Refrigeration cycle device

Abstract

A refrigeration cycle device according to one embodiment of the present invention comprises a refrigerant circuit, a refrigerant temperature sensor, a control device, and a high-temperature refrigerant supply means. The refrigerant circuit has a compressor, a heat-source-side heat exchanger that is an air-refrigerant heat exchanger, a use-side heat exchanger that is a water-refrigerant heat exchanger, a pressure reducer disposed between the heat-source-side heat exchanger and the use-side heat exchanger, and a flow path switching valve that switches the flow direction of refrigerant discharged from the compressor. The refrigerant temperature sensor detects the temperature of the refrigerant flowing into the use-side heat exchanger from the pressure-reducer side. When starting a reverse defrosting operation, the high-temperature refrigerant supply means supplies a heating refrigerant, which is a refrigerant having a temperature higher than the temperature of the refrigerant detected by the refrigerant temperature sensor, to the use-side heat exchanger.

Description

Refrigeration Cycle Equipment

[0001] The present invention relates to a refrigeration cycle apparatus that includes a water-refrigerant heat exchanger and is capable of performing a reverse defrosting operation.

[0002] There is a heat pump type heating system that performs heating operation by generating hot water by heat exchange between a high-temperature refrigerant and water in a heat pump unit and supplying the generated hot water to a panel heater or the like. In this heating system, when heating operation is performed, a low-temperature refrigerant is supplied to a heat exchanger (heat source side heat exchanger) that exchanges heat between outside air and the refrigerant, which can cause frost to form on the heat exchanger that exchanges heat between the outside air and the refrigerant. If frost forms on the heat exchanger, a defrosting operation is performed to remove the frost.

[0003] In the defrosting operation, a reverse defrosting operation is generally performed in which the refrigerant circulation direction is reversed from that in the heating operation, and a high-temperature refrigerant is supplied to a heat exchanger that exchanges heat between the refrigerant and the outside air. When the reverse defrosting operation is performed, a low-temperature refrigerant is supplied to a heat exchanger (a user-side heat exchanger) that exchanges heat between the refrigerant and water, which can cause water to freeze in the heat exchanger that exchanges heat between the refrigerant and water. If water freezes in the heat exchanger that exchanges heat between the refrigerant and water, the volume expansion of the water due to freezing can damage the heat exchanger.

[0004] A known technology for preventing damage to a heat exchanger that exchanges heat between a refrigerant and water due to such water freezing is described in, for example, Patent Document 1. This technology focuses on the fact that water circulating through a water circuit freezes in the heat exchanger when the flow rate of water circulating through the water circuit is equal to or less than a predetermined amount and the temperature of water flowing into the heat exchanger is equal to or less than a predetermined temperature. Specifically, a heater is provided to heat the water circulating through the water circuit, and when the flow rate and temperature of the water circulating through the water circuit during reverse defrosting operation reach conditions that will cause the water flowing through the heat exchanger that exchanges heat between the refrigerant and water to freeze, the heater heats the water circulating through the water circuit.

[0005] Meanwhile, a microchannel heat exchanger, as disclosed in Patent Document 2, is known as a heat exchanger that exchanges heat between a refrigerant and water. The microchannel heat exchanger is a heat exchanger in which a plurality of high-temperature flow passage layers, each having fine flow passages through which a high-temperature fluid flows, and a plurality of low-temperature flow passage layers, each having fine flow passages through which a low-temperature fluid flows, are alternately stacked. The microchannel heat exchanger has the advantage of being more compact than existing plate heat exchangers.

[0006] JP 2012-211750 A JP 2019-163908 A

[0007] The technology described in Patent Document 1 uses a heater to heat the water circulating through the water circuit to prevent the water circulating through the water circuit from freezing inside the heat exchanger, which results in a problem of high energy consumption. Furthermore, the heater's response to water heating is poor, and it takes time for the water to reach a temperature that prevents freezing. While this is acceptable for a plate heat exchanger or the like with a relatively wide flow path, in a microchannel heat exchanger with an extremely narrow flow path, the water cannot be heated in time to keep up with the freezing rate inside the heat exchanger immediately after switching from heating operation to reverse defrost operation. As a result, the inside of the heat exchanger freezes immediately after the start of reverse defrost operation, clogging the flow path and significantly reducing the water flow rate. This not only risks damage to the heat exchanger, but also makes it impossible to perform normal defrost operation due to the significant reduction in water flow rate.

[0008] In view of the above circumstances, an object of the present invention is to provide a refrigeration cycle device that can perform normal defrosting operation while preventing freezing of water circulating through a water circuit in a heat exchanger without using a heater.

[0009] A refrigeration cycle apparatus according to one aspect of the present invention includes a refrigerant circuit, a refrigerant temperature sensor, a control device, and a high-temperature refrigerant supply means. The refrigerant circuit includes a compressor, a heat-source-side heat exchanger that is an air-refrigerant heat exchanger, a user-side heat exchanger that is a water-refrigerant heat exchanger, a pressure reducer disposed between the heat-source-side heat exchanger and the user-side heat exchanger, and a flow path switching valve that switches the flow direction of refrigerant discharged from the compressor. The refrigerant temperature sensor detects the temperature of refrigerant flowing from the pressure reducer side into the user-side heat exchanger. The control device determines whether defrosting of the heat-source-side heat exchanger is necessary during heating operation, and, when it determines that defrosting of the heat-source-side heat exchanger is necessary, switches the flow path switching valve to perform a reverse defrosting operation in which the refrigerant discharged from the compressor flows into the heat-source-side heat exchanger. The high-temperature refrigerant supply means supplies a heating refrigerant, which is a refrigerant with a temperature higher than the refrigerant temperature detected by the refrigerant temperature sensor, to the user-side heat exchanger when starting the reverse defrosting operation.

[0010] The refrigeration cycle device supplies the heating refrigerant to the user-side heat exchangers to prevent the water flowing through the user-side heat exchangers from freezing without using a heater. This prevents a decrease in the amount of heat exchanged between the refrigerant and the water in the user-side heat exchangers, allowing for normal defrosting operation.

[0011] The reverse defrosting operation may include a process of stopping the compressor to interrupt the heating operation, a process of switching the flow path switching valve, and a process of restarting the compressor. The high-temperature refrigerant supply means may supply the heating refrigerant to the user-side heat exchanger after the flow path switching valve is switched and before the compressor is restarted or simultaneously with the compressor being restarted. By supplying the heating refrigerant to the user-side heat exchanger before or simultaneously with the compressor being restarted, it is possible to prevent water from freezing in the user-side heat exchanger immediately after the start of the defrosting operation.

