JP5332093B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus, and more particularly to a refrigeration apparatus in which a refrigerant enters a supercritical state during a refrigeration cycle.

Conventionally, a refrigeration apparatus including a refrigerant circuit in which a compressor, a radiator, a first expansion valve, a liquid receiver, a second expansion valve, and an evaporator are sequentially connected is publicly known (see, for example, Patent Document 1). .
JP-A-10-115470 (page 4, column 5, line 12-page 5, column 7, line 39, FIG. 3)

  When a supercritical refrigerant such as carbon dioxide is employed as the refrigerant in the refrigerant circuit of such a refrigeration apparatus, the refrigerant flows from the refrigerant discharge side of the compressor to the refrigerant inflow side of the first expansion valve (hereinafter referred to as a high-pressure side refrigerant). May become a subcritical state from the start of operation, or when the temperature of the refrigerant flowing into the radiator is low, the high-pressure side refrigerant may transition from the supercritical state to the subcritical state. In the situation where the high-pressure side refrigerant is in the subcritical state, when the supercooling of the refrigerant flowing out from the radiator is insufficient, the refrigerant flowing out from the first expansion valve becomes a gas-liquid two-phase state. Therefore, it is difficult to control the liquid level of the liquid receiver.

  An object of the present invention is to enable stable liquid level control of a liquid receiver even when the high-pressure side refrigerant is in a subcritical state in the refrigeration apparatus as described above.

The refrigeration apparatus according to the first invention includes a compression mechanism, a radiator, a first expansion mechanism, a liquid receiver, a second expansion mechanism, an evaporator, a control unit, a first temperature detection unit, and a second temperature detection unit. The compression mechanism compresses the refrigerant. The radiator is connected to the refrigerant discharge side of the compression mechanism. The first expansion mechanism is connected to the outlet side of the radiator. The liquid receiver is connected to the refrigerant outflow side of the first expansion mechanism. The second expansion mechanism is connected to the outlet side of the liquid receiver. The evaporator is connected to the refrigerant outflow side of the second expansion mechanism and to the refrigerant suction side of the compression mechanism. When the state of the refrigerant flowing from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism (hereinafter referred to as a high-pressure side refrigerant) transitions from the supercritical state to the subcritical state, the control unit uses the first expansion mechanism. Minimize the degree of decompression. A 1st temperature detection part is provided in the 1st specific area | region of a heat radiator. Here, the “first specific region” is a region where the high-pressure side refrigerant is in a gas-liquid two-phase state when the high-pressure side refrigerant transitions to the subcritical state. The second temperature detection unit is provided in the first specific region of the radiator. The control unit controls the first electric expansion valve and the second electric expansion valve so that the refrigerant flowing out of the first expansion mechanism is saturated when the high-pressure side refrigerant is in a supercritical state. Perform liquid level control. In addition, when the difference between the temperature detected by the first temperature detection unit and the temperature detected by the second temperature detection unit is equal to or less than a predetermined threshold , the control unit makes a transition to the subcritical state. And the second liquid receiver liquid level control is performed so that the degree of decompression by the first expansion mechanism is minimized and the refrigerant flowing out of the first expansion mechanism is saturated .

In this refrigeration apparatus, the control unit minimizes the degree of decompression by the first expansion mechanism when the state of the high-pressure side refrigerant changes from the supercritical state to the subcritical state. Therefore, in this refrigeration system, the refrigerant high-pressure side refrigerant flows out from the transition and also the first expansion mechanism from the supercritical state to a subcritical state may be saturated. Therefore, in this refrigeration apparatus, even if a high-pressure refrigerant transits from a supercritical state to a subcritical state by selecting an appropriate expansion mechanism (an expansion valve having an appropriate maximum opening in the case of an expansion valve), The refrigerant flowing out from the first expansion mechanism can be brought into a state close to saturation. Therefore, in this refrigeration apparatus, stable liquid level control of the receiver is possible even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state.

  Further, in this refrigeration apparatus, when the difference between the temperature detected by the first temperature detection unit and the temperature detected by the second temperature detection unit is equal to or less than a predetermined threshold value, the control unit uses the first expansion mechanism. Minimize the degree of decompression. For this reason, in this refrigeration apparatus, it can be easily determined whether or not the high-pressure side refrigerant is in a subcritical state.

  A refrigeration apparatus according to a second aspect of the present invention is the refrigeration apparatus according to the first aspect of the present invention, wherein the first expansion mechanism is a first expansion valve. Then, the control unit fully opens the first expansion valve when the state of the refrigerant flowing from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism transitions from the supercritical state to the subcritical state.

