JP2007285635A - Refrigerating cycle device and air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a refrigerating cycle preventing liquid compression by suppressing a liquid return amount to a compressor in transient operating states such as starting, defrosting, and stoppage of the refrigerating cycle, and at the same time, capable of stabilizing the refrigerating cycle during small capacity operation. <P>SOLUTION: In the refrigerating cycle, a bridge circuit 5 composed of a check valve is provided between an outdoor pressure reducing device and an indoor pressure reducing device, a receiver 6 and a pressure reducing device 11 are sequentially connected in a circuit flowing in one direction of the bridge circuit, and a receiver bypass circuit 12 and a constantly closed receiver opening and closing valve 13 opening and closing the receiver bypass circuit are provided such that a gas coolant of a receiver vertex part flows with respect to a piping connecting the pressure reducing device and the bridge circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a refrigeration cycle apparatus such as an air conditioner, and is particularly suitable for a receiver in which liquid refrigerant is stored and connected to an indoor heat exchanger and an outdoor heat exchanger by piping.

  In the case of a transient operation such as when the refrigeration cycle is started and when the defrosting operation is switched, the liquid refrigerant easily returns to the suction side of the compressor.Therefore, in the conventional refrigeration cycle, an accumulator is arranged in front of the compressor. The liquid refrigerant is stored in the accumulator, and the liquid refrigerant amount returning to the suction side of the compressor is set to a certain amount or less to prevent liquid compression. However, the arrangement of an accumulator is disadvantageous in that it causes performance degradation due to increased pressure loss and two-phase separation between oil and liquid refrigerant. However, if the accumulator is removed, the refrigerant is not sufficiently vaporized in the evaporator when starting the refrigeration cycle or when switching to the defrosting operation, and it is easy to return to the suction side of the compressor as a liquid refrigerant. Incurs a decline.

  On the other hand, according to the method described in Patent Document 1, as a means for establishing an accumulator-less refrigeration cycle configuration, a compressor, a condenser, a liquid receiver, a pressure reducing valve, and an evaporator are connected. In a refrigeration cycle which is a refrigerant circuit and configured so that the pressure reducing valve is downstream of the liquid receiver in any operation mode, a gas space above the liquid receiver and a liquid line downstream of the pressure reducing valve are provided. A bypass circuit to be connected and a normally closed on-off valve for opening and closing the bypass circuit are provided, and the on-off valve is opened when the compressor is started or defrosting operation is switched. By flowing to the downstream side, i.e., the inlet side of the evaporator, the liquid refrigerant in the condenser can be moved and stored in the receiver, and the degree of scrubbing of the refrigerant returning from the evaporator can be increased. Place But it is possible to suppress the amount of liquid refrigerant returns to the suction side of the compressor, how it is possible to prevent the liquid compression are proposed.

  Further, in Patent Document 2, the liquid receiver is provided with a bypass pipe as a gas-liquid flow rate adjusting means so as to bypass from the upper part of the liquid receiver to the pipes before and after the liquid receiver, On-line valves are provided with on-off valves, and each pipe from the top of the receiver is connected to the bypass pipe of each on-off valve, and gas for adjusting the gas flow rate flowing out from the receiver A flow control device is provided.

JP-A-5-332644 (FIG. 2) Japanese Patent No. 3331102 (paragraph 0027 and FIG. 1)

  In the thing of patent document 1, since the gas refrigerant of a receiver top is bypassed to the downstream of an expansion valve, when the operating capacity of a compressor is small or the evaporation temperature is low, the amount of refrigerant circulation in a refrigerating cycle is low. The following problem arises when there are few cases. That is, since the refrigerant flowing into the upstream side of the expansion valve is a liquid refrigerant that flows out from the liquid receiver, when the refrigerant circulation amount is small, the opening degree of the expansion valve must be used with a slight throttle. For this reason, when adjusting the opening degree of the expansion valve, the flow rate characteristic is sensitive to the opening degree. Therefore, the opening degree adjustment is not successful during the adjustment of the opening degree of the expansion valve, and the liquid refrigerant is easy to return. In some cases, not only the refrigeration cycle becomes unstable, but also the amount of liquid return to the compressor increases, leading to liquid compression.

  In the thing of patent document 2, it becomes the structure which extracts a gas refrigerant from a liquid receiver in both cooling and heating, and uses two on-off valves, and the cycle is complicated. In addition, since a pressure is applied to the on / off valves other than the on / off valve that opens to extract the gas refrigerant from the liquid receiver during the cooling or heating operation, a pressure is applied in the direction opposite to the flow direction, so that chattering occurs.

  An object of the present invention is to suppress the liquid return amount to the compressor in a transient operation state such as at the start of the refrigeration cycle, at the time of defrosting, at the time of stop, and the like, and to reduce failures due to liquid compression. is there.

