Multi-chamber type air conditioner

Abstract

To provide a multi-chamber type air conditioner capable of satisfactorily implementing a heating operation even if heat exchange capacities are different in respective indoor heat exchangers.SOLUTION: A multi-chamber type air conditioner 11 comprises: a plurality of indoor heat exchangers 14a-14d receiving supply of a coolant from one common compressor 15 in the case of a heating operation and having individually determined heat exchange capacities; expansion valves 18a-18d connected the downstream of the indoor heat exchangers in the case of the heating operation and adjusting a flow rate of the coolant in accordance with apertures; a temperature sensor 31 which outputs a first detection signal identifying a liquid temperature of the coolant for each indoor heat exchanger; a temperature sensor 32 which outputs a second detection signal identifying a temperature which falls with a spread of a liquid phase inside of the indoor heat exchanger; and a control section for decreasing the aperture of the expansion valve connected to the indoor heat exchanger at a maximum temperature in accordance with the first detection signal in the case of the heating operation. When the temperature identified by the second detection signal becomes lower than a determined temperature value regarding the indoor heat exchanger at the maximum temperature, the control section suspends the decrease of the aperture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-room air conditioner equipped with a plurality of indoor heat exchangers that receive a supply of refrigerant from a single common compressor during heating operation. [Background technology]

[0002] Patent Document 1 discloses an air conditioner in which a refrigerant circuit includes one outdoor heat exchanger and multiple indoor heat exchangers, and a common refrigerant circulates. During heating operation, the common refrigerant is distributed to each indoor heat exchanger. By individually controlling the opening of the expansion valve provided for each indoor heat exchanger, variations in liquid temperature among the multiple indoor heat exchangers are eliminated. To eliminate variations, the opening of the expansion valve connected to the indoor heat exchanger with the highest liquid temperature is decreased according to the control. The opening of the expansion valve connected to the indoor heat exchanger with the lowest liquid temperature is increased according to the control. The liquid temperatures in the multiple indoor heat exchangers converge toward the same temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-150678 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, a building has multiple partitioned rooms. The heating and cooling capacity required for each room may differ. The heat exchange capacity of the indoor heat exchanger can differ depending on the required heating and cooling capacity. When a common refrigerant is distributed to individual indoor heat exchangers during heating operation, a heat exchanger with a small heat exchange capacity requires a small refrigerant flow rate. The expansion valve provided for each indoor heat exchanger is throttled. A heat exchanger with a large heat exchange capacity requires a large flow rate. The expansion valve provided for each indoor heat exchanger is opened. If the expansion valve is throttled excessively in a heat exchanger with a small heat exchange capacity, the refrigerant circulation will be impeded and the range of liquid refrigerant (also called liquid phase) will expand within the heat exchanger. The temperature of the indoor heat exchanger will drop due to the expansion of the liquid phase. The discharge temperature of the indoor unit will drop. The heating capacity will decrease.

[0005] An object of the present invention is to provide a multi-room air conditioner that can achieve good heating operation even if the heat exchange capacities of the individual indoor heat exchangers differ. [Means for solving the problem]

[0006] According to one aspect of the present invention, a multi-room air conditioner includes a compressor, a plurality of indoor heat exchangers that receive refrigerant from a common compressor during heating operation and have individually determined heat exchange capacities, piping that extends downstream from the indoor heat exchanger for each of the indoor heat exchangers during heating operation to guide liquid refrigerant, expansion valves connected to each of the piping and adjust the flow rate of the refrigerant according to their opening degrees, a first temperature sensor that detects the liquid temperature of the liquid refrigerant in the piping for each of the indoor heat exchangers and outputs a first detection signal that identifies the liquid temperature, a second temperature sensor that outputs a second detection signal that identifies the temperature that decreases as the liquid phase spreads in each of the indoor heat exchangers, and a control unit that is connected to the expansion valves, the first temperature sensor, and the second temperature sensor, and that during heating operation reduces the opening degrees of the expansion valves connected to the indoor heat exchanger that is operating and has the highest temperature as determined by the first detection signal, and the control unit suspends the reduction in the opening degrees when the temperature determined by the second detection signal for the indoor heat exchanger with the highest temperature falls below a determined temperature value.

