REFRIGERATION CYCLE APPARATUS

Abstract

In a first operation mode, a flow path switching device connects a discharge port to a refrigerant inlet of a first heat exchanger, connects a refrigerant outlet of the first heat exchanger to a refrigerant inlet of a first flow path, connects a refrigerant outlet of a first expansion valve to a refrigerant inlet of a second heat exchanger, and connects a refrigerant outlet of the second heat exchanger to a suction port. In a second operation mode, the flow path switching device connects the discharge port to the refrigerant inlet of the second heat exchanger, connects the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path, connects the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger, and connects the refrigerant outlet of the first heat exchanger to the suction port.

Description

TECHNICAL FIELD

The present disclosure relates to a refrigeration cycle apparatus.

BACKGROUND

Conventionally, it has been known to use an injection circuit in order to improve the Coefficient of Performance (COP) of a refrigeration cycle apparatus.

For example, Japanese Patent Laying-Open No. 2020-186909 (PTL 1) discloses an injection circuit that causes part of refrigerant flowing from a heat exchanger to an expansion mechanism to be supplied to a suction side of a compressor, in which the heat exchanger serves as a heat radiator among a heat source-side heat exchanger and a use-side heat exchanger.

PATENT LITERATURE

• • PTL 1: Japanese Patent Laying-Open No. 2020-186909

The injection circuit disclosed in Japanese Patent Laying-Open No. 2020-186909 (PTL 1) is configured such that, in any of heating, cooling, and defrosting operations, part of liquid refrigerant before passing through the expansion mechanism is introduced into the injection circuit from a refrigerant outlet portion of a heat exchanger serving as a heat radiator. Thus, performance improvement by the injection circuit can be expected in any of the heating, cooling and defrosting operations.

However, since the flow direction of the refrigerant flowing through the heat source-side heat exchanger and the use-side heat exchanger is reversed between heating and cooling/defrosting, the efficiency improvement of the heat exchanger still needs to be enhanced.

SUMMARY

The present disclosure has been made in order to describe the embodiments that solve the above-described problems, and an object of the present disclosure is to provide a refrigeration cycle apparatus capable of improving the efficiency of a heat exchanger while improving the performance by an injection circuit.

The present disclosure relates to a refrigeration cycle apparatus. The refrigeration cycle apparatus includes: a compressor; a first heat exchanger; a second heat exchanger; a third heat exchanger; a first expansion valve; a second expansion valve; and a flow path switching device. The compressor, the first heat exchanger, the second heat exchanger, and the first expansion valve constitute a refrigerant circuit through which refrigerant circulates. The second expansion valve forms a portion of an injection flow path, the injection flow path being configured to reduce pressure of the refrigerant before passing through the first expansion valve in the refrigerant circuit and return the refrigerant to the compressor. The third heat exchanger includes a first flow path through which the refrigerant flows and a second flow path through which the refrigerant flows. The third heat exchanger is configured to exchange heat between the refrigerant passing through the first flow path and the refrigerant passing through the second flow path. The first flow path is disposed in the refrigerant circuit to cause the refrigerant to flow toward the first expansion valve. The second flow path is disposed to return, to the compressor, the refrigerant that has passed through the second expansion valve. In a first operation mode, the flow path switching device is configured to: connect a discharge port of the compressor to a refrigerant inlet of the first heat exchanger; connect a refrigerant outlet of the first heat exchanger to a refrigerant inlet of the first flow path; connect a refrigerant outlet of the first expansion valve to a refrigerant inlet of the second heat exchanger; and connect a refrigerant outlet of the second heat exchanger to a suction port of the compressor. In a second operation mode, the flow path switching device is configured to: connect the discharge port of the compressor to the refrigerant inlet of the second heat exchanger; connect the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path; connect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger; and connect the refrigerant outlet of the first heat exchanger to the suction port of the compressor.

According to the refrigeration cycle apparatus of the present disclosure, in each of the heat exchangers, the flow direction of the refrigerant does not change and a branch portion of the injection flow path is located on the inlet side of the first expansion valve, and thereby, the performance of the refrigeration cycle apparatus is improved in any of the plurality of operation modes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus according to a first embodiment.

FIG. 2 is a diagram showing a refrigerant circuit and a flow of refrigerant during a heating operation of the refrigeration cycle apparatus according to the first embodiment.

FIG. 3 is a diagram showing an arrangement of various sensors when refrigerant having no temperature gradient is used.

FIG. 4 is a p-h diagram showing a change in the state of refrigerant when refrigerant having no temperature gradient is used.

FIG. 5 is a flowchart for illustrating control of a second expansion valve 72 when refrigerant having no temperature gradient is used.

FIG. 6 is a diagram for illustrating symbols of various parameters of a first expansion valve 30.

FIG. 7 is a diagram for illustrating a process of deriving inlet portion pressure of first expansion valve 30.

FIG. 8 is a diagram showing an arrangement of various sensors when non-azeotropic refrigerant is used.

FIG. 9 is a p-h diagram showing a change in the state of refrigerant when non-azeotropic refrigerant is used.

FIG. 10 is a flowchart for illustrating control of second expansion valve 72 when non-azeotropic refrigerant is used.

FIG. 11 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to a second embodiment.

FIG. 12 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the second embodiment.

FIG. 13 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to a third embodiment.

FIG. 14 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the third embodiment.

FIG. 15 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to a fourth embodiment.

FIG. 16 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the fourth embodiment.

FIG. 17 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to a fifth embodiment.

FIG. 18 is a diagram showing the state of an eight-way valve 50B and the flow of the refrigerant in eight-way valve 50B during the cooling operation according to the fifth embodiment.

FIG. 19 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the fifth embodiment.

FIG. 20 is a diagram showing the state of eight-way valve 50B and the flow of the refrigerant in eight-way valve 50B during the heating operation according to the fifth embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Although the following describes a plurality of embodiments, it has been originally intended to combine the configurations described in the respective embodiments as appropriate. In the accompanying drawings, the same or corresponding portions are denoted by the same reference characters, and the description thereof will not be repeated.

First Embodiment

<Configuration of Refrigeration Cycle Apparatus 1>

FIG. 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus according to the first embodiment. FIG. 1 shows a refrigerant circuit and a flow of refrigerant during a cooling operation. The refrigerant circuit and the flow of refrigerant shown in FIG. 1 are also similarly applied in a defrosting operation performed during a heating operation. A refrigeration cycle apparatus 1 includes a compressor 10, a first heat exchanger 20, a second heat exchanger 40, a third heat exchanger 80, a first expansion valve 30, a second expansion valve 72, and a flow path switching device 50.