  In this refrigeration apparatus, the control unit fully opens the first expansion valve when the state of the refrigerant flowing from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism transitions from the supercritical state to the subcritical state. . For this reason, in this refrigeration apparatus, the refrigerant flowing out of the first expansion valve can be brought close to the saturated state even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state. Therefore, in this refrigeration system, if an expansion valve having an appropriate maximum opening is selected as the first expansion valve, the high-pressure refrigerant flows out of the first expansion mechanism even when the refrigerant transitions from the supercritical state to the subcritical state. The refrigerant to be made can be brought into a state close to saturation. Therefore, in this refrigeration apparatus, stable liquid level control of the receiver is possible even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state.

A refrigeration apparatus according to a third aspect includes a compression mechanism, a radiator, a first expansion mechanism, a liquid receiver, a second expansion mechanism, an evaporator, a control unit, and a third temperature detection unit. The compression mechanism compresses the refrigerant. The radiator is connected to the refrigerant discharge side of the compression mechanism. The first expansion mechanism is connected to the outlet side of the radiator. The liquid receiver is connected to the refrigerant outflow side of the first expansion mechanism. The second expansion mechanism is connected to the outlet side of the liquid receiver. The evaporator is connected to the refrigerant outflow side of the second expansion mechanism and to the refrigerant suction side of the compression mechanism. When the state of the refrigerant flowing from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism (hereinafter referred to as a high-pressure side refrigerant) transitions from the supercritical state to the subcritical state, the control unit uses the first expansion mechanism. Minimize the degree of decompression. The third temperature detector is provided in the second specific region of the radiator. Here, the “second specific region” refers to a region where the high-pressure side refrigerant is not below the critical point temperature when the high-pressure side refrigerant is in the supercritical state and the high-pressure side refrigerant is in the subcritical state. This is the region where the high-pressure side refrigerant reaches the saturation temperature. The control unit controls the first electric expansion valve and the second electric expansion valve so that the refrigerant flowing out of the first expansion mechanism is saturated when the high-pressure side refrigerant is in a supercritical state. Perform liquid level control. In addition, the control unit determines that the high-pressure side refrigerant has transitioned to the subcritical state when the temperature detected by the third temperature detection unit is equal to or lower than the critical point temperature of the refrigerant, and reduces the decompression by the first expansion mechanism. Second liquid receiver liquid level control is performed to minimize the degree and to saturate the refrigerant flowing out of the first expansion mechanism .

  In this refrigeration apparatus, the control unit minimizes the degree of decompression by the first expansion mechanism when the state of the high-pressure side refrigerant changes from the supercritical state to the subcritical state. For this reason, in this refrigeration apparatus, the refrigerant flowing out of the first expansion mechanism can be saturated even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state. Therefore, in this refrigeration apparatus, even if a high-pressure refrigerant transits from a supercritical state to a subcritical state by selecting an appropriate expansion mechanism (an expansion valve having an appropriate maximum opening in the case of an expansion valve), The refrigerant flowing out from the first expansion mechanism can be brought into a state close to saturation. Therefore, in this refrigeration apparatus, stable liquid level control of the receiver is possible even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state.

  Further, in this refrigeration apparatus, when the temperature detected by the third temperature detection unit becomes equal to or lower than the critical point temperature of the refrigerant, the control unit minimizes the degree of decompression by the first expansion mechanism. For this reason, in this refrigeration apparatus, it can be easily determined whether or not the high-pressure side refrigerant is in a subcritical state.

  A refrigeration apparatus according to a fourth aspect is the refrigeration apparatus according to the third aspect, wherein the first expansion mechanism is a first expansion valve. And a control part fully opens a 1st expansion valve, when the temperature detected by the 3rd temperature detection part becomes below the critical point temperature of a refrigerant | coolant.

  In this refrigeration apparatus, when the temperature detected by the third temperature detection unit becomes equal to or lower than the critical point temperature of the refrigerant, the control unit fully opens the first expansion valve. For this reason, in this refrigeration apparatus, it can be easily determined whether or not the high-pressure side refrigerant is in a subcritical state.

  In the refrigeration apparatus according to the first invention, the refrigerant flowing out of the first expansion mechanism can be brought close to the saturated state even when the high-pressure side refrigerant transits from the supercritical state to the subcritical state. Therefore, in this refrigeration apparatus, even if a high-pressure refrigerant transits from a supercritical state to a subcritical state by selecting an appropriate expansion mechanism (an expansion valve having an appropriate maximum opening in the case of an expansion valve), The refrigerant flowing out from the first expansion mechanism can be saturated. Therefore, in this refrigeration apparatus, stable liquid level control of the receiver is possible even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state. Further, when the difference between the temperature detected by the first temperature detection unit and the temperature detected by the second temperature detection unit is equal to or less than a predetermined threshold, the control unit minimizes the degree of decompression by the first expansion mechanism. To. For this reason, in this refrigeration apparatus, it can be easily determined whether or not the high-pressure side refrigerant is in a subcritical state.