[0007] When a common refrigerant is distributed to individual indoor heat exchangers during heating operation, a smaller refrigerant flow rate is required in an indoor heat exchanger with a smaller heat exchange capacity. The expansion valve is throttled, decreasing its opening. A larger flow rate is required in an indoor heat exchanger with a larger heat exchange capacity. The expansion valve is opened, increasing its opening. Even in indoor heat exchangers that meet the conditions for reducing the expansion valve opening, the control unit will refrain from reducing the opening rate if the temperature of the indoor heat exchanger drops due to the expansion of the liquid phase. This allows the refrigerant flow rate to be secured. The expansion of the liquid phase in the indoor heat exchanger can be avoided. The temperature of the indoor heat exchanger can be prevented from dropping due to the expansion of the liquid phase. The blowing of cold air can be prevented. The heating capacity can be maintained.

[0008] The temperature value may be set based on the difference between the maximum and minimum values ​​identified by the second detection signal. When the liquid phase expands in the indoor heat exchanger, the temperature identified by the second detection signal drops below normal. In an indoor heat exchanger operating normally, the temperature identified by the second detection signal is maintained at normal. Therefore, by detecting the difference between the maximum and minimum values ​​in the second detection signal, the indoor heat exchanger corresponding to the expansion of the liquid phase can be identified.

[0009] The control unit may, during heating operation, increase the aperture of the expansion valve connected to the indoor heat exchanger with the lowest temperature in the first detection signal during operation. When the aperture of the expansion valve connected to the indoor heat exchanger with the highest temperature in the first detection signal during operation is decreased, the liquid temperature of the refrigerant flowing out of the corresponding indoor heat exchanger decreases. Similarly, when the aperture of the expansion valve connected to the indoor heat exchanger with the lowest temperature in the first detection signal during operation is increased, the liquid temperature of the refrigerant flowing out of the corresponding indoor heat exchanger increases. In this way, the liquid temperatures of the multiple indoor heat exchangers can converge toward the same temperature. Refrigerant at a stable temperature can flow into the compressor.

[0010] The control unit may increase the amount of change in the opening degree as the temperature difference between the maximum temperature and the minimum temperature increases. Since the flow rate changes more significantly as the temperature difference increases, the control time required to eliminate the temperature difference can be shortened.

[0011] The control unit may set a target discharge temperature based on the condensing temperature of the indoor heat exchanger, the evaporating temperature of the outdoor heat exchanger, and the rotation speed of the compressor, compare the target discharge temperature with a discharge temperature detected from the refrigerant flowing out of the compressor, and generate a control signal that uniformly specifies an amount of change in the aperture of the expansion valve in accordance with the comparison result. By uniformly controlling the aperture of the expansion valve in this way, the discharge temperature of the compressor can be well controlled.

[0012] The control unit may generate a control signal to reduce the rotation speed of the corresponding fan when the temperature specified by the second detection signal falls below a threshold lower than the predetermined temperature value. When the temperature of the indoor heat exchanger falls below a threshold lower than the predetermined temperature value during heating operation, the rotation speed of the corresponding fan is reduced. When the liquid phase expands in the indoor heat exchanger and the temperature of the indoor heat exchanger drops, cool air is blown out from the indoor unit, but the impact of the cool air on the indoor environment can be suppressed by reducing the air volume. This type of control is called cold air prevention control. As described above, when the temperature of the indoor heat exchanger falls below a predetermined temperature value, the corresponding expansion valve refrains from reducing its opening, thereby suppressing the activation of the cold air prevention control. [Effects of the Invention]