Compressor 10, first heat exchanger 20, second heat exchanger 40, first expansion valve 30, and pipes 91 to 99 constitute a refrigerant circuit 90 through which refrigerant circulates.

First heat exchanger 20 is configured to exchange heat between the outdoor air blown by a fan 23 and the refrigerant. Second heat exchanger 40 is configured to exchange heat between a heat medium circulating through the use-side circuit and the refrigerant. Second heat exchanger 40 is a plate-type heat exchanger, for example.

The use-side circuit includes a pump WP, a use-side heat exchanger 123, and pipes 121, 122, and 124. The heat medium circulating through the use-side circuit is, for example, water, brine, or the like. Use-side heat exchanger 123 is, for example, a water heater, an air-conditioner for heating or cooling, or the like. Second heat exchanger 40 includes flow paths 41 and 42. Second heat exchanger 40 is configured to exchange heat between the refrigerant flowing through flow path 41 and the heat medium flowing through flow path 42.

An injection flow path 70 includes pipes 71 and 73 and a second expansion valve 72. Injection flow path 70 reduces the pressure of the refrigerant before passing through first expansion valve 30 in refrigerant circuit 90 and returns the refrigerant to compressor 10.

Third heat exchanger 80 includes a first flow path 81 and a second flow path 82 through which refrigerant flows. Third heat exchanger 80 is configured to exchange heat between the refrigerant passing through first flow path 81 and the refrigerant passing through second flow path 82.

First flow path 81 is disposed in refrigerant circuit 90 to cause the refrigerant to flow toward first expansion valve 30, and second flow path 82 is disposed to return, to compressor 10, the refrigerant having passed through second expansion valve 72.

In the first operation mode (cooling) shown in FIG. 1, flow path switching device 50 is configured to connect a discharge port of compressor 10 to a refrigerant inlet 21 of first heat exchanger 20, connect a refrigerant outlet of first heat exchanger 20 to a refrigerant inlet of first flow path 81, connect a refrigerant outlet of first expansion valve 30 to a refrigerant inlet of second heat exchanger 40, and connect a refrigerant outlet of second heat exchanger 40 to a suction port of compressor 10. In the first operation mode, not only a defrosting operation during cooling but also a defrosting operation during heating may be performed.

It is conceivable that flow path switching device 50 may have various configurations, but the first embodiment provides an example in which flow path switching device 50 includes a first four-way valve 51 and a second four-way valve 52.

First four-way valve 51 has ports PA, PB, PC, and PD. Second four-way valve 52 has ports PE, PF, PG, and PH.

First, connection of pipes of refrigerant circuit 90 will be described. Pipe 91 connects the discharge port of compressor 10 to port PA. Pipe 92 connects port PB to refrigerant inlet 21 of first heat exchanger 20. Pipe 93 connects a refrigerant outlet 22 of first heat exchanger 20 to port PF.

Pipe 94 connects port PE to the refrigerant inlet of first flow path 81. Pipe 95 connects a refrigerant outlet of first flow path 81 to a refrigerant inlet of first expansion valve 30. Pipe 96 connects the refrigerant outlet of first expansion valve 30 to port PC. Pipe 97 connects port PD to the refrigerant inlet of second heat exchanger 40. Pipe 98 connects the refrigerant outlet of second heat exchanger 40 to port PH. Pipe 99 connects port PG to the suction port of compressor 10.

The following describes connection of the pipes of injection flow path 70. Pipe 71 branches from pipe 95 and connects pipe 95 to a refrigerant inlet of second flow path 82. Second expansion valve 72 is disposed somewhere in the middle of pipe 71. Pipe 73 connects a refrigerant outlet of second flow path 82 to an intermediate pressure port of compressor 10.

Refrigeration cycle apparatus 1 further includes a controller 100 that controls flow path switching device 50. Controller 100 is configured to include a central processing unit (CPU) 101, a memory 102 (a read only memory (ROM)) and a random access memory (RAM)), an input/output buffer (not shown), and the like. CPU 101 deploys a program stored in the ROM into the RAM or the like and executes the program. The programs stored in the ROM describe the processing procedure for controller 100. Controller 100 controls each of devices in refrigeration cycle apparatus 1 according to these programs. Such control is not necessarily processed by software, but can also be processed by dedicated hardware (an electronic circuit).

<Switching Control of Flow Path Switching Device 50>

The following describes control of flow path switching device 50 executed by controller 100 in response to switching of the operation mode.

In the first operation mode (cooling), as indicated by solid lines in FIG. 1, first four-way valve 51 is set such that port PA communicates with port PB and port PC communicates with port PD. On the other hand, as indicated by broken lines in FIG. 1, first four-way valve 51 is set such that port PA does not communicate with port PD and port PB does not communicate with port PC. In other words, in the first operation mode (cooling), first four-way valve 51 is configured to connect the discharge port of compressor 10 to refrigerant inlet 21 of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40.

In the first operation mode (cooling), as indicated by solid lines in FIG. 1, second four-way valve 52 is set such that port PE communicates with port PF and port PG communicates with port PH. On the other hand, as indicated by broken lines in FIG. 1, second four-way valve 52 is set such that port PE does not communicate with port PH and port PF does not communicate with port PG. In other words, in the first operation mode (cooling), second four-way valve 52 is configured to connect the refrigerant outlet of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10.

FIG. 2 is a diagram showing the refrigerant circuit and the flow of the refrigerant during the heating operation of the refrigeration cycle apparatus according to the first embodiment.

In the second operation mode (heating), flow path switching device 50 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40, connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81, connect the refrigerant outlet of first expansion valve 30 to refrigerant inlet 21 of first heat exchanger 20, and connect refrigerant outlet 22 of first heat exchanger 20 to the suction port of compressor 10. In the second operation mode, not only a heating operation but also a warming operation to warm cold water by a water heater may be performed.

In the second operation mode (heating), first four-way valve 51 is set such that port PA communicates with port PD and port PC communicates with port PB. On the other hand, as indicated by broken lines in FIG. 2, first four-way valve 51 is set such that port PA does not communicate with port PB and port PC does not communicate with port PD. In other words, in the second operation mode (heating), first four-way valve 51 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of first heat exchanger 20.

