EP3109566A1 - Klimaanlagenvorrichtung - Google Patents

Klimaanlagenvorrichtung Download PDF

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Publication number
EP3109566A1
EP3109566A1 EP14883224.9A EP14883224A EP3109566A1 EP 3109566 A1 EP3109566 A1 EP 3109566A1 EP 14883224 A EP14883224 A EP 14883224A EP 3109566 A1 EP3109566 A1 EP 3109566A1
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EP
European Patent Office
Prior art keywords
refrigerant
heat exchanger
expansion device
air
compressor
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.)
Granted
Application number
EP14883224.9A
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English (en)
French (fr)
Other versions
EP3109566A4 (de
EP3109566B1 (de
Inventor
Takeshi Hatomura
Koji Yamashita
Soshi Ikeda
Shinichi Wakamoto
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Publication date
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Publication of EP3109566A1 publication Critical patent/EP3109566A1/de
Publication of EP3109566A4 publication Critical patent/EP3109566A4/de
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Publication of EP3109566B1 publication Critical patent/EP3109566B1/de
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Classifications

    • 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
    • F25B13/00—Compression machines, plants or systems, with reversible cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/80—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air
    • F24F11/83—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the supply of heat-exchange fluids to heat-exchangers
    • F24F11/84—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the supply of heat-exchange fluids to heat-exchangers using valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/80—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air
    • F24F11/83—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the supply of heat-exchange fluids to heat-exchangers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/89—Arrangement or mounting of control or safety devices
    • 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
    • F25B2313/00—Compression machines, plants or systems with reversible cycle not otherwise provided for
    • F25B2313/021—Indoor unit or outdoor unit with auxiliary heat exchanger not forming part of the indoor or outdoor unit
    • 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
    • F25B2313/00—Compression machines, plants or systems with reversible cycle not otherwise provided for
    • F25B2313/023—Compression machines, plants or systems with reversible cycle not otherwise provided for using multiple indoor units
    • F25B2313/0233—Compression machines, plants or systems with reversible cycle not otherwise provided for using multiple indoor units in parallel arrangements
    • 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
    • F25B2313/00—Compression machines, plants or systems with reversible cycle not otherwise provided for
    • F25B2313/027—Compression machines, plants or systems with reversible cycle not otherwise provided for characterised by the reversing means
    • F25B2313/02741—Compression machines, plants or systems with reversible cycle not otherwise provided for characterised by the reversing means using one four-way valve
    • 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
    • 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
    • F25B2600/2513—Expansion valves

Definitions

  • the present invention relates to an air-conditioning apparatus used as, for example, a multi-air-conditioning apparatus for buildings.
  • Some of air-conditioning apparatuses known in related art such as multi-air-conditioning apparatuses for buildings, have a refrigerant circuit in which, for example, an outdoor unit as a heat source unit disposed outside a building, and an indoor unit disposed inside the building are connected by pipes.
  • Refrigerant circulates in the refrigerant circuit, and air is heated or cooled by utilizing the rejection or removal of heat by the refrigerant, thus heating or cooling the air-conditioned space.
  • air-conditioning apparatuses employing fluorocarbon refrigerants with low global warming potentials, such as an R32 refrigerant have been considered for use in multi-air-conditioning apparatuses for buildings.
  • an R32 refrigerant is characterized by its high discharge temperature of the compressor.
  • the high discharge temperature causes problems such as degradation of the refrigerating machine oil, leading to damage to the compressor.
  • the rotation speed of the compressor needs to be lowered to reduce the compression ratio. For this reason, it is impossible to increase the rotation speed of the compressor, leading to insufficient cooling capacity or insufficient heating capacity.
  • the following approach is being proposed to address this problem.
  • Refrigerant in a two-phase gas-liquid state is injected into a medium-pressure chamber that attains a medium pressure during the compression process of the compressor, thus lowering the discharge temperature of the compressor while the rotation speed of the compressor is increased (see, for example, Patent Literature 1).
  • Patent Literature 1 Japanese Unexamined Patent Application Publication No. 2008-138921 ( Fig. 1, Fig. 2 , and other descriptions)
  • the air-conditioning apparatus according to Patent Literature 1 has a circuit configuration that allows injection to be performed also in cooling operation.
  • the air-conditioning apparatus according to Patent Literature 1 includes a bypass expansion device that controls the flow rate of refrigerant injected into the medium-pressure chamber of the compressor, and a refrigerant-to-refrigerant heat exchanger that cools the refrigerant flowing from the bypass expansion device.
  • the flow rate of refrigerant flowing into the refrigerant-to-refrigerant heat exchanger is controlled by the expansion device to control the discharge temperature at which refrigerant is discharged from the compressor.
  • the present invention has been made to address the above-mentioned problem, and ensures the reliability of the system of an air-conditioning apparatus even when an inexpensive compressor is used rather than a compressor having a special structure.
  • An air-conditioning apparatus is an air-conditioning apparatus including a refrigeration cycle in which refrigerant circulates, the refrigeration cycle including a compressor, a refrigerant flow switching device, a heat source-side heat exchanger, a load-side expansion device, and a load-side heat exchanger connected by a refrigerant pipe, the air-conditioning apparatus including a first expansion device provided between the heat source-side heat exchanger and the load-side expansion device, a bypass pipe having one end connected between the first expansion device and the heat source-side heat exchanger, and allowing refrigerant flowing out of the first expansion device to flow through the bypass pipe, an auxiliary heat exchanger connected to another end of the bypass pipe and a suction part of the compressor, and cooling refrigerant flowing through the bypass pipe and supplying the cooled refrigerant to the suction part of the compressor, a second expansion device provided on a refrigerant outlet side of the auxiliary heat exchanger, and regulating a flow rate of refrigerant allowed to flow into the
  • the controller is configured to control the first expansion device and the second expansion device to allow high-pressure refrigerant to flow into the auxiliary heat exchanger.
  • the controller is configured to control the first expansion device to allow medium-pressure refrigerant to flow into the auxiliary heat exchanger, and control the second expansion device to allow refrigerant cooled in the auxiliary heat exchanger to flow into the suction part of the compressor.
  • the state and flow rate of refrigerant flowing into the suction part of the compressor from the bypass pipe are controlled by using the auxiliary heat exchanger, the first expansion device, and the second expansion device under all operating conditions to limit a rise in the discharge temperature of refrigerant discharged from the compressor.
  • This configuration improves the reliability of the system inexpensively without employing a special structure for the compressor.
  • FIG. 1 is a schematic circuit configuration diagram illustrating an exemplary circuit configuration of the air-conditioning apparatus according to Embodiment 1.
  • An air-conditioning apparatus 100 illustrated in Fig. 1 includes an outdoor unit 1 and an indoor unit 2 that are connected by a main pipe 5. Although a single indoor unit 2 is connected to the outdoor unit 1 via the main pipe 5 in Fig. 1 , this is not intended to limit the number of indoor units 2 to one. Alternatively, multiple indoor units 2 may be connected.
  • a compressor 10 In the outdoor unit 1, a compressor 10, a refrigerant flow switching device 11, a heat source-side heat exchanger 12, an accumulator 19, an auxiliary heat exchanger 40, a first expansion device 45, a second expansion device 42, and a bypass pipe 41 are connected by a refrigerant pipe 4, and are mounted together with a fan 16 that is an air-sending device.
  • the compressor 10 sucks and compresses refrigerant to bring the refrigerant into a high-temperature, high-pressure state.
  • the compressor 10 may be an inverter compressor or other compressors whose capacity can be controlled.
  • the compressor 10 used is of, for example, one having a low-pressure shell structure in which a compression chamber is provided inside a hermetic container that is in a low refrigerant-pressure atmosphere to suck and compress the low-pressure refrigerant inside the hermetic container.
  • the refrigerant flow switching device 11 may be, for example, a four-way valve, and switches between the flow path of refrigerant in heating operation mode and the flow path of refrigerant in cooling operation mode.
  • the heating operation mode refers to a time when the heat source-side heat exchanger 12 acts as a condenser or a gas cooler, and the heating operation mode refers to a time when the heat source-side heat exchanger 12 acts as an evaporator.
  • the heat source-side heat exchanger 12 functions as an evaporator in heating operation mode, and functions as a condenser in cooling operation mode.
  • the heat source-side heat exchanger 12 allows heat to be exchanged between the air supplied from the fan 16 and the refrigerant.
  • the accumulator 19 is provided at the suction part of the compressor 10, and accumulates the excess refrigerant resulting from the difference between the heating operation mode and the cooling operation mode or the excess refrigerant for transient changes in operation.
  • the heat source-side heat exchanger 12 is disposed on the upper side, and the auxiliary heat exchanger 40 is disposed on the lower side, with adjacent heat transfer fins being shared by the two heat exchangers.
  • the air around the heat source-side heat exchanger 12 flows through both the heat source-side heat exchanger 12 and the auxiliary heat exchanger 40.
  • the auxiliary heat exchanger 40 is disposed so that its heat transfer area is smaller than the heat transfer area of the heat source-side heat exchanger 12.
  • the first expansion device 45 may be, for example, a device with a variable opening degree, such as an electronic expansion valve.
  • the first expansion device 45 is provided between the heat source-side heat exchanger 12 and a load-side expansion device 25.
  • the first expansion device 45 raises the pressure of refrigerant between the first expansion device 45 and the indoor unit 2, and allows the refrigerant flowing into from the indoor unit 2 in heating operation mode to expand.
  • the bypass pipe 41 is connected between the first expansion device 45 and the heat source-side heat exchanger 12. Part of refrigerant flowing out of the first expansion device 45 flows through the bypass pipe 41.
  • the bypass pipe 41 allows high-pressure or medium-pressure refrigerant to flow into the auxiliary heat exchanger 40, and allows liquid refrigerant condensed in the auxiliary heat exchanger 40 to flow into the suction part of the compressor 10 via the second expansion device 42.
  • One end of the bypass pipe 41 is connected to the part of the refrigerant pipe 4 between the heat source-side heat exchanger 12 and the indoor unit 2, and the other end is connected to the part of the refrigerant pipe 4 between the compressor 10 and the accumulator 19.
  • the second expansion device 42 may be, for example, a device with a variable opening degree, such as an electronic expansion valve.
  • the second expansion device 42 is located on the outflow side of the auxiliary heat exchanger 40.
  • the second expansion device 42 regulates the flow rate of the liquid refrigerant to flow into the suction part of the compressor 10 after the refrigerant is condensed in the auxiliary heat exchanger 40.
  • the outdoor unit 1 is provided with a discharge temperature sensor 43 that detects the temperature of high-temperature, high-pressure refrigerant discharged from the compressor 10.
  • a discharge temperature sensor 43 that detects the temperature of high-temperature, high-pressure refrigerant discharged from the compressor 10.
