JP4273493B2 - Refrigeration air conditioner - Google Patents

Description

The present invention relates to a refrigeration air conditioner, and more particularly to a refrigeration air conditioner that uses carbon dioxide (CO ₂ ) as a refrigerant.

A conventional refrigeration air conditioner uses CO ₂ as a refrigerant, and is provided with a receiver for storing the refrigerant at the outlet of the evaporator, and controls the amount of refrigerant in the receiver to control the operating high pressure of the apparatus and to perform predetermined cooling. There is one that provides the ability (see, for example, Patent Document 1).

Japanese Examined Patent Publication No. 7-18602 (page 1-5, Fig. 2)

  In the case of the refrigerating and air-conditioning apparatus of Patent Document 1, a container such as a receiver for storing the refrigerant is required, and there is a problem that the cost of the refrigerating and air-conditioning apparatus increases.

  In view of the above problems, the present invention achieves a low-cost refrigeration air conditioner by controlling the refrigerant amount distribution in the refrigeration air conditioner without using a container such as a receiver, and increases the pressure by controlling the refrigerant amount distribution. An object of the present invention is to obtain a refrigerating and air-conditioning apparatus that realizes high-efficiency operation by controlling to a high pressure that maximizes the COP.

The present invention relates to a refrigerating and air-conditioning apparatus in which a compressor, a radiator, a decompression device, and an evaporator are connected in an annular shape, and the high pressure is operated in a supercritical state, and the decompression device is located upstream of a connection pipe that connects the radiator and the evaporator. And at least three pressure detecting means for detecting the pressure before and after the compressor and the pressure of the connecting pipe, and operating the refrigeration air conditioner based on the detected pressure of the pressure detecting means. Is provided with a control device that controls the target state to a predetermined target state.

  In the present invention, by controlling the amount of refrigerant present in the connection pipe by the control device, the operation state of the refrigeration air conditioner can be controlled to a high pressure at which the COP is maximized. There is an effect that a low-cost refrigeration air conditioner can be obtained without requiring a container for controlling the amount of refrigerant.

[Embodiment 1]
1 is a refrigerant circuit diagram of a refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. In FIG. 1, a compressor 3, a four-way valve 4, an outdoor heat exchanger 5, and an outdoor expansion valve 6 are mounted in the outdoor unit 1. Moreover, indoor side expansion valves 8a and 8b and indoor heat exchangers 9a and 9b are mounted in the indoor units 2a and 2b. The liquid pipe 7 and the gas pipe 10 are connecting pipes that connect the outdoor unit 1 and the indoor units 2a and 2b. CO ₂ is used as the refrigerant of the refrigeration air conditioner.

  In the outdoor unit 1, a pressure sensor 11a is provided on the discharge side of the compressor 3, a pressure sensor 11b is provided on the suction side of the compressor 3, and a pressure sensor 11c is provided between the outdoor expansion valve 6 and the liquid pipe 7, respectively. Measure the refrigerant pressure at the installation site. Further, the temperature sensor 12a is provided on the discharge side of the compressor 3, and the temperature sensor 12b is provided between the outdoor heat exchanger 5 and the outdoor expansion valve 6, and respectively measures the refrigerant temperature at the installation location. The temperature sensor 12c measures the outside air temperature around the outdoor unit 1.

  In the indoor units 2a and 2b, temperature sensors 12d and 12f are provided between the indoor heat exchangers 9a and 9b and the indoor side expansion valves 8a and 8b, and a temperature sensor 12e12g is provided between the indoor heat exchangers 9a and 9b and the gas pipe 10. The refrigerant temperature at each installation location is measured.

  In addition, a measurement control device 13 is provided in the outdoor unit 1, and compression is performed based on measurement information such as the pressure sensors 11a to 11c and the temperature sensors 12a to 12c and contents instructed by a user of the refrigeration air conditioner. The operation method of the machine 3, the flow path switching of the four-way valve 4, the heat exchange amount of the outdoor heat exchanger 5, the opening degree of the outdoor expansion valve 6 and the like are controlled.

  Next, the operation of the refrigeration air conditioner will be described. First, the operation during the cooling operation will be described. During the cooling operation, the flow path of the four-way valve 4 is set in the direction of the solid line in FIG. The high-temperature and high-pressure gas refrigerant discharged from the compressor 3 flows into the outdoor heat exchanger 5 through the four-way valve 4 and decreases in temperature while radiating heat in the outdoor heat exchanger 5 serving as a radiator. At this time, if the high pressure is equal to or higher than the critical pressure, the refrigerant lowers the temperature and dissipates heat while maintaining the supercritical state. If the high pressure is below the critical pressure, the refrigerant dissipates heat while liquefying. The high-pressure and low-temperature refrigerant exiting the outdoor heat exchanger 5 is decompressed by the outdoor expansion valve 6 and then flows into the indoor units 2 a and 2 b via the liquid pipe 7. Then, after the pressure is reduced to the low-pressure two-phase state by the indoor side expansion valves 8a and 8b, it flows into the indoor heat exchangers 9a and 9b serving as evaporators, absorbs heat therein, and is converted into evaporative gas while the indoor units 2a and 2b. Supply cold energy to load side media such as air and water on the side. The low-pressure gas refrigerant that has exited the indoor heat exchangers 9a and 9b exits the indoor units 2a and 2b, flows into the outdoor unit 1 through the gas pipe 10, and is sucked into the compressor 3 through the four-way valve 4.

