EP4692677A1

EP4692677A1 - Refrigeration cycle device

Info

Publication number: EP4692677A1
Application number: EP24780243.2A
Authority: EP
Inventors: Hirotoshi Takeuchi; Yoshinari MAEMA; Kazuki KANEI; Kosuke Takahashi; Haruki IRITANI
Original assignee: Fujitsu General Ltd
Current assignee: Fujitsu General Ltd
Priority date: 2023-03-31
Filing date: 2024-03-26
Publication date: 2026-02-11
Also published as: JP2024145985A; WO2024204129A1; JP7601133B2

Abstract

In a refrigeration cycle apparatus, in a low-stage refrigerant circuit, a first refrigerant circulates. In a high-stage refrigerant circuit, a second refrigerant that is heat-exchanged with the first refrigerant in a cascade heat exchanger circulates. A water circuit includes a second indoor heat exchanger and a water-refrigerant heat exchanger, and water that is heat-exchanged with the second refrigerant in the water-refrigerant heat exchanger circulates therein. A heat dissipating device is connected to at least one of the high-stage refrigerant circuit and the water circuit, and is connected though the bypass flow path so as to bypass the second refrigerant or the water. The control device switches, during the heating operation by the indoor unit of the second indoor heat exchanger, to the first heating operation in which the second refrigerant or the water is flowed to only the bypass flow path, or to the second heating operation in which the second refrigerant or the water is flowed to both the heat dissipating device and the bypass flow path, and determines a rotation speed of the second compressor based on required capacities of the indoor unit of the second indoor heat exchanger and the heat dissipating device.

Description

Field

Embodiments of the present invention relates to a refrigeration cycle apparatus.

Background

Conventionally, there has been a refrigeration cycle apparatus having a low-stage refrigerant circuit in which a first refrigerant circulates, and a high-stage refrigerant circuit connected to the low-stage refrigerant circuit, in which a second refrigerant circulates to exchange heat with the first refrigerant, thereby forming a two-stage refrigeration cycle (Patent Literature 1).
In this refrigeration cycle apparatus, a hot water generation unit and an indoor unit are connected in parallel to an outdoor unit, thereby forming the low-stage refrigerant circuit. Moreover, the high-stage refrigerant circuit is forming in the hot water generation unit, a water circuit through which water circulates connects to the high-stage refrigerant circuit. In the hot water generation unit, hot water is generated by exchanging heat with the second refrigerant. This enables the refrigeration cycle apparatus to air-condition a living space of a user with an indoor unit connected to the low-stage refrigerant circuit, while enabling hot water supply using hot water generated by the hot water generation unit and air-conditioning using the indoor unit that utilizes the hot water.

Citation List

Patent Literature

Patent Literature 1: Japanese Laid-open Patent Publication No. 2018-179352

Summary

Technical Problem

However, in the conventional technique described above, when the temperature of hot water to be generated by the hot water generation unit is low and the thermal load on the hot water generation unit is small, a compression ratio in a compressor of the high-stage refrigerant circuit tends to decrease. As a result, there is a problem in that the reliability of the compressor in the high-stage refrigerant circuit deteriorates due to the occurrence of a so-called vane jumping phenomenon, in which the vane fails to follow the movement of the roller in the compressor. If the rotation speed of the compressor in the high-stage refrigerant circuit is increased to raise the compression ratio in order to avoid deterioration of reliability, the second refrigerant overheats the water, resulting in a loss of user comfort.
The present invention has been made in view of the above issues, and aims to provide a refrigeration cycle apparatus with high reliability.

Solution to Problem

According to an aspect of an embodiment, a refrigeration cycle apparatus includes a low-stage refrigerant circuit that includes an outdoor heat exchanger, a first compressor, a cascade heat exchanger, a first pressure-reducing unit, and a first indoor heat exchanger, and through which a first refrigerant circulates, a high-stage refrigerant circuit that includes a second compressor, a water-refrigerant heat exchanger, a second pressure-reducing unit, and the cascade heat exchanger, and through which a second refrigerant heat-exchanged with the first refrigerant in the cascade heat exchanger circulates, a water circuit that includes a circulation pump, a second indoor heat exchanger and the water-refrigerant heat exchanger, and through which water heat-exchanged with the second refrigerant in the water-refrigerant heat exchanger circulates, a heat dissipating device that is connected to at least one of the high-stage refrigerant circuit and the water circuit, to release heat of any one of the second refrigerant and the water, a bypass flow path that bypasses any one of the second refrigerant and the water without passing through the heat dissipating device, a flow path switching valve that switches flow paths of any one of the second refrigerant and the water flowing through the heat dissipating device and the bypass flow path, and a control device that is configured to control the first compressor, the first pressure-reducing unit, the second compressor, the second pressure-reducing unit, the circulation pump, and the flow path switching valve, wherein the control device switches, during heating operation by an indoor unit of the second indoor heat exchanger, to any one of first heating operation in which any one of the second refrigerant and the water is flowed to only the bypass flow path out of the heat dissipating device and the bypass flow path and second heating operation in which any one of the second refrigerant and the water is flowed to both the heat dissipating device and the bypass flow path, and determines a rotation speed of the second compressor based on a required capacity of the indoor unit of the second indoor heat exchanger and the heat dissipating device in the second heating operation.

Advantageous Effects of Invention

According to one aspect, the reliability of a refrigeration cycle apparatus can be improved.

Brief Description of Drawings

FIG. 1 is an explanatory diagram illustrating an example of a refrigeration cycle apparatus according to an embodiment.
FIG. 2 is a flowchart illustrating a control example of the refrigeration cycle apparatus according to the embodiment.
FIG. 3 is a timing chart illustrating an example of operation of the refrigeration cycle apparatus according to the embodiment.
FIG. 4 is a p-h diagram illustrating a refrigeration cycle of the refrigeration cycle apparatus according to the embodiment.
FIG. 5 is an explanatory diagram explaining a first modification of the refrigeration cycle apparatus according to the embodiment.
FIG. 6 is a flowchart illustrating a control example of the first modification of the refrigeration cycle apparatus according to the embodiment.
FIG. 7 is an explanatory diagram explaining a second modification of the refrigeration cycle apparatus according to the embodiment.
FIG. 8 is a flowchart illustrating a control example of the second modification of the refrigeration cycle apparatus according to the embodiment.

