Two-stage refrigeration cycle device and method for controlling two-stage refrigeration cycle device

Abstract

The purpose of the present invention is to maintain heat storage capacity without impairing comfort by sufficiently ensuring the amount of refrigerant in a refrigeration cycle circuit during operation when using a refrigeration cycle circuit that uses a multi-stage refrigeration circuit and that has a heat storage device, and to suppress a decline in heating capacity, when using a refrigeration cycle circuit that uses a multi-stage refrigeration circuit and that has a heat storage device. The present invention is provided with: a high-stage-side refrigerant circuit (1) through which a high-stage-side refrigerant circulates; a low-stage-side refrigerant circuit (2) through which a low-stage-side refrigerant circulates; a high-stage-side heat storage circuit (3) having a heat storage heat exchanger (H) provided in parallel with a stepped heat exchanger (C) through which a high-stage-side refrigerant circulates; a low-stage-side heat storage circuit (4) having a heat storage heat exchanger (H) through which a low-stage-side refrigerant circulates; a refrigerant temperature detection unit (5) that measures or calculates the saturation temperature of the low-stage-side refrigerant discharged from the low-stage-side compressor (21); a heat storage temperature sensor (HS) that measures the temperature of the heat storage material; and a control unit (6) that acquires information on the saturation temperature and information on the temperature of the heat storage material during the heating operation, and that controls the low-stage-side compressor (21) such that the temperature difference between the saturation temperature and the temperature of the heat storage material reaches a first prescribed value.

Description

Technical Field

[0001] Embodiments of the present invention relate to a two-stage refrigeration cycle device and a control method for the two-stage refrigeration cycle device. Background Art

[0002] In recent years, in order to reduce CO2 emissions, studies have been conducted to replace conventional combustion-type warm water air conditioners with heat pumps, for example. A heat pump is generally composed of an indoor unit installed indoors and an outdoor unit installed outdoors, and a refrigerant such as water circulates in a refrigeration circuit formed by connecting the indoor unit and the outdoor unit, thereby adjusting the indoor temperature and humidity.

[0003] When replacing a combustion-type hot water air conditioner with a heat pump, it can be expected that "discharging hot water at high temperature" and "ensuring comfort during defrosting operation" will become issues. That is, regarding the former, the temperature of the hot water discharged from the heat pump tends to be lower than that of the combustion-type hot water air conditioner. Therefore, in order to obtain a heating capacity equivalent to that of the combustion-type hot water air conditioner, a structure is required for the heat pump to increase the temperature of the hot water discharged.

[0004] When a heat pump is used, as a method of ensuring a higher temperature of discharged hot water, for example, a heat pump system disclosed in Patent Document 1 below is proposed, in which a low-pressure cycle and a high-pressure cycle are connected using a stepped condenser.

[0005] The stepped condenser functions as a condenser in the low-stage cycle and as an evaporator in the high-stage cycle. Moreover, by combining the refrigeration cycles in multiple stages, the COP can be improved compared to a case of a refrigeration cycle with only one stage, so that high-temperature hot water can be discharged more efficiently.

[0006] On the other hand, regarding the latter defrosting operation, when the air conditioner is generally in heating operation, a low-temperature refrigerant flows in the outdoor heat exchanger. Furthermore, in the case of absorbing heat from the outside air, the refrigerant needs to be cooler than the outside air. However, for example, in the case of a state where the outside air temperature is less than or equal to the freezing point, if it is lower than the dew point temperature of the outside air, frost adheres to the outdoor heat exchanger and it is difficult to exchange heat with the outside air. Therefore, in the case of heating operation, it is necessary to perform the defrosting operation regularly.

[0007] Thus, the defrosting operation is a necessary operation when the air conditioner is in operation, and the heating operation is stopped during the defrosting operation. The defrosting operation itself is an unnecessary operation for the combustion type warm water air conditioner. On this basis, during the defrosting operation, the heating operation is stopped, and the indoor temperature gradually decreases, which may impair comfort.

[0008] Therefore, Patent Document 2 below discloses an invention that can prevent a decrease in indoor temperature due to a temporary stop of the heating operation by continuing the heating operation during the defrosting operation, thereby maintaining comfort.

[0009] In the invention disclosed in Patent Document 2, a heat storage device is arranged in the refrigeration circuit separately from the indoor heat exchanger. In addition, during the defrosting operation, the heat stored in the heat storage device is utilized to avoid stopping the heating operation itself.

[0010] Patent Document 1: Japanese Patent Application Publication No. 2013-113534

[0011] Patent Document 2: International Publication No. 2015 / 128980 Summary of the invention

[0012] According to the above-mentioned Patent Documents 1 and 2, it is conceivable that, for example, a refrigeration cycle circuit using a multi-stage refrigeration circuit and having a heat storage device can be used. With such a circuit, high-temperature hot water can be discharged to supply air that is hotter than the indoor temperature, and even when a defrosting operation is performed, there is no need to stop the heating operation. Therefore, it is conceivable that an air conditioner can be provided that does not impair comfort.

[0013] However, when a refrigeration circuit using a multi-stage refrigeration circuit and having a heat storage device is used, the following problem may occur. That is, in the case of the multi-stage refrigeration circuit shown in Patent Document 1, in order to improve COP, the operation is performed in a manner that the pressure difference on the high-stage side and the pressure difference on the low-stage side are appropriate.

[0014] Furthermore, in the case of such a refrigeration circuit, in the case of having a heat storage device disclosed in Patent Document 2, refrigerant of the same temperature, that is, high-temperature refrigerant, is supplied to the stepped condenser and the heat storage device. In the heat storage device, the refrigerant in the gas phase flowing from the compressor is condensed by heat exchange, but at this time, if the temperature of the heat storage device is lower than the temperature of the refrigerant, the amount of the refrigerant in the liquid phase accumulated in the heat storage device increases to some extent.

[0015] The refrigerant in the gas phase condenses in the heat storage device and changes to the liquid phase. A portion of the refrigerant in the liquid phase flows into the expansion valve, but the rest of the refrigerant accumulates in the heat storage device. The lower the temperature of the heat storage device is relative to the temperature of the refrigerant, the more the refrigerant is supercooled in the heat storage device, and the more the amount of refrigerant accumulated in the heat storage device increases. If this state is achieved, the amount of refrigerant circulating in the refrigeration circuit will gradually decrease, and the amount of refrigerant to be transported to the step condenser will decrease. Therefore, the heat exchange capacity between the high-side cycle and the low-side cycle of the step condenser decreases, and as a result, the capacity of the heat pump decreases.

[0016] The object of the present invention is to provide a two-stage refrigeration cycle device and a control method for the two-stage refrigeration cycle device. Even if a refrigeration cycle circuit using such a multi-stage refrigeration circuit and having a heat storage device is used and a heating operation structure is maintained during defrosting operation by discharging high-temperature hot water and maintaining defrosting operation in the heat storage device, the refrigerant amount in the operating refrigeration cycle circuit can be fully ensured, the decrease in heating capacity can be suppressed, and comfort will not be impaired.

