JP6716037B2 - Air conditioning system - Google Patents

Description

The present invention relates to an air conditioning system that performs air conditioning.

An air conditioning system generally includes an outdoor unit including an outdoor heat exchanger as a compressor and a condenser, and an indoor unit including an indoor heat exchanger as an expansion valve and an evaporator. The outdoor unit and the indoor unit are connected by a connecting pipe.

In order to prevent the condensing pressure from becoming abnormally high, the conventional air conditioning system lowers the condensing temperature when the condensing temperature is higher than the upper limit temperature, and raises the condensing temperature when the condensing temperature is lower than the lower limit temperature. It is controlled (for example, see Patent Document 1).

By the way, in a general air conditioning system, the compression ratio of the compressor is lowered by lowering the condensing temperature. When the compression ratio is reduced, the input power of the compressor is reduced, so that the power consumption is expected to be reduced. Therefore, from the viewpoint of power consumption, it is desirable that the condensation temperature is low.

On the other hand, in the air conditioning system, the pressure of the refrigerant flowing into the expansion valve is lower than the pressure of the refrigerant flowing out of the outdoor heat exchanger due to the pressure loss in the connecting pipe. Therefore, if the condensation temperature is excessively lowered, the refrigerant flowing into the expansion valve may be in a gas-liquid two-phase state. When the gas-liquid two-phase refrigerant flows into the expansion valve, a refrigerant flow noise is generated when the refrigerant passes through the expansion valve, which causes noise in the indoor unit.

Further, in the air conditioning system, the refrigerant flow rate is controlled by the opening of the expansion valve, but the opening at this time is designed on the assumption that liquid refrigerant flows through the expansion valve. Therefore, when the gas-liquid two-phase refrigerant flows into the expansion valve, the refrigerant flow rate cannot be controlled as designed.

Therefore, in recent air conditioning systems, there is a system in which a lower limit value is set for the target condensing temperature so that the gas-liquid two-phase refrigerant does not flow into the expansion valve even if the pipe length of the connecting pipe becomes long.

Japanese Patent No. 5195543

However, since the pipe length of the connecting pipe differs depending on the installation location and the like, the target condensation temperature cannot be uniquely determined. Therefore, it is difficult to reduce the condensing temperature to reduce power consumption.

The present invention has been made in view of the above problems in the conventional art, and an object of the present invention is to provide an air conditioning system capable of reducing power consumption while preventing generation of noise.

The air conditioning system of the present invention is an air conditioning system in which an indoor unit including a compressor and an outdoor heat exchanger and an outdoor unit including an expansion valve and an indoor heat exchanger are connected by a connecting pipe, An outlet temperature sensor for detecting the outlet refrigerant temperature of the refrigerant flowing out of the outdoor heat exchanger at the time, an inlet temperature sensor for detecting the inlet refrigerant temperature of the refrigerant flowing into the expansion valve during the cooling operation, and the outlet Set the target condensation temperature during cooling operation based on the temperature difference between the outlet refrigerant temperature detected by the temperature sensor and the inlet refrigerant temperature detected by the inlet temperature sensor, and based on the set target condensation temperature, the compression And a control device for controlling the compressor frequency of the machine.

As described above, according to the present invention, by changing the target condensation temperature according to the phase state of the refrigerant flowing into the expansion valve during the cooling operation, it is possible to reduce the power consumption while preventing the generation of noise. it can.

It is a schematic diagram showing an example of composition of an air harmony system concerning Embodiment 1. It is a functional block diagram which shows an example of a structure of the control apparatus of FIG. It is a flowchart which shows an example of the flow of the determination process of the target condensation temperature at the time of cooling operation. It is a schematic diagram showing an example of composition of a modification of an air harmony system concerning Embodiment 1. 5 is a schematic diagram showing an example of a configuration of an air conditioning system according to Embodiment 2. FIG. It is a functional block diagram which shows an example of a structure of the control apparatus of FIG. It is a flowchart which shows an example of the flow of the determination process of the target condensation temperature at the time of cooling operation. FIG. 9 is a schematic diagram showing an example of a configuration of an air conditioning system according to a third embodiment. It is a functional block diagram which shows an example of a structure of the control apparatus of FIG. It is a flowchart which shows an example of the flow of the determination process of the target condensation temperature at the time of cooling operation.

Embodiment 1.
Hereinafter, the air conditioning system according to Embodiment 1 of the present invention will be described. FIG. 1 is a schematic diagram showing an example of the configuration of an air conditioning system 100 according to the first embodiment. As shown in FIG. 1, the air conditioning system 100 includes an outdoor unit 1, indoor units 2A and 2B, and a control device 3. The outdoor unit 1 and the indoor units 2A and 2B are connected by connection pipes 4A and 4B.