[0012] The high-temperature refrigerant supply means may include a receiver and a first flow control valve. The receiver is disposed in a liquid pipe connecting the user-side heat exchanger and the pressure reducer, and stores a portion of the refrigerant flowing from the user-side heat exchanger toward the pressure reducer during heating operation. The first flow control valve adjusts the flow rate of the refrigerant flowing from the receiver to the user-side heat exchanger during the reverse defrosting operation.

[0013] The first flow control valve may be controlled by the control device. Typically, the control device determines whether the refrigerant temperature detected by the refrigerant temperature sensor is equal to or lower than a preset threshold when the reverse defrosting operation is started, and opens the first flow control valve when the refrigerant temperature detected by the refrigerant temperature sensor is equal to or lower than the threshold.

[0014] The high-temperature refrigerant supply means may further include a second flow control valve that adjusts the flow rate of the refrigerant flowing from the user-side heat exchanger to the receiver during heating operation, and a third flow control valve that adjusts the flow rate of the refrigerant flowing from the heat-source-side heat exchanger to the user-side heat exchanger during cooling operation. The first flow control valve, the receiver, and the second flow control valve form a series circuit, and the third flow control valve is connected in parallel to the series circuit.

[0015] The first flow rate adjustment valve, the second flow rate adjustment valve, and the third flow rate adjustment valve may be controlled by the control device. For example, the control device closes the first flow rate adjustment valve and the second flow rate adjustment valve and opens the third flow rate adjustment valve during cooling operation.

[0016] Alternatively, the high-temperature refrigerant supply means may have a bypass pipe and a bypass expansion valve. The bypass pipe connects the discharge side of the compressor to a liquid pipe connecting the user-side heat exchanger and the pressure reducer. The bypass expansion valve is provided in the bypass pipe and reduces the pressure of the refrigerant flowing from the compressor to the user-side heat exchanger.

[0017] The bypass expansion valve may be controlled by the control device. Typically, the control device determines whether the refrigerant temperature detected by the refrigerant temperature sensor is equal to or lower than a preset threshold when the reverse defrosting operation is started, and opens the bypass expansion valve when the refrigerant temperature detected by the refrigerant temperature sensor is equal to or lower than the threshold.

[0018] The utilization side heat exchanger may be a micro-channel heat exchanger.

[0019] The heat exchanger may further include a water circuit having a pump for circulating water that exchanges heat with the refrigerant flowing through the utilization side heat exchanger.

[0020] According to the present invention, it is possible to perform a normal defrosting operation while preventing the water circulating through the water circuit from freezing in the heat exchanger without using a heater.

[0021] Fig. 1 is a refrigerant-water circuit diagram of a refrigeration cycle apparatus according to a first embodiment of the present invention. Fig. 2 is a block diagram showing the configuration of a control device in the refrigeration cycle apparatus. Fig. 3 is a flowchart showing an example of a processing procedure for reverse defrosting operation control in the first embodiment. Fig. 4 is a diagram showing changes over time in the state of each part of a refrigerant circuit during reverse defrosting operation in the refrigeration cycle apparatus. Fig. 5 is a refrigerant-water circuit diagram of a refrigeration cycle apparatus according to a second embodiment of the present invention. Fig. 6 is a flowchart showing an example of a processing procedure for reverse defrosting operation control in the second embodiment.

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] <First embodiment> Fig. 1 is a refrigerant-water circuit diagram of a refrigeration cycle apparatus 100 according to a first embodiment of the present invention. The refrigeration cycle apparatus 100 of this embodiment includes an outdoor unit 1 and an indoor unit 2. Details of the refrigeration cycle apparatus 100 will be described below.

[0024] [Overall Configuration of Refrigeration Cycle Device] The outdoor unit 1 includes a refrigerant circuit 10, a control device 30, a high-temperature refrigerant supply unit 40, and a circulation pump 23 connected to a water circuit 20. The indoor unit 2 includes an indoor heat exchanger 50 connected to the water circuit 20. The indoor unit 2 is, for example, a fan convector or a floor heating panel that operates as a hot water heater.

[0025] (Refrigerant Circuit) The refrigerant circuit 10 includes a compressor 11 , an outdoor heat exchanger 12 , a water-refrigerant heat exchanger 13 , an expansion valve 14 , a four-way valve 15 , an accumulator 16 , and an outdoor fan 17 .

[0026] The compressor 11 is a variable displacement compressor whose operating capacity can be changed by controlling its rotation speed with an inverter (not shown). The refrigerant discharge side of the compressor 11 is connected to port a of the four-way valve 15 via a discharge pipe 61. The refrigerant suction side of the compressor 21 is connected to the refrigerant outflow side of the accumulator 16 via a suction pipe 66.

[0027] The four-way valve 15 is a flow path switching valve that switches the flow direction of the refrigerant discharged from the compressor, and has four ports a, b, c, and d. As described above, port a is connected to the refrigerant discharge side of the compressor 11 via a discharge pipe 61. Port b is connected to one refrigerant inlet / outlet of the outdoor heat exchanger 12 via a refrigerant piping (gas pipe) 64. Port c is connected to the refrigerant suction side of the accumulator 16 via a refrigerant piping 65. Port d is connected to one refrigerant inlet / outlet of the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13 via a refrigerant piping (gas pipe) 62.

[0028] The outdoor heat exchanger 12 corresponds to the heat source side heat exchanger of the present invention and is, for example, an air-refrigerant heat exchanger that exchanges heat between air and a refrigerant, such as a parallel flow heat exchanger or a finned tube heat exchanger. The outdoor heat exchanger 12 functions as a condenser during cooling operation and as an evaporator during heating operation.

[0029] As described above, one of the refrigerant inlets and outlets of the outdoor heat exchanger 12 is connected to port b of the four-way valve 15 by a refrigerant pipe 64. The other of the refrigerant inlets and outlets of the outdoor heat exchanger 12 is connected to the other of the refrigerant inlets and outlets of the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13 by a refrigerant pipe (liquid pipe) 63.

[0030] The expansion valve 14 corresponds to a pressure reducer of the present invention and is, for example, an electronic expansion valve whose opening is controlled based on the number of pulses given to a stepping motor (not shown). The expansion valve 14 is disposed in the refrigerant pipe 63, and its opening is adjusted according to the operating capacity (cooling capacity or heating capacity) required by the indoor unit 2 (described later).

[0031] The outdoor fan 17 is disposed near the outdoor heat exchanger 12. The outdoor fan 17 is rotated by a fan motor (not shown) to take in outside air into the outdoor unit 1 through an air intake (not shown) of the outdoor unit 1, and discharges the outside air that has exchanged heat with the refrigerant in the outdoor heat exchanger 12 to the outside of the outdoor unit 1 through an air outlet (not shown) of the outdoor unit 1.