  • an outside-air temperature sensor 46 that measures the temperature around the outdoor unit 1 is provided at the air inlet part of the heat source-side heat exchanger 12.
  • the outdoor unit 1 is further provided with a pressure sensor 44 that detects the pressure of refrigerant between the first expansion device 45 and the indoor unit 2.
  • the indoor unit 2 has a load-side heat exchanger 26 and the load-side expansion device 25.
  • the load-side heat exchanger 26 is connected to the outdoor unit 1 via the main pipe 5, and exchanges heat between air and the refrigerant to generate the heating air or cooling air that is to be supplied to the indoor space.
  • Indoor air is sent to the load-side heat exchanger 26 from an air-sending device such as a fan (not illustrated).
  • the load-side expansion device 25 may be, for example, a device with a variable opening degree, such as an electronic expansion valve.
  • the load-side expansion device 25 functions as a pressure reducing valve or an expansion valve, and reduces the pressure of refrigerant to expand the refrigerant. In cooling only operation mode, the load-side expansion device 25 is located upstream of the load-side heat exchanger 26.
  • the indoor unit 2 is provided with an inlet-side temperature sensor 31 and an outlet-side temperature sensor 32 that may be thermistors or other sensors.
  • the inlet-side temperature sensor 31 detects the temperature of refrigerant flowing into the load-side heat exchanger 26, and is provided in the pipe at the refrigerant inlet side of the load-side heat exchanger 26.
  • the outlet-side temperature sensor 32 is located at the refrigerant outlet side of the load-side heat exchanger 26, and detects the temperature of refrigerant flowing out of the load-side heat exchanger 26.
  • a controller 60 may be a microcomputer or other devices.
  • the controller 60 performs various operation modes described later by controlling, for example, the driving frequency of the compressor 10, the rotation speed of the air-sending device (including turning on and off of the air-sending device), the switching action of the refrigerant flow switching device 11, the opening degree of the first expansion device 45, the opening degree of the second expansion device 42, and the opening degree of the load-side expansion device 25, on the basis of information detected by the various sensors mentioned above and instructions from a remote controller.
  • the controller 60 is illustrated to be provided in the outdoor unit 1, the controller 60 may be provided for each individual unit, or may be provided in the indoor unit 2.
  • a cooling operation mode and a heating operation mode are performed in each indoor unit 2 based on an instruction from the indoor unit 2.
  • Operation modes performed by the air-conditioning apparatus 100 illustrated in Fig. 1 include cooling operation mode in which all of the indoor units 2 being driven perform cooling operation, and a heating operation mode in which all of the indoor units 2 being driven perform heating operation.
  • each of the operation modes will be described with reference to the corresponding flow of refrigerant.
  • Fig. 2 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling operation mode of the air-conditioning apparatus 100.
  • a cooling only operation mode will be described with reference to, for example, a case where a cooling load is generated in the load-side heat exchanger 26.
  • the direction of flow of refrigerant is indicated by solid arrows.
  • low-temperature, low-pressure refrigerant is compressed by the compressor 10, and discharged from the compressor 10 as high-temperature, high-pressure gas refrigerant.
  • the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the heat source-side heat exchanger 12 via the refrigerant flow switching device 11.
  • the refrigerant changes to high-pressure liquid refrigerant while rejecting heat to the outdoor air supplied from the fan 16.
  • the high-pressure refrigerant flows out of the outdoor unit 1 via the first expansion device 45 that is set to the full opening degree.
  • the refrigerant then passes through the main pipe 5 to flow into the indoor unit 2.
  • the high-pressure refrigerant is expanded in the load-side expansion device 25, and changes to low-temperature, low-pressure refrigerant that is in a two-phase gas-liquid state.
  • the refrigerant in a two-phase gas-liquid state flows into the load-side heat exchanger 26 acting as an evaporator where the refrigerant removes heat from the indoor air, thus changing to low-temperature, low-pressure gas refrigerant while cooling the indoor air.
  • the opening degree of the load-side expansion device 25 is controlled by the controller 60 to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 and the temperature detected by the outlet-side temperature sensor 32.
  • the refrigeration cycle of the air-conditioning apparatus 100 uses, for example, a refrigerant such as an R32 refrigerant whose discharge temperature of the compressor 10 is higher than that of an R410A refrigerant (to be referred to as R410A hereinafter), it is necessary to lower the discharge temperature to prevent degradation of the refrigerating machine oil or burnout of the compressor 10.
  • a refrigerant such as an R32 refrigerant whose discharge temperature of the compressor 10 is higher than that of an R410A refrigerant (to be referred to as R410A hereinafter)
  • R410A refrigerant that has changed to subcooled liquid in the auxiliary heat exchanger 40
  • the controller 60 controls the first expansion device 45 and the second expansion device 42 so that high-pressure refrigerant flows into the auxiliary heat exchanger 40 from the bypass pipe 41. Then, in the auxiliary heat exchanger 40, the high-pressure liquid refrigerant changes to high-pressure subcooled liquid while rejecting heat to the outdoor air supplied from the fan 16, and the subcooled liquid refrigerant flows into the suction part of the compressor 10 via the second expansion device 42. Thus, the discharge temperature of refrigerant discharged from the compressor 10 can be lowered, ensuring safe use of the air-conditioning apparatus 100.
  • the controller 60 controls the opening degree of the second expansion device 42 on the basis of the discharge temperature of the compressor 10 detected by the discharge temperature sensor 43. That is, the discharge temperature of the compressor 10 drops when the amount of subcooled liquid refrigerant flowing into the suction part of the compressor 10 from the auxiliary heat exchanger 40 is increased by increasing the opening degree (opening area) of the second expansion device 42. By contrast, the discharge temperature of the compressor 10 rises when the amount of subcooled liquid refrigerant flowing into the suction part of the compressor 10 from the auxiliary heat exchanger 40 is decreased by decreasing the opening degree (opening area) of the second expansion device 42.
  • the controller 60 controls the second expansion device 42 to fully close. Then, the flow path of refrigerant flowing into the suction part of the compressor 10 from the auxiliary heat exchanger 40 via the bypass pipe 41 is cut off.
  • the discharge temperature threshold is set depending on the limit value of the discharge temperature of the compressor 10.
  • the controller 60 controls the second expansion device 42 to open to allow the refrigerant subcooled in the auxiliary heat exchanger 40 to flow into the suction part of the compressor 10. During this process, the controller 60 regulates the opening degree (opening area) of the second expansion device 42 so that the discharge temperature becomes equal to or lower than the discharge temperature threshold.
  • a table or mathematical expression associating discharge temperature with the opening degree of the second expansion device 42 is stored in the controller 60, and the controller 60 controls the opening degree of the second expansion device 42 on the basis of the discharge temperature.
  • the refrigerant flows into the suction part of the compressor 10 with its enthalpy at the inlet of the compressor 10 reduced, thus making it possible to limit an excessive rise in the discharge temperature of the compressor 10.
  • degradation of the refrigerating machine oil can be minimized and damage to the compressor 10 can be prevented.
  • the reliability of the system is ensured even when an inexpensive compressor is used rather than a compressor having a special structure.
  • limiting of an excessive rise in the discharge temperature of the compressor 10 allows for an increase in the rotation speed of the compressor 10 to ensure sufficient heating capacity, thus minimizing a decrease in user comfort.
  • the controller 60 causes part of the high pressure refrigerant flowing out of the heat source-side heat exchanger 12 to be subcooled in the auxiliary heat exchanger 40, thus ensuring that the refrigerant flowing into the second expansion device 42 be in a liquid state.
  • This configuration prevents refrigerant from flowing into the second expansion device 42 in a two-phase state, thus preventing noise generation in the second expansion device 42 and unstable control of discharge temperature of the compressor 10 by the second expansion device 42.
  • Fig. 3 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating operation mode of the air-conditioning apparatus 100.
  • a heating only operation mode will be described with reference to, for example, a case where a heating load is generated in the load-side heat exchanger 26.
  • the direction of flow of refrigerant is indicated by solid arrows.
  • low-temperature, low-pressure refrigerant is compressed by the compressor 10, and discharged from the compressor 10 as high-temperature, high-pressure gas refrigerant.
  • the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the refrigerant flow switching device 11 and then flows out of the outdoor unit 1.
  • the high-temperature, high-pressure gas refrigerant flowing out of the outdoor unit 1 passes through the main pipe 5, and as the refrigerant rejects heat to the indoor air in the load-side heat exchanger 26, the refrigerant changes to liquid refrigerant while heating the indoor space.
  • the liquid refrigerant flowing out of the load-side heat exchanger 26 is expanded in the load-side expansion device 25, changes to medium-temperature, medium-pressure refrigerant that is in a two-phase gas-liquid state, and then passes through the main pipe 5 to flow into the outdoor unit 1 again.
  • the medium-temperature, medium-pressure refrigerant in a two-phase gas-liquid state flowing into the outdoor unit 1 changes to low-temperature, low-pressure refrigerant that is in a two-phase gas-liquid state as the refrigerant passes through the first expansion device 45, and this refrigerant flows into the heat source-side heat exchanger 12.
  • the refrigerant changes to low-temperature, low-pressure gas refrigerant while removing heat from the outdoor air.
  • the refrigerant passes through the refrigerant flow switching device 11 and the accumulator 19 and then is sucked into the compressor 10 again.
  • the refrigerant used is, for example, a refrigerant that is discharged from the compressor 10 at a high temperature, such as R32, it is necessary to lower the discharge temperature to prevent degradation of the refrigerating machine oil or burnout of the compressor 10.
  • part of the medium-temperature, medium-pressure refrigerant in a two-phase gas-liquid state flowing out of the load-side expansion device 25 is allowed to flow into the auxiliary heat exchanger 40 via the bypass pipe 41.
  • the controller 60 controls the first expansion device 45 to allow medium-pressure refrigerant to flow into the auxiliary heat exchanger 40. Further, the controller 60 controls the first expansion device 45 and the second expansion device 42 so that the refrigerant cooled in the auxiliary heat exchanger 40 is allowed to flow into the flow path at the suction part of the compressor 10 or the compression chamber of the compressor 10. Then, in the auxiliary heat exchanger 40, the refrigerant changes to medium-pressure subcooled liquid while rejecting heat to the outdoor air supplied from the fan 16, and the liquid refrigerant flows into the suction part of the compressor 10 via the second expansion device 42. As a result, the temperature of the refrigerant discharged from the compressor 10 can be lowered to ensure safe use.
  • the controller 60 controls the opening degree of the second expansion device 42 on the basis of the discharge temperature of the compressor 10 detected by the discharge temperature sensor 43. That is, the discharge temperature of the compressor 10 drops when the amount of subcooled liquid refrigerant to flow into the suction part of the compressor 10 from the auxiliary heat exchanger 40 is increased by increasing the opening degree (opening area) of the second expansion device 42. By contrast, the discharge temperature of the compressor 10 rises when the amount of subcooled liquid refrigerant to flow into the suction part of the compressor 10 from the auxiliary heat exchanger 40 is decreased by decreasing the opening degree (opening area) of the second expansion device 42.