  In order to solve the above-described problems, according to one embodiment of the present invention, a refrigeration cycle apparatus includes a compressor, a four-way valve, an indoor heat exchanger, an indoor expansion valve, and an outdoor heat exchanger connected by a refrigerant pipe. In a cycle apparatus, a receiver connected to an indoor heat exchanger and an outdoor heat exchanger by a refrigerant pipe, and a bypass pipe for allowing a gas refrigerant in an upper part of the receiver to pass through and mixing with a liquid refrigerant flowing from the outlet of the receiver And a receiver open / close valve that adjusts the amount of gas refrigerant passing through the bypass pipe, and the refrigerant mixed with the gas refrigerant passing through the bypass pipe and the refrigerant flowing out of the receiver outlet is upstream of the indoor expansion valve. Or it is set as the structure which provided the switching part which switches and flows to the upstream of an outdoor expansion valve.

  Furthermore, it is desirable that the switching unit be a bridge circuit or a four-way valve composed of a check valve. Furthermore, a supercooler is connected to the downstream of the liquid receiver by a refrigerant pipe, the main stream part inlet of the supercooler is connected to the outlet pipe of the liquid receiver, the main stream part outlet of the supercooler is connected to the switching part, and the subcooler It is desirable that the substream inlet is connected to the pipe connecting the four-way valve and the compressor suction side, and the subflow outlet of the supercooler is connected to the receiver outlet. Furthermore, it is desirable to open the liquid receiver on / off valve for a predetermined time from the start of the compressor.

  ADVANTAGE OF THE INVENTION According to this invention, the failure by the liquid compression of a refrigeration cycle apparatus can be reduced with a simple structure, and the reliability of a refrigeration cycle apparatus can be improved.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a block diagram of a refrigeration cycle showing an embodiment of the present invention. The refrigeration cycle shown in FIG. 1 includes an outdoor unit composed of a compressor 1, a main four-way valve 2, an outdoor heat exchanger 3, an outdoor expansion valve 4, an indoor expansion valve 8, and an indoor heat exchanger 9. The machine is connected via a liquid blocking valve 7 and a gas blocking valve 10. Between the outdoor expansion valve 4 and the indoor expansion valve 8, a bridge circuit (switching unit) 5 composed of four check valves is provided, and the refrigerant flows into the circuit in which the refrigerant flows in one direction in the bridge circuit 5. A liquid receiver 6 for storing liquid refrigerant that has become surplus in the cycle is provided, and a pressure reducing device 11 having a certain pressure reducing effect is provided in the middle of a pipe connecting the outlet side of the liquid receiver 6 and the bridge circuit 5. In the middle of the pipe connecting the decompression device 11 and the bridge circuit 5, a liquid receiver bypass circuit 12 for flowing a gas refrigerant from the top of the liquid receiver 6 is provided, and in the middle of the liquid receiver bypass circuit 12. A normally closed receiver open / close valve 13 is provided. Here, the bridge circuit is a refrigerant circuit in which the midpoints of the refrigerant circuits arranged in parallel are connected by piping or the like. Further, the compressor 1 is provided with a start / stop control means 21 for controlling the start and stop of the compressor 1, and the main four-way valve 2 is heated when frost adheres to the heat exchanger acting as an evaporator. A defrost control means 22 for switching to a defrost operation mode for melting the frost of the exchanger is provided, and the receiver open / close valve 13 is based on signals from the start / stop control 21 and the defrost control means 22. On-off valve control means 23 for arbitrarily opening and closing the valve is provided.

  Next, the operation mode of the refrigeration cycle of the present invention will be described. The solid line arrows shown in this figure indicate the refrigerant flow during the heating operation, and the broken line arrows indicate the refrigerant flow during the cooling operation. During the heating operation, the high-temperature and high-pressure refrigerant compressed by the compressor 1 passes through the main four-way valve 2 and the gas blocking valve 10 and flows into the indoor heat exchanger 9, and the air and heat passing through the indoor heat exchanger 9. It is exchanged to condense and flow into the indoor expansion valve 8. In the indoor expansion valve 8, the refrigerant supercooling amount at the outlet of the indoor heat exchanger 9 is adjusted to be a certain constant value, and flows into the bridge circuit 5 through the liquid blocking valve 7. The liquid refrigerant that has flowed into the bridge circuit 5 is sent to the liquid receiver 6, the liquid refrigerant that is no longer necessary in the refrigeration cycle is stored, and the liquid refrigerant in the lower part of the liquid receiver 6 is sucked out and sent to the decompression device 11. The refrigerant sent to the decompression device 11 is decompressed by a certain amount, flows into the bridge circuit 5 again, and is sent to the outdoor expansion valve 4. The refrigerant sent to the outdoor expansion valve 4 is decompressed to a pressure that can be evaporated by the outdoor heat exchanger 3, flows into the outdoor heat exchanger 3, exchanges heat with air passing through the outdoor heat exchanger 3, and evaporates and gasifies. The refrigerant flows out, passes through the main four-way valve 2 and returns to the compressor 1 to form a refrigeration cycle.