[0013] As described above, according to one aspect of the present invention, a multi-room air conditioner can be provided that can achieve good heating operation even if the heat exchange capacities of the individual indoor heat exchangers differ. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram illustrating the configuration of a multi-room air conditioner according to an embodiment of the present invention. [Figure 2]FIG. 2 is a block diagram illustrating a control system of the multi-room air conditioner. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0016] (1) Configuration of multi-room air conditioner FIG. 1 shows a schematic configuration of a multi-room air conditioner 11 according to one embodiment of the present invention. The multi-room air conditioner 11 includes two or more indoor units 12a, 12b, 12c, and 12d and a single shared outdoor unit 13. The indoor units 12a to 12d are installed, for example, in an indoor space within a building. The indoor spaces may be individually partitioned. Alternatively, the indoor units 12a to 12d may be installed in spaces corresponding to the indoor spaces. Indoor heat exchangers 14a, 14b, 14c, and 14d are incorporated into the indoor units 12a to 12d, respectively. The indoor heat exchangers 14a to 14d have individually determined heat exchange capacities. The heat exchange capacities differ for each of the indoor heat exchangers 14a to 14d. The heat exchange capacity is set, for example, according to the size of the indoor space. The heat exchange capacity of at least one indoor heat exchanger may be different from the other indoor heat exchangers.

[0017] The outdoor unit 13 incorporates one compressor 15 common to the indoor heat exchangers 14a to 14d, one accumulator 16 common to the indoor heat exchangers 14a to 14d, one outdoor heat exchanger 17 common to the indoor heat exchangers 14a to 14d, expansion valves 18a, 18b, 18c, and 18d provided for each of the indoor heat exchangers 14a to 14d, and one four-way valve 19 common to the indoor heat exchangers 14a to 14d. The indoor heat exchangers 14a to 14d, the compressor 15, the accumulator 16, the outdoor heat exchanger 17, the expansion valves 18a to 18d, and the four-way valve 19 form a refrigerant circuit 21. The outdoor unit 13 is installed outdoors and exchanges heat with outdoor air.

[0018] The refrigerant circuit 21 includes a first circulation path 22. The first circulation path 22 interconnects the first port 19a and the second port 19b of the four-way valve 19. The compressor 15 and the accumulator 16 are disposed in the first circulation path 22. The suction pipe 15a of the compressor 15 is connected to the first port 19a of the four-way valve 19 via a refrigerant piping. Gas refrigerant is supplied from the first port 19a to the suction pipe 15a of the compressor 15. The compressor 15 compresses the low-pressure gas refrigerant to a predetermined pressure. The discharge pipe 15b of the compressor 15 is connected to the second port 19b of the four-way valve 19 via a refrigerant piping. The gas refrigerant is supplied from the discharge pipe 15b of the compressor 15 to the second port 19b of the four-way valve 19. The accumulator 16 is incorporated between the suction pipe 15a of the compressor 15 and the first port 19a of the four-way valve 19. The accumulator 16 separates the gas refrigerant and the liquid refrigerant from each other and serves to prevent the liquid refrigerant from flowing toward the compressor 15. The refrigerant piping may be, for example, copper piping.

[0019] The refrigerant circuit 21 further includes a second circulation path 23. The second circulation path 23 interconnects the third port 19c and the fourth port 19d of the four-way valve 19. The second circulation path 23 incorporates, in order from the third port 19c side, the outdoor heat exchanger 17, expansion valves 18a-18d, and indoor heat exchangers 14a-14d. The outdoor heat exchanger 17 exchanges thermal energy between the refrigerant passing through the outdoor heat exchanger 17 and the air contacting the outdoor heat exchanger 17. The indoor heat exchangers 14a-14d exchange thermal energy between the refrigerant passing through the indoor heat exchangers 14a-14d and the air contacting the indoor heat exchangers 14a-14d. The heat exchange capacity can be determined, for example, by the surface area in contact with room-temperature air. The second circulation path 23 branches in parallel between the outdoor heat exchanger 17 and the fourth port 19d of the four-way valve 19. Each branched path is equipped with one of the indoor heat exchangers 14a-14d and one of the expansion valves 18a-18d. Each expansion valve 18a-18d is connected to a pipe 21a, 21b, 21c, 21d that extends downstream from each indoor heat exchanger 14a-14d and guides the liquid refrigerant during heating operation.