[0017] A two-stage refrigeration cycle device according to one embodiment of the present invention is characterized in that it has: a high-stage refrigerant circuit, which uses refrigerant piping to connect the high-stage compressor, the high-stage heat exchanger, the first high-stage pressure reducing mechanism and the stepped heat exchanger in sequence for circulation of the high-stage refrigerant; a low-stage refrigerant circuit, which uses refrigerant piping to connect the low-stage compressor, the stepped heat exchanger, the first low-stage pressure reducing mechanism and the low-stage heat exchanger in sequence for circulation of the low-stage refrigerant; a high-stage heat storage circuit, which uses refrigerant piping to connect the high-stage compressor, the high-stage heat exchanger, the second high-stage pressure reducing mechanism and a heat storage heat exchanger which is arranged in parallel with the stepped heat exchanger and has a heat storage material in sequence for circulation of the high-stage refrigerant; a low-stage heat storage circuit, which uses refrigerant piping to connect the low-stage compressor, the high-stage heat exchanger, the second high-stage pressure reducing mechanism and the heat storage heat exchanger which is arranged in parallel with the stepped heat exchanger and has a heat storage material in sequence for circulation of the high-stage refrigerant A heat exchanger, a second low-stage side pressure reducing mechanism and a low-stage side heat exchanger are connected for circulation of low-stage side refrigerant; a refrigerant temperature detecting unit, which measures or calculates the saturation temperature of the low-stage side refrigerant discharged from the low-stage side compressor; a heat storage temperature sensor, which measures the temperature of the heat storage material arranged in the heat storage heat exchanger; and a control unit, which controls the high-stage side compressor, the low-stage side compressor, the first high-stage side pressure reducing mechanism, the second high-stage side pressure reducing mechanism, the first low-stage side pressure reducing mechanism and the second low-stage side pressure reducing mechanism respectively, the high-stage side refrigerant and the low-stage side refrigerant perform heat exchange in the stepped heat exchanger or the heat storage heat exchanger, and the control unit obtains the saturation temperature and the temperature of the heat storage material when performing heating operation, and controls the low-stage side compressor in such a way that the temperature difference between the saturation temperature and the temperature of the heat storage material reaches a first specified value.

[0018] In addition, regarding a control method for a two-stage refrigeration cycle device involved in one embodiment of the present invention, the two-stage refrigeration cycle device has: a high-stage refrigerant circuit, which uses refrigerant piping to connect the high-stage compressor, the high-stage heat exchanger, the first high-stage pressure reducing mechanism and the stepped heat exchanger in sequence for circulation of the high-stage refrigerant; a low-stage refrigerant circuit, which uses refrigerant piping to connect the low-stage compressor, the stepped heat exchanger, the first low-stage pressure reducing mechanism and the low-stage heat exchanger in sequence for circulation of the low-stage refrigerant; a high-stage heat storage circuit, which uses refrigerant piping to connect the high-stage compressor, the high-stage heat exchanger, the second high-stage pressure reducing mechanism and a heat storage heat exchanger arranged in parallel with the stepped heat exchanger and having a heat storage material in sequence for circulation of the high-stage refrigerant; a low-stage heat storage circuit, It utilizes refrigerant piping to sequentially connect a low-stage compressor, a heat storage heat exchanger, a second low-stage pressure reducing mechanism, and a low-stage heat exchanger for circulation of the low-stage refrigerant; a refrigerant temperature detection unit, which measures or calculates the saturation temperature of the low-stage refrigerant discharged from the low-stage compressor; a heat storage temperature sensor, which measures the temperature of the heat storage material provided in the heat storage heat exchanger; and a control unit, which controls the high-stage compressor, the low-stage compressor, the first high-stage pressure reducing mechanism, the second high-stage pressure reducing mechanism, the first low-stage pressure reducing mechanism, and the second low-stage pressure reducing mechanism, respectively. When performing heating operation, the control unit has the following steps: obtaining the saturation temperature and the temperature of the heat storage material; and controlling the low-stage compressor in such a way that the temperature difference between the saturation temperature and the temperature of the heat storage material reaches a first specified value.

[0019] Effects of the Invention

[0020] According to the present invention, even if a refrigeration cycle circuit using a multi-stage refrigeration circuit and a heat storage device is used to discharge high-temperature hot water and maintain a defrosting operation in the heat storage device during the heating operation, the refrigerant amount in the operating refrigeration cycle circuit can be fully ensured and the decrease in heating capacity can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a refrigerant circuit diagram of a two-stage refrigeration cycle device according to an embodiment of the present invention.

[0022] Figure 2 This is an explanatory diagram showing the concept of a method of controlling the heating / heat storage operation of the control unit of the two-stage refrigeration cycle device according to the embodiment of the present invention.

[0023] Figure 3 This is a refrigerant circuit diagram showing the flow of the refrigerant when the two-stage refrigeration cycle device according to the embodiment of the present invention performs a heating / heat storage operation.

[0024] Figure 4This is a refrigerant circuit diagram showing the flow of the refrigerant when the two-stage refrigeration cycle device according to the embodiment of the present invention performs a defrosting operation.

[0025] Figure 5 This is a flowchart showing a control flow when the two-stage refrigeration cycle device according to the embodiment of the present invention performs a heating / defrosting operation.

[0026] Figure 6 This is a flowchart showing a control flow when the two-stage refrigeration cycle device according to the embodiment of the present invention performs a heating / heat storage operation.

[0027] Figure 7 This is a flowchart showing a control flow during a defrosting operation in the two-stage refrigeration cycle device according to the embodiment of the present invention. DETAILED DESCRIPTION

[0028] Reference Figure 1 The structure of the two-stage refrigeration cycle apparatus S according to the embodiment of the present invention will be described. Figure 1 1 is a refrigerant circuit diagram of a two-stage refrigeration cycle device S according to an embodiment of the present invention. The two-stage refrigeration cycle device S is used for cooling operation when the high-stage side heat exchanger 12 described later is used as an evaporator. Furthermore, when the high-stage side heat exchanger 12 is used as a condenser, it is a refrigeration cycle device that can be used for operation of generating warm water or heating operation.

[0029] In addition, below, the operation of generating warm water and the operation of supplying warm air to the indoor space are sometimes collectively expressed as "heating operation". Moreover, in the embodiment of the present invention, the case where the two-stage refrigeration cycle device S is used for heating operation, the heat storage operation of storing heat in the heat storage heat exchanger H described later, and the defrosting operation for the low-stage side heat exchanger 23 are described.

[0030] Figure 1 The two-stage refrigeration cycle apparatus S according to the embodiment of the present invention shown in the figure has a two-stage refrigeration cycle having refrigerant circuits provided for the high-stage side and the low-stage side. A high-stage refrigerant circuit 1 is provided on the high-stage side, and a low-stage refrigerant circuit 2 is provided on the low-stage side.

[0031] The high-stage refrigerant circuit 1 connects the high-stage compressor 11, the high-stage heat exchanger 12, the first high-stage pressure reducing mechanism 13 and the stepped heat exchanger C in sequence by means of the refrigerant piping P, and circulates the high-stage refrigerant. The high-stage heat exchanger 12 is arranged inside the indoor unit installed in the indoor space, and performs heat exchange between the high-stage refrigerant and the water circulating in the water circuit not shown in the figure to generate warm water. Alternatively, heat exchange is performed between the high-stage refrigerant and the air flowing into the indoor unit, and heated air is supplied to the indoor space. In addition, a room temperature sensor for measuring the room temperature of the indoor space is provided in the indoor unit.

[0032] On the other hand, the low-stage refrigerant circuit 2 connects the low-stage compressor 21, the stepped heat exchanger C, the first low-stage pressure reducing mechanism 22 and the low-stage heat exchanger 23 in sequence by the refrigerant piping P, and circulates the low-stage refrigerant. In the low-stage heat exchanger 23, heat exchange is performed between the low-stage refrigerant and the outside air.

[0033] Here, the stepped heat exchanger C is a heat exchanger that exchanges heat between the high-pressure refrigerant and the low-pressure refrigerant. For example, when the two-stage refrigeration cycle device S performs a heating operation, the stepped heat exchanger C functions as an evaporator for the high-pressure refrigerant.

[0034] In addition, in the two-stage refrigeration cycle apparatus S according to the embodiment of the present invention, the high-stage heat storage circuit 3 and the low-stage heat storage circuit 4 are provided on the high-stage side and the low-stage side, respectively.

