JP2012189258A - Refrigeration cycle equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide refrigeration cycle equipment able to make a secondary refrigerant circuit effectively function when heating operation.SOLUTION: In a primary refrigerant circuit 12, a first expansion valve 23, a third heat exchanger 24 and a second expansion valve 25 are incorporated in this order in a refrigerant pathway 17 between a first heat exchanger 18 and a second heat exchanger 19. A second refrigerant in a secondary refrigerant circuit 13 absorbs heat from a first refrigerant in the third heat exchanger 24 when heating operation. Even if the secondary refrigerant circuit 13 operates in a similar fashion after switching from a refrigerated air conditioning operation to a heating operation as when the refrigerated air conditioning operation is performed, it is prevented that an efficiency of the first heat exchanger deteriorates due to excessive lowering beyond an intended temperature, of an evaporation temperature of the first heat exchanger serving as an evaporator, the excessive lowering may be being caused by action of the third heat exchanger.

Description

  The present invention relates to a refrigeration cycle apparatus such as an air conditioner.

  For example, as disclosed in FIG. 6 of Patent Document 1, a refrigeration cycle apparatus using a refrigerant having a low global warming potential such as carbon dioxide, that is, an air conditioner is widely known. This air conditioner includes a primary refrigerant circuit and a secondary refrigerant circuit. In the primary refrigerant circuit, carbon dioxide is used as a refrigerant (hereinafter referred to as “first refrigerant”). In the secondary refrigerant circuit, a refrigerant having energy consumption efficiency better than that of carbon dioxide (hereinafter referred to as “second refrigerant”), for example, propane is used as the refrigerant. The primary refrigerant circuit and the secondary refrigerant circuit are connected to each other by a refrigerant-refrigerant heat exchanger. The secondary refrigerant circuit absorbs heat from carbon dioxide between the outdoor heat exchanger and the expansion valve during the cooling operation by the function of the refrigerant-refrigerant heat exchanger. Thus, the enthalpy of carbon dioxide is sufficiently reduced prior to inflow into the indoor heat exchanger. In the transcritical cycle of carbon dioxide, even if the outside air temperature is higher than the critical temperature of carbon dioxide, a sufficient enthalpy difference (refrigeration effect) can be ensured in the indoor heat exchanger.

International Publication No. 2005/052467

  Such an air conditioner pauses the secondary refrigerant circuit during heating operation. This is because the outdoor heat exchanger changes its role from a radiator to an evaporator during heating operation. That is, when the primary refrigerant circuit is switched from the cooling operation to the heating operation, the position of the refrigerant-refrigerant heat exchanger is changed between the radiator and the expansion valve inlet to the expansion valve outlet and the evaporator. This is because if carbon dioxide is cooled between the expansion valve outlet and the evaporator, the evaporation temperature of carbon dioxide is excessively lowered, and the suction pressure of the compressor is lowered. A decrease in the suction pressure induces an increase in the compression ratio, and as a result, the compression power increases. In addition, the first refrigerant side of the air heat exchanger reaches a high pressure at the supercritical pressure during the cooling operation and becomes a low pressure at the subcritical pressure during the heating operation. In other words, it has a problem of withstand voltage. Therefore, it is desired that the secondary refrigerant circuit functions effectively even during heating operation.

  According to the present invention, the primary refrigerant circuit side of the third heat exchanger can be set to an intermediate pressure lower than the critical pressure during cooling operation and heating operation, and the secondary refrigerant circuit can function effectively during heating operation. A refrigeration cycle apparatus capable of performing the following can be provided.

  One form of the refrigeration cycle apparatus includes a first expansion valve, a third heat exchanger, and a second expansion valve that are sequentially incorporated in the refrigerant path between the first heat exchanger and the second heat exchanger. When the first high-temperature and high-pressure refrigerant is selectively supplied from the compressor to the first heat exchanger or the second heat exchanger, the second heat exchanger or the first heat exchanger passes through the refrigerant path. From the first refrigerant circuit for returning the first refrigerant to the first compressor and the third heat exchanger, and the high temperature and high pressure are connected to the fourth heat exchanger between the second compressor and the third expansion valve. And a secondary refrigerant circuit that returns the second refrigerant decompressed by the third expansion valve to the second compressor through the third heat exchanger.

