Freezing air conditioner

Abstract

To provide a freezing air conditioner capable of suppressing damage to the piping of an indoor unit for performing cooling operation.SOLUTION: A controller derives an evaporation temperature of an indoor heat exchanger from an indoor side pressure of an indoor unit for performing cooling operation; when the evaporation temperature exceeds a preset evaporation temperature, increases an opening of a corresponding three-way valve; and when the evaporation temperature is below the preset evaporation temperature, decreases the opening of the corresponding three-way valve, thereby preventing the piping of the indoor unit for performing cooling operation from freezing.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a refrigeration and air conditioning system that can simultaneously perform cooling operation and heating operation on a plurality of spaces to be air-conditioned. [Background technology]

[0002] Conventionally, in buildings with large, continuous spaces or many rooms, such as buildings and factories, air conditioners equipped with multiple indoor units have been installed, and these air conditioners perform cooling or heating operations. For example, Patent Document 1 discloses an air conditioner equipped with multiple indoor units, an outdoor unit that circulates a refrigerant through each indoor unit, and a control panel that controls the operation of these, and configured to blow out temperature-controlled air from each indoor unit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 155056 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the longer the piping between the indoor unit and the outdoor unit, the greater the pressure loss, resulting in a higher evaporating temperature of the indoor unit. Therefore, when the air conditioner is operating in cooling mode, particularly in heating-dominated mode, the evaporating temperature of the indoor unit performing cooling, which has the shortest piping length between the indoor unit and the outdoor unit, is the lowest compared to the other indoor units and may fall below 0°C. If the evaporating temperature falls below 0°C, the piping connected to that indoor unit may freeze and break. However, in the air conditioner described in Patent Document 1, the evaporating temperature of each indoor unit is controlled by a throttle valve device installed in the outdoor unit, making it impossible to control the evaporating temperature of each indoor unit differently. Therefore, the air conditioner described in Patent Document 1 had the risk of damaging the piping of the indoor unit performing cooling mode.

[0005] The present disclosure has been made in consideration of the problems in the above-described conventional technology, and aims to provide a refrigeration and air conditioning apparatus that can suppress damage to the piping of an indoor unit that performs cooling operation. [Means for solving the problem]

[0006] The refrigeration and air conditioning device according to the present disclosure is a refrigeration and air conditioning device capable of performing cooling-dominated operation and heating-dominated operation, and the refrigeration and air conditioning device includes an outdoor unit having a compressor and an outdoor heat exchanger, and a plurality of indoor units each having an indoor expansion valve and an indoor heat exchanger, and is connected between the outdoor unit and the indoor units, and has a plurality of three-way valves provided corresponding to the number of the indoor units for switching the flow of refrigerant and adjusting the flow rate of the refrigerant passing through, and distributes low-temperature refrigerant to the indoor units performing cooling operation and distributes high-temperature refrigerant to the indoor units performing heating operation. and a control device that controls the switching and opening of the three-way valve, and the indoor unit has an indoor pressure sensor that detects the indoor pressure, which is the pressure of the refrigerant passing through the indoor heat exchanger, and the control device derives the evaporation temperature of the indoor heat exchanger from the indoor pressure of the indoor unit that performs cooling operation, and when the evaporation temperature exceeds a predetermined set evaporation temperature, increases the opening of the corresponding three-way valve, and when the evaporation temperature is below the set evaporation temperature, decreases the opening of the corresponding three-way valve, thereby preventing the piping of the indoor unit that performs cooling operation from freezing. [Effects of the Invention]

[0007] According to the refrigeration and air conditioning system of the present disclosure, when the evaporation temperature of the indoor unit performing cooling operation exceeds a preset evaporation temperature, the aperture of the corresponding three-way valve is increased, and when the evaporation temperature is below the preset evaporation temperature, the aperture of the corresponding three-way valve is decreased to prevent the piping of the indoor unit performing cooling operation from freezing. As a result, the refrigeration and air conditioning system of the present disclosure can suppress damage to the piping of the indoor unit performing cooling operation. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a circuit diagram showing an example of the configuration of a refrigeration and air conditioning device according to a first embodiment. [Figure 2] 2 is a functional block diagram showing an example of the configuration of the control device of FIG. 1. FIG. [Figure 3]3 is a hardware configuration diagram showing an example of the configuration of the control device of FIG. 2. FIG. [Figure 4] 3 is a hardware configuration diagram showing another example of the configuration of the control device of FIG. 2. FIG. [Figure 5] 2 is a schematic diagram for explaining the flow of refrigerant in the refrigeration air-conditioning system of FIG. 1 in a cooling only operation mode. FIG. [Figure 6] 2 is a schematic diagram for explaining the flow of refrigerant in the refrigeration and air conditioning system of FIG. 1 in a heating only operation mode. FIG. [Figure 7] 2 is a schematic diagram for explaining the flow of refrigerant in the refrigeration air conditioning system of FIG. 1 in a cooling-dominated operation mode. FIG. [Figure 8] 2 is a schematic diagram for explaining the flow of refrigerant in the refrigeration and air conditioning system of FIG. 1 in a heating-dominated operation mode. FIG. [Figure 9] 4 is a flowchart showing an example of the flow of an evaporation temperature adjustment process according to the first embodiment. [Figure 10] 10 is a flowchart showing an example of the flow of a liquid backflow prevention process according to the first embodiment. [Figure 11] 11 is a flowchart showing an example of the flow of the first liquid backflow suppression process of FIG. 10. [Figure 12] 11 is a flowchart showing an example of the flow of the second liquid backflow suppression process of FIG. 10. [Figure 13] FIG. 6 is a circuit diagram showing an example of the configuration of a refrigeration and air conditioning device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments and can be modified in various ways without departing from the spirit of the present disclosure. Furthermore, the present disclosure includes all possible combinations of the configurations shown in the following embodiments. Furthermore, the levels of temperature, pressure, etc. are not determined in relation to absolute values, but are determined relatively in terms of the state and operation of a system, device, etc. Furthermore, in each drawing, parts with the same reference numerals are the same or equivalent, and this applies throughout the entire specification.

[0010] Embodiment 1 A description will be given of a refrigeration and air conditioning system according to Embodiment 1. The refrigeration and air conditioning system according to Embodiment 1 performs only cooling operation, only heating operation, or simultaneous cooling and heating operation on a plurality of spaces to be air-conditioned.

[0011] [Configuration of Refrigeration and Air Conditioning Device 100] FIG. 1 is a circuit diagram showing an example of the configuration of a refrigeration and air conditioning system according to the first embodiment. The refrigeration and air conditioning system 100 according to the first embodiment is configured to include an outdoor unit 10, a plurality of indoor units 20, a relay unit 30, and a control device 40. The example of FIG. 1 shows a case in which the refrigeration and air conditioning system 100 is configured with one outdoor unit 10, five indoor units 20a to 20e, and one relay unit 30. In the refrigeration and air conditioning system 100, a refrigerant circuit is formed by connecting the outdoor unit 10, the relay unit 30, and the indoor units 20a to 20e with high-pressure piping 101 and low-pressure piping 102. The number of indoor units 20 is not limited to this example, and may be two or more and four or less, or six or more.

[0012] In this example, the indoor units 20a to 20e are installed in rooms 1a to 1e, which are different spaces to be air-conditioned. The outdoor unit 10 and the relay unit 30, and the indoor units 20a to 20e and the relay unit 30 are connected by high-pressure piping 101 and low-pressure piping 102.

[0013] Since the indoor units 20a to 20e each have the same configuration, the indoor units 20c and 20d and the circuit configuration of the relay unit 30 that is connected to the indoor units 20c and 20d are not shown in Fig. 1. The circuit configuration of the indoor units 20b and 20e is also the same as that of the indoor unit 20a, and is therefore not shown.

[0014] (Outdoor unit 10) The outdoor unit 10 includes a compressor 11, a refrigerant flow switching device 12, an outdoor heat exchanger 13, an outdoor expansion valve 14, check valves 15a to 15d, and an accumulator 16. The outdoor unit 10 also includes an outdoor pressure sensor 17 and an outdoor temperature sensor 18.

[0015] The compressor 11 draws in a low-temperature, low-pressure refrigerant, compresses it, and discharges it into a high-temperature, high-pressure state. The compressor 11 may be, for example, an inverter compressor, whose capacity, or the amount of refrigerant delivered per unit time, can be controlled by arbitrarily changing the drive frequency. The drive frequency of the compressor 11 is controlled by a control device 40, which will be described later.

[0016] The refrigerant flow switching device 12 is, for example, a four-way valve, and switches between cooling operation and heating operation by switching the direction of refrigerant flow. The switching of the refrigerant flow switching device 12 is controlled by the control device 40. Note that the refrigerant flow switching device 12 is not limited to this example, and may be configured by combining other valves, such as a two-way valve or a three-way valve.

[0017] The outdoor heat exchanger 13 exchanges heat between the refrigerant and air (hereinafter referred to as "outdoor air") supplied by a blower such as a fan (not shown). Specifically, the outdoor heat exchanger 13 functions as a condenser that radiates heat from the refrigerant to the outdoor air during cooling operation to condense the refrigerant. Also, the outdoor heat exchanger 13 functions as an evaporator that evaporates the refrigerant and absorbs heat from the outdoor air as heat of vaporization during heating operation.