[0035] The high-stage heat storage circuit 3 is formed by connecting the high-stage compressor 11, the high-stage heat exchanger 12, the second high-stage pressure reducing mechanism 31, and the heat storage heat exchanger H in order by the refrigerant piping P, and the high-stage refrigerant circulates. On the other hand, the low-stage heat storage circuit 4 is formed by connecting the low-stage compressor 21, the heat storage heat exchanger H, the second low-stage pressure reducing mechanism 41, and the low-stage heat exchanger 23 in order by the refrigerant piping P, and the low-stage refrigerant circulates.

[0036] The heat storage heat exchanger H is a heat exchanger that performs heat exchange between the heat storage material filled therein and the high-stage refrigerant or the low-stage refrigerant. The heat storage heat exchanger H is provided with a heat storage tank therein. In the heat storage tank, for example, a high-stage heat exchanger formed by a flow path for the high-stage refrigerant to flow meanders and extends on the same surface, and a low-stage heat exchanger formed by a flow path for the low-stage refrigerant to flow meanders and extends on the same surface, are arranged at positions where the surfaces of each other are opposite. Moreover, the high-stage refrigerant flows in and out of the high-stage heat exchanger, and the low-stage refrigerant flows in and out of the low-stage heat exchanger, thereby performing heat exchange between the heat storage material and the high-stage refrigerant or the low-stage refrigerant.

[0037] In this way, the heat exchanger on the high-stage side and the heat exchanger on the low-stage side are arranged in the heat storage tank of the heat storage heat exchanger H, and the heat storage material is filled in a manner to cover the periphery. The heat supplied to the heat storage heat exchanger H is stored in the heat storage material, and the stored heat is used for heating operation on the high-stage side and for defrosting operation on the low-stage side as described later. In addition, the heat storage temperature sensor HS described later is provided at a position where the temperature of the heat storage material can be measured.

[0038] And, if Figure 1 As shown, the heat storage heat exchanger H is arranged in parallel with the stepped heat exchanger C to form the above-mentioned high-stage heat storage circuit 3 and low-stage heat storage circuit 4.

[0039] In the high-stage refrigerant circuit 1 , a high-stage four-way valve 14 that switches the high-stage refrigerant discharged from the high-stage compressor 11 to flow toward the high-stage heat exchanger 12 or toward the stepped heat exchanger C is connected to the discharge side of the high-stage compressor 11 .

[0040] Similarly, in the low-stage refrigerant circuit 2, a low-stage four-way valve 24 that switches the low-stage refrigerant discharged from the low-stage compressor 21 to flow toward the stepped heat exchanger C side or to the low-stage heat exchanger 23 side is connected to the discharge side of the low-stage compressor 21.

[0041] The two-stage refrigeration cycle device S is provided with a refrigerant temperature detection unit 5, which measures or calculates the saturation temperature of the low-stage refrigerant discharged from the low-stage compressor 21 circulating in the low-stage refrigerant circuit 2 and the low-stage heat storage circuit 4. In addition, the low-stage refrigerant circuit 2 is provided with: a pressure sensor 51 for measuring the discharge pressure of the low-stage refrigerant discharged from the low-stage compressor 21; and a refrigerant temperature sensor 52 for measuring the temperature of the low-stage refrigerant.

[0042] The refrigerant temperature detection unit 5 calculates the saturation temperature of the low-stage refrigerant using the pressure value measured by the pressure sensor 51. The saturation temperature, that is, the temperature of the saturated vapor, is specified according to the type of refrigerant and can be calculated based on the detection value of the pressure sensor 51, that is, the high pressure. In addition, the program for calculating the saturation temperature of the low-stage refrigerant can be stored in the refrigerant temperature detection unit 5, or can be stored in a storage unit that is not shown but is separately provided. The information on the saturation temperature of the low-stage refrigerant calculated by the refrigerant temperature detection unit 5 is sent to the control unit 6 described later.

[0043] As described above, the thermal storage temperature sensor HS is provided in the thermal storage heat exchanger H to measure the temperature of the thermal storage material provided in the thermal storage heat exchanger H. In other words, the thermal storage temperature sensor HS is a sensor for measuring the amount of thermal storage heat stored in the thermal storage heat exchanger H. Information on the temperature of the thermal storage material measured by the thermal storage temperature sensor HS is transmitted to the control unit 6.

[0044] The control unit 6 controls the opening degrees of the high-pressure side compressor 11 , the first high-pressure side decompression mechanism 13 , the second high-pressure side decompression mechanism 31 , the low-pressure side compressor 21 , the first low-pressure side decompression mechanism 22 , and the second low-pressure side decompression mechanism 41 .

[0045] In particular, the control unit 6 controls the opening degree of each pressure reducing mechanism, thereby being able to adjust the flow rates of the high-stage refrigerant and the low-stage refrigerant flowing in the high-stage refrigerant circuit 1, the low-stage refrigerant circuit 2, the high-stage heat storage circuit 3, and the low-stage heat storage circuit 4.

[0046] Furthermore, when performing the heating / heat storage operation in which the heating operation and the heat storage operation are performed in parallel, the control unit 6 controls the low-stage compressor 21 using the information of the saturation temperature calculated by the refrigerant temperature detection unit 5 and the information of the temperature of the heat storage material measured by the heat storage temperature sensor HS. Furthermore, the control during the defrosting operation of the low-stage heat exchanger 23 is also performed by the control unit 6.

[0047] Therefore, next, the control contents of the control unit 6 will be described in more detail. Figure 2 1 is an explanatory diagram showing the concept of a control method of the control unit 6 of the two-stage refrigeration cycle device S according to the embodiment of the present invention immediately after the start of the heating / heat storage operation. The heating / heat storage operation refers to an operation in which the high-stage heat exchanger 12 is used as a condenser for heating operation and the heat storage heat exchanger H is used to transfer heat from the refrigerant to the heat storage material to store heat.

[0048] exist Figure 2 In the illustrated diagram, the horizontal axis represents time (t) and the vertical axis represents temperature (T). First, the dotted line in the horizontal direction represents the set temperature in the room. That is, the dotted line is the set temperature, so it is constant from the temperature (T) on the vertical axis. Therefore, it is shown in a straight line in parallel with the horizontal axis.

[0049] In addition, a plurality of curves representing temperature are shown from left to right over time, and the solid line represents the room temperature. As described above, the room temperature sensor provided in the indoor unit measures the room temperature and sends the measurement result to the control unit 6 .

[0050] The control unit 6 controls the two-stage refrigeration cycle device S so that the room temperature reaches the set temperature or maintains the set temperature. Therefore, the room temperature shown by the solid line shows a trend of rapid rise at the beginning. This is because the two-stage refrigeration cycle device S is controlled so that the set temperature is reached as soon as possible.

[0051] Furthermore, if the room temperature temporarily reaches the set temperature, the room is heated in such a way that the room temperature can maintain the set temperature. Figure 2 As shown, the room temperature is lower or higher than the set temperature at a temperature close to the set temperature and the difference between the room temperature and the set temperature gradually decreases.

[0052] Next, the temperature of the thermal storage material in the thermal storage heat exchanger H is shown by a dotted line from where the initial temperature is substantially the same as the solid line indicating the room temperature. As described above, the temperature of the thermal storage material is the temperature measured by the thermal storage temperature sensor HS.

[0053] Regarding the temperature of the thermal storage material, Figure 2 The following curve indicates that the temperature gradually rises, exceeds the set temperature at about half the time of the horizontal axis representing time (t), and finally reaches a temperature higher than the room temperature and the set temperature. Figure 2 The temperature change of the heat storage material shown is an example, and may be different depending on the type of the heat storage material and various conditions after the heat storage heat exchanger H is placed.

[0054] On the other hand, the first saturation temperature of the low-stage refrigerant has a starting point slightly higher than the dotted line indicating the temperature of the heat storage material and shows a change substantially the same as the increase in the temperature of the heat storage material. This is a value calculated based on the detection value of the pressure sensor 51, that is, the high pressure. The first saturation temperature is Figure 2 In the figure, the first saturation temperature of the low-stage refrigerant is shown to be equal to the temperature of the heat storage material in the end. This is because the temperature of the heat storage material reaches the set value and no further heat exchange is performed.