  Next, operation during heating operation will be described. During the heating operation, the flow path of the four-way valve 4 is set in the direction of the dotted line in FIG. The high-temperature and high-pressure gas refrigerant discharged from the compressor 3 flows out of the outdoor unit 1 through the four-way valve 4, and flows into the indoor units 2 a and 2 b through the gas pipe 10. And it flows into indoor heat exchanger 9a, 9b, and temperature falls, radiating with indoor heat exchanger 9a, 9b used as a heat radiator. At this time, if the high pressure is equal to or higher than the critical pressure, the refrigerant lowers the temperature and dissipates heat while maintaining the supercritical state. If the high pressure is below the critical pressure, the refrigerant dissipates heat while liquefying. Heating is performed by applying heat radiated from the refrigerant to a load-side medium such as air or water on the load side. The high-pressure and low-temperature refrigerant that has exited the indoor heat exchangers 9a and 9b is decompressed by the indoor expansion valves 8a and 8b, and then flows into the outdoor unit 1 via the liquid pipe 7. After the pressure is reduced to a low-pressure two-phase state by the outdoor expansion valve 6, it flows into the outdoor heat exchanger 5 serving as an evaporator, where it absorbs heat and is evaporated and gasified. The low-pressure gas refrigerant exiting the outdoor heat exchanger 5 is sucked into the compressor 3 through the four-way valve 4.

Next, the operation control operation in this refrigeration air conditioner will be described. In a refrigeration cycle such as CO ₂ where the high pressure side is operated in a supercritical state, such as CO ₂ , there is a high pressure at which the operating efficiency is maximized, as is well known. FIG. 2 is a PH diagram showing the refrigeration cycle when the high pressure is changed when the radiator outlet temperature is the same. In FIG. 2, when the high pressure rises to P1, P2, and P3, the enthalpy difference ΔHe in the evaporator increases and the refrigeration capacity increases accordingly. On the other hand, when the high pressure rises, the enthalpy difference ΔHc in the compressor corresponding to the compressor input also increases. A tendency of changes due to high pressures of ΔHe and ΔHc at this time is shown in FIG. 3, and in a region where the increase rate of ΔHe corresponding to the capacity accompanying the increase in high pressure exceeds the increase rate of ΔHc corresponding to the input, ΔHe The efficiency COP of the refrigeration cycle represented by / ΔHc increases. Conversely, in the region where the increase rate of ΔHe corresponding to the capacity is lower than the increase rate of ΔHc corresponding to the input, the COP decreases. Therefore, there is a high pressure at which the COP is maximum, and this corresponds to the point P2 in FIG.

  The high pressure in the refrigeration air conditioner is determined by the amount of refrigerant present in the radiator. When the refrigerant state is supercritical, the density of the refrigerant increases according to the pressure. Therefore, the amount of refrigerant in the radiator when operating at the high pressure P3 in FIG. 2 is within the heat dissipation when operating at the high pressure P1. More than the amount of refrigerant. On the contrary, if the operation is performed so that the amount of refrigerant existing in the radiator increases, the high pressure increases, and if the operation is performed so that the amount of refrigerant existing in the radiator decreases, the high pressure decreases. Therefore, by controlling the amount of refrigerant present in the radiator, the high pressure is controlled to be the maximum COP pressure.

  Hereinafter, the control operation during the cooling operation will be described with reference to FIG. In the cooling operation, the operation capacity of the compressor 3 controlled by the rotational speed or the like is controlled such that the low pressure becomes a low pressure corresponding to a predetermined target value, for example, a saturation temperature of 10 ° C. The indoor expansion valve 8a has a target value of the refrigerant superheat degree at the outlet of the indoor heat exchanger 9a calculated by the temperature of the temperature sensor 12e-the temperature of the temperature sensor 12d, and the indoor expansion valve 8b Control is performed so that the refrigerant superheat degree at the outlet of the indoor heat exchanger 9b calculated by the temperature of the sensor 12g-the temperature of the temperature sensor 12f becomes a target value. As this target value, a predetermined target value, for example, 5 ° C. is used. The outdoor expansion valve 6 is controlled to a predetermined initial opening. In addition, the heat exchange amount of the outdoor heat exchanger 5 and the heat exchange amounts of the indoor heat exchangers 9a and 9b are operated in a state in which the number of rotations of a fan that conveys air or water as a heat transfer medium, the pump flow rate, and the like are set in advance. To do.