  In such a refrigeration cycle apparatus, the second refrigerant in the secondary refrigerant circuit absorbs heat from the first refrigerant in the third heat exchanger during the cooling operation. When the first heat exchanger acts as a radiator, the enthalpy of the first refrigerant decreases prior to the inflow into the second heat exchanger that acts as an evaporator. As a result, even if the outside air temperature is higher than the critical temperature of the first refrigerant, a sufficient enthalpy difference (refrigeration effect) can be ensured in the second heat exchanger. Also, instead of adding a secondary refrigerant circuit or a third heat exchanger, an internal heat exchanger is incorporated between the suction side of the compressor and the front of the expansion valve, and the enthalpy difference ( It is conceivable to increase the freezing effect). Unlike the case of such an internal heat exchanger, since the degree of superheat does not increase in one form of the refrigeration cycle apparatus according to the present invention, the discharge temperature of the first compressor can be suppressed from becoming excessively high. Therefore, a favorable cooling operation can be realized.

  Similarly, the second refrigerant in the secondary refrigerant circuit absorbs heat from the first refrigerant in the third heat exchanger during heating operation. When the second heat exchanger acts as a radiator, the enthalpy of the first refrigerant decreases prior to the inflow into the first heat exchanger that acts as an evaporator. Even if the secondary refrigerant circuit operates in the same way as during cooling operation after switching from cooling operation to heating operation, the evaporation temperature of the first heat exchanger that is the evaporator is the temperature intended by the function of the third heat exchanger. It can be avoided that the efficiency of the first heat exchanger is deteriorated due to excessive reduction. Moreover, unlike the case where the enthalpy difference (refrigeration effect) is increased using an internal heat exchanger, it is possible to suppress the discharge temperature of the compressor from becoming excessively high.

  The refrigeration cycle apparatus may further include a duct that feeds warm air that receives the thermal energy released from the fourth heat exchanger into an environment of warm air that receives the thermal energy released from the second heat exchanger. In the refrigeration cycle apparatus according to the above-described embodiment, the secondary refrigerant circuit can be operated not only during the cooling operation but also during the heating operation. Therefore, the fourth heat exchange functioning as a condenser of the secondary refrigerant circuit during the heating operation. Energy can be recovered from the vessel. That is, the low temperature heat recovered by the third heat exchanger can be converted to high temperature heat by the action of the second compressor. The heat energy extracted from the first refrigerant in the third heat exchanger can be added to the heat energy released from the second heat exchanger as warm air. Thus, heat energy can be used without waste. Overall, thermal energy can be used efficiently. As a result, good heating operation can be realized.

  The refrigeration cycle apparatus may further include an open / close plate that opens and closes the duct and a control circuit that controls opening and closing of the open / close plate. According to such an opening / closing plate, it is possible to prevent the heat energy released from the fourth heat exchanger from being added to the cold air generated by the second heat exchanger during the cooling operation. As a result, the air can be efficiently cooled in the second heat exchanger.

  In the refrigeration cycle apparatus, the pressure value of the first refrigerant flowing into the third heat exchanger is an intermediate value between the refrigerant pressure value in the first heat exchanger and the refrigerant pressure value in the second heat exchanger. In this way, the first expansion valve and the second expansion valve may be controlled. When the evaporation pressure of the second heat exchanger is set to a predetermined pressure, one of the first expansion valve and the second expansion valve is depressurized to the middle, and the other is adjusted to depressurize to the predetermined pressure. Thus, an intermediate pressure between the pressure of the first heat exchanger and the pressure of the second heat exchanger can be established between the first expansion valve and the second expansion valve.

  According to the present invention, the primary refrigerant circuit side of the third heat exchanger can be set to an intermediate pressure lower than the critical pressure during cooling operation and heating operation, and the secondary refrigerant circuit can function effectively during heating operation. It is possible to provide a refrigeration cycle apparatus capable of

It is a figure showing roughly the composition of the air harmony machine concerning one embodiment of the present invention. It is a block diagram which shows roughly the control system of an air conditioner. It is a figure which shows the flow of a 1st refrigerant | coolant and a 2nd refrigerant | coolant at the time of air_conditionaing | cooling operation. It is a Mollier diagram which shows roughly the state change of the 1st refrigerant at the time of air_conditionaing | cooling operation and heating operation. It is a figure which shows the flow of a 1st refrigerant | coolant and a 2nd refrigerant | coolant at the time of heating operation. It is a Mollier diagram which shows roughly the state change of the 1st refrigerant at the time of using an internal heat exchanger.

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

  FIG. 1 schematically shows a configuration of a refrigeration cycle apparatus according to an embodiment of the present invention, that is, an air conditioner 11. The air conditioner 11 includes a primary refrigerant circuit 12 and a secondary refrigerant circuit 13. The primary refrigerant circuit 12 and the secondary refrigerant circuit 13 each constitute a refrigeration circuit. In the primary refrigerant circuit 12, a natural refrigerant such as CO2 (oxygen dioxide) forming a transcritical cycle is used as the first refrigerant. However, for example, a substance other than CO 2 may be used as the first refrigerant as long as it is a substance that forms a transcritical cycle with a substance having a global warming potential smaller than that of chlorofluorocarbon. The first refrigerant exchanges heat energy between outside air (or air in the environment corresponding to the outdoor environment) and indoor air (or air in the environment corresponding to the indoor environment).