  • the controller 60 controls the second expansion device 42 to fully close. Then, the flow path of refrigerant flowing into the suction part of the compressor 10 from the auxiliary heat exchanger 40 via the bypass pipe 41 is cut off.
  • the discharge temperature threshold is set depending on the limit value of the discharge temperature of the compressor 10.
  • the controller 60 controls the second expansion device 42 to open so that the refrigerant passing through the auxiliary heat exchanger 40 flows to the suction part of the compressor 10.
  • the controller 60 regulates the opening degree (opening area) of the second expansion device 42 so that the discharge temperature becomes equal to or lower than the discharge temperature threshold.
  • a table or mathematical expression associating discharge temperature with the opening degree of the second expansion device 42 is stored in the controller 60, and the controller 60 controls the opening degree of the second expansion device 42 on the basis of the discharge temperature.
  • auxiliary heat exchanger 40 heat is exchanged in the auxiliary heat exchanger 40 between the air supplied from the fan 16, and medium-pressure, two-phase gas-liquid refrigerant that is at a saturation temperature higher than the temperature of air, resulting in subcooled medium-pressure liquid refrigerant.
  • This refrigerant is then allowed to flow into the suction part of the compressor 10 via the second expansion device 42.
  • low-pressure, low-temperature gas refrigerant flowing out of the accumulator 19, and the liquid refrigerant cooled in the auxiliary heat exchanger 40 mix together, resulting in low-pressure refrigerant that is in a two-phase gas-liquid state and at a high quality.
  • the refrigerant flows into the compressor 10 with its enthalpy at the inlet of the compressor 10 reduced, thus limiting an excessive rise in the discharge temperature of the compressor 10.
  • it is possible to minimize degradation of the refrigerating machine oil and prevent damage to the compressor 10.
  • the controller 60 controls the first expansion device 45 so that the refrigerant is at a medium pressure upstream of the first expansion device 45, thus allowing the refrigerant at a medium pressure to flow into the auxiliary heat exchanger 40.
  • the opening degree (opening area) of the first expansion device 45 When the opening degree (opening area) of the first expansion device 45 is small, the amount of refrigerant flowing out of the first expansion device 45 decreases, and the amount of refrigerant in the part of the refrigerant pipe 4 between the load-side expansion device 25 and the first expansion device 45 increases. Thus, the pressure of the medium-pressure, medium-temperature refrigerant in a two-phase gas-liquid state to flow into the auxiliary heat exchanger 40 increases.
  • the opening degree (opening area) of the first expansion device 45 when the opening degree (opening area) of the first expansion device 45 is large, the amount of refrigerant flowing out of the first expansion device 45 increases, and the amount of refrigerant in the part of the refrigerant pipe 4 between the load-side expansion device 25 and the first expansion device 45 decreases.
  • the pressure of the medium-pressure, medium-temperature refrigerant in a two-phase gas-liquid state to flow into the auxiliary heat exchanger 40 decreases.
  • the controller 60 calculates the saturation temperature of the medium-temperature, medium-pressure, two-phase gas-liquid refrigerant flowing out of the load-side expansion device 25, from the value detected by the pressure sensor 44.
  • the controller 60 then regulates the opening degree (opening area) of the first expansion device 45 so that the calculated saturation temperature of the medium-temperature, medium-pressure refrigerant in a two-phase gas-liquid state becomes sufficiently higher than a value detected by the outside-air temperature sensor 46 as a measurement of the ambient temperature of the outdoor unit 1.
  • the controller 60 regulates the opening degree of the first expansion device 45 so that the difference between the saturation temperature calculated from the value detected by the pressure sensor 44, and the value detected by the outside-air temperature sensor 46 approaches a temperature difference threshold (for example, 10 degrees C or higher, which ensures sufficient subcooling).
  • a temperature difference threshold for example, 10 degrees C or higher, which ensures sufficient subcooling.
  • part of the medium-pressure, medium-temperature refrigerant flowing into the outdoor unit 1 from the indoor unit 2 is changed to subcooled liquid in the auxiliary heat exchanger 40, and the subcooled liquid is allowed to flow into the suction part of the compressor 10 to limit a rise in the discharge temperature of the compressor 10.
  • This arrangement allows all of the high-pressure, high-temperature gas refrigerant discharged from the compressor 10 to be supplied to the indoor unit 2.
  • the reliability of the system is ensured even when an inexpensive compressor is used rather than a compressor having a special structure.
  • limiting of an excessive rise in the discharge temperature of the compressor 10 allows for an increase in the rotation speed of the compressor 10 to ensure sufficient heating capacity, thus minimizing a decrease in user comfort.
  • the refrigerant flowing out of the auxiliary heat exchanger 40 needs to be liquefied reliably. For this reason, the heat transfer area of the auxiliary heat exchanger 40 needs to be taken into consideration.
  • a conceivable environment that necessitates limiting of a rise in the discharge temperature of the compressor 10 in heating operation mode is a case where the outdoor unit 1 is installed under an environment of low temperature (for example, at an environmental temperature of -10 degrees C or lower).
  • the second expansion device 42 may be controlled as described above to raise the saturation temperature of the medium-pressure, medium-temperature refrigerant at a low quality that needs to be subcooled in the auxiliary heat exchanger 40, thus providing a large temperature difference from the environmental temperature.
  • a conceivable environment that necessitates limiting of a rise in the discharge temperature of the compressor 10 in cooling operation mode is a case where the outdoor unit 1 is installed under an environment of high temperature (for example, at an environmental temperature of 40 degrees C or higher). Under this environment, the difference between the temperature of high-pressure, low-temperature refrigerant cooled in the heat source-side heat exchanger 12 (for example, approximately 50 degrees C), the refrigerant temperature when the refrigerant cooled in the heat source-side heat exchanger 12 is further subcooled in the auxiliary heat exchanger 40, and the environmental temperature is small. Thus, for sufficient subcooling of refrigerant to occur in the auxiliary heat exchanger 40, the heat transfer area of the auxiliary heat exchanger 40 needs to be increased.
  • the heat transfer area of the auxiliary heat exchanger 40 may be selected to achieve a condition that maximizes the amount of subcooled liquid flowing into the suction part of the compressor 10 during the injection process in cooling operation mode.
  • This condition depends on the environmental temperature at which the air-conditioning apparatus 100 can be operated.
  • the condition that gives the greatest difference between the pressure of refrigerant cooled in the heat source-side heat exchanger 12 and the pressure of refrigerant heated in the load-side heat exchanger 26 is the condition that causes the greatest rise in the temperature of the high-pressure, high-temperature refrigerant discharged from the compressor 10.
  • the heat transfer area of the auxiliary heat exchanger 40 is determined on an assumption of the environment under which the rise in the temperature of high-pressure, high-temperature refrigerant discharged from the compressor 10 is greatest. For example, when the environmental temperature at which the air-conditioning apparatus 100 can be operated is assumed so that the maximum value of the environmental temperature at which the outdoor unit 1 is installed is 43 degrees C, and the minimum value of the environmental temperature at which the indoor unit 2 is installed is 15 degrees C, this environment is the condition that causes the greatest rise in the discharge temperature of refrigerant discharged from the compressor 10. The heat transfer area of the auxiliary heat exchanger 40 is determined based on this condition.
  • the flow rate (the amount of injection) of the subcooled liquid refrigerant that needs to flow into the suction part of the compressor 10 from the auxiliary heat exchanger 40 to make the discharge temperature of refrigerant discharged from the compressor 10 equal to or lower than a discharge temperature threshold may be calculated from the energy conversation law as represented by Equation (1).
  • Gr 1 (kg/h) and h 1 (kJ/kg) denote the flow rate and enthalpy of the low-temperature, low-pressure gas refrigerant that flows into the suction part of the compressor 10 from the accumulator 19
  • Gr 2 (kg/h) and h 2 (kJ/kg) denote the flow rate and enthalpy of the low-temperature, low-pressure liquid refrigerant injected from the auxiliary heat exchanger 40 to the suction part of the compressor 10 via the second expansion device 42 and the bypass pipe 41
  • Gr (kg/h) and h (kJ/kg) denote the total refrigerant flow rate after the two streams of refrigerant merge at the suction part of the compressor 10, and the enthalpy after merging.
  • the enthalpy after merging, h (kJ/kg), which is calculated using Equation (1), is less than the enthalpy h 1 (kJ/kg) of the low-temperature, low-pressure gas refrigerant that flows into the suction part of the compressor 10 from the accumulator 19. Consequently, the discharge temperature of refrigerant discharged from the compressor 10 is lower in a case where refrigerant is injected from the auxiliary heat exchanger 40 than in a case where no liquid refrigerant is injected from the auxiliary heat exchanger 40.
  • the refrigerant flow rate Gr 2 at which the temperature of gas refrigerant discharged from the compressor 10 becomes equal to or less than a discharge temperature threshold is derived from Equation (1).
  • Q1 (W) denotes the amount of heat exchange in the auxiliary heat exchanger 40
  • h 3 kJ/kg denotes the enthalpy of the high-pressure, low-temperature refrigerant at the outlet side of the heat source-side heat exchanger 12 in cooling operation mode and also denotes the enthalpy of the refrigerant at the inlet side of the auxiliary heat exchanger 40, and thus the general form of the equation defining the amount of heat exchange due to a change in enthalpy represented by Equation (2) holds.
  • Equation (3) is the general form of the equation defining the amount of heat exchange due to heat transmission, where A 1 (m 2 ) is the area in which the auxiliary heat exchanger 40 contacts the air of the environment under which the outdoor unit 1 is installed (to be referred to as total heat transfer area hereinafter), k (W/(m 2 ⁇ K)) is the overall heat transmission coefficient based on the side where the fins used in the auxiliary heat exchanger 40 and the outer surface of the heat transfer tubes contact the air of the environment of the installation location (to be referred to as "based on the tube's outer side” hereinafter), k (W/(m 2 ⁇ K)) also represents the ease with which heat is transmitted owing to the difference in temperature between refrigerant and air, and ⁇ Tm (K or degrees C) is the logarithmic mean temperature difference, which represents the temperature difference between refrigerant and air at each of the inlet and outlet of the
  • the overall heat transmission coefficient k based on the tube's outer side varies with changes in heat transfer coefficient due to changes in, for example, the specifications of the heat transfer tubes used in the auxiliary heat exchanger 40, which is a plate fin-tube heat exchanger, fin geometry, fan air velocity, or the operating state of the refrigeration cycle.