[0020] A blower fan 24 is incorporated in the outdoor unit 13. The blower fan 24 ventilates the outdoor heat exchanger 17. The blower fan 24 generates an airflow, for example, in response to the rotation of an impeller. The action of the blower fan 24 causes the airflow to pass through the outdoor heat exchanger 17. The outdoor air passes through the outdoor heat exchanger 17 and exchanges heat with the refrigerant. The heat-exchanged cool or warm air flow is blown out from the outdoor unit 13. The flow rate of the passing airflow is adjusted in response to the rotation speed of the impeller.

[0021] Each indoor unit 12a to 12d is individually equipped with a blower fan 25a, 25b, 25c, or 25d. The blower fans 25a to 25d ventilate the indoor heat exchangers 14a to 14d. The blower fans 25a to 25d generate airflow according to the rotation of their impellers. The blower fans 25a to 25d draw indoor air into the indoor units 12a to 12d. The indoor air passes through the indoor heat exchangers 14a to 14d and exchanges heat with the refrigerant. The cooled or warm air that has undergone heat exchange is blown out from the indoor units 12a to 12d. The flow rate of the passing airflow is adjusted according to the rotation speed of the impellers.

[0022] When cooling operation is performed in the refrigerant circuit 21, the four-way valve 19 interconnects the second port 19b and the third port 19c and interconnects the first port 19a and the fourth port 19d. Therefore, high-temperature, high-pressure gas refrigerant is supplied from the discharge pipe 15b of the compressor 15 to the outdoor heat exchanger 17. The refrigerant flows through the outdoor heat exchanger 17, expansion valves 18a-18d, and indoor heat exchangers 14a-14d. In the outdoor heat exchanger 17, the refrigerant dissipates heat into the outside air. The expansion valves 18a-18d reduce the pressure of the refrigerant to low pressure. The reduced-pressure refrigerant absorbs heat from the surrounding air in the indoor heat exchangers 14a-14d. Cool air is generated. The cool air is blown into the indoor space by the action of the blower fans 25a-25d.

[0023] When heating operation is performed in the refrigerant circuit 21, the four-way valve 19 interconnects the second port 19b and the fourth port 19d and interconnects the first port 19a and the third port 19c. High-temperature, high-pressure refrigerant is supplied from the compressor 15 to the indoor heat exchangers 14a-14d. The indoor heat exchangers 14a-14d receive refrigerant from the same compressor 15. The refrigerant flows through the indoor heat exchangers 14a-14d and expansion valves 18a-18d along each branched path before flowing into the outdoor heat exchanger 17. In the indoor heat exchangers 14a-14d, the refrigerant dissipates heat into the surrounding air. Warm air is generated. The warm air is blown into the indoor space by the action of the blower fans 25a-25d. The refrigerant is decompressed to low pressure by the expansion valves 18a-18d. The decompressed refrigerant absorbs heat from the surrounding air in the outdoor heat exchanger 17. The refrigerant then returns to the compressor 15.

[0024] The multi-room air conditioner 11 is equipped with a discharge temperature sensor 27, which is arranged on the discharge side of the compressor 15 in the first circulation path 22 and detects the temperature of the gas refrigerant discharged from the compressor 15; a discharge pressure sensor 28, which is arranged on the discharge side of the compressor 15 in the first circulation path 22 and detects the pressure of the gas refrigerant discharged from the compressor 15; and a suction pressure sensor 29, which is arranged upstream of the accumulator 16 in the first circulation path 22 and detects the pressure of the gas refrigerant flowing into the accumulator 16. The discharge temperature sensor 27 and the discharge pressure sensor 28 may be attached to, for example, the discharge pipe 15b of the compressor 15. The discharge temperature sensor 27 generates a detection signal that specifies the detected temperature. The discharge pressure sensor 28 generates a detection signal that specifies the detected pressure. The suction pressure sensor 29 generates a detection signal that specifies the detected pressure.

