EP4350247A1 - Refrigeration cycle device - Google Patents
Refrigeration cycle device Download PDFInfo
- Publication number
- EP4350247A1 EP4350247A1 EP21942943.8A EP21942943A EP4350247A1 EP 4350247 A1 EP4350247 A1 EP 4350247A1 EP 21942943 A EP21942943 A EP 21942943A EP 4350247 A1 EP4350247 A1 EP 4350247A1
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- EP
- European Patent Office
- Prior art keywords
- refrigerant
- pressure
- stage compressor
- inj
- low
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 238000005057 refrigeration Methods 0.000 title claims abstract description 59
- 239000003507 refrigerant Substances 0.000 claims abstract description 212
- 238000002347 injection Methods 0.000 claims abstract description 42
- 239000007924 injection Substances 0.000 claims abstract description 42
- 238000006073 displacement reaction Methods 0.000 claims abstract description 39
- 239000007788 liquid Substances 0.000 claims abstract description 30
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical group O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 20
- 238000013461 design Methods 0.000 claims description 19
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 17
- 230000007423 decrease Effects 0.000 claims description 11
- 239000001569 carbon dioxide Substances 0.000 claims description 3
- 230000001419 dependent effect Effects 0.000 claims 1
- 238000012545 processing Methods 0.000 description 36
- 238000000034 method Methods 0.000 description 20
- 230000003247 decreasing effect Effects 0.000 description 10
- 230000005494 condensation Effects 0.000 description 8
- 238000009833 condensation Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 7
- 238000007906 compression Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 239000011555 saturated liquid Substances 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 239000000470 constituent Substances 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000003252 repetitive effect Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B1/00—Compression machines, plants or systems with non-reversible cycle
- F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B41/00—Fluid-circulation arrangements
- F25B41/20—Disposition of valves, e.g. of on-off valves or flow control valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
- F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
- F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant being carbon dioxide
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2309/00—Gas cycle refrigeration machines
- F25B2309/06—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
- F25B2309/061—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide with cycle highest pressure above the supercritical pressure
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/04—Refrigeration circuit bypassing means
- F25B2400/0409—Refrigeration circuit bypassing means for the evaporator
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/04—Refrigeration circuit bypassing means
- F25B2400/0411—Refrigeration circuit bypassing means for the expansion valve or capillary tube
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/13—Economisers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/16—Receivers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/23—Separators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2500/00—Problems to be solved
- F25B2500/07—Exceeding a certain pressure value in a refrigeration component or cycle
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/02—Compressor control
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/02—Compressor control
- F25B2600/025—Compressor control by controlling speed
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/25—Control of valves
- F25B2600/2501—Bypass valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/25—Control of valves
- F25B2600/2509—Economiser valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/25—Control of valves
- F25B2600/2515—Flow valves
Definitions
- the present disclosure relates to a refrigeration cycle apparatus including an injection circuit.
- Some multistage-compression refrigeration cycle apparatus has been known that includes a low-stage compressor and a high-stage compressor and compresses refrigerant in two stages (see, for example, Patent Literature 1).
- the low-stage compressor, the high-stage compressor, a radiator, a heat inter changer, a first expansion valve, and an evaporator are connected by refrigerant pipes.
- an injection circuit is provided as a bypass for refrigerant having an intermediate pressure.
- One end of the injection circuit is connected between the radiator and the heat inter changer.
- the other end of the injection circuit is connected between a discharge port of the low-stage compressor and a suction port of the high-stage compressor.
- the injection circuit is provided with a second expansion valve.
- the heat inter changer described above is located downstream of the second expansion valve.
- the low-stage compressor compresses sucked refrigerant from a low pressure to an intermediate pressure.
- the high-stage compressor compresses the refrigerant discharged from the low-stage compressor and having an intermediate pressure to a high pressure.
- the refrigerant discharged from the high-stage compressor flows into the radiator. Through the radiator, the refrigerant exchanges heat with air, and is thus condensed.
- subcooling is provided to the refrigerant condensed through the radiator.
- this refrigerant to which subcooling has been provided is referred to as "first refrigerant.”
- the refrigerant condensed through the radiator is partially divided into the injection circuit.
- this refrigerant is decompressed by the second expansion valve and thereafter flows into the heat inter changer.
- this refrigerant provides subcooling to the first refrigerant.
- the refrigerant having provided subcooling to the first refrigerant is referred to as "second refrigerant.”
- the second refrigerant is guided to the discharge side of the low-stage compressor that is the suction side of the high-stage compressor.
- the first refrigerant to which subcooling has been provided in the heat inter changer is guided to the first expansion valve.
- the first refrigerant expanded to a low pressure by the first expansion valve flows into the evaporator.
- the first refrigerant exchanges heat with air, and thus evaporates.
- the first refrigerant having evaporated through the evaporator is sucked into the low-stage compressor.
- this refrigeration cycle apparatus causes the low-stage compressor and the high-stage compressor to start operating at individual rotating speeds that are lower than their respective maximum possible rotating speeds at which the low-stage compressor and the high-stage compressor exhibit maximum possible performance, and to increase the individual rotating speeds in stages.
- Patent Literature 1 Japanese Unexamined Patent Application Publication No. 2012-247154
- this refrigeration cycle apparatus controls the value of intermediate pressure
- this refrigeration cycle apparatus is supposed to, for example, increase or decrease the rotating speed of the high-stage compressor, thereby to control this value.
- the rotating speed of the high-stage compressor is simply increased to reduce the intermediate pressure, a condensation load in the radiator increases. There is thus a possibility that a discharge pressure (that is, a high pressure) of the high-stage compressor may excessively increase.
- the present disclosure has been made to solve the above problems, and it is an object of the present disclosure to provide a refrigeration cycle apparatus in which it is possible to reduce or eliminate an excessive increase in high pressure, while reducing an intermediate pressure.
- a refrigeration cycle apparatus includes a controller, a low-stage compressor configured to compress refrigerant from a first pressure to an intermediate pressure that is higher than the first pressure, a high-stage compressor configured to compress the refrigerant having the intermediate pressure from the intermediate pressure to a second pressure that is higher than the intermediate pressure, a condenser through which the refrigerant having the second pressure exchanges heat with air, an INJ branch unit through which the refrigerant flowing out from the condenser is divided into first refrigerant and second refrigerant, an expansion valve configured to expand the first refrigerant divided through the INJ branch unit to decompress the first refrigerant to the first pressure, an evaporator through which the first refrigerant flowing out from the expansion valve exchanges heat with air and from which the first refrigerant having the first pressure flows out toward the low-stage compressor, an INJ junction unit located between a discharge port of the low-stage compressor and a suction port of the high-stage compressor, and an injection circuit located
- the injection circuit includes an INJ expansion valve configured to expand the second refrigerant and a receiver configured to divide the second refrigerant expanded by the INJ expansion valve into liquid refrigerant and gas refrigerant and store the liquid refrigerant and the gas refrigerant.
- the stored liquid refrigerant flows out from the receiver toward the INJ junction unit.
- the controller is configured to control a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor.
- the displacement of the low-stage compressor is a value obtained by multiplying a volume of the low-stage compressor and a rotating speed of the low-stage compressor.
- the displacement of the high-stage compressor is a value obtained by multiplying a volume of the high-stage compressor and a rotating speed of the high-stage compressor.
- the injection circuit is provided with the receiver to control the ratio of the displacement of the high-stage compressor to the displacement of the low-stage compressor, and thereby control the intermediate pressure that is an internal pressure in the receiver. Therefore, the refrigeration cycle apparatus can reduce or eliminate an excessive increase in the high pressure that is a discharge pressure of the high-stage compressor, while reducing the intermediate pressure.
- Fig. 1 is a refrigerant circuit diagram illustrating the configuration of a refrigeration cycle apparatus according to Embodiment 1.
- the refrigeration cycle apparatus includes a refrigerant circuit as a main circuit in which a compressor 10, a condenser 20, a heat inter changer (HIC) 30, an expansion valve 40, and an evaporator 50 are connected by a refrigerant pipe 60.
- the compressor 10 includes a high-stage compressor 11 and a low-stage compressor 12.
- the refrigerant pipe 60 is provided with an INJ branch unit 61 and an INJ junction unit 62.
- the INJ branch unit 61 is located between the heat inter changer (HIC) 30 and the expansion valve 40.
- the INJ junction unit 62 is located between a discharge port of the low-stage compressor 12 and a suction port of the high-stage compressor 11.
- the refrigeration cycle apparatus includes an injection circuit 70.
- the injection circuit 70 is an intermediate-pressure refrigerant bypass circuit through which refrigerant having an intermediate pressure P M flows.
- the intermediate pressure P M will be described later.
- One end of the injection circuit 70 is connected to the INJ branch unit 61, while the other end of the injection circuit 70 is connected to the INJ junction unit 62.
- the injection circuit 70 is formed in which an INJ expansion valve 71, a receiver 72, and a flow control valve 73 are connected by an injection pipe 76.
- the injection circuit 70 may be provided with a gas vent pipe 74.
- the gas vent pipe 74 is a bypass pipe connected to the receiver 72 and the injection pipe 76.
- the gas vent pipe 74 may be provided with an on-off valve 75.
- refrigerant flows inside the refrigerant pipe 60 through the low-stage compressor 12, the INJ junction unit 62, the high-stage compressor 11, the condenser 20, the heat inter changer (HIC) 30, the INJ branch unit 61, the expansion valve 40, and the evaporator 50 in this order.
- the low-stage compressor 12 the INJ junction unit 62
- the high-stage compressor 11 the condenser 20
- the heat inter changer (HIC) 30 the INJ branch unit 61
- the expansion valve 40 the evaporator 50 in this order.