[0055] Here, two straight dotted lines are shown in a manner that intersects with the dotted line representing the set temperature and is parallel to the vertical axis. Among them, a straight dotted line close to the vertical axis representing temperature (T) extends downward from the point where the dotted line representing the set temperature and the solid line representing the room temperature first intersect as a base point, and intersects with the horizontal axis representing time (t). The time when this straight dotted line intersects with the horizontal axis of time (t) is hereinafter referred to as "time a".

[0056] That is, the period (time) from the start of the heating operation of the two-stage refrigeration cycle device S to the time a represents the time until the room temperature reaches the set temperature. And after the time a, the heating / heat storage operation of the two-stage refrigeration cycle device S is continued in such a manner that the room temperature can maintain the set temperature as described above.

[0057] In addition, regarding another straight dotted line away from the vertical axis representing temperature (T), the temperature of the heat storage material is equal to the temperature of the low-stage refrigerant. In this way, the temperature of the heat storage material is equal to the temperature of the low-stage refrigerant, indicating that the preset setting value of the heat storage material has been reached and sufficient heat has been stored in the heat storage heat exchanger H. The setting value is appropriately set according to the heat storage material of the heat storage heat exchanger H. Therefore, after the moment (hereinafter appropriately indicated as "moment b") at the point where the other straight dotted line intersects with time (t), further heat storage is suppressed by maintaining the temperature of the heat storage material at the same temperature as the temperature of the low-stage refrigerant (hereinafter referred to as heat storage operation stop).

[0058] Finally, the second saturation temperature of the low-stage refrigerant is indicated by a two-dot chain line starting from the intersection of the first saturation temperature of the low-stage refrigerant indicated by the dot-dash curve and the straight dot-dash line. The second saturation temperature of the low-stage refrigerant is a temperature further higher than the first saturation temperature of the low-stage refrigerant, but at the time b when the heat storage operation is stopped, it is the same as the first saturation temperature of the low-stage refrigerant and is lower than the temperature of the heat storage material.

[0059] In addition, the first saturation temperature and the second saturation temperature of the low-stage refrigerant represent the condensation temperature of the low-stage refrigerant. Figure 2 The saturation temperatures of the above two types of low-stage refrigerants are indicated in for the following reason.

[0060] As described above, in the two-stage refrigeration cycle device S according to the embodiment of the present invention, the stepped heat exchanger C and the heat storage heat exchanger H are connected in parallel. Figure 1 The flow is divided as shown, flowing into the stepped heat exchanger C and the heat storage heat exchanger H respectively.

[0061] For example, when heat is hardly stored in the thermal storage heat exchanger H and the temperature of the thermal storage material of the thermal storage heat exchanger H is not high, if the same high-temperature low-stage refrigerant as the low-stage refrigerant flowing from the low-stage compressor 21 into the stepped heat exchanger C flows into the thermal storage heat exchanger H, the low-stage refrigerant in the gas phase flowing into the thermal storage heat exchanger H exchanges heat with the thermal storage material in the thermal storage heat exchanger H and condenses. A part of the condensed lower-stage refrigerant in the liquid phase flows into the second low-stage pressure reducing mechanism 41 on the downstream side, and the rest of the lower-stage refrigerant is accumulated in the thermal storage heat exchanger H. The lower the temperature of the thermal storage material is relative to the temperature of the lower-stage refrigerant, the more the lower-stage refrigerant is overcooled in the thermal storage heat exchanger H, and the more the amount of refrigerant accumulated in the thermal storage heat exchanger H increases.

[0062] If this state is reached, as described above, the low-stage refrigerant in the liquid phase is distributed more in the heat storage heat exchanger H, and the amount of the relatively circulating low-stage refrigerant decreases. If the circulation amount of the low-stage refrigerant decreases, the amount of heat exchange with the high-stage refrigerant in the stepped heat exchanger C also decreases, and the heating capacity of the two-stage refrigeration cycle device S may decrease.

[0063] The reason why the low-stage refrigerant in the thermal storage heat exchanger H is distributed more in the liquid phase is that the difference between the saturation temperature of the low-stage refrigerant flowing into the thermal storage heat exchanger H and the temperature of the thermal storage medium constituting the thermal storage heat exchanger H is large. The larger the temperature difference, the greater the degree of supercooling of the low-stage refrigerant. The greater the degree of supercooling, the larger the liquid single-phase region in the path of the low-stage refrigerant in the thermal storage heat exchanger H, and therefore the amount of liquid-phase refrigerant accumulated increases.

[0064] Therefore, the control unit 6 controls the rotation speed of the low-stage compressor 21 so that the difference between the saturation temperature of the low-stage refrigerant and the temperature of the heat storage material does not increase. Specifically, the refrigerant temperature detection unit 5 calculates the saturation temperature of the low-stage refrigerant using the pressure value of the low-stage refrigerant discharged from the low-stage compressor 21 measured by the pressure sensor 51 and the temperature of the low-stage refrigerant measured by the refrigerant temperature sensor 52.

[0065] That is, the measurement results from the pressure sensor 51 and the refrigerant temperature sensor 52 are input to the refrigerant temperature detection unit 5. Then, information on the saturation temperature calculated by the refrigerant temperature detection unit 5 using the input measurement results is sent to the control unit 6. On the other hand, as described above, the temperature of the heat storage material is measured by the heat storage temperature sensor HS and input to the control unit 6.

[0066] The control unit 6 can thereby obtain information on the saturation temperature and the temperature of the thermal storage material. The control unit 6 controls the heating / heat storage operation based on the difference between the saturation temperature and the temperature of the thermal storage material according to the operating status of the two-stage refrigeration cycle apparatus S.

[0067] Therefore, first, the control in the state immediately after the two-stage refrigeration cycle device S starts to operate is described. In this case, it is necessary to heat the indoor space. That is, in the heating / heat storage operation, it is necessary to give priority to the heating operation over the heat storage operation. At this time, the second low-stage side pressure reducing mechanism 41 is controlled in such a manner that the flow rate of the refrigerant passing through the second low-stage side pressure reducing mechanism 41 is less than the flow rate of the refrigerant passing through the first low-stage side pressure reducing mechanism 22. Specifically, it is controlled to be in a slightly open state.

[0068] Therefore, the control unit 6 controls the heating / heat storage operation so that the difference between the first saturation temperature of the low-stage refrigerant and the temperature of the heat storage material reaches a predetermined "first predetermined value T1". The first predetermined value T1 is predetermined based on an appropriate value, for example, a value of 2°C to 3°C, as the temperature difference between the two obtained by experiments or the like.

[0069] The control unit 6 controls the rotation speed of the low-stage compressor 21 so as to maintain the value of the set first predetermined value T1. That is, the first saturation temperature of the low-stage refrigerant does not become too high relative to the temperature of the thermal storage material. In other words, in order to make the first saturation temperature of the low-stage refrigerant close to the temperature of the thermal storage material of the thermal storage heat exchanger H, the rotation speed of the low-stage compressor 21 is controlled so as not to increase.

[0070] By performing such control, the possibility of the low-stage refrigerant discharged from the low-stage compressor 21 condensing and becoming a liquid state when flowing into the heat storage heat exchanger H due to the first saturation temperature of the low-stage refrigerant rising sharply and the temperature difference with respect to the heat storage material increasing can be reduced.

[0071] In addition, the saturation temperature of the low-stage refrigerant and the temperature of the heat storage material required for the control of the control unit 6 are input from the refrigerant temperature detection unit 5 and the heat storage temperature sensor HS to the control unit 6 at any time. Alternatively, the information on the saturation temperature of the low-stage refrigerant and the temperature of the heat storage material may be sent from the refrigerant temperature detection unit 5 and the heat storage temperature sensor HS to the control unit 6 at regular intervals.

