated). The refrigerant flow path of the first heat exchanger 13 is provided in the refrigerant circuit 10.

[0038] Hereinafter, for convenience of description, in heating operation, an end portion of the refrigerant flow path of the first heat exchanger 13 into which the refrigerant flows is referred to as a first end 13aa, and an end portion of the refrigerant flow path from which the refrigerant flows out is referred to as a second end 13ab.(2-1-4) First Expansion Mechanism

[0039] The first expansion mechanism 14 decompresses the passing refrigerant to the 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.(2-1-5) Second Heat Exchanger

[0040] The second heat exchanger 15 is a water heat exchanger. In the present embodiment, the second heat exchanger 15 performs heat exchange between the refrigerant flowing through the refrigerant circuit 10 and the water flowing through the water circuit 30. The second heat exchanger 15 is a heat exchanger that functions as an evaporator of the refrigerant during cooling operation, and functions as a radiator of the refrigerant during heating operation. As the second heat exchanger 15, a heat exchanger suitable for an application such as a plate heat exchanger is employed.

[0041] The second heat exchanger 15 includes 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 to heat or cool the air in the target space.

[0042] Hereinafter, for convenience of description, in heating operation, an end portion of the refrigerant flow path 15a into which the refrigerant flows is referred to as a first end 15aa, and an end portion of the refrigerant flow path 15a from which the refrigerant flows out is referred to as a second end 15ab.(2-1-6) Liquid Pipe

[0043] The liquid pipe 16 connects a radiator (first heat exchanger 13 during cooling operation and second heat exchanger 15 during heating operation) and an evaporator (second heat exchanger 15 during cooling operation and 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 and the second end 15ab of the refrigerant flow path 15a of the second heat exchanger 15.(2-1-7) Branch Pipe

[0044] The branch pipe 18 is a refrigerant flow path branching from between the second heat exchanger 15 and the first expansion mechanism 14 in the liquid pipe 16.

[0045] Hereinafter, for convenience of description, a portion where the branch pipe 18 branches from the second heat exchanger 15 side in the liquid pipe 16 may be referred to as a first branch portion 18a, and a portion where the branch pipe 18 branches from the first expansion mechanism 14 side in the liquid pipe 16 may be referred to as a second branch portion 18b.(2-1-8) Injection Pipe

[0046] The injection pipe 19 causes a part of the refrigerant flowing from the radiator (second heat exchanger 15 in Fig. 1) to the evaporator (first heat exchanger 13 in Fig. 1) to branch, and sends the refrigerant to the compressor 11. Here, the injection pipe 19 branches from the liquid pipe 16 and is connected to the first suction portion 11e and the second suction portion 11f of the compressor 11. Therefore, the injection pipe 19 can join the low-pressure refrigerant of the compressor 11 and join the intermediate-pressure refrigerant between the high pressure and the low pressure of the compressor 11.

[0047] The injection pipe 19 branches from between the radiator and the economizer heat exchanger 21. In the present embodiment, the injection pipe 19 branches from 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 from the downstream side of the radiator and the upstream side of the economizer heat exchanger 21 during the heating operation.

[0048] In Fig. 1, the injection pipe 19 includes a first portion 19a, a second portion 19b, a third portion 19c, and a fourth portion 19d.

[0049] The first portion 19a branches from the liquid pipe 16 and is shared with the branch pipe 18. Here, the first portion 19a branches from the first branch portion 18a in the liquid pipe 16.

[0050] The second portion 19b causes the refrigerant that has flowed through the first portion 19a to flow into a first heat transfer pipe 21a (described later) of the economizer heat exchanger 21. The second portion 19b is connected to an end portion of the first portion 19a on a side opposite to a branch portion (here, the first branch portion 18a) from the liquid pipe 16. The second portion 19b is provided with the first heat transfer pipe 21a of the economizer heat exchanger 21 in the middle.

[0051] The third portion 19c causes the refrigerant that has flowed through the first heat transfer pipe 21a of the economizer heat exchanger 21 to flow into the first suction portion 11e of the compressor 11. The third portion 19c connects an end portion of the second portion 19b at the side opposite to the first portion 19a and the first suction portion 11e of the compressor 11.

[0052] The fourth portion 19d causes the refrigerant that has flowed through the first heat transfer pipe 21a of the economizer heat exchanger 21 to flow into the second suction portion 11f of the compressor 11. The fourth portion 19d connects an end portion of the second portion 19b at the side opposite to the first portion 19a and the second suction portion 11f of the compressor 11.

[0053] The injection pipe 19 has a pipe diameter larger than that of R32 in order to reduce a pressure loss. The injection pipe 19 according to the present embodiment has an outside diameter equal to or larger than 1 / 2 inch piping (12.7 mm). Note that, the pipe diameter of the refrigerant pipe connected to the first suction portion 11e of the compressor 11 is also larger than that of R32. The refrigerant pipe of the present embodiment has an outside diameter equal to or larger than 7 / 8 inch piping (22.2 mm).(2-1-9) Second Expansion Mechanism

[0054] The second expansion mechanism 20 decompresses the refrigerant passing through the injection pipe 19 to the intermediate pressure. The second expansion mechanism 20 is provided between the connection portion with the first portion 19a and the economizer heat exchanger 21 in the second portion 19b of the injection pipe 19.

[0055] The second expansion mechanism 20 is, for example, an on / off valve such as a solenoid valve or a flow rate control valve such as an electric expansion valve. In the present embodiment, the second expansion mechanism 20 is an electric expansion valve.(2-1-10) Economizer Heat Exchanger

[0056] 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 flowing from the radiator to the evaporator. The economizer heat exchanger 21 includes the first heat transfer pipe 21a and a second heat transfer pipe 21b. The economizer heat exchanger 21 exchanges heat between the refrigerant passing through the first heat transfer pipe 21a and the refrigerant passing through the second heat transfer pipe 21b.