  In the refrigeration apparatus according to the second aspect of the invention, the refrigerant flowing out of the first expansion valve can be brought close to the saturated state even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state. Therefore, in this refrigeration system, if an expansion valve having an appropriate maximum opening is selected as the first expansion valve, the high-pressure refrigerant flows out of the first expansion mechanism even when the refrigerant transitions from the supercritical state to the subcritical state. The refrigerant to be made can be brought into a state close to saturation. Therefore, in this refrigeration apparatus, stable liquid level control of the receiver is possible even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state.

  In the refrigeration apparatus according to the third aspect of the invention, the refrigerant flowing out of the first expansion mechanism can be brought close to the saturated state even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state. Therefore, in this refrigeration apparatus, even if a high-pressure refrigerant transits from a supercritical state to a subcritical state by selecting an appropriate expansion mechanism (an expansion valve having an appropriate maximum opening in the case of an expansion valve), The refrigerant flowing out from the first expansion mechanism can be saturated. Therefore, in this refrigeration apparatus, stable liquid level control of the receiver is possible even when the high-pressure side refrigerant transitions from the supercritical state to the subcritical state. Further, when the temperature detected by the third temperature detection unit becomes equal to or lower than the critical point temperature of the refrigerant, the control unit minimizes the degree of pressure reduction by the first expansion mechanism. For this reason, in this refrigeration apparatus, it can be easily determined whether or not the high-pressure side refrigerant is in a subcritical state.

<Configuration of air conditioner>
A schematic refrigerant circuit 2 of an air-conditioning apparatus 1 according to an embodiment of the present invention is shown in FIG.

  This air conditioner 1 is an air conditioner that can perform cooling operation and heating operation using carbon dioxide as a refrigerant. The air conditioner 1 mainly includes a refrigerant circuit 2, blower fans 26 and 32, a control device 23, a high pressure sensor 21, an intermediate pressure. It consists of a pressure sensor 24, a temperature sensor 22, and the like.

  The refrigerant circuit 2 mainly includes a compressor 11, a four-way switching valve 12, an outdoor heat exchanger 13, a first electric expansion valve 15, a liquid receiver 16, a second electric expansion valve 17, and an indoor heat exchanger 31. As shown in FIG. 1, each apparatus is connected via a refrigerant pipe.

  And in this Embodiment, the air conditioning apparatus 1 is a separation-type air conditioning apparatus, Comprising: The indoor unit 30 which mainly has the indoor heat exchanger 31 and the indoor fan 32, the compressor 11, and a four-way switching valve 12, the outdoor heat exchanger 13, the first electric expansion valve 15, the liquid receiver 16, the second electric expansion valve 17, the high pressure sensor 21, the temperature sensor 22, and the outdoor unit 10 mainly including the control device 23, A first connection pipe 41 that connects the refrigerant liquid pipe of the unit 30 and the refrigerant liquid pipe of the outdoor unit 10, and a second connection pipe that connects the refrigerant gas pipe of the indoor unit 30 and the refrigerant gas pipe of the outdoor unit 10. It can be said that it is composed of the communication pipe 42. The refrigerant liquid piping of the outdoor unit 10 and the first communication pipe 41 are connected via the first shut-off valve 18 of the outdoor unit 10, and the refrigerant gas piping and the second communication pipe 42 of the outdoor unit 10 are connected to the outdoor unit 10. The second closing valves 19 are connected to each other.

(1) Indoor unit The indoor unit 30 mainly includes an indoor heat exchanger 31 and an indoor fan 32.

  The indoor heat exchanger 31 is a heat exchanger for exchanging heat between indoor air, which is air in an air-conditioned room, and a refrigerant.

  The indoor fan 32 is a fan for taking in the air in the air-conditioned room into the unit 30 and sending out conditioned air, which is air after heat exchange with the refrigerant via the indoor heat exchanger 31, to the air-conditioned room again.

  By adopting such a configuration, the indoor unit 30 exchanges heat between the indoor air taken in by the indoor fan 32 and the liquid refrigerant flowing through the indoor heat exchanger 31 during the cooling operation, thereby conditioned air ( It is possible to generate conditioned air (warm air) by exchanging heat between the indoor air taken in by the indoor fan 32 and the supercritical refrigerant flowing through the indoor heat exchanger 31 during heating operation. Yes.