In the second operation mode (heating), second four-way valve 52 is set such that port PE communicates with port PH and port PG communicates with port PF. On the other hand, as indicated by broken lines in FIG. 2, second four-way valve 52 is set such that port PE does not communicate with port PF and port PG does not communicate with port PH. In other words, in the second operation mode (heating), second four-way valve 52 is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of first heat exchanger 20 to the suction port of compressor 10.

In general, the heat exchange efficiency of the heat exchanger is higher in the relation in which the heat medium that exchanges heat flows as a counterflow than in the relation in which the heat medium flows as a parallel-flow. In a heat exchanger in which the flow direction of the refrigerant is reversed between cooling and heating, when the heat medium flows in the counterflow relation during cooling, the heat medium flows in the parallel-flow relation during heating, with the result that the heat exchange efficiency in one of the two operation modes tends to deteriorate.

In contrast, as shown in FIGS. 1 and 2, in refrigeration cycle apparatus 1 according to the first embodiment, flow path switching device 50 is controlled to cause the refrigerant to flow in the same direction in any of the first operation mode (cooling) and the second operation mode (heating) in each of first heat exchanger 20, second heat exchanger 40, and third heat exchanger 80.

Therefore, regardless of whether the heating operation or the cooling operation, the counterflow relation can be implemented in each heat exchanger, so that the heat exchange efficiency can be improved in these two operation modes.

Further, regardless of whether the heating operation or the cooling operation, due to pipe 95 located on the refrigerant inlet side of each of first expansion valve 30 and second expansion valve 72, controlling the degree of dryness of the refrigerant in pipe 95 to be kept close to the state of a liquid phase makes it possible to satisfactorily achieve the pressure adjusting performance of first expansion valve 30 and second expansion valve 72.

<Control of Expansion Valve in Injection Flow Path 70>

Controller 100 calculates the degree of dryness of the refrigerant in pipe 95 on the inlet side of each of first expansion valve 30 and second expansion valve 72, and controls second expansion valve 72 such that the degree of dryness reaches a target value. If the degree of dryness of the refrigerant in pipe 95 rises too high, the gas-phase refrigerant is mixed into the inlets of first expansion valve 30 and second expansion valve 72, so that the pressure adjusting performance of the expansion valves decreases. Accordingly, when the degree of dryness rises too high, controller 100 controls the degree of opening of second expansion valve 72 to decrease the degree of dryness.

(a) Refrigerant Having No Temperature Gradient

FIG. 3 is a diagram showing an arrangement of various sensors when refrigerant having no temperature gradient is used. Controller 100 controls the degree of opening of second expansion valve 72 based on the outputs from various sensors shown in FIG. 3. Refrigeration cycle apparatus 1 includes pressure sensors 110 and 116, temperature sensors 112, 114, 115, and 117, and a flow rate sensor 113.

Pressure sensor 110 detects a discharge pressure Pd[MPa] of compressor 10. Pressure sensor 116 detects a suction pressure P_s[MPa] of compressor 10. Temperature sensor 112 detects a refrigerant inlet temperature T_e,in[° C.] of second heat exchanger 40. Temperature sensor 117 detects a refrigerant suction temperature Ts[° C.] of compressor 10. Temperature sensor 115 detects an inlet water temperature T_w,in[° C.] of second heat exchanger 40. Temperature sensor 114 detects an outlet water temperature T_w,out[° C.] of second heat exchanger 40. Flow rate sensor 113 detects a flow rate V_w[L/min] of water in second heat exchanger 40.

FIG. 4 is a p-h diagram showing a change in the state of refrigerant when refrigerant having no temperature gradient is used. The refrigerant discharged from compressor 10 flows through refrigerant circuit 90, and the state of the refrigerant changes in order of states A, B, C, D, and E. Further, the refrigerant branched from the outlet portion of first flow path 81 of refrigerant circuit 90 flows through injection flow path 70 and the state of the refrigerant changes in order of states C, F, and G.

The positions in FIG. 3 corresponding to states A to G are denoted by the same respective reference characters A to G.

The refrigerant in state J compressed to intermediate pressure by compressor 10 merges with the refrigerant in state G supplied through injection flow path 70, thus resulting in refrigerant in state K. The refrigerant in state K is further compressed by compressor 10, thus resulting in refrigerant in state A.

In the p-h diagram as described above, a target degree of dryness X_tgt is set such that state C is not significantly apart from a liquidus line, and controller 100 controls the degree of opening of second expansion valve 72 to achieve the target degree of dryness X_tgt.

FIG. 5 is a flowchart for illustrating control of second expansion valve 72 when refrigerant having no temperature gradient is used.

In the following flowchart, each symbol represents as follows. Cv_main[mm²] represents a Cv value of an expansion valve 30. C_p,w[kJ/(kg·K)] represents a specific heat of water. F_comp[Hz] represents an operating frequency of compressor 10. Gr_s[kg/h] represents a refrigerant circulation amount at the suction port of compressor 10. P_d[MPa] represents pressure of the refrigerant discharged from compressor 10. P_s[MPa] represents pressure of the refrigerant suctioned into compressor 10. T_e,in[° C.] represents a temperature of the refrigerant at the inlet of the evaporator. Ts[° C.] represents a temperature of the refrigerant suctioned into compressor 10.

T_w,in[° C.] represents a temperature of water at an inlet of a heat exchanger 40. T_w,out[° C.] represents a temperature of water at an outlet of heat exchanger 40. V_w[L/min] represents a flow rate of water in heat exchanger 40.

V_st[cc] represents a stroke volume of compressor 10. η_v[−] represents volumetric efficiency of compressor 10. ρ_LEV,in[kg/m] represents a refrigerant density at the inlet of expansion valve 30. ρ_s[kg/m³] represents a density of the refrigerant suctioned into compressor 10. Also, h_s represents an enthalpy at the suction port of compressor 10.

Further, fx(A,B) represents a function adopting A and B as inputs and x as an output, and this function is mapped in advance.

First, in step S1, controller 100 calculates a cooling capability Q_e by the following equation (1).

$\begin{array}{cc}{Q}_e=V_w·C_{p,w}\left(T_{w,\mathrm{in}}-T_{w,\mathrm{out}}\right)& \left(1\right)\end{array}$

Then, in step S2, controller 100 calculates a refrigerant circulation amount Gr_s on the low pressure side by the following equation (2).