Description of Embodiments

Hereinafter, a refrigeration cycle apparatus according to an embodiment will be explained with reference to the drawings. In the embodiment, identical reference symbols are assigned to components having an identical function, and duplicate explanation will be omitted. It is noted that the refrigeration cycle apparatus described in the following embodiments is merely an example and is not intended to limit the scope of the embodiments. Furthermore, the respective embodiments described below may be appropriately combined within a range not causing contradiction.
FIG. 1 is an explanatory diagram illustrating an example of a refrigeration cycle apparatus 1 according to the embodiment. As illustrated in FIG. 1, the refrigeration cycle apparatus 1 includes a low-stage refrigerant circuit 10, a high-stage refrigerant circuit 20, a water circuit 30, a heat storage device 33, a first flow path control valve 34a, a second flow path control valve 34b, a third flow path control valve 34c that serve as flow path switching valves, and a control device 50.
The low-stage refrigerant circuit 10 includes an outdoor heat exchanger 11, a low-stage compressor 12, a cascade heat exchanger 13, expansion valves 14a and 14b (first pressure-reducing unit), an indoor heat exchanger 15 (first indoor heat exchanger), switching valves 16a and 16b, and a four-way valve 17, and a refrigerant (first refrigerant) circulates therein.
The outdoor heat exchanger 11 exchanges heat between outdoor air and the refrigerant circulating in the low-stage refrigerant circuit 10 in an outdoor unit 11a installed outdoors.
The low-stage compressor 12 is a compressor that can vary operating capacity according to, for example, drive of a motor not illustrated, the rotation speed of which is controlled by an inverter under the control of the control device 50. The low-stage compressor 12 is one example of a first compressor that compresses the refrigerant circulating in the low-stage refrigerant circuit 10 by being driven at a rotation speed controlled by the control device 50.
The cascade heat exchanger 13 performs heat exchange between the refrigerant circulating in the low-stage refrigerant circuit 10 and a refrigerant (second refrigerant) that circulates in the high-stage refrigerant circuit 20.
The expansion valves 14a and 14b are electronic expansion valves that are driven by a pulse motor not illustrated under the control of the control device 50. The expansion valves 14a and 14b adjust a flow rate of the refrigerant that flows into the cascade heat exchanger 13 and the indoor heat exchanger 15 as its opening degree is adjusted according to the number of pulses given by the pulse motor.
The indoor heat exchanger 15 performs heat exchange between indoor air in a room and the refrigerant circulating in the low-stage refrigerant circuit 10 in a low-stage indoor unit 15a installed in a room.
The switching valves 16a and 16b are valves to switch between open and closed manually. The switching valves 16a and 16b are to switch between allowing and stopping flow of the refrigerant to the indoor heat exchanger 15, and are used when flowing the refrigerant to the indoor heat exchanger 15 after the low-stage indoor unit 15a is installed in a room, or when stopping the flow of the refrigerant into the indoor heat exchanger 15 when the low-stage indoor unit 15a is to be removed.
The four-way valve 17 is a valve to switch directions in which the refrigerant flows in the low-stage refrigerant circuit 10 under the control of the control device 50. Specifically, the four-way valve 17 switches the flow of the refrigerant such that the indoor heat exchanger 15 serves as an evaporator and the outdoor heat exchanger 11 serves as a condenser during cooling operation, and the indoor heat exchanger 15 serves as a condenser and the outdoor heat exchanger 11 serves as an evaporator during heating operation.
The high-stage refrigerant circuit 20 includes a high-stage compressor 21, a water-refrigerant heat exchanger 22, an expansion valve 23 (second pressure-reducing unit), and a cascade heat exchanger 13, and the refrigerant (second refrigerant) circulates that is heat-exchanged with the refrigerant (first refrigerant) circulating in the low-stage refrigerant circuit 10 in the cascade heat exchanger 13.
The high-stage compressor 21 is a compressor that can vary operating capacity according to, for example, drive of a motor not illustrated, the rotation speed of which is controlled by an inverter under control of the control device 50. The high-stage compressor 21 is one example of a second compressor that compresses the refrigerant circulating in the high-stage refrigerant circuit 20 by being driven at a rotation speed controlled by the control device 50.
The water-refrigerant heat exchanger 22 performs heat exchange between the refrigerant circulating in the high-stage refrigerant circuit 20 and water circulating in the water circuit 30.
The expansion valve 23 is an electronic expansion valve that is driven by a pulse motor not illustrated under the control of the control device 50. The expansion valve 23 adjusts a flow rate of the refrigerant that flows into the cascade heat exchanger 13 as its opening degree is adjusted according to the number of pulses given by the pulse motor.
The water circuit 30 includes a circulation pump 31, an indoor heat exchanger 32 (second indoor heat exchanger), a heat storage device 33, the first to third flow path control valves 34a to 34c, and a bypass flow path 40, and water that is heat-exchanged with the refrigerant (second refrigerant) circulating in the high-stage refrigerant circuit 20 in the water-refrigerant heat exchanger 22 circulates.
The circulation pump 31 is a pump that can vary operating capacity according to, for example, drive of a motor not illustrated, the rotation speed of which is controlled by an inverter under control of the control device 50. The circulation pump 31 can adjust the flow rate of water that circulates the low-stage refrigerant circuit 10 by being driven at a rotation speed controlled by the control device 50.
The indoor heat exchanger 32 performs heat exchange between air in the room and water circulating in the water circuit 30 at a high-stage indoor unit 32a installed in the room.
The heat storage device 33 includes a heat storage material 33a that absorbs and stores heat by exchanging heat with the water circulating in the water circuit 30. That is, the heat storage device 33 releases the heat of the water circulating in the water circuit 30. The heat storage material 33a that has absorbed the heats of the water through heat exchange is heated and stores heat. Moreover, the bypass flow path 40 is connected in parallel with the heat storage device 33. By flowing water circulating in the water circuit 30 into the bypass flow path 40, the water can be circulated without passing through the heat storage device 33.
The first flow path control valve 34a to the third flow path control valve 34c are control valves that can control the opening degree and that is driven by a pulse motor not illustrated under the control of the control device 50. The first flow path control valve 34a to the third flow path control valve 34c can adjust a flow path and a flow rate of the water that flows through the heat storage device 33 and the bypass flow path 40 as its opening degree is adjusted between a valve closed state and an open state according to the number of pulses given by the pulse motor.