  • the overall heat transmission coefficient k is set to approximately 25 (W/(m 2 ⁇ K)), which is a value obtained by the results of a large number of cooling operation mode tests.
  • Equation (4) T1 (K or degrees C) is the temperature of refrigerant flowing into the heat transfer tubes of the auxiliary heat exchanger 40
  • T2 K or degrees C
  • T3 K or degrees C
  • T4 K or degrees C
  • the total heat transfer area A 1 of the auxiliary heat exchanger 40 can be calculated by using Equations (1) to (4) above. For example, the following describes how the total heat transfer area A 1 is calculated for the air-conditioning apparatus 100 having capacity equivalent to 10 horsepower that uses an R32 refrigerant as the refrigerant.
  • the degree of subcooling that is the difference in temperature between the refrigerant at the inlet side of the auxiliary heat exchanger 40 and the liquid refrigerant at the outlet side of the auxiliary heat exchanger 40 is set to approximately 9 degrees C, in the auxiliary heat exchanger 40, saturated liquid at 54 degrees C exchanges heat with air at approximately 43 degrees C, and saturated liquid at 45 degrees C flows into the suction part of the compressor 10.
  • the enthalpy h 2 at the outlet of the auxiliary heat exchanger 40 is determined by the pressure calculated from the refrigerant saturation temperature of 54 degrees C, and the temperature of the liquid refrigerant at the outlet of the auxiliary heat exchanger 40.
  • the enthalpy h 2 is obtained as approximately 283 (kJ/kg).
  • the total refrigerant flow rate Gr and the enthalpies h 1 and h 2 in Equation (1) are determined on the basis of the above-mentioned condition under which the air-conditioning apparatus 100 can be operated or other conditions.
  • the enthalpy h 3 of the saturated liquid at 54 degrees C is approximately 307 (kJ/kg).
  • the amount of heat exchange Q1 required for the auxiliary heat exchanger 40 is calculated from Equation (2) to be approximately 80 (W).
  • the temperature T1 of refrigerant flowing into the heat transfer tubes of the auxiliary heat exchanger 40 is approximately 54 (degrees C)
  • the temperature T2 of refrigerant flowing out of the auxiliary heat exchanger 40 is 45 (degrees C)
  • the temperature T3 of air flowing into the auxiliary heat exchanger 40 is 43 (degrees C).
  • the temperature T4 of air flowing out of the auxiliary heat exchanger 40 it is regarded that the temperature of air remains substantially unchanged owing to the small amount of heat exchange Q1 in the auxiliary heat exchanger 40 of approximately 80 (W).
  • the temperature T4 is set as 44 (degrees C), on an assumption that the temperature of air rises by approximately one degree C from the temperature of incoming air.
  • Equation (3) the total heat transfer area A 1 required for the auxiliary heat exchanger 40 is calculated from Equation (3) to be approximately 0.644 (m 2 ).
  • the total heat transfer area A 2 required for the heat source-side heat exchanger 12 is approximately 141 (m 2 ).
  • the ratio A 1 /(A 1 + A 2 ) which is the ratio of the total heat transfer area A 1 of the auxiliary heat exchanger 40 to the sum of the total heat transfer area A 2 required for the heat source-side heat exchanger 12 and the total heat transfer area A 1 required for the auxiliary heat exchanger 40, equals 0.644/141.644, which is equal to or higher than approximately 0.46%.
  • the configuration is not limited to this configuration.
  • the air-conditioning apparatus 100 is configured so that even when the required cooling or heating capacity (horsepower) changes, the high-pressure/low-pressure operating state of refrigerant remains substantially unchanged with respect to the environmental temperature at which each of the outdoor unit 1 and the indoor unit 2 is installed, the cooling or heating capacity (horsepower) changes only with a change in the displacement of the compressor 10 (a change in total refrigerant flow rate Gr (kg/h)).
  • the flow rate Gr 2 of refrigerant allowed to flow into the auxiliary heat exchanger 40 may be made to vary with the rate of change in the displacement of the compressor 10, and the total heat transfer area A 1 of the auxiliary heat exchanger 40 may be calculated from Equation (2) and Equation (3).
  • the displacement of the compressor 10 required for the air-conditioning apparatus 100 having capacity equivalent to 14 horsepower is approximately 1.4 times greater than that required for an air-conditioning apparatus having capacity equivalent to 10 horsepower.
  • the amount of heat exchange Q1 in the auxiliary heat exchanger 40 is calculated from Equation (2) to be approximately 112 (W).
  • the total heat transfer area A 1 required for the auxiliary heat exchanger 40 equals 0.9016 (m 2 ), which is approximately 1.4 times the total heat transfer area A 1 of the auxiliary heat exchanger 40 for the air-conditioning apparatus having capacity equivalent to 10 horsepower.
  • the total heat transfer area A 2 required for the heat source-side heat exchanger 12 can be also regarded as approximately 1.4 times greater than that required for the air-conditioning apparatus having capacity equivalent to 10 horsepower.
  • the ratio A 1 /(A 1 + A 2 ), which is the ratio of the total heat transfer area A 1 of the auxiliary heat exchanger 40 to the sum of the total heat transfer area A 2 required for the heat source-side heat exchanger 12 and the total heat transfer area A 1 required for the auxiliary heat exchanger 40, is equal to or higher than approximately 0.46%.
  • the number of stages for the heat source-side heat exchanger 12 may not be able to increase owing to factors such as a constraint on the direction of height of the outdoor unit 1. If the auxiliary heat exchanger 40 constituting a part of the heat source-side heat exchanger 12 has an excessively large size in this case, the total heat transfer area A 1 of the heat source-side heat exchanger 12 decreases, resulting in deterioration of the performance of the heat source-side heat exchanger 12.
  • Fig. 4 is a graph illustrating the relationship between the ratio of the heat transfer area of the heat source-side heat exchanger 12 to the sum of the total heat transfer area A 2 of the heat source-side heat exchanger 12 and the total heat transfer area A 1 of the auxiliary heat exchanger 40 in the air-conditioning apparatus 100, and COP, which is an index of the performance of the air-conditioning apparatus 100.
  • COP which is an index of the performance of the air-conditioning apparatus 100.
  • the ratio A 2 /(A 1 + A 2 ) of the total heat transfer area A 2 of the heat source-side heat exchanger 12 to the sum A 1 + A 2 of the total heat transfer areas needs to be approximately 95%.
  • the corresponding ratio A 1 /(A 1 + A 2 ) for the total heat transfer area A 1 of the auxiliary heat exchanger 40 is equal to or less than 5%.
  • the ratio A 1 /(A 1 + A 2 ) does not need to be kept within approximately 5%.
  • the ratio A 1 /(A 1 + A 2 ) may be any value equal to or higher than approximately 0.46%.
  • Fig. 5 is a schematic circuit configuration diagram illustrating an exemplary circuit configuration of an air-conditioning apparatus according to Embodiment 2 of the present invention.
  • An air-conditioning apparatus 200 will be described below with reference to Fig. 5 .
  • parts configured in the same manner as those in the air-conditioning apparatus 100 illustrated in Fig. 1 will be denoted by the same reference signs to omit a description of these parts.
  • the air-conditioning apparatus 200 illustrated in Fig. 5 has a single outdoor unit 201 that is a heat source unit, a plurality of indoor units 2a to 2d, and a relay device 3 including an opening and closing device provided between the outdoor unit 201 and each of the indoor units 2a to 2d.
  • the outdoor unit 201 and the relay device 3 are connected by the main pipes 5 through which refrigerant flows, and the relay device 3 and the indoor units 2a to 2d are each connected by a branch pipe 6 through which refrigerant flows.
  • the cooling energy or heating energy generated by the outdoor unit 1 is allowed to pass through each of the indoor units 2a to 2d via the relay device 3.
  • the outdoor unit 201 and the relay device 3 are connected by using two main pipes 5, and the relay device 3 and each of the indoor units 2 are connected by two branch pipes 6. Using two pipes to connect the outdoor unit 201 with the relay device 3, and each of the indoor units 2a to 2d with the relay device 3 in this way allows for easy installation.
  • the compressor 10 the refrigerant flow switching device 11 such as a four-way valve, the heat source-side heat exchanger 12, the auxiliary heat exchanger 40, the first expansion device 45, the second expansion device 42, the bypass pipe 41, and the accumulator 19 are connected by the refrigerant pipe 4, and are mounted together with the fan 16, which is an air-sending device.
  • the outdoor unit 201 has a first connecting pipe 4a, a second connecting pipe 4b, and first backflow prevention devices 13a to 13d such as check valves or other devices.
  • the first backflow prevention device 13a prevents high-temperature, high-pressure gas refrigerant from flowing backward from the first connecting pipe 4a to the heat source-side heat exchanger 12 in heating only operation mode and heating main operation mode.
  • the first backflow prevention device 13b prevents high-pressure refrigerant that is in a liquid or two-phase gas-liquid state from flowing backward from the first connecting pipe 4a to the accumulator 19 in cooling only operation mode and cooling main operation mode.
  • the first backflow prevention device 13c prevents high-pressure refrigerant that is in a liquid or two-phase gas-liquid state from flowing backward from the first connecting pipe 4a to the accumulator 19 in cooling only operation mode and cooling main operation mode.
  • the first backflow prevention device 13d prevents high-temperature, high-pressure gas refrigerant from flowing backward from the flow path on the discharge side of the compressor 10 to the second connecting pipe 4b in heating only operation mode and heating main operation mode.
  • first connecting pipe 4a, the second connecting pipe 4b, and the first backflow prevention devices 13a to 13d allows the refrigerant flowing into the relay device 3 to flow in a fixed direction irrespective of the operation required for the indoor unit 2.
  • first backflow prevention devices 13a to 13d are illustrated to be check valves, their configuration is not limited as long as backflow of refrigerant can be prevented.
  • the first backflow prevention devices 13a to 13d may be opening and closing devices or expansion devices capable of full closing.
  • one end of the bypass pipe 41 is connected to the part of the second connecting pipe 4b between the first expansion device 45 and the first backflow prevention device 13c, and the other end is connected to the part of the refrigerant pipe 4 between the compressor 10 and the accumulator 19. That is, in the air-conditioning apparatus 200 illustrated in Fig. 5 as well, the first expansion device 45 is connected between the heat source-side heat exchanger 12 and the indoor units 2a to 2d (load-side expansion devices 25a to 26d), and the bypass pipe 41 is connected between the first expansion device 45 and the heat source-side heat exchanger 12 so that the refrigerant flowing out of the first expansion device 45 flows through the bypass pipe 41.
  • the indoor units 2a to 2d have, for example, the same configuration, and respectively include load-side heat exchangers 26a to 26d, and the load-side expansion devices 25a to 25d.
  • the load-side heat exchangers 26a to 26d are each connected to the outdoor unit 201 via the branch pipes 6, the relay device 3, and the main pipes 5.