  During the cooling operation, the high-temperature and high-pressure refrigerant compressed by the compressor 1 passes through the main four-way valve 2 and flows into the outdoor heat exchanger 3, and is condensed by exchanging heat with the air passing through the outdoor heat exchanger 3. It liquefies and flows into the outdoor expansion valve 4. In the outdoor expansion valve 4, the refrigerant supercooling amount at the outlet of the outdoor heat exchanger 3 is adjusted to be a certain value and flows into the bridge circuit 5. The liquid refrigerant that has flowed into the bridge circuit 5 is sent to the liquid receiver 6, the liquid refrigerant that is no longer necessary in the refrigeration cycle is stored, and the liquid refrigerant in the lower part of the liquid receiver 6 is sucked out and sent to the decompression device 11. The refrigerant sent to the decompression device 11 is decompressed by a certain amount, flows again into the bridge circuit 5, passes through the liquid blocking valve 7, and is sent to the indoor expansion valve 8. The refrigerant sent to the indoor expansion valve 8 is depressurized to a pressure that can be evaporated by the indoor heat exchanger 9, flows into the indoor heat exchanger 9, and exchanges heat with air passing through the indoor heat exchanger 9, thereby evaporating and gasifying. The refrigerant flows out, passes through the gas blocking valve 10 and the main four-way valve 2 and returns to the compressor 1 to form a refrigeration cycle.

  In the cooling operation and the heating operation, when the compressor 1 is started and stopped, when switching to the defrosting operation, or when switching from the defrosting operation to the normal operation, the receiver on-off valve 13 is opened to receive the air. The circuit configuration is such that the gas refrigerant at the top of the liquid container 6 flows through the liquid receiver bypass circuit 12. The pressure in the liquid receiver 6 and the outlet pressure of the liquid receiver bypass circuit 12 are the same as that of the liquid receiver bypass circuit 12 by the amount of pressure loss generated when the liquid refrigerant flowing out from the outlet of the liquid receiver 6 flows through the decompression device 11. The outlet pressure is reduced. Due to this pressure difference, the gas refrigerant at the top of the liquid receiver 6 flows into the liquid receiver bypass circuit 12 and merges with the gas-liquid two-phase refrigerant flowing out from the decompression device 11 to further increase the amount of gas. It becomes the degree of refrigerant clearance, and can flow into the expansion valve attached to the upstream side of the heat exchanger that acts as an evaporator through the bridge circuit 5.

  Next, the state of the refrigeration cycle when the liquid receiver on / off valve 13 is opened and closed will be described with reference to the Mollier diagram shown in FIG. In FIG. 2, the refrigeration cycle indicated by a solid line indicates a case where the liquid receiver open / close valve 13 is closed, and the refrigeration cycle indicated by a broken line indicates a case where the liquid receiver open / close valve 13 is opened. When the receiver open / close valve 13 is closed, the high-temperature and high-pressure gas refrigerant compressed by the compressor 1 becomes point a, condensates and liquefies by the condenser, and becomes point b, downstream of the heat exchanger that acts as a condenser. The pressure is reduced by the expansion valve attached to the side, and a saturated liquid state at point c is obtained and flows into the liquid receiver. The refrigerant flowing out of the liquid receiver 6 is depressurized by the decompression device 11 and an expansion valve attached upstream of the heat exchanger acting as an evaporator to be in the state of point d, and is evaporated into gas by the evaporator and is in the state of point e. Then, it is compressed again by the compressor 1. At this time, the degree of refrigerant X1 of the refrigerant at the point e flowing into the evaporator is smaller than the degree of liquid compression prevention limit of the compressor 1. On the other hand, when the liquid receiver open / close valve 13 is opened, the gas refrigerant is extracted from the top of the liquid receiver 6, so that the amount of liquid refrigerant stored in the liquid receiver 6 increases and flows in the refrigeration cycle. Since the effective refrigerant amount decreases, the operating pressure on the high pressure side decreases as compared with the case where the receiver open / close valve 13 is closed. That is, the high-temperature and high-pressure gas refrigerant compressed by the compressor 1 becomes a point a ′, is condensed and liquefied by the condenser to become a point b ′, and is decompressed by an expansion valve attached downstream of the heat exchanger acting as a condenser. Then, the gas-liquid two-phase state at the point c ′ is obtained and flows into the liquid receiver 6. The refrigerant state at the point c ′ is a refrigerant degree corresponding to the ratio of the amount of gas refrigerant flowing through the receiver bypass circuit 12 and the amount of liquid refrigerant flowing out of the outlet of the receiver 6 and flowing through the pressure reducing device 11. The refrigerant flowing out of the liquid receiver 6 is depressurized by the decompression device 11 and an expansion valve attached upstream of the heat exchanger acting as an evaporator to be in a state of a point d ′, and is evaporated into gas by the evaporator. The state becomes e ′ and is compressed again by the compressor 1. At this time, the degree of refrigerant X2 at the point e ′ flowing into the evaporator is higher than the degree X1 of refrigerant refrigerant at the point e when the receiver open / close valve 13 is closed and the degree of liquid compression prevention limit of the compressor 1. The decompression amount of the decompression device 11 is adjusted so that the amount of gas refrigerant flowing through the receiver bypass circuit 12 is adjusted so as to be a large value.