[0057] The refrigerant flowing through the injection pipe 19 passes through the first heat transfer pipe 21a. 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 portion 11e and the second suction portion 11f of the compressor 11 via the injection pipe 19.

[0058] The refrigerant flowing through the branch pipe 18 passes through the second heat transfer pipe 21b. The second heat transfer pipe 21b is provided in 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 first expansion mechanism 14 via the branch pipe 18.

[0059] In the present embodiment, during heating operation, the economizer heat exchanger 21 exchanges heat between the refrigerant passing through the first heat transfer pipe 21a and the refrigerant passing through the second heat transfer pipe 21b. On the other hand, during the cooling operation, the economizer heat exchanger 21 does not exchange heat between the refrigerant passing through the first heat transfer pipe 21a and the refrigerant passing through the second heat transfer pipe 21b. Specifically, the refrigerant flows through the first heat transfer pipe 21a and the second heat transfer pipe 21b during heating operation, and does not flow through the first heat transfer pipe 21a and the second heat transfer pipe 21b during cooling operation.(2-1-11) First Valve

[0060] The first valve 22 restricts the flow of the 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 is switched between an open state and a closed state.

[0061] The first valve 22 is in an open state in heating operation and is in a closed state in cooling operation.(2-1-12) Second Valve

[0062] The second valve 23 restricts the refrigerant flowing through the injection pipe 19 at the third portion 19c of the injection pipe 19 from flowing into the first suction portion 11e of the compressor 11. The second valve 23 is an on-off valve that is switched between an open state and a closed state.

[0063] The second valve 23 is in a closed state in heating operation and is in an open state in cooling operation.(2-1-13) Third Valve

[0064] In the branch pipe 18, the third valve 24 restricts the flow of the refrigerant from the second branch portion 18b to the second heat transfer pipe 21b. The third valve 24 is provided in the branch pipe 18. The third valve 24 is a check valve that restricts the flow of the refrigerant from the second branch portion 18b to the second heat transfer pipe 21b and allows the flow of the refrigerant from the second heat transfer pipe 21b to the second branch portion 18b.(2-1-14) Fourth Valve

[0065] The fourth valve 25 restricts the flow of the 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 restricts the flow of the refrigerant from the first branch portion 18a to the second branch portion 18b and allows the flow of the refrigerant from the second branch portion 18b to the first branch portion 18a.(2-1-15) Accumulator

[0066] The accumulator 26 is connected between the switching mechanism 12 and the first suction portion 11e of the compressor 11. Here, the accumulator 26 is provided in the refrigerant flow path connecting the third port P3 of the switching mechanism 12 and the first suction portion 11e of the compressor 11. The accumulator 26 separates the refrigerant flowing into the first suction portion 11e of the compressor 11 from the third port P3 of the switching mechanism 12 into a gas refrigerant and a liquid refrigerant.(2-1-16) Charging Amount of Refrigerant

[0067] The charging amount of the refrigerant containing R290 charged in the refrigerant circuit 10 of the present embodiment is smaller than the case where the refrigerant such as R32 is charged. Specifically, when volume of the outdoor heat exchanger in a case where the evaporator or the radiator is the outdoor heat exchanger (here, first heat exchanger 13) is V1 (m 3< ), volume of the economizer heat exchanger 21 is V2 (m 3< ), volume of a member in which the refrigerant is sealed other than the outdoor heat exchanger and the economizer heat exchanger 21 is V3 (m 3< ), and density of the refrigerant is D (g / m 3< ), the refrigerant charged in the refrigerant circuit 10 is 0.5 × (V1 + V2) × D + 0.1 × V3 × D or less.(2-2) Water Circuit

[0068] The water circuit 30 is a circuit in which water circulates during heating operation and cooling operation. The water circuit 30 includes the second heat exchanger 15, a pump 31, a gas-liquid separator 32, and the third heat exchanger 33.(2-2-1) Second Heat Exchanger

[0069] The water flow path 15b of the second heat exchanger 15 described above constitutes the water circuit 30.(2-2-2) Pump

[0070] The pump 31 applies predetermined pressure to the sucked water and discharges the sucked water. The pump 31 circulates water charged in the water circuit 30 in the water circuit 30 in a certain direction.(2-2-3) Gas-Liquid Separator

[0071] 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 an outlet of the water flow path 15b of the second heat exchanger 15 and an inlet of the third heat exchanger 33.(2-2-4) Third Heat Exchanger

[0072] The third heat exchanger 33 exchanges heat between the water flowing inside and the indoor air sent from a second fan 33a. As the third heat exchanger 33, a heat exchanger suitable for an application such as a radiator is employed.

[0073] The third heat exchanger 33 has a water flow path (not illustrated). A water flow path of the third heat exchanger 33 is provided in the water circuit 30.(2-3) Heat Source Device

[0074] The heat source device 2 is disposed in a space different from a target space to be heated or cooled. Here, the heat source device 2 is installed outdoors (on the rooftop of a building, in the vicinity of an outer wall surface of a building, or the like). The heat source device 2 includes the above-described refrigerant circuit 10, the first fan 13a, a part of the above-described water circuit 30, and various sensors. Here, the heat source device 2 includes the pump 31 and the gas-liquid separator 32 as a part of the water circuit 30.(2-3-1) First Fan

[0075] The first fan 13a sends outdoor air to the first heat exchanger 13. The first fan 13a is driven by a fan motor.(2-3-2) Sensor