[0025] The multi-room air conditioner 11 further includes liquid refrigerant temperature sensors (first temperature sensors) 31 disposed between each of the indoor heat exchangers 14a-14d and the corresponding expansion valves 18a-18d to detect the temperature of the liquid refrigerant flowing into the expansion valves 18a-18d during heating operation, and liquid phase range temperature sensors (second temperature sensors) 32 attached to each of the indoor heat exchangers 14a-14d to detect the temperature that decreases as the liquid phase expands during heating operation. The liquid refrigerant temperature sensors 31 generate a detection signal (hereinafter referred to as the "first detection signal") that identifies the detected temperature. The liquid phase range temperature sensors 32 generate a detection signal (hereinafter referred to as the "second detection signal") that identifies the detected temperature. The liquid phase range temperature sensors 32 are attached to the corresponding indoor heat exchangers 14a-14d at positions that detect the expansion of the liquid phase prior to the generation of cooled air. The generation of cooled air will be described later.

[0026] As shown in FIG. 2, the multi-room air conditioner 11 includes a control unit 34 that controls the operation of the multi-room air conditioner 11. The control unit 34 is connected to the discharge temperature sensor 27, the discharge pressure sensor 28, the suction pressure sensor 29, the liquid refrigerant temperature sensor 31, and the liquid-phase temperature sensor 32. The control unit 34 receives detection signals, a first detection signal, and a second detection signal from the discharge temperature sensor 27, the discharge pressure sensor 28, the suction pressure sensor 29, the liquid refrigerant temperature sensor 31, and the liquid-phase temperature sensor 32. The control unit 34 is connected to the compressor 15, the expansion valves 18a-18d, and the blower fans 25a-25d. The control unit 34 generates a control signal that specifies the rotation speed of the compressor 15. When the control signal is supplied to the compressor 15, the compressor 15 operates at the specified rotation speed. The control unit 34 generates a control signal that specifies the amount of change in the opening of each of the expansion valves 18a-18d. When the control signals are supplied to the expansion valves 18a to 18d, the expansion valves 18a to 18d operate at the specified change amount. The control unit 34 generates a control signal that specifies the rotation speed of the impeller for each of the blower fans 25a to 25d. When the control signals are supplied to the blower fans 25a to 25d, the blower fans 25a to 25d operate at the specified rotation speed.

[0027] (2) Operation of multi-room air conditioners Next, the operation of the multi-room air conditioner 11 will be described. During heating operation, the control unit 34 controls the opening degrees of the expansion valves 18a-18d based on the discharge temperature of the compressor 15. To perform this control, the control unit 34 determines the temperature of the gas refrigerant discharged from the compressor 15 based on the detection signal of the discharge temperature sensor 27. The determined temperature is compared with a target discharge temperature. The target discharge temperature is set based on the condensing temperatures of the indoor heat exchangers 14a-14d, the evaporating temperature of the outdoor heat exchanger 17, and the rotation speed of the compressor 15. The condensing temperatures of the indoor heat exchangers 14a-14d use high-pressure saturation temperatures calculated based on the pressure output from the discharge pressure sensor 28. The evaporating temperature of the outdoor heat exchanger 17 is calculated based on the pressure of the refrigerant flowing into the accumulator 16. If the determined temperature is higher than the target discharge temperature, a change amount that uniformly increases the opening degrees is set in the control signals of the expansion valves 18a-18d. When a control signal is supplied to each of the expansion valves 18a to 18d, the flow rate of refrigerant sucked into the compressor 15 increases. The discharge temperature decreases. If the specified temperature is lower than the target discharge temperature, a change amount that uniformly decreases the opening degree is set in the control signal for the expansion valves 18a to 18d. When a control signal is supplied to each of the expansion valves 18a to 18d, the flow rate of refrigerant sucked into the compressor 15 decreases. The discharge temperature increases. By uniformly controlling the opening degree of the expansion valves 18a to 18d in this way, the temperature of the refrigerant discharged from the compressor 15 can be well controlled.