Although two indoor units 2A and 2B are connected to the outdoor unit 1 in the example shown in FIG. 1, the invention is not limited to this, and one indoor unit or three or more indoor units may be connected. .. Also, a plurality of outdoor units 1 may be connected.

[Configuration of Air Conditioning System 100]
(Outdoor unit 1)
The outdoor unit 1 includes a compressor 11, a refrigerant flow switching device 12, an outdoor heat exchanger 13, an outdoor unit fan 14, and an accumulator 15.

The compressor 11 sucks a low-temperature low-pressure refrigerant, compresses the sucked refrigerant, and discharges a high-temperature high-pressure refrigerant. The compressor 11 is composed of, for example, an inverter compressor whose capacity, which is a delivery amount per unit time, is controlled by changing the compressor frequency. The compressor frequency of the compressor 11 is controlled by the control device 3.

The refrigerant channel switching device 12 is, for example, a four-way valve, and switches the cooling operation and the heating operation by switching the flowing direction of the refrigerant. The refrigerant flow switching device 12 switches to the state shown by the solid line in FIG. 1 during the cooling operation. Moreover, the refrigerant flow path switching device 12 switches to the state shown by the dotted line in FIG. 1 during the heating operation. Switching of the flow paths in the refrigerant flow path switching device 12 is controlled by the control device 3.

The outdoor heat exchanger 13 exchanges heat between the outdoor air and the refrigerant. The outdoor heat exchanger 13 functions as a condenser that radiates the heat of the refrigerant to the outdoor air and condenses the refrigerant during the cooling operation. Further, the outdoor heat exchanger 13 functions as an evaporator that evaporates the refrigerant during the heating operation and cools the outdoor air by the heat of vaporization at that time.

The outdoor unit fan 14 supplies outdoor air to the outdoor heat exchanger 13. The rotation speed of the outdoor unit fan 14 is controlled by the control device 3. By controlling the rotation speed, the amount of air blown to the outdoor heat exchanger 13 is adjusted.

The accumulator 15 is provided on the low pressure side which is the suction side of the compressor 11. The accumulator 15 stores the excess refrigerant generated due to the difference between the operation states of the cooling operation and the heating operation, or the excess refrigerant with respect to the transient change of the operation.

(Indoor units 2A and 2B)
The indoor unit 2A includes an indoor heat exchanger 21A, an expansion valve 22A, and an indoor unit fan 23A. The indoor unit 2B includes an indoor heat exchanger 21B, an expansion valve 22B and an indoor unit fan 23B. In the first embodiment, the indoor units 2A and 2B have the same configuration. Therefore, hereinafter, only the configuration of the indoor unit 2A will be described, and the description of the configuration of the indoor unit 2B will be omitted.

The indoor heat exchanger 21A exchanges heat between the air and the refrigerant. As a result, heating air or cooling air supplied to the indoor space is generated. The indoor heat exchanger 21A functions as an evaporator when the refrigerant carries cold heat during the cooling operation, and cools the air in the air-conditioned space to perform cooling. In addition, the indoor heat exchanger 21A functions as a condenser when the refrigerant carries hot heat during the heating operation, and heats the air in the air-conditioned space to perform heating.

The expansion valve 22A expands the refrigerant. The expansion valve 22A is composed of, for example, a valve such as an electronic expansion valve whose opening can be controlled. The opening degree of the expansion valve 22A is controlled by the control device 3 so that the refrigerant outlet temperature of the indoor heat exchanger 21A becomes optimum.

The indoor unit fan 23A supplies air to the indoor heat exchanger 21A. The rotation speed of the indoor unit fan 23A is controlled by the control device 3. By controlling the rotation speed, the amount of air blown to the indoor heat exchanger 21A is adjusted.

In the air conditioning system 100 according to Embodiment 1, the compressor 11, the refrigerant flow path switching device 12, the outdoor heat exchanger 13, the expansion valves 22A and 22B, and the indoor heat exchangers 21A and 21B are annularly connected by a refrigerant pipe. As a result, the refrigeration cycle is formed. An outlet temperature sensor 51 is provided on the refrigerant outlet side of the outdoor heat exchanger 13 during the cooling operation and on the refrigerant inlet side of the connection pipe 4A. An inlet temperature sensor 52 is provided on the refrigerant inlet side of the expansion valves 22A and 22B during the cooling operation and on the refrigerant outlet side of the connection pipe 4A.