[0076] The heat source device 2 is provided with various sensors. Specifically, the heat source device 2 is provided with an outdoor temperature sensor 41, a discharge pressure sensor 42, a discharge temperature sensor 43, a suction pressure sensor 44, and a suction temperature sensor 45. 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 pressure of the refrigerant discharged from the compressor 11. The discharge temperature sensor 43 detects a temperature of the refrigerant discharged from the compressor 11. The suction pressure sensor 44 detects pressure of a refrigerant sucked into the compressor 11. The suction temperature sensor 45 detects a temperature of the refrigerant sucked into the compressor 11.(2-4) utilization device

[0077] The utilization device 3 is installed in a building. The heat source device 2 and the utilization device 3 are thermally connected to each other via the second heat exchanger 15. Here, the water circuit 30 of the utilization device 3 is connected to the water flow path 15b of the second heat exchanger 15. The utilization device 3 includes a part of the water circuit 30 described above, the second fan 33a, and various sensors. Here, the utilization device 3 includes the third heat exchanger 33 as a part of the water circuit 30.(2-4-1) Second Fan

[0078] The second fan 33a sends indoor air to the third heat exchanger 33. The second fan 33a is driven by a fan motor.(2-4-2) Sensor

[0079] The utilization device 3 is provided with an indoor temperature sensor 46 that detects an indoor temperature that is the temperature of air taken in from the room and before passing through the third heat exchanger 33.(2-5) Control Unit

[0080] The control unit 4 controls components of the refrigeration cycle apparatus 1. As illustrated 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 second 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, and the indoor temperature sensor 46 so as to be able to transmit and receive signals. The control unit 4 acquires information such as an operating state of each device and a measurement value of each sensor. The control unit 4 controls each device of the refrigeration cycle apparatus 1 based on the acquired information to realize cooling operation, heating operation, and the like.

[0081] The control unit 4 is implemented by a computer. The control unit 4 includes a control calculator device and a storage device (which are not illustrated). The control calculator device may be a processor such as a CPU or a GPU. The control calculator device reads a program stored in the storage device and performs predetermined calculation processing according to the program. Furthermore, the control calculator device can write the calculation results in the storage device and read information stored in the storage device, according to the program.(3) Operation

[0082] The operation of the refrigeration cycle apparatus 1 will be described with reference to Figs. 1 to 5. The refrigeration cycle apparatus 1 performs cooling operation and heating operation. The operations of the refrigeration cycle apparatus 1 including these operations are performed by the control unit 4.(3-1) Cooling Operation

[0083] Hereinafter, operation of the refrigeration cycle apparatus 1 during cooling operation will be described with reference to Fig. 3. The cooling operation illustrated in Fig. 3 is performed when the control unit 4 that has received the command of the cooling operation controls driving 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 second fan 33a, and the like.

[0084] Specifically, the control unit 4 causes the compressor 11 to start operation, and controls the number of rotations 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. For example, the control unit 4 controls the opening degree of the first expansion mechanism 14 so that the degree of superheating of the refrigerant flowing out of the second heat exchanger 15 approaches a predetermined target degree of superheating. The second expansion mechanism 20 is controlled so that the opening degree is fully open or substantially fully open (Hereinafter, it is 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. In addition, the control unit 4 causes the pump 31 to start operation.(3-1-1) Refrigerant Circuit

[0085] When the compressor 11 starts operation, the low-pressure gas refrigerant in the refrigeration cycle is sucked from the first suction portion 11e. The first compression element 11b compresses the low-pressure refrigerant sucked by the first suction portion 11e to the intermediate pressure and discharges the refrigerant to the second compression element 11c. The second compression element 11c compresses the intermediate-pressure refrigerant discharged by the first compression element 11b to the high pressure in the refrigeration cycle, and discharges the refrigerant as a gas refrigerant to the discharge portion 11g.

[0086] Although details will be described later, the pressure of a part of the injection pipe 19 becomes low in the cooling operation. Therefore, the check valve of the second suction portion 11f restricts the outflow of the intermediate-pressure refrigerant from the inside to the outside of the casing 11a.

[0087] The high-pressure gas refrigerant that has flowed out of the discharge portion 11g passes through the switching mechanism 12 through the first port P1 and the fourth port P4 in this order, and flows into the refrigerant flow path of the first heat exchanger 13 from the second end 13ab. The refrigerant that has flowed into the first heat exchanger 13 exchanges heat with the outdoor air at the installation place of the first heat exchanger 13 to radiate heat, becomes a high-pressure liquid refrigerant, and flows out from the first end 13aa. As described above, the first heat exchanger 13 functions as a radiator.

[0088] The high-pressure refrigerant that has flowed out of the first heat exchanger 13 flows through the liquid pipe 16 and is decompressed to the low pressure when passing through the first expansion mechanism 14 to be in a gas-liquid two-phase state. Since 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.

[0089] Since the first valve 22 is in a closed state, the refrigerant that has passed through the fourth valve 25 flows into the refrigerant flow path of the second heat exchanger 15 from the second end 15ab without flowing into the branch pipe 18 and the injection pipe 19. The refrigerant that has flowed into the second heat exchanger 15 exchanges heat with water flowing through the water flow path 15b, evaporates, becomes a low-pressure gas refrigerant, and flows out from the first end 15aa. As described above, the second heat exchanger 15 functions as an evaporator.

[0090] The low-pressure refrigerant that has flowed out of the second heat exchanger 15 passes through the switching mechanism 12 through the second port P2 and the third port P3 in this order, passes through the accumulator 26, and is again sucked into the compressor 11 from the first suction portion 11e.