(2) Outdoor unit The outdoor unit 10 mainly includes a compressor 11, a four-way switching valve 12, an outdoor heat exchanger 13, a first electric expansion valve 15, a liquid receiver 16, a second electric expansion valve 17, and an outdoor fan. 26, a control device 23, a high pressure sensor 21, an intermediate pressure sensor 24, a temperature sensor 22, and the like.

  The compressor 11 is a device for sucking low-pressure gas refrigerant flowing through the suction pipe, compressing it into a supercritical state, and then discharging it to the discharge pipe.

  The four-way switching valve 12 is a valve for switching the flow direction of the refrigerant corresponding to each operation. During the cooling operation, the four-way switching valve 12 connects the discharge side of the compressor 11 and the high temperature side of the outdoor heat exchanger 13 and compresses them. The suction side of the compressor 11 and the gas side of the indoor heat exchanger 31 are connected, and during the heating operation, the discharge side of the compressor 11 and the second shut-off valve 19 are connected and the suction side of the compressor 11 and the outdoor heat exchanger are connected. 13 gas sides can be connected.

  The outdoor heat exchanger 13 can cool the high-pressure supercritical refrigerant discharged from the compressor 11 during the cooling operation using air outside the air conditioning room as a heat source, and the liquid returned from the indoor heat exchanger 31 during the heating operation. It is possible to evaporate the refrigerant.

  The first electric expansion valve 15 is for reducing the pressure of supercritical refrigerant (at the time of cooling operation) flowing out from the low temperature side of the outdoor heat exchanger 13 or liquid refrigerant (at the time of heating operation) flowing in through the receiver 16. It is.

  The liquid receiver 16 is for storing a surplus refrigerant according to the operation mode and the air conditioning load.

  The second electric expansion valve 17 depressurizes the liquid refrigerant flowing through the liquid receiver 16 (during cooling operation) or supercritical refrigerant flowing out from the low temperature side of the indoor heat exchanger 31 (during heating operation). belongs to.

  The outdoor fan 26 is a fan for taking in outdoor air into the unit 10 and exhausting the air after exchanging heat with the refrigerant via the outdoor heat exchanger 13.

  The high pressure sensor 21 is provided on the discharge side of the compressor 11.

  The temperature sensor 22 is provided on the outdoor heat exchanger side of the first electric expansion valve 15.

  The intermediate pressure sensor 24 is provided between the first electric expansion valve 15 and the liquid receiver 16.

  The control device 23 is communicatively connected to the high pressure sensor 21, the intermediate pressure sensor 24, the temperature sensor 22, the first electric expansion valve 15, the second electric expansion valve 17, and the like, and is sent from the temperature sensor 22. The opening degree of the first electric expansion valve 15 and the second electric expansion valve 17 based on the temperature information, the high pressure information sent from the high pressure sensor 21, and the intermediate pressure information sent from the intermediate pressure sensor 24. To control. Here, the opening control of the first electric expansion valve 15 and the second electric expansion valve 17 will be described in detail using the Mollier diagram.

When the high-pressure information transmitted from the high-pressure sensor 21 is equal to or higher than the critical pressure, the control device 23 is a refrigerant that flows from the refrigerant discharge side of the compressor 11 to the refrigerant inflow side of the first electric expansion valve 15 (hereinafter, high pressure). 1st receiver liquid level control and superheat degree control are performed. In the air conditioner 1 according to the present embodiment, the high pressure sensor 21 is disposed on the discharge side of the compressor 11 and the temperature sensor 22 is disposed on the outdoor heat exchanger side of the first electric expansion valve 15. The saturation pressure of the refrigerant flowing out from the first electric expansion valve 15 can be obtained using (see FIG. 2). Therefore, in this air conditioner 1, during the first liquid receiver liquid level control, the control device 23 causes the refrigerant flowing out of the first electric expansion valve 15 to be in the state of the point D _{0 in} FIG. The opening degrees of the first electric expansion valve 15 and the second electric expansion valve 17 are adjusted as appropriate so that the value indicated by the intermediate pressure sensor 24 matches the saturation pressure obtained above. In FIG. 2, A ₀ → B ₀ indicates a compression stroke, B ₀ → C ₀ indicates a cooling stroke, and C ₀ → D ₀ indicates a first expansion stroke (pressure reduction by the first electric expansion valve 15). D ₀ → E ₀ indicates the second expansion stroke (pressure reduction by the second electric expansion valve 17), and E ₀ → A ₀ indicates the evaporation stroke. K represents a critical point, and Tm represents an isotherm. At this time, since the superheat degree control is also performed at the same time, the control device 23 also controls the opening degree of the second electric expansion valve 17. In the present embodiment, the control device 23 uses the first electric expansion valve 15 and the pressure control device 24 so that the pressure indicated by the intermediate pressure sensor 24 is equal to or lower than the pressure of {critical pressure (MPa) -0.3 (MPa)}. The second electric expansion valve 17 is controlled. Here, the pressure of {critical pressure (MPa) -0.3 (MPa)} is determined as follows. From the result of the test conducted by the inventors, the pressure between the first electric expansion valve 15 and the second electric expansion valve 17 (hereinafter referred to as intermediate pressure) is controlled within ± 0.1 MPa from the target value in the case of refrigerant. It has become clear that it can be controlled within a range. In order to prevent the intermediate pressure from being close to the critical point, it is preferable that the safety factor is 3, and the target value of the intermediate pressure is critical pressure (MPa) −0.3 (MPa).