  In the secondary refrigerant circuit 13, a substance other than CO2, such as propane, is used as the second refrigerant. In addition, instead of propane, HFC, HFO, HC, ammonia, or a mixture thereof may be used for the second refrigerant. In particular, a substance having higher energy consumption efficiency than the first refrigerant may be used for the second refrigerant. A 2nd refrigerant | coolant absorbs heat from a 1st refrigerant | coolant, and discharge | releases a thermal energy toward external air, after making it the state of high temperature and pressure.

  The primary refrigerant circuit 12 includes a compressor (hereinafter referred to as “first compressor”) 14. The first compressor 14 is incorporated in the first circulation path 15. The first circulation path 15 connects the first port 16a and the second port 16b of the four-way valve 16 to each other. The suction port 14a of the first compressor 14 is connected to the first port 16a of the four-way valve 16 via a refrigerant pipe. The gas refrigerant is supplied from the first port 16 a to the suction port 14 a of the first compressor 14. The first compressor 14 compresses the low-pressure gas refrigerant to a predetermined pressure. The discharge port 14b of the first compressor 14 is connected to the second port 16b of the four-way valve 16 via a refrigerant pipe. Gas refrigerant is supplied to the second port 16 b of the four-way valve 16 from the discharge port 14 b of the first compressor 14. The first circulation path 15 is formed by a refrigerant pipe such as a copper pipe, for example.

  Refrigerant piping that forms the second circulation path 17 is connected to the third port 16 c and the fourth port 16 d of the four-way valve 16. The second circulation path 17 connects the third port 16c and the fourth port 16d of the four-way valve 16 to each other. A first heat exchanger, that is, an outdoor heat exchanger 18 and a second heat exchanger, that is, an indoor heat exchanger 19 are incorporated in the second circulation path 17 in order from the third port 16c side. The outdoor heat exchanger 18 has a first port 18a and a second port 18b. The refrigerant passes through the outdoor heat exchanger 18 between the first port 18a and the second port 18b. The outdoor heat exchanger 18 realizes heat energy exchange between the refrigerant passing therethrough and ambient air. The first port 18a of the outdoor heat exchanger 18 is connected to the third port 16c of the four-way valve 16 via a refrigerant pipe. By the action of the four-way valve 16, the first port 18 a of the outdoor heat exchanger 18 is switchably connected to either the suction port 14 a of the first compressor 14 or the discharge port 14 b of the compressor 14. The second circulation path 17 may be formed of a refrigerant pipe such as a copper pipe.

  A blower fan 21 is installed in association with the outdoor heat exchanger 18. The blower fan 21 generates an air flow according to the rotation of the impeller. The airflow passes through the outdoor heat exchanger 18. The flow rate of the passing air flow is adjusted according to the number of revolutions per minute of the impeller. In the outdoor heat exchanger 18, the amount of heat energy exchanged between the refrigerant and the air is adjusted according to the flow rate of the airflow.

  The indoor heat exchanger 19 has a first port 19a and a second port 19b. The refrigerant passes through the indoor heat exchanger 19 between the first port 19a and the second port 19b. The indoor heat exchanger 19 realizes heat energy exchange between the refrigerant passing therethrough and ambient air. The second port 19 b of the indoor heat exchanger 19 is connected to the fourth port 16 d of the four-way valve 16. By the action of the four-way valve 16, the second port 19b of the indoor heat exchanger 19 is switchably connected to either the suction port 14a of the first compressor 14 or the discharge port 14b of the compressor 14.

  A blower fan 22 is installed in association with the indoor heat exchanger 19. The blower fan 22 generates an air flow according to the rotation of the impeller. The airflow passes through the indoor heat exchanger 19. The flow rate of the passing air flow is adjusted according to the number of revolutions per minute of the impeller. The amount of heat energy exchanged between the refrigerant and the air can be adjusted in the indoor heat exchanger 19 according to the flow rate of the airflow. The indoor heat exchanger 19 and the blower fan 22 are incorporated in, for example, an indoor unit. The indoor unit is installed in an indoor space RM in a building, for example. In addition, the indoor unit may be installed in an environmental space corresponding to the indoor space RM.

  Between the outdoor heat exchanger 18 and the indoor heat exchanger 19, the first expansion valve 23 and the third heat exchanger, that is, the refrigerant-refrigerant heat exchanger, are sequentially provided in the second circulation path 17 from the outdoor heat exchanger 18 side. 24 and the second expansion valve 25 are incorporated. The first expansion valve 23 and the second expansion valve 25 each control the opening degree of the flow path of the first refrigerant. The circulation amount of the first refrigerant is adjusted according to the opening degree. In accordance with such adjustment, a pressure difference is generated in the first refrigerant upstream and downstream of the first expansion valve 23. Similarly, a pressure difference is generated in the first refrigerant upstream and downstream of the second expansion valve 25.