The outlet temperature sensor 51 detects the outlet refrigerant temperature T1 on the refrigerant outlet side of the outdoor heat exchanger 13 during the cooling operation. The inlet temperature sensor 52 detects the inlet refrigerant temperature T2 on the refrigerant inlet side of the expansion valves 22A and 22B during the cooling operation.

(Control device 3)
The control device 3 determines the compressor frequency of the compressor 11, the opening degrees of the expansion valves 22A and 22B, the outdoor unit fan 14, and the indoor unit fan based on the detection results of various sensors provided in each part of the air conditioning system 100. Control the number of rotations of 23A and 23B. Particularly, the control device 3 controls the compressor 11 and the like so that the condensing temperature becomes the target condensing temperature during the cooling operation. Then, the control device 3 sets the target condensing temperature of the outdoor heat exchanger 13 based on the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52.

The control device 3 realizes various functions by executing software on an arithmetic device such as a microcomputer, or is configured by hardware such as a circuit device that realizes various functions. In this example, the control device 3 is provided outside the outdoor unit 1 and the indoor units 2A, 2B, but the present invention is not limited to this, and the control device 3 may be provided in any of the outdoor unit 1 and the indoor units 2A, 2B. Good.

FIG. 2 is a functional block diagram showing an example of the configuration of the control device 3 of FIG. As shown in FIG. 2, the control device 3 includes a minimum condensing temperature calculating unit 31, a condensing temperature comparing unit 32, a temperature difference calculating unit 33, a phase state determining unit 34, a condensing temperature changing unit 35, and a storage unit 36. There is.

The minimum condensing temperature calculation unit 31 calculates the minimum condensing temperature target value CT_min that satisfies the required heat radiation amount of the outdoor heat exchanger 13. The minimum condensing temperature target value CT_min is a condensing temperature required to satisfy the required heat radiation amount when the air volume of the outdoor unit fan 14 is maximized.

The condensation temperature comparison unit 32 compares the minimum condensation temperature target value CT_min calculated by the minimum condensation temperature calculation unit 31 with the target condensation temperature CT. The temperature difference calculator 33 calculates a temperature difference ΔT between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52.

The phase state determination unit 34 compares the temperature difference ΔT calculated by the temperature difference calculation unit 33 with the threshold value δ stored in the storage unit 36. The temperature difference ΔT indicates the temperature change of the refrigerant when passing through the connection pipe 4A. The phase state determination unit 34 determines the phase state of the refrigerant flowing into the expansion valves 22A and 22B based on the comparison result.

The condensation temperature changing unit 35 changes the target condensation temperature CT based on the comparison result by the condensation temperature comparison unit 32 and the comparison result by the phase state determination unit 34. Specifically, the condensing temperature changing unit 35 lowers the target condensing temperature CT based on the comparison result of the condensing temperature comparing unit 32, and raises the target condensing temperature CT based on the judgment result of the phase state determining unit 34. When changing the target condensing temperature CT, the condensing temperature changing unit 35 changes the target condensing temperature CT so as to increase or decrease the target condensing temperature CT by the change amount ΔCT stored in the storage unit 36.

The storage unit 36 stores parameters and the like used when processing is performed by each unit of the control device 3. For example, the storage unit 36 stores the change amount ΔCT of the target condensing temperature CT used by the condensing temperature changing unit 35. Further, the storage unit 36 stores the threshold value δ used in the phase state determination unit 34.

[Determination of target condensing temperature]
The process for determining the target condensing temperature will be described. In the first embodiment, the process of determining the target condensing temperature for the outdoor heat exchanger 13 is performed so that the refrigerant flowing into the expansion valves 22A and 22B is not in the gas-liquid two-phase state. In the following description, the case where the air conditioning system 100 performs the cooling operation is targeted.

First, the minimum condensing temperature calculation unit 31 of the control device 3 calculates the minimum condensing temperature target value CT_min in the air conditioning system 100. The minimum condensing temperature target value CT_min is calculated based on the equation (1). In the formula (1), “Q” indicates a necessary heat radiation amount. “OA” indicates the outside air temperature. “AK” indicates the AK value obtained by the product of the heat transfer area A [m ² ] of the outdoor heat exchanger 13 and the heat transmission rate K [W/m ² ·K]. “AK ₁ ”indicates an AK value at the maximum air volume of the outdoor unit fan 14.

Next, the condensation temperature comparison unit 32 compares the current target condensation temperature CT with the calculated minimum condensation temperature target value CT_min. When the condensation temperature comparing unit 32 determines that the target condensation temperature CT is higher than the minimum condensation temperature target value CT_min, the condensation temperature changing unit 35 prevents the target condensation temperature CT from falling below the minimum condensation temperature target value CT_min. The target condensing temperature CT is gradually decreased by the change amount ΔCT. The change amount ΔCT is the change amount of the target condensing temperature CT in one processing and is set in advance.

