Refrigeration cycle equipment

Abstract

This refrigeration cycle device comprises: a compressor; a load-side heat exchanger; a heat source-side heat exchanger including a plurality of heat exchangers provided with a plurality of heat transfer tubes extending in the vertical direction, the plurality of heat exchangers being connected in parallel during a heating operation and being connected in series during a cooling operation and during a defrosting operation; a flow path switching device that switches, in accordance with operation mode, the flow direction of a coolant discharged from the compressor; a flow rate regulating valve provided to coolant piping through which the coolant flows from a heat exchanger on the downstream side during the cooling operation; a bypass valve provided to a bypass circuit connecting the a discharge port of the compressor to the area between the flow rate regulating valve and the heat source-side heat exchanger; and a controller. When heating capacity decreases during the heating operation, the controller switches the flow rate regulating valve from an open state to a closed state, and switches the bypass valve from a closed state to an open state, and after the coolant discharged from the compressor has passed through the bypass circuit and flowed through the downstream-side heat exchanger, switches the flow rate regulating valve from the closed state to the open state, switches the bypass valve from the open state to the closed state, and controls the flow path switching device so as to perform the defrosting operation.

Description

[Technical Field]

[0001] The present disclosure relates to a refrigeration cycle device having a heat exchanger that exchanges heat between air and a refrigerant. [Background technology]

[0002] Conventionally, a refrigeration cycle apparatus having a heat source-side heat exchanger equipped with a plurality of heat exchangers has been known. When the refrigeration cycle apparatus performs heating operation, frost may form on the surface of the heat source-side heat exchanger if the outdoor air temperature is low. An air conditioner that performs a defrosting operation to melt the frost formed on the surface of the heat source-side heat exchanger has been disclosed (see, for example, Patent Document 1). The air conditioner disclosed in Patent Document 1 performs the refrigeration cycle in cooling operation when performing the defrosting operation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-63033 Summary of the Invention [Problem to be solved by the invention]

[0004] The air conditioner disclosed in Patent Document 1 circulates refrigerant through the refrigerant circuit in the opposite direction to the refrigerant flow direction during heating operation when performing defrosting operation. In some conventional refrigeration cycle devices, the heat source side heat exchanger has multiple heat exchangers connected in parallel during heating operation and multiple heat exchangers connected in series during cooling operation.

[0005] When the defrosting method disclosed in Patent Document 1 is applied to such a refrigeration cycle apparatus, frost formed on the surface of the heat source-side heat exchanger during heating operation may remain unmelted even when defrosting operation is performed. Specifically, during defrosting operation, if a high-temperature gas refrigerant flows through the upstream heat exchanger and then the downstream heat exchanger during cooling operation, the heat content of the high-temperature gas refrigerant decreases before it reaches the downstream heat exchanger. As a result, the frost formed on the lower surface of the downstream heat exchanger may remain unmelted. In this case, even when the operating mode of the refrigeration cycle apparatus switches from defrosting operation to heating operation, the heating capacity decreases due to the frost adhering to the heat source-side heat exchanger.

[0006] The present disclosure has been made to solve the above-mentioned problems, and provides a refrigeration cycle device that suppresses a decrease in heating capacity. [Means for solving the problem]

[0007] A refrigeration cycle device according to the present disclosure includes a compressor that compresses and discharges a refrigerant, a load-side heat exchanger that exchanges heat between the refrigerant and air in a target space, and a heat source-side heat exchanger provided with a plurality of heat transfer tubes extending in a vertical direction, wherein the plurality of heat exchangers are connected in parallel during heating operation and the plurality of heat exchangers are connected in series during cooling operation and defrosting operation, a flow path switching device that causes the refrigerant discharged from the compressor to flow into the load-side heat exchanger during the heating operation and causes the refrigerant discharged from the compressor to flow into the heat source-side heat exchanger during the cooling operation and defrosting operation, a flow control valve provided in a refrigerant pipe from which the refrigerant flows out from a downstream heat exchanger of the plurality of heat exchangers that are connected in series during the cooling operation, and a flow control valve and a flow control valve in the refrigerant pipe. the refrigerant discharged from the compressor flows through the bypass circuit and the refrigerant piping to the downstream heat exchanger, and a controller for controlling the flow path switching device, the flow rate adjustment valve, and the bypass valve, wherein the controller has a defrost preparation means for switching the flow rate adjustment valve from an open state to a closed state and switching the bypass valve from a closed state to an open state when the heating capacity decreases during the heating operation, and a defrost operation control means for switching the flow rate adjustment valve from the closed state to the open state and switching the bypass valve from the open state to the closed state and controlling the flow path switching device to perform the defrost operation after the refrigerant discharged from the compressor flows through the bypass circuit and the refrigerant piping to the downstream heat exchanger. [Effects of the Invention]

[0008] The refrigeration cycle apparatus disclosed herein includes a flow control valve provided in a refrigerant pipe through which refrigerant flows out from a downstream heat exchanger during cooling operation, a bypass circuit connecting the downstream heat exchanger and the flow control valve with a refrigerant discharge port of the compressor, and a bypass valve provided in the bypass circuit. Before the start of a defrosting operation, the flow control valve is switched from an open state to a closed state, and the bypass valve is switched from a closed state to an open state. This allows high-temperature gas refrigerant to flow into the downstream heat exchanger during cooling operation before the start of the defrosting operation. Therefore, frost adhering to the lower surfaces of the heat transfer tubes of the downstream heat exchanger located farthest from the compressor in the flow path through which high-temperature gas refrigerant flows from the compressor during the defrosting operation can be melted in advance before the start of the defrosting operation. As a result, residual frost is suppressed in the heat source-side heat exchanger during the defrosting operation, thereby suppressing a decrease in heating capacity. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a refrigerant circuit diagram showing a configuration example of a refrigeration cycle device according to a first embodiment. [Figure 2] 2 is a refrigerant circuit diagram showing the flow of refrigerant in the refrigeration cycle device shown in FIG. 1 when a heating operation is performed. FIG. [Figure 3] 2 is a refrigerant circuit diagram showing the flow of refrigerant when performing cooling operation and defrosting operation in the refrigeration cycle device shown in FIG. 1. FIG. [Figure 4] 2 is a diagram showing an example of a heat source side unit in which the heat source side heat exchanger shown in FIG. 1 is mounted. FIG. [Figure 5] FIG. 5 is a schematic view showing the configuration of the heat source side heat exchanger shown in FIG. [Figure 6] 6 is a schematic diagram showing the flow of refrigerant in the heat source side heat exchanger shown in FIG. 5 during cooling operation. FIG. [Figure 7] 6 is a schematic diagram showing the flow of refrigerant in the heat source side heat exchanger shown in FIG. 5 during heating operation. FIG. [Figure 8] 2 is a functional block diagram showing an example of the configuration of a controller shown in FIG. 1. [Figure 9]9 is a hardware configuration diagram showing an example of the configuration of a controller shown in FIG. 8. FIG. [Figure 10] 9 is a hardware configuration diagram showing another example of the configuration of the controller shown in FIG. 8. FIG. [Figure 11] FIG. 4 is a refrigerant circuit diagram of a refrigeration cycle device of a comparative example. [Figure 12] 4 is a flowchart showing an example of an operation procedure of the refrigeration cycle device according to the first embodiment. [Figure 13] 13 is a flowchart showing the operation procedure of step S105 shown in FIG. [Figure 14] 13 is a diagram showing the flow of refrigerant when the processes of steps S102 and S103 of the flowchart shown in FIG. 12 are performed in the refrigeration cycle device shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiment 1 The configuration of the refrigeration cycle apparatus of the first embodiment will be described. Fig. 1 is a refrigerant circuit diagram showing an example of the configuration of the refrigeration cycle apparatus according to the first embodiment. The refrigeration cycle apparatus 1 has a heat source side unit 2 and a load side unit 3. The heat source side unit 2 has a compressor 4, a heat source side heat exchanger 5, a flow path switching device 8, a blower 11, an accumulator 12, and a controller 20. The load side unit 3 has a load side heat exchanger 6 and an expansion valve 7.