The heat storage device 33 may be configured without the heat storage material 33a, but may be configured as a heat dissipating device 22b (refer to FIG. 5) that simply releases the heat of the water. Furthermore, the heat storage device 33 (heat dissipating device 33) may be arranged on the high-stage refrigerant circuit side, and may be configured to be connected so as to bypass the refrigerant of the high-stage refrigerant circuit by the bypass flow path (refer to FIG. 7). That is, the heat storage device 33 (heat dissipating device 33b) may be configured to be connected such that the refrigerant of the high-stage refrigerant circuit 20 or the water in the water circuit 30 can be bypassed through the bypass flow path 40 to at least one of the high-stage refrigerant circuit 20 and the water circuit 30.
The control device 50 includes a control unit 51 that controls the entire refrigeration cycle apparatus 1, a storage unit 52 that stores various kinds of information, and a temperature detecting unit 53 (temperature detecting unit) that detects temperature of respective components in the refrigeration cycle apparatus 1.
The control unit 51 accepts required capacities relate to the low-stage indoor unit 15a, the high-stage indoor unit 32a, the heat storage device 33, and the like during heating or cooling operation. The control unit 51 controls operation of the respective components during the heating or cooling operation according to the accepted required capacity of the low-stage indoor unit 15a, the high-stage indoor unit 32a, the heat storage device 33, and the like. The required capacity of the low-stage indoor unit 15a is a value based on a difference between temperature set for the low-stage indoor unit 15a by a user and the room temperature. Moreover, the required capacity of the high-stage indoor unit 32a is, for example, a value based on a difference between temperature set for the high-stage indoor unit 32a by the user and the room temperature. Furthermore, the required capacity of the heat storage device 33 may be a surplus capacity calculated by subtracting the required capacity of the high-stage indoor unit 32a from a threshold A (details will be described later).
For example, the control unit 51 determines the rotation speed of the low-stage compressor 12 according to a total of all of the required capacities of the low-stage indoor unit 15a, the high-stage indoor unit 32a, and the heat storage device 33, and drives the low-stage compressor 12 with the determined rotation speed. Moreover, the control unit 51 determines the rotation speed of the high-stage compressor 21 according to a total of the required capacities of the high-stage indoor unit 32a and the heat storage device 33, and drives the high-stage compressor 21 with the determined rotation speed. Furthermore, the control unit 51 adjusts the flow rate of the refrigerant such that the refrigerant flowing through the indoor heat exchanger 15 and the cascade heat exchanger 13 can perform heat exchange efficiently, by adjusting the opening degree of the expansion valves 14a, 14b. Specifically, the control unit 51 adjusts the expansion valve 14a based on the temperature of the refrigerant in the indoor heat exchanger 15 detected by the temperature detecting unit 53, and adjusts the expansion valve 14b based on the temperature of the refrigerant in the cascade heat exchanger 13 detected by the temperature detecting unit 53. For example, the control unit 51 adjusts the expansion valves 14a, 14b such that a degree of subcooling of the refrigerant flowing out of the indoor heat exchanger 15 and the cascade heat exchanger 13 during heating operation and a degree of superheating of the refrigerant flowing out of the indoor heat exchanger 15 and the cascade heat exchanger 13 during cooling operation become a target value set in advance. Moreover, the control unit 51 may adjust the opening degree of the second flow path control valve 34b and the third flow path control valve 34c based on a ratio between the required capacity of the high-stage indoor unit 32a and the required capacity of the heat storage device 33 during second heating operation described later, to adjust a ratio the water flowing through the heat storage device 33 and the bypass flow path 40.
Furthermore, the control unit 51 switches, during heating operation by the high-stage indoor unit 32a of the indoor heat exchanger 32, to heating operation (first and third heating operation) in which the water of the water circuit 30 is flowed only to the bypass flow path 40 out of the heat storage device 33 and the bypass flow path 40, or to heating operation (second heating operation) in which the water of the water circuit 30 is flowed to both of the heat storage device 33 and the bypass flow path 40. Specifically, the control unit 51 performs switching of the heating operation described above by switching between opening and closing of the first flow path control valve 34a to the third flow path control valve 34c (details will be described later).
In the storage unit 52, a rotation speed table in which rotation speeds of the low-stage compressor 12, the high-stage compressor 21, and the like are defined corresponding to the required capacities of the low-stage indoor unit 15a, the high-stage indoor unit 32a, the heat storage device 33, and the like, for example, during heating or cooling operation is stored in advance. The control unit 51 can determine a rotation speed of the low-stage compressor 12, the high-stage compressor 21, and the like according to the required capacities by referring to the rotation speed table stored in the storage unit 52. Moreover, in the storage unit 52, information relating to various kinds of thresholds used for switching of the control is stored in advance. In the storage unit 52, a target pressure for controlling the low-stage compressor 12 and the high-stage compressor 21 in accordance with the required capacities may be stored in advance. Specifically, a target condensing pressure during heating operation and a target evaporating pressure during cooling operation may be stored. In this case also, because the rotation speed of the low-stage compressor 12 and the high-stage compressor 21 is adjusted according to the target pressure, it can be regarded that the rotation speed of the low-stage compressor 12 and the high-stage compressor 21 is determined based on the required capacities of the low-stage indoor unit 15a, the high-stage indoor unit 32a, the heat storage device 33, and the like.
The temperature detecting unit 53 acquires a detection value of a temperature sensor (not illustrated) arranged at respective components in the refrigeration cycle apparatus 1, to detect temperature of the respective components. For example, the temperature detecting unit 53 detects temperature (first temperature) of the water that flows into the indoor heat exchanger 32 and temperature (second temperature) of the heat storage material 33a. The temperature detecting unit 53 may be a pressure detecting unit that detects pressure at the respective components by acquiring a detection value of a pressure sensor (not illustrated) arranged at the respective components in the refrigeration cycle apparatus 1, or may be a detecting unit that detects both temperature and pressure at the respective components.