When the target condensation temperature CT is changed by the condensation temperature changing unit 35, the temperature difference calculating unit 33 determines the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52. The temperature difference ΔT (=T1−T2) is calculated. Then, the phase state determination unit 34 determines the phase state of the refrigerant flowing into the expansion valves 22A and 22B based on the temperature difference ΔT calculated by the temperature difference calculation unit 33.

Here, the refrigerant in the gas-liquid two-phase state has a larger temperature change due to the pressure change than in the liquid-phase state. Therefore, when the temperature difference ΔT is large, it can be considered that the refrigerant is in the gas-liquid two-phase state, and when the temperature difference ΔT is small, the refrigerant is in the liquid phase state. Therefore, when the temperature difference ΔT is larger than the preset threshold value δ, the phase state determination unit 34 determines that the phase state of the refrigerant is the gas-liquid two-phase state. When the temperature difference ΔT is equal to or less than the threshold δ, the phase state determination unit 34 determines that the phase state of the refrigerant is the liquid phase state. The threshold value δ is determined in advance based on the result of the temperature change with respect to the pressure change in each of the liquid phase state and the gas-liquid two phase state analyzed by the experiment or the like.

As a result of the determination by the phase state determination unit 34, when the temperature difference ΔT is equal to or less than the threshold value δ and the refrigerant is in the liquid phase state, the target condensing temperature CT is maintained in the state reduced by the change amount ΔCT. Then, the comparison by the condensation temperature comparison unit 32 and the change by the condensation temperature change unit 35 are performed again. On the other hand, when the temperature difference ΔT becomes larger than the threshold value δ and the phase state of the refrigerant changes from the liquid state to the gas-liquid two-phase state, the condensation temperature changing unit 35 adds the change amount ΔCT to the target condensation temperature CT, The target condensation temperature CT before the subtraction by the condensation temperature changing unit 35 is returned to. Then, the control device 3 controls the compressor frequency of the compressor 11 so that the condensation temperature of the outdoor heat exchanger 13 becomes the determined target condensation temperature.

FIG. 3 is a flowchart showing an example of the flow of a process for determining the target condensation temperature during the cooling operation. In step S1, the minimum condensing temperature calculation unit 31 calculates the minimum condensing temperature target value CT_min based on the equation (1).

In step S2, the condensation temperature comparison unit 32 compares the current target condensation temperature CT with the minimum condensation temperature target value CT_min calculated in step S1. As a result of the comparison, when it is determined that the target condensing temperature CT is the minimum condensing temperature target value CT_min or less (step S2; No), the current target condensing temperature CT is maintained.

On the other hand, when it is determined that the target condensing temperature CT is higher than the minimum condensing temperature target value CT_min (step S2; Yes), the condensing temperature changing unit 35 reads the change amount ΔCT from the storage unit 36 in step S3. Then, the condensing temperature changing unit 35 subtracts the read amount of change ΔCT from the target condensing temperature CT, and sets the subtracted value as the target condensing temperature CT.

Next, in step S4, the temperature difference calculation unit 33 calculates the temperature difference ΔT between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52. In step S5, the phase state determination unit 34 reads the threshold value δ for the temperature difference ΔT from the storage unit 36. The phase state determination unit 34 compares the refrigerant temperature difference ΔT calculated in step S4 with the read threshold δ to determine the phase state of the refrigerant flowing into the expansion valves 22A and 22B.

When the temperature difference ΔT is equal to or less than the threshold value δ as a result of the comparison (step S5; No), the phase state determination unit 34 determines that the refrigerant flowing into the expansion valves 22A and 22B is in the liquid state, and the process proceeds to step S2. Return. Then, the target condensing temperature CT decreases by the change amount ΔCT until the temperature difference ΔT becomes larger than the threshold value δ (steps S2 to S5).

When the temperature difference ΔT is larger than the threshold value δ (step S5; Yes), the phase state determination unit 34 determines that the refrigerant flowing into the expansion valves 22A and 22B is in the gas-liquid two-phase state. In step S6, the condensation temperature changing unit 35 reads the change amount ΔCT from the storage unit 36. Then, the condensing temperature changing unit 35 adds the change amount ΔCT read from the target condensing temperature CT, and sets the added value as the target condensing temperature CT. When the minimum condensing temperature target value CT_min is calculated again in step S1 and the target condensing temperature CT and the minimum condensing temperature target value CT_min are compared in step S2, the target condensing temperature CT is lower than the minimum condensing temperature target value CT_min. growing.