- refrigerant flows inside the injection pipe 76 through the INJ branch unit 61, the INJ expansion valve 71, the receiver 72, the flow control valve 73, the heat inter changer (HIC) 30, and the INJ junction unit 62 in this order.
- the low-stage compressor 12 compresses sucked refrigerant from a low pressure P L to the intermediate pressure P M , and discharges the compressed refrigerant.
- the low-stage compressor 12 is, for example, an inverter compressor.
- the rotating speed may be optionally changed by use of a drive circuit such as an inverter circuit to change the refrigerant delivery capacity of the low-stage compressor 12 per unit time.
- the drive circuit is controlled by a controller 90.
- the low pressure P L is a first pressure, which is set in advance.
- the high-stage compressor 11 compresses, to a high pressure P H , the refrigerant discharged from the low-stage compressor 12 and having the intermediate pressure P M , and the refrigerant flowing in from the injection circuit 70 and having the intermediate pressure P M .
- the refrigerant discharged from the high-stage compressor 11 flows into the condenser 20.
- the high-stage compressor 11 is, for example, an inverter compressor.
- the rotating speed may be optionally changed by use of a drive circuit such as an inverter circuit to change the refrigerant delivery capacity of the high-stage compressor 11 per unit time.
- the drive circuit is controlled by the controller 90.
- the high pressure P H is a second pressure, which is set in advance.
- the second pressure is higher than the first pressure.
- the intermediate pressure P M is higher than the first pressure and lower than the second pressure.
- the condenser 20 is located, for example, outdoors.
- the condenser 20 is a heat exchanger through which refrigerant flowing inside the heat exchanger exchanges heat with air.
- the condenser 20 is, for example, a fin-and-tube heat exchanger. Refrigerant condensed into liquid through the condenser 20 flows into the heat inter changer (HIC) 30.
- HIC heat inter changer
- the heat inter changer (HIC) 30 is configured to perform inter-refrigerant heat exchange to cool one refrigerant by the other refrigerant.
- the heat inter changer (HIC) 30 is formed by, for example, a double pipe.
- Fig. 2 is a perspective view illustrating an example of the configuration of the heat inter changer (HIC) 30 provided in the refrigeration cycle apparatus according to Embodiment 1.
- Fig. 2 illustrates a portion of the configuration of the heat inter changer (HIC) 30 in a transparent manner by use of dotted lines.
- the heat inter changer (HIC) 30 is formed by an outer pipe 31 located on the outside, and an inner pipe 32 located inside the outer pipe 31.
- a flow direction of refrigerant flowing through the outer pipe 31 (the direction of the arrows P1) is opposite to a flow direction of refrigerant flowing through the inner pipe 32 (the direction of the arrow P2).
- HIC heat inter changer
- refrigerant flowing through the injection pipe 76 may flow through the outer pipe 31, while refrigerant flowing out from the condenser 20 may flow through the inner pipe 32.
- the heat inter changer (HIC) 30 may have a configuration other than the configuration shown in Fig. 2 .
- refrigerant (second refrigerant, which will be described later) flowing out from the receiver 72 and flowing through the injection pipe 76 cools refrigerant flowing out from the condenser 20 to provide subcooling to this refrigerant flowing out from the condenser 20. Thereafter, the refrigerant (the second refrigerant) having provided subcooling still flows through the injection pipe 76 and is guided to the INJ junction unit 62.
- the INJ junction unit 62 is located on the discharge side of the low-stage compressor 12 that is the suction side of the high-stage compressor 11.
- refrigerant to which subcooling has been provided in the heat inter changer (HIC) 30 is divided into the first refrigerant and the second refrigerant through the INJ branch unit 61.
- the first refrigerant divided through the INJ branch unit 61 flows through the refrigerant pipe 60 and is guided to the expansion valve 40.
- the expansion valve 40 expands and decompresses the first refrigerant.
- the first refrigerant expanded to the low pressure P L flows into the evaporator 50.
- the expansion valve 40 is, for example, an electronic expansion valve. In a case where the expansion valve 40 is formed by an electronic expansion valve, the opening degree of the expansion valve 40 is controlled and adjusted by the controller 90.
- the evaporator 50 is located in, for example, a room space.
- the evaporator 50 is a heat exchanger through which refrigerant flowing inside the heat exchanger exchanges heat with air.
- the evaporator 50 is, for example, a fin-and-tube heat exchanger.
- the first refrigerant exchanges heat with air, and thus evaporates.
- the first refrigerant having evaporated into gas through the evaporator 50 is sucked into the low-stage compressor 12.
- the low-stage compressor 12 sucks refrigerant flowing out from the evaporator 50 and having the low pressure P L , then compresses this refrigerant to the intermediate pressure P M , and discharges the compressed refrigerant.
- the second refrigerant divided through the INJ branch unit 61 flows through the injection pipe 76 and then flows into the INJ expansion valve 71.
- the INJ expansion valve 71 expands and decompresses the second refrigerant.
- the second refrigerant expanded to the intermediate pressure P M flows into the receiver 72.
- the INJ expansion valve 71 is, for example, an electronic expansion valve. In a case where the INJ expansion valve 71 is formed by an electronic expansion valve, the opening degree of the INJ expansion valve 71 is controlled and adjusted by the controller 90.
- the receiver 72 stores the second refrigerant expanded to the intermediate pressure P M by the INJ expansion valve 71.
- the second refrigerant is divided into liquid refrigerant and gas refrigerant.
- the liquid refrigerant obtained by dividing the second refrigerant by the receiver 72 flows into the inner pipe 32 of the heat inter changer (HIC) 30 through the injection pipe 76.
- the second refrigerant flowing through the inner pipe 32 exchanges heat with refrigerant flowing through the outer pipe 31, and thereafter is guided to the INJ junction unit 62.
- the second refrigerant cools the refrigerant flowing through the outer pipe 31 in the heat inter changer (HIC) 30 to provide subcooling to this refrigerant flowing through the outer pipe 31.
- the heat inter changer (HIC) 30 is not necessarily provided, but may be provided only when needed.
- the flow control valve 73 is provided in the injection pipe 76 and between the receiver 72 and the heat inter changer (HIC) 30.
- the flow rate of the second refrigerant (liquid refrigerant) flowing out from the receiver 72 is adjusted by the opening degree of the flow control valve 73.
- the flow control valve 73 is, for example, an electronic adjusting valve. In this case, the opening degree of the flow control valve 73 is controlled by the controller 90.
- the second refrigerant flowing through the injection pipe 76 and having the intermediate pressure P M , and the first refrigerant discharged from the low-stage compressor 12 and having the intermediate pressure P M join together.
- the refrigerant having joined together at the INJ junction unit 62 is sucked into the high-stage compressor 11.
- the high-stage compressor 11 compresses the sucked refrigerant having the intermediate pressure P M to the high pressure P H , and discharges the compressed refrigerant.
- the gas vent pipe 74 is a bypass pipe connected between the receiver 72 and the injection pipe 76. One end of the gas vent pipe 74 is connected to an upper portion of the receiver 72, while the other end of the gas vent pipe 74 is connected to the injection pipe 76 at a location between the flow control valve 73 and the heat inter changer (HIC) 30.
- the gas vent pipe 74 allows gas refrigerant in the receiver 72 to flow out to the injection pipe 76 when the on-off valve 75 is in an open state, and stops the outflow of the gas refrigerant in the receiver 72 when the on-off valve 75 is in a closed state. With this configuration, composition of the refrigerant flowing in the injection circuit 70, that is, a gas density of this refrigerant can be finely adjusted.
- the gas vent pipe 74 is not necessarily provided, but may be provided only when needed.
- the controller 90 is formed by a processing circuit.
- the processing circuit is formed by dedicated hardware or a processor. Examples of the dedicated hardware include an application specific integrated circuit (ASIC) and a field programmable gate array (FPGA).
- the processor executes programs stored in a memory. Storage circuitry (not shown) provided in the controller 90 is formed by the memory.
- the memory is a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, and an erasable programmable ROM (EPROM), or a disk such as a magnetic disk, a flexible disk, and an optical disk.
- a first pressure sensor 81 configured to measure the intermediate pressure P M is installed between the INJ expansion valve 71 and the receiver 72. Information on the intermediate pressure P M detected by the first pressure sensor 81 is transmitted to the controller 90.
- the intermediate pressure P M is an internal pressure in the receiver 72.
- a second pressure sensor 82 configured to measure the high pressure P H is further installed between the discharge port of the high-stage compressor 11 and the condenser 20. Information on the high pressure P H detected by the second pressure sensor 82 is transmitted to the controller 90.
- the high pressure P H is a discharge pressure of the high-stage compressor 11.
- the refrigeration cycle apparatus described in Patent Literature 1 mentioned above is not supposed to use a high-pressure supercritical refrigerant such as CO 2 (carbon dioxide) as refrigerant.
- a high-pressure supercritical refrigerant such as CO 2 (carbon dioxide)
- Fig. 3 is a p-h diagram illustrating a refrigeration cycle when the refrigeration cycle apparatus described in Patent Literature 1 uses the high-pressure supercritical refrigerant such as CO 2 .
- the horizontal axis represents a specific enthalpy, while the vertical axis represents a pressure of refrigerant.
- a solid line 100 shows a saturated vapor line.
- a solid line 101 shows a saturated liquid line.
- K shows a critical point.
- a critical pressure that is a pressure at the critical point K is represented as P K .
- T1 shows a compression process performed by the high-stage compressor
- T2 shows a condensation process performed by the radiator
- T3 shows a heat exchange process performed by the heat inter changer
- T4 shows an expansion process performed by the first expansion valve
- T5 shows an evaporation process performed by the evaporator
- T6 shows a compression process performed by the low-stage compressor
- T7 shows an expansion process performed by the second expansion valve
- T8 shows a heat exchange process performed by the heat inter changer.