[0091] During the cooling operation, since the first valve 22 is in a closed state, the refrigerant flowing through the liquid pipe 16 does not flow into the injection pipe 19. In addition, during the cooling operation, since the first valve 22 is in the closed state, the second valve 23 is in the open state, and the second expansion mechanism 20 is fully open, when the compressor 11 operates, a 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, and a part of the branch pipe 18 become low pressure. Here, the part of the injection pipe 19 is specifically a portion between the first valve 22 and the first suction portion 11e of the compressor 11. In addition, the part of the branch pipe 18 is specifically a portion between the first valve 22 and the third valve 24.

[0092] As a result, at the time of switching from the heating operation to the cooling operation, the refrigerant remaining in the 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, and the part of the branch pipe 18 flows into the compressor 11 via the first suction portion 11e to be recovered.

[0093] As described above, the economizer heat exchanger 21 is configured such that the refrigerant does not flow during the cooling operation.(3-1-2) Water Circuit

[0094] When the pump 31 starts operation, water charged in the water circuit 30 is sucked from a suction portion of the pump 31 and then discharged from a discharge portion of the pump 31.

[0095] The water that has flowed 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 (is cooled) with the low-pressure refrigerant flowing through the refrigerant flow path 15a, and flows out.

[0096] The water that has flowed out of the second heat exchanger 15 flows into the gas-liquid separator 32. The gas-liquid separator 32 recovers the refrigerant in a case where the refrigerant leaks to the water side in the second heat exchanger 15.

[0097] The water that has flowed 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 at the installation place of the third heat exchanger 33. Accordingly, the air in the air conditioning target space is cooled.

[0098] The water that has exchanged heat with the air at the installation place of the third heat exchanger 33 is again sucked into the pump 31.(3-2) Heating Operation

[0099] Hereinafter, the operation of the refrigeration cycle apparatus 1 during the heating operation will be described with reference to Figs. 4 and 5.

[0100] The heating operation illustrated in Fig. 4 is performed when the control unit 4 that has received the command of the heating operation controls driving 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 second fan 33a, and the like.

[0101] Specifically, the control unit 4 causes the compressor 11 to start operation, and controls the number of rotations 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. For example, the control unit 4 controls the opening degree of the first expansion mechanism 14 so that the degree of subcooling of the refrigerant flowing out of the second heat exchanger 15 approaches a predetermined target degree of subcooling. In addition, for example, the control unit 4 controls the opening degree of the second expansion mechanism 20 so that the degree of superheating of the refrigerant flowing out of the second expansion mechanism 20 approaches a predetermined target degree of superheating. The first valve 22 is controlled to be in an open state. The second valve 23 is controlled to be in a closed state. In addition, the control unit 4 causes the pump 31 to start operation.(3-2-1) Refrigerant Circuit

[0102] When the compressor 11 starts operation, a low-pressure gas refrigerant (point A) in the refrigeration cycle is sucked from the first suction portion 11e, and an intermediate-pressure gas refrigerant (point L) in the refrigeration cycle is sucked from the second suction portion 11f. The first compression element 11b compresses the low-pressure refrigerant sucked by the first suction portion 11e to the intermediate pressure and discharges the refrigerant to the second compression element 11c (point B). The second compression element 11c compresses, to the high pressure in the refrigeration cycle, a refrigerant (point C) obtained by joining the intermediate-pressure refrigerant (point B) discharged by the first compression element 11b and the intermediate-pressure refrigerant (point L) sucked by the second suction portion 11f, and discharges the refrigerant as a gas refrigerant to the discharge portion 11g (point D).

[0103] The high-pressure gas refrigerant that has flowed out of the discharge portion 11g passes through the switching mechanism 12 through the first port P1 and the second port P2 in this order, and flows into the refrigerant flow path 15a of the second heat exchanger 15 from the first end 15aa (point E). The refrigerant that has flowed into the second heat exchanger 15 exchanges heat with water flowing through the water flow path 15b, radiates heat, becomes a high-pressure liquid refrigerant, and flows out from the second end 15ab (point F). In other words, the second heat exchanger 15 functions as a radiator.

[0104] The high-pressure refrigerant that has flowed out of the second heat exchanger 15 flows through the liquid pipe 16. Since the first valve 22 is in the open state 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 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 portion 19a, and then, at a point G, diverges into the second portion 19b of the injection pipe 19 and the branch pipe 18.

[0105] The refrigerant that has flowed into the second portion 19b of the injection pipe 19 is decompressed to the intermediate pressure when flowing through the second expansion mechanism 20 (point K). 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 flows out of the first heat transfer pipe 21a (point L).

[0106] Since the second valve 23 is in the closed state, the refrigerant that has flowed out of the first heat transfer pipe 21a flows into the fourth portion 19d of the injection pipe 19 without flowing into the third portion 19c of the injection pipe 19. The refrigerant that has flowed into the fourth portion 19d is again sucked into the compressor 11 from the second suction portion 11f.

[0107] The refrigerant that has flowed 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 of the second heat transfer pipe 21b (point H).

[0108] The refrigerant that has flowed out of the second heat transfer pipe 21b flows into the liquid pipe 16 from the second branch portion 18b through the branch pipe 18 and the third valve 24.

[0109] The refrigerant that has flowed into the liquid pipe 16 is decompressed to the low pressure when passing through the first expansion mechanism 14, becomes a refrigerant (point I) in a gas-liquid two-phase state, and flows 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 at the installation place of the first heat exchanger 13, evaporates, becomes a low-pressure gas refrigerant (point J), and flows out of the second end 13ab. In other words, the first heat exchanger 13 functions as an evaporator.

[0110] The low-pressure refrigerant that has flowed out of the first heat exchanger 13 passes through the switching mechanism 12 through the fourth port P4 and the third port P3 in this order, further passes through the accumulator 26, and is again sucked into the compressor 11 from the first suction portion 11e (point A).