  The high pressure when operating in this state is measured by the pressure sensor 11a. Then, the optimum high pressure that maximizes the COP is calculated by a predetermined calculation formula from the radiator outlet temperature measured by the temperature sensor 12b, the outside air temperature detected by the temperature sensor 12c, the operating capacity of the compressor 3, and the like. Compare the high pressure with the measured high pressure. If the current high pressure is lower than the optimum high pressure, the amount of refrigerant in the outdoor heat exchanger 5 that is a radiator is large. Conversely, if the current high pressure is higher than the optimum high pressure, the amount of refrigerant in the outdoor heat exchanger 5 is large. Control to reduce.

  Control of the amount of refrigerant in the outdoor heat exchanger 5 is performed by opening degree control of the outdoor expansion valve 6. FIG. 5 is a PH diagram showing a state change of the refrigeration air conditioner when the opening degree control of the outdoor expansion valve 6 is performed. The solid line cycle in FIG. 5 represents the operating state when the opening degree of the outdoor expansion valve 6 is reduced and the flow resistance is increased, and the dotted line cycle in FIG. 5 increases the opening degree of the outdoor expansion valve 6. Indicates the operating state when the flow resistance is reduced. ΔP1 is a differential pressure at the outdoor expansion valve 6, and ΔP2 is a differential pressure at the indoor expansion valves 8a and 8b. When the opening degree control of the outdoor expansion valve 6 is carried out in this way, the indoor expansion valves 8a and 8b are depressurized from the pressure at the outlet of the outdoor expansion valve 6 to a low pressure. Therefore, in the cycle shown by the solid line in FIG. The opening is increased so that ΔP2 is reduced, and the flow resistance is decreased. In the cycle indicated by the dotted line in FIG. 5, the opening is decreased so that ΔP2 is increased, and the flow resistance is increased. Driven.

The state of the liquid pipe 7 between the outdoor expansion valve 6 and the indoor expansion valves 8a and 8b becomes the state of point A in FIG. In the cycle indicated by the solid line in FIG. 5, the refrigerant present in the liquid pipe 7 is a refrigerant in a two-phase state close to low pressure, and in the cycle indicated by the dotted line in FIG. 5, the liquid pipe 7 is a refrigerant in a supercritical state close to high pressure. Therefore, in the liquid pipe 7, there is a refrigerant in a state close to high-pressure liquid in the dotted line cycle, and the amount of refrigerant increases, whereas in the solid line cycle, the refrigerant exists in a gas-liquid two-phase state and gas refrigerant exists. The amount of refrigerant present in the liquid pipe 7 is reduced by that amount.
FIG. 6 shows this situation as a correlation between the pressure P of the liquid pipe 7 and the refrigerant amount M in the case of the same enthalpy. When the pressure is higher than the saturation pressure, the amount of refrigerant in the liquid pipe 7 gradually increases according to the pressure. When the pressure is lower than the saturation pressure, gas is present, and at a pressure close to the saturation pressure, the volume ratio of the gas increases rapidly in accordance with the pressure drop, so the amount of refrigerant in the liquid pipe 7 decreases rapidly. When the pressure is reduced to a pressure close to a low pressure, the increase in the volume ratio of the gas accompanying the pressure drop becomes substantially constant, and the refrigerant amount in the liquid pipe 7 gradually decreases. Since such a refrigerant amount change occurs, the refrigerant amount existing in the liquid pipe 7 can be controlled by controlling the pressure of the liquid pipe 7 by controlling the opening degree of the outdoor expansion valve 6.

  When the amount of refrigerant existing in the liquid pipe 7 changes, the amount of refrigerant in the outdoor heat exchanger 5 that is a radiator changes accordingly. The amount of refrigerant charged in the refrigeration air conditioner is almost the same, and the amount of refrigerant present in the portion other than the liquid pipe 7 and the outdoor heat exchanger 5 is not large relative to the amount of refrigerant charged, and therefore exists in the liquid pipe 7. When the amount of refrigerant increases, the amount of refrigerant present in the outdoor heat exchanger 5 decreases and the high pressure decreases, and when the amount of refrigerant present in the liquid pipe 7 decreases, the amount of refrigerant present in the outdoor heat exchanger 5 increases, Rises. Therefore, as shown in FIG. 5, when the opening degree is increased by controlling the opening degree of the outdoor expansion valve 6, the amount of refrigerant existing in the liquid pipe 7 is increased and the high pressure is lowered. The amount of refrigerant present in the pipe 7 decreases and the high pressure increases. Thus, by controlling the opening of the outdoor expansion valve 6 so that the high pressure becomes the maximum COP pressure, an efficient operation of the refrigeration air conditioner can be realized.