[0032] The water-refrigerant heat exchanger 13 corresponds to a user-side heat exchanger of the present invention, and in this embodiment, it is a micro-channel heat exchanger. The micro-channel heat exchanger is a heat exchanger in which multiple high-temperature channel layers, each having fine channels through which a high-temperature fluid flows, and multiple low-temperature channel layers, each having fine channels through which a low-temperature fluid flows, are alternately stacked. In this embodiment, the channel width (W) is 0.55 mm, the channel height (H) is 0.20 mm, the plate thickness (δ) between the channels is 0.10 mm, the hydraulic diameter (Dh) is 0.17 mm, and the total heat transfer area (A) is 0.113 to 0.118 mm. ２ However, the dimensions of each part are not limited to the above example. The water-refrigerant heat exchanger 13 is not limited to a microchannel heat exchanger, and may be, for example, a plate heat exchanger or a double-pipe heat exchanger that exchanges heat between water and a refrigerant.

[0033] The water-refrigerant heat exchanger 13 has a refrigerant-side flow path 131 and a water-side flow path 132. As described above, one refrigerant inlet / outlet of the refrigerant-side flow path 131 is connected to port d of the four-way valve 15 via a refrigerant pipe 62, and the other refrigerant inlet / outlet is connected to the other refrigerant inlet / outlet of the outdoor heat exchanger 12 via a refrigerant pipe 63. The water-side flow path 132 is connected to the water circuit 20.

[0034] (Water Circuit) The water circuit 20 supplies water that has exchanged heat with the refrigerant in the water-refrigerant heat exchanger 13 to the indoor heat exchanger 50. The indoor heat exchanger 50 is connected to a water outlet of the water-side flow path 132 in the water-refrigerant heat exchanger 13 by a feed pipe 21, and is connected to a water inlet of the water-side flow path 132 by a return pipe 22. A circulation pump 23 is disposed in the return pipe 22. The circulation pump 23 is driven at a variable rotation speed by a pump motor (not shown), thereby circulating the water that exchanges heat with the refrigerant flowing through the water-refrigerant heat exchanger 13 in the water circuit 20 in the direction indicated by the arrow. Note that the circulation pump 23 does not necessarily have to be disposed in the return pipe 22, and may be disposed in the feed pipe 21.

[0035] In this embodiment, the indoor unit 2 including the indoor heat exchanger 50 is a panel heater for floor heating. That is, the refrigeration cycle apparatus 100 of this embodiment mainly performs heating operation. The indoor unit 2 may be a fan coil unit (FCU) equipped with a water-air heat exchanger that exchanges heat between water circulating through the water circuit 20 and indoor air as the indoor heat exchanger 50. In this case, the refrigeration cycle apparatus 100 performs heating operation and cooling operation.

[0036] (Sensors) Various sensors are provided in the refrigeration cycle apparatus 100. In the outdoor unit 1, the discharge pipe 61 is provided with a high-pressure sensor 71 that detects the pressure of the refrigerant discharged from the compressor 11, and a discharge temperature sensor 72 that detects the temperature of the refrigerant discharged from the compressor 11. The suction pipe 66 is provided with a low-pressure sensor 73 that detects the pressure of the refrigerant sucked into the compressor 11, and a suction temperature sensor 74 that detects the temperature of the refrigerant sucked into the compressor 11.

[0037] Furthermore, a refrigerant temperature sensor 75 is provided in the refrigerant pipe 63 between the water-refrigerant heat exchanger 13 and the expansion valve 14 to detect the temperature of the refrigerant flowing from the expansion valve 14 side into the water-refrigerant heat exchanger 13 at the start of a reverse defrosting operation (the inlet temperature of the water-refrigerant heat exchanger 13 at the start of a reverse defrosting operation, which will be described later). The location at which the refrigerant temperature sensor 75 is provided is not particularly limited, but in this embodiment, as shown in Fig. 1 , the refrigerant temperature sensor 75 is provided on the refrigerant pipe 63 between the water-refrigerant heat exchanger 13 and a high-temperature refrigerant supply unit 40, which will be described later.

[0038] The outdoor heat exchanger 12 is provided with a heat exchange temperature sensor 76 for detecting the temperature of the refrigerant flowing through the outdoor heat exchanger 12. An outdoor air temperature sensor 77 for detecting the temperature of the outdoor air flowing into the outdoor unit 1 (outdoor air temperature) is provided near an intake port (not shown) of the outdoor unit 1.

[0039] A first water temperature sensor 78 that detects the temperature of water flowing out from the water-refrigerant heat exchanger 13 is provided in the supply pipe 21 of the water circuit 20 of the indoor unit 2. A second water temperature sensor 79 that detects the temperature of water flowing out from the indoor heat exchanger 50 is provided in the return pipe 22. Furthermore, if the indoor unit 2 is a fan coil unit (FCU), a room temperature sensor that detects the temperature of the room (room temperature) may be provided.

[0040] (Control Device) The control device 30 is, for example, an outdoor unit control device provided in the outdoor unit 1, and is mounted on a control board stored in an electrical component box (not shown) of the outdoor unit 1. Fig. 2 is a block diagram showing the configuration of the control device 30. As shown in the figure, the control device 30 has a CPU (Central Processing Unit) 31, a storage unit 32, a communication unit 33, a sensor input unit 34, and a rotation speed detection unit 35.

[0041] The memory unit 32 is a non-volatile memory such as a flash memory, and stores the control program and control parameters of the outdoor unit 1, detection values ​​corresponding to detection signals from various sensors, the control states of the compressor 11 and outdoor fan 17, etc., the control state of the indoor unit 2 acquired via the communication unit 33 (the control state of the operation mode, etc. set and input by the user), etc.

[0042] The communication unit 33 is an interface for communicating with the indoor unit 2. The sensor input unit 34 receives detection results from the various sensors described above and outputs them to the CPU 31. The rotation speed detection unit 35 detects the rotation speed of the motor of the compressor 11 and outputs it to the CPU 31. The rotation speed detection unit 35 may be configured to directly detect the rotation speed of the motor using an encoder or the like attached to the drive shaft of the motor, or may be configured to detect the rotation speed of the motor from the drive current supplied to the motor. In the following description, the rotation speed of the compressor 11 refers to the rotation speed of the motor.

[0043] The CPU 31 is a control unit that controls the operation of each part of the outdoor unit 1, including the compressor 11, by executing a program stored in the storage unit 32. The program is installed in the control device 30, for example, via various recording media. Alternatively, the program may be installed via the Internet or the like.