Next, the characteristics of the opening degree and flow rate of the expansion valve attached to the upstream side of the heat exchanger acting as an evaporator will be described. FIG. 3 is a flow rate characteristic diagram of an expansion valve used in one embodiment of the present invention. The horizontal axis represents the expansion valve opening, and the vertical axis represents the flow rate. In the figure, the solid line represents the flow rate characteristic when the liquid receiver on / off valve 13 is closed, and the broken line represents the flow characteristic when the liquid receiver on / off valve 13 is open. The opening degree of the expansion valve at the flow rate Q1 is V1 when the liquid receiver on / off valve 13 is closed, V3 when the liquid receiver on / off valve 13 is open, and V1 <V3. When the flow rate is increased to Q2, V2 when the liquid receiver on / off valve 13 is closed, V4 when the liquid receiver on / off valve 13 is open, and V2 <V4. Here, the difference in the opening degree of the expansion valve necessary for changing the flow rate flowing through the expansion valve from Q1 to Q2 is when the liquid receiver on-off valve 13 is closed (V2-V1), and the liquid receiver on-off valve 13 (V4-V3) in the open state, and the relationship of (V2-V1) <(V4-V3) is established. That is, when the liquid receiver on / off valve 13 is opened, it is necessary to increase the expansion valve opening in order to flow the same flow rate as compared with the case where the liquid receiver on / off valve 13 is closed, and In order to increase the same flow rate, it is necessary to increase the change width of the expansion valve opening. That is, when the liquid receiver on / off valve 13 is opened, the flow rate characteristic of the expansion valve can be controlled at a gentle point compared to when the liquid receiver on / off valve 13 is closed, It can be said that the fluctuation of the refrigeration cycle is small and stable with respect to the control of the expansion valve.
Next, the operation of the receiver open / close valve 13 in each operation mode of the refrigeration cycle of the present invention will be described.

  FIG. 4 is a time chart when the refrigeration cycle of the embodiment of the present invention is operated for heating. The main four-way valve 2 before starting the compressor is in a state indicated by a broken line in the refrigeration cycle shown in FIG. 1. The receiver open / close valve 13 is opened and the indoor expansion valve 8 is fully opened before or simultaneously with starting the compressor. The outdoor expansion valve 4 is set to a predetermined opening at the time of activation. At the start of the refrigeration cycle, first, the compressor 1 is started at a predetermined frequency Hz1, and the receiver open / close valve 13 is open, so that it flows into the indoor heat exchanger 9 that acts as an evaporator at the time of startup. Since the degree of cooling of the refrigerant is equal to or higher than the liquid compression limit of the compressor 1 and returns to the compressor 1, it can be started smoothly without liquid compression. Next, after the passage of T1 seconds, the main four-way valve 2 is switched, and the heating operation is started in the state shown by the solid line in the refrigeration cycle shown in FIG. 1, but since the receiver open / close valve 13 is open at this time, Since the amount of liquid refrigerant in the outdoor heat exchanger 3 that has acted as a condenser before switching the main four-way valve 2 is small, it can be smoothly operated without liquid compression even after the main four-way valve 2 is switched. Next, the receiver open / close valve 13 is closed when the operating frequency of the compressor 1 rises to Hz2 and T2 seconds have elapsed when the temperature and pressure of the compressor 1 and the heat exchanger are sufficiently stabilized. At this time, by closing the receiver expansion valve 4 on the upstream side of the outdoor heat exchanger 3 acting as an evaporator before or simultaneously with closing the receiver open / close valve 13 by a predetermined amount, the receiver open / close valve 13 The liquid return that occurs when 13 is closed can be avoided. And the operating frequency of the compressor 1 is adjusted according to the load of a refrigerating cycle, the refrigerant | coolant subcooling amount in the indoor heat exchanger 9 is adjusted in the indoor expansion valve 8, and heating operation is continued. Next, when the refrigeration cycle is stopped, a recovery operation for recovering the liquid refrigerant accumulated in the indoor heat exchanger 9 acting as a condenser in the liquid receiver 6 is performed. In this recovery operation method, the operating frequency of the compressor 1 is lowered to Hz3, the indoor expansion valve 8 is fully opened, the receiver open / close valve 13 is opened, and the outdoor expansion valve 4 is fully closed. The suction side pressure is gradually decreased, and when the pressure does not become the atmospheric pressure or less, the operation frequency of the compressor 1 is set to 0 and stopped. As a result, excess liquid refrigerant in the indoor heat exchanger 9 that has acted as a condenser is recovered in the liquid receiver 6 and the outdoor expansion valve 4 is closed, so that the outdoor functioning as an evaporator is closed. Since no refrigerant is supplied into the heat exchanger 3, all the refrigerant downstream from the outdoor expansion valve 4 is collected in the liquid receiver 6, and there is almost no liquid refrigerant on the low-pressure side when it is started next time. Compression can be prevented.