  Next, the control operation during the heating operation will be described with reference to FIG. In the heating operation, the operating capacity of the compressor 3 controlled by the number of revolutions is a low pressure corresponding to a predetermined value at which the low pressure is determined in advance, for example, a saturation pressure at a temperature of the outside air temperature −5 ° C. measured by the temperature sensor 12c It is controlled to become. The indoor side expansion valves 8a and 8b are provided with a predetermined target value for the refrigerant temperature at the outlets of the indoor heat exchangers 9a and 9b measured by the temperature sensors 12d and 12f, for example, a load side medium temperature such as an indoor air temperature. It is controlled to be + 5 ° C. The outdoor expansion valve 6 is controlled to a predetermined initial opening. In addition, the heat exchange amount of the outdoor heat exchanger 5 and the heat exchange amounts of the indoor heat exchangers 9a and 9b are operated in a state in which the number of rotations of a fan that conveys air or water as a heat transfer medium, the pump flow rate, and the like are set in advance. To do.

  The high pressure when operating in this state is measured by the pressure sensor 11a. Then, the COP maximum is determined by a predetermined calculation formula based on the temperature of the medium supplied to the load side set by the operator of the refrigeration air conditioner, the outlet temperature of the indoor heat exchangers 9a and 9b, the operating capacity of the compressor 3, and the like. The optimum high pressure is calculated, and the optimum high pressure is compared with the measured high pressure. Then, if the current high pressure is lower than the optimum high pressure, the amount of refrigerant in the indoor heat exchangers 9a and 9b, which are radiators, is increased. Conversely, if the current high pressure is higher than the optimum high pressure, the indoor heat exchanger 9a. , 9b is controlled to reduce the amount of refrigerant.

  In the case of heating operation, if the opening degree of the outdoor expansion valve 6 is decreased and the flow resistance is increased, the pressure of the liquid pipe 7 increases, and the amount of refrigerant existing there increases, while the opening degree of the outdoor expansion valve 6 increases. When the flow resistance is decreased and the flow resistance is decreased, the pressure of the liquid pipe 7 is decreased, and the amount of refrigerant existing therein is decreased. As in the case of the cooling operation, when the amount of refrigerant in the liquid pipe 7 increases or decreases, the amount of refrigerant existing in the indoor heat exchangers 9a and 9b that are radiators also increases or decreases accordingly. Therefore, by controlling the opening degree of the outdoor expansion valve 6, the high pressure of the refrigeration cycle can be controlled, and by controlling the high pressure so as to become the maximum COP pressure, an efficient operation of the refrigeration air conditioner can be realized.

  In the control operation of the refrigerant amount in each of the above operations, the increase / decrease of the refrigerant amount present in the liquid pipe 7 changes the state in a situation where the refrigerant is always flowing compared to the case where the refrigerant amount existing in the container is increased / decreased. Since the amount of refrigerant is increased or decreased, the state change is performed quickly. Therefore, when the opening degree of the outdoor expansion valve 6 is controlled by feedback control so that the high pressure becomes the optimum high pressure, the high pressure can be quickly brought close to the optimum high pressure even if the optimum high pressure changes due to a change in operating conditions. The operation control can be stably performed, and more efficient operation of the refrigeration air conditioner can be realized.

When the refrigerant amount control of the liquid pipe 7 is performed by controlling the opening degree of the outdoor expansion valve 6, the pressure in the liquid pipe 7 is measured by the pressure sensor 11c, and the opening degree control is performed based on the measurement result. You may implement. For example, when the volume of the heat exchanger serving as a radiator is known, the high pressure change accompanying the change in the refrigerant amount can be estimated in advance, and the correlation between the refrigerant amount and the pressure in the liquid pipe 7 shown in FIG. 6 is known The amount of refrigerant present in the radiator and the amount of refrigerant in the liquid pipe 7 that realizes the amount of change are estimated from the deviation between the current high pressure and the optimum high pressure, and the amount of refrigerant in the liquid pipe 7 that realizes the amount of refrigerant is calculated. Set the target pressure. And the opening degree control of the outdoor side expansion valve 6 is implemented so that the pressure of the liquid pipe 7 may become a target pressure. By controlling in this way, feedback control can be performed using the pressure of the liquid pipe 7 that changes more directly as the opening of the outdoor expansion valve 6 changes, so that the high pressure can be quickly brought close to the optimum high pressure, The operation control can be stably performed, and more efficient operation of the refrigeration air conditioner can be realized.
When the high pressure and the low pressure are measured by the pressure sensors 11a and 11b, the pressure of the liquid pipe 7 is determined by the flow rate of each expansion valve determined from the opening ratio of the outdoor expansion valve 6 and the indoor expansion valve 8. It can be estimated from the resistance ratio. Therefore, the degree of opening of the outdoor expansion valve 6 may be controlled so that the estimated pressure becomes the target pressure.