[0018] The outdoor expansion valve 14 adjusts the flow rate of the refrigerant to reduce the pressure of the refrigerant and expand it. The outdoor expansion valve 14 is configured as a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the outdoor expansion valve 14 is controlled by the control device 40. Note that the outdoor expansion valve 14 is not limited to this example, and other throttling devices, such as a capillary, may also be used.

[0019] The check valves 15a to 15d allow the flow of refrigerant circulating in the refrigerant circuit only in a predetermined direction. The check valve 15a is provided in the high-pressure piping 101 between the outdoor heat exchanger 13 and the relay unit 30. The check valve 15a allows the flow of refrigerant only in the direction from the outdoor unit 10 to the relay unit 30 during cooling operation, including cooling-only operation and cooling-dominant operation, which will be described later. The check valve 15d is provided in the low-pressure piping 102 between the relay unit 30 and the refrigerant flow switching device 12. The check valve 15d allows the flow of refrigerant only in the direction from the relay unit 30 to the outdoor unit 10 during cooling operation.

[0020] Check valve 15b is provided in first connecting pipe 103 that connects the downstream side of check valve 15a in high-pressure pipe 101 to the downstream side of check valve 15d in low-pressure pipe 102. Check valve 15b allows refrigerant to flow only in the direction from compressor 11 to relay unit 30 during heating operation, including heating only operation and heating-dominant operation, which will be described later. Check valve 15c is provided in second connecting pipe 104 that connects the upstream side of check valve 15a in high-pressure pipe 101 to the upstream side of check valve 15d in low-pressure pipe 102. Check valve 15c allows refrigerant to flow only in the direction from relay unit 30 to compressor 11 during heating operation.

[0021] The accumulator 16 is provided on the low-pressure side, which is the suction side, of the compressor 11. The accumulator 16 stores excess refrigerant that occurs due to differences in operating conditions between cooling operation and heating operation, excess refrigerant due to transient changes in operation, etc. However, the accumulator 16 is not necessarily provided.

[0022] The outdoor pressure sensor 17 is provided in the piping between the refrigerant suction side of the compressor 11 and the refrigerant flow switching device 12. The outdoor pressure sensor 17 detects the suction pressure, which is the pressure of the refrigerant sucked into the compressor 11. The outdoor temperature sensor 18 is provided in the piping between the refrigerant suction side of the compressor 11 and the refrigerant flow switching device 12. The outdoor temperature sensor 18 detects the suction temperature, which is the temperature of the refrigerant sucked into the compressor 11.

[0023] (Indoor units 20a to 20e) The indoor units 20a to 20e cool and heat the air in, for example, rooms 1a to 1e, respectively. Each of the indoor units 20a to 20e includes an indoor expansion valve 21 and an indoor heat exchanger 22. Each of the indoor units 20a to 20e also includes an indoor pressure sensor 23. In the following description, when there is no need to particularly distinguish between the indoor units 20a to 20e, they will be simply referred to as "indoor unit 20" as appropriate.

[0024] The indoor expansion valve 21 adjusts the flow rate of the refrigerant to reduce the pressure of the refrigerant and expand it. The indoor expansion valve 21 is configured with a valve whose opening can be controlled, such as an electronic expansion valve. In this case, the opening of the indoor expansion valve 21 is controlled by the control device 40. Note that the indoor expansion valve 21 is not limited to this example, and other throttling devices such as a capillary may also be used.

[0025] The indoor heat exchanger 22 exchanges heat between the refrigerant and air supplied by a blower such as a fan (not shown). This generates air for heating or air for cooling to be supplied to the rooms 1a to 1e. Specifically, the indoor heat exchanger 22 functions as an evaporator during cooling operation, cooling the air in the rooms 1a to 1e, which are the spaces to be air-conditioned, to perform cooling. Furthermore, the indoor heat exchanger 22 functions as a condenser during heating operation, heating the air in the rooms 1a to 1e to perform heating.

[0026] The indoor pressure sensor 23 is provided in the low-pressure pipe 102 between the indoor heat exchanger 22 and the relay unit 30. The indoor pressure sensor 23 detects the indoor pressure, which is the pressure of the refrigerant passing through the indoor heat exchanger 22. In particular, during cooling operation in which the indoor heat exchanger 22 functions as an evaporator, the indoor pressure sensor 23 detects a pressure equivalent to the evaporation pressure in the indoor heat exchanger 22. The indoor pressure at this time is detected, for example, by inserting a sensor into the pipe, or by determining the relationship between the amount of deformation of the pipe detected by a strain sensor attached to the pipe and the pressure applied to the pipe.

[0027] (Relay unit 30) The relay unit 30 switches the flow of refrigerant depending on the operating conditions of the indoor units 20, so as to distribute low-temperature refrigerant to the indoor units 20 performing cooling operation and high-temperature refrigerant to the indoor units 20 performing heating operation.

[0028] The relay unit 30 includes a gas-liquid separator 31, a first refrigerant heat exchanger 32, a first relay expansion valve 33, a second refrigerant heat exchanger 34, a second relay expansion valve 35, a check valve 36, and a three-way linear expansion valve 37. The relay unit 30 also includes a gas pipe 105 through which gas refrigerant flows, and a liquid pipe 106 through which liquid refrigerant flows. The relay unit 30 also includes a branch pipe 107 and a junction pipe 108. The branch pipe 107 branches off from the liquid pipe 106 downstream of the second refrigerant heat exchanger 34 and is connected to the low-pressure pipe 102. The junction pipe 108 is connected to each indoor unit 20 and merges with the liquid pipe 106 between the first relay expansion valve 33 and the second refrigerant heat exchanger 34.

[0029] The gas-liquid separator 31 is connected to the high-pressure pipe 101, the gas pipe 105, and the liquid pipe 106, and separates the two-phase refrigerant flowing through the high-pressure pipe 101 into gas refrigerant and liquid refrigerant. The gas refrigerant separated by the gas-liquid separator 31 is supplied to the three-way linear expansion valve 37 via the gas pipe 105. The liquid refrigerant separated by the gas-liquid separator 31 is supplied to the first refrigerant heat exchanger 32 via the liquid pipe 106.

[0030] The first refrigerant heat exchanger 32 has a primary flow path and a secondary flow path, and performs heat exchange between the refrigerant flowing through the primary flow path and the refrigerant flowing through the secondary flow path, thereby subcooling the refrigerant flowing through the primary flow path. The primary flow path of the first refrigerant heat exchanger 32 is connected to the gas-liquid separator 31 and the first relay expansion valve 33, and liquid refrigerant separated in the gas-liquid separator 31 flows through it. The secondary flow path of the first refrigerant heat exchanger 32 is connected to the secondary flow path of the second refrigerant heat exchanger 34 and the low-pressure pipe 102, and refrigerant flowing out of the secondary flow path of the second refrigerant heat exchanger 34 flows through it.

[0031] The first relay expansion valve 33 is connected to the primary flow path of the first refrigerant heat exchanger 32 and the primary flow path of the second refrigerant heat exchanger 34. The first relay expansion valve 33 reduces the pressure of the refrigerant and expands it by adjusting the flow rate of the refrigerant. The first relay expansion valve 33 is configured, for example, as a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the first relay expansion valve 33 is controlled by the control device 40. Note that the first relay expansion valve 33 is not limited to this example, and other throttling devices, such as a capillary, may also be used.

[0032] The second refrigerant heat exchanger 34 has a primary side flow path and a secondary side flow path, and performs heat exchange between the refrigerant flowing through the primary side flow path and the refrigerant flowing through the secondary side flow path, thereby subcooling the refrigerant flowing through the primary side flow path. The first relay expansion valve 33 is connected to the primary side flow path of the second refrigerant heat exchanger 34, and the refrigerant flowing out from the first relay expansion valve 33 flows through it. The second side flow path of the second refrigerant heat exchanger 34 is connected to the second relay expansion valve 35 and the secondary side flow paths of the first refrigerant heat exchanger 32, and the refrigerant flowing out from the second relay expansion valve 35 flows through it.

[0033] The second relay expansion valve 35 is provided in the branch pipe 107, and its downstream side is connected to the secondary flow path of the second refrigerant heat exchanger 34. The second relay expansion valve 35 reduces the pressure of the refrigerant and expands it by adjusting the flow rate of the refrigerant. The second relay expansion valve 35 is configured, for example, as a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the second relay expansion valve 35 is controlled by the control device 40. Note that the second relay expansion valve 35 is not limited to this example, and other throttling devices, such as a capillary, may also be used.

[0034] The check valves 36 allow the refrigerant circulating through the refrigerant circuit to flow only in a predetermined direction. The check valves 36 are provided in accordance with the number of indoor units 20. Specifically, in the example of FIG. 1, check valves 36a1 and 36a2 are provided corresponding to indoor unit 20a, and check valves 36b1 and 36b2 are provided corresponding to indoor unit 20b. Furthermore, check valves 36c1 and 36c2 are provided corresponding to indoor unit 20c, and check valves 36d1 and 36d2 are provided corresponding to indoor unit 20d. Furthermore, check valves 36e1 and 36e2 are provided corresponding to indoor unit 20e.