  The refrigerant-refrigerant heat exchanger 24 includes a first flow passage 26 that provides the second circulation path 17 of the primary refrigerant circuit 12. The first flow passage 26 has a first port 26a and a second port 26b. The refrigerant passes through the first flow passage 26 between the first port 26a and the second port 26b. The first port 26a of the first flow passage 26 is connected to the first expansion valve 23 via a refrigerant pipe. The second port 26 b of the first flow passage 26 is connected to the second expansion valve 25.

  At the same time, the refrigerant-refrigerant heat exchanger 24 includes a second flow passage 27. The second flow passage 27 extends relative to the first flow passage. For example, the second flow passage 27 may extend parallel to the first flow passage 26. The second flow passage 27 has a first port 27a and a second port 27b. The refrigerant passes through the second flow passage 27 between the first port 27a and the second port 27b. Refrigerant piping that forms the third circulation path 28 is connected to the first port 27 a and the second port 27 b of the second flow passage 27. The third circulation path 28 connects the first port 27a and the second port 27b of the second flow passage 27 to each other. The third circulation path 28 is formed of a refrigerant pipe such as a copper pipe.

  In the third circulation path 28, a compressor (hereinafter referred to as "second compressor") 31, a fourth heat exchanger, that is, an air heat exchanger 32 and a third expansion valve 33 are sequentially incorporated. The second compressor 31 compresses the low-pressure gas refrigerant to a predetermined pressure. The second refrigerant compressed to a high temperature and high pressure by the action of the second compressor 31 is supplied to the air heat exchanger 32. The air heat exchanger 32 realizes heat energy exchange between the second refrigerant passing therethrough and ambient air. The air heat exchanger 32 functions as a condenser. Thermal energy is released from the air heat exchanger 32.

  As described above, the refrigerant-refrigerant heat exchanger 24 is incorporated in the second circulation path 17 of the primary refrigerant circuit 12 and at the same time is incorporated in the third circulation path 28 of the secondary refrigerant circuit 13. Exchange of thermal energy is realized between the first refrigerant in the first flow passage 26 and the second refrigerant in the second flow passage 27. In exchange of such heat energy, instead of the heat exchanger, for example, a structure in which the piping of the first flow passage 26 and the piping of the second flow passage 27 are brought into contact with each other may be employed. Thus, the first refrigerant is cooled by the refrigerant-refrigerant heat exchanger 24.

  A blower fan 34 is installed in association with the air heat exchanger 32. The blower fan 34 generates an air flow according to the rotation of the impeller. The airflow passes through the air heat exchanger 32. The flow rate of the passing air flow is adjusted according to the number of revolutions per minute of the impeller. The amount of heat energy exchanged between the refrigerant and the air can be adjusted in the air heat exchanger 32 according to the flow rate of the airflow.

  A duct 35 is connected to the air heat exchanger 32. The blower fan 34 is disposed in the duct 35. The duct 35 extends from the blower fan 34 to the exhaust port 36. A branch duct 37 is connected to the duct 35 between the blower fan 34 and the exhaust port 36. The branch duct 37 extends to the indoor heat exchanger 19, for example. The branch duct 37 can guide the airflow sent from the blower fan 34 to the indoor heat exchanger 19. Here, the warm air sent from the branch duct 37 is mixed with the air stream after the heat exchange sent from the blower fan 22 of the indoor heat exchanger 19. In addition, the airflow sent out from the blower fan 34 may be blown out directly from the branch duct 37 into the indoor space RM.

  An opening / closing plate 38 is installed in the duct 35. The opening / closing plate 38 is relatively displaced, for example, between a first position and a second position. When the opening / closing plate 38 is positioned at the first position, the exhaust port 36 of the duct 35 is opened. On the other hand, the entrance of the branch duct 37 is closed. Therefore, the airflow sent out from the blower fan 34 is discharged to the outside through the exhaust port 36, and the inflow of the airflow into the branch duct 37 is prevented. When the opening / closing plate 38 is positioned at the second position, the exhaust port 36 of the duct 35 is closed. On the other hand, the entrance of the branch duct 37 is opened. As a result, the air flow sent out from the blower fan 34 is guided from the branch duct 37 to the indoor heat exchanger 19, that is, the indoor space RM.

  All the components other than the indoor heat exchanger 19 and the blower fan 22 may be installed outside the indoor space RM, that is, outside the room. Components other than the indoor heat exchanger 19 and the blower fan 22 may be accommodated in, for example, one outdoor unit. The secondary refrigerant circuit 13 is desirably installed outside the building.

