Air-conditioning device

Abstract

A first refrigerant circuit is configured such that, when at least one indoor unit (30a) among a plurality of indoor units (30a, 30b, 30c) is to perform a reheat dehumidification operation, a refrigerant sequentially flows through a compressor (1), an outdoor heat exchanger (3), an internal heat exchanger (5), a first expansion valve (6), an internal heat exchanger (5), and the at least one indoor unit (30a). A second refrigerant circuit is configured such that, when at least one indoor unit (30b) is to perform a cooling operation, the refrigerant sequentially flows through the compressor (1), the outdoor heat exchanger (3), the internal heat exchanger (5), at least one second expansion valve (8b) among a plurality of second expansion valves, and the at least one indoor unit (30b).

Description

Air conditioner

[0001] The present disclosure relates to an air conditioner.

[0002] Conventionally, in dehumidification using the cooling operation in an air conditioner, since the indoor air is cooled below the dew point temperature for dehumidification, depending on the conditions of the sensible heat load and the latent heat load, the indoor temperature may drop too much. In this regard, in an air conditioner, there is a technique for preventing the discomfort of the user due to the indoor temperature dropping too much by performing an operation of reheating the cooled and dehumidified air (hereinafter referred to as the reheating dehumidification operation).

[0003] International Publication No. 2022 / 264254 (Patent Document 1) discloses a multi-room air conditioner in which a plurality of indoor units are connected to one outdoor unit, some of the plurality of indoor units are operated in a cooling mode, and the other indoor units are operated in a reheating dehumidification mode. The air conditioner of International Publication No. 2022 / 264254 supplies a gas-liquid two-phase refrigerant obtained by mixing the liquid refrigerant flowing out from the outdoor unit and a part of the gas refrigerant discharged from the compressor to the indoor unit performing the reheating dehumidification operation, and supplies the liquid refrigerant to the indoor unit performing the cooling operation.

[0004] International Publication No. 2022 / 264254

[0005] In the air conditioner of International Publication No. 2022 / 264254, the refrigerant flowing into the flow rate adjustment valve before the indoor unit performing the reheating dehumidification operation is in a gas-liquid two-phase state. Therefore, the flow rate passing through the valve can change according to the dryness of the refrigerant. Therefore, it is necessary to appropriately control the flow rate of the refrigerant flowing into each indoor unit and the flow rate of the gas refrigerant discharged from the compressor and divided, and the adjustment of the refrigerant flow rate becomes complicated, so there is a possibility that stable operation cannot be performed.

[0006] An object of the present disclosure is to provide an air conditioner capable of performing stable operation without complicating the adjustment of the refrigerant flow rate.

[0007] The air conditioning system of this disclosure comprises an outdoor unit and a plurality of indoor units connected to the outdoor unit. The outdoor unit comprises a compressor, an outdoor heat exchanger into which refrigerant discharged from the compressor flows, an internal heat exchanger into which refrigerant discharged from the outdoor heat exchanger flows, and a first expansion valve into which refrigerant discharged from the internal heat exchanger flows. The outdoor unit further comprises a plurality of second expansion valves connected to each of the plurality of indoor units, into which refrigerant discharged from the internal heat exchanger flows. The refrigerant discharged from the first expansion valve passes through the internal heat exchanger again and flows into the plurality of indoor units without passing through the plurality of second expansion valves. When at least one of the plurality of indoor units performs reheat dehumidification operation, the first refrigerant circuit is configured such that the refrigerant flows in the order of compressor, outdoor heat exchanger, internal heat exchanger, first expansion valve, internal heat exchanger, and at least one indoor unit. When at least one indoor unit is operating in cooling mode, the second refrigerant circuit is configured such that the refrigerant flows in the following order: compressor, outdoor heat exchanger, internal heat exchanger, at least one of the multiple second expansion valves, and at least one indoor unit.

[0008] According to the air conditioning system of this disclosure, the state of the refrigerant flowing into the first expansion valve when performing reheat dehumidification operation and the multiple second expansion valves when performing cooling operation can be made to be the liquid refrigerant discharged from the outdoor heat exchanger, thus enabling stable operation without complicating the adjustment of the refrigerant flow rate.

[0009] This is a refrigerant circuit diagram of the air conditioning system according to Embodiment 1. This is a diagram showing the p-h line according to Embodiment 1. This is a refrigerant circuit diagram when the operating state of the air conditioning system according to Embodiment 1 is changed. This is a flowchart showing the control of the air conditioning system according to Embodiment 1. This is a refrigerant circuit diagram of the air conditioning system according to Embodiment 2. This is a refrigerant circuit diagram of the air conditioning system according to Embodiment 3.

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the embodiments described below, when numbers, quantities, etc. are mentioned, the scope of this disclosure is not necessarily limited to those numbers, quantities, etc., unless otherwise specified. The same reference numerals will be used for the same parts and equivalent parts, and redundant descriptions will not be repeated. It is intended from the outset that the configurations in the embodiments will be used in appropriate combinations.

[0011] Embodiment 1. Figure 1 is a refrigerant circuit diagram of an air conditioning system 100 according to Embodiment 1. The air conditioning system 100 comprises an outdoor unit 20, a plurality of indoor units 30a, 30b, 30c connected to the outdoor unit 20, and a control device 50. Among the plurality of indoor units 30a, 30b, 30c, an indoor unit that performs reheat dehumidification operation is an example of a "first indoor unit," and an indoor unit that performs cooling operation is an example of a "second indoor unit." Indoor units 30a, 30b, and 30c may all be "first indoor units," or they may all be "second indoor units." Some of the indoor units 30a, 30b, and 30c may be "first indoor units," and the rest may be "second indoor units."

[0012] The outdoor unit 20 and the multiple indoor units 30a, 30b, and 30c are connected by piping through which refrigerant flows, forming a refrigerant circuit. As shown in Figure 1, each of the multiple indoor units 30a, 30b, and 30c is connected in parallel to one outdoor unit 20. Any type of refrigerant suitable for cooling, reheat dehumidification, and heating operations may be used. In Figure 1, the flow of refrigerant is indicated by arrows.