[0011] The refrigeration cycle device 1 has at least heating operation, cooling operation, and defrosting operation as operation modes. A compressor 4, a heat source side heat exchanger 5, a load side heat exchanger 6, and an expansion valve 7 are connected via refrigerant piping 9 to form a refrigerant circuit 10 through which the refrigerant circulates.

[0012] The heat source-side heat exchanger 5 has a first heat exchanger 15a and a second heat exchanger 15b. The first heat exchanger 15a has heat exchangers 15a-1 and 15a-2 connected in parallel. The heat source-side unit 2 has a first flow control valve 13a, a second flow control valve 13b, a check valve 14, a two-way valve 16, and a bypass circuit 17. The bypass circuit 17 is provided with a bypass valve 18. The bypass valve 18 is, for example, a two-way valve.

[0013] The refrigerant pipe 9 extending from the flow path switching device 8 to the heat source side heat exchanger 5 branches into a branch refrigerant pipe 9a and a branch refrigerant pipe 9b. The branch refrigerant pipe 9a further branches into a branch refrigerant pipe 9a-1 and a branch refrigerant pipe 9a-2. The branch refrigerant pipe 9a-1 is connected to one of two refrigerant flow ports of the heat exchanger 15a-1. The branch refrigerant pipe 9a-2 is connected to one of two refrigerant flow ports of the heat exchanger 15a-2.

[0014] The other of the two refrigerant flow ports of heat exchanger 15a-1 is connected to branch refrigerant pipe 9d-1. The other of the two refrigerant flow ports of heat exchanger 15a-2 is connected to branch refrigerant pipe 9d-2. Branch refrigerant pipe 9d-1 and branch refrigerant pipe 9d-2 join together and are connected to branch refrigerant pipe 9e. A first flow control valve 13a is provided on branch refrigerant pipe 9e.

[0015] On the other hand, the branch refrigerant pipe 9b is connected to the branch refrigerant pipe 9e. Specifically, as shown in Fig. 1, the branch refrigerant pipe 9b is connected between the junction of the branch refrigerant pipes 9d-1 and 9d-2 and the first flow control valve 13a. The branch refrigerant pipe 9b is provided with a check valve 14 and a two-way valve 16. A branch refrigerant pipe 9f branches off from the branch refrigerant pipe 9b. Specifically, the branch refrigerant pipe 9f is connected to the branch refrigerant pipe 9b between the check valve 14 and the two-way valve 16.

[0016] The branch refrigerant pipe 9f is connected to one of the two refrigerant flow ports of the second heat exchanger 15b. The other of the two refrigerant flow ports of the second heat exchanger 15b is connected to the branch refrigerant pipe 9c. The branch refrigerant pipe 9c is provided with a second flow control valve 13b. The branch refrigerant pipe 9c and the branch refrigerant pipe 9e merge into the refrigerant pipe 9 and are connected to the expansion valve 7.

[0017] One end of the bypass circuit 17 is connected to the refrigerant pipe 9 between the refrigerant discharge port of the compressor 4 and the flow path switching device 8. The other end of the bypass circuit 17 is connected to the branch refrigerant pipe 9c. Specifically, the other end of the bypass circuit 17 is connected between the second heat exchanger 15b and the second flow control valve 13b.

[0018] The load-side unit 3 is provided with a room temperature sensor 31 that detects a room temperature Trm, which is the temperature of the air in the room that is the target space. The heat-source-side unit 2 is provided with an outside air temperature sensor 32 that detects an outside air temperature Tout, an evaporation temperature sensor 33 that detects an evaporation temperature Tev of the refrigerant circuit 10, and a refrigerant temperature sensor 34.

[0019] In the exemplary configuration shown in FIG. 1, the evaporation temperature sensor 33 is provided in the refrigerant pipe 9 between the junction of the branch refrigerant pipe 9c and the branch refrigerant pipe 9e and the expansion valve 7. The refrigerant temperature sensor 34 is provided in the branch refrigerant pipe 9c near the refrigerant flow port of the second heat exchanger 15b. The refrigerant temperature sensor 34 detects the temperature Trf of the refrigerant flowing out from the second heat exchanger 15b during defrosting operation. The room temperature sensor 31, the outside air temperature sensor 32, the evaporation temperature sensor 33, and the refrigerant temperature sensor 34 are, for example, thermistors. Each of these temperature sensors is connected to the controller 20 via a signal line (not shown).

[0020] The compressor 4 draws in gas refrigerant, compresses it, and discharges it. The compressor 4 is, for example, an inverter compressor whose capacity can be changed. The expansion valve 7 decompresses the refrigerant to expand it. The check valve 14 allows refrigerant to flow in the branch refrigerant pipe 9b from the two-way valve 16 to the refrigerant pipe 9, but blocks refrigerant from the refrigerant pipe 9 to the two-way valve 16. The blower 11 draws in outside air and supplies the drawn outside air to the heat source side heat exchanger 5.

[0021] The flow path switching device 8 allows the refrigerant discharged from the compressor 4 to flow into the load-side heat exchanger 6 during heating operation, and allows the refrigerant discharged from the compressor 4 to flow into the heat-source-side heat exchanger 5 during cooling operation and defrosting operation. The flow path switching device 8 is, for example, a four-way valve. The accumulator 12 is connected to the refrigerant suction port side of the compressor 4. The accumulator 12 is a refrigerant circuit auxiliary device that has the function of preventing liquid refrigerant from being sucked into the compressor 4. The compressor 4, the expansion valve 7, the flow path switching device 8, and the blower 11 are connected to a controller 20 via signal lines (not shown).

[0022] Here, we will explain the flow of refrigerant in each operation mode in the refrigerant circuit 10 of the refrigeration cycle device 1. First, we will explain the case where the operation mode is heating operation. In heating operation, the first flow control valve 13a and the second flow control valve 13b are set to an open state, and the two-way valve 16 is set to a closed state. The bypass valve 18 is set to a closed state.

[0023] Fig. 2 is a refrigerant circuit diagram showing the flow of refrigerant during heating operation in the refrigeration cycle device shown in Fig. 1. In Fig. 2, the reference numerals of some of the branch refrigerant pipes shown in Fig. 1 are omitted.

[0024] The compressor 4 draws in low-temperature, low-pressure gas refrigerant, compresses the drawn-in low-temperature, low-pressure gas refrigerant, and discharges it as high-temperature, high-pressure gas refrigerant. When the high-temperature, high-pressure gas refrigerant is discharged from the compressor 4, it flows through the flow path switching device 8 and then flows into the load-side heat exchanger 6. The high-temperature, high-pressure gas refrigerant that flows into the load-side heat exchanger 6 exchanges heat with the indoor air, releasing heat and condensing, becoming high-temperature, high-pressure liquid refrigerant, which flows out of the load-side heat exchanger 6. The liquid refrigerant that flows out of the load-side heat exchanger 6 is expanded by the expansion valve 7 and becomes low-temperature, low-pressure, two-phase gas-liquid refrigerant. The low-temperature, low-pressure, two-phase gas-liquid refrigerant is branched into branch refrigerant pipes 9c and 9e and flows into the first heat exchanger 15a and the second heat exchanger 15b.