[0035] Check valves 36a1, 36b1, 36c1, 36d1, and 36e1 are provided between indoor units 20a to 20e and junction pipe 108, respectively. Check valves 36a1, 36b1, 36c1, 36d1, and 36e1 allow refrigerant to flow from indoor units 20a to 20e toward junction pipe 108.

[0036] The check valves 36a2, 36b2, 36c2, 36d2, and 36e2 are provided between the downstream side of the primary flow path of the second refrigerant heat exchanger 34 and the indoor units 20a to 20e, respectively. The check valves 36a2, 36b2, 36c2, 36d2, and 36e2 allow the flow of refrigerant from the second refrigerant heat exchanger 34 toward the indoor units 20a to 20e.

[0037] The three-way linear expansion valve 37 is connected to the indoor unit 20, the low-pressure pipe 102, and the gas pipe 105, and switches the direction of refrigerant flow depending on the operating conditions of the indoor unit 20. Specifically, when the indoor unit 20 is performing cooling operation, the three-way linear expansion valve 37 switches the connection so that the indoor unit 20 and the low-pressure pipe 102 are in communication. Also, when the indoor unit 20 is performing heating operation, the three-way linear expansion valve 37 switches the connection so that the gas pipe 105 and the indoor unit 20 are in communication.

[0038] The three-way linear expansion valve 37 also has the function of decompressing and expanding the refrigerant by adjusting the flow rate of the refrigerant. The three-way linear expansion valve 37 is configured as a valve whose opening can be controlled, such as an electronic expansion valve. The switching and opening of the three-way linear expansion valve 37 are controlled by the control device 40.

[0039] The three-way linear expansion valves 37 are provided in accordance with the number of indoor units 20. Specifically, in the example of Fig. 1, three-way linear expansion valves 37a to 37e are provided corresponding to the indoor units 20a to 20e, respectively.

[0040] (Control device 40) The control device 40 controls the entire refrigeration and air conditioning system 100. For example, the control device 40 controls the refrigerant flow switching device 12, the outdoor expansion valve 14, the indoor expansion valve 21, the first relay expansion valve 33, the second relay expansion valve 35, the three-way linear expansion valve 37, and the like, depending on the operating conditions of the refrigeration and air conditioning system 100. In particular, in the first embodiment, the control device 40 controls the opening degree of the three-way linear expansion valve 37 to perform an evaporation temperature adjustment process that individually adjusts the evaporation temperature of the indoor heat exchanger 22 provided in each indoor unit 20. The control device 40 also performs a liquid backflow suppression process that suppresses liquid backflow to the compressor 11. Details of these processes will be described later.

[0041] Fig. 2 is a functional block diagram showing an example of the configuration of the control device of Fig. 1. As shown in Fig. 2, control device 40 includes an information acquisition unit 41, a calculation unit 42, a comparison unit 43, a valve control unit 44, and a storage unit 45. Control device 40 is configured such that various functions are realized by executing software on a calculation device such as a microcomputer, or is configured with hardware such as circuit devices that realize various functions. Note that, of the functions of control device 40, only functions related to processing that is characteristic of the first embodiment will be described here.

[0042] The information acquisition unit 41 acquires the suction pressure detected by the outdoor pressure sensor 17, the suction temperature detected by the outdoor temperature sensor 18, and the indoor pressure detected by the indoor pressure sensor 23. The suction pressure is the pressure of the refrigerant sucked into the compressor 11. The suction temperature is the temperature of the refrigerant sucked into the compressor 11.

[0043] The calculation unit 42 derives the saturation temperature, which is the evaporation temperature, from the pressure acquired by the information acquisition unit 41. Specifically, during the evaporation temperature adjustment process, the calculation unit 42 derives the evaporation temperature of the indoor heat exchanger 22 provided in the indoor unit 20 performing cooling operation, from the indoor pressure detected by the indoor pressure sensor 23 and acquired by the information acquisition unit 41. During the liquid backflow suppression process, the calculation unit 42 derives the evaporation temperature based on the suction pressure detected by the outdoor pressure sensor 17 and acquired by the information acquisition unit 41. During the liquid backflow suppression process, the calculation unit 42 further calculates the degree of superheat based on the suction temperature detected by the outdoor temperature sensor 18 and acquired by the information acquisition unit 41 and the calculated evaporation temperature.

[0044] The comparison unit 43 compares the various values calculated by the calculation unit 42 with the set values stored in the memory unit 45. Specifically, during the evaporation temperature adjustment process, the comparison unit 43 compares the evaporation temperature derived by the calculation unit 42 with the set evaporation temperature stored in the memory unit 45. The set evaporation temperature is the evaporation temperature that should be set when cooling the room to the set temperature.

[0045] Furthermore, during the liquid backflow suppression process, the comparison unit 43 compares the degree of superheat calculated by the calculation unit 42 with the set degree of superheat stored in the storage unit 45. The set degree of superheat is a preset value for suppressing liquid backflow, and is determined by, for example, the outside air temperature, refrigerant pressure, refrigerant temperature, etc. inside the refrigeration and air conditioning unit 100.

[0046] The valve control unit 44 controls the valve openings of the outdoor expansion valve 14, the indoor expansion valve 21, and the three-way linear expansion valve 37 based on the comparison result by the comparison unit 43. For example, during the evaporation temperature adjustment process, the valve control unit 44 controls the valve opening of the three-way linear expansion valve 37 based on the comparison result by the comparison unit 43 between the evaporation temperature and the set evaporation temperature. Furthermore, during the liquid backflow suppression process, the valve control unit 44 controls the valve openings of the outdoor expansion valve 14, the indoor expansion valve 21, and the three-way linear expansion valve 37 based on the comparison result by the comparison unit 43 between the superheat degree and the set superheat degree.

[0047] The storage unit 45 stores various values and the like used in each part of the control device 40. For example, the storage unit 45 stores in advance a set evaporation temperature used when the comparison unit 43 compares the evaporation temperature, and a set degree of superheat used when the comparison unit 43 compares the degree of superheat.

[0048] Fig. 3 is a hardware configuration diagram showing an example of the configuration of the control device of Fig. 2. When the various functions of the control device 40 are executed by hardware, the control device 40 of Fig. 2 is configured by a processing circuit 51, as shown in Fig. 3. The functions of the information acquisition unit 41, the calculation unit 42, the comparison unit 43, the valve control unit 44, and the storage unit 45 of Fig. 2 are realized by the processing circuit 51.

[0049] When each function is executed by hardware, the processing circuit 51 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. The functions of each of the information acquisition unit 41, the calculation unit 42, the comparison unit 43, the valve control unit 44, and the storage unit 45 may be realized by the processing circuit 51 individually, or the functions of each unit may be realized by a single processing circuit 51.

[0050] Fig. 4 is a hardware configuration diagram showing another example of the configuration of the control device of Fig. 2. When the various functions of control device 40 are executed by software, control device 40 of Fig. 2 is configured with processor 52 and memory 53, as shown in Fig. 4. The functions of information acquisition unit 41, calculation unit 42, comparison unit 43, valve control unit 44, and storage unit 45 are realized by processor 52 and memory 53.

[0051] When each function is performed by software, the functions of the information acquisition unit 41, calculation unit 42, comparison unit 43, valve control unit 44, and storage unit 45 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in memory 53. The processor 52 realizes the function of each unit by reading and executing the programs stored in memory 53.

[0052] The memory 53 may be, for example, a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM). Alternatively, the memory 53 may be, for example, a removable recording medium such as a magnetic disk, a flexible disk, an optical disk, a compact disc (CD), a mini disc (MD), or a digital versatile disc (DVD).

[0053] [Refrigerant Operation in the Refrigeration and Air Conditioning Device 100] Next, we will explain the behavior of the refrigerant in various operation modes in the refrigeration and air conditioning system 100 configured as described above. The refrigeration and air conditioning system 100 according to the first embodiment operates in any one of the operation modes of cooling only operation, heating only operation, cooling-dominated operation, and heating-dominated operation.

[0054] All cooling operation is an operation in which all indoor units 20 perform cooling operation. All heating operation is an operation in which all indoor units 20 perform heating operation. Cooling-dominated operation is an operation performed when the cooling load of the indoor units 20 performing cooling operation exceeds the heating load of the indoor units 20 performing heating operation. Heating-dominated operation is an operation performed when the heating load of the indoor units 20 performing heating operation exceeds the cooling load of the indoor units 20 performing cooling operation.

[0055] The cooling load exceeds the heating load and cooling-dominated operation is performed, for example, when the number of indoor units 20 performing cooling operation is greater than the number of indoor units 20 performing heating operation. Also, the heating load exceeds the cooling load and heating-dominated operation is performed, for example, when the number of indoor units 20 performing heating operation is greater than the number of indoor units 20 performing cooling operation.