[0044] The CPU 31 receives the detection results of the above-mentioned sensors via the sensor input unit 34. Furthermore, the CPU 31 receives the control signal transmitted from the indoor unit 2 via the communication unit 33. The control signal transmitted from the indoor unit 2 includes the necessary operating capacity requested by the indoor unit 2, etc.

[0045] Based on the captured detection results and control signals, the CPU 31 controls the operation of the compressor 11, the outdoor fan 17, and the circulation pump 23, for example, by setting the command rotation speed at which these are driven. The CPU 31 also controls the switching of the four-way valve 15 based on the captured detection results and control signals. Furthermore, the CPU 31 controls the opening of the expansion valve 14 based on the captured detection results and control signals.

[0046] The CPU 31 further determines at predetermined time intervals whether a predetermined defrosting start condition is satisfied during heating operation. Specifically, if the outdoor air temperature is low while the refrigeration cycle apparatus 100 is performing heating operation, frost forms on the outdoor heat exchanger 12, which is a heat source-side heat exchanger that functions as an evaporator. If a large amount of frost forms on the outdoor heat exchanger 12, heat exchange between the refrigerant and the outdoor air by the outdoor heat exchanger 12 is hindered, reducing the heat exchange capacity of the outdoor heat exchanger 12. Therefore, when the CPU 31 determines that the predetermined defrosting start condition is satisfied during heating operation, it executes a defrosting operation to remove frost formed on the outdoor heat exchanger 12. In this embodiment, the defrosting operation is a reverse defrosting operation in which the refrigerant circulates in the opposite direction to that during heating operation, supplying high-temperature refrigerant to the outdoor heat exchanger 12.

[0047] On the other hand, when reverse defrosting operation is performed, a low-temperature refrigerant is supplied to the water-refrigerant heat exchanger 13, which is a user-side heat exchanger, and water may freeze in the water-refrigerant heat exchanger 13. If water freezes in the water-refrigerant heat exchanger 13, the volume of the water expands due to freezing, which may damage the water-refrigerant heat exchanger 13. While a technique using a heater to heat the water circulating through the water circuit is known to prevent the water circulating through the water circuit from freezing in the heat exchanger, the heater has poor responsiveness and takes time to heat the water to a temperature sufficient to prevent the water from freezing. Therefore, while this is acceptable for a plate heat exchanger or the like with a relatively wide flow path, in a microchannel heat exchanger with an extremely narrow flow path, immediately after switching from heating operation to reverse defrosting operation, the water cannot be heated in time to keep up with the freezing rate inside the heat exchanger. As a result, the inside of the heat exchanger freezes immediately after the start of reverse defrosting operation, clogging the flow path and significantly reducing the water flow rate. This not only risks damage to the heat exchanger, but also prevents normal defrosting operation due to the significant reduction in the water flow rate.

[0048] Therefore, the refrigeration cycle device 100 of this embodiment is equipped with a high-temperature refrigerant supply unit 40 that can supply high-temperature refrigerant to the water-refrigerant heat exchanger 13 when starting reverse defrosting operation, in order to prevent the water circulating through the water circuit from freezing in the heat exchanger without using a heater and to enable normal defrosting operation.

[0049] 1, the high-temperature refrigerant supply unit 40 has a first flow rate control valve 41, a second flow rate control valve 42, a third flow rate control valve 43, and a receiver 44. The high-temperature refrigerant supply unit 40 is a specific example of the high-temperature refrigerant supply means of the present invention.

[0050] The receiver 44 stores a portion of the refrigerant flowing from the water-refrigerant heat exchanger 13 toward the expansion valve 14 during heating operation. That is, as will be described later, the high-temperature refrigerant supply unit 40 supplies the high-temperature refrigerant (hereinafter also referred to as heating refrigerant) stored in the receiver 44 to the water-refrigerant heat exchanger 13 at the start of reverse defrosting operation, thereby preventing freezing of water in the water-side flow path 132 of the water-refrigerant heat exchanger 13.

[0051] The receiver 44 is connected to the refrigerant pipe 63 between the water-refrigerant heat exchanger 13 and the expansion valve 14 via the first branch pipe 45 and the second branch pipe 46. A connection point B between the refrigerant pipe 63 and the second branch pipe 46 is provided between the water-refrigerant heat exchanger 13 and the connection point A between the refrigerant pipe 63 and the first branch pipe 46.

[0052] The capacity of the receiver 44 is not particularly limited as long as it is large enough to store an amount of refrigerant that prevents water from freezing in the water-refrigerant heat exchanger 13 during the reverse defrost operation. More specifically, the receiver 44 only needs to be able to store an amount of refrigerant that maintains the inlet temperature of the water-refrigerant heat exchanger 13 at a temperature that does not freeze water when the reverse defrost operation starts, and the amount of refrigerant is set depending on the temperature of the refrigerant stored in the receiver 44 and the volume of the water-refrigerant heat exchanger 13. Here, the start of the reverse defrost operation refers to the period until the low-temperature refrigerant that was between the expansion valve 14 and the four-way valve 15 immediately before the start of the reverse defrost operation has finished passing through the connection point A between the refrigerant pipe 63 and the first branch pipe 45.

[0053] The first flow control valve 41 is disposed in the first branch pipe 45. The second flow control valve 41 is disposed in the second branch pipe 46. The third flow control valve 43 is disposed in the refrigerant pipe 63 between connection point A and connection point B. That is, the first flow control valve 41, the receiver 44, and the second flow control valve 42 form a series circuit, and the third flow control valve 43 is connected in parallel to this series circuit.

[0054] The first flow control valve 41 and the second flow control valve 42 close during cooling operation and open during heating operation. The third flow control valve 43 opens during cooling operation and closes during heating operation. During reverse defrosting operation, as described below, when the temperature detected by the refrigerant temperature sensor 77 is equal to or lower than a predetermined threshold, the first flow control valve 41 and the third flow control valve 43 open and the second flow control valve 42 closes.

[0055] The first flow rate adjustment valve 41, the second flow rate adjustment valve 42, and the third flow rate adjustment valve 43 may be, for example, electronic expansion valves whose opening degrees are controlled based on the number of pulses given to a stepping motor (not shown), or may be on-off valves that can be switched between two positions, fully open and fully closed. The opening degrees of the first flow rate adjustment valve 41, the second flow rate adjustment valve 42, and the third flow rate adjustment valve 43 are controlled by the control device 30.

