Refrigeration cycle device and control method for refrigeration cycle device

Abstract

To provide a refrigeration cycle device and a control method for the refrigeration cycle device capable of determining freezing prevention even when heat transfer performance differs depending on a type of a heat exchanger and avoiding leakage of a refrigerant to a living space by ensuing freezing prevention to improve safety of a user.SOLUTION: A refrigerant circuit C1 for circulating a first refrigerant includes: a compressor 1 that compresses the first refrigerant; an outdoor heat exchanger 4 that exchanges heat between outdoor air and the first refrigerant; an expansion valve 3; a different type refrigerant heat exchanger 2 that exchanges heat between the first refrigerant and a second refrigerant; a detection sensor 81 that detects a state detection value indicating a state of the first refrigerant flowing between the different type refrigerant heat exchanger 2 and the compressor 1; and a control device 9 that determines whether a freezing prevention operation is started on the basis of the state detection value detected by the detection sensor 81 according to the heat transfer performance of the different type refrigerant heat exchanger 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a refrigeration cycle device and a control method for a refrigeration cycle device. [Background technology]

[0002] Conventionally, there has been provided a system that supplies cold water or hot water (hereinafter also referred to as cold or hot water) to a room by, for example, exchanging heat between a refrigerant circulating in a refrigerant circuit and water circulating in a water circuit. In this system, particularly when supplying cold water, if the temperature of the refrigerant is low and drops to a temperature at which the water freezes, there is a possibility that the water will freeze in the heat exchanger that exchanges heat between the refrigerant and the water.

[0003] If water freezes in this way, it may cause damage such as cracks or ruptures in the pipes that form the flow paths inside the heat exchanger. Therefore, in order to prevent damage to a heat exchanger that exchanges heat between a refrigerant and water, for example, Patent Document 1 below discloses a technology for preventing water from freezing. Specifically, the temperature of the low-pressure refrigerant liquid flowing into the evaporator and the temperature of the cooled fluid are detected to determine the possibility of the cooled fluid freezing.

[0004] Meanwhile, in recent years, as one of the measures against global warming, for example, conversion of refrigerants used in refrigeration cycle devices such as air conditioners and heat pump devices to refrigerants with low global warming potential (GWP) has been considered. Low GWP refrigerants include flammable refrigerants such as propane (R290), and measures must be taken to prevent the refrigerant from leaking into living spaces.

[0005] One possible scenario in which a refrigerant leaks into the living space is when the heat exchanger in the hot and cold water supply system described above freezes, causing the propane refrigerant to enter the water circuit. If propane enters the water circuit, the water flow created by the water pump can carry the propane into the living space and cause it to leak into the room.

[0006] Therefore, when there is a possibility of such a risk occurring, a so-called double-wall heat exchanger, such as that disclosed in Patent Document 2, is employed, which makes it difficult for the refrigerant circulating in the refrigerant circuit to enter the water circuit even if the heat exchanger is damaged.

[0007] For example, a double-wall heat exchanger is made by stacking multiple heat transfer plates with openings at the four corners and uneven or corrugated surfaces, and joining the outer walls of the heat transfer plates and the periphery of the openings with brazing to form alternating first flow paths through which a first fluid flows and second flow paths through which a second fluid flows. Also, in a plate heat exchanger, the openings at the four corners are connected to form a first header through which the first fluid flows in and out of the first flow path and a second header through which the second fluid flows in and out of the second flow path, and each heat transfer plate is made of a double wall consisting of two overlapping metal plates.

[0008] Because the heat transfer plates have a double-wall structure, even if one of the heat transfer plates is damaged due to freezing, corrosion, or other factors, both flow paths remain connected, preventing refrigerant from leaking into the indoor area. However, if an air gap exists between the two metal plates, this creates thermal resistance, which can significantly reduce heat transfer performance. To address this issue, a technology is known that creates an air gap between the two metal plates while suppressing the reduction in heat transfer performance (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Application No. 2009-243828 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-66411 [Patent Document 3] Patent No. 6594598 Summary of the Invention [Problem to be solved by the invention]

[0010] While the use of a double-wall heat exchanger can prevent refrigerant from entering the water circuit, the first step is to prevent water from freezing, which can cause damage to the heat exchanger that exchanges heat between the refrigerant and water. However, double-wall heat exchangers, which have an air layer (thermal resistance), have significantly different heat transfer performance than conventional heat exchangers that do not have an air layer (single-wall heat exchangers made of a single metal plate). Therefore, the temperature change of the cooled fluid relative to the temperature of the refrigerant entering the heat exchanger differs, and the criteria for determining freeze prevention differ from those for conventional heat exchangers. Furthermore, even double-wall heat exchangers with different heat transfer performance can face similar issues.