[0025] The gas-liquid two-phase refrigerant that flows into the first heat exchanger 15a and the second heat exchanger 15b exchanges heat with outside air supplied by the blower 11, absorbing heat and evaporating, becoming a low-temperature, low-pressure gas refrigerant. In the first heat exchanger 15a, the refrigerant that has exchanged heat with the outside air flows out of the first heat exchanger 15a into the refrigerant pipe 9 via the branch refrigerant pipe 9a. In the second heat exchanger 15b, the refrigerant that has exchanged heat with the outside air flows through the branch refrigerant pipes 9f and 9b and merges with the refrigerant pipe 9. The low-temperature, low-pressure gas refrigerant that flows out of the heat source-side heat exchanger 5 flows through the flow path switching device 8 and the accumulator 12 and is drawn back into the compressor 4. In this way, in the heating operation, the first heat exchanger 15a and the second heat exchanger 15b are connected in parallel in the refrigerant circuit 10.

[0026] Next, the operation modes of the cooling operation and defrosting operation will be described. In the cooling operation and defrosting operation, the second flow control valve 13b and the two-way valve 16 are set to the open state, the first flow control valve 13a is set to the closed state, and the bypass valve 18 is set to the closed state.

[0027] Fig. 3 is a refrigerant circuit diagram showing the flow of refrigerant when performing cooling operation and defrosting operation in the refrigeration cycle device shown in Fig. 1. In Fig. 3, the reference numerals of some of the branch refrigerant pipes shown in Fig. 1 are omitted.

[0028] The compressor 4 draws in low-temperature, low-pressure gas refrigerant, compresses the drawn low-temperature, low-pressure gas refrigerant, and discharges high-temperature, high-pressure gas refrigerant. When the high-temperature, high-pressure gas refrigerant is discharged from the compressor 4, it flows through the flow path switching device 8 and then flows from the refrigerant pipe 9 into the branch refrigerant pipe 9a. The gas refrigerant that flows into the branch refrigerant pipe 9a flows through the first heat exchanger 15a and then flows into the branch refrigerant pipe 9b via the branch refrigerant pipe 9e. The refrigerant that flows into the branch refrigerant pipe 9b flows into the second heat exchanger 15b via the two-way valve 16 and the branch refrigerant pipe 9f. In the first heat exchanger 15a and the second heat exchanger 15b, the refrigerant exchanges heat with outside air supplied by the blower 11, thereby releasing heat and condensing, becoming high-temperature, high-pressure liquid refrigerant that flows out of the second heat exchanger 15b into the branch refrigerant pipe 9c.

[0029] The liquid refrigerant that flows into the branch refrigerant pipe 9c flows into the expansion valve 7 via the second flow control valve 13b. The liquid refrigerant is expanded by the expansion valve 7 and becomes a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The low-temperature, low-pressure, two-phase gas-liquid refrigerant flows into the load-side heat exchanger 6. The two-phase gas-liquid refrigerant that flows into the load-side heat exchanger 6 absorbs heat by exchanging heat with the indoor air, evaporating and becoming a low-temperature, low-pressure gas refrigerant. The low-temperature, low-pressure gas refrigerant flows out of the load-side heat exchanger 6. The low-temperature, low-pressure gas refrigerant that flows out of the load-side heat exchanger 6 passes through the flow switching device 8 and the accumulator 12 and is drawn back into the compressor 4. As described above, in the cooling operation and the defrosting operation, the first heat exchanger 15a and the second heat exchanger 15b are connected in series in the refrigerant circuit 10.

[0030] Next, the configuration of the heat source side heat exchanger 5 will be described. FIG. 4 is a diagram showing an example of a heat source side unit equipped with the heat source side heat exchanger shown in FIG. 1. In FIG. 4, the compressor 4, the two-way valve 16, the bypass circuit 17, the refrigerant piping 9, and the controller 20 are omitted. For ease of explanation, FIG. 4 shows three axes (X-axis, Y-axis, and Z-axis) that define the directions of the space in which the heat source side unit 2 is installed. The direction opposite to the Z-axis arrow is the vertical direction. As in FIG. 4, three axes are also shown in FIGS. 5 to 7.

[0031] The heat source side unit 2 has a rectangular parallelepiped housing 40. As shown in Fig. 4, the housing 40 has a blower 11 provided at the top, and a first heat exchanger 15a and a second heat exchanger 15b provided on side surfaces parallel to the vertical direction. Specifically, the housing 40 has two side surfaces parallel to the XZ plane, of which one has a heat exchanger 15a-1 provided on one side, and a heat exchanger 15a-2 provided on the other side. The housing 40 has two side surfaces parallel to the YZ plane, of which one has a second heat exchanger 15b provided on one side.

[0032] FIG. 5 is a schematic diagram showing the configuration of the heat source-side heat exchanger shown in FIG. 4. Heat exchanger 15a-1, heat exchanger 15a-2, and second heat exchanger 15b have similar configurations. Therefore, here, the configuration of second heat exchanger 15b will be described, and detailed descriptions of heat exchangers 15a-1 and 15a-2 will be omitted. In FIG. 5, the white arrows indicate the direction of air flow caused by the rotation of the propeller of blower 11. In FIG. 5, the solid arrows indicate the direction of refrigerant flow during cooling operation and defrosting operation.

[0033] The second heat exchanger 15b includes a first-row heat exchanger 41, a second-row heat exchanger 42, an upper header 43, and a lower header 44. The first-row heat exchanger 41 is located on the upwind side of the airflow generated by the blower 11, and the second-row heat exchanger 42 is located on the downwind side of the airflow generated by the blower 11. Each of the first-row heat exchanger 41 and the second-row heat exchanger 42 includes a plurality of heat transfer tubes 46 extending in the vertical direction and corrugated fins 47 provided between adjacent heat transfer tubes 46. That is, the heat transfer tubes 46 and the corrugated fins 47 are alternately arranged in the Y-axis direction. The lower header 44 includes a first lower header 45b and a second lower header 45a. In the first embodiment, the heat transfer tubes 46 are described as flat tubes, but the heat transfer tubes 46 are not limited to flat tubes.

[0034] The upper ends of the heat transfer tubes 46 of the first row-side heat exchanger 41 are connected to the upper header 43. The lower ends of the heat transfer tubes 46 of the first row-side heat exchanger 41 are connected to the first lower header 45b. The upper ends of the heat transfer tubes 46 of the second row-side heat exchanger 42 are connected to the upper header 43. The lower ends of the heat transfer tubes 46 of the second row-side heat exchanger 42 are connected to the second lower header 45a. The upper header 43 connects the first row-side heat exchanger 41 and the second row-side heat exchanger 42 at their upper parts, and serves to allow refrigerant flowing in from the first row-side heat exchanger 41 to flow out to the second row-side heat exchanger 42, and to allow refrigerant flowing in from the second row-side heat exchanger 42 to flow out to the first row-side heat exchanger 41.

[0035] In the cooling operation and defrosting operation, as shown in Fig. 5, the refrigerant flows into the second lower header 45a, rises through the multiple heat transfer tubes 46 of the second-row side heat exchanger 42, and flows into the upper header 43. The refrigerant that has merged with the upper header 43 from the multiple heat transfer tubes 46 branches off and falls through the multiple heat transfer tubes 46 of the first-row side heat exchanger 41, and flows into the first lower header 45b. In the cooling operation, the refrigerant flows countercurrently in the heat source side heat exchanger 5, improving heat exchange performance.