The processing from step S1 to step S6 is repeatedly performed according to preset conditions. The setting condition at this time is, for example, a case where the load fluctuates, such as a case where a fixed time has elapsed or a change value when the compressor frequency of the compressor 11 changes exceeds a set value.

As described above, in the first embodiment, the target condensation temperature CT is determined according to the phase state of the refrigerant flowing into the expansion valves 22A and 22B that is determined based on the temperature difference ΔT. As a result, the target condensation temperature can be lowered without confirming the magnitude of the pressure loss that differs depending on the pipe lengths of the connecting pipes 4A and 4B. Further, since the target condensing temperature is set so that the gas-liquid two-phase refrigerant does not flow into the expansion valves 22A and 22B, it is possible to suppress noise generation and reduce power consumption.

[Modification of Air Conditioning System 100]
FIG. 4 is a schematic diagram showing an example of a configuration of a modified example of the air conditioning system 100 according to the first embodiment. In the air conditioning system 100 according to the modified example, the outdoor unit 1 further includes a subcooling heat exchanger 16 and a second expansion valve 17 in addition to the configuration shown in FIG.

The supercooling heat exchanger 16 is provided to increase the degree of supercooling of the refrigerant that has passed through the outdoor heat exchanger 13. The supercooling heat exchanger 16 exchanges heat between the refrigerant flowing through the main circuit portion and the refrigerant flowing from the main circuit and flowing through the injection circuit connected to the accumulator 15. The second expansion valve 17 depressurizes the refrigerant flowing through the injection circuit branched from the main circuit.

The outlet temperature sensor 51 detects the temperature change based on the pressure loss due to the connecting pipe 4A when the refrigerant passes through the connecting pipe 4A. Therefore, the outlet temperature sensor 51 is on the refrigerant outlet side of the subcooling heat exchanger 16 during the cooling operation. Is provided on the refrigerant inlet side of the connection pipe 4A. The outlet temperature sensor 51 detects the outlet refrigerant temperature T1 on the refrigerant outlet side of the outdoor heat exchanger 13 during the cooling operation.

Even if the air conditioning system 100 further includes the subcooling heat exchanger 16, by providing the outlet temperature sensor 51 on the refrigerant outlet side of the subcooling heat exchanger 16, the air conditioning system shown in FIG. Similar to 100, the target condensing temperature determination process can be performed.

As described above, the air conditioning system 100 according to Embodiment 1 calculates the temperature difference ΔT between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52. To do. The target condensation temperature CT during the cooling operation is set based on the calculated temperature difference ΔT. Then, the compressor frequency of the compressor 11 is controlled based on the set target condensing temperature CT. As a result, the target condensation temperature CT is set so that the refrigerant in the gas-liquid two-phase state does not flow into the expansion valves 22A and 22B. Therefore, generation of noise due to the inflow of the gas-liquid two-phase refrigerant into the expansion valves 22A and 22B is suppressed, and power consumption can be reduced.

Further, in the air conditioning system 100, the temperature difference calculation unit 33 calculates the temperature difference ΔT between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52. Then, the phase state determination unit 34 determines that the phase state of the refrigerant is the gas-liquid two-phase state when the temperature difference ΔT is larger than the set threshold value δ, and when the temperature difference ΔT is the set threshold value δ or less, the refrigerant is It is determined that the phase state of is a liquid state. As a result, the phase state of the refrigerant flowing into the expansion valves 22A and 22B can be determined without recognizing the magnitude of the pressure loss due to the connecting pipe 4A.

When the condensing temperature changing unit 35 determines that the refrigerant is in the gas-liquid two-phase state, the target condensing temperature CT is set higher than the current value, and the target condensing temperature CT is lower than the minimum condensing temperature target value CT_min. Is higher, the target condensing temperature CT is made lower than the present value. As a result, the target condensing temperature CT is changed according to the phase state of the refrigerant flowing into the expansion valves 22A and 22B, so that power consumption can be reduced.

Embodiment 2.
Next, an air conditioning system according to Embodiment 2 of the present invention will be described. The second embodiment differs from the first embodiment in that an inlet temperature sensor 52 is provided on the refrigerant inlet side of the expansion valves 22A and 22B of each of the plurality of indoor units 2A and 2B.

[Configuration of Air Conditioning System 200]
FIG. 5 is a schematic diagram showing an example of the configuration of the air conditioning system 200 according to the second embodiment. In the following description, parts common to those of the air conditioning system 100 according to Embodiment 1 will be assigned the same reference numerals and detailed description thereof will be omitted. As shown in FIG. 5, the air conditioning system 200 includes an outdoor unit 1, indoor units 202A and 202B, and a control device 203.