[0056] (All cooling operation mode) Figure 5 is a schematic diagram for explaining the flow of refrigerant in the cooling only operation mode in the refrigeration and air conditioning system of Figure 1. In the cooling only operation mode, all of the indoor units 20a to 20e perform cooling operation. In Figure 5, the flow path indicated by the thick line is the refrigerant flow path in the cooling only operation mode, and the direction of refrigerant flow in the refrigerant flow path is indicated by arrows.

[0057] In the cooling only operation mode, first, the refrigerant flow switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the outdoor heat exchanger 13 and the suction side of the compressor 11 is connected to the low-pressure pipe 102. In addition, the three-way linear expansion valves 37a to 37e are each switched so that the indoor unit 20 is connected to the low-pressure pipe 102.

[0058] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and is discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows into the outdoor heat exchanger 13 via the refrigerant flow switching device 12. The high-temperature, high-pressure gas refrigerant that has flowed into the outdoor heat exchanger 13 condenses while exchanging heat with the outdoor air and releasing heat, and becomes a high-pressure liquid refrigerant that flows out of the outdoor heat exchanger 13. The high-pressure liquid refrigerant that has flowed out of the outdoor heat exchanger 13 flows out of the outdoor unit 10 via the check valve 15a and flows into the relay unit 30.

[0059] The high-pressure liquid refrigerant that has flowed into the relay unit 30 flows through the gas-liquid separator 31 into the primary-side flow path of the first refrigerant heat exchanger 32. The liquid refrigerant that has flowed into the primary-side flow path of the first refrigerant heat exchanger 32 is subcooled by the refrigerant flowing through the secondary-side flow path of the first refrigerant heat exchanger 32, and flows out from the primary-side flow path of the first refrigerant heat exchanger 32. The liquid refrigerant that has flowed out from the primary-side flow path of the first refrigerant heat exchanger 32 passes through the first relay expansion valve 33 and flows into the primary-side flow path of the second refrigerant heat exchanger 34. The liquid refrigerant that has flowed into the primary-side flow path of the second refrigerant heat exchanger 34 is further subcooled by the refrigerant flowing through the secondary-side flow path of the second refrigerant heat exchanger 34, and flows out from the primary-side flow path of the second refrigerant heat exchanger 34.

[0060] The liquid refrigerant flowing out from the primary side flow path of the second refrigerant heat exchanger 34 is divided, and a portion of the liquid refrigerant flows out of the relay unit 30 via check valves 36a2, 36b2, 36c2, 36d2, and 36e2. The liquid refrigerant flowing out from the relay unit 30 then flows into the indoor units 20a to 20e. The remainder of the liquid refrigerant flowing out from the primary side flow path of the second refrigerant heat exchanger 34 is decompressed and expanded by the second relay expansion valve 35 to become low-pressure gas refrigerant, and passes through the branch pipe 107. As a result, the low-pressure gas refrigerant contributes to supercooling the refrigerant flowing through the first refrigerant heat exchanger 32 and the second refrigerant heat exchanger 34 via the gas-liquid separator 31.

[0061] The liquid refrigerant that flows into the indoor unit 20a is decompressed and expanded by the indoor expansion valve 21 to become a low-temperature, low-pressure two-phase gas-liquid refrigerant or liquid refrigerant, and flows into the indoor heat exchanger 22. The low-temperature, low-pressure two-phase gas-liquid refrigerant or liquid refrigerant that flows into the indoor heat exchanger 22 exchanges heat with the indoor air, absorbing heat and evaporating, thereby cooling the indoor air, and becomes low-pressure gas refrigerant, which flows out of the indoor heat exchanger 22. The low-pressure gas refrigerant that flows out of the indoor heat exchanger 22 then flows out of the indoor unit 20a and flows into the relay unit 30.

[0062] Similarly, the liquid refrigerant that has flowed into each of the indoor units 20b to 20e becomes low-pressure gas refrigerant, flows out of the indoor units 20b to 20e, and flows into the relay unit 30.

[0063] The gas refrigerant that has flowed into the relay unit 30 passes through the three-way linear expansion valves 37a to 37e and reaches the low-pressure pipe 102. The low-pressure gas refrigerant flowing through the low-pressure pipe 102 flows out from the primary flow path of the second refrigerant heat exchanger 34, and merges with the refrigerant flowing through the branch pipe 107 via the second relay expansion valve 35, the second refrigerant heat exchanger 34, and the first refrigerant heat exchanger 32. This low-pressure gas refrigerant then flows out of the relay unit 30 and into the outdoor unit 10.

[0064] The low-pressure gas refrigerant that has flowed into the outdoor unit 10 passes through the check valve 15d, the refrigerant flow switching device 12, and the accumulator 16, and is then sucked into the compressor 11. Then, the above-described circulation is repeated thereafter.

[0065] (Full heating operation mode) Fig. 6 is a schematic diagram for explaining the flow of refrigerant in the heating only operation mode in the refrigeration and air conditioning system of Fig. 1. In the heating only operation mode, all of the indoor units 20a to 20e perform heating operation. In Fig. 6, the flow path indicated by the thick line is the refrigerant flow path in the heating only operation mode, and the direction of refrigerant flow in the refrigerant flow path is indicated by arrows.

[0066] In the heating only operation mode, first, the refrigerant flow switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the gas-liquid separator 31 of the relay unit 30, and so that the suction side of the compressor 11 is connected to the outdoor heat exchanger 13. In addition, the three-way linear expansion valves 37a to 37e are each switched so that the gas pipe 105 is connected to the indoor unit 20.

[0067] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and is discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows out of the outdoor unit 10 via the refrigerant flow switching device 12 and the check valve 15b, and flows into the relay unit 30. The high-temperature, high-pressure gas refrigerant that has flowed into the relay unit 30 flows out of the relay unit 30 via the gas-liquid separator 31 and the three-way linear expansion valves 37a to 37e, and flows into the indoor units 20a to 20e.

[0068] The high-temperature, high-pressure gas refrigerant that has flowed into the indoor unit 20a flows into the indoor heat exchanger 22, where it exchanges heat with the indoor air and condenses while releasing heat, heating the indoor air, and turns into high-pressure liquid refrigerant, which then flows out of the indoor heat exchanger 22. The high-pressure liquid refrigerant that has flowed out of the indoor heat exchanger 22 is reduced in pressure and expanded by the indoor expansion valve 21, becomes intermediate-pressure liquid refrigerant, flows out of the indoor unit 20a, and then flows into the relay unit 30.

[0069] Similarly, the high-temperature, high-pressure gas refrigerant that has flowed into each of the indoor units 20b to 20e becomes intermediate-pressure liquid refrigerant, flows out of the indoor units 20b to 20e, and flows into the relay unit 30.

[0070] The intermediate-pressure liquid refrigerant that has flowed into the relay unit 30 flows through the junction pipe 108 via check valves 36a1, 36b1, 36c1, 36d1, and 36e1. The intermediate-pressure liquid refrigerant then passes through the second refrigerant heat exchanger 34, becomes low-pressure liquid refrigerant by the second relay expansion valve 35, and reaches the low-pressure pipe 102 via the first refrigerant heat exchanger 32. The low-pressure liquid refrigerant flowing through the low-pressure pipe 102 then flows out of the relay unit 30 and into the outdoor unit 10.

[0071] The low-pressure liquid refrigerant that has flowed into the outdoor unit 10 flows into the outdoor heat exchanger 13 via the check valve 15c and the outdoor expansion valve 14. The low-pressure liquid refrigerant that has flowed into the outdoor heat exchanger 13 exchanges heat with the outdoor air, absorbs heat, and evaporates, becoming low-temperature, low-pressure gas refrigerant that flows out of the outdoor heat exchanger 13. The low-temperature, low-pressure gas refrigerant that has flowed out of the outdoor heat exchanger 13 passes through the refrigerant flow switching device 12 and the accumulator 16, and is drawn into the compressor 11. The above-described circulation is then repeated.

[0072] (Cooling-dominated operation mode) Figure 7 is a schematic diagram for explaining the flow of refrigerant in the cooling-dominated operation mode in the refrigeration and air conditioning system of Figure 1. Here, the case where indoor units 20a to 20d perform cooling operation and indoor unit 20e performs heating operation will be explained as an example. In Figure 7, the flow path indicated by the thick line is the refrigerant flow path in the cooling-dominated operation mode, and the direction of refrigerant flow in the refrigerant flow path is indicated by arrows.

[0073] In the cooling-dominated operation mode, first, the refrigerant flow switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the outdoor heat exchanger 13 and the suction side of the compressor 11 is connected to the low-pressure pipe 102. In addition, the three-way linear expansion valves 37a to 37d are each switched so that the indoor unit 20 is connected to the low-pressure pipe 102. The three-way linear expansion valve 37e is each switched so that the gas pipe 105 is connected to the indoor unit 20.