$\begin{array}{cc}G{r}_s=\mathrm{Fcomp}·V_{st}·f{\rho }_s\left(P_s,T_s\right)·{\eta }_v& \left(2\right)\end{array}$

In step S3, controller 100 calculates an evaporator inlet enthalpy h_e,in and an evaporator inlet pressure P_e,in by the following equations (3) and (4), respectively.

$\begin{array}{cc}{h}_{e,\mathrm{in}}=f_{hs}\left(P_s,T_s\right)-Q_e/{\mathrm{Gr}}_s& \left(3\right)\end{array}$ $\begin{array}{cc}{P}_{e,\mathrm{in}}=f_{\mathrm{Pe},\mathrm{in}}\left(h_{e,\mathrm{in}},T_{e,\mathrm{in}}\right)& \left(4\right)\end{array}$

Then, assuming that the change by expansion valve 30 is defined as an isenthalpic change, in step S4, controller 100 calculates a pressure P_LEV,in and a degree of dryness X_LEV,in of the refrigerant at the inlet portion of expansion valve 30 by the following equations (5) and (6), respectively.

$\begin{array}{cc}{P}_{\mathrm{LEV},\mathrm{in}}=f_{\mathrm{PLEV},\mathrm{in}}\left(G{r}_s,P_{e,\mathrm{in}},{\mathrm{Cv}}_{\mathrm{main}},f{\rho }_{\mathrm{LEV},\mathrm{in}}\left(P_{\mathrm{LEV},\mathrm{in}},h_{e,\mathrm{in}}\right)\right)& \left(5\right)\end{array}$ $\begin{array}{cc}{X}_{\mathrm{LEV},\mathrm{in}}=f_{\mathrm{XLEV},\mathrm{in}}\left(P_{\mathrm{LEV},\mathrm{in}},h_{e,\mathrm{in}}\right)& \left(6\right)\end{array}$

The degree of dryness X is defined such that 0<X<1 in the case of two-phase refrigerant, X≤0 in the case of liquid refrigerant (supercooled liquid), and X is negative in the case of supercooled liquid.

Then, in step S5, controller 100 calculates the target degree of dryness X_tgt of the refrigerant at the inlet portion of expansion valve 30 by the following equation (7).

$\begin{array}{cc}{X}_{\mathrm{tgt}}=f_{\mathrm{Xtgt}}\left(P_d,P_s,\mathrm{Fcomp}\right)& \left(7\right)\end{array}$

In step S6, controller 100 compares the target degree of dryness X_tgt with the calculated current degree of dryness X_LEV,in. When the degree of dryness X_LEV,in is equal to or less than the target degree of dryness X_tgt(YES in S6), then in step S7, controller 100 decreases the degree of opening of second expansion valve 72 disposed in injection flow path 70. On the other hand, when the degree of dryness X_LEV,in is not equal to or less than the target degree of dryness X_tgt(NO in S6), then in step S8, controller 100 increases the degree of opening of second expansion valve 72 disposed in injection flow path 70.

By the process as described above, controller 100 controls the degree of opening of second expansion valve 72 such that the degree of dryness X_LEV,in of the refrigerant flowing into first expansion valve 30 from first flow path 81 of third heat exchanger 80 does not increase above the target degree of dryness X_tgt.

In this case, it is necessary to perform convergence calculation in order to calculate inlet portion pressure P_LEV,in at first expansion valve 30 in step S4 in FIG. 5, which will be described below to some extent.

FIG. 6 is a diagram for illustrating symbols of various parameters of first expansion valve 30. First expansion valve 30 includes a stator coil 31 and a rotor 32 of a pulse motor, a screw 33, and a needle 34. When rotor 32 rotates, the amount of needle 34 inserted into an orifice 35 by screw 33 is changed. Thereby, the degree of opening of expansion valve 30 can be changed.

As shown in FIG. 6, P_LEV,in, h_LEV,in, and ρ_LEV,in represent the refrigerant pressure, the enthalpy, and the refrigerant density, respectively, at the inlet portion of first expansion valve 30. Further, Cv_main[mm²] represents the Cv value of expansion valve 30, Gr_s[kg/h] represents the refrigerant circulation amount at the suction port of compressor 10, h_LEV,in[kJ/kg] represents the enthalpy of the refrigerant at the inlet of expansion valve 30, and P_e,in[MPa] represents the pressure of the refrigerant at the inlet of expansion valve 30.

FIG. 7 is a diagram for illustrating a process of deriving the inlet portion pressure of first expansion valve 30.

First, in step S11, controller 100 sets an assumed value P_LEV,in1 of the inlet portion pressure of first expansion valve 30. In step S12, controller 100 calculates a refrigerant density ρ_LEV,in at the inlet portion of expansion valve 30 by applying assumed value P_LEV,in1 to the following equation (8).

$\begin{array}{cc}{\rho }_{\mathrm{LEV},\mathrm{in}}=f\left(P_{\mathrm{LEV},\mathrm{in}},h_{\mathrm{LEV},\mathrm{in}}\right)& \left(8\right)\end{array}$

Further, in step S13, controller 100 calculates a refrigerant pressure P_LEV,in2 at the inlet portion of expansion valve 30 by the following equation (9).

$\begin{array}{cc}{P}_{\mathrm{LEV},\mathrm{in}2}=f\left(G\mathrm{rs},P_{e,\mathrm{in}},{\mathrm{Cv}}_{\mathrm{main}},{\rho }_{\mathrm{LEV},\mathrm{in}}\right)& \left(9\right)\end{array}$

Then, in step S14, controller 100 compares assumed value P_LEV,in1 with the calculated refrigerant pressure P_LEV,in2, and determines whether or not these values are equal to each other. Note that P_LEV,in1=P_LEV,in2 represented in step S14 means whether or not the convergence condition is satisfied, and the convergence condition includes a condition that the error between the two values to be compared falls within a certain value.

When the convergence condition is not satisfied (NO in S14), the process returns to step S11, and the assumed value is reset. The assumed value may be reset by using Newton's Method, a binary method, or the like, each of which is generally used for convergence calculation.

(b) Non-Azeotropic Refrigerant Having Temperature Gradient

In contrast to the above-described case in which refrigerant having no temperature gradient is used, in the case of non-azeotropic refrigerant having a temperature gradient, the number of sensors can be reduced, and the degree of dryness X_LEV,in of the refrigerant can be calculated in a simplified process.