FIG. 2 is a flowchart illustrating a control example of the refrigeration cycle apparatus 1 according to the embodiment. Specifically, FIG. 2 is a flowchart illustrating a control example during heating operation by the high-stage indoor unit 32a of the indoor heat exchanger 32, and the low-stage indoor unit 15a may be stopped, but in this control example, it is assumed to be in heating operation. That is, for the low-stage compressor 12, the rotation speed is determined according to the total of all of the required capacities of the low-stage indoor unit 15a, the high-stage indoor unit 32a, the heat storage device 33, and the like, and it is assumed to be driving at the rotation speed.
As illustrated in FIG. 2, when processing is started, the control unit 51 sets the first flow path control valve 34a and the second flow path control valve 34b to CLOSE, and the third flow path control valve 34c to OPEN, to bring it into the heating operation in which the water of the water circuit 30 is flowed only to the bypass flow path 40 (first heating operation). Moreover, the control unit 51 determines a rotation speed of the high-stage compressor 21 according to the total of the required capacities of the high-stage indoor unit 32a and the heat storage device 33, and operates the high-stage compressor 21 at the determined rotation speed (S1).
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the predetermined threshold A (S2). This threshold A is set corresponding to a minimum required capacity to obtain a compressor rotation speed enabling to achieve a sufficient compression ratio to ensure reliability in the high-stage compressor 21. That is, when the required capacity of the high-stage indoor unit 32a is not equal to or lower than the threshold A, by driving the high-stage compressor 21 at the compressor rotation speed according to the required capacity, a compression ratio sufficient to ensure reliability of the high-stage compressor 21 can be obtained. Moreover, when the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A, if the high-stage compressor 21 is driven at the compressor rotation speed according to the required capacity, there is a possibility that a compression ratio sufficient to ensure reliability of the high-stage compressor 21 cannot be obtained.
When the required capacity of the high-stage indoor unit 32a is not equal to or lower than the threshold A (S2: NO), the control unit 51 returns the processing to S1. When the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A (S2: YES), the control unit 51 sets the second flow path control valve 34b and the third flow path control valve 34c to OPEN (S3). Thus, the control unit 51 switches to the heating operation (second heating operation) in which the water in the water circuit 30 is flowed to both the heat storage device 33 and the bypass flow path 40 (S4). The second heating operation is operation in which a load on the high-stage refrigerant circuit 20 is increased by flowing the refrigerant to the heat storage device 33 to obtain the compressor rotation speed that enables to obtain the compression ratio.
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the predetermined threshold A (S5). This is processing similar to S2, but is performed because the processing from S4 to S6 is repeatedly performed as described later and the required capacity may change during that process. When the required capacity of the high-stage indoor unit 32a is not equal to or lower than the threshold A (S5: NO), the control unit 51 returns the processing to S1. Thus, when it is not equal to or lower than the threshold A, it is switched to the first heating operation from the second heating operation.
When the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A (S5: YES), the control unit 51 determines whether a temperature difference between temperature (first temperature) of the water flowing into the indoor heat exchanger 32 and temperature (second temperature) of the heat storage device 33 is equal to or smaller than first predetermined temperature (S6). The first predetermined temperature is set to a sufficiently small value that allows a determination that the first temperature and the second temperature have become close to each other, and is, for example, 2.0 deg. When the temperature difference is not equal to or smaller than the first predetermined temperature (S6: NO), the control unit 51 returns the processing to S4, and continues the second heating operation.
When the temperature difference is equal to or smaller than the first predetermined temperature (S6: YES), it means that the water circulating in the water circuit 30 hardly releases heat to the heat storage material 33a, and that little heat is being stored in the heat storage material 33a. The control unit 51 stops the operation of the high-stage compressor 21, and sets the first flow path control valve 34a to OPEN, and the second flow path control valve 34b and the third flow path control valve 34c to CLOSE (S7). Thus, the control unit 51 allows the water of the water circuit 30 to flow only to the heat storage device 33, and release heat stored in the heat storage device 33 (heating of water by heat release), that is, switches to the heating operation (third heating operation) utilizing heat stored of the heat storage device 33 (S8). The third heating operation is operation in which the high-stage compressor 21 is stopped by releasing heat stored in the heat storage device 33, thereby enabling heating without causing a problem related to the compression ratio of the high-stage compressor 21.
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A (S9). This is the same processing as S2, but it is performed because the processing at S8 to S10 is repeatedly performed as described later and the required capacity may change during that process. When the required capacity of the high-stage indoor unit 32a is not equal to or lower than the threshold A (S9: NO), the control unit 51 returns the processing to S1. Thus, when it is not equal to or lower than the threshold A, it is switched to the first heating operation from the third heating operation.
When the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A (S9: YES), the control unit 51 determines whether a temperature difference between the temperature of the water flowing into the indoor heat exchanger 32 (first temperature) and the temperature of the heat storage device 33 (second temperature) is equal to or larger than the second predetermined temperature based on a detection result of the temperature detecting unit 53 (S10). The second predetermined temperature is set to a sufficiently large value that allows it to be determined that the first temperature and the second temperature have diverged, and is, for example, 5 degrees. When the temperature difference is not equal to or larger than the second predetermined temperature (S10: NO), the control unit 51 returns the processing to S8, and continues the third heating operation. When the temperature difference is equal to or larger than the second predetermined temperature (S10: YES), it means that heat stored in the heat storage material 33a has been used sufficiently. Therefore, the control unit 51 starts the operation of the high-stage compressor 21 (S11), and returns the processing to S1.