[0074] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and is discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows into the outdoor heat exchanger 13 via the refrigerant flow switching device 12. The high-temperature, high-pressure gas refrigerant that has flowed into the outdoor heat exchanger 13 condenses while exchanging heat with the outdoor air and releasing heat, and becomes a high-pressure two-phase gas-liquid refrigerant that flows out of the outdoor heat exchanger 13. The high-pressure two-phase gas-liquid refrigerant that has flowed out of the outdoor heat exchanger 13 flows out of the outdoor unit 10 via the check valve 15a and flows into the relay unit 30.

[0075] The high-pressure gas-liquid two-phase refrigerant that has flowed into the relay unit 30 flows into the gas-liquid separator 31 and is separated into high-pressure gas refrigerant and high-pressure liquid refrigerant. The high-pressure liquid refrigerant separated by the gas-liquid separator 31 flows into the primary-side flow path of the first refrigerant heat exchanger 32.

[0076] The liquid refrigerant that flows into the primary flow path of the first refrigerant heat exchanger 32 is subcooled by the refrigerant flowing through the secondary flow path of the first refrigerant heat exchanger 32, and flows out of the primary flow path of the first refrigerant heat exchanger 32. The liquid refrigerant that flows out of the primary flow path of the first refrigerant heat exchanger 32 passes through the first relay expansion valve 33 and flows into the primary flow path of the second refrigerant heat exchanger 34. The intermediate-pressure liquid refrigerant that flows into the primary flow path of the second refrigerant heat exchanger 34 is further subcooled by the refrigerant flowing through the secondary flow path of the second refrigerant heat exchanger 34, and flows out of the primary flow path of the second refrigerant heat exchanger 34.

[0077] The liquid refrigerant flowing out from the primary side flow path of the second refrigerant heat exchanger 34 is divided, and a portion of the liquid refrigerant flows out of the relay unit 30 via check valves 36a2, 36b2, 36c2, and 36d2. The liquid refrigerant flowing out from the relay unit 30 then flows into the indoor units 20a to 20d. The remainder of the liquid refrigerant flowing out from the primary side flow path of the second refrigerant heat exchanger 34 is decompressed and expanded by the second relay expansion valve 35 to become low-pressure gas refrigerant, and passes through the branch pipe 107. As a result, the low-pressure gas refrigerant contributes to supercooling the refrigerant flowing through the first refrigerant heat exchanger 32 and the second refrigerant heat exchanger 34 via the gas-liquid separator 31.

[0078] The liquid refrigerant that flows into the indoor unit 20a is decompressed and expanded by the indoor expansion valve 21 to become a low-temperature, low-pressure two-phase gas-liquid refrigerant or liquid refrigerant, and flows into the indoor heat exchanger 22. The low-temperature, low-pressure two-phase gas-liquid refrigerant or liquid refrigerant that flows into the indoor heat exchanger 22 exchanges heat with the indoor air, absorbing heat and evaporating, thereby cooling the indoor air, and becomes low-pressure gas refrigerant, which flows out of the indoor heat exchanger 22. The low-pressure gas refrigerant that flows out of the indoor heat exchanger 22 then flows out of the indoor unit 20a and flows into the relay unit 30.

[0079] The liquid refrigerant that has flowed into each of the indoor units 20b to 20d similarly becomes low-pressure gas refrigerant, flows out of the indoor units 20b to 20e, and flows into the relay unit 30. The refrigerant that has flowed into the relay unit 30 reaches the low-pressure pipe 102 via the three-way linear expansion valves 37a to 37d.

[0080] Meanwhile, the high-pressure gas refrigerant separated by the gas-liquid separator 31 flows out of the relay unit 30 via the three-way linear expansion valve 37e and flows into the indoor unit 20e in heating operation. The high-temperature, high-pressure gas refrigerant that has flowed into the indoor unit 20e flows into the indoor heat exchanger 22, where it exchanges heat with the indoor air and condenses while releasing heat, heating the indoor air, and turns into high-pressure liquid refrigerant, which flows out of the indoor heat exchanger 22. The high-pressure liquid refrigerant that has flowed out of the indoor heat exchanger 22 is decompressed and expanded by the indoor expansion valve 21, turns into liquid refrigerant, flows out of the indoor unit 20e, and then flows into the relay unit 30.

[0081] The refrigerant that has flowed into the relay unit 30 flows through the junction pipe 108 via the check valve 36e1, the second refrigerant heat exchanger 34, the second relay expansion valve 35, and the first refrigerant heat exchanger 32, and then reaches the low-pressure pipe 102.

[0082] In this way, the refrigerant flowing out from each of the indoor units 20a to 20d performing cooling operation and the indoor unit 20e performing heating operation joins together in the low-pressure pipe 102, flows out from the relay unit 30, and then flows into the outdoor unit 10. The low-pressure gas refrigerant that has flowed into the outdoor unit 10 passes through the check valve 15d, the refrigerant flow switching device 12, and the accumulator 16, and is sucked into the compressor 11. Then, the above-mentioned circulation is repeated thereafter.

[0083] (Heating-dominant operation mode) Figure 8 is a schematic diagram for explaining the flow of refrigerant in the heating-dominated operation mode in the refrigeration and air conditioning system of Figure 1. Here, the case where indoor units 20a to 20d perform heating operation and indoor unit 20e performs cooling operation will be explained as an example. In Figure 8, the flow path indicated by the thick line is the refrigerant flow path in the heating-dominated operation mode, and the direction of refrigerant flow in the refrigerant flow path is indicated by arrows.

[0084] In the heating-dominated operation mode, first, the refrigerant flow switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the gas-liquid separator 31 of the relay unit 30, and so that the suction side of the compressor 11 is connected to the outdoor heat exchanger 13. In addition, the three-way linear expansion valves 37a to 37d are each switched so that the gas piping 105 is connected to the indoor unit 20. The three-way linear expansion valve 37e is switched so that the indoor unit 20 is connected to the low-pressure piping 102.

[0085] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and is discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows out of the outdoor unit 10 via the refrigerant flow switching device 12 and the check valve 15b, and flows into the relay unit 30. The high-temperature, high-pressure gas refrigerant that has flowed into the relay unit 30 flows out of the relay unit 30 via the gas-liquid separator 31 and the three-way linear expansion valves 37a to 37d, and flows into the indoor units 20a to 20d.

[0086] The high-temperature, high-pressure gas refrigerant that has flowed into the indoor unit 20a flows into the indoor heat exchanger 22, where it exchanges heat with the indoor air and condenses while releasing heat, heating the indoor air, and turns into high-pressure liquid refrigerant, which then flows out of the indoor heat exchanger 22. The high-pressure liquid refrigerant that has flowed out of the indoor heat exchanger 22 is reduced in pressure and expanded by the indoor expansion valve 21, becomes intermediate-pressure liquid refrigerant, flows out of the indoor unit 20a, and then flows into the relay unit 30.

[0087] Similarly, the high-temperature, high-pressure gas refrigerant that has flowed into each of the indoor units 20b to 20d becomes intermediate-pressure liquid refrigerant, flows out of the indoor units 20b to 20d, and flows into the relay unit 30.

[0088] The intermediate-pressure liquid refrigerant that has flowed into relay unit 30 flows through junction pipe 108 via check valves 36a1, 36b1, 36c1, and 36d1, and flows into the primary-side flow path of second refrigerant heat exchanger 34. The low-pressure liquid refrigerant that has flowed into the primary-side flow path of second refrigerant heat exchanger 34 is subcooled by the refrigerant flowing through the secondary-side flow path of second refrigerant heat exchanger 34, and flows out of the primary-side flow path of second refrigerant heat exchanger 34.

[0089] The intermediate-pressure liquid refrigerant flowing out from the primary-side flow path of the second refrigerant heat exchanger 34 is branched, and a portion of the liquid refrigerant flows out of the relay unit 30 via the check valve 36e2. The liquid refrigerant flowing out from the relay unit 30 then flows into the indoor unit 20e in cooling operation. The remainder of the intermediate-pressure liquid refrigerant flowing out from the primary-side flow path of the second refrigerant heat exchanger 34 flows through the branch pipe 107 into the secondary-side flow path of the second refrigerant heat exchanger 34.

[0090] The low-pressure liquid refrigerant that has flowed into the indoor unit 20e is decompressed and expanded by the indoor expansion valve 21 to become a low-pressure two-phase gas-liquid refrigerant or liquid refrigerant, and then flows into the indoor heat exchanger 22. The low-pressure two-phase gas-liquid refrigerant or liquid refrigerant that has flowed into the indoor heat exchanger 22 exchanges heat with the indoor air, absorbing heat and evaporating, thereby cooling the indoor air, and becomes low-pressure gas refrigerant, which then flows out of the indoor heat exchanger 22. The low-pressure gas refrigerant that has flowed out of the indoor heat exchanger 22 then flows out of the indoor unit 20e and into the relay unit 30. The gas refrigerant that has flowed into the relay unit 30 reaches the low-pressure pipe 102 via the three-way linear expansion valve 37e.

[0091] The low-pressure gas refrigerant flowing through the low-pressure piping 102 flows out from the primary flow path of the second refrigerant heat exchanger 34, and merges with the refrigerant flowing through the branch piping 107 via the second relay expansion valve 35, the second refrigerant heat exchanger 34, and the first refrigerant heat exchanger 32. Then, this low-pressure gas refrigerant flows out from the relay unit 30 and flows into the outdoor unit 10.