FIG. 8 is a diagram showing an arrangement of various sensors when non-azeotropic refrigerant is used. When FIG. 8 is compared with FIG. 3, FIG. 8 is the same as FIG. 3 in that refrigeration cycle apparatus 1 includes pressure sensors 110 and 116 except that, in FIG. 8, temperature sensor 111 and pressure sensor 118 are additionally provided but temperature sensors 112, 114, 115, 117, and flow rate sensor 113 are not provided.

FIG. 9 is a p-h diagram showing a change in the state of refrigerant when non-azeotropic refrigerant is used. When FIG. 9 is compared with FIG. 4, in FIG. 9, an isothermal line TL is not parallel to the horizontal axis in a two-phase region, and thus, condensing steps A to C show a temperature change. When the degree of dryness X increases, a point C shifts in the direction approaching a point A, so that a temperature T_LEV,in also rises. Therefore, it is understood that, when non-azeotropic refrigerant exhibiting a temperature gradient in the two-phase region is used, the degree of dryness X_LEV,in can be calculated from pressure P_LEV,in and temperature T_LEV,in also in the two-phase region.

FIG. 10 is a flowchart for illustrating control of second expansion valve 72 when non-azeotropic refrigerant is used.

First, in step S21, controller 100 calculates the degree of dryness X_LEV,in of the refrigerant at the inlet portion of expansion valve 30 by the following equation (10).

$\begin{array}{cc}{X}_{\mathrm{LEV},\mathrm{in}}=f_{\mathrm{XLEV},\mathrm{in}}\left(P_{\mathrm{LEV},\mathrm{in}},T_{\mathrm{LEV},\mathrm{in}}\right)& \left(10\right)\end{array}$

Then, in step S22, controller 100 calculates the target degree of dryness X_tgt of the refrigerant at the inlet portion of expansion valve 30 by the following equation (11).

$\begin{array}{cc}{X}_{\mathrm{tgt}}=f_{\mathrm{Xtgt}}\left(P_d,P_s,F_{\mathrm{comp}}\right)& \left(11\right)\end{array}$

Then, controller 100 changes the degree of opening of second expansion valve 72 such that X_LEV,in becomes equal to X_tgt. Specifically, in step S23, controller 100 compares the target degree of dryness X_tgt with the calculated current degree of dryness X_LEV,in. When the degree of dryness X_LEV,in is equal to or less than the target degree of dryness X_tgt(YES in S23), then in step S24, controller 100 decreases the degree of opening of second expansion valve 72 disposed in injection flow path 70. On the other hand, when the degree of dryness X_LEV,in is not equal to or less than the target degree of dryness X_tgt(NO in S23), then in step S25, controller 100 increases the degree of opening of second expansion valve 72 disposed in injection flow path 70.

By repeatedly performing the process in FIG. 10, the degree of opening of second expansion valve 72 is controlled such that the degree of dryness X_LEV,in becomes equal to the target degree of dryness X_tgt.

<Comparison with Study Example>

The following describes a study of comparison between a refrigeration cycle apparatus designed mainly for heating as a study example and the refrigeration cycle apparatus according to the first embodiment.

In particular, the refrigeration cycle apparatus according to the present embodiment is suitably used in a heat pump machine mainly for heating, such as a water heater or a circulation-type warmer.

In a heat pump machine mainly for heating, such as a water heater or a circulation-type warmer, the amount of refrigerant required during a heating operation is generally enclosed, and the amount of refrigerant becomes insufficient during a cooling operation. This is because, during the cooling operation, an air heat exchanger larger in volume than a load-side heat exchanger serves as a condenser (high pressure), and thus, the amount of refrigerant required to fill the outlet of the condenser with liquid refrigerant increases.

In recent years, low GWP refrigerant has been increasingly used due to regulations for refrigerant, but such refrigerant is less available in market and higher in unit cost than conventional refrigerant (R410A, R32, and the like). This causes a concern that a larger amount of refrigerant may lead to a higher prime cost of each device. Therefore, the amount of refrigerant enclosed in a heat pumping machine also tends to be reduced. Although natural refrigerant such as propane (R290) is used due to regulations for refrigerant, such natural refrigerant is flammable refrigerant, and thus, the maximum amount of such natural refrigerant to be enclosed may be limited from the viewpoint of safety.

At this time, when the refrigerant becomes insufficient during the cooling operation or the defrosting operation, the refrigerant at the inlet of the expansion valve becomes two-phase refrigerant and the refrigerant density decreases, which consequently decreases the pressure on the low pressure side due to insufficient degree of opening of the expansion valve. When the low pressure decreases, freezing occurs in the load-side heat exchanger, and when the load-side heat exchanger is damaged, there is a possibility that refrigerant may leak due to rupture.

When the refrigeration cycle apparatus is designed mainly for a heating operation, the refrigerant and the heat medium (air, water, refrigerant, and the like) are arranged to flow as counterflows to each other in the heat exchanger during a heating operation for the purpose of ensuring the performance during the heating operation. Thus, during the cooling operation and the defrosting operation, the flow direction of the refrigerant in the heat exchanger is reversed and a parallel flow occurs, so that the performance decreases.

On the other hand, according to the refrigeration cycle apparatus of the first embodiment as described above, the following effects are achieved.

In any of the heating operation, the cooling operation, and the defrosting operation, each refrigerant flowing into a respective one of three heat exchangers can be caused to flow in the same direction as a counterflow, and therefore, the performance is expected to be improved as compared with the conventional refrigeration cycle apparatus in which a parallel flow mixedly exists.

In any of the heating operation, the cooling operation, and the defrosting operation, the internal heat exchange using third heat exchanger 80 and second expansion valve 72 disposed in injection flow path 70 can be used for the refrigerant at the outlet portion of the condenser, and therefore, the performance of the refrigeration cycle apparatus is expected to be improved by injection of the refrigerant.

Further, since the degree of dryness X_LEV,in of the refrigerant on the inlet side of first expansion valve 30 can be decreased, the refrigerant density at the inlet of first expansion valve 30 increases, so that the pressure decrease of the refrigerant suctioned into compressor 10 can be suppressed.

Further, suppressing a pressure decrease in the low pressure portion can avoid freezing in the load-side heat exchanger.

<Various Modifications of Flow Path Switching Device>

In the following second to fifth embodiments, various modifications of the flow path switching device will be described.

Second Embodiment

FIG. 11 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to the second embodiment. Flow path switching device 50 in a refrigeration cycle apparatus 201 shown in FIG. 11 includes a six-way valve 51A and a four-way valve 52.