FIG. 3 is a timing chart (horizontal axis represents time t0 to t13, period T1: time t0 to t1, period T2: time t1 to t2, ..., period T13: time t12 to t13) illustrating an example of operation of the refrigeration cycle apparatus according to the embodiment. In the timing chart in FIG. 3, sequentially from top, the rotational speed of the low-stage compressor 12, the required capacity of the low-stage indoor unit 15a, the rotational speed of the high-stage compressor 21, the total required capacity of the high-stage indoor unit 32a and the heat storage device 33, the required capacity of the high-stage indoor unit 32a, the temperature of the heat storage device 33, the required capacity of the heat storage device 33, and the open/close states of the first flow path control valve 34a, the second flow path control valve 34b, and the third flow path control valve 34c are indicated on the vertical axis.
As illustrated in FIG. 3, in the first period (T1 to T3), the control unit 51 sets the first flow path control valve 34a and the second flow path control valve 34b to CLOSE, and the third flow path control valve 34c to OPEN, to perform the heating operation (first heating operation) in which the water in the water circuit 30 is flowed only to the bypass flow path 40. In this case, heat of the water circulating in the water circuit 30 is not released in the heat storage device 33, and is released only in the high-stage indoor unit 32a. Thus, in the period (T1 to T3), because the heating in a room is efficiently performed, the required capacity of the high-stage indoor unit 32a decreases.
Subsequently, at time t3, because the required capacity of the high-stage indoor unit 32a becomes lower than the threshold A, that is, because the required capacity becomes lower than the minimum required capacity to obtain the compressor rotation speed enabling to ensure the compression ratio, the control unit 51 sets the second flow path control valve 34b and the third flow path control valve 34c to OPEN. Thus, because the control unit 51 performs the heating operation in which the water of the water circuit 30 is flowed to both the heat storage device 33 and the bypass flow path 40, the load on the high-stage refrigerant circuit 20 increases by the amount of heat of the water circulating in the water circuit 30 released at the heat storage device 33. Therefore, even when the required capacity of the high-stage indoor unit 32a keeps decreasing, the control unit 51 can obtain the compressor rotation speed enabling to ensure the compression ratio, and deterioration in reliability of the high-stage compressor 21 can be suppressed
The control device 50 varies the threshold A based on a pressure state (condensing pressure) of the refrigerant in the low-stage refrigerant circuit 10.
FIG. 4 is a p-h diagram explaining the refrigeration cycle of the refrigeration cycle apparatus 1 according to the embodiment. In FIG. 4, a refrigeration cycle C1 is the refrigeration cycle of the low-stage refrigerant circuit 10, and a graph G1 shows a saturated liquid line and saturated vapor line of the refrigerant in the low-stage refrigerant circuit 10. A refrigeration cycle C1 represents the refrigeration cycle of the low-stage refrigerant circuit 10, and a graph G1 represents a saturation liquid line and a saturation vapor line of the refrigerant of the low-stage refrigerant circuit 10. Similarly, a refrigeration cycle C2 represents the refrigeration cycle of the high-stage refrigerant circuit 20, and a graph G2 represents a saturation liquid line and a saturation vapor line of the refrigerant of the high-stage refrigerant circuit 20. As illustrated in FIG. 4, when a condensing pressure in the refrigeration cycle C1 rises from a dotted line position C1a to a solid line position, an evaporating pressure in the refrigeration cycle C2 also rises from the dotted-line position C2a to the solid-line position. As a result, the compression ratio in the refrigeration cycle C2 becomes small.
Therefore, because the rotation speed necessary for ensuring the compression ratio in the high-stage compressor 21 increases with the rise of the condensing pressure in the refrigeration cycle C1, the value of the threshold A is increased according to the rise of the condensing pressure in the refrigeration cycle C1. The condensing pressure in the refrigeration cycle C1 is acquired, for example, by detecting condensing temperature at the cascade heat exchanger 13 of the refrigerant circulating in the low-stage refrigerant circuit 10, and by converting into a saturation pressure. Alternatively, it may be detected by arranging a pressure sensor between a high pressure section of the low-stage refrigerant circuit 10, that is an outlet of the low-stage compressor 12 and the expansion valve 14a or 14b. The control unit 51 then refers to the table indicating correspondence between a condensing pressure and the threshold A or the like, to acquire the value of the threshold A corresponding to the condensing pressure.
Moreover, the control device 50 may regard the required capacity of the heat storage device 33 as a surplus capacity calculated by subtracting the required capacity of the high-stage indoor unit 32a from the threshold A. In this case, in the refrigeration cycle apparatus 1, a surplus heating capacity resulting from operation at the rotational speed to ensure the compression ratio can be stored in the heat storage device 33, and it is possible to avoid operation causing a low compression ratio in the high-stage compressor 21 without wasting power.
Returning back to FIG. 3, in the period T4 to T8, by continuing the heating operation in which the water of the water circuit 30 is flowed to both the heat storage device 33 and the bypass flow path 40, the temperature of the heat storage device 33 increases. Thus, the temperature of the heat storage device 33 increases until a temperature difference between the temperature of the water flowing into the indoor heat exchanger 32 (first temperature) and the temperature of the heat storage device 33 (second temperature) becomes equal to or lower than a predetermined threshold (time t8).
When the temperature difference between the first temperature and the second temperature becomes equal to or smaller than a predetermined threshold, the control unit 51 stops the operation of the high-stage compressor 21 and sets the first flow path control valve 34a to OPEN, and the second flow path control valve 34b and the third flow path control valve 34c to CLOSE, thereby switching to the heating operation utilizing the heat of the heat storage device 33. At this time, the control unit 51 replaces the required capacity of the high-stage indoor unit 32a with 0. That is, when determining the rotation speed according to the total of all of the required capacities of the low-stage compressor 12, the low-stage indoor unit 15a, the high-stage indoor unit 32a, and the heat storage device 33, the control unit 51 sets the required capacity of the high-stage indoor unit 32a to 0. During the heating operation utilizing the heat of the heat storage device 33, the high-stage indoor unit 32a performs heating utilizing the heat stored in the heat storage device 33, and the high-stage compressor 21 is stopped. Therefore, it is not necessary to determine the rotation speed of the low-stage compressor 12 based on the high-stage refrigerant circuit 20. Therefore, by replacing the required capacity of the high-stage indoor unit 32a with 0 as described above, the control unit 51 can determined the rotation speed of the low-stage compressor 12 only based on the required capacity of the low-stage indoor unit 15a. Thus, the control unit 51 can set the rotation speed of the low-stage compressor 12 to a speed appropriate for the heating operation utilizing the heat of the heat storage device 33, and highly reliable operation can be achieved in the entire two-stage refrigeration cycle.