  Three pressure sensors 41, 42 and 43 are attached to the second circulation path 17 of the primary refrigerant circuit 12. The pressure sensor 41 is disposed on the second port 18 b side of the outdoor heat exchanger 18. The pressure sensor 41 detects the pressure of the outdoor heat exchanger 18. The pressure sensor 41 outputs a pressure information signal. This pressure information signal specifies the detected pressure value. Similarly, the pressure sensor 42 is disposed on the first port 19 a side of the indoor heat exchanger 19. The pressure sensor 42 detects the pressure of the indoor heat exchanger 19. The pressure sensor 42 outputs a pressure information signal. This pressure information signal specifies the detected pressure value. The pressure sensor 43 is disposed on the first port 26 a side of the refrigerant-refrigerant heat exchanger 24. The pressure sensor 43 detects the pressure of the refrigerant-refrigerant heat exchanger 24. That is, the pressure sensor 43 detects the refrigerant pressure between the first expansion valve 23 and the second expansion valve 25. The pressure sensor 43 outputs a pressure information signal. This pressure information signal specifies the detected pressure value. The pressure sensor 43 may be disposed on the second port 26b side of the refrigerant-refrigerant heat exchanger 24. Such a pressure sensor 43 may be attached to either the first port 26a side or the second port 26b side, or may be attached to both the first port 26a side and the second port 26b side.

  As shown in FIG. 2, the air conditioner 11 includes a control circuit 45. The control circuit 45 includes a four-way valve 16, a first compressor 14, a second compressor 31, a first expansion valve 23, a second expansion valve 25, a third expansion valve 33, a drive source 46 for the opening / closing plate 38, and the blower fan 21. The blower fan 34 and the blower fan 22 are connected. The control circuit 45 includes a four-way valve 16, a first compressor 14, a second compressor 31, a first expansion valve 23, a second expansion valve 25, a third expansion valve 33, a drive source 46, a blower fan 21, a blower fan 34, and A control signal is supplied to each of the blower fans 22. The control signal includes the operation of the four-way valve 16, the operating frequencies of the first compressor 14 and the second compressor 31, the opening degrees of the first expansion valve 23, the second expansion valve 25 and the third expansion valve 33, the blower fan 21. These are signals for controlling the number of revolutions per minute of the blower fan 22 and the blower fan 34 and the drive amount of the drive source 46. The four-way valve 16 is set to the first state or the second state according to the control signal. In the first state, in the four-way valve 16, the first port 16a is connected to the fourth port 16d and at the same time the second port 16b is connected to the third port 16c. In the second state, in the four-way valve 16, the first port 16a is connected to the third port 16c and at the same time the second port 16b is connected to the fourth port 16d. The first compressor 14 and the second compressor 31 operate at a frequency specified by the control signal. The first expansion valve 23, the second expansion valve 25, and the third expansion valve 33 adjust the flow rate of the refrigerant by the opening degree specified by the control signal. In the blower fans 21, 22, and 34, the rotational speed is controlled by a control signal in accordance with the heat exchange amount. The drive source 46 drives the open / close plate 38 between the first position and the second position in accordance with the drive amount specified by the control signal.

  The control circuit 45 is connected to pressure sensors 41, 42, 43, a first opening sensor 47, a second opening sensor 48, and a third opening sensor 49. The first opening sensor 47 measures the opening of the first expansion valve 23. The second opening sensor 48 measures the opening of the second expansion valve 25. The third opening sensor 49 measures the opening of the third expansion valve 33. The first opening sensor 47, the second opening sensor 48, and the third opening sensor 49 each supply an opening information signal to the control circuit 45. In the individual opening information signals, the opening measured by the first opening sensor 47, the second opening sensor 48, and the third opening sensor 49 is specified. The control circuit 45 corrects the difference between the opening of the expansion valve specified by the opening information signal and the expansion valve opening corresponding to the target pressure at the time of this control. The control circuit 45 is supplied with pressure information signals from the pressure sensors 41, 42, 43.

  Next, the operation of the air conditioner 11 will be briefly described. When the cooling operation is set, the control circuit 45 supplies a control signal to the four-way valve 16. As shown in FIG. 3, the four-way valve 16 is set to the first state. The control circuit 45 supplies a control signal to the drive source 46. The opening / closing plate 38 is positioned at the first position. The exhaust port 36 is opened. The control circuit 45 detects the opening degrees of the first expansion valve 23 and the second expansion valve 25. It is determined whether the opening degree of the first expansion valve 23 is larger than a threshold value. If the opening degree of the first expansion valve 23 is larger than the threshold value, the control circuit 45 reduces the opening degree of the first expansion valve 23 to the threshold value opening degree. When the opening degree is adjusted, a control signal is supplied from the control circuit 45 to the first expansion valve 23. The threshold is set in advance.