[0111] As described above, the economizer heat exchanger 21 is configured such that the refrigerant flows during the heating operation.(3-2-2) Water Circuit

[0112] When the pump 31 starts operation, water charged in the water circuit 30 is sucked from a suction portion of the pump 31 and then discharged from a discharge portion of the pump 31.

[0113] The water that has flowed 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 (is heated) with the low-pressure refrigerant flowing through the refrigerant flow path 15a, and flows out.

[0114] The water that has flowed out of the second heat exchanger 15 flows into the gas-liquid separator 32. The gas-liquid separator 32 recovers the refrigerant in a case where the refrigerant leaks to the water side in the second heat exchanger 15.

[0115] The water that has flowed 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 at the installation place of the third heat exchanger 33. Accordingly, the air in the air conditioning target space is heated.

[0116] The water that has exchanged heat with the air at the installation place of the third heat exchanger 33 is again sucked into the pump 31.(3-2-3) Injection Conditions

[0117] Here, in the refrigeration cycle apparatus 1 in which the refrigerant flowing through the injection pipe 19 branching from between the second heat exchanger 15 as a radiator and the economizer heat exchanger 21 joins the intermediate-pressure refrigerant between the high pressure and the low pressure of the compressor 11 during the heating operation, preferable conditions for increasing the discharge degree of superheating will be described.

[0118] The pressure of the intermediate-pressure refrigerant (points B, C, and L) is 0.7 MPa or more and 0.9 MPa or less. In the compressor 11, the refrigerant (point C) after joining with the refrigerant (point L) flowing in from the injection pipe 19 rises by 1.2°C or more with respect to the refrigerant (point B) before joining and more preferably rises by 1.2°C or more and 1.6°C or less. The intermediate pressure (points B, C, and L) is higher than the low pressure (points A, J) by 0.1 MPa or more and 0.4 MPa or less. The intermediate pressure (point B, C, and L) is lower than the high pressure (point D) by 0.3 MPa or more and 0.6 MPa or less. The high pressure (point D) is 1.2 MPa or more and 1.4 MPa or less, and the low pressure (points A, J) is 0.4 MPa or more and 0.6 MPa or less.

[0119] The present inventors have found that the discharge degree of superheating can be set to 9°C or higher when the heating operation is performed under this condition.

[0120] Note that, the discharge degree of superheating is a difference (Td - Tc) between a discharge temperature Td of the compressor 11 and a condensation temperature Tc of the compressor 11. The discharge temperature Td is detected by the discharge temperature sensor 43. The condensation temperature Tc is calculated from the discharge pressure of the discharge pressure sensor 42.(4) Characteristics

[0121] (4-1) The refrigeration cycle apparatus 1 according to the present embodiment is a refrigeration cycle apparatus including the refrigerant circuit 10 through which the refrigerant containing R290 circulates, and includes the compressor 11, the radiator (second heat exchanger 15 or first heat exchanger 13), the evaporator (first heat exchanger 13 or second heat exchanger 15), the injection pipe 19, the second expansion mechanism 20, and the economizer heat exchanger 21. The compressor 11 sucks a low-pressure refrigerant from the refrigerant circuit 10, compresses the refrigerant, and discharges a high-pressure refrigerant. The high-pressure refrigerant radiates heat in the radiator. The low-pressure refrigerant evaporates in the evaporator. The injection pipe 19 causes a part of the refrigerant flowing from the radiator to the evaporator to branch and sends the refrigerant to the compressor 11. The second expansion mechanism 20 decompresses the refrigerant passing through the injection pipe 19. The economizer heat exchanger 21 exchanges heat between the refrigerant decompressed by the second expansion mechanism 20 and the refrigerant flowing from the radiator to the evaporator. The injection pipe 19 branches from between the radiator and the economizer heat exchanger 21.

[0122] Here, the refrigerant containing R290 passing through the injection pipe 19 branching from between the radiator and the economizer heat exchanger 21 is sent to the compressor 11. Therefore, even if the economizer heat exchanger 21 that causes the discharge temperature to decrease is provided, it is possible to suppress an excessive decrease in the temperature of the refrigerant containing R290 returning to the compressor 11. Therefore, it is possible to suppress a decrease in the discharge temperature of the compressor 11. Therefore, the reliability of the compressor 11 can be improved.

[0123] Note that, since the injection pipe 19 branches from the upstream of the economizer heat exchanger 21, the capacity of the economizer heat exchanger 21 can be reduced.

[0124] In addition, since R290 is a flammable refrigerant, it is desirable to reduce the amount of the refrigerant charged in the refrigerant circuit 10 from the viewpoint of safety. Here, since the refrigerant circuit 10 includes the economizer heat exchanger 21, the operation efficiency can be improved. Therefore, even when the amount of the refrigerant containing R290 is small, the refrigeration cycle apparatus 1 can operate efficiently.

[0125] (4-2) In the refrigeration cycle apparatus 1 according to the present embodiment, the injection pipe 19 preferably joins the intermediate-pressure refrigerant between the high pressure and the low pressure of the compressor 11.

[0126] The present inventor has focused on the fact that when intermediate injection is performed using the economizer heat exchanger 21, in some cases, the refrigerant in the middle of compression is excessively cooled, and the temperature of the refrigerant containing R290 discharged from the compressor 11 is excessively lowered. Therefore, here, the intermediate-pressure refrigerant is joined (intermediate-injected) with the refrigerant being compressed from the injection pipe 19 branching from between the radiator and the economizer heat exchanger 21 via the economizer heat exchanger 21. As described above, since the refrigerant branching from between the radiator and the economizer heat exchanger 21 can be sent to the midpoint of the compression stroke of the compressor 11, it is possible to suppress an excessive decrease in the temperature of the refrigerant compressed to the intermediate pressure in the compressor 11.