[0092] The low-pressure gas refrigerant that has flowed into the outdoor unit 10 flows into the outdoor heat exchanger 13 via the check valve 15c and the outdoor expansion valve 14. The low-pressure gas refrigerant that has flowed into the outdoor heat exchanger 13 exchanges heat with the outdoor air, absorbs heat, evaporates, is further gasified, and flows out of the outdoor heat exchanger 13. The low-temperature, low-pressure gas refrigerant that has flowed out of the outdoor heat exchanger 13 passes through the refrigerant flow switching device 12 and the accumulator 16, and is drawn into the compressor 11. Then, the above-mentioned circulation is repeated thereafter.

[0093] [Evaporation temperature adjustment process] The evaporation temperature adjustment process according to the first embodiment will now be described. Generally, the evaporation temperature of a refrigeration and air conditioning system is controlled to 0°C by controlling the compressor drive frequency, the expansion valve opening, and the like, to prevent the piping of the indoor unit from freezing. Meanwhile, the longer the piping between the indoor unit and the outdoor unit, the greater the pressure loss, resulting in a higher evaporation temperature of the indoor unit. Therefore, when the refrigeration and air conditioning system is operating in cooling mode, particularly in heating-dominated mode, the evaporation temperature of the indoor unit performing cooling operation, which has the shortest piping length between the indoor unit and the outdoor unit, will be the lowest compared to the other indoor units and may fall below 0°C. If the evaporation temperature falls below 0°C, the piping connected to that indoor unit may freeze and be damaged.

[0094] To prevent this type of pipe freezing, conventional refrigeration and air conditioning systems adjust the opening of the expansion valve installed in the outdoor unit to match the evaporation temperature of the indoor unit performing cooling operation, which has the shortest pipe length. This causes the evaporation temperature of the other indoor units performing cooling operation to become higher, which can result in insufficient cooling capacity when the cooling load is high, and the room may not be cooled sufficiently.

[0095] Therefore, in this embodiment 1, when there are multiple indoor units 20 performing cooling operation, an evaporation temperature adjustment process is performed to control the opening degree of the three-way linear expansion valve 37 provided in the relay unit 30 and individually adjust the evaporation temperature of each indoor unit 20.

[0096] 9 is a flowchart showing an example of the flow of the evaporation temperature adjustment process according to the first embodiment. In step S1, the control device 40 determines whether the current operation is heating-dominated operation, cooling-dominated operation, or cooling-only operation. If the current operation is heating-dominated operation, cooling-dominated operation, or cooling-only operation (step S1: YES), the valve control unit 44 of the control device 40 sets the valve openings of all the three-way linear expansion valves 37a to 37e to initial openings in step S2. The initial openings of the three-way linear expansion valves 37a to 37e are preset openings that are set according to the capacities of the respective three-way linear expansion valves 37a to 37e.

[0097] On the other hand, if the current operation is not the heating-dominated operation, the cooling-dominated operation, or the cooling-only operation, that is, if the current operation is the heating-only operation (step S1: NO), the series of processes ends.

[0098] In step S3, the indoor pressure is detected by the indoor pressure sensor 23 provided in each of the indoor units 20a to 20e. The information acquisition unit 41 acquires the indoor pressure detected by the indoor pressure sensor 23. The acquired pressure is a pressure that is considered to be equivalent to the evaporation pressure of the corresponding indoor heat exchanger 22.

[0099] For example, water boils at 100°C in an environment of 1 atmosphere or less, and enters a two-phase gas-liquid state. It is generally known that in a two-phase gas-liquid state, there is a correlation between pressure and temperature, and in a two-phase gas-liquid state, one of the pressure and the temperature can be derived from the other. Therefore, by utilizing this relationship between pressure and temperature, the calculation unit 42 derives the evaporation temperature from the evaporation pressure.

[0100] In step S4, the calculation unit 42 converts the pressure, which is the evaporation pressure acquired in step S3, into the evaporation temperature of the indoor heat exchanger 22 in the indoor unit 20 performing the cooling operation, and derives the evaporation temperature.

[0101] In step S5, the comparison unit 43 determines whether the evaporation temperature of the indoor heat exchanger 22 in the indoor unit 20 performing cooling operation is equal to or higher than a preset set evaporation temperature. If the evaporation temperature is lower than the set evaporation temperature (step S5: NO), in step S6, the valve control unit 44 reduces the aperture of the corresponding three-way linear expansion valve 37 by the set aperture so that the evaporation temperature approaches the set evaporation temperature.

[0102] For example, when the indoor unit 20a is performing cooling operation and the evaporation temperature of the indoor heat exchanger 22 of this indoor unit 20a is lower than the set evaporation temperature, the valve control unit 44 reduces the aperture of the three-way linear expansion valve 37a corresponding to the indoor unit 20a by the set aperture. Note that the set aperture in this case is determined in advance depending on the capacity of the corresponding indoor unit 20, etc. On the other hand, when the evaporation temperature is equal to or higher than the set evaporation temperature (step S5: YES), the process proceeds to step S7.

[0103] In step S7, the comparison unit 43 determines whether the evaporation temperature of the indoor heat exchanger 22 in the indoor unit 20 performing cooling operation is the set evaporation temperature. If the evaporation temperature is the set evaporation temperature (step S7: YES), the process returns to step S3.

[0104] On the other hand, if the evaporation temperature is not the set evaporation temperature (step S7: NO), in step S8, the valve control unit 44 increases the opening of the corresponding three-way linear expansion valve 37 by the set opening so that the evaporation temperature approaches the set evaporation temperature. Then, the process returns to step S3.

[0105] In this way, by controlling the opening of the three-way linear expansion valve 37 so that the evaporation temperature becomes the set evaporation temperature, it is possible to individually adjust the evaporation temperature of the indoor heat exchanger 22 in each indoor unit 20. As a result, it is possible to perform cooling operation according to the air conditioning load of the room in which each indoor unit 20 is installed, and it is possible to avoid the above-mentioned conventional problem of not being able to sufficiently cool the room.

[0106] For example, even in a heating-dominated operation where cooling is performed in a room with a low air-conditioning load, such as a server room, and a room with a high air-conditioning load, such as a living space, and heating is performed in the other rooms, by performing this evaporation temperature adjustment process, it is possible to perform cooling operation according to the air-conditioning load of each room. Furthermore, this opening degree control can be applied not only to heating-dominated operation, but also to cooling-dominated operation and full cooling operation.

[0107] In this example, the evaporation temperature of the indoor heat exchanger 22 is derived based on the indoor pressure detected by the indoor pressure sensor 23, but this is not limited to this example. For example, a thermocouple may be inserted into the piping of the indoor heat exchanger 22 so that the refrigerant temperature, which is the evaporation temperature, is directly detected. Also, for example, a thermocouple may be attached to the outer wall surface of the piping so that the refrigerant temperature is detected.

[0108] [Liquid backflow prevention treatment] The liquid backflow prevention process will now be described. In the refrigeration and air conditioning system 100, if liquid backflow occurs, in which liquid refrigerant is sucked into the compressor 11 provided in the outdoor unit 10, the compressor 11 may break down.

[0109] Therefore, in the first embodiment, a liquid backflow suppression process is performed to suppress the liquid refrigerant from being drawn into the compressor 11. In the liquid backflow suppression process, a first liquid backflow suppression process is performed when the operation mode of the refrigeration and air conditioning apparatus 100 is heating-dominated operation or full heating operation, and a second liquid backflow suppression process is performed when the operation mode is cooling-dominated operation or full cooling operation.

[0110] 10 is a flowchart showing an example of the flow of the liquid backflow suppression process according to Embodiment 1. In step S100, the control device 40 determines whether the operation mode of the refrigeration and air conditioning device 100 is heating-dominated operation or heating-only operation.

[0111] If the operation mode is heating-dominated operation or full heating operation (step S100: YES), the control device 40 performs a first liquid return suppression process in step S10. On the other hand, if the operation mode is not heating-dominated operation or full heating operation, that is, if the operation mode is cooling-dominated operation or full cooling operation (step S100: NO), the control device 40 performs a second liquid return suppression process in step S30.

[0112] (First liquid backflow prevention treatment) Fig. 11 is a flowchart showing an example of the flow of the first liquid return suppression process of Fig. 10. In step S11, the outdoor pressure sensor 17 provided in the outdoor unit 10 detects the suction pressure P17 of the refrigerant sucked into the compressor 11. The information acquisition unit 41 acquires the suction pressure P17 detected by the outdoor pressure sensor 17. When the operation mode is heating-dominated operation or heating-only operation, the acquired suction pressure P17 is a pressure that is considered to be equivalent to the evaporation pressure of the outdoor heat exchanger 13.

[0113] In step S12, the outdoor temperature sensor 18 provided in the outdoor unit 10 detects the suction temperature T18 of the refrigerant sucked into the compressor 11. The information acquisition unit 41 acquires the suction temperature T18 detected by the outdoor temperature sensor 18.