[0036] In the heating operation, although the flow of the refrigerant is not shown in Fig. 5, when the refrigerant flows into the first lower header 45b, it flows upward through the plurality of heat transfer tubes 46 of the first row-side heat exchanger 41 and flows into the upper header 43. The refrigerant that has merged into the upper header 43 from the plurality of heat transfer tubes 46 branches off through the plurality of heat transfer tubes 46 of the second row-side heat exchanger 42, flows downward, and flows into the second lower header 45a.

[0037] Fig. 6 is a schematic diagram showing the flow of refrigerant during cooling operation in the heat source side heat exchanger shown in Fig. 5. In Fig. 6, the flow direction of air generated by the rotation of the propeller of blower 11 is indicated by white arrows, and the flow direction of refrigerant is indicated by solid arrows. Here, the flow of refrigerant during cooling operation will be explained, but the flow of refrigerant during defrosting operation will also be the same as during cooling operation, so its explanation will be omitted.

[0038] As shown in FIG. 6, in the heat exchanger 15a-1, the refrigerant that flows into the second-row heat exchanger 42 flows into the first-row heat exchanger 41 via the upper header 43 shown in FIG. 5. Meanwhile, in the heat exchanger 15a-2, the refrigerant that flows into the second-row heat exchanger 42 flows into the first-row heat exchanger 41 via the upper header 43 shown in FIG. 5. The refrigerant that flows out of the first-row heat exchanger 41 of the heat exchanger 15a-1 and the refrigerant that flows out of the first-row heat exchanger 41 of the heat exchanger 15a-2 join together and flow into the second-row heat exchanger 42 of the second heat exchanger 15b. The refrigerant that flows into the second-row heat exchanger 42 of the second heat exchanger 15b flows into the first-row heat exchanger 41 via the upper header 43 shown in FIG. 5. The refrigerant that flows into the first-row heat exchanger 41 flows into the branch refrigerant pipe 9c shown in FIG. 3.

[0039] Fig. 7 is a schematic diagram showing the flow of refrigerant during heating operation in the heat source side heat exchanger shown in Fig. 5. In Fig. 7, the flow direction of air generated by the rotation of the propeller of the blower 11 is indicated by white arrows, and the flow direction of the refrigerant is indicated by solid arrows.

[0040] As shown in FIG. 7, in the heat exchanger 15a-1, the refrigerant that flows into the first-row heat exchanger 41 flows into the second-row heat exchanger 42 via the upper header 43 shown in FIG. 5. The refrigerant that flows into the second-row heat exchanger 42 flows out into the branch refrigerant pipe 9a shown in FIG. 2. In the heat exchanger 15a-2, the refrigerant that flows into the first-row heat exchanger 41 flows into the second-row heat exchanger 42 via the upper header 43 shown in FIG. 5. The refrigerant that flows into the second-row heat exchanger 42 flows out into the branch refrigerant pipe 9a shown in FIG. 2. Meanwhile, in the second heat exchanger 15b, the refrigerant that flows into the first-row heat exchanger 41 flows into the second-row heat exchanger 42 via the upper header 43 shown in FIG. 5. The refrigerant that flows into the second-row heat exchanger 42 flows out into the branch refrigerant pipe 9b via the branch refrigerant pipe 9f shown in FIG. 2.

[0041] In the first embodiment, the configuration of the load-side heat exchanger 6 is the same as that described with reference to Fig. 5, and therefore detailed description thereof will be omitted. Furthermore, the load-side heat exchanger 6 is not limited to the configuration described with reference to Fig. 5.

[0042] Next, the configuration of the controller 20 will be described. Fig. 8 is a functional block diagram showing an example of the configuration of the controller shown in Fig. 1. The controller 20 is, for example, a microcomputer. The controller 20 has refrigeration cycle control means 21, defrost preparation means 22, defrost operation control means 23, and a timer 24 that measures time.

[0043] When the operation mode is heating operation, the refrigeration cycle control means 21 controls the flow path switching device 8 so that the refrigerant discharged from the compressor 4 flows into the load-side heat exchanger 6. When the operation mode is heating operation, the refrigeration cycle control means 21 controls the first flow control valve 13a and the second flow control valve 13b to be in an open state and controls the two-way valve 16 to be in a closed state. When the operation mode is heating operation, the refrigeration cycle control means 21 controls the operation frequency of the compressor 4, the opening of the expansion valve 7, and the rotation speed of the blower 11 so that the room temperature Trm detected by the room temperature sensor 31 becomes the set temperature Tst.

[0044] On the other hand, when the operation mode is cooling operation, the refrigeration cycle control means 21 controls the flow path switching device 8 so that the refrigerant discharged from the compressor 4 flows into the heat source side heat exchanger 5. When the operation mode is cooling operation, the refrigeration cycle control means 21 controls the second flow control valve 13b and the two-way valve 16 to be open, and controls the first flow control valve 13a to be closed. When the operation mode is cooling operation, the refrigeration cycle control means 21 controls the operating frequency of the compressor 4, the opening of the expansion valve 7, and the rotation speed of the blower 11 so that the room temperature Trm detected by the room temperature sensor 31 becomes the set temperature Tst.

[0045] Furthermore, when the refrigeration cycle control means 21 receives an operation switching signal from the defrosting operation control means 23 to switch the operation mode from the defrosting operation to the heating operation, it controls the flow path switching device 8 so that the refrigerant discharged from the compressor 4 flows into the load-side heat exchanger 6. In addition, the refrigeration cycle control means 21 switches the first flow control valve 13a from a closed state to an open state, and switches the two-way valve 16 from an open state to a closed state.

[0046] When the defrost preparation means 22 determines that the heating capacity of the refrigeration cycle apparatus 1 has decreased during heating operation, it switches the bypass valve 18 from a closed state to an open state. For example, the defrost preparation means 22 determines that the heating capacity has decreased when the outside air temperature Tout is equal to or lower than a predetermined outside air temperature threshold th1 and the time during which the evaporation temperature Tev is equal to or lower than a predetermined evaporation temperature threshold th2 is equal to or higher than a predetermined time threshold th3.

[0047] When frost begins to form on the surface of the heat source-side heat exchanger 5, which functions as an evaporator, the heat exchange performance of the heat source-side heat exchanger 5 decreases, and the low-pressure pressure of the refrigerant circuit 10 decreases. When the low-pressure pressure decreases, the evaporation temperature also decreases. When the high-pressure pressure decreases in conjunction with the decrease in the low-pressure pressure, the heating capacity decreases. When the outside air temperature Tout is higher than the outside air temperature threshold th1, there is no problem of a decrease in heating capacity, but when the outside air temperature Tout is equal to or lower than the outside air temperature threshold th1, there is a problem of a decrease in heating capacity. Therefore, the defrost preparation means 22 monitors the outside air temperature Tout and the evaporation temperature Tev, and determines that the heating capacity has decreased when the time during which the outside air temperature Tout is equal to or lower than the outside air temperature threshold th1 and the evaporation temperature Tev is equal to or lower than the evaporation temperature threshold th2 is equal to or higher than a time threshold th3.

[0048] The defrosting operation control means 23 starts the defrosting operation when a predetermined time has elapsed since the refrigerant discharged from the compressor 4 via the bypass circuit 17 started to flow into the heat source-side heat exchanger 5. Specifically, the defrosting operation control means 23 switches the second flow control valve 13b from a closed state to an open state, switches the bypass valve 18 from an open state to a closed state, and controls the flow path switching device 8 to cause the refrigerant discharged from the compressor 4 to flow into the heat source-side heat exchanger 5. For example, the defrosting operation control means 23 refers to the time measured by the timer 24 and determines whether the elapsed time tk from the time the bypass valve 18 was switched from a closed state to an open state is equal to or greater than a predetermined time threshold th4. The time threshold th4 is, for example, 3 to 5 minutes. If the elapsed time tk is equal to or greater than the time threshold th4, the defrosting operation control means 23 starts the defrosting operation.