Six-way valve 51A includes ports PB2 and PC2 in addition to ports PA to PD. Ports PA to PD are connected to the respective pipes of the refrigerant circuit as in FIG. 1. Ports PB2 and PC2 are connected by a pipe outside six-way valve 51A.

By the connection as described above, six-way valve 51A can be used for switching the connection similarly to four-way valve 51 shown in FIG. 1. In recent years, a six-way valve has become produced, and if a six-way valve can be used in place of a four-way valve, it may be convenient, for example, in terms of inventory adjustment for raw materials.

Since four-way valve 52 and other connection portions in refrigeration cycle apparatus 201 shown in FIG. 11 have the same configurations as those in refrigeration cycle apparatus 1 shown in FIG. 1, the description thereof will not be repeated.

In the first operation mode (cooling), six-way valve 51A is configured to connect the discharge port of compressor 10 to refrigerant inlet 21 of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40. At this time, a flow path is formed inside six-way valve 51A such that port PA communicates with port PB, port PC communicates with port PD, and port PB2 communicates with port PC2.

In the first operation mode (cooling), four-way valve 52 is configured to connect refrigerant outlet 22 of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10.

FIG. 12 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the second embodiment.

In the second operation mode (heating), six-way valve 51A is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to refrigerant inlet 21 of first heat exchanger 20. At this time, a flow path is formed inside six-way valve 51A such that port PA communicates with port PD, port PB communicates with port PB2, and port PC2 communicates with port PC. As a result, port PB communicates with port PC through an external pipe.

In the second operation mode (heating), four-way valve 52 is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect refrigerant outlet 22 of first heat exchanger 20 to the suction port of compressor 10.

According to refrigeration cycle apparatus 201 of the second embodiment configured as described above, the same effect as that in the first embodiment can be achieved.

Third Embodiment

FIG. 13 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to the third embodiment. Flow path switching device 50 of a refrigeration cycle apparatus 202 shown in FIG. 13 includes a four-way valve 51 and a six-way valve 52A.

Six-way valve 52A includes ports PG2 and PH2 in addition to ports PE to PH. Ports PE to PH are connected to the respective pipes of the refrigerant circuit as in FIG. 1. Ports PG2 and PH2 are connected by a pipe outside six-way valve 52A.

By the connection as described above, six-way valve 52A can be used for switching the connection similarly to four-way valve 52 shown in FIG. 1.

In the first operation mode (cooling), the four-way valve is configured to connect the discharge port of compressor 10 to refrigerant inlet 21 of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40.

In the first operation mode (cooling), six-way valve 52A is configured to connect refrigerant outlet 22 of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10. At this time, a flow path is formed inside six-way valve 52A such that port PE communicates with port PF, port PG communicates with port PG2, and port PH2 communicates with port PH. As a result, ports PG and PH communicate with each other through an external pipe.

FIG. 14 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the third embodiment.

In the second operation mode (heating), four-way valve 51 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to refrigerant inlet 21 of first heat exchanger 20.

In the second operation mode (heating), six-way valve 52A is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect refrigerant outlet 22 of first heat exchanger 20 to the suction port of compressor 10. At this time, a flow path is formed inside six-way valve 52A such that port PG communicates with port PF, port PE communicates with port PH, and port PG2 communicates with port PH2.

According to refrigeration cycle apparatus 202 of the third embodiment configured as described above, the same effect as that in the first and second embodiments can also be achieved.

Fourth Embodiment

FIG. 15 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to the fourth embodiment. Flow path switching device 50 in a refrigeration cycle apparatus 203 shown in FIG. 15 includes a first six-way valve 51A and a second six-way valve 52A. Since first six-way valve 51A is connected in the same way as that in the second embodiment and second six-way valve 52A is connected in the same way as that in the third embodiment, the description thereof will not be repeated.

In the first operation mode (cooling), first six-way valve 51A is configured to connect the discharge port of compressor 10 to refrigerant inlet 21 of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40.

In the first operation mode (cooling), second six-way valve 52A is configured to connect refrigerant outlet 22 of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10.

FIG. 16 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the fourth embodiment.

In the second operation mode (heating), first six-way valve 51A is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to refrigerant inlet 21 of first heat exchanger 20.

In the second operation mode (heating), second six-way valve 52A is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect refrigerant outlet 22 of first heat exchanger 20 to the suction port of compressor 10.

According to refrigeration cycle apparatus 203 of the fourth embodiment configured as described above, the same effect as that in the first to third embodiments can also be achieved.

Fifth Embodiment

Flow path switching device 50 in a refrigeration cycle apparatus 204 according to the fifth embodiment includes an eight-way valve 50B.

FIG. 17 is a diagram showing a refrigerant circuit and a flow of refrigerant during a cooling operation of a refrigeration cycle apparatus according to the fifth embodiment. FIG. 18 is a diagram showing the state of eight-way valve 50B and the flow of the refrigerant in eight-way valve 50B during the cooling operation according to the fifth embodiment.

As shown in FIG. 18, eight-way valve 50B includes a cylindrical valve main body 308. Ports PA and PE are formed on one side in the circumferential direction of valve main body 308 while ports PB, PC, PD, PF, PG, and PH are formed on the other side thereof.

Since ports PA to PH are connected to the same destinations as those in FIG. 1, the description thereof will not be repeated. A piston 312 formed by connecting three pressure receiving slide members 310A, 310B, and 310C to a connecting rod 311 is provided inside valve main body 308 of eight-way valve 50B. Slide valve bodies 313A and 313B are fixed to connecting rod 311.

As piston 312 moves, slide valve body 313A slides on a valve seat provided with ports PB, PC, and PD, and slide valve body 313B slides on a valve seat provided with ports PF, PG, and PH.

Piston 312 provides partitions between a first chamber R1, a second chamber R2, a third chamber R3, and a fourth chamber R4. Eight-way valve 50B further includes a pilot solenoid valve 514 for switching the slide valve body. Pilot solenoid valve 514 includes a valve body 516 coupled to a plunger 515, a solenoid coil 517, and a coil spring 518.