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a refrigeration cycle device and a control method for a refrigeration cycle device that can determine whether freezing is prevented even when heat transfer performance differs depending on the type of heat exchanger. [Means for solving the problem]

[0012] A refrigeration cycle device according to one embodiment of the present invention includes a refrigerant circuit for circulating a first refrigerant, the refrigerant circuit including a compressor for compressing the first refrigerant, an outdoor heat exchanger for exchanging heat between outdoor air and the first refrigerant, an expansion valve, a different-type refrigerant heat exchanger for exchanging heat between the first refrigerant and a second refrigerant, a detection sensor for detecting a state detection value indicating the state of the first refrigerant flowing between the different-type refrigerant heat exchanger and the compressor, and a control device for determining whether to start ice protection operation based on the state detection value detected by the detection sensor in accordance with the heat transfer performance of the different-type refrigerant heat exchanger.

[0013] In addition, a control method for a refrigeration cycle device according to one embodiment of the present invention includes a refrigerant circuit that circulates a first refrigerant, the refrigerant circuit including a compressor that compresses the first refrigerant, an outdoor heat exchanger that exchanges heat between outdoor air and the first refrigerant, an expansion valve, a different-type refrigerant heat exchanger that exchanges heat between the first refrigerant and a second refrigerant, a detection sensor that detects a state detection value indicating the state of the first refrigerant flowing between the different-type refrigerant heat exchanger and the compressor, and a control device that determines whether to start ice protection operation based on the state detection value detected by the detection sensor in accordance with the heat transfer performance of the different-type refrigerant heat exchanger, wherein the heat transfer performance is determined based on a distance d between one refrigerant passage through which the first refrigerant flows and the other refrigerant passage through which the second refrigerant flows, and the control device varies the determination criteria for starting ice protection operation depending on the distance d. [Effects of the Invention]

[0014] According to the present invention, it is possible to determine whether or not a heat exchanger is freezing-proof, even if the heat transfer performance of the heat exchanger is different. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a refrigerant circuit diagram of a refrigeration cycle device according to an embodiment of the present invention. [Figure 2] 3 is a refrigerant circuit diagram showing the flow of refrigerant when performing hot water generating operation in the refrigeration cycle device according to the embodiment of the present invention. FIG. [Figure 3] 3 is a refrigerant circuit diagram showing the flow of refrigerant when performing a chilled water generating operation in the refrigeration cycle device according to the embodiment of the present invention. FIG. [Figure 4] FIG. 1 is an explanatory diagram illustrating the structure of a single-wall heat exchanger, which is an example of a different-type refrigerant heat exchanger. [Figure 5] 1 is an explanatory diagram illustrating the structure of a double-wall heat exchanger, which is an example of a different-type refrigerant heat exchanger used in a refrigeration cycle apparatus according to an embodiment of the present invention. FIG. [Figure 6] 1 is a block diagram showing functions performed by a control device in a refrigeration cycle device according to an embodiment of the present invention, with blocks for each function. [Figure 7]1 is a graph showing an example of temperature changes for different dissimilar refrigerant heat exchangers in a refrigeration cycle device according to an embodiment of the present invention, with respect to changes in temperature of the refrigerant flowing out from the outlet of the dissimilar refrigerant heat exchanger. [Figure 8] 10 is a graph showing an example of temperature changes of the refrigerant temperature and the water temperature for each of different heterogeneous refrigerant heat exchangers when a freeze protection operation is performed in the refrigeration cycle device according to the embodiment of the present invention. [Figure 9] 4 is a graph illustrating a first determination method for controlling the start of a freeze protection operation in the refrigeration cycle device according to the embodiment of the present invention. [Figure 10] 4 is a flowchart showing a processing flow in a first determination method for controlling the start of ice protection operation in the refrigeration cycle apparatus according to the embodiment of the present invention. [Figure 11] This is a graph explaining a second judgment method for controlling the start of ice protection operation in a refrigeration cycle device of an embodiment of the present invention, and is a graph explaining the changes in refrigerant temperature and water temperature when a single-wall heat exchanger is used. [Figure 12] 10 is a graph illustrating a second determination method for controlling the start of the freeze protection operation in the refrigeration cycle device according to the embodiment of the present invention, and is a graph illustrating changes in the refrigerant temperature and the water temperature when a double-wall heat exchanger is used. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Refrigeration cycle device structure> The structure of a refrigeration cycle apparatus S according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a refrigerant circuit diagram of the refrigeration cycle apparatus S according to the embodiment of the present invention. The refrigeration cycle apparatus S is an apparatus that supplies cold or hot water to a living space, and includes an outdoor unit OU installed outside the living space and an indoor unit IU installed inside the living space.