The initial opening degree of the outdoor expansion valve 6 may be controlled to a state close to a state in which the refrigerant amount in the liquid pipe 7 is presumed to achieve the optimum high pressure in advance depending on the operation state and the operation state of the refrigeration air conditioner. For example, in the cooling operation and the heating operation, heat exchangers serving as radiators are different, and generally the volume of the outdoor heat exchanger 5 serving as a radiator during cooling operations is large. Therefore, it is desirable that the amount of refrigerant that should be present in the heat exchanger as a radiator for realizing the optimum high pressure in the cooling operation is larger and the amount of refrigerant present in the liquid pipe 7 is smaller. Therefore, during the cooling operation, the operation is performed so that the initial opening degree of the outdoor expansion valve 6 is reduced and the pressure of the liquid pipe 7 is lowered so that the amount of refrigerant existing in the liquid pipe 7 is reduced. On the other hand, compared with the cooling operation, the amount of refrigerant that should be present in the heat exchanger that is a radiator for realizing the optimum high pressure is reduced during heating operation, and it is desirable that the amount of refrigerant existing in the separation pipe 7 is increased. . Therefore, during the heating operation, the initial opening degree of the outdoor expansion valve 6 is appropriately reduced, and the operation is performed in a state where the pressure of the liquid pipe 7 is higher than that during the cooling operation.
By controlling the opening degree of the outdoor expansion valve 6 in this manner, the amount of refrigerant existing in the heat exchanger serving as a radiator becomes the amount of refrigerant that realizes the optimum high pressure regardless of the operation mode of cooling operation or heating operation. Initial operation can be performed in a close state, high pressure can be quickly brought close to the optimum high pressure, operation control can be stably performed, and more efficient operation of the refrigeration air conditioner can be realized.

In addition, when the liquid pipe 7 is long and the volume of the liquid pipe 7 is larger than the volume of the heat exchanger serving as a radiator, the pressure change of the liquid pipe 7 is large, and when the fluctuation of the amount of refrigerant existing there increases, The effect on the refrigerant amount fluctuation of the vessel becomes large, and the fluctuation of high pressure also becomes large. Therefore, it is desirable to set the initial opening of the outdoor expansion valve 6 in this case so that the pressure of the liquid pipe 7 does not change greatly. Therefore, during the cooling operation, the initial opening degree of the outdoor expansion valve 6 is increased so that the pressure of the liquid pipe 7 is close to a high pressure, and also during the heating operation, the initial opening degree of the outdoor expansion valve 6 is appropriately set. The pressure in the liquid pipe 7 is made close to a high pressure. By this control, the refrigerant amount fluctuation of the liquid pipe 7 can be reduced, the excessive refrigerant quantity fluctuation of the radiator can be suppressed, the excessive high pressure fluctuation can be suppressed, and the operation control can be more stably performed.
Further, during the cooling operation, the initial opening degree of the outdoor expansion valve 6 is appropriately reduced, the pressure of the liquid pipe 7 is set to a pressure close to a low pressure, and also during the heating operation, the initial opening degree of the outdoor expansion valve 6 is set. The pressure in the liquid pipe 7 may be increased to a pressure close to a low pressure. Also in this case, the refrigerant amount fluctuation of the liquid pipe 7 can be reduced, the excessive refrigerant quantity fluctuation of the radiator can be suppressed, the excessive high pressure fluctuation can be suppressed, and the operation control can be more stably performed.

[Embodiment 2]
A second embodiment of the present invention is shown in FIG. 8 is the same as FIG. 1 except for the high / low pressure heat exchanger 14 and the bypass expansion valve 15, and the operation and effects thereof are also the same as those in the first embodiment, so that the description thereof is omitted. The high / low pressure heat exchanger 14 is a double pipe heat exchanger, and the inner pipe side is a main side flow path and the outer pipe side is a bypass side flow path.

  First, the operation of the high / low pressure heat exchanger 14 and the bypass expansion valve 15 in the cooling operation in this embodiment will be described. In the cooling operation, the low-temperature and high-pressure refrigerant that has exited the outdoor heat exchanger 5 serving as a radiator is decompressed by the outdoor unit-side expansion valve 6 and then passes through the main-side flow path of the high-low pressure heat exchanger 14. A part of the refrigerant in the main-side flow channel exiting the high-low pressure heat exchanger 14 is bypassed in the bypass-side flow channel of the high-low pressure heat exchanger 14, and the pressure is reduced to low-pressure two-phase refrigerant by the bypass expansion valve 15. It flows in after. Then, the refrigerant in the main-side channel having a relatively high pressure and the refrigerant in the bypass-side channel having a low pressure exchange heat, and heat is transferred from the refrigerant in the main-side channel to the refrigerant in the bypass-side channel. Accordingly, the refrigerant in the main-side refrigerant flow path is further cooled and then flows into the liquid pipe 7. On the other hand, the refrigerant in the bypass-side flow channel absorbs heat and evaporates and is then sucked into the compressor 3.