[0028] At this time, the control unit 34 performs equalization control. When a control signal is output to the expansion valves 18a-18d based on the discharge temperature, the control unit 34 adjusts the aperture of each of the expansion valves 18a-18d individually based on the temperature of the liquid refrigerant flowing into the expansion valves 18a-18d. Control based on the discharge temperature and control based on the temperature of the liquid refrigerant are performed alternately at specific time intervals. In adjusting the aperture, the control unit 34 identifies the liquid temperature for each of the indoor heat exchangers 14a-14d based on the first detection signal. The control unit 34 acquires the first detection signal for the indoor heat exchangers 14a-14d that are in operation. The control unit 34 identifies the indoor heat exchanger 14a-14d with the highest temperature and the indoor heat exchanger 14a-14d with the lowest temperature based on the first detection signal while in operation. The control unit 34 generates a control signal to decrease the aperture of the expansion valve 18a-18d connected to the indoor heat exchanger 14a-14d with the highest temperature. The control signal specifies the amount of change by which the aperture is decreased. When a control signal is supplied to a corresponding expansion valve 18a-18d, the refrigerant flow rate in the corresponding indoor heat exchanger 14a-14d decreases. The liquid temperature of the refrigerant flowing out of the indoor heat exchanger 14a-14d decreases. At the same time, the control unit 34 generates a control signal to increase the aperture of the expansion valve 18a-18d connected to the indoor heat exchanger 14a-14d with the lowest temperature. The control signal specifies the amount of change in aperture. When a control signal is supplied to a corresponding expansion valve 18a-18d, the refrigerant flow rate in the corresponding indoor heat exchanger 14a-14d increases. The liquid temperature of the refrigerant flowing out of the indoor heat exchanger 14a-14d increases. In this way, the liquid temperatures in the multiple indoor heat exchangers 14a-14d can converge toward the same temperature. Refrigerant at a stable temperature can flow into the compressor 15. Here, the control unit 34 increases the amount of change in aperture the greater the temperature difference between the maximum and minimum temperatures. As the change in the opening degree increases, the change in the flow rate that accompanies the change in the opening degree also increases. Therefore, the larger the temperature difference, the larger the change in the flow rate, so the control time required to eliminate the temperature difference can be shortened.

[0029] The control unit 34 acquires the second detection signal when performing equalization control. The control unit 34 suspends the reduction in the opening degree when the temperature specified by the second detection signal for the indoor heat exchanger 14a-14b with the highest temperature falls below a predetermined temperature value. The control unit 34 suspends the reduction in the opening degree when the temperature of the indoor heat exchangers 14a-14d that meet the conditions for reducing the opening degree of the expansion valves 18a-18d decreases due to the expansion of the liquid phase, even in the indoor heat exchangers 14a-14d. This ensures the flow rate of the refrigerant. The expansion of the liquid phase in the indoor heat exchangers 14a-14d can be avoided. The temperature of the indoor heat exchangers 14a-14d can be prevented from decreasing due to the expansion of the liquid phase. The blowing of cool air can be prevented. The heating capacity can be maintained. Here, the control unit 34 calculates the difference between the maximum and minimum values ​​specified by the second detection signal when setting the predetermined temperature value. When the liquid phase expands in the indoor heat exchangers 14a-14d, the temperature specified by the second detection signal drops below normal. In the indoor heat exchangers 14a-14d operating normally, the temperature specified by the second detection signal is maintained at normal. Therefore, if the difference between the maximum and minimum values ​​of the second detection signal is detected, the indoor heat exchanger 14a-14d corresponding to the expansion of the liquid phase can be identified.