  Next, the case of the cooling operation will be described. FIG. 5 is a time chart when the refrigeration cycle of the embodiment of the present invention is in a cooling operation. The main four-way valve 2 before starting the compressor is in a state indicated by a broken line in the refrigeration cycle shown in FIG. 1, and the receiver open / close valve 13 is opened and the indoor expansion valve 8 is started before or simultaneously with the start of the compressor. The predetermined opening at the time and the outdoor expansion valve 4 are set to fully open. At the start of the refrigeration cycle, first, the compressor 1 is started at a predetermined frequency Hz4 and the receiver open / close valve 13 is open, so that it flows into the indoor heat exchanger 9 that acts as an evaporator at the time of startup. Since the degree of cooling of the refrigerant is equal to or higher than the liquid compression limit of the compressor 1 and returns to the compressor 1, it can be started smoothly without liquid compression. Next, when T3 seconds elapse, the operating frequency of the compressor 1 rises to Hz5, and when the temperature and pressure of the compressor 1 and the heat exchanger, etc. sufficiently stabilize until T4 seconds elapses, the receiver open / close valve 13 is turned on. close. At this time, by closing the receiver expansion valve 8 on the upstream side of the indoor heat exchanger 9 acting as an evaporator before or simultaneously with closing the receiver open / close valve 13 by a predetermined amount, the receiver open / close valve 13 The liquid return that occurs when 13 is closed can be avoided. Then, the operating frequency of the compressor 1 is adjusted according to the load of the refrigeration cycle, the refrigerant expansion heat amount in the indoor heat exchanger 9 is adjusted in the indoor expansion valve 8, and the cooling operation is continued. Next, when the refrigeration cycle is stopped, a recovery operation for recovering the liquid refrigerant accumulated in the outdoor heat exchanger 3 acting as a condenser in the liquid receiver 6 is performed. In this recovery operation method, the operating frequency of the compressor 1 is lowered to Hz6, the indoor expansion valve 8 is fully closed, and the receiver open / close valve 13 is opened, so that the suction side pressure of the compressor 1 gradually decreases, The operation is performed by setting the operation frequency of the compressor 1 to 0 and stopping when the pressure does not become the atmospheric pressure or less. As a result, excess liquid refrigerant in the outdoor heat exchanger 3 that has acted as a condenser is recovered in the liquid receiver 6 and the indoor expansion valve 8 is closed, so that the room that has acted as an evaporator. Since no refrigerant is supplied into the heat exchanger 9, all of the refrigerant downstream from the indoor expansion valve 8 is recovered in the liquid receiver 6, and there is almost no liquid refrigerant on the low pressure side when it is next started. Compression can be prevented.

  Next, the case of defrosting operation will be described. FIG. 6 is a time chart when the refrigeration cycle of the embodiment of the present invention is defrosted. If the temperature of the air flowing into the heat exchanger acting as an evaporator is low, the evaporation temperature will be negative, and frost will adhere to the surface of the heat exchanger, which will significantly reduce the performance of the heat exchanger. Perform frost operation. In particular, in the case of a refrigeration cycle, there are many cases of heating operation in which the outdoor heat exchanger 3 that is in contact with outside air acts as an evaporator, and therefore, in this embodiment, a defrosting operation during heating operation will be described. In addition, when operating the indoor heat exchanger 9 as an evaporator at a low temperature, it also occurs in the cooling operation, but the basic operation method is the same as the heating operation. The indoor expansion valve 8 on the downstream side of the indoor heat exchanger 9 acting as a condenser at the time T5 seconds before the start of the defrosting operation is fully opened, and the receiver open / close valve 13 is opened to collect in the condenser. The refrigerant | coolant currently collect | recovered in the liquid receiver 6 is performed. Thereafter, the operating frequency of the compressor 1 is lowered, and the main four-way valve 2 is switched from the solid line to the broken line to perform the reverse cycle defrosting operation. According to the above operation method, the amount of liquid refrigerant in the indoor heat exchanger 9 that acts as a condenser during heating operation and acts as an evaporator during defrosting operation can be reduced when the main four-way valve 2 is switched. It is possible to prevent the liquid from returning to the compressor 1. Then, simultaneously with the start of the defrosting operation, the indoor expansion valve 8 is throttled to a predetermined opening, and simultaneously with or after the switching of the main four-way valve 2, the receiver open / close valve 13 is closed, and the defrosting operation is continued. Here, the purpose of reducing the operating frequency of the compressor 1 immediately before the defrosting operation is to reduce the impact noise when the main four-way valve 2 is switched. Next, at the end of the defrosting operation, after determining the end of the defrosting operation, the operating frequency of the compressor 1 is first lowered, and the receiver open / close valve 13 is opened. As a result, the liquid refrigerant accumulated in the outdoor heat exchanger 3 can be recovered in the liquid receiver 6 and the amount of liquid refrigerant flowing into the indoor heat exchanger 9 can be reduced. When switched, the amount of liquid return to the compressor 1 can be reduced, and liquid compression can be prevented. Next, the main four-way valve 2 is switched from the broken line to the solid line to perform the heating operation. At this time, the indoor expansion valve 8 is fully opened simultaneously with the switching of the main four-way valve 2 or after the switching. Thereafter, the operation is the same as the activation of the heating operation.