[0056] As will be described later, the reverse defrosting operation mainly includes a process of stopping the compressor 11 to interrupt the heating operation, a process of switching the four-way valve 15, and a process of restarting the compressor 11. After the four-way valve 15 is switched, the high-temperature refrigerant supply unit 40 supplies the heating refrigerant stored in the receiver 44 to the connection point A between the first branch pipe 45 and the refrigerant pipe 63 before the compressor 11 is restarted or simultaneously with the restart of the compressor 11. By supplying the heating refrigerant to the refrigerant pipe 63 before or simultaneously with the restart of the compressor 11 in this manner, the temperature of the refrigerant flowing into the water-refrigerant heat exchanger 13 increases, thereby preventing water from freezing in the water-refrigerant heat exchanger 13 immediately after the start of the defrosting operation.

[0057] [Basic Operation of Refrigeration Cycle Apparatus] Next, a description will be given of the basic operation of the refrigeration cycle apparatus 100 configured as above. Hereinafter, the heating operation and the reverse defrosting operation will be described.

[0058] (Heating Operation) When the refrigeration cycle apparatus 100 performs heating operation, the control device 30 switches the four-way valve 15 to the state shown by the solid lines in FIG. 1 , i.e., the state where port a communicates with port d and port b communicates with port c. The control device 30 also opens (fully opens) the first flow control valve 41 and the second flow control valve 42 and closes the third flow control valve 43. In this state, the control device 30 drives the compressor 11 and the circulation pump 23. Driving the compressor 11 causes refrigerant to circulate through the refrigerant circuit 10 in the direction indicated by the solid arrows, and driving the circulation pump 23 causes water to circulate through the water circuit 20 in the direction indicated by the arrows. As a result, the outdoor heat exchanger 12 functions as an evaporator, and the water-refrigerant heat exchanger 13 functions as a condenser.

[0059] The refrigerant compressed by the compressor 11 to a high temperature and high pressure is discharged from the compressor 11, flows through the discharge pipe 61, and flows into the four-way valve 15. From the four-way valve 15, it flows into the refrigerant pipe 62 and into the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13. The refrigerant that has flowed into the refrigerant-side flow path 131 exchanges heat with water flowing in the water-side flow path 132, warming the water. The refrigerant condensed by the heat exchange with the water flowing in the water-side flow path 132 flows out into the refrigerant pipe 63.

[0060] The water that flows out of the water-side flow path 132 flows through the supply pipe 21 to the indoor heat exchanger 50, and heats the air in the room where the indoor unit 2 including the indoor heat exchanger 50 is installed. The water that flows out of the indoor heat exchanger 50 flows back into the water-side flow path 132 of the water-refrigerant heat exchanger 13 through the return pipe 22, and is heated again by exchanging heat with the refrigerant flowing through the refrigerant-side flow path 131.

[0061] On the other hand, the refrigerant that has flowed out into the refrigerant pipe 63 flows into the second branch pipe 46, a portion of which is stored in the receiver 44, and then flows out into the refrigerant pipe 63 via the first branch pipe 45. The refrigerant that has flowed out into the refrigerant pipe 63 is decompressed when passing through the expansion valve 14 and flows into the outdoor heat exchanger 12.

[0062] The refrigerant that passes through the expansion valve 14 and flows into the outdoor heat exchanger 12 evaporates by exchanging heat with outside air that has been drawn into the outdoor unit 1 by the rotation of the outdoor fan 17. The refrigerant that flows out of the outdoor heat exchanger 12 flows through the refrigerant pipe 64, and is drawn into the compressor 11 via the four-way valve 15, the refrigerant pipe 65, the accumulator 16, and the suction pipe 66, where it is compressed again.

[0063] (Reverse defrosting operation) The control device 30 determines whether defrosting of the outdoor heat exchanger is necessary during heating operation, and when it determines that defrosting of the outdoor heat exchanger is necessary, executes reverse defrosting operation by switching the four-way valve 15 to allow the refrigerant discharged from the compressor 11 to flow into the outdoor heat exchanger. The reverse defrosting operation will be described below.

[0064] Fig. 3 is a flowchart showing an example of a processing procedure for reverse defrosting operation control executed by the CPU 31 of the control device 30. Fig. 4 shows changes over time in the state of each part of the refrigerant circuit 10 during reverse defrosting operation, in which (A) shows the operating state of the compressor 11, (B) shows the opening degree of the expansion valve 14, (C) shows the outlet pressure of the outdoor heat exchanger 12 and the inlet pressure of the water-refrigerant heat exchanger 13, (D) shows the refrigerant inlet temperature of the water-refrigerant heat exchanger 13, and (E) shows the flow rate of water in the water-refrigerant heat exchanger 13.

[0065] The control device 30 starts the defrosting operation control when it determines that a predetermined defrosting operation start condition is satisfied. The defrosting operation start condition is not particularly limited, and for example, it is determined that the defrosting operation start condition is satisfied when the temperature of the outdoor heat exchanger 12, which functions as an evaporator, drops to a temperature equal to or lower than a preset temperature at which frost forms on the outdoor heat exchanger 12. Note that the defrosting operation start condition is not limited to the above example, and other requirements may be added.

[0066] When the control device 30 determines that the defrosting operation start condition is satisfied, for example, at time T1 ( FIG. 4 ), it continues the heating operation and closes the first flow control valve 41 and the second flow control valve 42, and opens the third flow control valve 43 (ST101). As a result, a quantity of high-temperature refrigerant (refrigerant at a temperature corresponding to the condensation temperature) according to the capacity of the receiver 44 is stored in the receiver 44, and the flow of refrigerant is switched from the water-refrigerant heat exchanger 13 to the exterior heat exchanger 12.

[0067] Next, the control device 30 stops the operation of the compressor 11 and executes a pressure equalization process to equalize the pressure in the refrigerant circuit 10 (ST102).

[0068] When the compressor 11 is stopped, the refrigerant compression process ceases, and the refrigerant flows from the high-pressure side (high-temperature side) to the low-pressure side (low-temperature side) during heating operation, gradually equalizing the overall pressure (temperature) of the refrigerant circuit 10. That is, as shown in Figure 4(C), the pressure of the refrigerant flowing into the water-refrigerant heat exchanger 13 on the high-pressure side (water-refrigerant heat exchanger inlet pressure) decreases over time, and the pressure of the refrigerant flowing out of the outdoor heat exchanger 12 on the low-pressure side (outdoor heat exchanger outlet pressure) gradually increases over time, and finally, around time T2, the refrigerant heat exchanger inlet pressure and the outdoor heat exchanger outlet pressure become the same.

[0069] To promote pressure equalization, the opening of the expansion valve 14 is increased to a preset opening (see FIG. 4B). This control of the opening of the expansion valve 14 is performed after a given time has elapsed since the compressor 11 was stopped, but it may also be performed simultaneously with the stopping of the compressor 11.