[0013] The outdoor unit 20 includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, an outdoor fan 4, an internal heat exchanger 5, a first expansion valve 6, a plurality of solenoid valves 7a, 7b, 7c, and a plurality of second expansion valves 8a, 8b, 8c. The indoor unit 30a includes a first indoor heat exchanger 9a, a second indoor heat exchanger 10a, a third expansion valve 11a, and an indoor fan 12a. The indoor unit 30b includes a first indoor heat exchanger 9b, a second indoor heat exchanger 10b, a third expansion valve 11b, and an indoor fan 12b. The indoor unit 30c includes a first indoor heat exchanger 9c, a second indoor heat exchanger 10c, a third expansion valve 11c, and an indoor fan 12c.

[0014] Compressor 1 draws in low-temperature, low-pressure refrigerant, compresses it, and discharges it as high-temperature, high-pressure gaseous refrigerant. Compressor 1 is driven, for example, by an inverter, and its capacity (the amount of refrigerant discharged per unit time) is controlled. The four-way valve 2 switches the direction of refrigerant circulation according to the operating mode of the air conditioning system 100.

[0015] The outdoor heat exchanger 3 has multiple heat transfer tubes and performs heat exchange between the refrigerant passing through the multiple heat transfer tubes and the air from outside that is blown in by the outdoor fan 4 installed next to the outdoor heat exchanger 3. The refrigerant discharged from the compressor 1 flows into the outdoor heat exchanger 3. The outdoor fan 4 blows air from outside into the outdoor heat exchanger 3 and also discharges the air that has exchanged heat with the refrigerant in the outdoor heat exchanger 3.

[0016] The internal heat exchanger 5 is a device that exchanges heat between refrigerants internally. Refrigerant flowing out from the outdoor heat exchanger 3 flows into the internal heat exchanger 5, as well as refrigerant flowing out from the first expansion valve 6. The first expansion valve 6 expands and depressurizes the refrigerant. The first expansion valve 6 is composed of, for example, an electronic expansion valve whose valve opening degree can be controlled.

[0017] The state of each of the multiple solenoid valves 7a, 7b, and 7c can be switched between an open state and a closed state. The multiple second expansion valves 8a, 8b, and 8c expand and depressurize the refrigerant. The multiple second expansion valves 8a, 8b, and 8c are composed of, for example, electronic expansion valves whose valve opening degree can be controlled. Solenoid valve 7a and second expansion valve 8a are connected to the indoor unit 30a. Solenoid valve 7b and second expansion valve 8b are connected to the indoor unit 30b. Solenoid valve 7c and second expansion valve 8c are connected to the indoor unit 30c. The arrangement of the multiple solenoid valves 7a, 7b, and 7c and the multiple second expansion valves 8a, 8b, and 8c on the outdoor unit 20 is shown, but at least one of them may be located on the indoor unit side.

[0018] The first indoor heat exchanger 9a and the second indoor heat exchanger 10a each have multiple heat transfer tubes and perform heat exchange between air from the room, which is blown by an indoor fan 12a located next to the first indoor heat exchanger 9a and the second indoor heat exchanger 10a, and a refrigerant that passes through the multiple heat transfer tubes. The first indoor heat exchanger 9a is located on the upstream side of the flow path through which the refrigerant flows. The second indoor heat exchanger 10a is located on the downstream side of the flow path through which the refrigerant flows.

[0019] The third expansion valve 11a is positioned between the first indoor heat exchanger 9a and the second indoor heat exchanger 10a. The third expansion valve 11a expands and depressurizes the refrigerant. The third expansion valve 11a is, for example, an electronic expansion valve whose valve opening degree can be controlled. The indoor fan 12a blows air from the room to the first indoor heat exchanger 9a and the second indoor heat exchanger 10a, and also discharges the air that has exchanged heat with the refrigerant in the first indoor heat exchanger 9a and the second indoor heat exchanger 10a.

[0020] The first indoor heat exchanger 9b and the second indoor heat exchanger 10b each have multiple heat transfer tubes and perform heat exchange between air from the room, which is blown by an indoor fan 12b located next to the first indoor heat exchanger 9b and the second indoor heat exchanger 10b, and a refrigerant that passes through the multiple heat transfer tubes. The first indoor heat exchanger 9b is located on the upstream side of the flow path through which the refrigerant flows. The second indoor heat exchanger 10b is located on the downstream side of the flow path through which the refrigerant flows.

[0021] The third expansion valve 11b is positioned between the first indoor heat exchanger 9b and the second indoor heat exchanger 10b. The third expansion valve 11b expands and depressurizes the refrigerant. The third expansion valve 11b is composed of, for example, an electronic expansion valve whose valve opening degree can be controlled. The indoor fan 12b blows air from the room to the first indoor heat exchanger 9b and the second indoor heat exchanger 10b, and also discharges the air that has exchanged heat with the refrigerant in the first indoor heat exchanger 9b and the second indoor heat exchanger 10b.

[0022] The first indoor heat exchanger 9c and the second indoor heat exchanger 10c each have multiple heat transfer tubes and perform heat exchange between air from the room, which is blown by an indoor fan 12c located next to the first indoor heat exchanger 9c and the second indoor heat exchanger 10c, and a refrigerant that passes through the multiple heat transfer tubes. The first indoor heat exchanger 9c is located on the upstream side of the flow path through which the refrigerant flows. The second indoor heat exchanger 10c is located on the downstream side of the flow path through which the refrigerant flows.

[0023] The third expansion valve 11c is positioned between the first indoor heat exchanger 9c and the second indoor heat exchanger 10c. The third expansion valve 11c expands and depressurizes the refrigerant. The third expansion valve 11c is composed of, for example, an electronic expansion valve whose valve opening degree can be controlled. The indoor fan 12c blows air from the room to the first indoor heat exchanger 9c and the second indoor heat exchanger 10c, and also discharges the air that has exchanged heat with the refrigerant in the first indoor heat exchanger 9c and the second indoor heat exchanger 10c.

[0024] The control device 50 comprises a control unit 51 and a storage unit 52. The control device 50 is capable of communicating with each device in order to control the frequency of the compressor 1, the switching of the four-way valve 2, the rotational speed of the outdoor fan 4, the rotational speed of the indoor fans 12a, 12b, 12c, the opening degree of the first expansion valve 6, the opening degree of the second expansion valves 8a, 8b, 8c, the opening degree of the third expansion valves 11a, 11b, 11c, and the switching of the opening and closing of the solenoid valves 7a, 7b, 7c. The control device 50 may be placed, for example, on the outdoor unit 20. The control device 50 may be placed anywhere as long as it is in a position where it can communicate with each device.