- this refrigeration cycle apparatus is supposed to, for example, increase or decrease the rotating speed of the high-stage compressor, thereby to control the intermediate pressure P M .
- this refrigeration cycle apparatus is supposed to, for example, increase or decrease the rotating speed of the high-stage compressor, thereby to control the intermediate pressure P M .
- the rotating speed of the high-stage compressor is simply increased to reduce the intermediate pressure P M , this results in an increase in condensation load in the radiator located downstream of the high-stage compressor.
- the high pressure P H that is a discharge pressure of the high-stage compressor may excessively increase.
- the intermediate pressure P M may possibly exceed the critical pressure P K as shown in Fig. 3 .
- the injection circuit 70 is provided with the receiver 72 and the flow control valve 73 as shown in Fig. 1 .
- the controller 90 controls the intermediate pressure P M that is an internal pressure in the receiver 72 such that the intermediate pressure P M is reduced to the critical pressure P K or lower.
- the controller 90 decreases the opening degree of the flow control valve 73 to allow liquid refrigerant to be stored in the receiver 72, thereby to decrease the high pressure P H .
- a control method (M1) described below is used to control the intermediate pressure P M .
- a control method (M2) described below is used to control the high pressure P H . Note that the control by use of the control method (M2) is exercised only when necessary.
- Control method (M1) The intermediate pressure P M is controlled to become lower than or equal to the critical pressure P K . Specifically, the intermediate pressure P M is reduced by increasing the ratio of a displacement of the high-stage compressor 11 to a displacement of the low-stage compressor 12.
- Control method (M2) The high pressure P H is controlled not to exceed a design pressure of the high-stage compressor 11. Specifically, the high pressure P H is decreased by reducing the outflow amount of liquid refrigerant that flows out from the receiver 72 to store the liquid refrigerant in the receiver 72.
- Fig. 4 is a flowchart illustrating a processing flow of the control method (M1) in the refrigeration cycle apparatus according to Embodiment 1.
- the intermediate pressure P M is controlled to become lower than or equal to a first threshold.
- step S1 the controller 90 obtains a detection value of the intermediate pressure P M from the first pressure sensor 81.
- step S2 the controller 90 compares the intermediate pressure P M with the first threshold.
- the process proceeds to step S3.
- a result of the comparison shows that the intermediate pressure P M is lower than or equal to the first threshold
- the processing of flow in Fig. 4 is terminated with no further processing.
- step S3 the controller 90 performs first processing, which is set in advance, on the intermediate pressure P M such that the intermediate pressure P M becomes lower than or equal to the first threshold.
- the first processing will be described below. With this first processing, the intermediate pressure P M is decreased.
- the first threshold is, for example, the critical pressure P K . Since Embodiment 1 is supposed to use CO 2 (carbon dioxide) as refrigerant, the first threshold is, for example, the critical pressure P K of CO 2 . CO 2 is known to have a critical temperature of 31.1 degrees C and a critical pressure P K of 7.1 MPa. Therefore, the first threshold is, for example, 7.1 MPa. As described above, CO 2 is a refrigerant that can be brought into a supercritical state under relatively mild conditions such as the critical temperature of 31.1 degrees C and the critical pressure P K of 7.1 MPa.
- the following processing is performed.
- the controller 90 increases the ratio of a displacement of the high-stage compressor 11 to a displacement of the low-stage compressor 12. That is, the controller 90 increases the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12.
- the displacements of the low-stage compressor 12 and the high-stage compressor 11 are calculated by Expression (2) below. That is, not only the ratio of rotating speed between the low-stage compressor 12 and the high-stage compressor 11 is considered, but the ratio of volume between the low-stage compressor 12 and the high-stage compressor 11 is also considered.
- Displacement of low-stage compressor volume of low-stage compressor ⁇ rotating speed of low-stage compressor
- Displacement of high-stage compressor volume of high-stage compressor ⁇ rotating speed of high-stage compressor
- the controller 90 may increase the ratio of displacement by a given amount that is set in advance. However, instead, the controller 90 may increase the ratio of displacement by an amount according to the value of intermediate pressure P M .
- a data table is stored in advance. In the data table, the amounts of increase in the ratio of displacement are associated with the values of intermediate pressure P M .
- the ratio of the rotating speed of the high-stage compressor 11 to the rotating speed of the low-stage compressor 12 may be increased. Specifically, at least one of the rotating speed of the low-stage compressor 12 and the rotating speed of the high-stage compressor 11 is controlled
- step S3 the controller 90 performs the first processing, which is set in advance. With this first processing, the intermediate pressure P M is decreased. The controller 90 repeats the processing of flow in Fig. 4 at given intervals. With this repetitive processing, the controller 90 can control the intermediate pressure P M such that intermediate pressure P M becomes lower than or equal to the critical pressure P K . The intermediate pressure P M is controlled to be constantly lower than or equal to the critical pressure P K in the manner as described above. Consequently, this can ensure that liquid refrigerant is stored at the critical pressure P K or lower in the receiver 72.
- step S3 as the first processing, the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12 is increased, instead of simply increasing the displacement of the high-stage compressor 11.
- the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12 is increased. This can prevent an increase in the condensation load in the condenser 20, and accordingly can reduce or eliminate an excessive increase in the high pressure P H . Since an increase in the condensation load in the condenser 20 can be prevented, the condenser 20 can be decreased in size (in other words, downsized), and manufacturing costs of the refrigeration cycle apparatus can be reduced accordingly.
- Fig. 5 is a flowchart illustrating a processing flow of the control method (M2) in the refrigeration cycle apparatus according to Embodiment 1.
- the high pressure P H is controlled not to exceed a design pressure Pcomp of the high-stage compressor 11.
- a design pressure Pcomp and a proof pressure Pmax are set for a compressor.
- the design pressure Pcomp refers to a reference pressure value used for design calculation for a strength of a compressor.
- the design pressure Pcomp is set to a value greater than or equal to the maximum possible value of internal pressure P in a compressor, which can be generated during normal operation of the compressor.
- the design pressure Pcomp is obtained by multiplying the maximum possible value of internal pressure P, which can be generated during normal operation of the compressor, by a coefficient larger than or equal to 1 (for example, 1.1).
- the design pressure Pcomp is obtained by adding a certain value (for example, 0.1 Mpa) to the maximum possible value of internal pressure P, which can be generated during normal operation of the compressor.
- the proof pressure Pmax of the compressor is a legally-specified value based on the design pressure Pcomp of the compressor.
- the proof pressure Pmax is set at a value greater than the design pressure Pcomp of the compressor in accordance with the law.
- a value of breaking pressure Pbr at which the compressor can possibly be broken has a tolerance on the higher-pressure side from the proof pressure Pmax. That is, the value of breaking pressure Pbr is larger than the value of proof pressure Pmax.
- the breaking pressure Pbr is obtained by durability experiments on the compressor or other experiments.
- a compressor is designed to ensure the proof pressure Pmax, which is legally specified according to the design pressure Pcomp. Therefore, the high pressure P H is controlled not to exceed the design pressure Pcomp of the high-stage compressor 11, and the high-stage compressor 11 is thus surely prevented from being broken.
- step S11 the controller 90 obtains a detection value of the high pressure P H from the second pressure sensor 82.
- step S12 the controller 90 compares the high pressure P H with the second threshold.
- the process proceeds to step S13.
- the processing of flow in Fig. 5 is terminated with no further processing.
- step S13 the controller 90 performs second processing, which is set in advance, on the high pressure P H such that the high pressure P H becomes lower than or equal to the second threshold.
- the second processing will be described below. With this second processing, the high pressure P H is decreased.
- the second threshold is, for example, the design pressure Pcomp of the high-stage compressor 11.
- the design pressure Pcomp is obtained by multiplying the maximum possible value of internal pressure P, which can be generated during normal operation of the high-stage compressor 11, by a coefficient larger than or equal to 1 (for example, 1.1).
- the design pressure Pcomp is obtained by adding a certain value (for example, 0.1 Mpa) to the maximum possible value of internal pressure P, which can be generated during normal operation of the high-stage compressor 11.
- the following processing is performed.
- the controller 90 decreases the opening degree of the flow control valve 73 as the second processing.
- the controller 90 may decrease the opening degree of the flow control valve 73 by a given amount that is set in advance. However, instead, the controller 90 may increase the opening degree of the flow control valve 73 by an amount according to the value of high pressure P H .
- a data table is stored in advance. In the data table, the amounts of decrease in the opening degree of the flow control valve 73 are associated with the values of high pressure P H .
- step S13 the controller 90 performs the second processing, which is set in advance. With this second processing, the high pressure P H is decreased.
- the controller 90 repeats the processing of flow in Fig. 5 at given intervals in parallel with the processing of flow in Fig. 4 .
- the processing of flow in Fig. 4 and the processing of flow in Fig. 5 are performed alternately.
- the controller 90 can control the high pressure P H to prevent the high pressure P H from exceeding the design pressure Pcomp of the high-stage compressor 11. That is, the controller 90 can control the high pressure P H such that the high pressure P H constantly satisfies the following relationship: the high pressure P H > the second threshold. In this manner, the controller 90 controls the high pressure P H such that the high pressure P H is constantly lower than or equal to the second threshold.
- the flat tubes are smaller in internal volume of the flow passage through which refrigerant flows (that is, cross-sectional area of the flow passage) than circular tubes.
- Embodiment 1 liquid refrigerant is stored in the receiver 72, which can increase the amount of surplus refrigerant in the receiver 72. This makes it possible to reduce the high pressure P H . As a consequence, it is possible to use the flat tubes as the heat transfer tubes of the condenser 20.