[0072] As described above, from the start of the heating / heat storage operation to the time a, the control unit 6 controls the two-stage refrigeration cycle device S in such a manner that the heating operation is given priority among the heating operation and the heat storage operation. That is, in the low-stage refrigerant circuit 2, the openings of the first low-stage pressure reducing mechanism 22 and the second low-stage pressure reducing mechanism 41 are controlled in such a manner that more refrigerant flows into the stepped heat exchanger C than into the heat storage heat exchanger H. In this way, the indoor space can be heated quickly to provide comfort.

[0073] Furthermore, if the room temperature reaches the set temperature, a heating operation is calculated to maintain the room temperature at the set temperature in the future based on the relationship between the room temperature and the set temperature. That is, during the period from time a to time b, the load of the two-stage refrigeration cycle device S during the heating operation is reduced compared to the period from the start of the heating / heat storage operation to time a, and the surplus capacity of the heating capacity of the two-stage refrigeration cycle device S can be allocated to the heat storage operation. At this time, in the low-stage refrigerant circuit 2, the openings of the first low-stage pressure reducing mechanism 22 and the second low-stage pressure reducing mechanism 41 are controlled in such a manner that more refrigerant flows into the heat storage heat exchanger H than into the stepped heat exchanger C.

[0074] Therefore, during the period (time) between time a and time b, the control unit 6 controls the two-stage refrigeration cycle device S to prioritize heat storage over heating. However, this does not mean that the heating operation is not performed during this period, but that the heating operation and the heat storage operation are performed so as not to impair comfort.

[0075] If the control unit 6 knows that the room temperature has reached the set temperature, the control unit 6 sets the second predetermined value T2 to continue the heating operation and give priority to the heat storage operation. This is a target value of the difference between the second saturation temperature of the low-stage refrigerant and the temperature of the heat storage material, and the second predetermined value T2 is predetermined in advance so as to be greater than or equal to the first predetermined value T1.

[0076] exist Figure 2 In FIG. 8 , the second predetermined value T2 is a value indicated by a double-dashed arrow between a double-dashed curve indicating the second saturation temperature of the low-pressure side refrigerant and a dotted curve indicating the temperature of the heat storage material.

[0077] Furthermore, by setting the second predetermined value T2 which is set to T1≤T2, the rotation speed of the low-stage compressor 21 is increased compared to the current state, thereby increasing the saturation temperature of the low-stage refrigerant, thereby making it possible to perform more heat storage using the heat storage heat exchanger H. That is, the heat storage capacity of the heat storage heat exchanger H is increased in such a way that the heat storage operation is prioritized over the heating operation. In this sense, it can be said that the first predetermined value T1 and the second predetermined value T2 are set in order to adjust the heat storage capacity.

[0078] As described above, the control unit 6 acquires information related to the temperature of the heat storage material from the heat storage temperature sensor HS. In addition, when the temperature of the heat storage material is higher than a preset value, that is, when the control unit 6 determines that a sufficient amount of heat is stored in the heat storage material, the heat storage operation is stopped. The opening of the second low-stage side pressure reducing mechanism 41 is controlled to be slightly opened to limit the amount of low-stage side refrigerant flowing into the heat storage heat exchanger H, and the temperature of the heat storage material is maintained to be the same as the temperature of the low-stage side refrigerant, thereby stopping the heat storage operation.

[0079] exist Figure 2 In FIG. 1 , at time b, the temperature of the heat storage material reaches a maximum value, which is a value greater than the saturation temperature of the low-stage refrigerant. Therefore, the time indicated by time b corresponds to the heat storage stop time.

[0080] In the heating / heat storage operation, the control unit 6 controls the low-pressure compressor 21 to set the first predetermined value T1 and the second predetermined value T2 and maintain the values, but controls each decompression mechanism as follows.

[0081] That is, the control unit 6 performs control such that, during the heating / heat storage operation, the first high-stage pressure reducing mechanism 13, the first low-stage pressure reducing mechanism 22, and the second low-stage pressure reducing mechanism 41 are opened, and the second high-stage pressure reducing mechanism 31 is closed. The control to close the second high-stage pressure reducing mechanism 31 is performed in order not to use the heat stored in the heat storage heat exchanger H during the heating / heat storage operation.

[0082] Figure 3 1 is a refrigerant circuit diagram showing the flow of the refrigerant when the two-stage refrigeration cycle apparatus S according to the embodiment of the present invention performs the heating / heat storage operation. As described above, the control unit 6 performs control to close the second high-stage side pressure-reducing mechanism 31 .

[0083] Therefore, in this circuit diagram, the high-stage refrigerant does not flow through the refrigerant pipe P, which is connected to the second high-stage pressure reducing mechanism 31 at one end, sandwiches the heat storage heat exchanger H, and is connected to the step heat exchanger C and the high-stage four-way valve 14 at the other end, as shown by the dotted line. Therefore, the high-stage refrigerant does not circulate in the high-stage heat storage circuit 3. In addition, the refrigerant pipe P through which the low-stage refrigerant and the high-stage refrigerant flow is shown by the solid line.

[0084] On the high-stage side, the control unit 6 controls the first high-stage side pressure reducing mechanism 13 to be opened. Figure 3As shown by the arrow, the high-side refrigerant discharged from the high-side compressor 11 in the high-side refrigerant circuit 1 flows from the high-side four-way valve 14 to the high-side heat exchanger 12, flows through the first high-side pressure reducing mechanism 13 and the stepped heat exchanger C and is sucked into the high-side compressor 11.

[0085] On the other hand, the low-stage refrigerant discharged from the low-stage compressor 21 in the low-stage refrigerant circuit 2 on the low-stage side flows into the stepped heat exchanger C from the low-stage four-way valve 24, flows through the first low-stage pressure reducing mechanism 22 and the low-stage heat exchanger 23, and is sucked into the low-stage compressor 21.

[0086] At this time, heat exchange is performed between the low-stage refrigerant and the high-stage refrigerant in the stepped heat exchanger C. Furthermore, the stepped heat exchanger C functions as an evaporator for the high-stage refrigerant, so that in the high-stage refrigerant circuit 1, the high-stage refrigerant and air and water are heat exchanged in the high-stage heat exchanger 12. Thus, warm air and warm water are supplied to the indoor space.

[0087] In addition, the control unit 6 controls the first low-stage side decompression mechanism 22 and the second low-stage side decompression mechanism 41 to be opened. That is, the low-stage side refrigerant discharged from the low-stage side compressor flows not only in the stepped heat exchanger C, but also in the heat storage heat exchanger H provided in parallel with the stepped heat exchanger C.

[0088] As described above, the low-stage heat storage circuit 4 is configured such that one end is connected between the low-stage four-way valve 24 and the stepped heat exchanger C, and the other end is connected between the first low-stage pressure reducing mechanism 22 and the low-stage heat exchanger 23 .

[0089] When the heating / heat storage operation is performed in the two-stage refrigeration cycle device S, Figure 3 As shown by the arrow, the low-stage refrigerant discharged from the low-stage compressor 21 in the low-stage refrigerant circuit 2 flows out from the low-stage four-way valve 24, and flows into the heat storage heat exchanger H through the low-stage heat storage circuit 4. Then, it flows through the low-stage heat exchanger 23 through the second low-stage pressure reducing mechanism 41 and is sucked into the low-stage compressor 21.

[0090] As described above, the control unit 6 controls the rotation speed of the low-stage compressor 21 in such a manner that the difference between the first saturation temperature of the low-stage refrigerant and the temperature of the heat storage material is set to the first predetermined value T1 and the first predetermined value T1 is maintained at the control unit 6 at the start of the heating operation. Therefore, the low-stage refrigerant flows into the heat storage heat exchanger H in a state where the difference between the first saturation temperature of the low-stage refrigerant and the temperature of the heat storage material does not increase.