[0025] The control unit 51 is a computing entity (computer) that controls each device by executing various programs. The control unit 51 is composed of a computer such as a processor. The processor is composed of, for example, a microcontroller, a CPU (central processing unit), or an MPU (micro-processing unit). The processor has the function of executing various processes by executing programs, but some or all of these functions may be implemented using dedicated hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). The term "processor" is not limited to processors in the narrow sense that execute processing in a stored-program manner, such as a CPU or MPU, but may also include hardwired circuits such as ASICs or FPGAs. For this reason, the processor can also be read as a processing circuitry in which processing is predefined by computer-readable code and / or hardwired circuits. The processor may consist of one chip or multiple chips. Furthermore, the processor and related processing circuits may consist of multiple computers interconnected by wired or wireless connections via a local area network or wireless network. The processor and associated processing circuits may be configured as a cloud computer that remotely performs calculations based on input data and outputs the calculation results to other devices located remotely.

[0026] The storage unit 52 provides a storage area for storing program code or work memory when the processor of the control unit 51 executes various programs. The storage unit 52 may be one or more non-transitory computer-readable media. Examples of the storage unit 52 include volatile memory such as DRAM (dynamic random access memory) and SRAM (static random access memory), or non-volatile memory such as ROM (Read Only Memory) and flash memory. The storage unit 52 may also be one or more computer-readable storage media. Examples of storage media include storage devices such as HDD (Hard Disk Drive) and SSD (Solid State Drive). The control unit 51 controls each device by executing programs stored in the storage unit 52.

[0027] The flow of refrigerant when reheat dehumidification and cooling operations are performed simultaneously will be explained. The control device 50 switches the refrigerant circuit so that, for example, indoor unit 30a performs reheat dehumidification and indoor units 30b and 30c perform cooling. In this case, indoor unit 30a is an example of a "first indoor unit," and indoor units 30b and 30c are examples of "second indoor units." The control device 50 opens the solenoid valve 7a connected to indoor unit 30a among the multiple solenoid valves 7a, 7b, and 7c, and closes the solenoid valve 7b connected to indoor unit 30b and the solenoid valve 7c connected to indoor unit 30c among the multiple solenoid valves 7a, 7b, and 7c.

[0028] The refrigerant discharged from the compressor 1 flows into the outdoor heat exchanger 3 via the four-way valve 2. The refrigerant flowing out of the outdoor heat exchanger 3 flows into the internal heat exchanger 5. The refrigerant flowing out of the internal heat exchanger 5 flows into each of the multiple second expansion valves 8a, 8b, and 8c, and a portion is bypassed and flows into the first expansion valve 6. The flow path of the refrigerant flowing from the internal heat exchanger 5 to the first expansion valve 6 is also called the bypass flow path. The control device 50 adjusts the flow rate of the refrigerant flowing into the first expansion valve 6 and the multiple second expansion valves 8a, 8b, and 8c by adjusting the opening degrees of the first expansion valve 6 and the multiple second expansion valves 8a, 8b, and 8c. For example, the control device 50 increases the opening degree of the first expansion valve 6 the greater the amount of heating required in reheat dehumidification operation.

[0029] The refrigerant discharged from the first expansion valve 6 passes through the internal heat exchanger 5 again and flows into the indoor unit 30a that performs reheat dehumidification without passing through the multiple second expansion valves 8a, 8b, and 8c. The refrigerant discharged from the internal heat exchanger 5 that did not pass through the bypass channel flows into each of the multiple second expansion valves 8a, 8b, and 8c. The second expansion valve 8a is connected to the indoor unit 30a. The second expansion valve 8b is connected to the indoor unit 30b. The second expansion valve 8c is connected to the indoor unit 30c.

[0030] The refrigerant discharged from the second expansion valve 8a merges with the refrigerant that has passed through the solenoid valve 7a and then flows into the indoor unit 30a where reheat dehumidification operation is performed. The refrigerant discharged from the second expansion valve 8b flows into the indoor unit 30b where cooling operation is performed. The refrigerant discharged from the second expansion valve 8c flows into the indoor unit 30c where cooling operation is performed.

[0031] The refrigerant flowing into indoor unit 30a flows through the first indoor heat exchanger 9a, the third expansion valve 11a, and the second indoor heat exchanger 10a in that order, and then flows out from indoor unit 30a. The refrigerant flowing into indoor unit 30b flows through the first indoor heat exchanger 9b, the third expansion valve 11b, and the second indoor heat exchanger 10b in that order, and then flows out from indoor unit 30b. The refrigerant flowing into indoor unit 30c flows through the first indoor heat exchanger 9c, the third expansion valve 11c, and the second indoor heat exchanger 10c in that order, and then flows out from indoor unit 30c.

[0032] The refrigerant flowing from indoor unit 30a, indoor unit 30b, and indoor unit 30c merge and then flow into compressor 1 via four-way valve 2. In this way, when at least one indoor unit (for example, indoor unit 30a) is performing reheat dehumidification operation, a refrigerant circuit in which the refrigerant flows in the order of compressor 1, outdoor heat exchanger 3, internal heat exchanger 5, first expansion valve 6, internal heat exchanger 5, solenoid valve 7a, and at least one indoor unit (for example, indoor unit 30a) is also called the "first refrigerant circuit". Furthermore, when cooling operation is performed, a refrigerant circuit in which the refrigerant flows in the order of compressor 1, outdoor heat exchanger 3, internal heat exchanger 5, at least one second expansion valve (for example, second expansion valve 8b), and at least one indoor unit (for example, indoor unit 30b) is also called the "second refrigerant circuit".

[0033] The control device 50 controls the multiple indoor units 30a, 30b, and 30c so that refrigerant flows through the first refrigerant circuit when they are performing only reheat dehumidification operation. The control device 50 controls the multiple indoor units 30a, 30b, and 30c so that refrigerant flows through the second refrigerant circuit when they are performing only cooling operation. The control device 50 configures the first refrigerant circuit so that refrigerant flows through some of the multiple indoor units 30a, 30b, and 30c so that refrigerant flows through the other indoor units when some of the multiple indoor units 30a, 30b, and 30c are performing reheat dehumidification operation and the other indoor units are performing cooling operation.