- the controller 90 controls the high pressure P H such that the high pressure P H is constantly lower than or equal to the second threshold. Consequently, the flat tubes can be employed for the condenser 20, and accordingly the condenser 20 and thus the refrigeration cycle apparatus can both be decreased in size.
- Fig. 6 is a p-h diagram illustrating a refrigeration cycle of the refrigeration cycle apparatus according to Embodiment 1.
- the horizontal axis represents a specific enthalpy, while the vertical axis represents a pressure of refrigerant.
- the points A to J in Fig. 6 correspond to the points A to J shown on the refrigerant circuit diagram in Fig. 1 .
- the point C and the point C1 are at the same position, however, in Fig. 6 , these points C and C1 are shown slightly apart from each other for convenience of description.
- the high-stage compressor 11 sucks refrigerant having the intermediate pressure P M (at the point J) and compresses the refrigerant to the high pressure P H (at the point A).
- the high-temperature and high-pressure gas refrigerant transfers heat to air and is condensed to become refrigerant having the high pressure P H (at the point B).
- the high-pressure refrigerant passes through the heat inter changer (HIC) 30 in the direction of the arrow P1 in Fig.
- the remaining portion of the refrigerant passing through the heat inter changer (HIC) 30 flows into the expansion valve 40.
- the refrigerant having the high pressure P H is decompressed to the low pressure P L , and becomes two-phase gas-liquid refrigerant (at the point D).
- the two-phase refrigerant having the low pressure P L flows into the evaporator 50.
- the two-phase refrigerant having the low pressure P L receives heat from air and thus evaporates to become gas refrigerant having the low pressure P L (at the point E). This gas refrigerant having the low pressure P L flows into the low-stage compressor 12.
- the low-stage compressor 12 sucks refrigerant having the low pressure P L and compresses the refrigerant to the intermediate pressure P M (at the point F).
- the gas refrigerant having the intermediate pressure P M and discharged from the low-stage compressor 12 (at the point F) joins (at the point J) with the two-phase refrigerant having the intermediate pressure P M and flowing out from the heat inter changer (HIC) 30 in the direction of the arrow P2 (at the point I).
- This refrigerant is sucked into the high-stage compressor 11, and the same cycle is repeated again.
- the refrigeration cycle apparatus includes the injection circuit 70 including the receiver 72 and the flow control valve 73.
- the controller 90 controls the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12 such that, even when a high-pressure supercritical refrigerant such as CO 2 is used, the controller 90 can still control the intermediate pressure P M to prevent it from exceeding the critical pressure P K . With this control, the internal pressure in the receiver 72 can be maintained at the critical pressure P K or lower. This makes it possible to always store liquid refrigerant in the receiver 72.
- Embodiment 1 can ensure that, even when a CO 2 refrigerant is used, at least a portion of the CO 2 refrigerant is stored as liquid refrigerant at the critical pressure P K or lower in the receiver 72.
- the high pressure P H that is a discharge pressure of the high-stage compressor 11 can be prevented from excessively increasing, and accordingly an increase in the condensation load in the condenser 20 can be reduced or eliminated.
- an increase in the condensation load in the condenser 20 can be reduced or eliminated in the manner as described above. It is thus possible to decrease the condenser 20 in size (downsize the condenser 20). As the condenser 20 is decreased in size, the manufacturing costs of the condenser 20 are reduced accordingly. This consequently leads to a reduction in the manufacturing costs of the refrigeration cycle apparatus in its entirety.
- the controller 90 controls the opening degree of the flow control valve 73 according to a detection value of high pressure P H , such that the high pressure P H does not exceed the design pressure Pcomp of the high-stage compressor 11.
- the outflow amount of liquid refrigerant that flows out from the receiver 72 is reduced and the liquid refrigerant can thus be stored in the receiver 72.
- the outflow amount of liquid refrigerant that flows out from the receiver 72 is reduced, and accordingly the amount of refrigerant to be sucked into the high-stage compressor 11 is decreased so that the high pressure P H that is a discharge pressure of the high-stage compressor 11 can be decreased.
- Embodiment 1 an increase in the high pressure P H can be reduced or eliminated by storing liquid refrigerant in the receiver 72. It is thus possible for the condenser 20 provided downstream of the high-stage compressor 11 to use flat tubes whose flow passages have a relatively small internal volume.
- the refrigeration cycle apparatus according to Embodiment 1 which is capable of controlling the intermediate pressure P M to prevent it from exceeding the critical pressure P K , is effective particularly when CO 2 is used as refrigerant.
- the heat inter changer (HIC) 30 is provided and thus the degree of subcooling can be increased. Therefore, the performance of the refrigeration cycle apparatus can further be improved.
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Abstract
A refrigeration cycle apparatus includes a controller, a low-stage compressor configured to compress refrigerant from a first pressure to an intermediate pressure that is higher than the first pressure, a high-stage compressor configured to compress the refrigerant having the intermediate pressure from the intermediate pressure to a second pressure that is higher than the intermediate pressure, a condenser through which the refrigerant having the second pressure exchanges heat with air, an INJ branch unit through which the refrigerant flowing out from the condenser is divided into first refrigerant and second refrigerant, an expansion valve configured to expand the first refrigerant divided through the INJ branch unit to decompress the first refrigerant to the first pressure, an evaporator through which the first refrigerant flowing out from the expansion valve exchanges heat with air and from which the first refrigerant having the first pressure flows out toward the low-stage compressor, an INJ junction unit located between a discharge port of the low-stage compressor and a suction port of the high-stage compressor, and an injection circuit located between the INJ branch unit and the INJ junction unit and through which the second refrigerant divided through the INJ branch unit is sucked into the high-stage compressor. The injection circuit includes an INJ expansion valve configured to expand the second refrigerant and a receiver configured to divide the second refrigerant expanded by the INJ expansion valve into liquid refrigerant and gas refrigerant and store the liquid refrigerant and the gas refrigerant. The stored liquid refrigerant flows out from the receiver toward the INJ junction unit. The controller is configured to control a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor. The displacement of the low-stage compressor is a value obtained by multiplying a volume of the low-stage compressor and a rotating speed of the low-stage compressor. The displacement of the high-stage compressor is a value obtained by multiplying a volume of the high-stage compressor and a rotating speed of the high-stage compressor.
Description
- The present disclosure relates to a refrigeration cycle apparatus including an injection circuit.
- Some multistage-compression refrigeration cycle apparatus has been known that includes a low-stage compressor and a high-stage compressor and compresses refrigerant in two stages (see, for example, Patent Literature 1).
- In the refrigeration cycle apparatus described in Patent Literature 1, the low-stage compressor, the high-stage compressor, a radiator, a heat inter changer, a first expansion valve, and an evaporator are connected by refrigerant pipes.
- In the refrigeration cycle apparatus described in Patent Literature 1, an injection circuit is provided as a bypass for refrigerant having an intermediate pressure. One end of the injection circuit is connected between the radiator and the heat inter changer. The other end of the injection circuit is connected between a discharge port of the low-stage compressor and a suction port of the high-stage compressor. The injection circuit is provided with a second expansion valve. The heat inter changer described above is located downstream of the second expansion valve.
- The low-stage compressor compresses sucked refrigerant from a low pressure to an intermediate pressure. The high-stage compressor compresses the refrigerant discharged from the low-stage compressor and having an intermediate pressure to a high pressure. The refrigerant discharged from the high-stage compressor flows into the radiator. Through the radiator, the refrigerant exchanges heat with air, and is thus condensed. In the heat inter changer, subcooling is provided to the refrigerant condensed through the radiator. Hereinafter, this refrigerant to which subcooling has been provided is referred to as "first refrigerant."
- Meanwhile, the refrigerant condensed through the radiator is partially divided into the injection circuit. In the injection circuit, this refrigerant is decompressed by the second expansion valve and thereafter flows into the heat inter changer. In the heat inter changer, this refrigerant provides subcooling to the first refrigerant. Hereinafter, the refrigerant having provided subcooling to the first refrigerant is referred to as "second refrigerant." Thereafter, the second refrigerant is guided to the discharge side of the low-stage compressor that is the suction side of the high-stage compressor.
- Meanwhile, the first refrigerant to which subcooling has been provided in the heat inter changer is guided to the first expansion valve. The first refrigerant expanded to a low pressure by the first expansion valve flows into the evaporator. Through the evaporator, the first refrigerant exchanges heat with air, and thus evaporates. The first refrigerant having evaporated through the evaporator is sucked into the low-stage compressor.
- At the start-up of the refrigeration cycle apparatus described in Patent Literature 1, this refrigeration cycle apparatus causes the low-stage compressor and the high-stage compressor to start operating at individual rotating speeds that are lower than their respective maximum possible rotating speeds at which the low-stage compressor and the high-stage compressor exhibit maximum possible performance, and to increase the individual rotating speeds in stages.
- Patent Literature 1:
Japanese Unexamined Patent Application Publication No. 2012-247154 - If the refrigeration cycle apparatus described in Patent Literature 1 controls the value of intermediate pressure, this refrigeration cycle apparatus is supposed to, for example, increase or decrease the rotating speed of the high-stage compressor, thereby to control this value. When the rotating speed of the high-stage compressor is simply increased to reduce the intermediate pressure, a condensation load in the radiator increases. There is thus a possibility that a discharge pressure (that is, a high pressure) of the high-stage compressor may excessively increase.
- The present disclosure has been made to solve the above problems, and it is an object of the present disclosure to provide a refrigeration cycle apparatus in which it is possible to reduce or eliminate an excessive increase in high pressure, while reducing an intermediate pressure.