  As described above, the bridge circuit 5 and the receiver open / close valve 13 expand the gas refrigerant at the top of the receiver 6 on the upstream side of the heat exchanger that acts as an evaporator in both the cooling operation and the heating operation. Since the refrigerant can be introduced to the upstream side of the valve and can be evaporated by the evaporator while keeping the degree of cooling of the refrigerant flowing into the evaporator large, the refrigerant can be guided to the suction side of the compressor 1. The amount of liquid refrigerant returning to step S is suppressed, and liquid compression can be prevented. Even when the operating capacity of the compressor 1 is small, or when the expansion valve opening generated when the evaporation temperature is low, etc., the opening of the expansion valve is positively converted into a gas-liquid two-phase before the expansion valve. Can be kept large, and when the opening degree of the expansion valve is adjusted, a place where the flow rate characteristic is gentle can be used. Therefore, the refrigeration cycle is easily stabilized and the reliability of the refrigeration cycle can be improved. In addition, a bridge circuit 5 is provided so that the gas refrigerant at the top of the receiver is introduced before the outdoor expansion valve during heating, and is introduced before the indoor expansion valve during cooling, so that liquid compression is performed both when heating is started and when cooling is started. Can be prevented.

  FIG. 7 is a piping system diagram of a refrigeration cycle showing another embodiment of the present invention. In the figure, the same reference numerals as those in FIG. In the refrigeration cycle of the present invention, instead of the decompression device 11 shown in FIG. 1, a supercooler 14 having a main flow portion and a subflow portion having the same pressure loss as the decompression device 11 is provided. The part inlet 24 is connected to the outlet pipe of the liquid receiver 6, and the main stream part outlet 25 is connected to the bridge circuit 5. On the other hand, the subflow inlet 26 of the supercooler 14 is connected to the subcooling bypass circuit 15 from the main flow inlet 24 via the subcooling expansion valve 16 that adjusts the amount of refrigerant flowing through the subcooling bypass circuit 15. The flow outlet 27 is connected by piping so as to join the piping connecting the main four-way valve 2 and the suction side of the compressor 1. Other than that, it is the same as that of FIG.

At the time of starting the refrigeration cycle, the pressure loss in the supercooler 14 is configured to be equivalent to that of the decompression device 11 in FIG. 1 by closing the opening of the expansion valve 16 for supercooling. When the receiver open / close valve 13 is opened, the amount of gas refrigerant flowing through the receiver bypass circuit 12 is equal, so that the amount of liquid refrigerant in the heat exchanger acting as a condenser is reduced while the evaporator is used. Since the degree of cooling of the refrigerant flowing to the acting heat exchanger can be equal to or higher than the limit of prevention of liquid compression, the refrigeration cycle can be started while ensuring the reliability of the compressor 1.
When the receiver open / close valve 13 is kept open, the performance due to a shortage of heat generated due to a decrease in discharge pressure due to a decrease in the amount of liquid in the condenser or a decrease in latent heat of evaporation due to an increase in the degree of preheating of the evaporator. A decrease occurs. For this reason, it is necessary to close the receiver open / close valve 13 and return the performance of the refrigeration cycle to a predetermined value when the operation state of the refrigeration cycle becomes a state where liquid compression is not performed. However, in the refrigeration cycle shown in FIG. 1, when the receiver open / close valve 13 is closed, the supply of the gas refrigerant flowing from the top of the receiver 6 is lost, so the upstream of the heat exchanger acting as an evaporator is eliminated. Since the refrigerant state before the expansion valve on the side changes from the gas-liquid two-phase state to the liquid single-phase state, the amount of refrigerant flowing through the expansion valve becomes extremely large and the liquid refrigerant easily returns to the compressor 1, which is the worst case. May cause liquid compression. For this reason, in the refrigeration cycle shown in FIG. 7, when the operation state of the refrigeration cycle becomes a state where liquid compression is not performed, the supercooling expansion valve 16 is opened and the low-temperature and low-pressure refrigerant flow flowing through the subflow portion of the subcooler 14. Is increased so that the liquid refrigerant at the outlet 25 of the main flow portion of the supercooler 14 is in a supercooled state, and the degree of flushing after the merge of the liquid receiver bypass circuit 12 is reduced according to the opening degree of the expansion valve 16 for supercooling. Adjust as follows. The expansion on the upstream side of the heat exchanger acting as an evaporator is closed by closing the receiver open / close valve 13 when the degree of pre-flow after the merge of the receiver bypass circuit 12 becomes sufficiently small. Since there is almost no change in the refrigerant state before the valve, there is almost no change in the flow characteristics of the expansion valve, and even when the receiver open / close valve 13 is closed, liquid return to the compressor 1 does not occur, and it is stable. A refrigeration cycle can be provided. When the receiver open / close valve 13 is closed and the subcooling expansion valve 16 is controlled to a certain opening, the amount of refrigerant flowing to the evaporator is reduced, so that the pressure loss in the evaporator is reduced and the refrigeration cycle is reduced. There is also an advantage that the performance is improved. In addition, by providing a bridge circuit and connecting the bridge circuit to the downstream side of the liquid receiver, it is possible to operate without degrading performance during heating and cooling.