When the refrigeration cycle apparatus is started while solenoid coil 517 of pilot solenoid valve 514 is energized, plunger 515 is suctioned so that valve body 516 is moved to thereby: cause a low-pressure communication pipe 519 reaching a suction pipe of compressor 10 to communicate with a conduit 522 for fourth chamber R4; and cause a high-pressure introduction pipe 521 to communicate with a conduit 520 for first chamber R1. When compressor 10 is started in this state, high pressure is introduced into first chamber R1, and piston 312 and slide valve bodies 313A and 313B are moved toward fourth chamber R4 and fixed as shown in FIG. 18.

Slide valve body 313A is provided with two communication inner cavities through which two ports adjacent in phase between ports PB, PC, and PD communicate with each other. In the state in FIG. 18, the communication inner cavities allow communication between ports PC and PD, and port PA communicates with port PB through second chamber R2.

Slide valve body 313B is provided with two communication inner cavities through which two ports adjacent in phase between ports PF, PG, and PH communicate with each other. In the state in FIG. 18, the communication inner cavities allow communication between ports PG and PH, and port PE communicates with port PF through third chamber R3.

In this way, eight-way valve 50B is arranged at the cooling operation position in which refrigerant circulates through the path indicated by a solid line in FIG. 17.

FIG. 19 is a diagram showing the refrigerant circuit and the flow of the refrigerant during a heating operation of the refrigeration cycle apparatus according to the fifth embodiment. FIG. 20 is a diagram showing the state of eight-way valve 50B and the flow of the refrigerant in eight-way valve 50B during the heating operation according to the fifth embodiment.

Valve body 516 biased by coil spring 518 when solenoid coil 517 is not energized causes low-pressure communication pipe 519 to communicate with conduit 520 for first chamber R1 and causes high-pressure introduction pipe 521 to communicate with conduit 522 for fourth chamber R4. Thus, high pressure is introduced into fourth chamber R4, so that piston 312 and slide valve bodies 313A and 313B move toward first chamber R1.

In the state in FIG. 20, the communication inner cavities of slide valve body 313A allow communication between ports PB and PC, and port PA communicates with port PD through second chamber R2.

Similarly, in the state in FIG. 20, the communication inner cavities of slide valve body 313B allow communication between ports PF and PG, and port PE communicates with port PH through third chamber R3.

In this way, eight-way valve 50B is arranged at the heating operation position in which refrigerant circulates through the path indicated by a solid line in FIG. 19.

By using the eight-way valve as described above, in the refrigeration cycle apparatus according to the fifth embodiment, the same effect as that in the first to fourth embodiments can be achieved, and the number of components and the number of ports used in a substrate can be reduced.

Summary

The following summarizes the first to fifth embodiments again with reference to the accompanying drawings.

A refrigeration cycle apparatus 1 shown in FIG. 1 includes a compressor 10, a first heat exchanger 20, a second heat exchanger 40, a third heat exchanger 80, a first expansion valve 30, a second expansion valve 72, and a flow path switching device 50.

Compressor 10, first heat exchanger 20, second heat exchanger 40, and first expansion valve 30 constitute a refrigerant circuit 90 through which refrigerant circulates. Second expansion valve 72 forms a portion of injection flow path 70, injection flow path 70 being configured to reduce pressure of the refrigerant before passing through first expansion valve 30 in refrigerant circuit 90 and return the refrigerant to compressor 10.

Third heat exchanger 80 includes a first flow path 81 through which the refrigerant flows, and a second flow path 82 through which the refrigerant flows. Third heat exchanger 80 is configured to exchange heat between the refrigerant passing through first flow path 81 and the refrigerant passing through second flow path 82. First flow path 81 is disposed in refrigerant circuit 90 to cause the refrigerant to flow toward first expansion valve 30. Second flow path 82 is disposed to return, to compressor 10, the refrigerant that has passed through second expansion valve 72.

In a first operation mode (cooling), flow path switching device 50 is configured to connect a discharge port of compressor 10 to a refrigerant inlet of first heat exchanger 20, connect a refrigerant outlet of first heat exchanger 20 to a refrigerant inlet of first flow path 81, connect a refrigerant outlet of first expansion valve 30 to a refrigerant inlet of second heat exchanger 40, and connect a refrigerant outlet of second heat exchanger 40 to a suction port of compressor 10.

In a second operation mode (heating), flow path switching device 50 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40, connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81, connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of first heat exchanger 20, and connect the refrigerant outlet of first heat exchanger 20 to the suction port of compressor 10.

Preferably, in any of the first operation mode and the second operation mode, the refrigerant flows in the same direction in each of first heat exchanger 20, second heat exchanger 40, third heat exchanger 80, first expansion valve 30, and second expansion valve 72.

Preferably, first heat exchanger 20, second heat exchanger 40, and third heat exchanger 80 are configured to perform heat exchange in a relation in which a heat medium that exchanges heat flows as a counterflow in any of the first operation mode and the second operation mode. In this case, the heat medium that exchanges heat with the refrigerant is air in first heat exchanger 20, water or brine in second heat exchanger 40, and refrigerant in third heat exchanger 80.

Preferably, as shown in FIGS. 1 and 2, flow path switching device 50 includes a first four-way valve 51 and a second four-way valve 52. In the first operation mode (cooling), first four-way valve 51 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40, and in the second operation mode (heating), first four-way valve 51 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of first heat exchanger 20. In the first operation mode (cooling), second four-way valve 52 is configured to connect the refrigerant outlet of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10, and in the second operation mode (heating), second four-way valve 52 is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of first heat exchanger 20 to the suction port of compressor 10.

Preferably, as shown in FIGS. 11 and 12, flow path switching device 50 includes a six-way valve 51A and a four-way valve 52. In the first operation mode (cooling), six-way valve 51A is configured to connect the discharge port of compressor 10 to the refrigerant inlet of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40, and in the second operation mode (heating), six-way valve 51A is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of first heat exchanger 20. In the first operation mode (cooling), four-way valve 52 is configured to connect the refrigerant outlet of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10, and in the second operation mode (heating), four-way valve 52 is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of first heat exchanger 20 to the suction port of compressor 10.

Preferably, as shown in FIGS. 13 and 14, flow path switching device 50 includes a four-way valve 51 and a six-way valve 52A. In the first operation mode (cooling), four-way valve 51 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40, and in the second operation mode (heating), four-way valve 51 is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of first heat exchanger 20. In the first operation mode (cooling), six-way valve 52A is configured to connect the refrigerant outlet of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10, and in the second operation mode (heating), six-way valve 52A is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of first heat exchanger 20 to the suction port of compressor 10.