Then, here, when the high-pressure side refrigerant is in a subcritical state, the control device 23 performs the second liquid receiver liquid level control simultaneously with the superheat degree control. When the high-pressure side refrigerant enters the subcritical state, the refrigeration cycle becomes a refrigeration cycle as shown by a solid line in FIG. 3 is a refrigeration cycle shown in FIG. 2, that is, a refrigeration cycle when the high-pressure refrigerant is in a supercritical state. As is apparent from FIG. 3, when the high-pressure side refrigerant is in a subcritical state, the pressure is significantly reduced. In this state, when the control device 23 requests the first electric expansion valve 15 to have the same opening degree as that during the first receiver liquid level control, the refrigeration cycle is A ₀ → B ₁ → C ₁ → D ₁ → From E _{0 to} A ₀ , the refrigerant flowing out of the first electric expansion valve 15 enters a gas-liquid two-phase state, and the liquid level of the stored refrigerant in the liquid receiver 16 cannot be stabilized substantially. Therefore, when the high-pressure information transmitted from the high-pressure sensor 21 becomes less than the critical pressure, that is, when the high-pressure side refrigerant is in the subcritical state, the control device 23 opens the first electric expansion valve 15 in the fully open state. The second liquid receiver liquid level control is performed. Then, the refrigeration cycle is a refrigeration cycle indicated by a solid line in FIG. Note that the refrigeration cycle indicated by a broken line in FIG. 4 is the refrigeration cycle shown in FIG. 2, that is, the refrigeration cycle when the high-pressure side refrigerant is in a supercritical state. That is, since the refrigeration cycle is A ₀ → B ₀ → C ₀ → C ₁ → D ₂ → E ₀ → A ₀ , the refrigerant flowing out from the first electric expansion valve 15 is in a state close to saturation. In the air conditioner 1, such stable liquid receiver liquid level control is realized during the cooling operation.

<Operation of air conditioner>
The operation of the air conditioner 1 will be described with reference to FIG. As described above, the air conditioner 1 can perform a cooling operation and a heating operation.

(1) Cooling operation During the cooling operation, the four-way switching valve 12 is in the state indicated by the solid line in FIG. 1, that is, the discharge side of the compressor 11 is connected to the high temperature side of the outdoor heat exchanger 13, and the compressor 11 The suction side is connected to the second closing valve 19. At this time, the first closing valve 18 and the second closing valve 19 are opened.

  When the compressor 11 is started in the state of the refrigerant circuit 2, the gas refrigerant is sucked into the compressor 11 and compressed to become a supercritical state, and then the outdoor heat exchanger via the four-way switching valve 12. 13 and is cooled in the outdoor heat exchanger 13.

  Then, the cooled supercritical refrigerant is sent to the first electric expansion valve 15. The supercritical refrigerant sent to the first electric expansion valve 15 is reduced in pressure and saturated, and then sent to the second electric expansion valve 17 via the liquid receiver 16. The saturated refrigerant sent to the second electric expansion valve 17 is reduced in pressure to become liquid refrigerant, and then supplied to the indoor heat exchanger 31 via the first closing valve 18 to cool and evaporate the indoor air. It becomes a gas refrigerant.

  Then, the gas refrigerant is sucked into the compressor 11 again via the second closing valve 19, the internal heat exchanger 14, and the four-way switching valve 12. In this way, the cooling operation is performed. In addition, the control apparatus 23 performs the said control in this cooling operation.