(Indoor units 202A and 202B)
The indoor unit 202A includes an indoor heat exchanger 21A, an expansion valve 22A, an indoor unit fan 23A, and an inlet temperature sensor 52A. The inlet temperature sensor 52A detects an inlet refrigerant temperature T2A on the refrigerant inlet side of the expansion valve 22A during the cooling operation. The indoor unit 202B includes an indoor heat exchanger 21B, an expansion valve 22B, an indoor unit fan 23B, and an inlet temperature sensor 52B. The inlet temperature sensor 52B detects the inlet refrigerant temperature T2B on the refrigerant inlet side of the expansion valve 22B during the cooling operation.

(Control device 203)
FIG. 6 is a functional block diagram showing an example of the configuration of the control device 203 of FIG. As shown in FIG. 6, the control device 203 includes a minimum condensing temperature calculating unit 31, a condensing temperature comparing unit 32, a temperature difference calculating unit 233, a phase state determining unit 234, a condensing temperature changing unit 35, and a storage unit 36. There is.

The temperature difference calculation unit 233 calculates a temperature difference ΔT _A between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2A detected by the inlet temperature sensor 52A. Further, the temperature difference calculation unit 233 calculates the temperature difference ΔT _B between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2B detected by the inlet temperature sensor 52B.

The phase state determination unit 234 compares the temperature difference ΔT _A calculated by the temperature difference calculation unit 233 with the threshold value δ, and also compares the temperature difference ΔT _B calculated by the temperature difference calculation unit 233 with the threshold value δ. The phase state determination unit 234 determines the phase state of the refrigerant flowing into each of the expansion valves 22A and 22B based on the comparison result.

[Determination of target condensing temperature]
The process for determining the target condensing temperature will be described. FIG. 7 is a flowchart showing an example of the flow of a process for determining the target condensation temperature during the cooling operation. The processes from step S1 to step S3 are the same as those in the first embodiment shown in FIG.

In step S14, the temperature difference calculation unit 233 calculates the temperature difference ΔT _A between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2A detected by the inlet temperature sensor 52A. Further, the temperature difference calculation unit 233 calculates the temperature difference ΔT _B between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2B detected by the inlet temperature sensor 52B.

In step S15, the phase state determination unit 234 reads the threshold value δ from the storage unit 36. The phase state determination unit 234 compares the temperature differences ΔT _A and ΔT _{B of} the refrigerant calculated in step S14 with the read threshold value δ, respectively, and determines the phase state of the refrigerant flowing into the expansion valves 22A and 22B.

As a result of the comparison, when both the temperature differences ΔT _A and ΔT _B are equal to or less than the threshold value δ (step S15; No), the phase state determination unit 34 determines that the refrigerant flowing into each of the expansion valves 22A and 22B is in the liquid state. The determination is made, and the process returns to step S2. Then, the target condensing temperature CT decreases by the change amount ΔCT until at least one of the temperature differences ΔT _A and ΔT _B becomes larger than the threshold value δ (step S2 to step S15).

When at least one of the temperature differences ΔT _A and ΔT _B is larger than the threshold value δ (step S15; Yes), the phase state determination unit 234 determines that at least one of the refrigerants flowing into the expansion valves 22A and 22B is gas-liquid two-phase. It is determined to be in a state. Then, in step S6, the condensation temperature changing unit 35 adds the change amount ΔCT from the target condensation temperature CT, and sets the added value as the target condensation temperature CT.

As described above, in the air conditioning system 200 according to Embodiment 2, the temperature difference calculation unit 233 causes the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the outlet refrigerant temperature T1A detected by the inlet temperature sensor 52A. The temperature difference ΔT _A between Further, the temperature difference calculation unit 233 calculates a temperature difference ΔT _B between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the outlet refrigerant temperature T1B detected by the inlet temperature sensor 52B. Then, the phase state determination unit 234 determines the phase state of the refrigerant flowing into each of the plurality of expansion valves 22A and 22B based on the temperature differences ΔT _A and ΔT _B. As a result, the phase state of the refrigerant flowing into each of the expansion valves 22A and 22B can be determined without recognizing the magnitude of the pressure loss due to the connecting pipe 4A.

Further, in the air conditioning system 200, when the condensation temperature changing unit 35 determines that the phase state of at least one of the refrigerant flowing into each of the plurality of expansion valves 22A and 22B is the gas-liquid two-phase state. Moreover, the target condensing temperature CT is made higher than the current value. Further, when the target condensing temperature CT is higher than the minimum condensing temperature target value CT_min, the target condensing temperature CT is made lower than the current value. As a result, the target condensing temperature CT is changed according to the phase state of the refrigerant flowing into the expansion valves 22A and 22B, so that power consumption can be reduced.