  The heat exchange amount in the high / low pressure heat exchanger 14 increases / decreases depending on the refrigerant flow rate of the bypass side flow path serving as a cold heat source, and the heat exchange amount decreases when the refrigerant flow rate flowing through the bypass side flow path is small. As the flow rate of the refrigerant flowing through increases, the amount of heat exchange increases. FIG. 9 shows a PH diagram of the refrigeration cycle when the heat exchange amount fluctuates. Point A in FIG. 9 is the main channel outlet in the high-low pressure heat exchanger 14, that is, the refrigerant state of the liquid pipe 7. However, when the amount of heat exchange increases, the refrigerant state of the liquid pipe 7 is further cooled and becomes enthalpy. It becomes a low state and follows the dotted line path of FIG. On the other hand, when the amount of heat exchange decreases, the amount of cooling decreases and follows the path of the solid line in FIG.

At this time, when the state of the liquid pipe 7 is a gas-liquid two-phase, when the amount of heat exchange in the high / low pressure heat exchanger 14 is large and the amount of cooling is increased, the dryness is lower and the two-phase state is rich in liquid refrigerant. Thus, the amount of refrigerant existing in the liquid pipe 7 increases. On the other hand, if the amount of heat exchange in the high / low pressure heat exchanger 14 is small and the amount of cooling is reduced, the dryness remains high, a two-phase state with a large amount of gas refrigerant, and the amount of refrigerant present in the liquid pipe 7 decreases. To do. Therefore, the amount of refrigerant existing in the liquid pipe 7 can be changed by changing the heat exchange amount in the high / low pressure heat exchanger 14 by controlling the flow rate in the bypass side expansion valve 15.
Further, when the state of the liquid pipe 7 is a single-phase state such as a supercritical state, when the amount of heat exchange in the high-low pressure heat exchanger 14 is large and the cooling amount is increased, the refrigerant state of the liquid pipe 7 is more It becomes a low state. On the other hand, when the amount of heat exchange in the high / low pressure heat exchanger 14 is small and the amount of cooling decreases, the refrigerant state of the liquid pipe 7 remains high. In a single-phase refrigerant, since the density increases as the temperature decreases, the amount of heat exchange in the high / low pressure heat exchanger 14 increases, and as the cooling amount increases, the amount of refrigerant in the liquid pipe 7 increases, and the high / low pressure heat exchanger increases. When the amount of heat exchange at 14 is small and the amount of cooling decreases, the amount of refrigerant in the liquid pipe 7 decreases. Therefore, even if the liquid pipe 7 is in a single-phase state, the amount of heat exchange in the high-low pressure heat exchanger 14 is changed by controlling the flow rate in the bypass side expansion valve 15 as in the case of the gas-liquid two-phase state. As a result, the amount of refrigerant present in the liquid pipe 7 can be changed.

Therefore, a control method for achieving an optimum high pressure when operating the refrigeration air conditioner will be described with reference to FIG. First, when the high pressure is lower than the optimum high pressure at which the COP is maximum, the refrigerant amount in the liquid pipe 7 is decreased so as to increase the refrigerant amount in the heat exchanger serving as a radiator and increase the high pressure. The opening degree of the bypass side expansion valve 15 is decreased, the bypass flow rate is decreased, and the heat exchange amount in the high / low pressure heat exchanger 14 is decreased. On the contrary, when the high pressure is higher than the optimum high pressure at which the COP is maximum, the refrigerant amount in the liquid pipe 7 is increased in order to reduce the refrigerant amount in the heat exchanger serving as a radiator and lower the high pressure. The opening degree of the bypass side expansion valve 15 is increased, the bypass flow rate is increased, and the heat exchange amount in the high / low pressure heat exchanger 14 is increased.
By controlling the opening of the bypass side expansion valve 15 so that the high pressure becomes the maximum COP pressure, an efficient operation of the refrigerating and air-conditioning apparatus can be realized.

  Next, the operation of the high / low pressure heat exchanger 14 and the bypass expansion valve 15 in the heating operation in this embodiment will be described. In the heating operation, the low-temperature and high-pressure refrigerant that has exited the indoor heat exchangers 9a and 9b serving as radiators is decompressed by the indoor expansion valves 8a and 8b, and after passing through the liquid pipe 7, the high-low pressure heat exchanger 14 It passes through the main channel. A part of the refrigerant in the main side flow path at the inlet of the high / low pressure heat exchanger 14 is bypassed in the bypass side flow path of the high / low pressure heat exchanger 14, and the pressure is reduced to a low pressure two-phase refrigerant by the bypass expansion valve 15. It will flow later. Then, the refrigerant in the main-side channel having a relatively high pressure and the refrigerant in the bypass-side channel having a low pressure exchange heat, and heat is transferred from the refrigerant in the main-side channel to the refrigerant in the bypass-side channel. Along with this, the refrigerant in the main-side refrigerant flow path is further cooled and then reduced to a low pressure by the outdoor expansion valve 6 and flows into the outdoor heat exchanger 5 that is an evaporator. On the other hand, the refrigerant in the bypass-side flow channel absorbs heat and evaporates and is then sucked into the compressor 3.