(2) Heating operation During the heating operation, the four-way switching valve 12 is in the state indicated by the broken line in FIG. 1, that is, the discharge side of the compressor 11 is connected to the second closing valve 19 and the suction side of the compressor 11 is It is in the state connected to the gas side of the outdoor heat exchanger 13. At this time, the first closing valve 18 and the second closing valve 19 are opened.

  When the compressor 11 is started in the state of the refrigerant circuit 2, the gas refrigerant is sucked into the compressor 11 and compressed to become a supercritical state, and then the four-way switching valve 12 and the second closing valve 19 are opened. It is supplied to the indoor heat exchanger 31 via.

  Then, the supercritical refrigerant is cooled while heating the indoor air in the indoor heat exchanger 31. The cooled supercritical refrigerant is sent to the second electric expansion valve 17 through the first closing valve. The supercritical refrigerant sent to the second electric expansion valve 17 is decompressed and saturated, and then sent to the first electric expansion valve 15 via the liquid receiver 16. The saturated refrigerant sent to the first electric expansion valve 15 is reduced in pressure to become a liquid refrigerant, and then sent to the outdoor heat exchanger 13 via the internal heat exchanger 14, and in the outdoor heat exchanger 13. It is evaporated to become a gas refrigerant. Then, this gas refrigerant is sucked into the compressor 11 again via the four-way switching valve 12. In this way, the heating operation is performed.

<Characteristics of air conditioner>
In the air conditioning apparatus 1 according to the present embodiment, when the high-pressure pressure information transmitted from the high-pressure sensor 21 is less than the critical pressure, that is, when the high-pressure refrigerant enters the subcritical state. The first electric expansion valve 15 can be fully opened, and the refrigerant flowing out of the first electric expansion valve 15 can be brought into a state close to saturation. For this reason, in this air conditioner 1, stable liquid receiver liquid level control can be performed even when the high-pressure side refrigerant is in a subcritical state.

<Modification>
(A)
In the previous embodiment, the present invention was applied to the separate type air conditioner 1 in which one indoor unit 30 is provided for one outdoor unit 10, but the present invention is shown in FIG. The present invention may be applied to a multi-type air conditioner 101 in which a plurality of indoor units are provided for a single outdoor unit. In addition, in FIG. 5, the same code | symbol is used about the same component as the component of the air conditioning apparatus 1 which concerns on previous embodiment. In FIG. 5, reference numeral 102 indicates a refrigerant circuit, reference numeral 110 indicates an outdoor unit, reference numerals 130a and 130b indicate indoor units, reference numerals 31a and 31b indicate indoor heat exchangers, and reference numerals 32a and 32b indicate indoor units. A fan is shown, the code | symbols 33a and 33b show the 2nd electric expansion valve, the codes | symbols 34a and 34b show the indoor control apparatus, and the codes | symbols 141 and 142 show the connection piping. In such a case, the control device 23 controls the second electric expansion valves 33a and 33b via the indoor control devices 34a and 34b. In the present modification, the second electric expansion valves 33a and 33b are accommodated in the indoor units 130a and 130b. However, the second electric expansion valves 33a and 33b may be accommodated in the outdoor unit 110.

(B)
Although not particularly mentioned in the air conditioner 1 according to the previous embodiment, a supercooling heat exchanger (even if it is an internal heat exchanger) is provided between the liquid receiver 16 and the second electric expansion valve 17. May be provided. In such a case, in the first receiver liquid level control, the opening degree of the first electric expansion valve 15 is controlled by the control device 23 so that the refrigeration cycle as shown in FIG. 6 is realized. In FIG. 6, A ₀ → B ₀ indicates the compression stroke, B ₀ → C ₀ indicates the cooling stroke, and C ₀ → D ₀ indicates the first expansion stroke (pressure reduction by the first electric expansion valve 15). , D ₀ → F ₀ indicates a supercooling step (cooling by a supercooling heat exchanger), F ₀ → E ₃ indicates a second expansion stroke (pressure reduction by the second electric expansion valve 17), and E ₃ → A ₀ Indicates the evaporation process. K represents a critical point, and Tm represents an isotherm. That is, in the first liquid receiver liquid level control, the control device 23 controls the opening degree of the first electric expansion valve 15 so that the refrigerant flowing out from the first electric expansion valve 15 is saturated.