Embodiment 3.
Next, an air conditioning system according to Embodiment 3 of the present invention will be described. In the third embodiment, the compressor frequency of the compressor 11, the condensing temperature of the outdoor heat exchanger 13, and the phase state of the refrigerant flowing into the expansion valves 22A and 22B are learned in association with each other, and the target is obtained based on the learning result. Determine the condensation temperature.

[Configuration of Air Conditioning System 300]
FIG. 8 is a schematic diagram showing an example of the configuration of the air conditioning system 300 according to the third embodiment. In the following description, parts common to the air conditioning systems 100 and 200 are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 8, the air conditioning system 300 includes an outdoor unit 1, indoor units 2A and 2B, and a control device 303.

(Control device 303)
The control device 303 determines the phase state of the refrigerant flowing into the expansion valves 22A and 22B during the cooling operation based on the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52. judge. The control device 303 controls the target condensing temperature of the outdoor heat exchanger 13 based on the determined phase state and the compressor frequency of the compressor 11.

FIG. 9 is a functional block diagram showing an example of the configuration of the control device 303 of FIG. As shown in FIG. 9, the control device 303 includes a compressor frequency acquisition unit 331, a temperature difference calculation unit 33, a phase state determination unit 334, a condensation temperature changing unit 335, and a storage unit 336.

The compressor frequency acquisition unit 331 acquires the compressor frequency of the compressor 11. The compressor frequency acquisition unit 331 supplies the acquired compressor frequency to the condensation temperature changing unit 335 and the storage unit 336.

The phase state determination unit 334 compares the temperature difference ΔT calculated by the temperature difference calculation unit 33 with the threshold value δ. The phase state determination unit 334 determines the phase state of the refrigerant flowing into the expansion valves 22A and 22B based on the comparison result. The phase state determination unit 334 supplies the phase state information indicating the determined phase state to the storage unit 336.

The storage unit 336 stores parameters such as a threshold value δ used when each unit of the control device 303 performs processing. Further, the storage unit 336 stores a table in which the compressor frequency supplied from the compressor frequency acquisition unit 331, the phase state information supplied from the phase state determination unit 334, and the condensing temperature are associated by learning. ..

The condensation temperature changing unit 335 refers to the table stored in the storage unit 336 based on the compressor frequency supplied from the compressor frequency acquisition unit 331. Then, the condensing temperature changing unit 335 searches the condensing temperature associated with the acquired compressor frequency so that the phase state of the refrigerant becomes the liquid phase state, and the obtained condensing temperature is the target condensing temperature. The target condensing temperature CT is changed to CT.

[Determination of target condensing temperature]
The process for determining the target condensing temperature will be described. FIG. 10 is a flowchart showing an example of the flow of a process for determining the target condensation temperature during the cooling operation. In step S21, the compressor frequency acquisition unit 331 acquires the compressor frequency of the compressor 11. The acquired compressor frequency is supplied to the condensing temperature changing unit 335 and the storage unit 336. In step S22, the temperature difference calculation unit 33 calculates the temperature difference ΔT between the outlet refrigerant temperature T1 detected by the outlet temperature sensor 51 and the inlet refrigerant temperature T2 detected by the inlet temperature sensor 52.

In step S23, the phase state determination unit 334 reads the threshold value δ from the storage unit 36. The phase state determination unit 334 compares the refrigerant temperature difference ΔT calculated in step S22 with the read threshold value δ to determine the phase state of the refrigerant flowing into the expansion valves 22A and 22B. The phase state information obtained by the determination is supplied to the condensation temperature changing unit 335 and the storage unit 336.

In step S24, the storage unit 336 stores the supplied compressor frequency, condensing temperature, and phase state information in association with each other as a table. Compressor frequency, condensing temperature, and phase state information are stored in the table one by one by learning.

In step S25, the condensation temperature changing unit 335 refers to the table stored in the storage unit 336. Then, the condensing temperature changing unit 335 searches the condensing temperature associated with the supplied compressor frequency for a condensing temperature at which the phase state of the refrigerant becomes the liquid phase state. In step S26, the condensing temperature changing unit 335 determines the target condensing temperature CT so that the condensing temperature obtained by the search is the target condensing temperature CT.

The target condensing temperature determination process according to the third embodiment can be combined with the air conditioning system 200 according to the second embodiment described above.