[0091] Therefore, it is possible to reduce the area filled with the low-stage refrigerant in the liquid phase in the thermal storage heat exchanger H. Therefore, it is possible to suppress the low-stage refrigerant in the liquid phase from being distributed more in the thermal storage heat exchanger H. The low-stage refrigerant flowing out of the thermal storage heat exchanger H passes through the second low-stage pressure reducing mechanism 41 and the low-stage heat exchanger 23 and is sucked into the low-stage compressor 21.

[0092] On the other hand, one end of the high-stage side heat storage circuit 3 is connected between the high-stage side heat exchanger 12 and the first high-stage side pressure reducing mechanism 13, and the other end is connected between the step heat exchanger C and the high-stage side four-way valve 14, but as mentioned above, the second high-stage side pressure reducing mechanism 31 is controlled by the control unit 6 to be in a closed state.

[0093] Therefore, the high-stage refrigerant does not flow in the high-stage heat storage circuit 3, and does not exchange heat with the low-stage refrigerant in the heat storage heat exchanger H. In addition, in the high-stage heat exchanger 12, when the high-stage refrigerant exchanges heat with the air or water, the heat stored in the heat storage heat exchanger H is not used.

[0094] The control unit 6 performs control such that the first low-stage pressure reducing mechanism 22, the second low-stage pressure reducing mechanism 41, and the first high-stage pressure reducing mechanism 13 are opened, and the second high-stage pressure reducing mechanism 43 is closed. The control unit 6 performs this control, so that the two-stage refrigeration cycle device S can perform heating operation and the heat storage heat exchanger H can perform heat storage operation.

[0095] That is, the stepped heat exchanger C functions as an evaporator for the high-stage refrigerant, and the low-stage refrigerant and the high-stage refrigerant exchange heat via the stepped heat exchanger C. In contrast, the low-stage refrigerant flows into the thermal storage heat exchanger H, but the high-stage refrigerant does not flow in. Therefore, the heat stored in the thermal storage heat exchanger H is not used in the heating operation, and the heat of the low-stage refrigerant is stored in the thermal storage material of the thermal storage heat exchanger H.

[0096] The above is the control method of the control unit 6 for heating / heat storage operation. Figure 3 Therefore, the following describes the situation where the defrosting operation is performed in the two-stage refrigeration cycle device S.

[0097] As described above, in the case of heating operation, it is necessary to perform defrosting operation periodically. Furthermore, in the case of defrosting operation, in order to supply the warm low-stage refrigerant discharged from the low-stage compressor 21 to the low-stage heat exchanger 23, the low-stage four-way valve 24 is switched from the heating operation state to the cooling operation state, so the heating operation is stopped during the defrosting operation. Therefore, warm air and warm water are not supplied to the indoor space during the defrosting operation, which may impair comfort.

[0098] Therefore, in the two-stage refrigeration cycle apparatus S according to the embodiment of the present invention, by performing the defrosting operation without stopping the heating operation, it is possible to ensure comfort and maintain the heating capacity of the two-stage refrigeration cycle apparatus S.

[0099] Figure 4 1 is a refrigerant circuit diagram showing the flow of refrigerant when the two-stage refrigeration cycle device S according to an embodiment of the present invention performs a defrosting operation. As described above, when performing a defrosting operation, it is necessary to supply warm low-stage refrigerant to the low-stage heat exchanger 23, so the low-stage four-way valve 24 is switched so that the low-stage refrigerant is not supplied to the stepped heat exchanger C and the heat storage heat exchanger H, but to the low-stage heat exchanger 23.

[0100] That is, the low-stage refrigerant discharged from the low-stage compressor 21 first flows into the low-stage heat exchanger 23 through the low-stage four-way valve 24. Then, the frost adhering to the low-stage heat exchanger 23 is melted by the low-stage refrigerant that has flowed in.

[0101] Furthermore, when performing the defrosting operation, the control unit 6 controls the first low-stage pressure reducing mechanism 22 to be in a closed state, and the second low-stage pressure reducing mechanism 41 to be in an open state. By controlling the first low-stage pressure reducing mechanism 22 and the second low-stage pressure reducing mechanism 41 in this way, the low-stage refrigerant flowing out of the low-stage heat exchanger 23 does not flow into the low-stage refrigerant circuit 2, but flows into the low-stage heat storage circuit 4.

[0102] Therefore, the low-stage refrigerant flowing out of the low-stage heat exchanger 23 passes through the second low-stage decompression mechanism 41 and the heat storage heat exchanger H and is sucked into the low-stage compressor 21. Therefore, the low-stage refrigerant does not flow into the stepped heat exchanger C during the defrosting operation.

[0103] On the other hand, on the high-stage side, as described above, the low-stage refrigerant does not flow into the stepped heat exchanger C. In addition, since the low-stage refrigerant is originally heat-exchanged in the low-stage heat exchanger 23 for defrosting the low-stage heat exchanger 23, heat exchange cannot be performed between the low-stage refrigerant and the high-stage refrigerant in the stepped heat exchanger C.

[0104] Therefore, the control unit 6 controls the first high-stage pressure reducing mechanism 13 to be closed. However, when heat exchange in the stepped heat exchanger C is not possible, warm air cannot be supplied to the indoor space, and the room temperature gradually decreases, which may impair comfort.

[0105] In order to avoid such a situation, the two-stage refrigeration cycle device S according to the embodiment of the present invention performs control to continuously perform the heating operation using the heat stored in the heat storage heat exchanger H. That is, the control unit 6 controls so that the second high-stage side pressure reducing mechanism 31 is in an open state, and guides the high-stage side refrigerant flowing out of the high-stage side heat exchanger 12 to the high-stage side heat storage circuit 3.

[0106] When the high-stage refrigerant passes through the thermal storage heat exchanger H, the high-stage refrigerant absorbs heat stored in the thermal storage heat exchanger H and flows into the high-stage heat exchanger 12 again via the high-stage compressor 11, thereby providing warm air to the indoor space.

[0107] As described above, the control unit 6 sets the first high-stage pressure reducing mechanism 13 and the first low-stage pressure reducing mechanism 22 to the closed state. Figure 4 As shown by the dotted line, control is performed to prevent the high-stage refrigerant and the low-stage refrigerant from circulating in the high-stage refrigerant circuit 1 and the low-stage refrigerant circuit 2. By performing such control, the control unit 6 defrosts the low-stage heat exchanger 23 and continues the heating operation using the heat stored in the heat storage heat exchanger H.

[0108] In addition, the control unit 6 controls the first low-stage side pressure reducing mechanism 22 and the first high-stage side pressure reducing mechanism 13 to be closed, so that neither the low-stage side refrigerant nor the high-stage side refrigerant flows into the stepped heat exchanger C, and no heat exchange is performed therebetween. Therefore, the low-stage side refrigerant used for defrosting the low-stage side heat exchanger 23 does not flow into the stepped heat exchanger C, thereby preventing the cold source heat on the low-stage side from being transferred to the high-stage side.

[0109] [action]

[0110] Next, use Figures 5 to 7 The flow of control of the two-stage refrigeration cycle apparatus S by the control unit 6 during the heating / heat storage operation and the defrosting operation will be described. Figure 5 and Figure 6 : is a flowchart showing a control flow when the two-stage refrigeration cycle device S according to the embodiment of the present invention performs heating / heat storage operation. Figure 7 This is a flowchart showing a control flow when the defrosting operation is performed in the two-stage refrigeration cycle device S according to the embodiment of the present invention.

[0111] First, the flow of heating / heat storage operation will be explained. Figure 5As shown, if the heating / heat storage operation is started in the two-stage refrigeration cycle device S (ST1), the control unit 6 adjusts the opening of the pressure reducing mechanism to a predetermined initial opening (ST2) in such a way that the low-stage refrigerant discharged from the low-stage compressor 21 flows into the step heat exchanger C and the heat storage heat exchanger H.