[0127] (4-3) In the refrigeration cycle apparatus 1 according to the present embodiment, the pressure of the intermediate-pressure refrigerant is preferably 0.7 MPa or more and 0.9 MPa or less.

[0128] The pressure of the intermediate-pressure refrigerant of the intermediate injection is controlled within this range, so that the discharge degree of superheating can be increased to, for example, 9°C or more.

[0129] (4-4) In the refrigeration cycle apparatus 1 according to the present embodiment, the refrigerant after joining preferably rises by 1.2°C or more with respect to the refrigerant before joining in the compressor 11.

[0130] The temperature of the refrigerant after the joining of the intermediate pressures of the intermediate injection is controlled within this range, so that the discharge degree of superheating can be increased to, for example, 9°C or more.

[0131] (4-5) In the refrigeration cycle apparatus 1 according to the present embodiment, the radiator or the evaporator (second heat exchanger 15) is preferably a water heat exchanger that exchanges heat between a refrigerant and water. The refrigeration cycle apparatus 1 further includes the water circuit 30 in which water flowing through the water heat exchanger circulates.

[0132] As described above, even when the water heat exchanger is used, it is possible to suppress a decrease in the discharge temperature of the compressor 11.

[0133] (4-6) In the refrigeration cycle apparatus 1 according to the present embodiment, the water circuit 30 preferably includes the gas-liquid separator 32 disposed downstream of the water heat exchanger (second heat exchanger 15).

[0134] Here, in a case where the refrigerant containing R290 leaks to the water side in the water heat exchanger, the refrigerant can be recovered by the gas-liquid separator 32.

[0135] (4-7) In the refrigeration cycle apparatus 1 according to the present embodiment, assuming that the volume of the outdoor heat exchanger is V1 (m 3< ) in a case where the evaporator or the radiator (first heat exchanger 13) is an outdoor heat exchanger, the volume of the economizer heat exchanger 21 is V2 (m 3< ), the volume of a member in which the refrigerant is sealed other than the outdoor heat exchanger and the economizer heat exchanger 21 is V3 (m 3< ), and the density of the refrigerant is D (g / m 3< ), the refrigerant charged in the refrigerant circuit 10 is preferably 0.5 × (V1 + V2) × D + 0.1 × V3 × D or less.

[0136] Here, since R290 is flammable, from the viewpoint of safety, the coefficient of the outdoor heat exchanger with respect to the volume V1 is reduced in the above formula to reduce the charging amount of the refrigerant. However, when the charging amount of the refrigerant is small, the discharge temperature of the compressor 11 tends to be low, which causes a large problem. In order to solve this problem, here, the refrigerant branching from between the radiator and the economizer heat exchanger 21 is sent to the compressor 11. This configuration therefore achieves both improvement in safety and suppression of decrease in discharge temperature.(5) Modification(5-1) First Modification

[0137] As illustrated in Fig. 6, a refrigeration cycle apparatus 5 according to the present modification further includes a liquid-gas heat exchanger 17.(5-1-1) Detailed Description

[0138] The liquid-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-gas heat exchanger 17 is a precooling heat exchanger that cools the refrigerant flowing from the radiator to the evaporator. The liquid-gas heat exchanger 17 includes a first heat transfer pipe 17a and a second heat transfer pipe 17b.

[0139] The refrigerant flowing from the evaporator to the first suction portion 11e of the compressor 11 passes through the first heat transfer pipe 17a. One end of 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 portion 11e of the compressor 11 via the accumulator 26.

[0140] The refrigerant flowing from the radiator to the evaporator passes through the second heat transfer pipe 17b. Both ends of the second heat transfer pipe 17b are connected to the branch pipe 18. In other words, the second heat transfer pipe 17b is provided in the middle of the branch pipe 18. One end of the second heat transfer pipe 17b is connected to the second heat transfer pipe 21b of the economizer heat exchanger 21 via the branch pipe 18. The other end of the second heat transfer pipe 17b is connected to the third valve 24 via the branch pipe 18.

[0141] In the present modification, during the 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 the 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 the heating operation, and does not flow through the second heat transfer pipe 17b during the cooling operation.(5-1-2) Operation

[0142] The operation of the refrigeration cycle apparatus 5 according to the present modification will be described with reference to Figs. 6 and 7.(5-1-2-1) Cooling Operation

[0143] In the cooling operation illustrated in Fig. 7, the operation of the water circuit 30 is similar to that of the above embodiment. The operation of the refrigerant circuit 10 will be described below.

[0144] When the compressor 11 starts operation, the low-pressure gas refrigerant in the refrigeration cycle is sucked from the first suction portion 11e. The first compression element 11b compresses the low-pressure refrigerant sucked by the first suction portion 11e to the intermediate pressure and discharges the refrigerant to the second compression element 11c. The second compression element 11c compresses the intermediate-pressure refrigerant discharged by the first compression element 11b to the high pressure in the refrigeration cycle, and discharges the refrigerant as a gas refrigerant to the discharge portion 11g.

[0145] The high-pressure gas refrigerant that has flowed out of the discharge portion 11g flows into the refrigerant flow path of the first heat exchanger 13 through the switching mechanism 12. The refrigerant that has flowed into the first heat exchanger 13 exchanges heat with the outdoor air to radiate heat, and becomes a high-pressure liquid refrigerant to flow out. The high-pressure refrigerant that has flowed out of the first heat exchanger 13 flows through the liquid pipe 16 and is decompressed to the low pressure when passing through the first expansion mechanism 14 to be in a gas-liquid two-phase state. The refrigerant flowing through the liquid pipe 16 passes through the fourth valve 25 without flowing into the branch pipe 18. The refrigerant that has passed through the fourth valve 25 flows into 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 water flowing through the water flow path 15b to evaporate, and becomes a low-pressure gas refrigerant to flow out of the second heat exchanger 15.