  • the load-side heat exchangers 26a to 26d allow heat to be exchanged between air supplied from an air-sending device such as a fan (not illustrated), and refrigerant to thereby generate the heating air or cooling air to be supplied to the indoor space.
  • the load-side expansion devices 25a to 25d may each be, for example, a device with a variable opening degree, such as an electronic expansion valve.
  • the load-side expansion devices 25a to 25d each function as a pressure reducing valve or expansion valve to cause refrigerant to be reduced in pressure and expand.
  • the load-side expansion devices 25a to 25d are located upstream of the load-side heat exchangers 26a to 26d with respect to the flow of refrigerant in cooling only operation mode.
  • the indoor units 2 are provided with inlet-side temperature sensors 31 a to 31 d that each detect the temperature of refrigerant flowing into the corresponding load-side heat exchanger 26, and outlet-side temperature sensors 32a to 32d that each detect the temperature of refrigerant flowing out of the corresponding load-side heat exchanger 26.
  • the inlet-side temperature sensor 31 a to 31 d and the outlet-side temperature sensor 32a to 32d may be, for example, thermistors or other sensors, and the detected inlet-side temperatures and outlet-side temperatures of the load-side heat exchangers 26a to 26d are sent to the controller 60.
  • the number of indoor units 2 connected is not limited to four but may be any number equal to or greater than two.
  • the relay device 3 has a gas-liquid separator 14, a refrigerant-to-refrigerant heat exchanger 50, a third expansion device 15, a fourth expansion device 27, a plurality of first opening and closing devices 23a to 23d, a plurality of second opening and closing devices 24a to 24d, a plurality of second backflow prevention devices 21 a to 21 d that are backflow prevention devices such as check valves and a plurality of third backflow prevention devices 22a to 22d that are backflow prevention devices such as check valves.
  • the gas-liquid separator 14 separates high-pressure, two-phase gas-liquid refrigerant generated in the outdoor unit 201 into liquid and gas.
  • the liquid is allowed to flow into the pipe located on the lower side in Fig. 5 to supply cooling energy to the indoor unit 2, and the gas is allowed to flow into the pipe located on the upper side in Fig. 5 to supply heating energy to the indoor unit 2.
  • the gas-liquid separator 14 is installed at the inlet of the relay device 3.
  • the refrigerant-to-refrigerant heat exchanger 50 may be, for example, a double-pipe heat exchanger or a plate heat exchanger. In cooling only operation mode, cooling main operation mode, and heating main operation mode, the refrigerant-to-refrigerant heat exchanger 50 allows heat to be exchanged between high-pressure or medium-pressure refrigerant and low-pressure refrigerant to provide a sufficient degree of subcooling for the liquid or two-phase gas-liquid refrigerant to be supplied to the load-side expansion device 25 of the indoor unit 2 in which a cooling load is generated.
  • the flow path of high-pressure or medium-pressure refrigerant of the refrigerant-to-refrigerant heat exchanger 50 is connected between the third expansion device 15 and the second backflow prevention devices 21 a to 21 d.
  • One end of the flow path of low-pressure refrigerant is connected between the second backflow prevention devices 21 a to 21 d, and the outlet side of the flow path of high-pressure or medium-pressure refrigerant of the refrigerant-to-refrigerant heat exchanger 50, and the other end communicates with the low-pressure pipe at the outlet side of the relay device 3 via the fourth expansion device 27 and the refrigerant-to-refrigerant heat exchanger 50.
  • the third expansion device 15 functions as a pressure reducing valve or an opening and closing valve, and reduces the pressure of liquid refrigerant to a predetermined pressure, or opens or closes the flow path of the liquid refrigerant.
  • the third expansion device 15 may be, for example, a device with a variable opening degree, such as an electronic expansion valve.
  • the third expansion device 15 is provided on the pipe to which the liquid refrigerant flowing out of the gas-liquid separator 14 flows.
  • the fourth expansion device 27 functions as a pressure reducing valve or an opening and closing valve. In heating only operation mode, the fourth expansion device 27 opens or closes the flow path of refrigerant, and in heating main operation mode, the fourth expansion device 27 regulates the flow rate of a bypass liquid depending on the indoor-side load. In cooling only operation mode, cooling main operation mode, and heating main operation mode, the fourth expansion device 27 allows refrigerant to flow into the refrigerant-to-refrigerant heat exchanger 50, and regulates the degree of subcooling of the refrigerant supplied to the load-side expansion device 25 of the indoor unit 2 in which a cooling load is generated.
  • the fourth expansion device 27 may be, for example, a device with a variable opening degree, such as an electronic expansion valve.
  • the fourth expansion device 27 is located in the flow path on the inlet side of low-pressure refrigerant of the refrigerant-to-refrigerant heat exchanger 50.
  • the number (four in this case) of first opening and closing devices 23a to 23d equal to the number of indoor units 2a to 2d to be installed are provided, individually for the corresponding indoor units 2a to 2d.
  • the first opening and closing devices 23a to 23d may each be, for example, a solenoid valve or other devices, and open or close the flow path of the high-temperature, high-pressure gas refrigerant supplied to the corresponding indoor units 2a to 2d.
  • the first opening and closing devices 23a to 23d are each connected to the gas-side pipe of the gas-liquid separator 14.
  • the first opening and closing devices 23a to 23d are only required to be able to open and close a flow path, and may be expansion devices capable of full closing.
  • the number (four in this case) of second opening and closing devices 24a to 24d equal to the number of indoor units 2a to 2d to be installed are provided, individually for the corresponding indoor units 2a to 2d.
  • the second opening and closing devices 24a to 24d may each be, for example, a solenoid valve or other devices, and open and close the flow path of the low-pressure, low-temperature gas refrigerant flowing out of the corresponding indoor units 2a to 2d.
  • the second opening and closing devices 24a to 24d are each connected to the low-pressure pipe that communicates with the outlet side of the relay device 3.
  • the second opening and closing devices 24a to 24d are only required to be able to open and close a flow path, and may be expansion devices capable of full closing.
  • the number (four in this case) of second backflow prevention devices 21 a to 21 d equal to the number of indoor units 2a to 2d to be installed are provided, individually for the corresponding indoor units 2a to 2d.
  • the second backflow prevention devices 21 a to 21 d allow high-pressure liquid refrigerant to flow into the indoor units 2a to 2d in which cooling operation is being performed, and are each connected to the pipe at the outlet side of the third expansion device 15.
  • this configuration is able to prevent medium-temperature, medium-pressure, liquid or two-phase gas-liquid refrigerant yet to attain a sufficient degree of subcooling that has flowed out of the load-side expansion device 25 of the indoor unit 2 that is performing heating operation, from flowing into the load-side expansion device 25 of the indoor unit 2 that is performing cooling operation.
  • the second backflow prevention devices 21 a to 21 d are depicted as if the second backflow prevention devices 21 a to 21 d are check valves in Fig. 5
  • the second backflow prevention devices 21 a to 21 d used may be any devices capable of preventing backflow of refrigerant and may be opening and closing devices or expansion devices capable of full closing.
  • the number (four in this case) of third backflow prevention devices 22a to 22d equal to the number of indoor units 2a to 2d to be installed are provided, individually for the corresponding indoor units 2a to 2d.
  • the third backflow prevention devices 22a to 22d allow high-pressure liquid refrigerant to flow into the indoor unit 2 that is performing cooling operation, and are connected to the outlet pipe of the third expansion device 15.
  • the third backflow prevention devices 22a to 22d prevent medium-temperature, medium-pressure, liquid or two-phase gas-liquid refrigerant yet to attain a sufficient degree of subcooling that has flowed out of the third expansion device 15, from flowing into the load-side expansion device 25 of the indoor unit 2 that is performing cooling operation.
  • the third backflow prevention devices 22a to 22d are depicted as if the third backflow prevention devices 22a to 22d are check valves in Fig. 5 , the third backflow prevention devices 22a to 22d used may be any devices capable of preventing backflow of refrigerant and may be opening and closing devices or expansion devices capable of full closing.
  • an inlet-side pressure sensor 33 is provided on the inlet side of the third expansion device 15, and an outlet-side pressure sensor 34 is provided on the outlet side of the third expansion device 15.
  • the inlet-side pressure sensor 33 detects the pressure of high-pressure refrigerant.
  • the outlet-side pressure sensor 34 detects, in cooling main operation mode, the intermediate pressure of liquid refrigerant at the outlet of the third expansion device 15.
  • the relay device 3 is further provided with a temperature sensor 51 that detects the temperature of the high-pressure or medium-pressure refrigerant flowing out of the refrigerant-to-refrigerant heat exchanger 50.
  • the temperature sensor 51 is provided to the pipe at the outlet side of the flow path of high-pressure or medium-pressure refrigerant of the refrigerant-to-refrigerant heat exchanger 50, and may preferably be a thermistor or other sensors.
  • the controller 60 performs various operation modes described later by controlling, for example, the driving frequency of the compressor 10, the rotation speed of the air-sending device (including turning on and off of the air-sending device), the switching action of the refrigerant flow switching device 11, the opening degree of the first expansion device 45, the opening degree of the second expansion device 42, the opening degree of the load-side expansion device 25, and the opening and closing actions of the first opening and closing devices 23a to 23d, the second opening and closing devices 24a to 24d, the fourth expansion device 27, and the third expansion device 15, on the basis of information detected by the various sensors and instructions from a remote controller.
  • the controller 60 may be provided for each individual unit, or may be provided in the outdoor unit 201 or the relay device 3.
  • the air-conditioning apparatus 200 is capable of performing, on the basis of an instruction from each indoor unit 2, either cooling operation or heating operation in the corresponding indoor unit 2. That is, the air-conditioning apparatus 200 allows all of the indoor units 2 to perform the same operation, and also allows each individual indoor unit 2 to perform a different operation.
  • the cooling operation mode includes a cooling only operation mode, in which all of the indoor units 2 being driven perform cooling operation, and a cooling main operation mode that is a cooling and heating mixed operation mode in which the cooling load is comparatively greater
  • the heating operation mode includes a heating only operation mode, in which all of the indoor units 2 being driven perform heating operation, and a heating main operation mode that is a cooling and heating mixed operation mode in which the heating load is comparatively greater.
  • Fig. 6 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling only operation mode of the air-conditioning apparatus 200.
  • pipes indicated by thick lines represent pipes through which refrigerant flows, and the direction of flow of refrigerant is indicated by solid arrows.
  • the cooling only operation mode will be described with reference to, for example, a case where a cooling load is generated only in the load-side heat exchanger 26a and the load-side heat exchanger 26b.
  • the controller 60 switches the refrigerant flow switching device 11 of the outdoor unit 201 so that the refrigerant discharged from the compressor 10 is allowed to flow into the heat source-side heat exchanger 12.