[0114] In step S13, the calculation unit 42 converts the suction pressure P17, which is the evaporation pressure acquired in step S11, into the evaporation temperature Te of the outdoor heat exchanger 13, and derives the evaporation temperature Te. In step S14, the calculation unit 42 calculates the degree of superheat SH1 (=T18-Te) of the refrigerant sucked into the compressor 11, based on the suction temperature T18 acquired in step S12 and the evaporation temperature Te derived in step S13.

[0115] In step S15, the comparison unit 43 determines whether the superheat degree SH1 is equal to or less than the set superheat degree. If the superheat degree SH1 is equal to or less than the set superheat degree (step S15: YES), the process proceeds to step S16. On the other hand, if the superheat degree SH1 is less than the set superheat degree (step S15: NO), the process returns to step S11.

[0116] In step S16, the valve control unit 44 reduces the aperture of the three-way linear expansion valve 37 corresponding to the indoor unit 20 performing cooling operation by a set aperture so as to prevent liquid backflow of the refrigerant drawn into the compressor 11. Note that the set aperture in this case is determined in advance depending on the amount of refrigerant in the refrigeration and air conditioning device 100, the outside air temperature, the refrigerant pressure, the refrigerant temperature, etc.

[0117] In step S17, the outdoor pressure sensor 17 detects the suction pressure P17, and the information acquisition unit 41 acquires the suction pressure P17 detected by the outdoor pressure sensor 17. In step S18, the outdoor temperature sensor 18 detects the suction temperature T18, and the valve control unit 44 acquires the suction temperature T18 detected by the outdoor temperature sensor 18.

[0118] In step S19, the calculation unit 42 converts the suction pressure P17 acquired in step S17 into the evaporation temperature Te of the outdoor heat exchanger 13, and derives the evaporation temperature Te. In step S20, the calculation unit 42 calculates the degree of superheat SH1 based on the suction temperature T18 acquired in step S18 and the evaporation temperature Te derived in step S19.

[0119] In step S21, the comparison unit 43 determines whether the superheat degree SH1 is equal to or less than the set superheat degree. If the superheat degree SH1 is equal to or less than the set superheat degree (step S21: YES), the process proceeds to step S22. On the other hand, if the superheat degree SH1 is less than the set superheat degree (step S21: NO), the process returns to step S11.

[0120] In step S22, the valve control unit 44 reduces the opening of the outdoor expansion valve 14 provided in the outdoor unit 10 by the set opening so as to prevent liquid backflow of the refrigerant sucked into the compressor 11. Then, the processing returns to step S11.

[0121] As described above, in the present embodiment 1, the first liquid backflow suppression process is performed when the heating-dominated operation or the heating-only operation is being performed. This ensures that the liquid refrigerant is gasified before being drawn into the compressor 11, thereby preventing breakdown of the compressor 11.

[0122] When the heating-dominant operation or the heating-only operation is performed, the first liquid backflow suppression process is performed in parallel with the evaporation temperature adjustment process described above. In both processes, a step of controlling the aperture of the three-way linear expansion valve 37 is included, but when the superheat degree SH1 of the refrigerant drawn into the compressor 11 falls below the set superheat degree, priority is given to protecting the compressor 11. That is, priority is given to the control of the aperture of the three-way linear expansion valve 37 performed in step S16 of the first liquid backflow suppression process.

[0123] (Second liquid backflow prevention treatment) Fig. 12 is a flowchart showing an example of the flow of the second liquid backflow suppression process of Fig. 10. In step S31, the outdoor pressure sensor 17 provided in the outdoor unit 10 detects the suction pressure P17 of the refrigerant sucked into the compressor 11. The information acquisition unit 41 acquires the suction pressure P17 detected by the outdoor pressure sensor 17.

[0124] In step S32, the outdoor temperature sensor 18 provided in the outdoor unit 10 detects the suction temperature T18 of the refrigerant sucked into the compressor 11. The information acquisition unit 41 acquires the suction temperature T18 detected by the outdoor temperature sensor 18.

[0125] In step S33, the calculation unit 42 converts the suction pressure P17 acquired in step S11 into the evaporation temperature Te of the outdoor heat exchanger 13, and derives the evaporation temperature Te. In step S34, the calculation unit 42 calculates the degree of superheat SH2 (=T18-Te) of the refrigerant sucked into the compressor 11, based on the suction temperature T18 acquired in step S12 and the evaporation temperature Te derived in step S13.

[0126] In step S35, the comparison unit 43 determines whether the superheat degree SH2 is equal to or less than the set superheat degree. If the superheat degree SH2 is equal to or less than the set superheat degree (step S35: YES), the process proceeds to step S36. On the other hand, if the superheat degree SH2 is less than the set superheat degree (step S35: NO), the process returns to step S31.

[0127] In step S36, the valve control unit 44 reduces the opening degree of the indoor expansion valve 21 provided in the indoor unit 20 performing heating operation by the set opening degree so that the refrigerant sucked into the compressor 11 does not liquid backflow.

[0128] In step S37, the outdoor pressure sensor 17 detects the suction pressure P17, and the information acquisition unit 41 acquires the suction pressure P17 detected by the outdoor pressure sensor 17. In step S38, the outdoor temperature sensor 18 detects the suction temperature T18, and the information acquisition unit 41 acquires the suction temperature T18 detected by the outdoor temperature sensor 18.

[0129] In step S39, the calculation unit 42 converts the suction pressure P17 acquired in step S37 into the evaporation temperature Te of the outdoor heat exchanger 13, and derives the evaporation temperature Te. In step S40, the calculation unit 42 calculates the degree of superheat SH2 based on the suction temperature T18 acquired in step S38 and the evaporation temperature Te derived in step S39.

[0130] In step S41, the comparison unit 43 determines whether the superheat degree SH2 is equal to or less than the set superheat degree. If the superheat degree SH2 is equal to or less than the set superheat degree (step S41: YES), the process proceeds to step S42. On the other hand, if the superheat degree SH2 is less than the set superheat degree (step S41: NO), the process returns to step S31.

[0131] In step S42, the valve control unit 44 reduces the opening of the three-way linear expansion valve 37 corresponding to the indoor unit 20 performing cooling operation by the set opening so as to prevent liquid backflow of the refrigerant sucked into the compressor 11. Then, the process returns to step S31.

[0132] In this way, in the present embodiment 1, the second liquid-back suppression process is performed when the cooling-dominated operation or the cooling-only operation is being performed. This ensures that the liquid refrigerant is gasified before being drawn into the compressor 11, thereby preventing breakdown of the compressor 11.

[0133] When the cooling-dominant operation or the cooling-only operation is performed, the second liquid backflow suppression process is performed in parallel with the evaporation temperature adjustment process described above. In both processes, a step of controlling the aperture of the three-way linear expansion valve 37 is included, but when the superheat degree SH2 of the refrigerant drawn into the compressor 11 falls below the set superheat degree, priority is given to protecting the compressor 11. That is, priority is given to the aperture control of the three-way linear expansion valve 37 performed in step S42 of the second liquid backflow suppression process.

[0134] As described above, in the refrigeration and air conditioning system 100 according to the first embodiment, the opening degree of the corresponding three-way linear expansion valve 37 is controlled based on the indoor pressure of the indoor unit 20 performing cooling operation. Specifically, the evaporation temperature is derived from the indoor pressure of the indoor unit 20 performing cooling operation, and the opening degree of the three-way linear expansion valve 37 is controlled according to the comparison result between the evaporation temperature and the set evaporation temperature. In this way, the evaporation temperature is adjusted for each indoor unit 20 performing cooling operation, making it possible to control each indoor unit individually.

[0135] In addition, in the refrigeration and air conditioning system 100, the evaporation temperature is derived from the suction pressure, and the degree of superheat is calculated based on the suction temperature and the evaporation temperature. When the degree of superheat is equal to or lower than a constant degree of superheat, the opening degree of at least one of the three-way linear expansion valve 37, the outdoor expansion valve 14, and the indoor expansion valve 21 is controlled. This allows the refrigerant drawn into the compressor 11 to be sufficiently superheated, thereby suppressing liquid backflow into the compressor 11.

[0136] Embodiment 2 The present embodiment 2 will be described. The present embodiment 2 differs from the embodiment 1 in that an indoor unit that draws in outside air and blows it out into the room is used. In the present embodiment 2, parts that are common to the embodiment 1 are given the same reference numerals, and detailed explanations will be omitted.

[0137] [Configuration of Refrigeration and Air Conditioning Device 100A] Fig. 13 is a circuit diagram showing an example of the configuration of a refrigeration and air conditioning system according to Embodiment 2. The refrigeration and air conditioning system 100A according to Embodiment 2 is configured to include an outdoor unit 10, a plurality of indoor units 120, a relay unit 30, and a control device 40. The example of Fig. 13 shows a case in which the refrigeration and air conditioning system 100A is configured with one outdoor unit 10, five indoor units 120a to 120e, and one relay unit 30. In the refrigeration and air conditioning system 100, a refrigerant circuit is formed by connecting the outdoor unit 10, the relay unit 30, and the indoor units 120a to 120e with high-pressure piping 101 and low-pressure piping 102. The number of indoor units 120 is not limited to this example and may be two or more and four or less, or six or more.