Further, in the second liquid receiver liquid level control, the refrigeration cycle becomes a refrigeration cycle as shown by a solid line in FIG. 7, and the controller 23 controls the liquid receiver liquid level control with respect to the first electric expansion valve 15 in this state. When the same opening degree is requested, the refrigeration cycle becomes A ₀ → B ₁ → C ₁ → D ₁ → F ₁ → E ₃ → A ₀ , and the refrigerant flowing out from the first electric expansion valve 15 is gas-liquid. As a result, it becomes impossible to stabilize the liquid level of the stored refrigerant in the liquid receiver 16. Therefore, when the high-pressure information transmitted from the high-pressure sensor 21 becomes less than the critical pressure, that is, when the high-pressure side refrigerant is in the subcritical state, the control device 23 opens the first electric expansion valve 15 in the fully open state. And Then, the refrigeration cycle becomes a refrigeration cycle indicated by a solid line in FIG. That is, since the refrigeration cycle is A ₀ → B ₁ → C ₁ → D ₀ → F ₀ → E ₃ → A ₀ , the refrigerant flowing out of the first electric expansion valve 15 is in a state close to saturation. In the air conditioner 1, such a stable liquid receiver liquid level control is realized during the cooling operation.

(C)
In the air conditioner 1 according to the previous embodiment, the first electric expansion valve 15, the liquid receiver 16, the second electric expansion valve 17, and the like are arranged in the outdoor unit 10, but these arrangements are particularly limited. Not. For example, the second electric expansion valve 17 may be disposed in the indoor unit 30.

(D)
In the air-conditioning apparatus 1 according to the previous embodiment, the electric expansion valve is employed as the refrigerant decompression unit, but an expander or the like may be employed instead.

(E)
Although not particularly mentioned in the air conditioner 1 according to the previous embodiment, the venting circuit may be formed by connecting the liquid receiver 16 and the suction pipe of the compressor 11. In such a case, it is preferable to provide an electric expansion valve, an electromagnetic valve, or the like in the degassing circuit.

(F)
In the air conditioning apparatus 1 according to the previous embodiment, the intermediate pressure sensor 24 is provided, but the intermediate pressure sensor 24 may be removed. In such a case, at the time of the first liquid receiver liquid level control, for example, the total opening degree of the first electric expansion valve 15 and the second electric expansion valve 17 is previously functionalized with the degree of superheat in the suction pipe of the compressor 11 as a variable. Or by creating a control table representing the relationship between the total opening and the degree of superheat, the opening ratio of the first electric expansion valve 15 and the second electric expansion valve 17 is set to the high pressure and the first It can be considered that the electric expansion valve inlet temperature is made into a function as a variable. If it does in this way, the opening degree of the 1st electric expansion valve 15 and the 2nd electric expansion valve 17 can be determined uniquely.

(G)
In the air conditioner 1 according to the previous embodiment, the high-pressure sensor 21 detects that the high-pressure side refrigerant has transitioned from the supercritical state to the subcritical state. However, there are other methods for detecting that the high-pressure refrigerant has transitioned from the supercritical state to the subcritical state. For example, two temperature sensors are installed in a region where the high-pressure refrigerant enters a gas-liquid two-phase state when the high-pressure refrigerant transitions to the subcritical state, specifically in a specific region of the heat transfer tube of the radiator, If the temperature information obtained from the two temperature sensors is almost the same (for example, it is judged that the temperature information is almost the same when the difference between the temperature information is equal to or less than a predetermined threshold), the high-pressure refrigerant has transitioned to the subcritical state It can be judged. Further, for example, a region where the high-pressure side refrigerant is not below the critical point temperature when the high-pressure side refrigerant is in the supercritical state, and a region where the high-pressure side refrigerant is at the saturation temperature when the high-pressure side refrigerant is in the subcritical state, Specifically, a temperature sensor is installed in a specific area of the heat exchanger tube of the radiator, and when the temperature information obtained from the temperature sensor falls below the critical point temperature, it is determined that the high-pressure side refrigerant has transitioned to the subcritical state. be able to. In such a case, one temperature sensor is sufficient.

  The refrigerating apparatus according to the present invention has a feature that the liquid level control of the liquid receiver can be stably performed, and is particularly useful for a refrigerating apparatus that employs carbon dioxide or the like as a refrigerant.

It is a refrigerant circuit figure of the air harmony device concerning an embodiment of the invention. It is a figure for demonstrating 1st electric expansion valve control when the high pressure side refrigerant | coolant is a supercritical state in the air conditioning apparatus which concerns on embodiment of this invention. It is a figure for demonstrating a state when the high pressure side refrigerant | coolant will be in a subcritical state in the air conditioning apparatus which concerns on embodiment of this invention. It is a figure for demonstrating 1st electric expansion valve control when the high pressure side refrigerant | coolant will be in a subcritical state in the air conditioning apparatus which concerns on embodiment of this invention. It is a refrigerant circuit figure of the air harmony device concerning modification (A). It is a figure for demonstrating 1st electric expansion valve control when the high pressure side refrigerant | coolant is a supercritical state in the air conditioning apparatus which concerns on a modification (B). It is a figure for demonstrating a state when the high pressure side refrigerant | coolant will be in a subcritical state in the air conditioning apparatus which concerns on a modification (B). It is a figure for demonstrating 1st electric expansion valve control when the high pressure side refrigerant | coolant will be in a subcritical state in the control apparatus of the air conditioning apparatus which concerns on a modified example (B).