[0070] Next, the control device 30 determines whether a predetermined time has elapsed since the compressor 11 was stopped (ST103). The predetermined time is the time from the stopping of the compressor 11 until the pressure in the refrigerant circuit 10 is equalized, and is typically several seconds to several tens of seconds, and is 3 seconds in this embodiment.

[0071] After pressure equalization is complete, the refrigerant temperature is uniform throughout the refrigerant circuit 10. Furthermore, the outdoor heat exchanger 12 occupies a large volume within the refrigerant circuit 10, and low-pressure gas-liquid two-phase refrigerant is distributed in the outdoor heat exchanger 12 during heating operation. Therefore, when heating operation is stopped and pressure equalization is performed, the entire refrigerant circuit 10 is filled with two-phase refrigerant that is closer to low pressure.

[0072] When the control device 30 determines that the predetermined time has elapsed (Yes in ST103), it stops driving the outdoor fan 17 (ST104). Furthermore, the control device 30 switches the four-way valve 15 to the state shown by the dashed lines in Fig. 1, i.e., the state in which ports a and b are connected and ports c and d are connected, and controls the expansion valve 14 to be fully open (ST105). The processes of stopping the outdoor fan 17, switching the four-way valve 15, and controlling the expansion valve 14 to be fully open are not limited to being performed in the above-mentioned order, and may be performed simultaneously, for example.

[0073] Next, the control device 30 acquires the temperature detected by the refrigerant temperature sensor 75 and determines whether the temperature detected by the refrigerant temperature sensor 75 is equal to or lower than a preset threshold value (ST106). The threshold value is set to the temperature at which water flowing through the water-side flow path 132 freezes when refrigerant at that temperature flows into the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13 (hereinafter also referred to as the freezing temperature). This threshold value is experimentally determined in advance and is −10°C in this embodiment.

[0074] When the controller 30 determines that the temperature detected by the refrigerant temperature sensor 75 is below the freezing temperature (YES in ST106), it opens the first flow control valve 41 to supply the heating refrigerant from the receiver 44 to the junction A between the first branch pipe 45 and the refrigerant pipe 63, and merges the heating refrigerant with the low-temperature refrigerant that flows from the outdoor heat exchanger 12 through the refrigerant pipe 63 and into the junction A when the reverse defrosting operation is started. The heating refrigerant and the low-temperature refrigerant are mixed, and the refrigerant whose temperature is above the freezing temperature is supplied to the water-refrigerant heat exchanger 13 (ST107). The controller 30 then restarts the compressor 11 to start the reverse defrosting operation (ST108, time T3 in FIG. 4 ).

[0075] When the control device 30 determines that the temperature detected by the refrigerant temperature sensor 75 exceeds the freezing temperature (No in ST106), there is no risk of freezing of the water circulating through the water-refrigerant heat exchanger 13, so the control device 30 starts reverse defrosting operation by restarting the compressor 11 without supplying the heating refrigerant from the high-temperature refrigerant supply unit 40 (ST108).

[0076] The supply of heating refrigerant increases the refrigerant inlet temperature of the water-refrigerant heat exchanger 13, as shown in Figure 4(D). Therefore, even if the low-temperature refrigerant remaining in the outdoor heat exchanger 12 attempts to flow into the water-refrigerant heat exchanger 13 when the compressor 11 is subsequently restarted, freezing of the water in the water-refrigerant heat exchanger 13 can be prevented, and a constant amount of water circulating in the water circuit 20 can be maintained (Figure 4(E)). On the other hand, if the compressor 11 is restarted at time T3 without supplying heating refrigerant to the water-refrigerant heat exchanger 13, freezing of the water in the water-refrigerant heat exchanger 13 cannot be prevented, and the amount of water circulating in the water circuit 20 will be significantly reduced after the compressor 11 is restarted, as shown by the dashed line in Figure 4(E).

[0077] Here, the reason why the water inside the water-refrigerant heat exchanger 13 does not freeze even when the entire refrigerant circuit 10 drops below the freezing temperature after the pressure equalization process (ST102) is that the compressor 11 is stopped and no refrigerant flows during pressure equalization, resulting in a low heat transfer coefficient between the refrigerant and water inside the water-refrigerant heat exchanger 13. After pressure equalization, when the defrosting operation starts and refrigerant flows, the heat transfer coefficient increases instantaneously, and it is thought that the water inside the water-refrigerant heat exchanger 13 begins to freeze rapidly.

[0078] As the compressor 11 is driven, refrigerant circulates through the refrigerant circuit 10 in the direction of the dashed arrow. The high-temperature, high-pressure refrigerant discharged from the compressor 11 flows into the outdoor heat exchanger 12 and melts frost on the outdoor heat exchanger 12. The refrigerant flowing out of the outdoor heat exchanger 12 passes through the fully open expansion valve 14, merges with the heating refrigerant, and flows into the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13. The refrigerant flowing into the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13 exchanges heat with water flowing through the water-side flow path 132, evaporates, and is drawn into the compressor 11 via the refrigerant pipe 62, the four-way valve 15, the refrigerant pipe 65, the accumulator 16, and the suction pipe 61, where it is compressed again.

[0079] This reverse defrosting operation continues until a preset defrosting operation termination condition is met (ST109). The defrosting operation termination condition is determined, for example, after a certain period of time (e.g., 15 minutes) has elapsed since the defrosting operation began, or based on whether the temperature of the outdoor heat exchanger 12 has reached a predetermined temperature (e.g., 16°C or higher). When the control device 30 determines that the defrosting operation termination condition is met (Yes in ST109), it terminates the reverse defrosting operation and resumes the heating operation.

[0080] The first flow control valve 41 and the third flow control valve 43 in the high-temperature refrigerant supply unit 40 are fully open until the reverse defrost operation is completed, but the supply of heating refrigerant to the water-refrigerant heat exchanger 13 is stopped when all the heating refrigerant stored in the receiver 44 is discharged. After the reverse defrost operation is completed, the third flow control valve 43 is closed, and the second flow control valve 42 is fully opened like the first flow control valve 41 when the heating operation is resumed.

[0081] As described above, in this embodiment, when the temperature detected by the refrigerant temperature sensor 75 at the start of reverse defrosting operation is equal to or lower than the freezing point of water in the water-refrigerant heat exchanger 13, a heating refrigerant having a temperature higher than the temperature detected by the refrigerant temperature sensor 75 is supplied from the high-temperature refrigerant supply unit 40 to the water-refrigerant heat exchanger 13. This prevents the water flowing through the water-refrigerant heat exchanger 13 from freezing without using a heater, and thereby suppresses a decrease in the amount of heat exchanged between the refrigerant and water in the water-refrigerant heat exchanger, enabling normal defrosting operation.