  • low-temperature, low-pressure refrigerant is compressed by the compressor 10, and discharged from the compressor 10 as high-temperature, high-pressure gas refrigerant.
  • the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the heat source-side heat exchanger 12 via the refrigerant flow switching device 11.
  • the refrigerant changes to high-pressure liquid refrigerant as the refrigerant rejects heat to the outdoor air.
  • the high-pressure liquid refrigerant flowing out of the heat source-side heat exchanger 12 passes through the first backflow prevention device 13a and flows out of the outdoor unit 201, and then flows into the relay device 3 through the main pipe 5.
  • the high-pressure liquid refrigerant After flowing into the relay device 3, the high-pressure liquid refrigerant passes through the gas-liquid separator 14 and the third expansion device 15 and then is sufficiently subcooled in the refrigerant-to-refrigerant heat exchanger 50. Then, most of the subcooled high-pressure refrigerant passes through the second backflow prevention devices 21 a and 21 b and the branch pipe 6, is expanded in the load-side expansion device 25, and changes to low-temperature, low-pressure refrigerant that is in a two-phase gas-liquid state. The remaining part of the high-pressure refrigerant is expanded in the fourth expansion device 27, and thus changes to low-temperature, low-pressure refrigerant that is in a two-phase gas-liquid state.
  • the low-temperature, low-pressure refrigerant in a two-phase gas-liquid state exchanges heat with the high-pressure liquid refrigerant in the refrigerant-to-refrigerant heat exchanger 50, changes to low-temperature, low-pressure gas refrigerant, and then flows into the low-pressure pipe at the outlet side of the relay device 3.
  • the opening degree of the fourth expansion device 27 is controlled to maintain a constant level of subcooling (degree of subcooling) calculated as the difference between a value obtained by converting the pressure detected by the outlet-side pressure sensor 34 into a saturation temperature, and the temperature detected by the temperature sensor 51.
  • the opening degree of the load-side expansion device 25a is controlled to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 a and the temperature detected by the outlet-side temperature sensor 32a.
  • the opening degree of the load-side expansion device 25b is controlled to maintain a constant level of superheat calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 b and the temperature detected by the outlet-side temperature sensor 32b.
  • the gas refrigerant flowing out of each of the load-side heat exchangers 26a and 26b passes through the branch pipe 6 and the second opening and closing device 24, and merges with the gas refrigerant flowing out of the refrigerant-to-refrigerant heat exchanger 50.
  • the merged refrigerant flows out of the relay device 3, and passes through the main pipe 5 to flow into the outdoor unit 201 again.
  • the refrigerant flowing into the outdoor unit 201 passes through the first backflow prevention device 13d, the refrigerant flow switching device 11, and the accumulator 19 and then is sucked into the compressor 10 again.
  • the opening degree of the load-side expansion device 25c or the load-side expansion device 25d is controlled to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 and the temperature detected by the outlet-side temperature sensor 32.
  • Fig. 7 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling main operation mode of the air-conditioning apparatus 200.
  • the cooling main operation mode will be described with reference to, for example, a case where a cooling load is generated in the load-side heat exchanger 26a and a heating load is generated in the load-side heat exchanger 26b.
  • pipes indicated by thick lines represent pipes through which refrigerant circulates, and the direction of flow of refrigerant is indicated by solid arrows.
  • the refrigerant flow switching device 11 is switched to allow the heat source-side refrigerant discharged from the compressor 10 to flow into the heat source-side heat exchanger 12.
  • the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the heat source-side heat exchanger 12 via the refrigerant flow switching device 11.
  • the gas refrigerant changes to two-phase gas-liquid refrigerant while rejecting heat to the outdoor air.
  • the refrigerant flowing out of the heat source-side heat exchanger 12 passes through the first backflow prevention device 13a and the main pipe 5, and flows into the relay device 3.
  • the two-phase gas-liquid refrigerant is separated in the gas-liquid separator 14 into high-pressure gas refrigerant and high-pressure liquid refrigerant.
  • the high-pressure gas refrigerant passes through the first opening and closing device 23b and the branch pipe 6, and flows into the load-side heat exchanger 26b acting as a condenser, where the high-pressure gas refrigerant rejects heat to the indoor air and thus changes to liquid refrigerant while heating the indoor space.
  • the opening degree of the load-side expansion device 25b is controlled to maintain a constant level of subcooling (degree of subcooling) calculated as the difference between a value obtained by converting the pressure detected by the inlet-side pressure sensor 33 into a saturation temperature, and the temperature detected by the inlet-side temperature sensor 31 b.
  • the liquid refrigerant flowing out of the load-side heat exchanger 26b is expanded in the load-side expansion device 25b, and then passes through the branch pipe 6 and the third backflow prevention device 22b.
  • the opening degree of the third expansion device 15 is controlled to provide a predetermined pressure difference (for example, 0.3 MPa) between the pressure detected by the inlet-side pressure sensor 33, and the pressure detected by the outlet-side pressure sensor 34.
  • the opening degree of the fourth expansion device 27 is controlled to maintain a constant level of subcooling (degree of subcooling) calculated as the difference between a value obtained by converting the pressure detected by the outlet-side pressure sensor 34 into a saturation temperature, and the temperature detected by the temperature sensor 51. Then, the low-temperature, low-pressure refrigerant in a two-phase gas-liquid state exchanges heat with the medium-pressure liquid refrigerant in the refrigerant-to-refrigerant heat exchanger 50, changes to low-temperature, low-pressure gas refrigerant, and then flows into the low-pressure pipe at the outlet side of the relay device 3.
  • a constant level of subcooling degree of subcooling
  • the high-pressure liquid refrigerant separated in the gas-liquid separator 14 passes through the refrigerant-to-refrigerant heat exchanger 50 and the second backflow prevention device 21 a, and flows into the indoor unit 2a.
  • Most of the refrigerant in a two-phase gas-liquid state expanded in the load-side expansion device 25a of the indoor unit 2a flows into the load-side heat exchanger 26a acting as an evaporator where the refrigerant removes heat from the indoor air, and changes to low-temperature, low-pressure gas refrigerant while cooling the indoor air.
  • the opening degree of the load-side expansion device 25a is controlled to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 a and the temperature detected by the outlet-side temperature sensor 32b.
  • the gas refrigerant flowing out of the load-side heat exchanger 26a passes through the branch pipe 6 and the second opening and closing device 24a and merges with the remaining part of the gas refrigerant that has flowed out of the refrigerant-to-refrigerant heat exchanger 50.
  • the merged refrigerant then flows out of the relay device 3, and passes through the main pipe 5 to flow into the outdoor unit 201 again.
  • the refrigerant flowing into the outdoor unit 201 passes through the first backflow prevention device 13d, the refrigerant flow switching device 11, and the accumulator 19 and then is sucked into the compressor 10 again.
  • the opening degree of the load-side expansion device 25c or the load-side expansion device 25d is controlled to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 and the temperature detected by the outlet-side temperature sensor 32.
  • Fig. 8 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating only operation mode of the air-conditioning apparatus 200.
  • pipes indicated by thick lines represent pipes through which refrigerant flows, and the direction of flow of refrigerant is indicated by solid arrows.
  • the heating only operation mode will be described with reference to, for example, a case where a cooling load is generated only in the load-side heat exchanger 26a and the load-side heat exchanger 26b.
  • the refrigerant flow switching device 11 is switched so that the heat source-side refrigerant discharged from the compressor 10 is allowed to flow into the relay device 3 without passing through the heat source-side heat exchanger 12.
  • low-temperature, low-pressure refrigerant is compressed by the compressor 10, and discharged from the compressor 10 as high-temperature, high-pressure gas refrigerant.
  • the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the refrigerant flow switching device 11 and the first backflow prevention device 13b, and then flows out of the outdoor unit 201.
  • the high-temperature, high-pressure gas refrigerant flowing out of the outdoor unit 201 flows into the relay device 3 through the main pipe 5.
  • the high-temperature, high-pressure gas refrigerant After flowing into the relay device 3, the high-temperature, high-pressure gas refrigerant passes through the gas-liquid separator 14, the first opening and closing devices 23a and 23b, and the branch pipes 6, and flows into each of the load-side heat exchanger 26a and the load-side heat exchanger 26b that act as a condenser.
  • the refrigerant flowing into each of the load-side heat exchanger 26a and the load-side heat exchanger 26b rejects heat to the indoor air, and thus changes to liquid refrigerant while heating the indoor space.
  • the opening degree of the load-side expansion device 25b is controlled to maintain a constant level of subcooling (degree of subcooling) calculated as the difference between a value obtained by converting the pressure detected by the inlet-side pressure sensor 33 into a saturation temperature, and the temperature detected by the inlet-side temperature sensor 31 b.
  • the refrigerant flowing into the outdoor unit 201 passes through the first backflow prevention device 13c, is expanded in the first expansion device 45 and changes to low-temperature, low-pressure refrigerant that is in a two-phase gas-liquid state, and then changes to low-temperature, low-pressure gas refrigerant in the heat source-side heat exchanger 12 while removing heat from the outdoor air.
  • the low-temperature, low-pressure gas refrigerant then passes through the refrigerant flow switching device 11 and the accumulator 19 and then is sucked into the compressor 10 again.
  • the opening degree of the load-side expansion device 25c or the load-side expansion device 25d is controlled to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 and the temperature detected by the outlet-side temperature sensor 32.
  • Fig. 9 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating main operation mode of the air-conditioning apparatus 200.
  • pipes indicated by thick lines represent pipes through which refrigerant circulates, and the direction of flow of refrigerant is indicated by solid arrows.
  • the heating main operation mode will be described with reference to, for example, a case where a cooling load is generated in the load-side heat exchanger 26a, and a heating load is generated in the load-side heat exchanger 26b.
  • the refrigerant flow switching device 11 is switched so that the heat source-side refrigerant discharged from the compressor 10 is allowed to flow into the relay device 3 without passing through the heat source-side heat exchanger 12.
  • Low-temperature, low-pressure refrigerant is compressed by the compressor 10, and discharged from the compressor 10 as high-temperature, high-pressure gas refrigerant.
  • the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the refrigerant flow switching device 11 and the first backflow prevention device 13b, and then flows out of the outdoor unit 201.
  • the high-temperature, high-pressure gas refrigerant flowing out of the outdoor unit 201 flows into the relay device 3 through the main pipe 5.
  • the high-temperature, high-pressure gas refrigerant flowing into the relay device 3 passes through the gas-liquid separator 14, the third expansion device 15, the first opening and closing device 23b, and the branch pipe 6, and flows into the load-side heat exchanger 26b acting as a condenser.
  • the refrigerant flowing into the load-side heat exchanger 26b rejects heat to the indoor air, and thus changes to liquid refrigerant while heating the indoor space.