1,101 Air conditioning equipment (refrigeration equipment)
11 Compressor (compression mechanism)
13 Outdoor Heat Exchanger 15 First Electric Expansion Valve (First Expansion Mechanism)
16 liquid receiver 17, 33a, 33b 2nd electric expansion valve (2nd expansion mechanism)
21 High pressure sensor (pressure detector)
23 control device 31, 31a, 31b indoor heat exchanger

Claims (4)

A compression mechanism (11) for compressing the refrigerant;
A radiator (13) connected to the refrigerant discharge side of the compression mechanism;
A first expansion mechanism (15) connected to the outlet side of the radiator;
A liquid receiver (16) connected to the refrigerant outflow side of the first expansion mechanism;
A second expansion mechanism (17, 33a, 33b) connected to the outlet side of the liquid receiver;
An evaporator (31, 31a, 31b) connected to the refrigerant outflow side of the second expansion mechanism and connected to the refrigerant suction side of the compression mechanism;
A control unit that minimizes the degree of decompression by the first expansion mechanism when the state of the refrigerant flowing from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism transitions from a supercritical state to a subcritical state. (23)
A first temperature detector provided in a first specific region of the radiator;
A second temperature detector provided in the first specific region of the radiator;
With
The first specific region is a region where the high-pressure side refrigerant is in a gas-liquid two-phase state when the high-pressure side refrigerant transitions to the subcritical state,
The controller is
When the high-pressure side refrigerant is in a supercritical state, the first liquid receiver liquid level control is performed to control the first electric expansion valve and the second electric expansion valve so that the refrigerant flowing out from the first expansion mechanism is saturated. Done
When the difference between the temperature detected by the first temperature detector and the temperature detected by the second temperature detector is equal to or less than a predetermined threshold, it is determined that the high-pressure side refrigerant has transitioned to the subcritical state. performs second liquid receiver liquid level control to minimize the vacuum pressure of by the first expansion mechanism,
Refrigeration equipment (1, 101). The first expansion mechanism is a first expansion valve;
The control unit fully opens the first expansion valve when a difference between a temperature detected by the first temperature detection unit and a temperature detected by the second temperature detection unit becomes a predetermined threshold value or less. ,
The refrigeration apparatus according to claim 1. A compression mechanism (11) for compressing the refrigerant;
A radiator (13) connected to the refrigerant discharge side of the compression mechanism;
A first expansion mechanism (15) connected to the outlet side of the radiator;
A liquid receiver (16) connected to the refrigerant outflow side of the first expansion mechanism;
A second expansion mechanism (17, 33a, 33b) connected to the outlet side of the liquid receiver;
An evaporator (31, 31a, 31b) connected to the refrigerant outflow side of the second expansion mechanism and connected to the refrigerant suction side of the compression mechanism;
A control unit that minimizes the degree of decompression by the first expansion mechanism when the state of the refrigerant flowing from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism transitions from a supercritical state to a subcritical state. (23)
A third temperature detector provided in a second specific region of the radiator;
With
The second specific region is a region where the high-pressure side refrigerant does not fall below a critical point temperature when the high-pressure side refrigerant is in a supercritical state, and when the high-pressure side refrigerant is in a subcritical state, the high-pressure side refrigerant reaches a saturation temperature. Is an area that
The controller is
When the high-pressure side refrigerant is in a supercritical state, the first liquid receiver liquid level control is performed to control the first electric expansion valve and the second electric expansion valve so that the refrigerant flowing out from the first expansion mechanism is saturated. Done
When the temperature detected by the third temperature detection unit is equal to or lower than the critical point temperature of the refrigerant, it is determined that the high-pressure side refrigerant has transitioned to the subcritical state, and the degree of decompression by the first expansion mechanism is minimized. The second liquid receiver liquid level control is performed .
Refrigeration equipment. The first expansion mechanism is a first expansion valve;
The control unit fully opens the first expansion valve when the temperature detected by the third temperature detection unit is equal to or lower than the critical point temperature of the refrigerant.
The refrigeration apparatus according to claim 3.

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