- A refrigeration cycle apparatus according to an embodiment of the present disclosure includes a controller, a low-stage compressor configured to compress refrigerant from a first pressure to an intermediate pressure that is higher than the first pressure, a high-stage compressor configured to compress the refrigerant having the intermediate pressure from the intermediate pressure to a second pressure that is higher than the intermediate pressure, a condenser through which the refrigerant having the second pressure exchanges heat with air, an INJ branch unit through which the refrigerant flowing out from the condenser is divided into first refrigerant and second refrigerant, an expansion valve configured to expand the first refrigerant divided through the INJ branch unit to decompress the first refrigerant to the first pressure, an evaporator through which the first refrigerant flowing out from the expansion valve exchanges heat with air and from which the first refrigerant having the first pressure flows out toward the low-stage compressor, an INJ junction unit located between a discharge port of the low-stage compressor and a suction port of the high-stage compressor, and an injection circuit located between the INJ branch unit and the INJ junction unit and through which the second refrigerant divided through the INJ branch unit is sucked into the high-stage compressor. The injection circuit includes an INJ expansion valve configured to expand the second refrigerant and a receiver configured to divide the second refrigerant expanded by the INJ expansion valve into liquid refrigerant and gas refrigerant and store the liquid refrigerant and the gas refrigerant. The stored liquid refrigerant flows out from the receiver toward the INJ junction unit. The controller is configured to control a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor. The displacement of the low-stage compressor is a value obtained by multiplying a volume of the low-stage compressor and a rotating speed of the low-stage compressor. The displacement of the high-stage compressor is a value obtained by multiplying a volume of the high-stage compressor and a rotating speed of the high-stage compressor.
- In the refrigeration cycle apparatus according to an embodiment of the present disclosure, the injection circuit is provided with the receiver to control the ratio of the displacement of the high-stage compressor to the displacement of the low-stage compressor, and thereby control the intermediate pressure that is an internal pressure in the receiver. Therefore, the refrigeration cycle apparatus can reduce or eliminate an excessive increase in the high pressure that is a discharge pressure of the high-stage compressor, while reducing the intermediate pressure.
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- [
Fig. 1] Fig. 1 is a refrigerant circuit diagram illustrating the configuration of a refrigeration cycle apparatus according to Embodiment 1. - [
Fig. 2] Fig. 2 is a perspective view illustrating an example of the configuration of a heat inter changer (HIC) 30 provided in the refrigeration cycle apparatus according to Embodiment 1. - [
Fig. 3] Fig. 3 is a p-h diagram illustrating a refrigeration cycle when a refrigeration cycle apparatus described in Patent Literature 1 uses a high-pressure supercritical refrigerant such as CO2. - [
Fig. 4] Fig. 4 is a flowchart illustrating a processing flow of a control method (M1) in the refrigeration cycle apparatus according to Embodiment 1. - [
Fig. 5] Fig. 5 is a flowchart illustrating a processing flow of a control method (M2) in the refrigeration cycle apparatus according to Embodiment 1. - [
Fig. 6] Fig. 6 is a p-h diagram illustrating a refrigeration cycle of the refrigeration cycle apparatus according to Embodiment 1. - Hereinafter, an embodiment of a refrigeration cycle apparatus according to the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the embodiment described below, and can be variously modified without departing from the scope of the present disclosure. In addition, the present disclosure includes all combinations of configurations that can be combined among the configurations shown in the embodiment described below and its modification. In the drawings below, the same reference signs denote the same or equivalent components, which are common throughout the entire specification. Note that the relative relationship of sizes of the constituent components, the shapes of the constituent components, and other features in the drawings may differ from those of actual ones.
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Fig. 1 is a refrigerant circuit diagram illustrating the configuration of a refrigeration cycle apparatus according to Embodiment 1. As shown inFig. 1 , the refrigeration cycle apparatus includes a refrigerant circuit as a main circuit in which acompressor 10, acondenser 20, a heat inter changer (HIC) 30, anexpansion valve 40, and anevaporator 50 are connected by arefrigerant pipe 60. Thecompressor 10 includes a high-stage compressor 11 and a low-stage compressor 12. - As shown in
Fig. 1 , therefrigerant pipe 60 is provided with an INJbranch unit 61 and an INJjunction unit 62. The INJbranch unit 61 is located between the heat inter changer (HIC) 30 and theexpansion valve 40. TheINJ junction unit 62 is located between a discharge port of the low-stage compressor 12 and a suction port of the high-stage compressor 11. - As shown in
Fig. 1 , the refrigeration cycle apparatus includes aninjection circuit 70. Theinjection circuit 70 is an intermediate-pressure refrigerant bypass circuit through which refrigerant having an intermediate pressure PM flows. The intermediate pressure PM will be described later. One end of theinjection circuit 70 is connected to theINJ branch unit 61, while the other end of theinjection circuit 70 is connected to theINJ junction unit 62. - The
injection circuit 70 is formed in which anINJ expansion valve 71, areceiver 72, and aflow control valve 73 are connected by aninjection pipe 76. Theinjection circuit 70 may be provided with agas vent pipe 74. Thegas vent pipe 74 is a bypass pipe connected to thereceiver 72 and theinjection pipe 76. Thegas vent pipe 74 may be provided with an on-offvalve 75. - In the main circuit, refrigerant flows inside the
refrigerant pipe 60 through the low-stage compressor 12, theINJ junction unit 62, the high-stage compressor 11, thecondenser 20, the heat inter changer (HIC) 30, theINJ branch unit 61, theexpansion valve 40, and theevaporator 50 in this order. - In the
injection circuit 70, refrigerant flows inside theinjection pipe 76 through theINJ branch unit 61, theINJ expansion valve 71, thereceiver 72, theflow control valve 73, the heat inter changer (HIC) 30, and theINJ junction unit 62 in this order. - The configurations of the devices that form the refrigeration cycle apparatus shown in
Fig. 1 are described below. - The low-
stage compressor 12 compresses sucked refrigerant from a low pressure PL to the intermediate pressure PM, and discharges the compressed refrigerant. The low-stage compressor 12 is, for example, an inverter compressor. In a case where the low-stage compressor 12 is an inverter compressor, the rotating speed may be optionally changed by use of a drive circuit such as an inverter circuit to change the refrigerant delivery capacity of the low-stage compressor 12 per unit time. In this case, the drive circuit is controlled by acontroller 90. Note that the low pressure PL is a first pressure, which is set in advance. - The high-
stage compressor 11 compresses, to a high pressure PH, the refrigerant discharged from the low-stage compressor 12 and having the intermediate pressure PM, and the refrigerant flowing in from theinjection circuit 70 and having the intermediate pressure PM. The refrigerant discharged from the high-stage compressor 11 flows into thecondenser 20. The high-stage compressor 11 is, for example, an inverter compressor. In a case where the high-stage compressor 11 is an inverter compressor, the rotating speed may be optionally changed by use of a drive circuit such as an inverter circuit to change the refrigerant delivery capacity of the high-stage compressor 11 per unit time. In this case, the drive circuit is controlled by thecontroller 90. Note that the high pressure PH is a second pressure, which is set in advance. The second pressure is higher than the first pressure. The intermediate pressure PM is higher than the first pressure and lower than the second pressure. - The
condenser 20 is located, for example, outdoors. Thecondenser 20 is a heat exchanger through which refrigerant flowing inside the heat exchanger exchanges heat with air. Thecondenser 20 is, for example, a fin-and-tube heat exchanger. Refrigerant condensed into liquid through thecondenser 20 flows into the heat inter changer (HIC) 30. - The heat inter changer (HIC) 30 is configured to perform inter-refrigerant heat exchange to cool one refrigerant by the other refrigerant. As shown in
Fig. 2 , the heat inter changer (HIC) 30 is formed by, for example, a double pipe.Fig. 2 is a perspective view illustrating an example of the configuration of the heat inter changer (HIC) 30 provided in the refrigeration cycle apparatus according to Embodiment 1. For convenience of description,Fig. 2 illustrates a portion of the configuration of the heat inter changer (HIC) 30 in a transparent manner by use of dotted lines. In the example inFig. 2 , the heat inter changer (HIC) 30 is formed by anouter pipe 31 located on the outside, and aninner pipe 32 located inside theouter pipe 31. Refrigerant flowing out from thecondenser 20 in the direction of arrows P1 inFig. 2 flows through theouter pipe 31. Refrigerant flowing through theinjection pipe 76 in the direction of an arrow P2 inFig. 2 flows inside theinner pipe 32. As shown by the arrows inFig. 2 , a flow direction of refrigerant flowing through the outer pipe 31 (the direction of the arrows P1) is opposite to a flow direction of refrigerant flowing through the inner pipe 32 (the direction of the arrow P2). These refrigerant flows face each other. Note that the heat inter changer (HIC) 30 is not limited to the example inFig. 2 . For example, refrigerant flowing through theinjection pipe 76 may flow through theouter pipe 31, while refrigerant flowing out from thecondenser 20 may flow through theinner pipe 32. The heat inter changer (HIC) 30 may have a configuration other than the configuration shown inFig. 2 . - In the heat inter changer (HIC) 30, refrigerant (second refrigerant, which will be described later) flowing out from the