  Subsequently, the control circuit 45 operates the first compressor 14. In operation, the first compressor 14 is supplied with a control signal from the control circuit 45. A high-temperature and high-pressure gas refrigerant is discharged from the first compressor 14. The first refrigerant, that is, CO 2 circulates in the primary refrigerant circuit 12. The first refrigerant flows through the second circulation path 17 from the third port 16c to the fourth port 16d of the four-way valve 16, and is returned from the first port 16a of the four-way valve 16 to the suction port 14a of the first compressor 14. At this time, the control circuit 45 sets the opening degree of the first expansion valve 23 after fully opening the second expansion valve 25. A control signal is supplied from the control circuit 45 to the first expansion valve 23 and the second expansion valve 25. The opening degree of the first expansion valve 23 is set so that the evaporation pressure in the indoor heat exchanger 19, that is, the evaporator, becomes higher than the target evaporation pressure set according to the difference between the set temperature and room temperature.

  Similarly, the control circuit 45 operates the second compressor 31. In operation, the second compressor 31 is supplied with a control signal from the control circuit 45. A high-temperature and high-pressure gas refrigerant is discharged from the second compressor 31. The second refrigerant circulates in the third circulation path 28 of the secondary refrigerant circuit 13. The second refrigerant in the gas state is condensed in the air heat exchanger 32. The condensed second refrigerant is decompressed by the third expansion valve 33. The decompressed second refrigerant is supplied to the refrigerant-refrigerant heat exchanger 24. In the refrigerant-refrigerant heat exchanger 24, the second refrigerant in the second flow passage 27 absorbs heat from the first refrigerant in the first flow passage 26 and evaporates. The evaporated second refrigerant is returned to the second compressor 31.

  The control circuit 45 adjusts the opening degree of the second expansion valve 25 so as to achieve the target evaporation pressure. The evaporation pressure is detected by a pressure sensor 42 provided on the first port 19a side of the indoor heat exchanger 19. Thus, the indoor heat exchanger 19 obtains the evaporation pressure to be targeted. Here, since the control of the first expansion valve 23 precedes the control of the second expansion valve 25, high-pressure refrigerant is prevented from flowing into the first flow passage 26 of the refrigerant-refrigerant heat exchanger 24. . In addition to this control, the control circuit 45 also detects the pressure of the radiator with the pressure sensor 41 provided on the second port 18 b side of the outdoor heat exchanger 18, and refrigerant-refrigerant heat exchange is performed from the pressures of the pressure sensors 41 and 42. The intermediate pressure in the first flow passage 26 of the vessel 24 is calculated. The opening of the first expansion valve 23 and the opening of the second expansion valve 25 may be controlled so that the value detected by the pressure sensor 43 matches the intermediate pressure.

  In the primary refrigerant circuit 12, high-temperature and high-pressure first refrigerant is supplied from the first compressor 14 to the outdoor heat exchanger 18. The first refrigerant flows through the outdoor heat exchanger 18, the first expansion valve 23, the refrigerant-refrigerant heat exchanger 24, the second expansion valve 25, and the indoor heat exchanger 19 in order. At this time, as shown in FIG. 4, the first refrigerant is held at a high pressure pd between the first compressor 14 and the first expansion valve 23. In the outdoor heat exchanger 18, the thermal energy of the first refrigerant is released to the outside air at a constant pressure. Subsequently, the first refrigerant is maintained at the intermediate pressure pm between the first expansion valve 23 and the second expansion valve 25. In the refrigerant-refrigerant heat exchanger 24, the thermal energy of the first refrigerant is transferred to the second refrigerant at a constant pressure. As a result, the enthalpy of the refrigerant decreases at the inlet of the second expansion valve 25, and a large enthalpy difference (refrigeration effect) is secured in the indoor heat exchanger 19. Thereafter, the first refrigerant is decompressed to a low pressure ps by the second expansion valve 25. The decompressed first refrigerant absorbs heat from the surrounding air in the indoor heat exchanger 19. Cold air is generated. The cold air is caused to flow into the indoor space RM by the function of the blower fan 22.

  Next, when the heating operation is set, the control circuit 45 supplies a control signal to the four-way valve 16. At this time, as shown in FIG. 5, the four-way valve 16 is set to the second state. The control circuit 45 supplies a control signal to the drive source 46. The opening / closing plate 38 is positioned at the second position. The exhaust port 36 is closed. The control circuit 45 detects the opening degrees of the first expansion valve 23 and the second expansion valve 25. It is determined whether the opening degree of the second expansion valve 25 is larger than a threshold value. If the opening degree of the second expansion valve 25 is larger than the threshold value, the control circuit 45 reduces the opening degree of the second expansion valve 25 to the threshold value opening degree. When the opening degree is adjusted, a control signal is supplied from the control circuit 45 to the second expansion valve 25. The threshold value may be set as described above.