[0146] The low-pressure refrigerant that has flowed out of the second heat exchanger 15 flows into the first heat transfer pipe 17a of the liquid-gas heat exchanger 17 through the switching mechanism 12. As described later, during the cooling operation, the refrigerant in the second heat transfer pipe 17b is recovered by the compressor 11. Therefore, the refrigerant that has flowed into the first heat transfer pipe 17a flows out of the first heat transfer pipe 17a without exchanging heat. The refrigerant that has flowed out of the first heat transfer pipe 17a passes through the accumulator 26 and is sucked again from the first suction portion 11e into the compressor 11.

[0147] During the cooling operation, the first valve 22 is in the closed state, the second valve 23 is in the open state, and the second expansion mechanism 20 is fully open. Therefore, when the compressor 11 operates, a 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 a part of the branch pipe 18 become low pressure. As a result, at the time of switching from the heating operation to the cooling operation, the refrigerant remaining in the 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 the part of the branch pipe 18 flows into the compressor 11 via the first suction portion 11e and is recovered.

[0148] As described above, the liquid-gas heat exchanger 17 is configured such that the refrigerant does not flow through the second heat transfer pipe 17b during the cooling operation. In addition, the economizer heat exchanger 21 is configured such that the refrigerant does not flow therethrough during the cooling operation.(5-1-2-2) Heating Operation

[0149] In the heating operation illustrated in Fig. 8, the operation of the water circuit 30 is similar to that of the above embodiment. The operation of the refrigerant circuit 10 will be described below.

[0150] When the compressor 11 starts operation, a low-pressure gas refrigerant in the refrigeration cycle is sucked from the first suction portion 11e, and an intermediate-pressure gas refrigerant in the refrigeration cycle is sucked from the second suction portion 11f. The first compression element 11b compresses the low-pressure refrigerant sucked by the first suction portion 11e to the intermediate pressure and discharges the refrigerant to the second compression element 11c. The second compression element 11c compresses, to the high pressure in the refrigeration cycle, a refrigerant obtained by joining the intermediate-pressure refrigerant discharged from the first compression element 11b and the intermediate-pressure refrigerant sucked by the second suction portion 11f, and discharges the refrigerant as a gas refrigerant to the discharge portion 11g.

[0151] The high-pressure gas refrigerant that has flowed out of the discharge portion 11g flows into the refrigerant flow path 15a of the second heat exchanger 15 through the switching mechanism 12. The refrigerant that has flowed into the second heat exchanger 15 exchanges heat with water flowing through the water flow path 15b to radiate heat, and becomes a high-pressure liquid refrigerant to flow out of the second heat exchanger 15. In other words, the second heat exchanger 15 functions as a radiator.

[0152] The high-pressure refrigerant that has flowed out of the second heat exchanger 15 flows through the liquid pipe 16. The refrigerant flowing through the liquid pipe 16 flows into the injection pipe 19 at the first branch portion 18a. The refrigerant that has flowed into the injection pipe 19 passes through the first valve 22 at the first portion 19a, and then is diverted to the second portion 19b of the injection pipe 19 and the branch pipe 18.

[0153] The refrigerant that has flowed into the second portion 19b of the injection pipe 19 is decompressed to the intermediate pressure when flowing 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 flows out of the first heat transfer pipe 21a.

[0154] The refrigerant that has flowed out of the first heat transfer pipe 21a flows into the fourth portion 19d of the injection pipe 19. The refrigerant that has flowed into the fourth portion 19d is sucked again into the compressor 11 from the second suction portion 11f.

[0155] The refrigerant that has flowed 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 of the second heat transfer pipe 21b.

[0156] The refrigerant that has flowed out of the second heat transfer pipe 21b flows into the second heat transfer pipe 17b of the liquid-gas heat exchanger 17 through the branch pipe 18. The refrigerant that has flowed into the second heat transfer pipe 17b exchanges heat with the refrigerant passing 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 portion 18b.

[0157] The refrigerant that has flowed into the liquid pipe 16 is decompressed to the low pressure when passing through the first expansion mechanism 14, becomes a refrigerant in a gas-liquid two-phase state, and flows 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 at the installation place of the first heat exchanger 13 to evaporate, and becomes a low-pressure gas refrigerant to flow out of the first heat exchanger 13.

[0158] The low-pressure refrigerant that has flowed out of the first heat exchanger 13 flows into the first heat transfer pipe 17a of the liquid-gas heat exchanger 17 through the switching mechanism 12. The refrigerant that has flowed into the first heat transfer pipe 17a exchanges heat with the refrigerant passing through the second heat transfer pipe 17b of the liquid-gas heat exchanger 17, and flows out of the first heat transfer pipe 17a. The refrigerant that has flowed out of the first heat transfer pipe 17a passes through the accumulator 26 and is sucked again from the first suction portion 11e into the compressor 11.

[0159] As described above, the liquid-gas heat exchanger 17 and the economizer heat exchanger 21 are configured such that the refrigerant flows during the heating operation.(5-1-3) Characteristics

[0160] The refrigeration cycle apparatus 5 of the present modification further includes the liquid-gas heat exchanger 17. The liquid-gas heat exchanger 17 exchanges heat between the refrigerant flowing from the radiator to the evaporator and the refrigerant flowing from the evaporator to the compressor 11.