receiver 72 and flowing through theinjection pipe 76 cools refrigerant flowing out from thecondenser 20 to provide subcooling to this refrigerant flowing out from thecondenser 20. Thereafter, the refrigerant (the second refrigerant) having provided subcooling still flows through theinjection pipe 76 and is guided to theINJ junction unit 62. As described above, theINJ junction unit 62 is located on the discharge side of the low-stage compressor 12 that is the suction side of the high-stage compressor 11. - In contrast, refrigerant to which subcooling has been provided in the heat inter changer (HIC) 30 is divided into the first refrigerant and the second refrigerant through the
INJ branch unit 61. The first refrigerant divided through theINJ branch unit 61 flows through therefrigerant pipe 60 and is guided to theexpansion valve 40. Theexpansion valve 40 expands and decompresses the first refrigerant. The first refrigerant expanded to the low pressure PL flows into theevaporator 50. Theexpansion valve 40 is, for example, an electronic expansion valve. In a case where theexpansion valve 40 is formed by an electronic expansion valve, the opening degree of theexpansion valve 40 is controlled and adjusted by thecontroller 90. - The
evaporator 50 is located in, for example, a room space. Theevaporator 50 is a heat exchanger through which refrigerant flowing inside the heat exchanger exchanges heat with air. Theevaporator 50 is, for example, a fin-and-tube heat exchanger. Through theevaporator 50, the first refrigerant exchanges heat with air, and thus evaporates. The first refrigerant having evaporated into gas through theevaporator 50 is sucked into the low-stage compressor 12. The low-stage compressor 12 sucks refrigerant flowing out from theevaporator 50 and having the low pressure PL, then compresses this refrigerant to the intermediate pressure PM, and discharges the compressed refrigerant. - In contrast, the second refrigerant divided through the
INJ branch unit 61 flows through theinjection pipe 76 and then flows into theINJ expansion valve 71. - The
INJ expansion valve 71 expands and decompresses the second refrigerant. The second refrigerant expanded to the intermediate pressure PM flows into thereceiver 72. TheINJ expansion valve 71 is, for example, an electronic expansion valve. In a case where theINJ expansion valve 71 is formed by an electronic expansion valve, the opening degree of theINJ expansion valve 71 is controlled and adjusted by thecontroller 90. - The
receiver 72 stores the second refrigerant expanded to the intermediate pressure PM by theINJ expansion valve 71. In thereceiver 72, the second refrigerant is divided into liquid refrigerant and gas refrigerant. The liquid refrigerant obtained by dividing the second refrigerant by thereceiver 72 flows into theinner pipe 32 of the heat inter changer (HIC) 30 through theinjection pipe 76. The second refrigerant flowing through theinner pipe 32 exchanges heat with refrigerant flowing through theouter pipe 31, and thereafter is guided to theINJ junction unit 62. At this time, the second refrigerant cools the refrigerant flowing through theouter pipe 31 in the heat inter changer (HIC) 30 to provide subcooling to this refrigerant flowing through theouter pipe 31. Note that the heat inter changer (HIC) 30 is not necessarily provided, but may be provided only when needed. - The
flow control valve 73 is provided in theinjection pipe 76 and between thereceiver 72 and the heat inter changer (HIC) 30. The flow rate of the second refrigerant (liquid refrigerant) flowing out from thereceiver 72 is adjusted by the opening degree of theflow control valve 73. Theflow control valve 73 is, for example, an electronic adjusting valve. In this case, the opening degree of theflow control valve 73 is controlled by thecontroller 90. - At the
INJ junction unit 62, the second refrigerant flowing through theinjection pipe 76 and having the intermediate pressure PM, and the first refrigerant discharged from the low-stage compressor 12 and having the intermediate pressure PM join together. The refrigerant having joined together at theINJ junction unit 62 is sucked into the high-stage compressor 11. The high-stage compressor 11 compresses the sucked refrigerant having the intermediate pressure PM to the high pressure PH, and discharges the compressed refrigerant. - The
gas vent pipe 74 is a bypass pipe connected between thereceiver 72 and theinjection pipe 76. One end of thegas vent pipe 74 is connected to an upper portion of thereceiver 72, while the other end of thegas vent pipe 74 is connected to theinjection pipe 76 at a location between theflow control valve 73 and the heat inter changer (HIC) 30. Thegas vent pipe 74 allows gas refrigerant in thereceiver 72 to flow out to theinjection pipe 76 when the on-offvalve 75 is in an open state, and stops the outflow of the gas refrigerant in thereceiver 72 when the on-offvalve 75 is in a closed state. With this configuration, composition of the refrigerant flowing in theinjection circuit 70, that is, a gas density of this refrigerant can be finely adjusted. However, thegas vent pipe 74 is not necessarily provided, but may be provided only when needed. - The
controller 90 is formed by a processing circuit. The processing circuit is formed by dedicated hardware or a processor. Examples of the dedicated hardware include an application specific integrated circuit (ASIC) and a field programmable gate array (FPGA). The processor executes programs stored in a memory. Storage circuitry (not shown) provided in thecontroller 90 is formed by the memory. The memory is a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, and an erasable programmable ROM (EPROM), or a disk such as a magnetic disk, a flexible disk, and an optical disk. - As shown in
Fig. 1 , in Embodiment 1, afirst pressure sensor 81 configured to measure the intermediate pressure PM is installed between theINJ expansion valve 71 and thereceiver 72. Information on the intermediate pressure PM detected by thefirst pressure sensor 81 is transmitted to thecontroller 90. The intermediate pressure PM is an internal pressure in thereceiver 72. - As shown in
Fig. 1 , in Embodiment 1, a second pressure sensor 82 configured to measure the high pressure PH is further installed between the discharge port of the high-stage compressor 11 and thecondenser 20. Information on the high pressure PH detected by the second pressure sensor 82 is transmitted to thecontroller 90. The high pressure PH is a discharge pressure of the high-stage compressor 11. - The refrigeration cycle apparatus described in Patent Literature 1 mentioned above is not supposed to use a high-pressure supercritical refrigerant such as CO2 (carbon dioxide) as refrigerant. In contrast, in the refrigeration cycle apparatus according to Embodiment 1, it is possible to use a high-pressure supercritical refrigerant such as CO2. If the refrigeration cycle apparatus described in Patent Literature 1 uses the high-pressure supercritical refrigerant such as CO2, the intermediate pressure may exceed a critical pressure.
-
Fig. 3 is a p-h diagram illustrating a refrigeration cycle when the refrigeration cycle apparatus described in Patent Literature 1 uses the high-pressure supercritical refrigerant such as CO2. InFig. 3 , the horizontal axis represents a specific enthalpy, while the vertical axis represents a pressure of refrigerant. Asolid line 100 shows a saturated vapor line. Asolid line 101 shows a saturated liquid line. The intersection of the saturatedvapor line 100 and the saturatedliquid line 101 is represented as K showing a critical point. A critical pressure that is a pressure at the critical point K is represented as PK. - In
Fig. 3 , T1 shows a compression process performed by the high-stage compressor, T2 shows a condensation process performed by the radiator, and T3 shows a heat exchange process performed by the heat inter changer. T4 shows an expansion process performed by the first expansion valve. T5 shows an evaporation process performed by the evaporator. T6 shows a compression process performed by the low-stage compressor. T7 shows an expansion process performed by the second expansion valve. T8 shows a heat exchange process performed by the heat inter changer. - When the refrigeration cycle apparatus described in Patent Literature 1 mentioned above controls the intermediate pressure PM, this refrigeration cycle apparatus is supposed to, for example, increase or decrease the rotating speed of the high-stage compressor, thereby to control the intermediate pressure PM. At this time, when the rotating speed of the high-stage compressor is simply increased to reduce the intermediate pressure PM, this results in an increase in condensation load in the radiator located downstream of the high-stage compressor. As a consequence, there is a possibility that the high pressure PH that is a discharge pressure of the high-stage compressor may excessively increase. In this case, the intermediate pressure PM may possibly exceed the critical pressure PK as shown in
Fig. 3 . - In view of the above, in the refrigeration cycle apparatus according to Embodiment 1, the
injection circuit 70 is provided with thereceiver 72 and theflow control valve 73 as shown inFig. 1 . Further, in the refrigeration cycle apparatus according to Embodiment 1, thecontroller 90 controls the intermediate pressure PM that is an internal pressure in thereceiver 72 such that the intermediate pressure PM is reduced to the critical pressure PK or lower. During the control, when the high pressure PH increases excessively, thecontroller 90 decreases the opening degree of theflow control valve 73 to allow liquid refrigerant to be stored in thereceiver 72, thereby to decrease the high pressure PH. Specifically, a control method (M1) described below is used to control the intermediate pressure PM. In addition, a control method (M2) described below is used to control the high pressure PH. Note that the control by use of the control method (M2) is exercised only when necessary. - Control method (M1): The intermediate pressure PM is controlled to become lower than or equal to the critical pressure PK. Specifically, the intermediate pressure PM is reduced by increasing the ratio of a displacement of the high-
stage compressor 11 to a displacement of the low-stage compressor 12. - Control method (M2): The high pressure PH is controlled not to exceed a design pressure of the high-
stage compressor 11. Specifically, the high pressure PH is decreased by reducing the outflow amount of liquid refrigerant that flows out from thereceiver 72 to store the liquid refrigerant in thereceiver 72. - First, the control method (M1) is explained.