  • the liquid refrigerant flowing out of the load-side heat exchanger 26b is expanded in the load-side expansion device 25b, passes through the branch pipe 6 and the third backflow prevention device 22b, and then is sufficiently subcooled in the refrigerant-to-refrigerant heat exchanger 50.
  • This refrigerant then exchanges heat with the liquid refrigerant in the refrigerant-to-refrigerant heat exchanger 50 to change to low-temperature, medium-pressure refrigerant that is in a gaseous or two-phase gas-liquid state, and then flows into the low-pressure pipe at the outlet side of the relay device 3.
  • the merged refrigerant then flows out of the relay device 3, and passes through the main pipe 5 to flow into the outdoor unit 201 again.
  • the refrigerant flowing into the outdoor unit 201 passes through the first backflow prevention device 13c, and is expanded in the first expansion device 45 to change to low-temperature, low-pressure refrigerant that is in a two-phase gas-liquid state.
  • This refrigerant then changes to low-temperature, low-pressure gas refrigerant in the heat source-side heat exchanger 12 while removing heat from the outdoor air.
  • the low-temperature, low-pressure gas refrigerant then passes through the refrigerant flow switching device 11 and the accumulator 19 and then is sucked into the compressor 10 again.
  • the opening degree of the load-side expansion device 25b is controlled to maintain a constant level of subcooling (degree of subcooling) calculated as the difference between a value obtained by converting the pressure detected by the inlet-side pressure sensor 33 into a saturation temperature, and the temperature detected by the inlet-side temperature sensor 31 b.
  • the opening degree of the load-side expansion device 25a is controlled to maintain a constant level of superheat (degree of superheat) calculated as the difference between the temperature detected by the inlet-side temperature sensor 31 a and the temperature detected by the outlet-side temperature sensor 32b.
  • the opening degree of the fourth expansion device 27 is controlled to maintain a constant level of subcooling (degree of subcooling) calculated as the difference between a value obtained by converting the pressure detected by the outlet-side pressure sensor 34 into a saturation temperature, and the temperature detected by the temperature sensor 51.
  • the opening degree of the fourth expansion device 27 is controlled to provide a predetermined pressure difference (for example, 0.3 MPa) between the pressure detected by the inlet-side pressure sensor 33, and the pressure detected by the outlet-side pressure sensor 34.
  • the calculation method for and the size of the required total heat transfer area A 1 (m 2 ), which represents the area in which the auxiliary heat exchanger 40 contacts the air of the environment under which the outdoor unit 201 is installed, are the same as those in Embodiment 1.
  • Fig. 10 is a schematic circuit configuration diagram illustrating an exemplary circuit configuration of an air-conditioning apparatus according to Embodiment 3 and the flow of refrigerant in cooling only operation mode.
  • Embodiment 3 will mainly focus on differences from Embodiment 2, and parts that are the same as those in Embodiment 2 will be denoted by the same reference signs.
  • An air-conditioning apparatus 300 illustrated in Fig. 10 differs from the air-conditioning apparatus 200 illustrated in Figs. 5 to 9 in the configuration of an outdoor unit 301.
  • one end of the bypass pipe 41 is connected to a first diverging pipe 48 and a second diverging pipe 49.
  • the bypass pipe 41 is thus diverged in two directions.
  • One end of the first diverging pipe 48 is connected to the part of the second connecting pipe 4b between the first expansion device 45 and the first backflow prevention device 13c, and the other end is connected to the bypass pipe 41.
  • One end of the second diverging pipe 49 is connected to the part of the refrigerant pipe 4 between the merging point of the first backflow prevention device 13a and the first connecting pipe 4a, and the main pipe 5, and the other end is connected to the bypass pipe 41.
  • An opening and closing device 47 is provided in the second diverging pipe 49. Operation of the opening and closing device 47 is controlled by the controller 60.
  • the opening and closing device 47 is only required to be able to open and close a flow path, and may be an expansion device capable of full closing.
  • the controller 60 controls the first expansion device 45 to be fully closed, and controls the opening and closing device 47 to be open. Then, part of the high-pressure refrigerant flowing out of the heat source-side heat exchanger 12 flows into the auxiliary heat exchanger 40, via the second diverging pipe 49, the opening and closing device 47 controlled to open, and the bypass pipe 41. In the auxiliary heat exchanger 40, the refrigerant changes to high-pressure subcooled liquid while rejecting heat to the outdoor air supplied from the fan 16. The subcooled liquid flows into the suction part of the compressor 10 via the second expansion device 42. As a result, the discharge temperature of refrigerant discharged from the compressor 10 can be lowered.
  • heating operation mode heating only operation mode and heating main operation mode
  • the opening and closing device 47 is controlled to be closed by the controller 60 to limit a rise in the discharge temperature of refrigerant discharged from the compressor 10.
  • the operation and control of the air-conditioning apparatus 300 when the opening and closing device 47 is closed are substantially the same as those in the air-conditioning apparatus 200. Further, the effect of the circuit configuration of the air-conditioning apparatus 300 is also similar to that of the air-conditioning apparatus 200.
  • Fig. 11 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling only operation mode of the air-conditioning apparatus according to a modification of Embodiment 3 of the present invention.
  • a backflow prevention device 13g is provided in the first diverging pipe 48.
  • the backflow prevention device 13g prevents the high-pressure gas refrigerant discharged from the compressor 10 from flowing backward to the second connecting pipe 4b, which is a flow path of low-pressure refrigerant.
  • the opening and closing device 47 is controlled to open, allowing high-pressure gas refrigerant to flow into the auxiliary heat exchanger 40 from the second diverging pipe 49.
  • the controller 60 controls the opening and closing device 47 to open, thus allowing high-pressure gas refrigerant to flow into the auxiliary heat exchanger 40 from the first connecting pipe 4a.
  • refrigerant that has been changed to subcooled liquid in the auxiliary heat exchanger 40 can be allowed to flow into the suction part of the compressor 10, thus making it possible to limit an excessive rise in the discharge temperature of the compressor 10.
  • the backflow prevention device 13g may be any device capable of preventing backflow of refrigerant, and may be an opening and closing device or an expansion device capable of full closing.
  • a first diverging-pipe opening and closing device such as an opening and closing device and an expansion device capable of full closing that can open and close a flow path, may be provided instead of the backflow prevention device 13g.
  • the controller 60 may control the first diverging-pipe opening and closing device and the opening and closing device 47 to close, and control the second expansion device 42 to a small opening degree just short of full closure. This configuration can minimize stagnation of refrigeration in the bypass pipe 41 and the auxiliary heat exchanger 40.
  • the above configuration prevents an excessive amount of liquid refrigerant from flowing into the suction part of the compressor 10 from the second expansion device 42, thus preventing damage to the compressor 10 due to excessive liquid return to the compressor 10.
  • refrigerant is injected into the suction part of the compressor 10 via the auxiliary heat exchanger 40 and the second expansion device 42, and thus the reliability of the system is ensured even when an inexpensive compressor is used rather than a compressor having a special structure. Further, limiting an excessive rise in the discharge temperature of the compressor 10 allows for an increase in the rotation speed of the compressor 10 to ensure sufficient heating capacity, thus minimizing a decrease in user comfort.
  • the calculation method for and the size of the required total heat transfer area A 1 (m 2 ), which represents the area in which the auxiliary heat exchanger 40 contacts the air of the environment under which the outdoor unit 201 is installed, are the same as those in Embodiment 1.
  • Fig. 12 is a schematic circuit configuration diagram illustrating an exemplary circuit configuration of an air-conditioning apparatus according to Embodiment 4, and the flow of refrigerant in cooling operation mode.
  • Embodiment 4 will mainly focus on differences from Embodiments mentioned above, and parts that are the same as those in Embodiment 1 will be denoted by the same reference signs.
  • An air-conditioning apparatus 400 illustrated in Fig. 12 differs from the air-conditioning apparatus 100 in the configuration of an outdoor unit 401.
  • one end of the bypass pipe 41 is diverged in two directions into the first diverging pipe 48 and the second diverging pipe 49.
  • One end of the first diverging pipe 48 is connected to the part of the refrigerant pipe 4 between the first expansion device 45 and the load-side expansion device 25, and the other end of the first diverging pipe 48 merges with the second diverging pipe 49 via the backflow prevention device 13g and is connected to the bypass pipe 41.
  • the backflow prevention device 13g prevents the high-pressure gas refrigerant discharged from the compressor 10 from flowing backward to the refrigerant pipe 4, which is a flow path of high-pressure, liquid or two-phase gas-liquid refrigerant flowing out of the heat source-side heat exchanger 12.
  • One end of the second diverging pipe 49 is connected to the part of the refrigerant pipe 4 between the flow path on the discharge side of the compressor 10 and the refrigerant flow switching device 11.
  • the second diverging pipe 49 is provided with the opening and closing device 47.
  • the other end of the second diverging pipe 49 merges with the first diverging pipe 48 via the opening and closing device 47, and is connected to the bypass pipe 41.
  • the air-conditioning apparatus 400 when a rise in the discharge temperature of refrigerant discharged from the compressor 10 is to be limited in cooling operation mode, part of the high-pressure gas refrigerant discharged from the compressor 10 allowed to flow into the auxiliary heat exchanger 40, via the second diverging pipe 49, the opening and closing device 47 controlled to open, and the bypass pipe 41.
  • the refrigerant then changes to high-pressure subcooled liquid in the auxiliary heat exchanger 40 while rejecting heat to the outdoor air supplied from the fan 16, and the high-pressure subcooled liquid refrigerant flows into the suction part of the compressor 10 via the second expansion device 42.
  • the discharge temperature of refrigerant discharged from the compressor 10 can be lowered.
  • the opening and closing device 47 is controlled to be closed, and other operation and control of the air-conditioning apparatus 400 are similar to those of the air-conditioning apparatus 100. Further, the effect of the circuit configuration of the air-conditioning apparatus 400 is also similar to that of the air-conditioning apparatus 100.
  • the backflow prevention device 13g is depicted as if the backflow prevention device 13g is a check valve, the backflow prevention device 13g may be any device capable of preventing backflow of refrigerant, and may be an opening and closing device or an expansion device capable of full closing. Further, the opening and closing device 47 is only required to be able to open and close a flow path, and may be an expansion device capable of full closing.
  • a first diverging-pipe opening and closing device such as an opening and closing device and an expansion device capable of full closing that can open and close a flow path, may be provided instead of the backflow prevention device 13g.
  • the first diverging-pipe opening and closing device and the opening and closing device 47 may be controlled to be closed, and the second expansion device 42 may be controlled to a small opening degree just short of full closure. This configuration can minimize stagnation of refrigeration in the bypass pipe 41 and the auxiliary heat exchanger 40.
  • the above configuration prevents an excessive amount of liquid refrigerant from flowing into the suction part of the compressor 10 from the second expansion device 42, thus preventing damage to the compressor 10 due to excessive liquid return to the compressor 10.