  Subsequently, the control circuit 45 operates the first compressor 14. In operation, the first compressor 14 is supplied with a control signal from the control circuit 45. A high-temperature and high-pressure gas refrigerant is discharged from the first compressor 14. The first refrigerant, that is, CO 2 circulates in the primary refrigerant circuit 12. The first refrigerant flows through the second circulation path 17 from the fourth port 16d of the four-way valve 16 to the third port 16c, and is returned from the first port 16a of the four-way valve 16 to the suction port 14a of the first compressor 14. At this time, the control circuit 45 sets the opening degree of the second expansion valve 25 after fully opening the first expansion valve 23. A control signal is supplied from the control circuit 45 to the first expansion valve 23 and the second expansion valve 25. The opening degree of the second expansion valve 25 is set so that the evaporation pressure in the outdoor heat exchanger 18, that is, the evaporator, becomes higher than the target evaporation pressure set according to the difference from the outside air temperature.

  Similarly, the control circuit 45 operates the second compressor 31. In operation, the second compressor 31 is supplied with a control signal from the control circuit 45. A high-temperature and high-pressure gas refrigerant is discharged from the second compressor 31. The second refrigerant circulates in the third circulation path 28 of the secondary refrigerant circuit 13. The second refrigerant in the gas state is condensed in the air heat exchanger 32. The condensed second refrigerant is decompressed by the third expansion valve 33. The decompressed second refrigerant is supplied to the refrigerant-refrigerant heat exchanger 24. In the refrigerant-refrigerant heat exchanger 24, the second refrigerant in the second flow passage 27 absorbs heat from the first refrigerant in the first flow passage 26 and evaporates. The evaporated second refrigerant is returned to the second compressor 31.

  The control circuit 45 adjusts the opening degree of the first expansion valve 23 so as to achieve the target evaporation pressure. The evaporation pressure is detected by a pressure sensor 41 provided on the second port 18b side of the outdoor heat exchanger 18. In this way, the outdoor heat exchanger 18 obtains a target evaporation pressure. Here, since the control of the second expansion valve 25 precedes the control of the first expansion valve 23, high-pressure refrigerant is prevented from flowing into the first flow passage 26 of the refrigerant-refrigerant heat exchanger 24. . In addition to this control, the control circuit 45 also detects the pressure of the radiator with the pressure sensor 42 provided on the first port 19a side of the indoor heat exchanger 19, and refrigerant-refrigerant heat exchange is performed from the pressure of the pressure sensors 41 and 42. The intermediate pressure in the first flow passage 26 of the vessel 24 is calculated. The opening of the first expansion valve 23 and the opening of the second expansion valve 25 may be controlled so that the value detected by the pressure sensor 43 matches the intermediate pressure.

  In the primary refrigerant circuit 12, the high-temperature and high-pressure first refrigerant is supplied from the first compressor 14 to the indoor heat exchanger 19. The first refrigerant flows through the indoor heat exchanger 19, the second expansion valve 25, the refrigerant-refrigerant heat exchanger 24, the first expansion valve 23, and the outdoor heat exchanger 18 in order. At this time, as shown in FIG. 4, the first refrigerant is held at a high pressure pd between the first compressor 14 and the second expansion valve 25. Subsequently, the first refrigerant is maintained at the intermediate pressure pm between the second expansion valve 25 and the first expansion valve 23. In the refrigerant-refrigerant heat exchanger 24, the thermal energy of the first refrigerant is transferred to the second refrigerant at a constant pressure. As a result, the enthalpy at the inlet of the first expansion valve 23 is reduced, and a large enthalpy difference (refrigeration effect) is secured in the outdoor heat exchanger 18. Thereafter, the first expansion valve 23 reduces the first refrigerant to a low pressure ps. The decompressed first refrigerant absorbs heat from the surrounding air in the outdoor heat exchanger 18. Thereafter, the first refrigerant is returned to the first compressor 14.

  As shown in FIG. 6, instead of adding the secondary refrigerant circuit 13 and the refrigerant-refrigerant heat exchanger 24, an internal heat exchanger is incorporated between the suction side of the compressor and the front of the expansion valve. As indicated by the dotted line, the enthalpy difference (refrigeration effect) can be increased in a heat exchanger that acts as an evaporator. However, in this case, since the degree of superheating increases on the suction side of the compressor due to the action of the internal heat exchanger, the discharge temperature of the compressor rises to an excessively high temperature.