[0082] In this embodiment, when the temperature detected by the refrigerant temperature sensor 75 is below the freezing temperature and reverse defrosting operation is performed, the high-temperature refrigerant supply unit 40 supplies the heating refrigerant to the connection point A between the first branch pipe 45 and the refrigerant pipe 63 immediately before restarting the compressor 11. However, the heating refrigerant may be supplied to the connection point A between the first branch pipe 45 and the refrigerant pipe 63 simultaneously with restarting the compressor 11. In this case, the same effects as those described above can be obtained.

[0083] 5 is a refrigerant-water circuit diagram of a refrigeration cycle apparatus 200 according to a second embodiment of the present invention. In the figure, parts corresponding to those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions thereof will be omitted or simplified.

[0084] The refrigeration cycle apparatus 200 of this embodiment differs from the first embodiment in that a high-temperature refrigerant supply unit 401 serving as a high-temperature refrigerant supply means of the present invention includes a bypass pipe 48 and a bypass expansion valve 49. The bypass pipe 48 connects the discharge side (discharge pipe 61) of the compressor 11 to a refrigerant pipe (liquid pipe) 63 that connects the water-refrigerant heat exchanger 13 and the expansion valve 14. The bypass expansion valve 49 is provided in the bypass pipe 48 and reduces the pressure of the refrigerant flowing from the compressor 11 to the water-refrigerant heat exchanger 13.

[0085] The bypass expansion valve 49 is controlled by the control device 30. When starting a reverse defrosting operation, the control device 30 determines whether the refrigerant temperature detected by the refrigerant temperature sensor 75 is equal to or lower than a preset threshold value (freezing temperature), and opens the bypass expansion valve 49 from a fully closed state to a predetermined opening degree when the refrigerant temperature detected by the refrigerant temperature sensor 75 is equal to or lower than the threshold value. The predetermined opening degree is set to an opening degree that allows the high-temperature, high-pressure gas refrigerant discharged from the compressor 11 to be reduced in temperature to a medium-temperature, low-pressure gas refrigerant.

[0086] The reverse defrosting operation in this embodiment will be described in detail below. Fig. 6 is a flowchart showing an example of a procedure for controlling the reverse defrosting operation in this embodiment, which is executed by the control device 30.

[0087] (Reverse defrosting operation) When the control device 30 determines that the above-described defrosting operation start condition is satisfied, it stops the operation of the compressor 11 and executes a pressure equalization process (ST201) to equalize the pressure in the refrigerant circuit 10. The pressure equalization process is similar to the pressure equalization process (ST102 in FIG. 3) in the first embodiment described above, and therefore will not be described here.

[0088] Next, the control device 30 determines whether a predetermined time has elapsed since the compressor 11 was stopped (ST202). The predetermined time is the time from the stopping of the compressor 11 until the pressure in the refrigerant circuit 10 is equalized, and is typically several seconds to several tens of seconds, and is 3 seconds in this embodiment.

[0089] When the controller 30 determines that the predetermined time has elapsed (Yes in ST202), it stops driving the outdoor fan 17 (ST203). Furthermore, the controller 30 switches the four-way valve 15 to the state shown by the dashed lines in Fig. 1, i.e., the state in which ports a and b are in communication and ports c and d are in communication, and controls the expansion valve 14 to be fully open (ST204).

[0090] Next, the control device 30 acquires the temperature detected by the refrigerant temperature sensor 75 and determines whether the temperature detected by the refrigerant temperature sensor 75 is equal to or lower than a preset threshold (ST205). As in the first embodiment, the threshold is set to the temperature (freezing temperature) at which water flowing through the water-side flow path 132 freezes when refrigerant at that temperature flows into the refrigerant-side flow path 131 of the water-refrigerant heat exchanger 13. This threshold is experimentally determined in advance and is −10° C. in this embodiment.

[0091] When the control device 30 determines that the temperature detected by the refrigerant temperature sensor 75 is below the freezing temperature (Yes in ST205), it opens the bypass expansion valve 49 from the fully closed state to the predetermined opening degree, and supplies the medium-temperature gas refrigerant, which is obtained by decompressing the high-temperature, high-pressure gas refrigerant discharged from the compressor 11, to the connection point C between the bypass pipe 48 and the refrigerant piping 63 as heating refrigerant.When the reverse defrosting operation is started, this medium-temperature gas refrigerant is merged with the low-temperature refrigerant flowing from the outdoor heat exchanger 12 through the refrigerant piping 63 and into the connection point C, and the refrigerant obtained by mixing the heating refrigerant and the low-temperature refrigerant and having a temperature above the freezing temperature is supplied to the water-refrigerant heat exchanger 13 (ST206).

[0092] Next, the control device 30 restarts the compressor 11 to start the reverse defrosting operation (ST207). The supply of the heating refrigerant increases the refrigerant inlet temperature of the water-refrigerant heat exchanger 13. Therefore, even if the low-temperature refrigerant remaining in the outdoor heat exchanger 12 attempts to flow into the water-refrigerant heat exchanger 13 due to the subsequent restart of the compressor 11, freezing of the water in the water-refrigerant heat exchanger 13 can be prevented, and a constant amount of water circulating in the water circuit 20 can be maintained.

[0093] When the control device 30 determines that the temperature detected by the refrigerant temperature sensor 75 exceeds the freezing temperature (No in ST205), there is no risk of freezing of the water circulating through the water-refrigerant heat exchanger 13, and therefore the control device 30 restarts the compressor 11 without supplying the heating refrigerant to the water-refrigerant heat exchanger 13, thereby starting reverse defrosting operation (ST207).

[0094] Next, the control device 30 acquires the detected temperature of the heat exchanger temperature sensor 76 attached to the outdoor heat exchanger 12 and determines whether the detected temperature of the heat exchanger temperature sensor 76 exceeds the freezing temperature (ST208). When the control device 30 determines that the detected temperature of the heat exchanger temperature sensor 76 exceeds the freezing temperature (Yes in ST208), it closes the bypass expansion valve 49 to stop the supply of heating refrigerant to the water-refrigerant heat exchanger 13 (ST209). This prevents unnecessary bypassing of high-temperature, high-pressure gas refrigerant, thereby suppressing inefficient defrosting operation.

[0095] On the other hand, when the control device 30 determines that the temperature detected by the heat exchanger temperature sensor 76 has not yet exceeded the freezing temperature (No in ST208), it continues to supply the heating refrigerant through the bypass pipe 48.