Subsequently, when the temperature difference between the temperature of the water flowing into the indoor heat exchanger 32 (first temperature) and the temperature of the heat storage device 33 (second temperature) becomes equal to or larger than the predetermined threshold (time t12), the control unit 51 starts operation of the high-stage compressor 21, and switches to the heating operation in which the first flow path control valve 34a is CLOSE, and the second flow path control valve 34b and the third flow path control valve 34c are OPEN.
FIG. 5 is an explanatory diagram explaining a first modification of the refrigeration cycle apparatus 1 according to the embodiment. As illustrated in FIG. 5, the heat storage device 33 may be replaced with the heat dissipating device 33b in a water circuit 30a.
FIG. 6 is a flowchart illustrating a control example of the first modification of the refrigeration cycle apparatus 1 according to the embodiment. As illustrated in FIG. 6, when processing is started, the control unit 51 sets the first flow path control valve 34a and the second flow path control valve 34b to CLOSE, and the third flow path control valve 34c to OPEN, to start the heating operation in which the water of the water circuit 30a is flowed only to the bypass flow path 40 (first heating operation). Moreover, the control unit 51 determines the rotation speed of the high-stage compressor 21 according to the total required capacity of the high-stage indoor unit 32a and the heat dissipating device 33b, and drives the high-stage compressor 21 at the determined rotation speed (S21).
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A (S22). When it is not equal to or lower than the threshold A (S22: NO), the control unit 51 returns the processing to S21. When it is equal to or lower than the threshold A (S22: YES), the control unit 51 sets the second flow path control valve 34b and the third flow path control valve 34c to OPEN (S23). Thus, the control unit 51 switches to the heating operation (second heating operation) in which the water of the water circuit 30a is flowed to both the heat dissipating device 33b and the bypass flow path 40 (S24).
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the predetermined threshold A (S25). When it is not equal to or lower than the threshold A (S25: NO), the control unit 51 returns the processing to S21. Thus, when it is not equal tor lower than the threshold A, it is switched from the second heating operation to the first heating operation. When it is equal to or lower than the threshold A (S25: YES), the control unit 51 returns the processing to S24, and continues the second heating operation.
FIG. 7 is an explanatory diagram explaining a second modification of the refrigeration cycle apparatus 1 according to the embodiment. As illustrated in FIG. 7, the heat dissipating device 33b may be arranged in a high-stage refrigerant circuit 20a, and may be configured to be connected so as to bypass the refrigerant of the high-stage refrigerant circuit 20a by a bypass flow path 40a.
A first flow path control valve 35a to a third flow path control valve 35c are control valves that can control the opening degree and that is driven by a pulse motor not illustrated under the control of the control device 50. The first flow path control valve 35a to the third flow path control valve 35c can adjust a flow rate of the refrigerant that flows through the heat dissipating device 33b and the bypass flow path 40 as its opening degree is adjusted between a valve closed state and an open state according to the number of pulses given by the pulse motor.
FIG. 8 is a flowchart illustrating a control example of a second modification of the refrigeration cycle apparatus 1 according to the embodiment. As illustrated in FIG. 8, when the processing is started, the control unit 51 sets the first flow path control valve 35a and the second flow path control valve 35b to CLOSE, and the third path flow control valve 35c to OPEN, to switch to the heating operation (first heating operation) in which the refrigerant of the high-stage refrigerant circuit 20a is flowed only to the bypass flow path 40a. Moreover, the control unit 51 determines the rotation speed of the high-stage compressor 21 according to the total required capacity of the high-stage indoor unit 32a and the heat dissipating device 33b, and drives the high-stage compressor 21 at the determined rotation speed (S31).
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the predetermined threshold A (S32). When it is not equal to or lower than the threshold A (S32: NO), the control unit 51 returns the processing to S31. When it is equal to or lower than the threshold A (S32: YES), the control unit 51 sets the second flow path control valve 35b and the third flow path control valve 35c to OPEN (S33). Thus, the control unit 51 switches to the heating operation in which the refrigerant of the high-stage refrigerant circuit 20a is flowed to both the heat dissipating device 33b and the bypass flow path 40 (second heating operation (S34). In the second heating operation, the control unit 51 may adjust the opening degree of the second flow path control valve 35b and the third flow path control valve 35c based on the ratio between the required capacity of the high-stage indoor unit 32a and the required capacity of the heat dissipating device 33b, and may adjust the ratio of the refrigerant flowing though the heat dissipating device 33b and the bypass flow path 40a.
Subsequently, the control unit 51 determines whether the required capacity of the high-stage indoor unit 32a is equal to or lower than the threshold A (S35). When it is not equal to or lower than the threshold A (S35: NO), the control unit 51 returns the processing to S31. Thus, when it is not equal to or lower than the threshold A, it is switched from the second heating operation to the first heating operation. When it is equal to or lower than the threshold A (S35: YES), the control unit 51 returns the processing to S34, and continues the second heating operation.
As described above, the refrigeration cycle apparatus 1 includes the low-stage refrigerant circuit 10, the high-stage refrigerant circuit 20, the water circuit 30, the heat dissipating device (the heat storage device 33, the heat dissipating device 33b), the bypass flow path, the control valves (34a, 34b, 34c, 35a, 35b, 35c), and the control device 50. The low-stage refrigerant circuit 10 includes the outdoor heat exchanger 11, the low-stage compressor 12, the cascade heat exchanger 13, the expansion valves 14a, 14b, and the indoor heat exchanger 15, and the first refrigerant circulated therethrough. The high-stage refrigerant circuit 20 includes the high-stage compressor 21, the water-refrigerant heat exchanger 22, the expansion valve 23, and the cascade heat exchanger 13, and the second refrigerant that is heat-exchanged with the first refrigerant in the cascade heat exchanger 13 circulates therethrough. The water circuit 30 includes the circulation pump 31, the indoor heat exchanger 32, and the water-refrigerant heat exchanger 22, and water that is heat-exchanged with the second refrigerant in the water-refrigerant