  In the air conditioner 11 according to the present embodiment, during the heating operation, the indoor heat exchanger 19 releases the thermal energy of the first refrigerant into the room at a constant pressure. Thermal energy released from the indoor heat exchanger 19 is transferred to the air around the indoor heat exchanger 19. The warm air is caused to flow into the indoor space RM by the action of the blower fan 22. At the same time, the air heat exchanger 32 releases the thermal energy of the second refrigerant. Thermal energy released from the air heat exchanger 32 is transferred to the air around the air heat exchanger 32. Warm air is supplied to the indoor space RM by the action of the blower fan 34 and the branch duct 37. As a result, the thermal efficiency during heating can be increased.

The inventor calculated the coefficient of performance (COP) of the air conditioner 11. In the calculation, the inventor set the operating conditions and operating points shown in [Table 1]. The air conditioning capacity was set to 10 horsepower (= about 28 kW). R32 (HFC-32) was adopted as the refrigerant of the secondary refrigerant circuit 13. During the heating operation, heat for heat recovery was calculated from the condenser of the secondary refrigerant circuit 13, that is, the air heat exchanger 32, and added to the heat of the radiator of the primary refrigerant circuit 12, that is, the indoor heat exchanger 19. As a result, about 10% of the entire heating capacity was secured in the secondary refrigerant circuit 13.

In the calculation, the present inventor set the first comparative example and the second comparative example. In the first comparative example, a simple refrigeration cycle circuit was used. That is, an air conditioner corresponding to the primary refrigerant circuit 12 was set. In addition, in this air conditioner, the first expansion valve 23 and the refrigerant-refrigerant heat exchanger 24 are deleted from the primary refrigerant circuit 12. The air conditioning capacity was set to 10 horsepower (= about 28 kW). In the calculation, the present inventor set the operating conditions in [Table 2].

In the second comparative example, a general internal heat exchanger was employed in the refrigeration cycle apparatus. The air conditioning capacity was set to 10 horsepower (= about 28 kW). In the calculation, the present inventor set the operating conditions shown in [Table 3].

  As a result of the calculation, it was confirmed that the COP increased by 10% in the second comparative example during the cooling operation compared to the first comparative example. It was confirmed that COP increased by 18.9% in the air conditioner 11 as compared with the first comparative example. On the other hand, during heating operation, it was confirmed that the COP increased by 2.2% in the second comparative example compared to the first comparative example. It was confirmed that COP increased by 5.0% in the air conditioner 11 compared to the first comparative example.

  DESCRIPTION OF SYMBOLS 11 Air conditioner, 12 Primary refrigerant circuit, 13 Secondary refrigerant circuit, 14 1st compressor, 17 Refrigerant path, 18 1st heat exchanger (outdoor heat exchanger), 19 2nd heat exchanger (indoor heat exchange) 23) first expansion valve, 24 third heat exchanger (refrigerant-refrigerant heat exchanger), 25 second expansion valve, 31 second compressor, 32 fourth heat exchanger (air heat exchanger), 33 Third expansion valve, 35 duct, 37 duct (branch duct), 38 open / close plate, 45 control circuit.

Claims (4)

A first expansion valve, a third heat exchanger, and a second expansion valve that are sequentially incorporated in the refrigerant path between the first heat exchanger and the second heat exchanger, and the first compressor selectively from the first compressor; When the high-temperature and high-pressure first refrigerant is supplied to the first heat exchanger or the second heat exchanger, the first refrigerant is passed through the refrigerant path from the second heat exchanger or the first heat exchanger. A primary refrigerant circuit returning to one compressor;
The second heat exchanger connected to the third heat exchanger is supplied between the second compressor and the third expansion valve to supply a high-temperature and high-pressure second refrigerant to the fourth heat exchanger, and is depressurized by the third expansion valve. A refrigeration cycle apparatus comprising: a secondary refrigerant circuit that returns two refrigerants to the second compressor through the third heat exchanger. The refrigeration cycle apparatus according to claim 1,
A refrigeration further comprising a duct for sending warm air receiving thermal energy released from the fourth heat exchanger to an environment of warm air receiving thermal energy released from the second heat exchanger during heating operation Cycle equipment. The refrigeration cycle apparatus according to claim 2,
An opening and closing plate for opening and closing the duct;
The refrigeration cycle apparatus further comprising: a control circuit that controls opening and closing of the opening and closing plate. In the refrigerating cycle device according to any one of claims 1 to 3,
The first refrigerant flowing into the third heat exchanger has a pressure value intermediate between a refrigerant pressure value in the first heat exchanger and a refrigerant pressure value in the second heat exchanger. The refrigeration cycle apparatus further comprising a control circuit for controlling the first expansion valve and the second expansion valve.

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