  FIG. 8 is a piping system diagram of a refrigeration cycle showing still another embodiment of the present invention. In the figure, the same reference numerals as those in FIG. The refrigeration cycle of the present invention has a configuration in which a sub four-way valve 17 is provided instead of the bridge circuit 5 configured by four check valves shown in FIG. 1 or FIG. Other than that, it is the same as that of FIG.

When the auxiliary four-way valve 17 is switched as indicated by a solid line, it operates as a heating operation, and when it is switched as indicated by a broken line, it operates as a cooling operation, and is equivalent to the bridge circuit 5 constituted by four check valves shown in FIG. Can have functions.
In the case of the bridge circuit 5 composed of four check valves, there are 12 welding locations in total, whereas when the auxiliary four-way valve 17 is used, the number of welding locations is very small, 4 locations. For this reason, the frequency of occurrence of refrigerant leakage from the welded portion is reduced, and a highly reliable refrigeration cycle can be provided.

FIG. 9 is a piping system diagram of a refrigeration cycle showing still another embodiment of the present invention. In the figure, the same reference numerals as those in FIG. The refrigeration cycle of the present invention is different from the refrigeration cycle shown in FIG. 7 in that a compressor bypass circuit 18 that bypasses the gas refrigerant from the discharge side piping to the suction side piping of the compressor is provided. The compressor open / close valve 19 that is normally closed is provided on the way. Other than that, it is the same as that of FIG.
In the refrigeration cycle of the present invention, even when the compressor 1 is started in a state where the liquid refrigerant is stored in the pipe connected to the suction side of the heat exchanger and the compressor 1 acting as an evaporator, the opening and closing of the compressor By opening the valve 19 and causing a part of the gas refrigerant flowing on the discharge side of the compressor 1 to flow to the suction side of the compressor 1, the state of the refrigerant returning to the suction side of the compressor 1 is made higher than the liquid compression limit clearance degree. Therefore, liquid compression of the compressor 1 can be prevented, and the reliability of the compressor 1 can be further improved. In addition, since a part of the high-temperature gas refrigerant is bypassed on the suction side of the compressor 1, it is possible to prevent a decrease in suction pressure and to quickly raise the temperature of the compressor 1, thereby speeding up the start-up of the refrigeration cycle. When the refrigeration cycle of the present invention is used as an air conditioner, the comfort of the air-conditioning station can be improved.

  According to the above-mentioned embodiment, at least a compressor, a four-way valve, an outdoor heat exchanger, an outdoor pressure reducing device, an indoor pressure reducing device, a refrigeration cycle connected to the indoor heat exchanger, a bridge constituted by a check valve A circuit is provided between the outdoor pressure reducing device and the indoor pressure reducing device, and a liquid receiver and a pressure reducing device are sequentially connected in a circuit flowing in one direction of the bridge circuit, and the liquid is received with respect to a pipe connecting the pressure reducing device and the bridge circuit. A receiver bypass circuit and a normally closed receiver open / close valve that opens and closes the receiver bypass circuit so that the gas refrigerant at the top of the receiver flows are provided, and when the refrigeration cycle start and stop commands are received, Start / stop control means for starting and stopping, defrost control means for controlling the four-way valve to perform a defrost operation by a defrost command during operation of the refrigeration cycle, the start / stop control means and the defrost Control means With the open / close valve control means for opening and closing the receiver open / close valve as desired, the bridge circuit and the receiver open / close valve act as an evaporator for the cooling and heating operation of the gas refrigerant at the top of the receiver. The refrigerant can be introduced upstream of the expansion valve disposed upstream of the heat exchanger, evaporating with the evaporator while keeping the degree of cooling of the refrigerant flowing into the evaporator large, and the refrigerant is supplied to the suction side of the compressor. Therefore, the amount of liquid refrigerant returning to the suction side of the compressor is suppressed, and liquid compression can be prevented. Even when the operating capacity of the compressor is small, or when the expansion valve opening that occurs when the evaporation temperature is low, etc., the opening of the expansion valve is reduced in order to actively make the gas-liquid two-phase before the expansion valve. It can be kept large, and when adjusting the opening degree of the expansion valve, a place where the flow characteristic is gentle can be used. Therefore, the refrigeration cycle can be easily stabilized and the reliability of the refrigeration cycle can be improved.