[0161] Here, the liquid-gas heat exchanger 17 can further suppress a decrease in the discharge temperature of the compressor.(5-2) Second Modification

[0162] In the above embodiment and the first modification, the description has been given by exemplifying the refrigeration cycle apparatuses 1 and 5 in which the injection pipe 19 branches from between the radiator and the economizer heat exchanger 21 during the heating operation, but the present invention is not limited thereto. The refrigeration cycle apparatus according to the present disclosure may be configured such that the injection pipe branches from between the radiator and the economizer heat exchanger during the cooling operation.(5-3) Third Modification

[0163] In the above embodiment, the economizer heat exchanger 21 is configured not to perform heat exchange in the cooling operation. In addition, in the first modification, the economizer heat exchanger 21 and the liquid-gas heat exchanger 17 are configured not to perform heat exchange in the cooling operation. However, the refrigeration cycle apparatus according to the present disclosure is not limited thereto. At least one of the economizer heat exchanger 21 and the liquid-gas heat exchanger 17 may perform heat exchange during the cooling operation.(5-4) Fourth Modification

[0164] In the above embodiment, the refrigeration cycle apparatus 1 including one third heat exchanger 33 has been described as an example, but the present invention is not limited thereto. The refrigeration cycle apparatus 1 may include a plurality of third heat exchangers 33.

[0165] In the present modification, the plurality of third heat exchangers 33 is connected to the second heat exchanger 15 in parallel. Then, there are also a plurality of utilization devices 3 including the third heat exchanger 33. The plurality of utilization devices 3 may or may not be capable of individually performing the cooling operation or the heating operation.(5-5) Fifth Modification

[0166] In the above embodiment, in the second heat exchanger 15, the refrigerant flowing through the refrigerant circuit 10 exchanges heat with the water flowing through the water circuit 30, but the present invention is not limited thereto. In the present modification, the refrigerant flowing through the refrigerant circuit 10 may exchange heat with the air in the target space. In this case, the water circuit 30 is omitted, and the second heat exchanger 15 is disposed in the target space.(5-6) Sixth Modification

[0167] In the above embodiment, the flammable refrigerant is used as a refrigerant, but the present invention is not limited thereto. In the present modification, a low-pressure refrigerant having a pressure of more than 0.08 MPa and 0.8 MPa or less at a condensation temperature of 25°C is used as a refrigerant.

[0168] While the embodiments according to the present disclosure have been described above, it will be understood that various changes in forms and details can be made without departing from the gist and scope of the present disclosure recited in the claims.REFERENCE SIGNS LIST

[0169] 1, 5: Refrigeration cycle apparatus 10: Refrigerant Circuit 11: Compressor 13: First heat exchanger (evaporator or radiator) 15: Second heat exchanger (radiator or evaporator) 17: Liquid-gas heat exchanger 19: Injection Pipe 20: Second expansion mechanism (expansion mechanism) 21: Economizer Heat Exchanger 30: Water Circuit 32: Gas-Liquid Separator CITATION LIST PATENT LITERATURE

[0170] Patent Literature 1: WO 2020 / 100228 A

Claims

1. A refrigeration cycle apparatus (1) including a refrigerant circuit (10) in which a refrigerant containing R290 circulates, the refrigeration cycle apparatus comprising: a compressor (11) configured to suck the low-pressure refrigerant from the refrigerant circuit, compress the refrigerant, and discharge the high-pressure refrigerant; a radiator (15 or 13) through which the high-pressure refrigerant radiates heat; an evaporator (13 or 15) through which the low-pressure refrigerant evaporates; an injection pipe (19) configured to cause a part of the refrigerant flowing from the radiator to the evaporator to branch and send the branched refrigerant to the compressor; an expansion mechanism (20) configured to decompress the refrigerant passing through the injection pipe; and an economizer heat exchanger (21) configured to perform heat exchange between the refrigerant having been decompressed by the expansion mechanism and the refrigerant flowing from the radiator to the evaporator, the injection pipe branches from between the radiator and the economizer heat exchanger.

2. The refrigeration cycle apparatus according to claim 1, wherein the injection pipe is configured to join the intermediate-pressure refrigerant between the high pressure and the low pressure of the compressor.

3. The refrigeration cycle apparatus according to claim 2, wherein a pressure of the intermediate-pressure refrigerant is 0.7 MPa or more and 0.9 MPa or less.

4. The refrigeration cycle apparatus according to claim 2 or 3, wherein in the compressor, the refrigerant after joining rises by 1.2°C or more with respect to the refrigerant before joining.

5. The refrigeration cycle apparatus (5) according to any one of claims 1 to 4, further comprising a liquid-gas heat exchanger (17) configured to perform heat exchange between the refrigerant flowing from the radiator to the evaporator and the refrigerant flowing from the evaporator to the compressor.

6. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the radiator or the evaporator is a water heat exchanger configured to perform heat exchange between the refrigerant and water, and the refrigeration cycle apparatus further comprising a water circuit (30) in which the water flowing through the water heat exchanger circulates.

7. The refrigeration cycle apparatus according to claim 6, wherein the water circuit has a gas-liquid separator (32) disposed downstream of the water heat exchanger.

8. The refrigeration cycle apparatus according to any one of claims 1 to 7, wherein assuming that volume of an outdoor heat exchanger is V1 (m3) in a case where the evaporator or the radiator is the outdoor heat exchanger, volume of the economizer heat exchanger is V2 (m3), volume of a member in which the refrigerant is sealed other than the outdoor heat exchanger and the economizer heat exchanger is V3 (m3), and density of the refrigerant is D (g / m3), the refrigerant charged in the refrigerant circuit is 0.5 × (V1 + V2) × D + 0.1 × V3 × D or less.

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