[0034] Next, the state of the refrigerant flowing through the first and second refrigerant circuits will be described. Figure 2 is a p-h diagram according to Embodiment 1. First, the state of the refrigerant flowing through the first refrigerant circuit will be described. The high-temperature, high-pressure gaseous refrigerant at point A discharged from the compressor 1 is condensed in the outdoor heat exchanger 3 to become a high-temperature liquid refrigerant at point B. The high-temperature liquid refrigerant at point B that flows out from the outdoor heat exchanger 3 is heat-exchanged with the liquid refrigerant at point F passing through the bypass channel in the internal heat exchanger 5 to become a supercooled liquid refrigerant as shown at point C.

[0035] The liquid refrigerant passing through the bypass channel is depressurized by the first expansion valve 6 as shown by the dashed line, and becomes liquid at point F. Note that the state of the refrigerant at point F may be made a gas-liquid two-phase state by controlling the opening of the first expansion valve 6. The liquid refrigerant at point F that flows out from the first expansion valve 6 is heat-exchanged with the high-temperature liquid refrigerant in the internal heat exchanger 5, becoming the gaseous refrigerant shown at point G.

[0036] In the bypass flow path, the gaseous refrigerant at point G, which has flowed out from the internal heat exchanger 5, passes through the solenoid valve 7a and is mixed with the gaseous two-phase refrigerant that has been depressurized by the second expansion valve 8a. As a result, before reaching the first indoor heat exchanger 9a, it becomes a gaseous two-phase state with a high gas content, as shown at point H. The gaseous two-phase refrigerant with a high gas content is heat-exchanged with indoor air in the first indoor heat exchanger 9a, resulting in a gaseous two-phase state with an increased liquid content, as shown at point I. The gaseous two-phase refrigerant with an increased liquid content is depressurized by the third expansion valve 11a, resulting in the gaseous two-phase state shown at point J. The gaseous two-phase refrigerant at point J is heat-exchanged with indoor air in the second indoor heat exchanger 10a, resulting in the gaseous refrigerant at point E.

[0037] Next, the state of the refrigerant flowing through the second refrigerant circuit will be explained. In the second refrigerant circuit, the third expansion valve 11b of indoor unit 30b and the third expansion valve 11c of indoor unit 30c are controlled to be fully open. The high-temperature, high-pressure gaseous refrigerant at point A discharged from compressor 1 is condensed in outdoor heat exchanger 3 to become high-temperature liquid refrigerant at point B. The high-temperature liquid refrigerant at point B that flows out from outdoor heat exchanger 3 is heat-exchanged with the liquid refrigerant at point F passing through the bypass channel in internal heat exchanger 5 to become supercooled liquid refrigerant as shown at point C.

[0038] The supercooled liquid refrigerant is depressurized in the second expansion valves 8b and 8c, becoming a gas-liquid two-phase refrigerant with a higher liquid content, as shown at point D. This gas-liquid two-phase refrigerant with a higher liquid content is then subjected to heat exchange with the indoor air in the first indoor heat exchanger 9b and the second indoor heat exchanger 10b, becoming a gaseous refrigerant at point E.

[0039] Next, we will explain the case when the operating state of the air conditioning system 100 is changed. Figure 3 is a refrigerant circuit diagram when the operating state of the air conditioning system 100 according to Embodiment 1 is changed. The refrigerant circuit shown in Figure 3 is a diagram of the refrigerant circuit when all indoor units 30a, 30b, and 30c are performing cooling operation, or when all indoor units 30a, 30b, and 30c are performing reheat dehumidification operation.

[0040] When all indoor units 30a, 30b, and 30c are performing cooling or reheat dehumidification, the control device 50 closes the first expansion valve 6 completely and closes all solenoid valves 7a, 7b, and 7c. As a result, the refrigerant circulates through the second refrigerant circuit. Specifically, the refrigerant discharged from the compressor 1 flows through the outdoor heat exchanger 3, the internal heat exchanger 5, the second expansion valves 8a, 8b, and 8c, and then through the indoor units 30a, 30b, and 30c, before returning to the compressor 1. In this way, when all indoor units 30a, 30b, and 30c are performing cooling or reheat dehumidification, the refrigerant does not flow through the bypass path, and therefore no heat exchange occurs in the internal heat exchanger 5.

[0041] When the control device 50 operates all indoor units 30a, 30b, and 30c in cooling mode, it fully opens the third expansion valves 11a, 11b, and 11c. The liquid refrigerant discharged from the outdoor heat exchanger 3 is depressurized in the second expansion valves 8a, 8b, and 8c, and then exchanges heat with indoor air in the first indoor heat exchangers 9a, 9b, and 9c and the second indoor heat exchangers 10a, 10b, and 10c to become a gaseous state, which then discharges from the indoor units 30a, 30b, and 30c.

[0042] On the other hand, when the control device 50 performs reheating and dehumidifying operation on all the indoor units 30a, 30b, and 30c, it adjusts the third expansion valves 11a, 11b, and 11c to be opened at an opening degree smaller than the fully open state. The liquid refrigerant flowing out from the outdoor heat exchanger 3 is depressurized at the second expansion valves 8a, 8b, and 8c, and then exchanges heat with the air from the room in the first indoor heat exchangers 9a, 9b, and 9c, heating the air and becoming a gas-liquid two-phase state with a large amount of liquid. The refrigerant in the gas-liquid two-phase state with a large amount of liquid is depressurized by the third expansion valves 11a, 11b, and 11c, and then exchanges heat with the air from the room in the second indoor heat exchangers 10a, 10b, and 10c, cooling the air and becoming a gaseous state and flowing out from the indoor units 30a, 30b, and 30c.

[0043] The process executed by the control device 50 will be described using a flowchart. FIG. 4 is a flowchart showing the control of the air conditioner 100 according to the first embodiment. The process of the flowchart in FIG. 4 is repeatedly called as a subroutine and executed from the main routine in the control of the control device 50.