Preferably, as shown in FIGS. 15 and 16, the flow path switching device includes a first six-way valve 51A and a second six-way valve 52A. In the first operation mode (cooling), first six-way valve 51A is configured to connect the discharge port of compressor 10 to the refrigerant inlet of first heat exchanger 20 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of second heat exchanger 40, and in the second operation mode (heating), first six-way valve 51A is configured to connect the discharge port of compressor 10 to the refrigerant inlet of second heat exchanger 40 and connect the refrigerant outlet of first expansion valve 30 to the refrigerant inlet of first heat exchanger 20. In the first operation mode (cooling), second six-way valve 52A is configured to connect the refrigerant outlet of first heat exchanger 20 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of second heat exchanger 40 to the suction port of compressor 10, and in the second operation mode (heating), second six-way valve 52A is configured to connect the refrigerant outlet of second heat exchanger 40 to the refrigerant inlet of first flow path 81 and connect the refrigerant outlet of first heat exchanger 20 to the suction port of compressor 10.

Preferably, as shown in FIGS. 17 to 20, flow path switching device 50 includes an eight-way valve 50B.

Preferably, as shown in FIGS. 5 and 7, the refrigeration cycle apparatus further includes a controller 100 configured to control first expansion valve 30 and second expansion valve 72. Controller 100 is configured to control a degree of opening of second expansion valve 72 such that a degree of dryness of refrigerant flowing into first expansion valve 30 from first flow path 81 of third heat exchanger 80 does not increase above a target degree of dryness.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims, rather than the description of the embodiments set forth above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.

Claims

1. A refrigeration cycle apparatus comprising: a compressor; a first heat exchanger; a second heat exchanger; a third heat exchanger; a first expansion valve; a second expansion valve; and a flow path switching device, wherein the compressor, the first heat exchanger, the second heat exchanger, and the first expansion valve constitute a refrigerant circuit through which refrigerant circulates,the second expansion valve forms a portion of an injection flow path, the injection flow path being configured to reduce pressure of the refrigerant before passing through the first expansion valve in the refrigerant circuit and return the refrigerant to the compressor,the third heat exchanger comprises a first flow path through which the refrigerant flows and a second flow path through which the refrigerant flows, and the third heat exchanger is configured to exchange heat between the refrigerant passing through the first flow path and the refrigerant passing through the second flow path,the first flow path is disposed in the refrigerant circuit to cause the refrigerant to flow toward the first expansion valve,the second flow path is disposed to return, to the compressor, the refrigerant that has passed through the second expansion valve,in a first operation mode, the flow path switching device is configured to connect a discharge port of the compressor to a refrigerant inlet of the first heat exchanger,connect a refrigerant outlet of the first heat exchanger to a refrigerant inlet of the first flow path,connect a refrigerant outlet of the first expansion valve to a refrigerant inlet of the second heat exchanger, andconnect a refrigerant outlet of the second heat exchanger to a suction port of the compressor,in a second operation mode, the flow path switching device is configured to connect the discharge port of the compressor to the refrigerant inlet of the second heat exchanger,connect the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path,connect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger, andconnect the refrigerant outlet of the first heat exchanger to the suction port of the compressor andin any of the first operation mode and the second operation mode, the refrigerant flows in a same direction in each of the first heat exchanger, the second heat exchanger, the third heat exchanger, the first expansion valve, and the second expansion valve.

2. (canceled)

3. The refrigeration cycle apparatus according to claim 1, wherein the first heat exchanger, the second heat exchanger, and the third heat exchanger are configured to perform heat exchange in a relation in which a heat medium that exchanges heat flows as a counterflow.

4. The refrigeration cycle apparatus according to claim 1, wherein the flow path switching device comprises a first four-way valve and a second four-way valve,in the first operation mode, the first four-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the first heat exchanger,connect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the second heat exchanger,in the second operation mode, the first four-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the second heat exchanger, and connect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger,in the first operation mode, the second four-way valve is configured to connect the refrigerant outlet of the first heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the second heat exchanger to the suction port of the compressor, andin the second operation mode, the second four-way valve is configured to connect the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the first heat exchanger to the suction port of the compressor.

5. The refrigeration cycle apparatus according to claim 1, wherein the flow path switching device comprises a six-way valve and a four-way valve,in the first operation mode, the six-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the first heat exchanger, andconnect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the second heat exchanger,in the second operation mode, the six-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the second heat exchanger, andconnect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger,in the first operation mode, the four-way valve is configured to connect the refrigerant outlet of the first heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the second heat exchanger to the suction port of the compressor, andin the second operation mode, the four-way valve is configured to connect the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the first heat exchanger to the suction port of the compressor.

6. The refrigeration cycle apparatus according to claim 1, wherein the flow path switching device comprises a six-way valve and a four-way valve,in the first operation mode, the four-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the first heat exchanger, andconnect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the second heat exchanger,in the second operation mode, the four-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the second heat exchanger, andconnect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger,in the first operation mode, the six-way valve is configured to connect the refrigerant outlet of the first heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the second heat exchanger to the suction port of the compressor, andin the second operation mode, the six-way valve is configured to connect the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path, and connect the refrigerant outlet of the first heat exchanger to the suction port of the compressor.

7. The refrigeration cycle apparatus according to claim 1, wherein the flow path switching device comprises a first six-way valve and a second six-way valve,in the first operation mode, the first six-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the first heat exchanger, andconnect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the second heat exchanger,in the second operation mode, the first six-way valve is configured to connect the discharge port of the compressor to the refrigerant inlet of the second heat exchanger, andconnect the refrigerant outlet of the first expansion valve to the refrigerant inlet of the first heat exchanger,in the first operation mode, the second six-way valve is configured to connect the refrigerant outlet of the first heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the second heat exchanger to the suction port of the compressor, andin the second operation mode, the second six-way valve is configured to connect the refrigerant outlet of the second heat exchanger to the refrigerant inlet of the first flow path, andconnect the refrigerant outlet of the first heat exchanger to the suction port of the compressor.

8. The refrigeration cycle apparatus according to claim 1, wherein the flow path switching device comprises an eight-way valve.

9. The refrigeration cycle apparatus according to claim 1, further comprising a controller configured to control the first expansion valve and the second expansion valve, wherein the controller is configured to control a degree of opening of the second expansion valve such that a degree of dryness of the refrigerant flowing into the first expansion valve from the first flow path of the third heat exchanger does not increase above a target degree of dryness.