It is a block diagram of the refrigerating cycle which shows one Embodiment of this invention. It is a Mollier diagram which shows the driving | running state of one Embodiment of this invention. It is a flow characteristic figure of an expansion valve used in one embodiment of the present invention. It is a time chart figure at the time of heating operation of the refrigerating cycle of one embodiment of the present invention. It is a time chart figure at the time of cooling operation of the refrigerating cycle of one embodiment of the present invention. It is a time chart figure at the time of carrying out defrost operation of the refrigerating cycle of one embodiment of the present invention. It is a piping system diagram of the refrigerating cycle which shows other embodiments of the present invention. It is a piping system diagram of the refrigerating cycle which shows other embodiments of the present invention. It is a piping system diagram of the refrigerating cycle which shows other embodiments of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Main four-way valve, 3 ... Outdoor heat exchanger, 4 ... Outdoor expansion valve, 5 ... Bridge circuit, 6 ... Receiver, 7 ... Liquid blocking valve, 8 ... Indoor expansion valve, 9 ... Indoor Heat exchanger, 10 ... gas blocking valve, 11 ... decompression device, 12 ... receiver receiver bypass circuit, 13 ... receiver receiver on-off valve, 14 ... supercooler, 15 ... supercooling bypass circuit, 16 ... expansion for supercooling Valves 17: Sub four-way valve 18 ... Compressor bypass circuit 19 ... Compressor on / off valve 21 ... Start / stop control means 22 ... Defrost control means 23 ... Open / close valve control means 24 ... Main stream inlet 25 ... main stream part outlet, 26 ... side stream part inlet, 27 ... side stream part outlet.

Claims (10)

  In the refrigeration cycle apparatus in which a compressor, a four-way valve, an indoor heat exchanger, an indoor expansion valve, an outdoor expansion valve, and an outdoor heat exchanger are connected by a refrigerant pipe, the indoor heat exchanger and the outdoor heat exchanger and the refrigerant pipe A receiver that is connected to store the refrigerant, a bypass pipe that allows the gas refrigerant in the upper part of the receiver to pass through and mixes with the refrigerant that flows out of the outlet of the receiver, and the amount of the gas refrigerant that passes through the bypass pipe. A liquid receiver open / close valve to be adjusted, and the refrigerant in which the gas refrigerant passing through the bypass pipe and the refrigerant flowing out of the liquid receiver outlet are mixed is switched to flow upstream of the indoor expansion valve or upstream of the outdoor expansion valve. A refrigeration cycle apparatus comprising a switching unit.   2. The refrigeration cycle apparatus according to claim 1, wherein the switching unit is a bridge circuit including a check valve.   The refrigeration cycle apparatus according to claim 1, wherein the switching unit is a four-way valve.   2. The subcooler is connected to the downstream of the liquid receiver by a refrigerant pipe, the main stream part inlet of the subcooler is connected to the outlet pipe of the liquid receiver, and the main stream part outlet of the subcooler is In the switching unit, the subflow inlet of the supercooler is connected to a refrigerant pipe connecting the four-way valve and the compressor suction side, and the subflow outlet of the supercooler is connected to the receiver outlet. A refrigeration cycle apparatus characterized by that.   2. The refrigeration cycle apparatus according to claim 1, wherein the receiver open / close valve is opened for a predetermined time from the start of the compressor.   In the refrigeration cycle apparatus in which a compressor, a four-way valve, an indoor heat exchanger, an indoor expansion valve, an outdoor expansion valve, and an outdoor heat exchanger are connected by a refrigerant pipe, the indoor heat exchanger and the outdoor heat exchanger and the refrigerant pipe Adjusting the amount of gas refrigerant passing through the bypass pipe, connected to the liquid receiver for storing the refrigerant, bypass pipe for allowing the gas refrigerant in the upper part of the liquid receiver to pass through and mixing with the refrigerant flowing out from the outlet of the liquid receiver A liquid receiver open / close valve that switches the refrigerant that is mixed with the gas refrigerant that has passed through the bypass pipe and the refrigerant that has flowed out of the outlet of the liquid receiver to flow upstream of the indoor expansion valve or upstream of the outdoor expansion valve An air conditioner characterized by providing a section.   The air conditioner according to claim 6, wherein the switching unit is a bridge circuit including a check valve.   The air conditioner according to claim 6, wherein the switching unit is a four-way valve.   The supercooler is connected to the downstream of the liquid receiver by a refrigerant pipe, the main stream part inlet of the supercooler is connected to the outlet pipe of the liquid receiver, and the main stream part outlet of the subcooler is the The sub-flow part inlet of the supercooler is connected to the pipe connecting the four-way valve and the compressor suction side, and the sub-flow part outlet of the supercooler is connected to the receiver outlet. Air conditioner characterized by. 7. The air conditioner according to claim 6, wherein the receiver open / close valve is opened for a predetermined time from the start of the compressor.

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