  In the case of heating operation, the amount of refrigerant in the outdoor heat exchanger 5 serving as an evaporator can be increased or decreased depending on the amount of heat exchange in the high-low pressure heat exchanger 14 although the amount of refrigerant in the liquid pipe 7 does not change. FIG. 9 shows a PH diagram of the refrigeration cycle when the heat exchange amount at this time varies. A point B in FIG. 9 is a state where the main side flow path in the high / low pressure heat exchanger 14 is discharged and the pressure is reduced by the outdoor expansion valve 6, that is, the refrigerant state at the inlet of the outdoor heat exchanger 5. When the amount of heat exchange increases, the refrigerant state at the inlet of the outdoor heat exchanger 5 is further cooled, the enthalpy is low, and the dryness is small, and the path of the dotted line in FIG. 9 is followed. On the other hand, when the heat exchange amount decreases, the cooling amount decreases, the enthalpy is high, and the dryness remains large, and the path of the solid line in FIG. 9 is followed.

  If the refrigerant state at the evaporator inlet has a lower dryness, the volume occupied by the liquid refrigerant increases at least near the evaporator inlet. As a result, the amount of refrigerant present in the entire evaporator increases. Therefore, when the amount of heat exchange in the high / low pressure heat exchanger 14 is large and the amount of cooling is increased, the refrigerant state at the inlet of the outdoor heat exchanger 5 becomes a two-phase state with a low degree of dryness and a large amount of liquid refrigerant. The amount of refrigerant present in the exchanger 5 increases. On the other hand, when the amount of heat exchange in the high / low pressure heat exchanger 14 is small and the amount of cooling is reduced, the refrigerant state at the inlet of the outdoor heat exchanger 5 remains in a high dryness state and becomes a two-phase state with a large amount of gas refrigerant. The amount of refrigerant present in the outdoor heat exchanger 5 is reduced. Therefore, the amount of refrigerant existing in the outdoor heat exchanger 5 can be changed by changing the heat exchange amount in the high / low pressure heat exchanger 14 by controlling the flow rate in the bypass side expansion valve 15.

Therefore, when operating the refrigerating and air-conditioning apparatus, control for achieving an optimum high pressure is performed as follows. First, when the high pressure is lower than the optimum high pressure at which the COP is maximum, the amount of refrigerant in the outdoor heat exchanger 5 decreases in order to increase the amount of refrigerant in the heat exchanger serving as a radiator and increase the high pressure. Thus, the opening degree of the bypass side expansion valve 15 is reduced, the bypass flow rate is reduced, and the heat exchange amount in the high / low pressure heat exchanger 14 is reduced. Conversely, when the high pressure is higher than the optimum high pressure at which the COP is maximum, the amount of refrigerant in the outdoor heat exchanger 5 is increased in order to reduce the amount of refrigerant in the heat exchanger serving as a radiator and lower the high pressure. Thus, the opening degree of the bypass side expansion valve 15 is increased, the bypass flow rate is increased, and the heat exchange amount in the high / low pressure heat exchanger 14 is increased.
In this way, by controlling the opening of the bypass side expansion valve 15 so that the high pressure becomes the pressure that maximizes the COP, an efficient operation of the refrigeration air conditioner can be realized.

  The control of the heat exchange amount in the high / low pressure heat exchanger 14 and the control of the pressure of the liquid pipe 7 described in the first embodiment may be performed in combination. In this case, the fluctuation range of the refrigerant amount in the liquid pipe 7 can be increased, and even when the volume of the liquid pipe 7 is smaller than the volume of the heat exchanger serving as a radiator, the optimum high pressure is obtained. The amount of refrigerant in the radiator can be controlled, and efficient operation of the refrigeration air conditioner can be realized.

  In addition, as a form of the high and low pressure heat exchanger 14 for changing the refrigerant state of the heat exchanger inlet serving as the liquid pipe 7 or the evaporator, as long as it performs transfer of heat for changing the refrigerant state, Other than the form of FIG. 8 can be taken. For example, as in the refrigerant circuit shown in FIG. 11, heat exchange with the refrigerant sucked by the compressor 3 may be performed. In this circuit, a part of the refrigerant sucked into the compressor 3 is supplied to the high / low pressure heat exchanger 14 via the bypass side valve 15. The amount of heat exchange in the high / low pressure heat exchanger 14 can be increased by increasing the opening degree of the bypass side valve 15 and increasing the flow rate of the refrigerant flowing into the high / low pressure heat exchanger 14, as shown in FIG. Similarly, the amount of refrigerant in the radiator can be controlled so as to obtain an optimum high pressure.