[0044] First, in step S (hereinafter simply referred to as "S") 1, the control device 50 determines whether all the indoor units 30a, 30b, and 30c are in the cooling operation. The control device 50 may execute the determination in S1 by receiving the operation state of the air conditioner 100 changed by the user's operation. When the control device 50 determines that all the indoor units 30a, 30b, and 30c are in the cooling operation (YES in S1), it proceeds to the process of S11.

[0045] In the process of S11, the control device 50 closes the first expansion valve 6 and closes all the solenoid valves 7a, 7b, and 7c. Next, the control device 50 adjusts the second expansion valves 8a, 8b, and 8c to be opened at an opening degree smaller than the fully open state (S12). Next, the control device 50 sets the third expansion valves 11a, 11b, and 11c to the fully open state (S13), and returns the process from the subroutine to the main routine.

[0046] When the control device 50 determines in S1 that not all of the indoor units 30a, 30b, and 30c are in the cooling operation, it determines whether all of the indoor units 30a, 30b, and 30c are in the reheating and dehumidifying operation (S2). When the control device 50 determines that all of the indoor units 30a, 30b, and 30c are in the reheating and dehumidifying operation (YES in S2), it proceeds to the process of S7.

[0047] In the process of S7, the control device 50 operates the outdoor fan 4 at a low speed or stops the outdoor fan 4. Next, the control device 50 closes the first expansion valve 6 and closes all of the solenoid valves 7a, 7b, and 7c (S8). Next, the control device 50 adjusts the second expansion valves 8a, 8b, and 8c to open at an opening degree smaller than the fully open state (S9). Next, the control device 50 adjusts the opening degrees of the third expansion valves 11a, 11b, and 11c to be smaller than the fully open state so that the refrigerant is decompressed (S10), and returns the process from the subroutine to the main routine.

[0048] When the control device 50 determines in S2 that not all of the indoor units 30a, 30b, and 30c are in the reheating and dehumidifying operation (NO in S2), it proceeds to the process of S3. The process of S3 is a case where it is determined in the process of S1 that not all of the indoor units 30a, 30b, and 30c are in the cooling operation, and it is determined in the process of S2 that not all of the indoor units 30a, 30b, and 30c are in the reheating and dehumidifying operation. That is, the processes after S3 are processes in the case where some of the indoor units 30a, 30b, and 30c execute the cooling operation and some of the others execute the reheating and dehumidifying operation.

[0049] In S3, the control device 50 opens the solenoid valve connected to the indoor unit performing the reheating and dehumidifying operation. For example, as shown in FIG. 1, the control device 50 opens the solenoid valve 7a connected to the indoor unit 30a performing the reheating and dehumidifying operation. Next, the control device 50 adjusts the opening degree of the first expansion valve 6 so as to open the indoor unit 30a at an opening degree corresponding to the amount of heat required in the indoor unit 30a (S4).

[0050] Next, the control device 50 adjusts the second expansion valves 8a, 8b, and 8c to open to an opening less than fully open (S5). Then, the control device 50 adjusts the third expansion valve 11a of the indoor unit 30a performing reheat dehumidification to open to an opening less than fully open, opens the third expansion valve 11b of the indoor unit 30b performing cooling operation to its fullest extent, and further opens the third expansion valve 11c of the indoor unit 30c performing cooling operation to its fullest extent (S6), and returns the processing from the subroutine to the main routine.

[0051] Here, the flow rate of refrigerant flowing through the refrigerant circuit in an air conditioning system can be expressed by the following equation (1).

[0052]

[0053] In equation (1) above, Gr represents the refrigerant flow rate. A represents a constant. Cv represents the flow coefficient. ρ represents the refrigerant density. ΔP represents the pressure difference across the expansion valve.

[0054] The flow coefficient Cv can be determined from a predetermined relational equation. Therefore, the adjustment of the refrigerant flow rate Gr, or the adjustment of the pressure difference ΔP, is greatly affected by the refrigerant density ρ, which changes depending on the state of the refrigerant. For example, when adjusting the refrigerant flow rate Gr, the effect of refrigerant density ρ can be reduced by keeping the refrigerant flowing into the equipment used for adjusting the refrigerant flow rate Gr in the same state.

[0055] In the first embodiment, the air conditioning system 100 can make the refrigerant flowing into the first expansion valve 6 and the plurality of second expansion valves 8a, 8b, 8c be liquid refrigerant discharged from the outdoor heat exchanger 3. This allows the air conditioning system 100 to easily adjust the refrigerant flow rate regardless of the operating state. For example, when the air conditioning system 100 performs reheat dehumidification operation with the indoor unit 30a, the refrigerant flowing into the first expansion valve 6 and the second expansion valves 8a at a position where the refrigerant flow rate before flowing into the indoor unit 30a can be adjusted can all be made into liquid refrigerant. Therefore, the air conditioning system 100 can perform stable reheat dehumidification operation without complicating the adjustment of the refrigerant flow rate.

[0056] In the air conditioning system 100, the indoor unit 30a that performs reheat dehumidification operation opens the third expansion valve 11a to an opening smaller than fully open, and heats the air with a gas-liquid two-phase refrigerant with a high gas content in the first indoor heat exchanger 9a located upstream of the refrigerant flow, thereby preventing user discomfort caused by the indoor temperature dropping too low.

[0057] The air conditioning system 100 can improve its cooling capacity because, in the indoor units 30b and 30c that perform cooling operation, the air can be cooled by a gas-liquid two-phase refrigerant with a high liquid content.

[0058] Because the air conditioning system 100 can achieve a degree of supercooling in its internal heat exchanger 5, it can increase the cooling capacity of the indoor units 30b and 30c that perform cooling operation. As a result, when the cooling capacity of the air conditioning system 100 is maintained at the same level as an air conditioning system without an internal heat exchanger 5, the amount of refrigerant circulated can be reduced and the rotational speed of the compressor 1 can be reduced, thereby improving energy-saving performance.

[0059] Embodiment 2. Next, the air conditioning system 200 of Embodiment 2 will be described. The air conditioning system 200 in Embodiment 2 differs from the air conditioning system 100 of Embodiment 1 in the configuration of the multiple indoor units 31a, 31b, and 31c. In the following, the differences from Embodiment 1 will be the focus of the description, and the same configuration as in Embodiment 1 will not be described. Figure 5 is a refrigerant circuit diagram of the air conditioning system 200 according to Embodiment 2.