heat exchanger 22 circulates therethrough. The heat dissipating device is connected to at least one of the high-stage refrigerant circuit 20 and the water circuit 30, and heat of the second refrigerant or the water is released. The bypass flow path bypasses heat of the second refrigerant or the water without passing through the heat dissipating device. The control valve adjusts a flow rate of the second refrigerant or the water flowing through the heat dissipating device and the bypass flow path 40. The control device 50 controls the low-stage compressor 12, the expansion valves 14a, 14b, the high-stage compressor 21, the expansion valve 23, the circulation pump 31, and the control valve. During the heating operation by the high-stage indoor unit 32a of the indoor heat exchanger 32, the control device 50 switches between the first heating operation in which the second refrigerant or the water is flowed only to the bypass flow path 40 and the second heating operation in which the second refrigerant or the water is flowed to both the heat dissipating device and the bypass flow path 40. In the second heating operation, the control device 50 determines the rotation speed of the high-stage compressor 21 based on the required capacity of the high-stage indoor unit 32a and the heat dissipating device.
Thus, in the refrigeration cycle apparatus 1, because a load on the high-stage refrigerant circuit 20 increases by an amount of heat dissipation by the heat dissipating device during the second heating operation, even it is possible to prevent the capacity of the high-stage indoor unit 32a from becoming excessive even if the high-stage compressor 21 is operated at the rotation speed enabling to ensure the compression ratio, and it is possible to prevent deterioration in reliability of the high-stage compressor 21 without losing user comfort.
Furthermore, the heat dissipating device is the heat storage device 33 including the heat storage material 33a that exchanges heat with the second refrigerant or water to release heat. During the heating operation by the high-stage indoor unit 32a of the indoor heat exchanger 32, the control device 50 further switches to the third heating operation in which the second refrigerant or the water is flowed only to the heat storage device 33 out of the heat storage device 33 and the bypass flow path 40. Thus, in the refrigeration cycle apparatus 1, the heat stored in the heat storage device 33 can be effectively used, and the compression ratio of the high-stage compressor 21 can be obtained without wasting electric power.
Moreover, the heat storage device 33 is arranged in the water circuit 30, and the control device 50 stops the high-stage compressor 21 in the third heating operation. Thus, in during the third heating operation in which heat stored in the heat storage device 33 is released, because the high-stage compressor 21 is stopped, a problem relating to the compression ratio in the high-stage compressor 21 does not occur, and it is possible to prevent deterioration in reliability of the high-stage compressor 21.
Furthermore, the low-stage refrigerant circuit 10 includes the four-way valve 17 for switching paths through which the first refrigerant circulates between the heating operation and the cooling operation by the low-stage indoor unit 15a of the indoor heat exchanger 15 under the control of the control device 50. During the heating operation by the low-stage indoor unit 15a of the indoor heat exchanger 15 and when the heating operation is the first heating operation by the high-stage indoor unit 32a of the indoor heat exchanger 32, the control device 50 switches from the first heating operation to the second heating operation when the required capacity of the high-stage indoor unit 32a of the indoor heat exchanger 32 becomes lower than a predetermined value. Thus, the refrigeration cycle apparatus 1 can avoid operation causing a low compression ratio in the high-stage compressor 21 by switching to the second heating operation when the high-stage compressor 21 for which the required capacity of the high-stage indoor unit 32a becomes lower than the predetermined value tends to become a low compression ratio.
Moreover, the control device 50 changes the predetermined value described above based on the condensing pressure of the first refrigerant in the low-stage refrigerant circuit 10. Thus, the refrigeration cycle apparatus 1 can appropriately switch to the second heating operation under an operating condition in which the high-stage compressor 21 becomes a low compression ratio due to the condensing pressure of the first refrigerant, and it is possible to avoid operation in which the high-stage compressor 21 becomes a low compression ratio.
Furthermore, the control device 50 adjusts the opening degree of the second flow path control valve 34b and the third flow path control valve 34c based on a ratio between the required capacity of the high-stage indoor unit 32a of the indoor heat exchanger 32 and the required capacity of the heat dissipating device (the heat storage device 33 and the heat dissipating device 33b), and adjusts a ratio of the second refrigerant or the water flowing into the heat dissipating device and the bypass flow path 40 during the second heating operation. Thus, the refrigeration cycle apparatus 1 can circulate the refrigerant or the water at an appropriate balance according to the required capacity.
Furthermore, in the refrigeration cycle apparatus 1, the required capacity of the heat dissipating device 33b is a surplus capacity calculated by subtracting the required capacity of the high-stage indoor unit 32a of the indoor heat exchanger 32 from the predetermined value described above. Thus, the refrigeration cycle apparatus 1 can store the excessive heating capacity in the high-stage indoor unit 32a in the heat storage device 33, and can avoid operation in which the high-stage compressor 21 becomes a low compression ratio without wasting electric power.
Moreover, the refrigeration cycle apparatus 1 further includes the temperature detecting unit 53 that detects the first temperature of the water flowing into the indoor heat exchanger 32 and the second temperature of the heat storage device 33. The control device 50 switches to the third heating operation when a temperature difference between the first temperature and the second temperature becomes smaller than a predetermined temperature during second heating operation. Thus, in the refrigeration cycle apparatus 1, excessive heating of the water can be suppressed by preventing release of heat to the heat storage material 33a.
Furthermore, the control device 50 determines the rotation speed of the low-stage compressor 12 based on a total of the required capacity of the low-stage indoor unit 15a of the indoor heat exchanger 15, the required capacity of the high-stage indoor unit 32a of the indoor heat exchanger 32, and the required capacity of the heat dissipating device 33b. Moreover, during the third heating operation, the rotation speed of the low-stage compressor 12 is determined, replacing the required capacity of the high-stage indoor unit 32a of the indoor heat exchanger 32 with 0. Thus, the refrigeration cycle apparatus 1 can set the rotation speed of the low-stage compressor 12 to an appropriate speed suitable for the second heating operation, and highly reliable operation can be performed in the entire two-stage refrigeration cycle.