Fig. 4 is a flowchart illustrating a processing flow of the control method (M1) in the refrigeration cycle apparatus according to Embodiment 1. InFig. 4 , the intermediate pressure PM is controlled to become lower than or equal to a first threshold. - As shown in
Fig. 4 , in step S1, thecontroller 90 obtains a detection value of the intermediate pressure PM from thefirst pressure sensor 81. - Next, in step S2, the
controller 90 compares the intermediate pressure PM with the first threshold. When a result of the comparison shows that the intermediate pressure PM is higher than the first threshold, the process proceeds to step S3. In contrast, when a result of the comparison shows that the intermediate pressure PM is lower than or equal to the first threshold, the processing of flow inFig. 4 is terminated with no further processing. - In step S3, the
controller 90 performs first processing, which is set in advance, on the intermediate pressure PM such that the intermediate pressure PM becomes lower than or equal to the first threshold. The first processing will be described below. With this first processing, the intermediate pressure PM is decreased. - The first threshold is, for example, the critical pressure PK. Since Embodiment 1 is supposed to use CO2 (carbon dioxide) as refrigerant, the first threshold is, for example, the critical pressure PK of CO2. CO2 is known to have a critical temperature of 31.1 degrees C and a critical pressure PK of 7.1 MPa. Therefore, the first threshold is, for example, 7.1 MPa. As described above, CO2 is a refrigerant that can be brought into a supercritical state under relatively mild conditions such as the critical temperature of 31.1 degrees C and the critical pressure PK of 7.1 MPa.
- As an example of the first processing, the following processing is performed.
- As the first processing, the
controller 90 increases the ratio of a displacement of the high-stage compressor 11 to a displacement of the low-stage compressor 12. That is, thecontroller 90 increases the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12. The displacements of the low-stage compressor 12 and the high-stage compressor 11 are calculated by Expression (2) below. That is, not only the ratio of rotating speed between the low-stage compressor 12 and the high-stage compressor 11 is considered, but the ratio of volume between the low-stage compressor 12 and the high-stage compressor 11 is also considered. - The
controller 90 may increase the ratio of displacement by a given amount that is set in advance. However, instead, thecontroller 90 may increase the ratio of displacement by an amount according to the value of intermediate pressure PM. In this case, in the storage circuitry of thecontroller 90, a data table is stored in advance. In the data table, the amounts of increase in the ratio of displacement are associated with the values of intermediate pressure PM. When the volume of the low-stage compressor 12 and the high-stage compressor 11 is considered constant, the ratio of the rotating speed of the high-stage compressor 11 to the rotating speed of the low-stage compressor 12 may be increased. Specifically, at least one of the rotating speed of the low-stage compressor 12 and the rotating speed of the high-stage compressor 11 is controlled - In the manner as described above, in step S3, the
controller 90 performs the first processing, which is set in advance. With this first processing, the intermediate pressure PM is decreased. Thecontroller 90 repeats the processing of flow inFig. 4 at given intervals. With this repetitive processing, thecontroller 90 can control the intermediate pressure PM such that intermediate pressure PM becomes lower than or equal to the critical pressure PK. The intermediate pressure PM is controlled to be constantly lower than or equal to the critical pressure PK in the manner as described above. Consequently, this can ensure that liquid refrigerant is stored at the critical pressure PK or lower in thereceiver 72. - In step S3, as the first processing, the ratio of the displacement of the high-
stage compressor 11 to the displacement of the low-stage compressor 12 is increased, instead of simply increasing the displacement of the high-stage compressor 11. When the displacement of the high-stage compressor 11 is simply increased, a condensation load in thecondenser 20 increases, and there is a possibility that the high pressure PH may excessively increase. In view of that, in Embodiment 1, the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12 is increased. This can prevent an increase in the condensation load in thecondenser 20, and accordingly can reduce or eliminate an excessive increase in the high pressure PH. Since an increase in the condensation load in thecondenser 20 can be prevented, thecondenser 20 can be decreased in size (in other words, downsized), and manufacturing costs of the refrigeration cycle apparatus can be reduced accordingly. - Next, the control method (M2) is explained.
Fig. 5 is a flowchart illustrating a processing flow of the control method (M2) in the refrigeration cycle apparatus according to Embodiment 1. InFig. 5 , the high pressure PH is controlled not to exceed a design pressure Pcomp of the high-stage compressor 11. - In general, a design pressure Pcomp and a proof pressure Pmax are set for a compressor. The design pressure Pcomp refers to a reference pressure value used for design calculation for a strength of a compressor. The design pressure Pcomp is set to a value greater than or equal to the maximum possible value of internal pressure P in a compressor, which can be generated during normal operation of the compressor. The design pressure Pcomp is obtained by multiplying the maximum possible value of internal pressure P, which can be generated during normal operation of the compressor, by a coefficient larger than or equal to 1 (for example, 1.1). Alternatively, the design pressure Pcomp is obtained by adding a certain value (for example, 0.1 Mpa) to the maximum possible value of internal pressure P, which can be generated during normal operation of the compressor.
- The proof pressure Pmax of the compressor is a legally-specified value based on the design pressure Pcomp of the compressor. The proof pressure Pmax is set at a value greater than the design pressure Pcomp of the compressor in accordance with the law.
- A value of breaking pressure Pbr at which the compressor can possibly be broken has a tolerance on the higher-pressure side from the proof pressure Pmax. That is, the value of breaking pressure Pbr is larger than the value of proof pressure Pmax. When the internal pressure in the compressor exceeds the breaking pressure Pbr, a pressure vessel that forms a housing of the compressor may possibly be broken. Note that the breaking pressure Pbr is obtained by durability experiments on the compressor or other experiments.
- In the manner as described above, a compressor is designed to ensure the proof pressure Pmax, which is legally specified according to the design pressure Pcomp. Therefore, the high pressure PH is controlled not to exceed the design pressure Pcomp of the high-
stage compressor 11, and the high-stage compressor 11 is thus surely prevented from being broken. - As shown in
Fig. 5 , in step S11, thecontroller 90 obtains a detection value of the high pressure PH from the second pressure sensor 82. - Next, in step S12, the
controller 90 compares the high pressure PH with the second threshold. When a result of the comparison shows that the high pressure PH is higher than the second threshold, the process proceeds to step S13. In contrast, when a result of the comparison shows that the high pressure PH is lower than or equal to the second threshold, the processing of flow inFig. 5 is terminated with no further processing. - In step S13, the
controller 90 performs second processing, which is set in advance, on the high pressure PH such that the high pressure PH becomes lower than or equal to the second threshold. The second processing will be described below. With this second processing, the high pressure PH is decreased. - The second threshold is, for example, the design pressure Pcomp of the high-
stage compressor 11. The design pressure Pcomp is obtained by multiplying the maximum possible value of internal pressure P, which can be generated during normal operation of the high-stage compressor 11, by a coefficient larger than or equal to 1 (for example, 1.1). Alternatively, the design pressure Pcomp is obtained by adding a certain value (for example, 0.1 Mpa) to the maximum possible value of internal pressure P, which can be generated during normal operation of the high-stage compressor 11. - As an example of the second processing, the following processing is performed.
- The
controller 90 decreases the opening degree of theflow control valve 73 as the second processing. - The
controller 90 may decrease the opening degree of theflow control valve 73 by a given amount that is set in advance. However, instead, thecontroller 90 may increase the opening degree of theflow control valve 73 by an amount according to the value of high pressure PH. In this case, in the storage circuitry of thecontroller 90, a data table is stored in advance. In the data table, the amounts of decrease in the opening degree of theflow control valve 73 are associated with the values of high pressure PH. - In the manner as described above, in step S13, the
controller 90 performs the second processing, which is set in advance. With this second processing, the high pressure PH is decreased. Thecontroller 90 repeats the processing of flow inFig. 5 at given intervals in parallel with the processing of flow inFig. 4 . However, it is desirable to delay the timing at which the processing of flow inFig. 5 starts, compared to the timing at which the processing of flow inFig. 4 starts, by a length of time, which is set in advance. Specifically, for example, the processing of flow inFig. 4 and the processing of flow inFig. 5 are performed alternately. By performing the processing inFig. 5 , thecontroller 90 can control the high pressure PH to prevent the high pressure PH from exceeding the design pressure Pcomp of the high-stage compressor 11. That is, thecontroller 90 can control the high pressure PH such that the high pressure PH constantly satisfies the following relationship: the high pressure PH > the second threshold. In this manner, thecontroller 90 controls the high pressure PH such that the high pressure PH is constantly lower than or equal to the second threshold. This makes it possible to use flat tubes as heat transfer tubes of thecondenser 20. The flat tubes are smaller in internal volume of the flow passage through which refrigerant flows (that is, cross-sectional area of the flow passage) than circular tubes. For this reason, when the high pressure PH is a high-pressure-side pressure, it is difficult to use flat tubes whose flow passages have a relatively small cross-sectional area. In Embodiment 1, liquid refrigerant is stored in thereceiver 72, which can increase the amount of surplus refrigerant in thereceiver 72. This makes it possible to reduce the high pressure PH. As a consequence, it is possible to use the flat tubes as the heat transfer tubes of thecondenser 20. In Embodiment 1, thecontroller 90 controls the high pressure PH such that the high pressure PH is constantly lower than or equal to the second threshold. Consequently, the flat tubes can be employed for thecondenser 20, and accordingly thecondenser 20 and thus the refrigeration cycle apparatus can both be decreased in size. -
Fig. 6 is a p-h diagram illustrating a refrigeration cycle of the refrigeration cycle apparatus according to Embodiment 1. InFig. 6 , the horizontal axis represents a specific enthalpy, while the vertical axis represents a pressure of refrigerant. Note that the points A to J inFig. 6 correspond to the points A to J shown on the refrigerant circuit diagram inFig. 1 . Actually, the point C and the point C1 are at the same position, however, inFig. 6 , these points C and C1 are shown slightly apart from each other for convenience of description. - First, the high-