[0017] The refrigeration cycle apparatus S according to the embodiment of the present invention includes a first refrigerant circuit C1 through which a first refrigerant circulates and an indoor refrigerant circuit C2 through which a second refrigerant circulates (hereinafter, this circuit will be referred to as the "second refrigerant circuit C2" as appropriate). For example, R290 is used as the first refrigerant. On the other hand, for example, water is used as the second refrigerant. A different-type refrigerant heat exchanger (described later) disposed in the outdoor unit OU exchanges heat between the first refrigerant and the second refrigerant, thereby supplying hot and cold water to the indoor unit IU.

[0018] The outdoor unit OU has a compressor 1, a different type of refrigerant heat exchanger 2, an expansion valve 3, an outdoor heat exchanger 4, and a switching valve 5 arranged inside it, which are connected in sequence via piping to form a first refrigerant circuit C1 that circulates a first refrigerant.

[0019] A second refrigerant circuit C2 that circulates a second refrigerant is connected to the different refrigerant heat exchanger 2, and is connected to a circulation pump 6 and an indoor terminal 7. Of these, the circulation pump 6 is disposed inside the outdoor unit OU, and the indoor terminal 7 is disposed inside the living space as an indoor unit IU.

[0020] The compressor 1 compresses a first refrigerant circulating inside the first refrigerant circuit C1. The different-type refrigerant heat exchanger 2 exchanges heat between the first refrigerant and a second refrigerant circulating in the second refrigerant circuit C2. The different-type refrigerant heat exchanger 2 will be described later.

[0021] In this embodiment of the present invention, a first refrigerant circulates through the first refrigerant circuit C1 and a second refrigerant circulates through the second refrigerant circuit C2. As described above, R290 (propane) is used as the first refrigerant. On the other hand, water, for example, is used as the second refrigerant. Note that the first refrigerant may be a refrigerant such as R32, which has been conventionally used as a refrigerant with a low GWP.

[0022] The expansion valve 3 is a valve whose opening degree can be adjusted. The outdoor heat exchanger 4 exchanges heat between outdoor air and the first refrigerant. The structures of the compressor 1 and the outdoor heat exchanger 4 will not be described here, but devices with various structures can be used.

[0023] The switching valve 5 switches the circulation path of the first refrigerant in the first refrigerant circuit C1 between a hot water generation operation in which the different-type refrigerant heat exchanger 2 functions as a condenser and the outdoor heat exchanger 4 functions as an evaporator, and a cold water generation operation in which the outdoor heat exchanger 4 functions as a condenser and the different-type refrigerant heat exchanger 2 functions as an evaporator.

[0024] The circulation pump 6 circulates the second refrigerant in the second refrigerant circuit C2. The indoor terminal 7 is, for example, a floor heating device or a hot water tank, and is placed in the living space. Hot water or cold water is supplied to the living space via the indoor terminal 7. Alternatively, hot water is used for heating, and cold water is used for cooling.

[0025] The refrigeration cycle apparatus S according to the embodiment of the present invention is provided with a plurality of sensors 8. Of these, the following two sensors are shown in Fig. 1. First, the first refrigerant circuit C1 is provided with a detection sensor 81 that detects a state detection value indicating the state of the first refrigerant flowing between the different-type-refrigerant heat exchanger 2 and the compressor 1.