As described above, in the air conditioning system 300 according to the third embodiment, among the condensation temperatures corresponding to the acquired compressor frequency, the condensation temperature at which the phase state of the refrigerant becomes the liquid state is the target condensation temperature CT. .. As a result, when the compressor frequency is acquired, the target condensing temperature CT at which the phase state of the refrigerant flowing into the expansion valves 22A and 22B becomes the liquid phase state is set. Therefore, the condensation temperature can be changed without the refrigerant in the gas-liquid two-phase state flowing through the expansion valves 22A and 22B.

1 outdoor unit, 2A, 2B, 202A, 202B indoor unit, 3, 203, 303 control device, 4A, 4B connection piping, 11 compressor, 12 refrigerant flow path switching device, 13 outdoor heat exchanger, 14 outdoor unit fan, 15 Accumulator, 16 Supercooling heat exchanger, 17 2nd expansion valve, 21A, 21B Indoor heat exchanger, 22A, 22B Expansion valve, 23A, 23B Indoor unit fan, 31 Minimum condensation temperature calculation part, 32 Condensation temperature comparison part , 33, 233 Temperature difference calculation unit, 34, 234, 334 Phase state determination unit, 35, 335 Condensation temperature change unit, 36, 336 Storage unit, 51 Outlet temperature sensor, 52, 52A, 52B Inlet temperature sensor, 100, 200 , 300 Air conditioning system, 331 Compressor frequency acquisition unit.

Claims (6)

An air conditioning system in which an indoor unit including a compressor and an outdoor heat exchanger, and an outdoor unit including an expansion valve and an indoor heat exchanger are connected by a connecting pipe,
An outlet temperature sensor for detecting the outlet refrigerant temperature of the refrigerant flowing out of the outdoor heat exchanger during the cooling operation,
An inlet temperature sensor for detecting the inlet refrigerant temperature of the refrigerant flowing into the expansion valve during the cooling operation,
Set the target condensation temperature during cooling operation based on the temperature difference between the outlet refrigerant temperature detected by the outlet temperature sensor and the inlet refrigerant temperature detected by the inlet temperature sensor, based on the set target condensation temperature, An air conditioning system comprising: a controller that controls a compressor frequency of the compressor. The control device is
A temperature difference calculator that calculates a temperature difference between the refrigerant temperature detected by the outlet temperature sensor and the refrigerant temperature detected by the inlet temperature sensor,
Based on the calculated temperature difference, having a phase state determination unit that determines the phase state of the refrigerant flowing into the expansion valve,
The phase state determination unit,
If the temperature difference is greater than a set threshold, it is determined that the refrigerant phase state is a gas-liquid two-phase state,
The air conditioning system according to claim 1, wherein the phase state of the refrigerant is determined to be a liquid phase state when the temperature difference is equal to or less than the set threshold. The control device is
A condensing temperature comparison unit that compares the target condensing temperature and the minimum condensing temperature target value,
Based on the phase state of the refrigerant and the target condensation temperature, further having a condensation temperature changing unit for changing the target condensation temperature,
The condensing temperature changing unit,
When the phase state of the refrigerant is determined to be a gas-liquid two-phase state, the target condensation temperature is higher than the current value,
The air conditioning system according to claim 2, wherein when the target condensing temperature is higher than the minimum condensing temperature target value, the target condensing temperature is made lower than the current value. The control device is
A storage unit that stores the phase state, the compressor frequency of the compressor, and the condensing temperature in association with each other;
The air conditioning system according to claim 2, wherein, of the obtained condensation temperatures corresponding to the compressor frequency, a condensation temperature at which a refrigerant phase state is a liquid phase state is set as the target condensation temperature. A plurality of the outdoor units,
The inlet temperature sensor is provided on the refrigerant inlet side of the expansion valve provided in each of the plurality of outdoor units,
The temperature difference calculation unit,
The temperature difference between the refrigerant temperature detected by the outlet temperature sensor and the refrigerant temperature detected by each inlet temperature sensor is calculated,
The phase state determination unit,
The air conditioning system according to claim 2, wherein the phase state of the refrigerant flowing into each of the plurality of expansion valves is determined based on the plurality of calculated temperature differences. The control device is
A condensing temperature comparison unit that compares the target condensing temperature and the minimum condensing temperature target value,
Based on the phase state of the refrigerant and the target condensation temperature, further having a condensation temperature changing unit for changing the target condensation temperature,
The condensing temperature changing unit,
When it is determined that the phase state of at least one refrigerant in the refrigerant flowing into each of the plurality of expansion valves is a gas-liquid two-phase state, the target condensation temperature is higher than the current value,
The air conditioning system according to claim 5, wherein when the target condensing temperature is higher than the minimum condensing temperature target value, the target condensing temperature is made lower than the current value.

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