stage compressor 11 sucks refrigerant having the intermediate pressure PM (at the point J) and compresses the refrigerant to the high pressure PH (at the point A). High-temperature and high-pressure gas refrigerant discharged from the high-stage compressor 11 (at the point A) flows into thecondenser 20. In thecondenser 20, the high-temperature and high-pressure gas refrigerant transfers heat to air and is condensed to become refrigerant having the high pressure PH (at the point B). The high-pressure refrigerant passes through the heat inter changer (HIC) 30 in the direction of the arrow P1 inFig. 1 , and is brought into a state in which the degree of subcooling is further increased (at the points C and C1). A portion of the refrigerant passing through the heat inter changer (HIC) 30 (at the point C1) flows into theINJ expansion valve 71 via theINJ branch unit 61. In theINJ expansion valve 71, the refrigerant having the high pressure PH is decompressed to the intermediate pressure PM, and flows into thereceiver 72 to become two-phase gas-liquid refrigerant (at the point H). Thereafter, the liquid refrigerant flowing out from thereceiver 72 passes through the heat inter changer (HIC) 30 in the direction of the arrow P2 that is opposite to the direction of the arrow P1 described above. This brings the liquid refrigerant into two-phase refrigerant having the intermediate pressure PM with the increased temperature (at the point I). - In contrast, the remaining portion of the refrigerant passing through the heat inter changer (HIC) 30 (at the point C) flows into the
expansion valve 40. In theexpansion valve 40, the refrigerant having the high pressure PH is decompressed to the low pressure PL, and becomes two-phase gas-liquid refrigerant (at the point D). The two-phase refrigerant having the low pressure PL (at the point D) flows into theevaporator 50. In theevaporator 50, the two-phase refrigerant having the low pressure PL receives heat from air and thus evaporates to become gas refrigerant having the low pressure PL (at the point E). This gas refrigerant having the low pressure PL flows into the low-stage compressor 12. The low-stage compressor 12 sucks refrigerant having the low pressure PL and compresses the refrigerant to the intermediate pressure PM (at the point F). The gas refrigerant having the intermediate pressure PM and discharged from the low-stage compressor 12 (at the point F) joins (at the point J) with the two-phase refrigerant having the intermediate pressure PM and flowing out from the heat inter changer (HIC) 30 in the direction of the arrow P2 (at the point I). This refrigerant is sucked into the high-stage compressor 11, and the same cycle is repeated again. - As described above, the refrigeration cycle apparatus according to Embodiment 1 includes the
injection circuit 70 including thereceiver 72 and theflow control valve 73. Thecontroller 90 controls the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12 such that, even when a high-pressure supercritical refrigerant such as CO2 is used, thecontroller 90 can still control the intermediate pressure PM to prevent it from exceeding the critical pressure PK. With this control, the internal pressure in thereceiver 72 can be maintained at the critical pressure PK or lower. This makes it possible to always store liquid refrigerant in thereceiver 72. In the manner as described above, Embodiment 1 can ensure that, even when a CO2 refrigerant is used, at least a portion of the CO2 refrigerant is stored as liquid refrigerant at the critical pressure PK or lower in thereceiver 72. As a consequence, the high pressure PH that is a discharge pressure of the high-stage compressor 11 can be prevented from excessively increasing, and accordingly an increase in the condensation load in thecondenser 20 can be reduced or eliminated. - In Embodiment 1, an increase in the condensation load in the
condenser 20 can be reduced or eliminated in the manner as described above. It is thus possible to decrease thecondenser 20 in size (downsize the condenser 20). As thecondenser 20 is decreased in size, the manufacturing costs of thecondenser 20 are reduced accordingly. This consequently leads to a reduction in the manufacturing costs of the refrigeration cycle apparatus in its entirety. - In Embodiment 1, the
controller 90 controls the opening degree of theflow control valve 73 according to a detection value of high pressure PH, such that the high pressure PH does not exceed the design pressure Pcomp of the high-stage compressor 11. With this control, the outflow amount of liquid refrigerant that flows out from thereceiver 72 is reduced and the liquid refrigerant can thus be stored in thereceiver 72. In this manner, the outflow amount of liquid refrigerant that flows out from thereceiver 72 is reduced, and accordingly the amount of refrigerant to be sucked into the high-stage compressor 11 is decreased so that the high pressure PH that is a discharge pressure of the high-stage compressor 11 can be decreased. In Embodiment 1, an increase in the high pressure PH can be reduced or eliminated by storing liquid refrigerant in thereceiver 72. It is thus possible for thecondenser 20 provided downstream of the high-stage compressor 11 to use flat tubes whose flow passages have a relatively small internal volume. - Since CO2 is a supercritical refrigerant, it is conceivable that the intermediate pressure PM may exceed the critical pressure PK. Therefore, the refrigeration cycle apparatus according to Embodiment 1, which is capable of controlling the intermediate pressure PM to prevent it from exceeding the critical pressure PK, is effective particularly when CO2 is used as refrigerant.
- In the refrigeration cycle apparatus according to Embodiment 1, the heat inter changer (HIC) 30 is provided and thus the degree of subcooling can be increased. Therefore, the performance of the refrigeration cycle apparatus can further be improved.
- 10: compressor, 11: high-stage compressor, 12: low-stage compressor, 20: condenser, 31: outer pipe, 32: inner pipe, 40: expansion valve, 50: evaporator, 60: refrigerant pipe, 61: INJ branch unit, 62: INJ junction unit, 70: injection circuit, 71: INJ expansion valve, 72: receiver, 73: flow control valve, 74: gas vent pipe, 75: on-off valve, 76: injection pipe, 81: first pressure sensor, 82: second pressure sensor, 90: controller, 100: solid line (saturated vapor line), 101: solid line (saturated liquid line), K: critical point, P: internal pressure, P1: arrow, P2: arrow, PH: high pressure, PK: critical pressure, PL: low pressure, PM: intermediate pressure, Pbr: breaking pressure, Pcomp: design pressure, Pmax: proof pressure
Claims (11)
- A refrigeration cycle apparatus, comprising:a controller;a low-stage compressor configured to compress refrigerant from a first pressure to an intermediate pressure that is higher than the first pressure;a high-stage compressor configured to compress the refrigerant having the intermediate pressure from the intermediate pressure to a second pressure that is higher than the intermediate pressure;a condenser through which the refrigerant having the second pressure exchanges heat with air;an INJ branch unit through which the refrigerant flowing out from the condenser is divided into first refrigerant and second refrigerant;an expansion valve configured to expand the first refrigerant divided through the INJ branch unit to decompress the first refrigerant to the first pressure;an evaporator through which the first refrigerant flowing out from the expansion valve exchanges heat with air and from which the first refrigerant having the first pressure flows out toward the low-stage compressor;an INJ junction unit located between a discharge port of the low-stage compressor and a suction port of the high-stage compressor; andan injection circuit located between the INJ branch unit and the INJ junction unit and through which the second refrigerant divided through the INJ branch unit is sucked into the high-stage compressor,the injection circuit includingan INJ expansion valve configured to expand the second refrigerant, anda receiver configured to divide the second refrigerant expanded by the INJ expansion valve into liquid refrigerant and gas refrigerant and store the liquid refrigerant and the gas refrigerant, the stored liquid refrigerant flowing out from the receiver toward the INJ junction unit,the controller being configured to control a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor,the displacement of the low-stage compressor being a value obtained by multiplying a volume of the low-stage compressor and a rotating speed of the low-stage compressor,the displacement of the high-stage compressor being a value obtained by multiplying a volume of the high-stage compressor and a rotating speed of the high-stage compressor.
- The refrigeration cycle apparatus of claim 1, wherein the controller is configured to control the ratio of the displacement of the high-stage compressor to the displacement of the low-stage compressor, and thereby control the intermediate pressure that is an internal pressure in the receiver such that the intermediate pressure becomes lower than or equal to a first threshold.
- The refrigeration cycle apparatus of claim 2, wherein the controller is configured to increase the ratio of the displacement of the high-stage compressor to the displacement of the low-stage compressor to decrease the intermediate pressure.
- The refrigeration cycle apparatus of claim 2 or 3, wherein the first threshold is a critical pressure that is a pressure at a critical point of the refrigerant.
- The refrigeration cycle apparatus of any one of claims 1 to 4, wherein the refrigerant is carbon dioxide.
- The refrigeration cycle apparatus of any one of claims 1 to 5, whereinthe injection circuit includesa flow control valve located between the receiver and the INJ junction unit, and configured to adjust an outflow amount of the liquid refrigerant flowing out from the receiver, andthe controller is configured to control an opening degree of the flow control valve, and thereby control the second pressure such that the second pressure becomes lower than or equal to a second threshold.
- The refrigeration cycle apparatus of claim 6, wherein the controller is configured to decrease the opening degree of the flow control valve to decrease the second pressure.
- The refrigeration cycle apparatus of claim 6 or 7, wherein the second threshold is a design pressure of the high-stage compressor.
- The refrigeration cycle apparatus of any one of claims 1 to 8, comprising a heat inter changer located between the condenser and the INJ branch unit, and configured to provide subcooling to the refrigerant flowing out from the condenser, whereinthe refrigerant flowing out from the heat inter changer is divided through the INJ branch unit into the first refrigerant and the second refrigerant, andthe liquid refrigerant flows out from the receiver toward the INJ junction unit through the heat inter changer.
- The refrigeration cycle apparatus of claim 2 or any one of claims 3 to 9 as dependent on claim 2, comprising a first pressure sensor located between the INJ expansion valve and the receiver, and configured to detect the intermediate pressure that is an internal pressure in the receiver, wherein
the controller is configured to control the intermediate pressure according to the intermediate pressure detected by the first pressure sensor such that the intermediate pressure becomes lower than or equal to the first threshold. - The refrigeration cycle apparatus of any one of claims 6 to 8, comprising a second pressure sensor located on a discharge port side of the high-stage compressor, and configured to detect the second pressure that is a discharge pressure of the high-stage compressor, wherein
the controller is configured to control the second pressure according to the second pressure detected by the second pressure sensor such that the second pressure becomes lower than or equal to the second threshold.
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