[0060] The air conditioning system 200 comprises a plurality of indoor units 31a, 31b, and 31c. Indoor unit 31a comprises a first indoor heat exchanger 13a, a second indoor heat exchanger 14a, a third expansion valve 11a, and an indoor fan 12a. Indoor unit 31b comprises a first indoor heat exchanger 13b, a second indoor heat exchanger 14b, a third expansion valve 11b, and an indoor fan 12b. Indoor unit 31c comprises a first indoor heat exchanger 13c, a second indoor heat exchanger 14c, a third expansion valve 11c, and an indoor fan 12c.

[0061] The first indoor heat exchanger 13a and the second indoor heat exchanger 14a each have multiple heat transfer tubes and perform heat exchange between air from the room, which is blown by an indoor fan 12a located next to the first indoor heat exchanger 13a and the second indoor heat exchanger 14a, and a refrigerant that passes through the multiple heat transfer tubes. The first indoor heat exchanger 13a is located upstream of the flow path through which the refrigerant flows, and downstream (downwind) of the second indoor heat exchanger 14a in the airflow path through which the air flows. The second indoor heat exchanger 14a is located downstream of the flow path through which the refrigerant flows, and upstream (upwind) of the first indoor heat exchanger 13a in the airflow path through which the air flows.

[0062] The first indoor heat exchanger 13b and the second indoor heat exchanger 14b each have multiple heat transfer tubes and perform heat exchange between air from the room, which is blown by an indoor fan 12b located next to the first indoor heat exchanger 13b and the second indoor heat exchanger 14b, and a refrigerant passing through the multiple heat transfer tubes. The first indoor heat exchanger 13b is located upstream of the flow path through which the refrigerant flows, and downstream (downwind) of the second indoor heat exchanger 14b in the airflow path through which the air flows. The second indoor heat exchanger 14b is located downstream of the flow path through which the refrigerant flows, and upstream (upwind) of the first indoor heat exchanger 13b in the airflow path through which the air flows.

[0063] The first indoor heat exchanger 13c and the second indoor heat exchanger 14c each have multiple heat transfer tubes and perform heat exchange between air from the room, which is blown by an indoor fan 12c located next to the first indoor heat exchanger 13c and the second indoor heat exchanger 14c, and a refrigerant that passes through the multiple heat transfer tubes. The first indoor heat exchanger 13c is located upstream of the flow path through which the refrigerant flows, and downstream (downwind) of the second indoor heat exchanger 14c in the airflow path through which the air flows. The second indoor heat exchanger 14c is located downstream of the flow path through which the refrigerant flows, and upstream (upwind) of the first indoor heat exchanger 13c in the airflow path through which the air flows.

[0064] In the air conditioning system 200, the first indoor heat exchangers 13a, 13b, and 13c are positioned downstream (downwind) of the second indoor heat exchangers 14a, 14b, and 14c in the direction of airflow generated by the operation of the indoor fans 12a, 12b, and 12c. As a result, when the indoor unit 31a performs reheat dehumidification, for example, the air flowing into the indoor unit 31a can be cooled and dehumidified by the upwind second indoor heat exchanger 14a, and then heated by the downwind first indoor heat exchanger 13a, making it easier to lower the humidity of the air.

[0065] Embodiment 3. Next, the air conditioning system 300 of Embodiment 3 will be described. The air conditioning system 200 in Embodiment 3 differs from the air conditioning system 100 of Embodiment 1 in that the outdoor unit 20 is equipped with a first sensor 41 and a second sensor 42. In the following, the differences from Embodiment 1 will be the focus of the description, and the same configuration as in Embodiment 1 will not be described. Figure 6 is a refrigerant circuit diagram of the air conditioning system 300 according to Embodiment 3.

[0066] The first sensor 41 is located in the middle of the outdoor heat exchanger 3 and detects the temperature of the refrigerant in the outdoor heat exchanger 3 (condensation temperature of high-pressure refrigerant). The second sensor 42 is located in the piping at the outlet of the internal heat exchanger 5 and detects the temperature of the refrigerant flowing to the multiple second expansion valves 8a, 8b, and 8c (temperature of the subcooled liquid refrigerant). The difference between the temperature detected by the first sensor 41 and the temperature detected by the second sensor 42 is the degree of subcooling.

[0067] The control device 50 controls the rotation speed of the outdoor fan 4 so that the degree of supercooling, calculated based on the difference between the temperature detected by the first sensor 41 and the temperature detected by the second sensor 42, reaches a preset target value. Specifically, if the control device 50 determines that the degree of supercooling is greater than the target value, it reduces the rotation speed of the outdoor fan 4 because the refrigerant is being excessively cooled in the outdoor heat exchanger 3. On the other hand, if the control device 50 determines that the degree of supercooling is less than the target value, it increases the rotation speed of the outdoor fan 4 because the refrigerant is not being adequately cooled in the outdoor heat exchanger 3.

[0068] The air conditioning system 300 can reliably maintain a liquid refrigerant state at the outlet of the internal heat exchanger 5 and stabilize control by controlling the rotation speed of the outdoor fan 4 while monitoring the degree of subcooling at the outlet of the internal heat exchanger 5. Since the rotation speed of the outdoor fan 4 can be set based on the relationship between the target value and the calculated degree of subcooling, energy savings can be achieved by operating with reduced power consumption.

[0069] Here, if the number of indoor units performing reheat dehumidification operation in the air conditioning system 300 increases, the amount of refrigerant flowing through the bypass channel increases, which in turn increases the amount of heat exchanged in the internal heat exchanger 5. As a result, there is no longer a need to actively cool the refrigerant in the outdoor heat exchanger 3. The air conditioning system 300 controls the rotation speed of the outdoor fan 4 while monitoring the degree of supercooling at the outlet of the internal heat exchanger 5. This allows the system to operate with the minimum necessary rotation speed of the outdoor fan 4 even when the number of indoor units performing reheat dehumidification operation increases, thereby enabling operation with reduced power consumption.

[0070] The first sensor 41 and the second sensor 42 may be arranged in the air conditioning system 200 in Embodiment 2.