[0049] When the defrosting operation control means 23 starts the defrosting operation, it monitors the defrosting time tj, which is the time since the start of the defrosting operation, and determines whether the defrosting time tj is equal to or greater than a predetermined time threshold th5. The time threshold th5 is, for example, 10 to 12 minutes. When the defrosting time tj is equal to or greater than the time threshold th5, the defrosting operation control means 23 transmits an operation switching signal to the refrigeration cycle control means 21 to switch the operation mode from the defrosting operation to the heating operation. This is because if the defrosting time tj is too long, the room temperature Trm will drop, and the user of the refrigeration cycle apparatus 1 may feel cold.

[0050] Furthermore, when the defrosting operation starts, the defrosting operation control means 23 monitors the refrigerant temperature Trf detected by the refrigerant temperature sensor 34 and determines whether the temperature Trf is equal to or higher than a predetermined temperature threshold th6. The temperature threshold th6 is, for example, 10°C. When the temperature Trf becomes equal to or higher than the temperature threshold th6, the defrosting operation control means 23 transmits an operation switching signal to the refrigeration cycle control means 21 to switch the operation mode from the defrosting operation to the heating operation. This is because, in the heat source side heat exchanger 5, when the refrigerant temperature Trf in the branch refrigerant pipe 9c near the refrigerant flow port of the second heat exchanger 15b, where frost is least likely to melt, becomes sufficiently higher than 0°C, it is considered that defrosting has been completed to a state in which the entire heat source side heat exchanger 5 can function as an evaporator.

[0051] Here, an example of hardware of the controller 20 shown in Fig. 8 will be described. Fig. 9 is a hardware configuration diagram showing an example of the configuration of the controller shown in Fig. 8. When the various functions of the controller 20 are executed by hardware, the controller 20 shown in Fig. 8 is configured by a processing circuit 80 as shown in Fig. 9. The functions of the refrigeration cycle control means 21, defrost preparation means 22, defrost operation control means 23, and timer 24 shown in Fig. 8 are realized by the processing circuit 80.

[0052] When each function is executed by hardware, the processing circuit 80 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. The functions of each of the refrigeration cycle control means 21, the defrost preparation means 22, the defrost operation control means 23, and the timer 24 may be realized by the processing circuit 80. Furthermore, the functions of each of the refrigeration cycle control means 21, the defrost preparation means 22, the defrost operation control means 23, and the timer 24 may be realized by a single processing circuit 80.

[0053] Another example of hardware for the controller 20 shown in Fig. 8 will now be described. Fig. 10 is a hardware configuration diagram showing another example of the configuration of the controller shown in Fig. 8. When the various functions of the controller 20 are executed by software, the controller 20 shown in Fig. 8 has a processor 81 such as a CPU (Central Processing Unit) and a memory 82, as shown in Fig. 10. The functions of the refrigeration cycle control means 21, the defrost preparation means 22, and the defrost operation control means 23 are realized by the processor 81 and the memory 82. Fig. 10 shows that the processor 81 and the memory 82 are communicably connected to each other via a bus 83.

[0054] When each function is executed by software, the functions of the refrigeration cycle control means 21, the defrost preparation means 22, and the defrost operation control means 23 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 82. The processor 81 realizes the function of each means by reading and executing the programs stored in the memory 82.

[0055] For example, non-volatile semiconductor memory such as ROM (Read Only Memory), flash memory, EPROM (Erasable and Programmable ROM), and EEPROM (Electrically Erasable and Programmable ROM) may be used as the memory 82. Alternatively, volatile semiconductor memory such as RAM (Random Access Memory) may be used as the memory 82. Furthermore, removable recording media such as magnetic disks, flexible disks, optical disks, CDs (Compact Discs), MDs (Mini Discs), and DVDs (Digital Versatile Discs) may be used as the memory 82.

[0056] The refrigerant circuit shown in FIG. 1 shows a configuration in which the first heat exchanger 15a is configured as two heat exchangers, heat exchangers 15a-1 and 15a-2, connected in parallel, but the first heat exchanger 15a may also be a single heat exchanger.

[0057] Next, the configuration and operation of a refrigeration cycle device of a comparative example will be described to make it easier to understand the effects of the refrigeration cycle device 1 of the present embodiment 1. Fig. 11 is a refrigerant circuit diagram of the refrigeration cycle device of the comparative example.

[0058] 11, a refrigeration cycle apparatus 100 of the comparative example has a heat source side unit 102 and a load side unit 103. The heat source side unit 102 has a compressor 104, a heat source side heat exchanger 105, a flow path switching device 108, and an accumulator 112. The load side unit 103 has a load side heat exchanger 106 and an expansion valve 107. The compressor 104, the heat source side heat exchanger 105, the load side heat exchanger 106, and the expansion valve 107 are connected via refrigerant piping 109 to form a refrigerant circuit 110 in which the refrigerant circulates.

[0059] The heat source-side heat exchanger 105 has a first heat exchanger 115a and a second heat exchanger 115b. The heat source-side unit 102 has a first flow rate adjustment valve 113a, a second flow rate adjustment valve 113b, a check valve 114, and a two-way valve 116. The refrigerant pipe 109 extending from the flow path switching device 108 to the heat source-side heat exchanger 105 branches into branch refrigerant pipe 109a, which is connected to the refrigerant pipe 109 via the first heat exchanger 115a and the first flow rate adjustment valve 113a. The refrigerant pipe 109 extending from the flow path switching device 108 to the heat source-side heat exchanger 105 is connected to the second heat exchanger 115b via the check valve 114.

[0060] In branch refrigerant pipe 109a, branch refrigerant pipe 109b extends from between first heat exchanger 115a and first flow rate adjustment valve 113a and is connected to refrigerant pipe 109 between check valve 114 and second heat exchanger 115b. Branch refrigerant pipe 109b is provided with two-way valve 116. Second heat exchanger 115b is connected to second flow rate adjustment valve 113b via refrigerant pipe 109c. Second flow rate adjustment valve 113b is connected to expansion valve 107 via refrigerant pipe 109.

[0061] The flow of refrigerant when switching from heating operation to defrosting operation in the refrigeration cycle apparatus 100 of the comparative example shown in Fig. 11 will be described. The flow path switching device 108 switches the flow path of the refrigerant circuit 110 so that the refrigerant discharged from the compressor 104 flows into the heat source side heat exchanger 105. The second flow control valve 113b remains open. The two-way valve 116 switches from a closed state to an open state. The first flow control valve 113a switches from an open state to a closed state.

[0062] The high-temperature, high-pressure gas refrigerant discharged from the compressor 104 flows through the flow path switching device 108 and then flows from the refrigerant pipe 109 into the branch refrigerant pipe 109a. The gas refrigerant that flows into the branch refrigerant pipe 109a flows through the first heat exchanger 15a and then flows into the second heat exchanger 115b via the two-way valve 116. In the first heat exchanger 115a and the second heat exchanger 115b, the high-temperature, high-pressure gas refrigerant melts frost adhering to the surfaces of the first heat exchanger 115a and the second heat exchanger 115b. The refrigerant that flows out of the second heat exchanger 115b passes through the second flow control valve 113b, the expansion valve 107, the load-side heat exchanger 106, the flow path switching device 108, and the accumulator 112, and is again drawn into the compressor 104.