[0096] This reverse defrosting operation continues until the above-described defrosting operation termination condition is met (ST210). When the control device 30 determines that the defrosting operation termination condition is met (Yes in ST210), it terminates the reverse defrosting operation and resumes the heating operation.

[0097] As described above, this embodiment can also achieve the same effects as the first embodiment. That is, according to this embodiment, when the temperature detected by the heat exchanger temperature sensor 76 at the start of the reverse defrosting operation is equal to or lower than the freezing temperature of the water in the water-refrigerant heat exchanger 13, a heating refrigerant having a temperature higher than the temperature detected by the heat exchanger temperature sensor 76 is supplied from the high-temperature refrigerant supply unit 401 to the water-refrigerant heat exchanger 13. This prevents the water flowing through the water-refrigerant heat exchanger 13 from freezing without using a heater, thereby suppressing a decrease in the amount of heat exchanged between the refrigerant and water in the water-refrigerant heat exchanger and enabling normal defrosting operation. In this embodiment, the heat exchanger temperature sensor 76 corresponds to the "refrigerant temperature sensor" of the present invention, which detects the temperature of the refrigerant flowing from the pressure reducer (expansion valve 14) side to the user-side heat exchanger (water-refrigerant heat exchanger 13).

[0098] Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments and that various modifications can be made.

[0099] For example, in the first embodiment described above, two branch pipes 45, 46 connect the receiver 44 in the high-temperature refrigerant supply unit 40 to the refrigerant pipe 63, and the first flow control valve 41 and the second flow control valve 42 are provided in each of these branch pipes 45, 46. However, instead, a single branch pipe may connect the receiver 44 to the refrigerant pipe 63. In this case, the single flow control valve provided in the branch pipe can store the heating refrigerant in the receiver 44 during heating operation and supply the heating refrigerant to the water-refrigerant heat exchanger 13 during reverse defrost operation.

[0100] DESCRIPTION OF SYMBOLS 10... Refrigerant circuit 11... Compressor 12... Outdoor heat exchanger (heat source side heat exchanger) 13... Water-refrigerant heat exchanger (use side heat exchanger) 14... Expansion valve (pressure reducer) 15... Four-way valve (flow path switching valve) 20... Water circuit 23... Circulation pump 30... Control device 40, 401... High temperature refrigerant supply unit (high temperature refrigerant supply means) 41... First flow control valve 42... Second flow control valve 43... Third flow control valve 44... Receiver 48... Bypass pipe 49... Bypass expansion valve 50... Indoor unit 75... Refrigerant temperature sensor

Claims

1. A refrigeration cycle device comprising: a refrigerant circuit having a compressor, a heat source side heat exchanger which is an air-refrigerant heat exchanger, a user side heat exchanger which is a water-refrigerant heat exchanger, a pressure reducer arranged between the heat source side heat exchanger and the user side heat exchanger, and a flow path switching valve which switches the flow direction of refrigerant discharged from the compressor; a refrigerant temperature sensor which detects the temperature of refrigerant flowing from the pressure reducer side into the user side heat exchanger; a control device which determines whether defrosting of the heat source side heat exchanger is necessary during heating operation, and when it determines that defrosting of the heat source side heat exchanger is necessary, performs a reverse defrosting operation by switching the flow path switching valve to allow the refrigerant discharged from the compressor to flow into the heat source side heat exchanger; and high-temperature refrigerant supply means which, when starting the reverse defrosting operation, supplies the user side heat exchanger with a heating refrigerant which has a temperature higher than the refrigerant detected by the refrigerant temperature sensor.

2. A refrigeration cycle device as claimed in claim 1, wherein the reverse defrosting operation includes a process of stopping the compressor to suspend heating operation, a process of switching the flow path switching valve, and a process of restarting the compressor, and the high-temperature refrigerant supply means supplies the heating refrigerant to the user-side heat exchanger after the flow path switching valve has been switched and before the compressor is restarted or simultaneously with the compressor being restarted.

3. A refrigeration cycle apparatus according to claim 1, wherein the high-temperature refrigerant supply means comprises: a receiver arranged in a liquid pipe connecting the user-side heat exchanger and the pressure reducer, for storing a portion of the refrigerant flowing from the user-side heat exchanger toward the pressure reducer during heating operation; and a first flow control valve for adjusting the flow rate of the refrigerant flowing from the receiver to the user-side heat exchanger during reverse defrosting operation.

4. A refrigeration cycle device according to claim 3, wherein the first flow rate control valve is controlled by the control device, and the control device determines whether the refrigerant temperature detected by the refrigerant temperature sensor when the reverse defrosting operation is started is equal to or lower than a preset threshold value, and opens the first flow rate control valve when the refrigerant temperature detected by the refrigerant temperature sensor is equal to or lower than the threshold value.

5. A refrigeration cycle device according to claim 3, wherein the high-temperature refrigerant supply means further comprises a second flow control valve for adjusting the flow rate of refrigerant flowing from the user-side heat exchanger toward the receiver during heating operation, and a third flow control valve for adjusting the flow rate of refrigerant flowing from the heat source-side heat exchanger toward the user-side heat exchanger during cooling operation, wherein the first flow control valve, the receiver, and the second flow control valve form a series circuit, and the third flow control valve is connected in parallel to the series circuit.

6. A refrigeration cycle device according to claim 5, wherein the first flow rate adjustment valve, the second flow rate adjustment valve and the third flow rate adjustment valve are controlled by the control device, and the control device closes the first flow rate adjustment valve and the second flow rate adjustment valve and opens the third flow rate adjustment valve during cooling operation.

7. A refrigeration cycle device according to claim 1, wherein the high-temperature refrigerant supply means comprises: a bypass pipe connecting the discharge side of the compressor with a liquid pipe connecting the user-side heat exchanger and the pressure reducer; and a bypass expansion valve provided in the bypass pipe for reducing the pressure of the refrigerant flowing from the compressor to the user-side heat exchanger.

8. A refrigeration cycle device according to claim 7, wherein the bypass expansion valve is controlled by the control device, and the control device determines whether the refrigerant temperature detected by the refrigerant temperature sensor when the reverse defrosting operation is started is equal to or lower than a preset threshold, and opens the bypass expansion valve when the refrigerant temperature detected by the refrigerant temperature sensor is equal to or lower than the threshold.

9. A refrigeration cycle device according to claim 1, wherein the utilization side heat exchanger is a micro-channel heat exchanger.

10. A refrigeration cycle device according to any one of claims 1 to 9, further comprising a water circuit having a pump for circulating water that exchanges heat with the refrigerant flowing through the user-side heat exchanger.

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