[0071] <Summary> The air conditioning system 100 of this disclosure comprises an outdoor unit 20 and a plurality of indoor units 30a, 30b, 30c connected to the outdoor unit 20. The outdoor unit 20 comprises a compressor 1, an outdoor heat exchanger 3 into which refrigerant discharged from the compressor 1 flows, an internal heat exchanger 5 into which refrigerant discharged from the outdoor heat exchanger 3 flows, and a first expansion valve 6 into which refrigerant discharged from the internal heat exchanger 5 flows. The air conditioning system 100 further comprises a plurality of second expansion valves 8a, 8b, 8c connected to each of the plurality of indoor units 30a, 30b, 30c, into which refrigerant discharged from the internal heat exchanger 5 flows. The refrigerant discharged from the first expansion valve 6 passes through the internal heat exchanger 5 again and flows into the plurality of indoor units 30a, 30b, 30c without passing through the plurality of second expansion valves 8a, 8b, 8c. When at least one of the multiple indoor units 30a, 30b, and 30c, one indoor unit 30a, performs reheat dehumidification operation, the first refrigerant circuit is configured such that the refrigerant flows in the following order: compressor 1, outdoor heat exchanger 3, internal heat exchanger 5, first expansion valve 6, internal heat exchanger 5, and at least one indoor unit 30a. When at least one indoor unit 30b performs cooling operation, the second refrigerant circuit is configured such that the refrigerant flows in the following order: compressor 1, outdoor heat exchanger 3, internal heat exchanger 5, at least one of the multiple second expansion valves, one second expansion valve 8b, and at least one indoor unit 30b.

[0072] With the above configuration, the state of the refrigerant flowing into the first expansion valve 6 and the multiple second expansion valves 8a, 8b, and 8c can be made to be the liquid refrigerant discharged from the outdoor heat exchanger 3. As a result, the air conditioning system 100 can operate stably without complicating the adjustment of the refrigerant flow rate.

[0073] Preferably, when the first indoor unit (indoor unit 30a) among the multiple indoor units 30a, 30b, 30c performs reheat dehumidification operation and the second indoor unit (indoor unit 30b) among the multiple indoor units 30a, 30b, 30c performs cooling operation, the refrigerant circuit is configured such that the refrigerant flowing through the first refrigerant circuit and the refrigerant flowing through the second refrigerant circuit both flow through the first indoor unit (indoor unit 30a), and the refrigerant flowing through the second refrigerant circuit also flows through the second indoor unit (indoor unit 30b).

[0074] With the above configuration, when reheat dehumidification and cooling operations are performed simultaneously, the state of the refrigerant flowing into the first expansion valve 6 when performing reheat dehumidification and the second expansion valve 8b when performing cooling can be made to be the liquid refrigerant discharged from the outdoor heat exchanger 3. This makes it easy for the air conditioning system 100 to adjust the refrigerant flow rate when reheat dehumidification and cooling operations are performed simultaneously.

[0075] Preferably, the system further includes a plurality of solenoid valves 7a, 7b, 7c connected to each of the plurality of indoor units 30a, 30b, 30c, through which the refrigerant that has passed through the first expansion valve 6 and the internal heat exchanger 5 flows, and a control device 50. When the first indoor unit (indoor unit 30a) is performing reheat dehumidification operation and the second indoor unit (indoor unit 30b) is performing cooling operation, the control device 50 opens the first solenoid valve 7a connected to the first indoor unit (indoor unit 30a) among the plurality of solenoid valves 7a, 7b, 7c, and closes the second solenoid valve 7b connected to the second indoor unit (indoor unit 30b) among the plurality of solenoid valves 7a, 7b, 7c.

[0076] With the above configuration, the control device 50 controls the opening and closing states of a plurality of solenoid valves 7a, 7b, and 7c according to the operating state, thereby enabling the refrigerant flowing into the first indoor unit (indoor unit 30a) performing reheat dehumidification operation to be in a gas-liquid two-phase state with a higher gas content, and the refrigerant flowing into the second indoor unit (indoor unit 30b) performing cooling operation to be in a gas-liquid two-phase state with a higher liquid content. This makes it possible to improve the efficiency of both reheat dehumidification and cooling operations.

[0077] Preferably, when the first indoor unit (indoor unit 30a) performs reheat dehumidification operation, the control device 50 opens the first expansion valve 6 to an opening degree corresponding to the amount of heat required by the first indoor unit (indoor unit 30a).

[0078] With the above configuration, the opening degree of the first expansion valve 6 can be set to an opening degree corresponding to the amount of heat required for reheat dehumidification operation. Therefore, by adjusting the flow rate of the first expansion valve 6 into which the liquid refrigerant flows, reheat dehumidification operation can be suitably performed.

[0079] Preferably, when the second indoor unit (indoor unit 30b) is operating in cooling mode, the control device 50 opens the second expansion valve 8b, which is connected to the second indoor unit (indoor unit 30b) among the plurality of second expansion valves 8a, 8b, 8c, to an opening less than fully open.

[0080] With the above configuration, a gas-liquid two-phase refrigerant with a high liquid content can be introduced into the indoor unit 30b where cooling operation is performed, thus enabling effective cooling operation.

[0081] Preferably, each of the multiple indoor units 30a, 30b, 30c includes a first indoor heat exchanger 9a, 9b, 9c located upstream of the flow path through which the refrigerant flows, a second indoor heat exchanger 10a, 10b, 10c located downstream of the flow path, and a third expansion valve 11a, 11b, 11c located between the first indoor heat exchangers 9a, 9b, 9c and the second indoor heat exchangers 10a, 10b, 10c. When the first indoor unit (indoor unit 30a) is performing reheat dehumidification operation and the second indoor unit (indoor unit 30b) is performing cooling operation, the control device 50 opens the third expansion valve 11a of the first indoor unit (indoor unit 30a) to an opening less than fully open, and opens the third expansion valve 11b of the second indoor unit (indoor unit 30b) to its fullest.

[0082] With the above configuration, the state of the third expansion valve 11a of the indoor unit 30a that performs reheat dehumidification operation can be optimized, and the state of the third expansion valve 11b of the indoor unit 30b that performs cooling operation can be optimized.