[0112] Here, the term "decompression mechanism" is used collectively. For example, the decompression mechanism Figure 3 The first low-stage pressure reducing mechanism 22 and the second low-stage pressure reducing mechanism 41 are shown. The initial opening is set to ensure reliability at the time of startup.

[0113] The first low-stage pressure reducing mechanism 22 is set to an opening degree that prevents the discharge temperature from excessively increasing and avoids liquid backflow to the low-stage compressor 21. The second low-stage pressure reducing mechanism 41 is set to an opening degree that prevents liquid accumulation in the thermal storage heat exchanger H and prevents the flow rate of the refrigerant flowing to the thermal storage heat exchanger H from being excessive.

[0114] In addition, on the high-stage side, the control unit 6 adjusts the opening degree of the first high-stage side pressure reducing mechanism 13 so that the opening degree reaches a predetermined initial opening degree (ST3). On the other hand, the control unit 6 adjusts the opening degree of the second high-stage side pressure reducing mechanism 31 so that it is closed (ST4). The initial opening degree is set to ensure reliability at the time of startup. The first high-stage side pressure reducing mechanism 13 is set to an opening degree so that the discharge temperature does not rise excessively and the liquid backflow to the high-stage side compressor 11 can be avoided.

[0115] By the control of the control unit 6, the high-stage refrigerant circulates only in the high-stage refrigerant circuit 1 and does not flow into the high-stage heat storage circuit 3. Therefore, the heat stored in the heat storage heat exchanger H is not used in the heating operation, so the heat storage operation can be performed and the heating operation can be given priority, so that the indoor space can be heated.

[0116] Next, the refrigerant temperature detection unit 5 calculates the saturation temperature of the low-stage refrigerant using the results measured by the pressure sensor 51 and the refrigerant temperature sensor 52. In addition, the temperature of the thermal storage material is measured using the thermal storage temperature sensor HS provided in the thermal storage heat exchanger H. The information on the calculated saturation temperature and the temperature of the thermal storage material is input to the control unit 6 (ST5).

[0117] The control unit 6 obtains the first predetermined value T1 (ST6) from the storage unit (not shown), for example, and controls the rotation speed of the low-stage compressor 21 in such a manner as to maintain the first predetermined value T1 obtained by obtaining the difference between the saturation temperature of the low-stage refrigerant and the temperature of the heat storage material (ST7).

[0118] In addition, the control sequence of the control unit 6 until step ST7 after the heating / heat storage operation of step ST1 is started is described in the above order for the sake of convenience, but the order is not limited to the order described and the order may be changed. In addition, the control of each pressure reducing mechanism may be performed simultaneously.

[0119] During the heating / heat storage operation, the room temperature is measured at a constant cycle by a room temperature sensor in the indoor unit (ST8) because it is necessary to confirm that the room temperature has reached the set temperature or is maintained at the set temperature.

[0120] The control unit 6 compares the room temperature measured by the room temperature sensor with the set temperature to determine whether the room temperature has reached the set temperature (ST9). If the room temperature has not yet reached the set temperature (NO in ST9), the process returns to step ST7 to continue the heating / heat storage operation and measure the room temperature. The newly measured room temperature is compared with the set temperature.

[0121] On the other hand, when the room temperature reaches the set temperature (YES in ST9), the control unit 6 obtains the information of the recalculated saturation temperature and the information of the temperature of the thermal storage material ( Figure 6 The control unit 6 obtains a second predetermined value T2 (e.g., 5° C.) predetermined based on the temperature difference between the saturation temperature obtained by an experiment or the like and the temperature of the heat storage material from the storage unit (ST11). The second predetermined value T2 is set so that the relationship between the first predetermined value T1 and the second predetermined value T2 becomes T1≤T2.

[0122] Then, the control unit 6 controls the low-pressure compressor 21 to maintain the second predetermined value T2 and performs heat storage operation (ST12). The control unit 6 acquires information on the temperature of the heat storage material from the heat storage temperature sensor HS at any time (ST13).

[0123] Then, it is determined whether the acquired temperature of the thermal storage material is greater than or equal to a predetermined setting value (ST14). The setting value can be appropriately set according to the thermal storage material of the thermal storage heat exchanger H.

[0124] If the temperature of the heat storage material has not reached the set value (NO in ST14), the process returns to step ST12 and the heat storage operation is continued. On the other hand, if the temperature of the heat storage material has reached the set value (YES in ST14), the heat storage operation is stopped (ST15). The opening of the second low-stage side pressure reducing mechanism 41 is controlled to be slightly open to limit the amount of low-stage side refrigerant flowing into the heat storage heat exchanger H, and the temperature of the low-stage side refrigerant and the temperature of the heat storage material are maintained at the same temperature, thereby stopping the heat storage operation. As described above, the heating / heat storage operation is terminated.

[0125] Next, use Figure 7 The control flow of the defrosting operation is described. As described above, the defrosting operation is performed periodically during the heating operation. For example, when the heating operation is continued for 3 hours at an outside air temperature of 5°C or less, and the temperature of the low-stage heat exchanger 23 is less than or equal to -15°C, the defrosting operation is switched. However, the timing for switching between the heating operation and the defrosting operation can be arbitrarily set.

[0126] When the defrosting operation is started (ST31), the control unit 6 adjusts the opening degree so that the first low-stage pressure reducing mechanism 22 is closed so that the low-stage refrigerant flowing out of the low-stage heat exchanger 23 does not flow into the stepped heat exchanger C (ST32). Furthermore, the opening degree is adjusted so that the first high-stage pressure reducing mechanism 13 is closed so that the high-stage refrigerant does not flow from the high-stage heat exchanger 12 into the stepped heat exchanger C (ST33).

[0127] In addition, the control unit 6 adjusts the opening degree so that the second low-stage side pressure reducing mechanism 41 and the second high-stage side pressure reducing mechanism 31 are in the open state (ST34, ST35) in such a manner that both the low-stage side refrigerant and the high-stage side refrigerant flow into the heat storage heat exchanger H. In addition, as described above, the control order of the control unit 6 on each pressure reducing mechanism can be controlled in any order or in parallel as described above.

[0128] The control unit 6 performs the defrosting operation and determines whether the defrosting of the low-stage heat exchanger 23 is completed, that is, whether the defrosting operation is terminated (ST36). For example, when the defrosting operation time has passed a predetermined time or the temperature of the low-stage heat exchanger 23 reaches a predetermined temperature, it is determined that the defrosting is completed. When the control unit 6 determines that the defrosting of the low-stage heat exchanger 23 is not yet completed (NO in ST36), the defrosting operation is continued.

[0129] On the other hand, when the control unit 6 determines that the defrosting of the low-stage heat exchanger 23 is completed (YES in ST36), the defrosting operation is stopped (ST37).

[0130] If it is a two-stage refrigeration cycle device having the refrigerant circuit described above and a control method for the two-stage refrigeration cycle device, then in the case of a refrigeration cycle circuit that adopts a multi-stage refrigeration circuit and has a heat storage device, it is possible to fully ensure the amount of refrigerant in the operating refrigeration cycle circuit, suppress the decrease in heating capacity and maintain the heat storage capacity without compromising comfort.

[0131] In addition, the present invention is not limited to the above-mentioned embodiment, which shows an example of the present invention. The structural elements can be deformed and concretized in the implementation stage without departing from the scope of the main purpose, and various changes or improvements can be applied to the above-mentioned embodiment. In addition, various inventions can be formed by appropriately combining multiple structural elements disclosed in the above-mentioned embodiment.

[0132] For example, some structural elements may be deleted from all the structural elements shown in the embodiment. Furthermore, the structural elements of different embodiments may be appropriately combined, and the method in which such changes or improvements are applied may also be included in the present invention. The embodiment and its variations are included in the scope and gist of the invention, and are included in the scope equivalent to the invention described in the claims.