  • the calculation method for and the size of the required total heat transfer area A 1 (m 2 ), which represents the area in which the auxiliary heat exchanger 40 contacts the air of the environment under which the outdoor unit 201 is installed, are the same as those in Embodiment 1.
  • Fig. 13 is a schematic circuit configuration diagram, illustrating an exemplary circuit configuration of an air-conditioning apparatus according to Embodiment 5, and the flow of refrigerant in cooling only operation mode.
  • Embodiment 5 will mainly focus on differences from Embodiment 2, and parts that are the same as those in Embodiment 2 will be denoted by the same reference signs.
  • An air-conditioning apparatus 500 illustrated in Fig. 13 differs from the air-conditioning apparatus 200 in the configuration of an outdoor unit 501.
  • one end of the bypass pipe 41 is diverged in two directions into the first diverging pipe 48 and the second diverging pipe 49.
  • One end of the first diverging pipe 48 is connected to the part of the second connecting pipe 4b between the first expansion device 45 and the first backflow prevention device 13c, and the other end merges with the second diverging pipe 49 and is connected to the bypass pipe 41.
  • One end of the second diverging pipe 49 is connected to the part of the refrigerant pipe 4 between the flow path on the discharge side of the compressor 10 and the refrigerant flow switching device 11, and the other end merges with the first diverging pipe 48 via the opening and closing device 47 and is connected to the bypass pipe 41.
  • the opening and closing device 47 is only required to be able to open and close a flow path, and may be an expansion device capable of full closing.
  • the first expansion device 45 is controlled by the controller 60 to be fully closed, and part of the high-pressure gas refrigerant discharged from the compressor 10 is allowed to flow into the auxiliary heat exchanger 40, via the second diverging pipe 49, the opening and closing device 47 controlled to open, and the bypass pipe 41.
  • the opening and closing device 47 is controlled by the controller 60 to be closed, and other operation and control of the air-conditioning apparatus 500 are similar to those of the air-conditioning apparatus 200. Further, the effect of the circuit configuration of the air-conditioning apparatus 500 is also similar to that of the air-conditioning apparatus 200.
  • the first diverging pipe 48 is provided with the backflow prevention device 13g.
  • the function of the backflow prevention device 13g is to prevent the high-pressure gas refrigerant discharged from the compressor 10 from flowing backward to the second connecting pipe 4b, which is a flow path of low-pressure refrigerant, when high-pressure gas refrigerant is allowed to the auxiliary heat exchanger 40 in heating only operation mode and heating main operation mode.
  • the circuit configuration is employed so that, for example, in heating only operation mode and heating main operation mode, the controller 60 controls the opening and closing device 47 to open, allowing high-pressure gas refrigerant to flow into the auxiliary heat exchanger 40 from the second diverging pipe 49.
  • the high-pressure gas refrigerant from the first connecting pipe 4a is allowed to flow into the auxiliary heat exchanger 40, and in the auxiliary heat exchanger 40, the high-pressure gas refrigerant is changed to subcooled liquid and is allowed to flow into the suction part of the compressor 10 to thereby limit an excessive rise in the discharge temperature of the compressor 10.
  • the backflow prevention device may be any device capable of preventing backflow of refrigerant, and may be an opening and closing device or an expansion device capable of full closing.
  • a first diverging-pipe opening and closing device such as an opening and closing device and an expansion device capable of full closing that can open and close a flow path, may be provided instead of such a backflow prevention device.
  • the first diverging-pipe opening and closing device and the opening and closing device 47 may be controlled to be closed, and the second expansion device 42 may be controlled to a small opening degree just short of full closure, thus minimizing stagnation of refrigerant in the bypass pipe 41 and the auxiliary heat exchanger 40.
  • this configuration prevents an excessive amount of liquid refrigerant from flowing into the suction part of the compressor 10 from the second expansion device 42, thus preventing damage to the compressor 10 due to excessive liquid return to the compressor 10.
  • refrigerant is injected into the suction part of the compressor 10 via the auxiliary heat exchanger 40 and the second expansion device 42 in cooling operation mode and heating operation mode, and thus the reliability of the system is ensured even when an inexpensive compressor is used rather than a compressor having a special structure. Further, limiting an excessive rise in the discharge temperature of the compressor 10 allows for an increase in the rotation speed of the compressor 10 to ensure sufficient heating capacity, thus minimizing a decrease in user comfort.
  • the calculation method for and the size of the required total heat transfer area A 1 (m 2 ), which represents the area in which the auxiliary heat exchanger 40 contacts the air of the environment under which the outdoor unit 201 is installed, are the same as those in Embodiment 1.
  • the air-conditioning apparatus 500 illustrated in Fig. 13 employs the outdoor unit 201 as in Embodiment 2
  • the air-conditioning apparatus 500 may employ the outdoor unit 301 illustrated in Figs. 10 and 11 .
  • Embodiments of the present invention are not limited to Embodiments mentioned above, and various modifications can be made.
  • the discharge temperature threshold may be any value determined depending on the limit value of the discharge temperature of the compressor 10. For example, if the limit value of the discharge temperature of the compressor 10 is 120 degrees C, the operation of the compressor 10 is controlled by the controller 60 so that the discharge temperature does not exceed this value. Specifically, when the discharge temperature exceeds 110 degrees C, the controller 60 lowers the frequency of the compressor 10 to lower the rotation speed of the compressor 10.
  • the discharge temperature threshold is preferably set to a temperature between 100 degrees C and 110 degrees C (for example, 105 degrees C), slightly lower than the temperature threshold of 110 degrees C at which the frequency of the compressor 10 is to be lowered. If, for example, the frequency of the compressor 10 is not lowered at the discharge temperature of 110 degrees C, the discharge temperature threshold at which the injection is to be performed to lower the discharge temperature may be set to a value between 100 degrees C and 120 degrees C (for example, 115 degrees C).
  • the discharge temperature under the same operating condition is higher by approximately 20 degrees C than the discharge temperature in a case where R410A is used.
  • the discharge temperature needs to be lowered, and the effect of the above-mentioned injection is significant in this respect.
  • the effect of the above-mentioned injection is particularly significant when a refrigerant with a comparatively high discharge temperature is used.
  • the effect of lowering discharge temperature through injection in the air-conditioning apparatuses 100 to 500 mentioned above is high.
  • the kinds of refrigerant present in a refrigerant mixture are not limited to the above.
  • Use of a refrigerant mixture containing a small amount of one or more other refrigerant components does not significantly affect discharge temperature and thus provides the same effect.
  • the configuration employed may be used also for, for example, a refrigerant mixture containing R32, HFO1234yf, and a small amount of one or more other refrigerants.
  • R32, HFO1234yf a refrigerant mixture containing R32, HFO1234yf
  • Embodiments 1 to 5 are directed to a case where the auxiliary heat exchanger 40 and the heat source-side heat exchanger 12 are integrated, the auxiliary heat exchanger 40 may be disposed as an independent component. In another alternative configuration, the auxiliary heat exchanger 40 may be disposed on the upper side.
  • the foregoing description is directed to a case where the auxiliary heat exchanger 40 is located on the lower side of the fins, and the heat source-side heat exchanger 12 is located on the upper side of the heat transfer fins, the auxiliary heat exchanger 40 may be located on the upper side, and the heat source-side heat exchanger 12 may be located on the lower side.
  • the air-conditioning apparatus capable of concurrent cooling and heating operation employs a pipe connection in which two main pipes 5 are used to connect the outdoor unit 201 and the relay device 3, the pipe connection is not limited to this configuration but various known methods may be used.
  • an excessive rise in the temperature of high-pressure, high-temperature gas refrigerant discharged from the compressor 10 can be limited as in Embodiment 2 mentioned above also when the air-conditioning apparatus capable of concurrent cooling and heating operation is configured so that the outdoor unit 1 and the relay device 3 are connected by using three main pipes 5.
  • the present invention is also applicable to compressors including an injection port for allowing refrigerant to flow into the medium-pressure part of the compressor.
  • the present invention is not limited to this configuration.
  • devices such as panel heaters that utilize radiation may be also used as the load-side heat exchangers 26a to 26d.
  • the heat source-side heat exchanger 12 used may be a water-cooled heat exchanger that uses a fluid such as water and antifreeze to exchange heat. Any heat exchanger that allows refrigerant to reject heat or remove heat may be used.
  • a water-cooled heat exchanger for example, a water-to-refrigerant heat exchanger, such as a plate heat exchanger and a double-pipe heat exchanger, may be installed for use as the auxiliary heat exchanger 40, or alternatively, a controller-cooling heat exchanger with a fan mounted to cool the controller 60 may be used.
  • a water-to-refrigerant heat exchanger such as a plate heat exchanger and a double-pipe heat exchanger
  • the present invention is also applicable to an air-conditioning apparatus in which refrigerant is circulated in an intervening area A between the outdoor unit and the relay unit, a heat medium such as water and brine is circulated in an intervening area B between the relay unit and the heat exchangers (load-side heat exchangers) provided in the indoor units 2, and the refrigerant and the heat medium are allowed to exchange heat in the relay device 3 for air conditioning.
  • refrigerant is circulated in an intervening area A between the outdoor unit and the relay unit
  • a heat medium such as water and brine
  • the refrigerant and the heat medium are allowed to exchange heat in the relay device 3 for air conditioning.

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WO2021005737A1 (ja) * 2019-07-10 2021-01-14 三菱電機株式会社 室外機および空気調和装置
CN110542852B (zh) * 2019-09-04 2022-08-26 上海乐研电气有限公司 一种气体密度继电器的改造方法
JPWO2023139713A1 (de) * 2022-01-20 2023-07-27
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JPS63290359A (ja) * 1987-05-20 1988-11-28 三洋電機株式会社 空気調和機
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JP4459776B2 (ja) * 2004-10-18 2010-04-28 三菱電機株式会社 ヒートポンプ装置及びヒートポンプ装置の室外機
JP4812606B2 (ja) * 2006-11-30 2011-11-09 三菱電機株式会社 空気調和装置
JP2009228979A (ja) * 2008-03-24 2009-10-08 Mitsubishi Electric Corp 空気調和装置

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11022354B2 (en) 2016-09-30 2021-06-01 Daikin Industries, Ltd. Air conditioner
CN108548242A (zh) * 2018-03-30 2018-09-18 青岛海尔空调器有限总公司 一种空调系统的控制方法及装置
CN108548242B (zh) * 2018-03-30 2021-01-29 青岛海尔空调器有限总公司 一种空调系统的控制方法及装置

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WO2015125219A1 (ja) 2015-08-27
JP6038382B2 (ja) 2016-12-07
EP3109566A4 (de) 2017-10-18
EP3109566B1 (de) 2018-08-08

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