[0083] Preferably, each of the multiple indoor units 31a, 31b, 31c is further provided with indoor fans 12a, 12b, 12c for taking in air from the room. The first indoor heat exchangers 13a, 13b, 13c are positioned downstream of the second indoor heat exchangers 14a, 14b, 14c in the direction of airflow generated by the operation of the indoor fans 12a, 12b, 12c.

[0084] According to the above configuration, when the air conditioning system 200 performs reheat dehumidification operation in the indoor unit 31a, the air flowing into the indoor unit 31a can be cooled and dehumidified by the second indoor heat exchanger 14a on the windward side, and then heated by the first indoor heat exchanger 13a on the leeward side, making it easier to lower the humidity of the air.

[0085] Preferably, the outdoor unit 20 further includes a first sensor 41 for detecting the temperature of the refrigerant in the outdoor heat exchanger 3, a second sensor 42 for detecting the temperature of the refrigerant flowing from the internal heat exchanger 5 to a plurality of second expansion valves 8a, 8b, 8c, and an outdoor fan 4 for supplying air from outside to the outdoor heat exchanger 3. The control device 50 controls the rotation speed of the outdoor fan 4 so that the degree of subcooling, calculated based on the difference between the temperature detected by the first sensor 41 and the temperature detected by the second sensor 42, reaches a preset target value.

[0086] With the above configuration, by controlling the rotation speed of the outdoor fan 4 while monitoring the degree of supercooling at the outlet of the internal heat exchanger 5, the state of the refrigerant at the outlet of the internal heat exchanger 5 can be reliably made into liquid refrigerant, and the control can be stabilized.

[0087] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included.

[0088] 1 Compressor, 2 Four-way valve, 3 Outdoor heat exchanger, 4 Outdoor fan, 5 Internal heat exchanger, 6 First expansion valve, 7a, 7b, 7c Solenoid valve, 8a, 8b, 8c Second expansion valve, 9a, 9b, 9c, 13a, 13b, 13c First indoor heat exchanger, 10a, 10b, 10c, 14a, 14b, 14c Second indoor heat exchanger, 11a, 11b, 11c Third expansion valve, 12a, 12b, 12c Indoor fan, 20 Outdoor unit, 30a, 30b, 30c, 31a, 31b, 31c Indoor unit, 41 First sensor, 42 Second sensor, 50 Control device, 51 Control unit, 52 Memory unit, 100, 200, 300 Air conditioning system.

Claims

1. The system comprises an outdoor unit and a plurality of indoor units connected to the outdoor unit, wherein the outdoor unit comprises a compressor, an outdoor heat exchanger into which refrigerant discharged from the compressor flows, an internal heat exchanger into which refrigerant discharged from the outdoor heat exchanger flows, and a first expansion valve into which refrigerant discharged from the internal heat exchanger flows, and further comprises a plurality of second expansion valves connected to each of the plurality of indoor units, into which refrigerant discharged from the internal heat exchanger flows, the refrigerant discharged from the first expansion valves flows again through the internal heat exchanger and into the plurality of indoor units without passing through the plurality of second expansion valves, and when at least one of the plurality of indoor units performs reheat dehumidification operation, the first refrigerant circuit is configured such that the refrigerant flows in the order of the compressor, the outdoor heat exchanger, the internal heat exchanger, the first expansion valve, the internal heat exchanger, and the at least one indoor unit. An air conditioning system comprising a second refrigerant circuit configured such that when at least one indoor unit is performing cooling operation, the refrigerant flows in the following order: the compressor, the outdoor heat exchanger, the internal heat exchanger, at least one of the plurality of second expansion valves, and the at least one indoor unit.

2. The air conditioning system according to claim 1, wherein when a first indoor unit among the plurality of indoor units performs the reheat dehumidification operation and a second indoor unit among the plurality of indoor units performs the cooling operation, the refrigerant circuit is configured such that the refrigerant flowing through the first refrigerant circuit and the refrigerant flowing through the second refrigerant circuit both flow through the first indoor unit, and the refrigerant circuit is configured such that the refrigerant flowing through the second refrigerant circuit both flow through the second indoor unit.

3. The air conditioning system according to claim 2, further comprising a plurality of solenoid valves connected to each of the plurality of indoor units, through which the refrigerant that has passed through the first expansion valve and the internal heat exchanger flows, and a control device, wherein when the first indoor unit performs the reheat dehumidification operation and the second indoor unit performs the cooling operation, the control device opens the first solenoid valve connected to the first indoor unit and closes the second solenoid valve connected to the second indoor unit.

4. The air conditioning device according to claim 3, wherein the control device opens the first expansion valve to an opening degree corresponding to the amount of heat required by the first indoor unit when the first indoor unit performs the reheat dehumidification operation.

5. The air conditioning device according to claim 3 or 4, wherein when the second indoor unit performs the cooling operation, the control device opens the second expansion valve connected to the second indoor unit among the plurality of second expansion valves to an opening less than fully open.

6. The air conditioning system according to any one of claims 3 to 5, wherein each of the plurality of indoor units comprises a first indoor heat exchanger located upstream of a flow path through which a refrigerant flows, a second indoor heat exchanger located downstream of the flow path, and a third expansion valve located between the first indoor heat exchanger and the second indoor heat exchanger, and the control device opens the third expansion valve of the first indoor unit to an opening less than fully open and opens the third expansion valve of the second indoor unit to its fullest extent when the first indoor unit performs the reheat dehumidification operation and the second indoor unit performs the cooling operation.

7. The air conditioning system according to claim 6, wherein each of the plurality of indoor units further comprises an indoor fan for taking in air from the room, and the first indoor heat exchanger is positioned downstream of the second indoor heat exchanger in the direction in which the air generated by the operation of the indoor fan flows.

8. The air conditioning device according to any one of claims 3 to 7, wherein the outdoor unit further comprises a first sensor for detecting the temperature of the refrigerant in the outdoor heat exchanger, a second sensor for detecting the temperature of the refrigerant flowing from the internal heat exchanger to the plurality of second expansion valves, and an outdoor fan for supplying air from outside to the outdoor heat exchanger, and the control device controls the rotation speed of the outdoor fan so that the degree of subcooling calculated based on the difference between the temperature detected by the first sensor and the temperature detected by the second sensor becomes a preset target value.

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