  Further, as in the refrigerant circuit shown in FIG. 12, the heat quantity of the external heat source 16 may be exchanged by the high and low pressure heat exchanger 14. Also in this case, the amount of heat exchange in the high / low pressure heat exchanger 14 can be changed by controlling the opening degree of the bypass side valve 15, and as in the case of FIG. The amount of refrigerant can be controlled. In addition, as the external heat source 16, a cold heat source such as ice or water stored at night or outside air around the outdoor unit can be used. In addition, the main refrigerant in the high-low pressure heat exchanger 14 can be changed not only by cooling but also by heating, and in this case as well, the refrigerant amount in the liquid pipe 7 and the outdoor heat exchanger 5 can be reduced. Can be controlled. That is, by being heated by the high-low pressure heat exchanger 14, the refrigerant state at the inlet of the liquid pipe 7 and the outdoor heat exchanger 5 becomes a dryness and high-temperature refrigerant, and the amount of refrigerant existing there decreases. As the external heat source 16 serving as a heating source, hot water stored at night or outside air around the outdoor unit can be used.

It is a refrigerant circuit diagram of the refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. FIG. 3 is a PH diagram showing an operation state of the refrigeration air conditioner during high pressure fluctuation according to the first embodiment. It is a figure which shows the correlation with the high efficiency of Embodiment 1, and the operation efficiency COP. FIG. 3 is a flowchart showing a control operation during the cooling operation of the first embodiment. FIG. 6 is a PH diagram showing a change in the operating status of the refrigeration air conditioner during outdoor outdoor expansion valve opening degree control of the first embodiment. FIG. 3 is a diagram showing a correlation between the pressure of the liquid pipe and the amount of refrigerant in the first embodiment. FIG. 4 is a flowchart showing a control operation during heating operation in the first embodiment. It is a refrigerant circuit diagram of the refrigerating and air-conditioning apparatus according to Embodiment 2 of the present invention. It is a PH diagram showing the change of the driving | running state of the refrigerating air conditioner at the time of heat exchange amount control of the high-low pressure heat exchanger of Embodiment 2. FIG. 6 is a flowchart showing a control operation during cooling operation of the second embodiment. It is a refrigerant circuit figure of the refrigerating and air-conditioning apparatus of the other example of Embodiment 2. It is a refrigerant circuit figure of the refrigerating and air-conditioning apparatus of the other example of Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Outdoor unit 2a, 2b Indoor unit, 3 Compressor, 4 Four way valve, 5 Outdoor heat exchanger, 6 Outdoor expansion valve, 7 Liquid pipe, 8a, 8b Indoor expansion valve, 9a, 9b Indoor heat exchanger, 10 Gas pipe, 11a, 11b, 11c Pressure sensor, 12a, 12b, 12c, 12d, 12e, 12f, 12g Temperature sensor, 13 Measurement control device, 14 High / low pressure heat exchanger, 15 Bypass side expansion valve, Bypass side valve, 16 External heat source.

Claims (9)

In a refrigeration air conditioner in which a compressor, a radiator, a decompressor, and an evaporator are connected in a ring and the high pressure is operated in a supercritical state,
The decompression device is installed on the upstream side and the downstream side of the connecting pipe connecting the radiator and the evaporator, and at least three pressure detecting means for detecting the pressure before and after the compressor and the pressure of the connecting pipe are provided. A refrigerating and air-conditioning apparatus comprising a control device that controls the operation of the refrigerating and air-conditioning apparatus to a predetermined target state based on a pressure detected by a pressure detecting means .   2. The refrigerating and air-conditioning apparatus according to claim 1, wherein a predetermined target state is a high pressure of the refrigerating and air-conditioning apparatus.   The refrigeration according to claim 2, wherein when the high pressure of the refrigeration air conditioner is higher than a target value, the ratio of the flow resistance in the downstream pressure reduction device to the flow resistance in the upstream pressure reduction device is controlled to be large. Air conditioner.   3. The refrigeration according to claim 2, wherein when the high pressure of the refrigeration air conditioner is lower than a target value, the ratio of the flow resistance in the downstream pressure reduction device to the flow resistance in the upstream pressure reduction device is controlled to be small. Air conditioner.   The initial ratio of the flow resistance in the downstream decompression device to the flow resistance in the upstream decompression device during the initial operation of the refrigeration air conditioner is switched depending on the operation mode of the refrigeration air conditioning device. Refrigeration air conditioner.   A compressor, radiator, decompressor, and evaporator are connected in a ring, and in a refrigeration air conditioner that operates in a supercritical state at high pressure, a heat exchange device is provided to cool or heat the refrigerant between the radiator and the decompressor. By controlling the amount of heat exchange in this heat exchange device, the amount of refrigerant existing in the evaporator and the connecting pipe connecting the decompression device and the evaporator is controlled, and the operating state of the refrigeration air conditioner is set to a predetermined target. A refrigeration air conditioner comprising a control device for controlling the state.   The refrigerating and air-conditioning apparatus according to claim 6, wherein a predetermined target state is set to a high pressure of the refrigerating and air-conditioning apparatus.   The refrigeration air conditioner according to claim 7, wherein when the high pressure of the refrigeration air conditioner is higher than a target value, the cooling amount in the heat exchange device is increased or the heating amount is decreased. The refrigeration air conditioner according to claim 8, wherein when the high pressure of the refrigeration air conditioner is lower than a target value, the cooling amount in the heat exchange device is decreased or the heating amount is increased.

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