[0133] Description of the label

[0134] 1…high-stage refrigerant circuit, 2…lowering-stage refrigerant circuit, 3…high-stage heat storage circuit, 4…lowering-stage heat storage circuit, 5…refrigerant temperature detection unit, 11…high-stage compressor, 12…high-stage heat exchanger, 13…first high-stage pressure reducing mechanism, 14…high-stage four-way valve, 21…lowering-stage compressor, 22…first low-stage pressure reducing mechanism, 23…lowering-stage heat exchanger, 24…lowering-stage four-way valve, 31…second high-stage pressure reducing mechanism, 41…second low-stage pressure reducing mechanism, 51…pressure sensor, 52…refrigerant temperature sensor, C…step heat exchanger, H…heat storage heat exchanger, HS…heat storage temperature sensor, P…refrigerant piping, S…two-stage refrigeration cycle device

Claims

1. A two-stage refrigeration cycle device, characterized in that: The two-stage refrigeration cycle device comprises: A high-stage refrigerant circuit, which sequentially connects the high-stage compressor, the high-stage heat exchanger, the first high-stage pressure reducing mechanism and the stepped heat exchanger by means of a refrigerant pipe, for circulation of the high-stage refrigerant; A low-stage refrigerant circuit, which sequentially connects the low-stage compressor, the stepped heat exchanger, the first low-stage pressure reducing mechanism, and the low-stage heat exchanger by refrigerant piping for circulation of the low-stage refrigerant; a high-stage heat storage circuit, which sequentially connects the high-stage compressor, the high-stage heat exchanger, the second high-stage pressure reducing mechanism, and the heat storage heat exchanger arranged in parallel with the stepped heat exchanger by means of a refrigerant piping, so that the high-stage refrigerant circulates; A low-stage heat storage circuit, which sequentially connects the low-stage compressor, the heat storage heat exchanger, the second low-stage pressure reducing mechanism, and the low-stage heat exchanger by refrigerant piping, so that the low-stage refrigerant circulates; a refrigerant temperature detection unit for measuring or calculating a saturation temperature of the low-stage refrigerant discharged from the low-stage compressor; a thermal storage temperature sensor for measuring the temperature of a thermal storage material disposed in the thermal storage heat exchanger; as well as a control unit that controls the openings of the high-stage compressor, the low-stage compressor, the first high-stage pressure reducing mechanism, the second high-stage pressure reducing mechanism, the first low-stage pressure reducing mechanism, and the second low-stage pressure reducing mechanism, The high-stage refrigerant and the low-stage refrigerant perform heat exchange in the stepped heat exchanger or the heat storage heat exchanger. The control unit acquires information on the saturation temperature and information on the temperature of the thermal storage material during heating operation, and controls the low-pressure compressor so that a temperature difference between the saturation temperature and the temperature of the thermal storage material reaches a first predetermined value.

2. The two-stage refrigeration cycle device according to claim 1, characterized in that: An indoor unit is provided in the indoor space, and the indoor unit has the high-pressure side heat exchanger and a room temperature sensor for measuring the room temperature of the indoor space. When the room temperature reaches a set temperature set in the indoor unit, the control unit controls the low-pressure side compressor in such a manner that the temperature difference between the saturation temperature and the temperature of the heat storage material reaches the second specified value.

3. The two-stage refrigeration cycle device according to claim 2, characterized in that: The control unit sets the second predetermined value to be greater than or equal to the first predetermined value.

4. The two-stage refrigeration cycle device according to claim 3, characterized in that: The control unit acquires information on the temperature of the thermal storage material, and stops storing heat in the thermal storage heat exchanger when the temperature of the thermal storage material reaches a predetermined temperature.

5. The two-stage refrigeration cycle device according to any one of claims 1 to 4, characterized in that: The control unit performs control to open the first high-stage pressure-reducing mechanism, the first low-stage pressure-reducing mechanism, and the second low-stage pressure-reducing mechanism and to close the second high-stage pressure-reducing mechanism during the heating operation using the first predetermined value or the second predetermined value.

6. The two-stage refrigeration cycle device according to claim 1, characterized in that: The control unit performs control to close the first low-stage pressure-reducing mechanism and the first high-stage pressure-reducing mechanism when performing a defrosting operation on the low-stage heat exchanger.

7. A control method for a two-stage refrigeration cycle device, characterized in that: The two-stage refrigeration cycle device comprises: A high-stage refrigerant circuit, which sequentially connects the high-stage compressor, the high-stage heat exchanger, the first high-stage pressure reducing mechanism and the stepped heat exchanger by means of a refrigerant pipe, for circulation of the high-stage refrigerant; A low-stage refrigerant circuit, which sequentially connects the low-stage compressor, the stepped heat exchanger, the first low-stage pressure reducing mechanism, and the low-stage heat exchanger by refrigerant piping for circulation of the low-stage refrigerant; a high-stage heat storage circuit, which sequentially connects the high-stage compressor, the high-stage heat exchanger, the second high-stage pressure reducing mechanism, and the heat storage heat exchanger arranged in parallel with the stepped heat exchanger by means of a refrigerant piping, so that the high-stage refrigerant circulates; A low-stage heat storage circuit, which sequentially connects the low-stage compressor, the low-stage heat exchanger, the second low-stage pressure reducing mechanism, the heat storage heat exchanger, and the low-stage compressor by refrigerant piping, so that the low-stage refrigerant circulates; a refrigerant temperature detection unit for measuring or calculating a saturation temperature of the low-stage refrigerant discharged from the low-stage compressor; a thermal storage temperature sensor for measuring the temperature of a thermal storage material disposed in the thermal storage heat exchanger; as well as a control unit that controls the openings of the high-stage compressor, the low-stage compressor, the first high-stage pressure reducing mechanism, the second high-stage pressure reducing mechanism, the first low-stage pressure reducing mechanism, and the second low-stage pressure reducing mechanism, The control method comprises the following steps: During heating operation, the control unit acquires information on the saturation temperature and the temperature of the heat storage material; and The low-pressure side compressor is controlled so that the temperature difference between the saturation temperature and the temperature of the heat storage material reaches a first predetermined value.

8. The control method of the two-stage refrigeration cycle device according to claim 7, characterized in that: The control method comprises the following steps: An indoor unit is provided in the indoor space, the indoor unit having the high-stage heat exchanger and a room temperature sensor for measuring the room temperature of the indoor space, and determining whether the room temperature reaches a set temperature set in the indoor unit; When it is determined that the room temperature has reached the set temperature, acquiring information on the saturation temperature and information on the temperature of the thermal storage material; as well as The low-pressure side compressor is controlled so that the temperature difference between the saturation temperature and the temperature of the heat storage material reaches a second predetermined value.

9. The control method of the two-stage refrigeration cycle device according to claim 8, characterized in that: The control unit sets the second predetermined value to be greater than or equal to the first predetermined value.

10. The control method of the two-stage refrigeration cycle device according to claim 8, characterized in that: The control method comprises the following steps: Acquiring information on the temperature of the thermal storage material; determining whether the temperature of the thermal storage material reaches a predetermined temperature; and When it is determined that the temperature of the heat storage material has reached a predetermined temperature, heat storage in the heat storage heat exchanger is stopped.

11. The control method of a two-stage refrigeration cycle device according to any one of claims 7 to 10, characterized in that: The control method comprises the following steps: During the heating operation using the first predetermined value or the second predetermined value, the first high-stage pressure-reducing mechanism, the first low-stage pressure-reducing mechanism, and the second low-stage pressure-reducing mechanism are opened; and The second high-stage side pressure reducing mechanism is closed.

12. The control method of the two-stage refrigeration cycle device according to claim 7, characterized in that: The control method further includes the step of closing the first low-stage pressure reducing mechanism and the first high-stage pressure reducing mechanism when performing a defrosting operation on the low-stage heat exchanger.

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