[0063] As described above, in the defrosting operation, the refrigerant flows from the compressor 104 into the first heat exchanger 115a in a high temperature state. Therefore, it is possible to melt the frost that has adhered to the surface of the first heat exchanger 115a. However, thermal energy is consumed to melt the frost while the refrigerant flows through the first heat exchanger 115a, and the temperature of the refrigerant flowing into the second heat exchanger 115b is lower than the temperature of the refrigerant discharged from the compressor 104. Therefore, the efficiency of melting frost in the second heat exchanger 115b is lower than that of the first heat exchanger 115a.

[0064] When the second heat exchanger 115b has the configuration shown in FIG. 5, frost formed on the surface of the first-row heat exchanger 41, which is located downstream of the second-row heat exchanger 42 in the refrigerant flow direction, is difficult to melt. In particular, frost formed on the surface of the lower part of the first-row heat exchanger 41 is difficult to melt. This is because the lower part of the first-row heat exchanger 41 in the second heat exchanger 115b is located farthest from the compressor 104 in the refrigerant flow path during defrosting operation. In the lower part of the first-row heat exchanger 41, the refrigerant temperature drops to 0°C or below, and there is a risk of insufficient heat to melt the frost, resulting in residual frost. In the second heat exchanger 115b shown in FIG. 11, the portion where residual frost has formed is schematically indicated by a diagonal line.

[0065] 5 and 6, the first-row heat exchanger 41 of the second heat exchanger 115b is located on the upwind side of the second-row heat exchanger 42. Therefore, the first-row heat exchanger 41 is more easily cooled by outside air than the second-row heat exchanger 42, and the lower the outside air temperature Tout, the lower the surface temperature of the first-row heat exchanger 41. As a result, frost is more likely to form on the first-row heat exchanger 41 than on the second-row heat exchanger 42.

[0066] If the operation mode of the refrigeration cycle apparatus 100 is switched from the defrosting operation to the heating operation before the frost attached to the surface of the second heat exchanger 115b is completely melted, the remaining frost will grow into ice. In this case, if the refrigeration cycle apparatus 100 performs the heating operation with ice attached to the surface of the second heat exchanger 115b, the heating capacity will be reduced.

[0067] Next, an operation of the refrigeration cycle apparatus 1 according to the present embodiment 1 will be described. Fig. 12 is a flowchart showing an example of an operation procedure of the refrigeration cycle apparatus according to the embodiment 1. Fig. 13 is a flowchart showing the operation procedure of step S105 shown in Fig. 12.

[0068] During the heating operation of the refrigeration cycle apparatus 1, the defrost preparation means 22 periodically determines whether the heating capacity has decreased (step S101). For example, the defrost preparation means 22 determines that the heating capacity has decreased if the outdoor air temperature Tout is equal to or lower than the outdoor air temperature threshold th1 and the time during which the evaporation temperature Tev is equal to or lower than the evaporation temperature threshold th2 is equal to or higher than the time threshold th3. If the defrost preparation means 22 determines in step S101 that the heating capacity has not decreased, it repeats the determination in step S101. On the other hand, if the defrost preparation means 22 determines in step S101 that the heating capacity has decreased, it switches the second flow rate control valve 13b from the open state to the closed state (step S102). In addition, the defrost preparation means 22 switches the bypass valve 18 from the closed state to the open state (step S103).

[0069] Fig. 14 is a diagram showing the flow of refrigerant when the processes of steps S102 and S103 of the flowchart shown in Fig. 12 are performed in the refrigeration cycle apparatus shown in Fig. 1. In Fig. 14, the reference numerals of some of the branch refrigerant pipes shown in Fig. 1 are omitted. The first flow rate control valve 13a is in an open state, and the second flow rate control valve 13b is in a closed state.

[0070] As shown in FIG. 14, high-temperature gas refrigerant discharged from the compressor 4 is divided into a refrigerant pipe 9 and a bypass circuit 17. The gas refrigerant circulating through the refrigerant pipe 9 flows into the load-side heat exchanger 6 via the flow switching device 8. In the load-side heat exchanger 6, the gas refrigerant exchanges heat with the indoor air, releasing heat to warm the indoor air, and condenses into a high-temperature, high-pressure liquid refrigerant, which flows out of the load-side heat exchanger 6. The liquid refrigerant flowing out of the load-side heat exchanger 6 is expanded by the expansion valve 7 and becomes a low-temperature, low-pressure two-phase gas-liquid refrigerant. The low-temperature, low-pressure two-phase gas-liquid refrigerant flows through the branch refrigerant pipe 9e and flows into the first heat exchanger 15a.

[0071] The gas-liquid two-phase refrigerant that has flowed into the first heat exchanger 15a absorbs heat and evaporates as a result of heat exchange with outside air supplied by the blower 11, becoming a low-temperature, low-pressure gas refrigerant. In the first heat exchanger 15a, the refrigerant that has exchanged heat with the outside air flows out of the first heat exchanger 15a into the refrigerant pipe 9 via the branch refrigerant pipe 9a. The low-temperature, low-pressure gas refrigerant that has flowed into the refrigerant pipe 9 is drawn into the compressor 4 via the flow path switching device 8 and the accumulator 12. In this way, the first heat exchanger 15a functions as an evaporator, allowing the refrigeration cycle apparatus 1 to continue heating operation.

[0072] Meanwhile, the high-temperature gas refrigerant that has flowed into the bypass circuit 17 flows into the second heat exchanger 15b via the bypass valve 18 and the branch refrigerant pipe 9c. In the second heat exchanger 15b shown in FIG. 5, the high-temperature, high-pressure gas refrigerant flows from the first lower header 45b into each of the plurality of heat transfer tubes 46 of the first-row heat exchanger 41 from the lower side of the plurality of heat transfer tubes 46. Because the gas refrigerant is high in temperature, it has a large amount of heat and can melt frost that has adhered to the surfaces of the plurality of heat transfer tubes 46 of the first-row heat exchanger 41. This makes it possible to prevent residual frost from forming in the first-row heat exchanger 41 shown in FIG. 5. The high-temperature gas refrigerant that has flowed into the first-row heat exchanger 41 shown in FIG. 5 passes through the upper header 43 and is diverted to the plurality of heat transfer tubes 46 of the second-row heat exchanger 42. The refrigerant that has been branched out of the plurality of heat transfer tubes 46 of the second row side heat exchanger 42 joins the second lower header 45a, and then flows out into the refrigerant pipe 9 via the branch refrigerant pipes 9f and 9b.

[0073] 12, the defrosting operation control means 23 refers to the time measured by the timer 24 and determines whether or not the elapsed time tk from when the bypass valve 18 was opened is equal to or greater than the time threshold value th4 (step S104). If the elapsed time tk has not reached the time threshold value th4, the defrosting operation control means 23 returns to step S104. On the other hand, if the result of the determination in step S104 is that the elapsed time tk is equal to or greater than the time threshold value th4, the defrosting operation control means 23 starts the defrosting operation (step S105).

[0074] 13, the defrosting operation control means 23 switches the second flow control valve 13b from a closed state to an open state (step S141). Also, the defrosting operation control means 23 switches the bypass valve 18 from an open state to a closed state (step S142). Next, the defrosting operation control means 23 controls the flow path switching device 8 so that the refrigerant discharged from the compressor 4 flows into the heat source side heat exchanger 5 (step S143).