[0030] During heating operation, the control unit 34 can implement so-called cold air prevention control. In this cold air prevention control, when the temperature determined by the second detection signal falls below a threshold value lower than the predetermined temperature value, the control unit 34 generates a control signal to reduce the rotation speed of the corresponding blower fan 25a-25d. When the control signal is supplied to the corresponding blower fan 25a-25d, the rotation speed of the impeller of the blower fan 25a-25d is reduced. Therefore, the air volume is reduced. When the liquid phase expands in the indoor heat exchangers 14a-14d and the temperature of the indoor heat exchangers 14a-14d drops, cold air is blown out from the indoor units 12a-12d. However, the reduced air volume reduces the impact of the cold air on the indoor environment. As described above, when the temperature of the indoor heat exchangers 14a-14d falls below the predetermined temperature value, the reduction in the opening degree of the corresponding expansion valves 18a-18d is suspended, thereby suppressing the activation of the cold air prevention control.

[0031] In this embodiment, the liquid phase temperature sensors 32 are attached to the corresponding indoor heat exchangers 14a-14d at positions that detect the expansion of the liquid phase prior to the generation of cold air. The control unit 34 can detect the expansion of the liquid phase before the temperature of the indoor heat exchangers 14a-14d drops to a temperature at which cold air is generated. When the expansion of the liquid phase is detected, the control unit 34 suspends the reduction in the opening of the corresponding expansion valves 18a-18d. Further expansion of the liquid phase can be avoided. Therefore, the generation of cold air can be effectively prevented during heating operation. [Explanation of symbols]

[0032] 11...multi-room air conditioner, 14a...indoor heat exchanger, 14b...indoor heat exchanger, 14c...indoor heat exchanger, 14d...indoor heat exchanger, 15...compressor, 18a...expansion valve, 18b...expansion valve, 18c...expansion valve, 18d...expansion valve, 21a...piping, 21b...piping, 21c...piping, 21d...piping, 31...first temperature sensor (liquid refrigerant temperature sensor), 32...second temperature sensor (liquid phase temperature sensor), 34...control unit

Claims

1. A compressor; a plurality of indoor heat exchangers each having a predetermined heat exchange capacity and each receiving a refrigerant from the common compressor during heating operation; a pipe extending downstream from each of the indoor heat exchangers during heating operation to guide the liquid refrigerant; an expansion valve connected to each of the pipes and adjusting the flow rate of the refrigerant according to its opening degree; a first temperature sensor that detects a liquid temperature of the liquid refrigerant in the pipe for each of the indoor heat exchangers and outputs a first detection signal that specifies the liquid temperature; a second temperature sensor that outputs a second detection signal that identifies a temperature that decreases as the liquid phase spreads within each of the indoor heat exchangers; a control unit connected to the expansion valve, the first temperature sensor, and the second temperature sensor, and configured to reduce the opening of the expansion valve connected to the indoor heat exchanger that is in operation and has the highest temperature in response to the first detection signal during heating operation; The control unit suspends the reduction of the opening degree when the temperature specified by the second detection signal for the indoor heat exchanger with the maximum temperature falls below a predetermined temperature value. A multi-room air conditioner characterized by the above features.

2. 2. The multi-room air conditioner according to claim 1, wherein the temperature value is set based on a difference between a maximum value and a minimum value specified by the second detection signal.

3. 2. The multi-room air conditioner according to claim 1, wherein the control unit, during heating operation, increases the opening of the expansion valve connected to the indoor heat exchanger that is in operation and has the lowest temperature in response to the first detection signal.

4. 4. The multi-room air conditioner according to claim 3, wherein the control unit increases the amount of change in the opening degree as the temperature difference between the maximum temperature and the minimum temperature increases.

5. 5. The multi-room air conditioner according to claim 4, wherein the control unit sets a target discharge temperature based on the condensing temperature of the indoor heat exchanger, the evaporating temperature of the outdoor heat exchanger, and the rotation speed of the compressor, compares the target discharge temperature with the discharge temperature detected from the refrigerant flowing out of the compressor, and generates a control signal that uniformly specifies the amount of change in the opening of the expansion valve depending on the result of the comparison.

6. 6. The multi-room air conditioner according to claim 5, wherein the control unit generates a control signal to reduce the rotation speed of the corresponding fan when the temperature specified by the second detection signal falls below a threshold value that is lower than the determined temperature value.

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