[0138] Since the indoor units 120a to 120e each have the same configuration, illustration of the indoor units 120c and 120d and the configuration connected to the indoor units 120c and 120d out of the circuit configuration of the relay unit 30 is omitted in Fig. 13. The circuit configuration of the indoor units 120b and 120e is also omitted from illustration because it is the same as that of the indoor unit 120a.

[0139] In the refrigeration and air conditioning system 100A according to the second embodiment, the outdoor unit 10, the relay unit 30, and the control device 40 have the same configurations as those in the first embodiment, and therefore description thereof will be omitted here.

[0140] The indoor units 120a to 120e draw in outside air, condition it, and then blow the conditioned air into the rooms, and each cools or heats the air in, for example, rooms 1a to 1e. In this way, the indoor units 120a to 120e condition the outside air they draw in and blow the conditioned air into the rooms, so they can cool or heat the rooms 1a to 1e while ventilating them.

[0141] The indoor units 120a to 120e are provided with an outdoor air inlet 151 that draws in outdoor air and an air outlet 152 that blows out air. Each of the indoor units 120a to 120e is equipped with an indoor expansion valve 21 and an indoor heat exchanger 122. Each of the indoor units 120a to 120e is also equipped with an indoor pressure sensor 23 and a blown-out air temperature sensor 24. In the following description, when there is no need to particularly distinguish between the indoor units 120a to 120e, they will be simply referred to as "indoor unit 120" as appropriate.

[0142] The indoor heat exchanger 122 exchanges heat between the refrigerant and outside air supplied from the outside air inlet 151 by a blower such as a fan (not shown). This generates air for heating or air for cooling to be supplied to the rooms 1a to 1e.

[0143] The blown air temperature sensor 24 is provided at the air outlet 152 of the indoor unit 120. The blown air temperature sensor 24 detects the temperature of the air blown out from the air outlet 152, that is, the blown air temperature.

[0144] In this example, all indoor units provided in the refrigeration and air conditioning apparatus 100A are described as indoor units 120 that draw in outside air, but this is not limited to this example. For example, the refrigeration and air conditioning apparatus 100A may have at least one of all indoor units as the indoor unit 120 that draws in outside air, and the remaining indoor units as the indoor units 20 described in the first embodiment.

[0145] In this embodiment 2, the control device 40 controls the opening degree of the indoor expansion valve 21 of the indoor unit 120 and the three-way linear expansion valve 37 of the relay unit 30 so that the blown air temperature detected by the blown air temperature sensor 24 of the indoor unit 120 becomes the set temperature.

[0146] [Operation of refrigeration and air conditioning unit 100A] In the present embodiment 1, the refrigerant operation, evaporation temperature adjustment process, and liquid backflow suppression process in the refrigeration and air conditioning device 100A are the same as those in the refrigeration and air conditioning device 100 according to embodiment 1. Therefore, a description thereof will be omitted here.

[0147] As described above, the refrigeration and air conditioning system 100A according to the second embodiment uses the indoor unit 120 that draws in and blows out outside air. This makes it possible to ventilate the room in which the indoor unit 120 is installed, while achieving the same effects as those of the first embodiment. [Explanation of symbols]

[0148] 1a, 1b, 1c, 1d, 1e room, 10 outdoor unit, 11 compressor, 12 refrigerant flow switching device, 13 outdoor heat exchanger, 14 outdoor expansion valve, 15a, 15b, 15c, 15d, 15e check valve, 16 accumulator, 17 outdoor pressure sensor, 18 outdoor temperature sensor, 20, 20a, 20b, 20c, 20d, 20e, 120, 120a, 120b, 120c, 120d, 120e indoor unit, 21 indoor expansion valve, 22, 122 indoor heat exchanger, 23 indoor pressure sensor, 24 blown air temperature sensor, 30 relay unit, 31 gas-liquid separator, 32 first refrigerant heat exchanger, 33 first relay expansion valve, 34 second refrigerant heat exchanger, 35 Second relay expansion valve, 36, 36a1, 36a2, 36b1, 36b2, 36c1, 36c2, 36d1, 36d2, 36e1, 36e2 check valve, 37, 37a, 37b, 37c, 37d, 37e three-way linear expansion valve, 40 control device, 41 information acquisition unit, 42 calculation unit, 43 comparison unit, 44 valve control unit, 45 memory unit, 51 processing circuit, 52 processor, 53 memory, 100, 100A refrigeration and air conditioning unit, 101 high-pressure piping, 102 low-pressure piping, 103 first connecting piping, 104 second connecting piping, 105 gas piping, 106 liquid piping, 107 branch piping, 108 junction piping, 151 outside air intake port, 152 air outlet.

Claims

1. A refrigeration and air conditioning device capable of performing cooling-dominant operation and heating-dominant operation, The refrigeration and air conditioning device an outdoor unit having a compressor and an outdoor heat exchanger; a plurality of indoor units each having an indoor expansion valve and an indoor heat exchanger; a relay unit that is connected between the outdoor unit and the indoor unit, has a plurality of three-way valves provided corresponding to the number of the indoor units, and switches the flow of the refrigerant and adjusts the flow rate of the refrigerant passing through, and distributes the low-temperature refrigerant to the indoor unit performing cooling operation and distributes the high-temperature refrigerant to the indoor unit performing heating operation; a control device for controlling the switching and opening of the three-way valve; Equipped with The indoor unit is an indoor pressure sensor that detects the indoor pressure, which is the pressure of the refrigerant passing through the indoor heat exchanger; The control device deriving an evaporation temperature of the indoor heat exchanger from the indoor pressure of the indoor unit performing cooling operation; When the evaporation temperature exceeds a preset evaporation temperature, the opening degree of the corresponding three-way valve is increased; When the evaporation temperature is lower than the set evaporation temperature, the opening degree of the corresponding three-way valve is reduced to prevent freezing of the pipes of the indoor unit performing cooling operation. Refrigeration and air conditioning equipment.

2. The outdoor unit is an outdoor expansion valve that reduces the pressure of the refrigerant and expands it; an outdoor pressure sensor that detects a suction pressure of the refrigerant sucked into the compressor; an outdoor temperature sensor that detects an intake temperature, which is the temperature of the refrigerant that is sucked into the compressor; and The control device Deriving an evaporation temperature from the suction pressure; calculating a degree of superheat based on the suction temperature and the evaporation temperature; When the degree of superheat is equal to or less than a preset set degree of superheat, the opening degree of at least one of the three-way valve, the outdoor expansion valve, and the indoor expansion valve is controlled. The refrigeration and air conditioning system according to claim 1.

3. The control device When heating-dominant operation or full heating operation is in progress, When the degree of superheat is equal to or less than the set degree of superheat, the opening degree of the three-way valve corresponding to the indoor unit performing the cooling operation is reduced. The refrigeration and air conditioning system according to claim 2.

4. The control device When the degree of superheat is equal to or less than the set degree of superheat in a state where the degree of opening of the three-way valve is reduced, the degree of opening of the outdoor expansion valve is reduced. The refrigeration and air conditioning system according to claim 3.

5. The control device When cooling-dominant operation or full cooling operation is in progress, When the degree of superheat is equal to or less than the set degree of superheat, the opening degree of the indoor expansion valve of the indoor unit performing heating operation is reduced. The refrigeration and air conditioning system according to claim 2.

6. The control device When the degree of superheat is equal to or less than the set degree of superheat with the degree of opening of the indoor expansion valve reduced, the degree of opening of the three-way valve corresponding to the indoor unit performing cooling operation is reduced. The refrigeration and air conditioning system according to claim 5.

7. A refrigeration and air conditioning device capable of performing cooling-dominant operation and heating-dominant operation, The refrigeration and air conditioning device an outdoor unit having a compressor and an outdoor heat exchanger; a plurality of indoor units each having an indoor expansion valve and an indoor heat exchanger; a relay unit that is connected between the outdoor unit and the indoor unit, has a plurality of three-way valves provided corresponding to the number of the indoor units, and switches the flow of the refrigerant and adjusts the flow rate of the refrigerant passing through, and distributes the low-temperature refrigerant to the indoor unit performing cooling operation and distributes the high-temperature refrigerant to the indoor unit performing heating operation; a control device for controlling the switching and opening degree of the three-way valve; Equipped with The indoor unit is a temperature sensor for detecting an evaporation temperature of the indoor heat exchanger of the indoor unit that performs cooling operation; The control device When the evaporation temperature exceeds a preset evaporation temperature, the opening degree of the corresponding three-way valve is increased; When the evaporation temperature is lower than the set evaporation temperature, the opening degree of the corresponding three-way valve is reduced to prevent freezing of the pipes of the indoor unit performing cooling operation. Refrigeration and air conditioning equipment.

8. At least one of the indoor units is It draws in outside air and blows conditioned air into the room. The refrigeration and air conditioning system according to any one of claims 1 to 7.

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