[0075] As described with reference to FIG. 3, high-temperature gas refrigerant discharged from the compressor 4 is diverted from the branch refrigerant pipe 9a to the heat exchangers 15a-1 and 15a-2. In each of the heat exchangers 15a-1 and 15a-2, the high-temperature gas refrigerant flows from the second lower header 45a shown in FIG. 5 into each of the plurality of heat transfer tubes 46 of the second-row heat exchanger 42 from the lower side of the plurality of heat transfer tubes 46. The high-temperature gas refrigerant that has flowed into the second-row heat exchanger 42 passes through the upper header 43 and is diverted to the plurality of heat transfer tubes 46 of the first-row heat exchanger 41. This makes it possible to melt frost adhering to the surfaces of the plurality of heat transfer tubes 46 of the first-row heat exchanger 41 of the heat exchangers 15a-1 and 15a-2.

[0076] In the heat exchangers 15a-1 and 15a-2, the gas refrigerant that has been diverted from the multiple heat transfer tubes 46 of the first column heat exchanger 41 merges with the first lower header 45b. The gas refrigerant that flows out of the first lower header 45b of each of the heat exchangers 15a-1 and 15a-2 flows into the second heat exchanger 15b via the branch refrigerant pipes 9b and 9f. The temperature of the gas refrigerant that flows into the second heat exchanger 15b is lower than the temperature of the gas refrigerant when it was flowing through the first heat exchanger 15a, but after the process of step S103, the frost on the second heat exchanger 15b has already melted. The refrigerant flowing through the second heat exchanger 15b flows out from the second heat exchanger 15b into the branch refrigerant pipe 9c. The refrigerant that flows into the branch refrigerant pipe 9c flows into the load-side heat exchanger 6 via the second flow control valve 13b and the expansion valve 7. The refrigerant that has flowed into the load-side heat exchanger 6 passes through the flow switching device 8 and the accumulator 12 and is then drawn into the compressor 4.

[0077] In step S105 shown in Fig. 12, when the defrosting operation control means 23 starts the defrosting operation, it monitors the defrosting time tj by referring to the time measured by the timer 24. Then, the defrosting operation control means 23 determines whether the defrosting time tj is equal to or greater than a time threshold value th5 (step S106). If the defrosting time tj is less than the time threshold value th5, the defrosting operation control means 23 determines whether the refrigerant temperature Trf detected by the refrigerant temperature sensor 34 is equal to or greater than a temperature threshold value th6 (step S107). If the refrigerant temperature Trf is less than the temperature threshold value th6, the defrosting operation control means 23 returns to the determination process of step S106.

[0078] If it is determined in step S106 that the defrosting time tj is equal to or greater than the time threshold value th5, or if it is determined in step S107 that the refrigerant temperature Trf is equal to or greater than the temperature threshold value th6, the defrosting operation control means 23 transmits an operation switching signal to the refrigeration cycle control means 21. Upon receiving the operation switching signal from the defrosting operation control means 23, the refrigeration cycle control means 21 switches from the defrosting operation to the heating operation (step S108). Specifically, the refrigeration cycle control means 21 controls the flow path switching device 8 so that the refrigerant discharged from the compressor 4 flows into the load-side heat exchanger 6. Furthermore, the refrigeration cycle control means 21 switches the first flow control valve 13a from a closed state to an open state, and switches the two-way valve 16 from an open state to a closed state.

[0079] In this way, the refrigeration cycle apparatus 1 can cause high-temperature gas refrigerant to flow into the first-row heat exchanger 41 from the lower side of the first-row heat exchanger 41 located on the windward side in the second heat exchanger 15b while continuing the heating operation before starting the defrosting operation. Therefore, in the flow path through which high-temperature gas refrigerant flows from the compressor 4 during the defrosting operation, frost that has adhered to the surfaces of the heat transfer tubes 46 of the first-row heat exchanger 41 located farthest from the compressor 4 can be melted in advance before the defrosting operation starts. Even if the outside air temperature Tout is low, the formation of residual frost during the defrosting operation can be suppressed. As a result, the growth of residual frost into ice in the heat source-side heat exchanger 5 can be suppressed, and a decrease in the heating capacity of the refrigeration cycle apparatus 1 can be suppressed.

[0080] In the flowchart shown in Fig. 12, the order of the processes in steps S102 and S103 may be reversed, and the order of the determination processes in steps S106 and S107 may be reversed. Only one of the determination processes in steps S106 and S107 may be performed. Furthermore, in the flowchart shown in Fig. 13, the order of the processes in steps S141 and S142 may be reversed.

[0081] The refrigeration cycle apparatus 1 of the first embodiment includes a compressor 4 that compresses and discharges a refrigerant, a load-side heat exchanger 6 that exchanges heat between the refrigerant and air in a target space, a heat-source-side heat exchanger 5, a flow switching device 8, a second flow control valve 13b, a bypass circuit 17, and a controller 20. The heat-source-side heat exchanger 5 includes a first heat exchanger 15a and a second heat exchanger 15b as a plurality of heat exchangers each having a plurality of heat transfer tubes 46 extending in the vertical direction. The first heat exchanger 15a and the second heat exchanger 15b are connected in parallel during heating operation, and the first heat exchanger 15a and the second heat exchanger 15b are connected in series during cooling operation and defrosting operation. The second flow control valve 13b is provided in a branch refrigerant pipe 9c, which is a refrigerant pipe through which the refrigerant flows out from the second heat exchanger 15b, which is the downstream heat exchanger during cooling operation. The flow path switching device 8 allows the refrigerant discharged from the compressor 4 to flow into the load-side heat exchanger 6 during heating operation, and allows the refrigerant discharged from the compressor 4 to flow into the heat-source-side heat exchanger 5 during cooling operation and defrosting operation. A bypass circuit 17 connects the branch refrigerant pipe 9c between the second flow control valve 13b and the second heat exchanger 15b to the refrigerant discharge port of the compressor 4. A bypass valve 18 is provided in the bypass circuit 17. A controller 20 controls the flow path switching device 8, the second flow control valve 13b, and the bypass valve 18. The controller 20 has defrost preparation means 22 and defrosting operation control means 23. When the heating capacity decreases during heating operation, the defrost preparation means 22 switches the second flow control valve 13b from an open state to a closed state and switches the bypass valve 18 from a closed state to an open state. After the refrigerant discharged from the compressor 4 flows through the bypass circuit 17 and the branch refrigerant piping 9c to the second heat exchanger 15b, the defrosting operation control means 23 switches the second flow control valve 13b from a closed state to an open state, switches the bypass valve 18 from an open state to a closed state, and controls the flow path switching device 8 to perform defrosting operation.

[0082] According to the first embodiment, the system includes a second flow control valve 13b provided in the branch refrigerant pipe 9c through which refrigerant flows out from the downstream second heat exchanger 15b during cooling operation, a bypass circuit 17 connecting a section between the second heat exchanger 15b and the second flow control valve 13b with a refrigerant discharge port of the compressor 4, and a bypass valve 18 provided in the bypass circuit 17. Before the start of the defrosting operation, the second flow control valve 13b is switched from an open state to a closed state, and the bypass valve 18 is switched from a closed state to an open state. As a result, before the start of the defrosting operation, high-temperature gas refrigerant flows from the branch refrigerant pipe 9c side into the second heat exchanger 15b. Therefore, in the flow path through which high-temperature gas refrigerant flows from the compressor 4 during the defrosting operation, frost that has adhered to the lower surfaces of the plurality of heat transfer tubes 46 of the second heat exchanger 15b, which is located farthest from the compressor 4, can be melted in advance before the start of the defrosting operation. As a result, the generation of residual frost in the heat source side heat exchanger 5 during the defrosting operation can be suppressed, and the heating capacity of the refrigeration cycle apparatus 1 can be suppressed from decreasing.