Reference Signs List

1 REFRIGERATION CYCLE APPARATUS
10 LOW-STAGE REFRIGERANT CIRCUIT
11 INDOOR HEAT EXCHANGER
11a OUTDOOR UNIT
12 LOW-STAGE COMPRESSOR
13 CASCADE HEAT EXCHANGER
14a, 14b, 23 EXPANSION VALVE
15 INDOOR HEAT EXCHANGER
15a LOW-STAGE INDOOR UNIT
16a, 16b CONTROL VALVE
17 FOUR-WAY VALVE
20, 20a HIGH-STAGE REFRIGERANT CIRCUIT
21 HIGH-STAGE COMPRESSOR
22 WATER-REFRIGERANT HEAT EXCHANGER
30, 30a, 30b WATER CIRCUIT
31 CIRCULATION PUMP
32 INDOOR HEAT EXCHANGER
32a HIGH-STAGE INDOOR UNIT
33 HEAT STORAGE DEVICE
33a HEAT STORAGE MATERIAL
33b HEAT DISSIPATING DEVICE
34a, 35a FIRST FLOW PATH CONTROL VALVE
34b, 35b SECOND FLOW PATH CONTROL VALVE
34c, 35c THIRD FLOW PATH CONTROL VALVE
40, 40a BYPASS FLOW PATH
50 CONTROL DEVICE
51 CONTROL UNIT
52 STORAGE UNIT
53 TEMPERATURE DETECTING UNIT
A THRESHOLD
C1, C2 REFRIGERATION CYCLE
G1, G2 GRAPH
t0 to t13 TIME
T1 to T13 PERIOD

Claims

A refrigeration cycle apparatus comprising:
a low-stage refrigerant circuit that includes an outdoor heat exchanger, a first compressor, a cascade heat exchanger, a first pressure-reducing unit, and a first indoor heat exchanger, and through which a first refrigerant circulates;

a high-stage refrigerant circuit that includes a second compressor, a water-refrigerant heat exchanger, a second pressure-reducing unit, and the cascade heat exchanger, and through which a second refrigerant heat-exchanged with the first refrigerant in the cascade heat exchanger circulates;

a water circuit that includes a circulation pump, a second indoor heat exchanger and the water-refrigerant heat exchanger, and through which water heat-exchanged with the second refrigerant in the water-refrigerant heat exchanger circulates;

a heat dissipating device that is connected to at least one of the high-stage refrigerant circuit and the water circuit, to release heat of any one of the second refrigerant and the water;

a bypass flow path that bypasses any one of the second refrigerant and the water without passing through the heat dissipating device;

a flow path switching valve that switches flow paths of any one of the second refrigerant and the water flowing through the heat dissipating device and the bypass flow path; and

a control device that is configured to control the first compressor, the first pressure-reducing unit, the second compressor, the second pressure-reducing unit, the circulation pump, and the flow path switching valve, wherein

the control device switches, during heating operation by an indoor unit of the second indoor heat exchanger, to any one of first heating operation in which any one of the second refrigerant and the water is flowed to only the bypass flow path out of the heat dissipating device and the bypass flow path and second heating operation in which any one of the second refrigerant and the water is flowed to both the heat dissipating device and the bypass flow path, and determines a rotation speed of the second compressor based on a required capacity of the indoor unit of the second indoor heat exchanger and the heat dissipating device in the second heating operation.
The refrigeration cycle apparatus according to claim 1, wherein
the heat dissipating device is a heat storage device that includes a heat storage material absorbing and storing heat by performing heat exchange with any one of the second refrigerant and the water, and

the control device further switches, during heating operation by the indoor unit of the second indoor heat exchanger, to third heating operation in which any one of the second refrigerant and the water is flowed to only the heat storage device out of the heat storage device and the bypass flow path to release heat stored in the heat storage device, thereby heating any one of the second refrigerant and the water.
The refrigeration cycle apparatus according to claim 2, wherein
the heat storage device is arranged in the water circuit, and

the control device stops the second compressor in the third heating operation.
The refrigeration cycle apparatus according to claim 1, wherein
the low-stage refrigerant circuit includes a switching valve that switches paths through which the first refrigerant circulates between heating operation and cooling operation by an indoor unit of the first indoor heat exchanger under control of the control device, and

the control device switches, during heating operation by the indoor unit of the first indoor heat exchanger and when the heating operation of the indoor unit of the second indoor heat exchanger is the first heating operation, from the first heating operation to the second heating operation when a required capacity of the indoor unit of the second indoor heat exchanger becomes lower than a predetermined value.
The refrigeration cycle apparatus according to claim 4, wherein
the control device changes the predetermined value based on a condensing pressure of the first refrigerant in the low-stage refrigerant circuit.
The refrigeration cycle apparatus according to claim 1, wherein
the flow path switching valve is a control valve that can adjust a flow rate of any one of the second refrigerant and the water flowing through the heat dissipating device and the bypass flow path,

the control device adjusts, in the second heating operation, an opening degree of the control valve based on a ratio between a required capacity of the indoor unit of the second indoor heat exchanger and a required capacity of the heat dissipating device, and adjusts a ratio of any one of the second refrigerant and the water flowing into the heat dissipating device and the bypass flow path.
The refrigeration cycle apparatus according to claim 4, wherein
the required capacity of the heat dissipating device is a surplus capacity calculated by subtracting the required capacity of the indoor unit of the second indoor heat exchanger from the predetermined value.
The refrigeration cycle apparatus according to claim 2, further comprising
a temperature detecting unit that detects first temperature of the water that flows into the second indoor heat exchanger and second temperature of the heat storage device, wherein

the control device switches, during the second heating operation, to the third heating operation when a temperature difference between the first temperature and the second temperature becomes smaller than a predetermined temperature difference.
The refrigeration cycle apparatus according to claim 2, wherein
the control device determines a rotation speed of the first compressor based on a total of the required capacity of an indoor unit of the first indoor heat exchanger, the required capacity of the indoor unit of the second indoor heat exchanger and the required capacity of the heat dissipating device, and

the rotation speed of the first compressor is determined by replacing the required capacity of the indoor unit of the second indoor heat exchanger with 0 in the third heating operation.