[0083] Furthermore, in the first embodiment, the second heat exchanger 15b located downstream during cooling operation may include a first row-side heat exchanger 41 located upwind of the airflow generated by the blower 11, a first lower header 45b provided below the first row-side heat exchanger 41, a second row-side heat exchanger 42 located downwind, and an upper header 43 connecting the first row-side heat exchanger 41 and the second row-side heat exchanger 42. In this case, the bypass circuit 17 is connected to the first lower header 45b via the branch refrigerant pipe 9c during defrosting operation.

[0084] As shown in FIG. 5 , the first-row heat exchanger 41 of the second heat exchanger 15b is located on the windward side of the second-row heat exchanger 42. Therefore, the first-row heat exchanger 41 is more easily cooled by outside air than the second-row heat exchanger 42. The lower the outside air temperature Tout, the lower the surface temperature of the first-row heat exchanger 41. As a result, frost is more likely to form on the first-row heat exchanger 41 than on the second-row heat exchanger 42. In contrast, according to the first embodiment, before the defrosting operation starts, high-temperature gas refrigerant flows from the first lower header 45b into the first-row heat exchanger 41 of the second heat exchanger 15b via the branch refrigerant pipe 9c. This prevents residual frost from forming below the first-row heat exchanger 41 of the second heat exchanger 15b and prevents the residual frost from growing into ice. This prevents a decrease in the heating capacity of the refrigeration cycle apparatus 1. [Explanation of symbols]

[0085] REFRIGERATION CYCLE DEVICE, 2 HEAT SOURCE SIDE UNIT, 3 LOAD SIDE UNIT, 4 COMPRESSOR, 5 HEAT SOURCE SIDE HEAT EXCHANGER, 6 LOAD SIDE HEAT EXCHANGER, 7 EXPANSION VALVE, 8 FLOW CHANNEL SWITCHING DEVICE, 9 REFRIGERANTE PIPE, 9a, 9a-1, 9a-2, 9b, 9c, 9d-1, 9d-2, 9e, 9f BRANCH REFRIGERANTE PIPE, 10 REFRIGERANTE CIRCUIT, 11 BLOWER, 12 ACCUMULATOR, 13a FIRST FLOW CONTROL VALVE, 13b SECOND FLOW CONTROL VALVE, 14 CHECK VALVE, 15a FIRST HEAT EXCHANGER, 15a-1, 15a-2 HEAT EXCHANGER, 15b SECOND HEAT EXCHANGER, 16 TWO-WAY VALVE, 17 BYPASS CIRCUIT, 18 BYPASS VALVE, 20 CONTROLLER, 21 REFRIGERATION CYCLE CONTROL MEANS, 22 DEFROST PREPARATION MEANS, 23 DEFROST OPERATION CONTROL MEANS, 24 TIMER, 31 ROOM TEMPERATURE SENSOR, 32 Outdoor air temperature sensor, 33 Evaporation temperature sensor, 34 Refrigerant temperature sensor, 40 Housing, 41 First row heat exchanger, 42 Second row heat exchanger, 43 Upper header, 44 Lower header, 45a Second lower header, 45b First lower header, 46 Heat transfer tube, 47 Corrugated fin, 80 Processing circuit, 81 Processor, 82 Memory, 83 Bus, 100 Refrigeration cycle device, 102 Heat source side unit, 103 Load side unit, 104 Compressor, 105 Heat source side heat exchanger, 106 Load side heat exchanger, 107 Expansion valve, 108 Flow switching device, 109 Refrigerant piping, 109a, 109b Branch refrigerant piping, 109c Refrigerant piping, 110 Refrigerant circuit, 112 Accumulator, 113a First flow control valve, 113b A second flow control valve, 114 a check valve, 115a a first heat exchanger, 115b a second heat exchanger, and 116 a two-way valve.

Claims

1. a compressor that compresses and discharges a refrigerant; a load-side heat exchanger for exchanging heat between the air in the target space and the refrigerant; a heat source-side heat exchanger including a plurality of heat exchangers each having a plurality of heat transfer tubes extending in a vertical direction, the plurality of heat exchangers being connected in parallel during heating operation and being connected in series during cooling operation and defrosting operation; a flow path switching device that causes the refrigerant discharged from the compressor to flow into the load-side heat exchanger during the heating operation and causes the refrigerant discharged from the compressor to flow into the heat-source-side heat exchanger during the cooling operation and the defrosting operation; a flow rate regulating valve provided in a refrigerant pipe through which the refrigerant flows out from a downstream heat exchanger among the plurality of heat exchangers connected in series during the cooling operation; a bypass circuit connecting a portion of the refrigerant pipe between the flow rate control valve and the downstream heat exchanger and a refrigerant discharge port of the compressor; a bypass valve provided in the bypass circuit; a controller for controlling the flow path switching device, the flow rate adjustment valve, and the bypass valve, The controller a defrost preparation means for switching the flow rate control valve from an open state to a closed state and switching the bypass valve from a closed state to an open state when the heating capacity decreases during the heating operation; and a defrosting operation control means for switching the flow rate control valve from the closed state to the open state, switching the bypass valve from the open state to the closed state, and controlling the flow path switching device to perform the defrosting operation after the refrigerant discharged from the compressor has circulated to the downstream heat exchanger via the bypass circuit and the refrigerant piping. Refrigeration cycle equipment.

2. a blower that supplies outside air to the heat source-side heat exchanger, the downstream heat exchanger includes a first row-side heat exchanger located on the upwind side of the airflow generated by the fan, a first lower header provided below the first row-side heat exchanger, a second row-side heat exchanger located on the downwind side of the airflow generated by the fan, and an upper header connecting the first row-side heat exchanger and the second row-side heat exchanger, the bypass circuit is connected to the first lower header via the refrigerant piping during the defrosting operation. The refrigeration cycle device according to claim 1.

3. the heat source side heat exchanger includes a first heat exchanger that is an upstream heat exchanger among the plurality of heat exchangers that are connected in series during the cooling operation, and a second heat exchanger that is the downstream heat exchanger; the first heat exchanger has a configuration in which two heat exchangers are connected in parallel, each of the two heat exchangers includes a first row-side heat exchanger located on the upwind side, a second row-side heat exchanger located on the downwind side, a second lower header provided below the second row-side heat exchanger, and an upper header connecting the first row-side heat exchanger and the second row-side heat exchanger; During the defrosting operation, the refrigerant discharged from the compressor passes through the flow path switching device and flows into the second lower headers of the two heat exchangers. The refrigeration cycle device according to claim 2.

4. The defrosting operation control means when a predetermined time has elapsed since the refrigerant discharged from the compressor started to circulate through the heat source side heat exchanger via the bypass circuit, the flow rate control valve and the bypass valve are switched to control the flow path switching device. The refrigeration cycle device according to any one of claims 1 to 3.

5. an outside air temperature sensor for detecting an outside air temperature; an evaporation temperature sensor for detecting an evaporation temperature; The defrost preparation means includes: During the heating operation, if the time during which the outside air temperature detected by the outside air temperature sensor is equal to or lower than a predetermined outside air temperature threshold and the evaporation temperature detected by the evaporation temperature sensor is equal to or lower than a predetermined evaporation temperature threshold becomes equal to or higher than a predetermined time threshold, it is determined that the heating capacity has decreased. The refrigeration cycle device according to any one of claims 1 to 3.

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