[0026] The detection sensor 81 detects, for example, the pressure or temperature of the first refrigerant as a state detection value. It should be noted that the detection sensor 81 is assumed to be a pressure sensor. However, instead of a pressure sensor, a temperature sensor may be used as the detection sensor 81. The operation of the compressor 1 is controlled based on the state of the first refrigerant detected by the detection sensor 81. For example, when the refrigeration cycle apparatus S performs a hot water generation operation, the expansion valve 3 is controlled based on the pressure of the first refrigerant acquired by the detection sensor 81, thereby controlling the refrigerant temperature to an appropriate temperature for a target water temperature.

[0027] Meanwhile, the second refrigerant circuit C2 is provided with a heat exchanger outlet temperature sensor 82 that detects the temperature of the second refrigerant flowing between the different-type refrigerant heat exchanger 2 and the circulation pump 6. This heat exchanger outlet temperature sensor 82 detects the temperature of the second refrigerant flowing out of the different-type refrigerant heat exchanger 2.

[0028] When the refrigeration cycle device S performs hot water generation operation, the rotation speed of the compressor 1 is controlled based on the temperature of the second refrigerant obtained by the heat exchanger outlet temperature sensor 82, and it is determined whether the generated hot water is at the temperature desired by the user.

[0029] Furthermore, the refrigeration cycle apparatus S according to the embodiment of the present invention is provided with a control device 9 that controls each part of the refrigeration cycle apparatus S. Specifically, the control device 9 controls the operation of each part such as the compressor 1, the expansion valve 3, and the switching valve 5, and also determines whether to start the ice protection operation described below. The internal configuration of the control device 9 and the role of each part will be described later.

[0030] <Operational mode of refrigeration cycle device> Here, the operating modes of the refrigeration cycle apparatus include a hot water generating operation for generating hot water and a cold water generating operation for generating cold water. The operating modes performed in the refrigeration cycle apparatus S according to the embodiment of the present invention will be described in order using the circuit diagram of the refrigeration cycle apparatus S according to the embodiment of the present invention shown in Figures 2 and 3.

[0031] First, the hot water generating operation will be described. Fig. 2 is a refrigerant circuit diagram showing the flow of refrigerant when the hot water generating operation is performed in the refrigeration cycle apparatus S according to the embodiment of the present invention. In Fig. 2, the arrows shown near the first refrigerant circuit C1 or the second refrigerant circuit C2 indicate the direction in which the first refrigerant or the second refrigerant flows.

[0032] As shown in FIG. 2, the first refrigerant discharged from the compressor 1 flows into the different-type refrigerant heat exchanger 2 via the switching valve 5. In the different-type refrigerant heat exchanger 2, heat is exchanged between the first refrigerant (R290) and the second refrigerant (water) circulating through the second refrigerant circuit C2. That is, the second refrigerant absorbs heat from the first refrigerant and is heated, and then flows into the indoor terminal 7 by the circulation pump 6. This supplies hot water to the living space. Therefore, the different-type refrigerant heat exchanger 2 functions as a condenser.

[0033] The first refrigerant flowing out of the different-type refrigerant heat exchanger 2 passes through an expansion valve 3 and flows into an outdoor heat exchanger 4. The outdoor heat exchanger 4 functions as an evaporator, and heat is exchanged between the first refrigerant and the outdoor air. The first refrigerant flowing out of the outdoor heat exchanger 4 flows into the compressor 1 via a switching valve 5.

[0034] Next, the chilled water generating operation will be described. Fig. 3 is a refrigerant circuit diagram showing the flow of refrigerant when the chilled water generating operation is performed in the refrigeration cycle apparatus S according to the embodiment of the present invention.

[0035] The refrigerant compressed in the compressor 1 and discharged in a high-temperature, high-pressure state flows into the outdoor heat exchanger 4 via the switching valve 5, as shown by the arrow in FIG.

[0036] In the outdoor heat exchanger 4, heat is exchanged between the first refrigerant and the outdoor air. That is, the first refrigerant is cooled by the outdoor air, and the first refrigerant condenses. Therefore, in the cold water production operation, the outdoor heat exchanger 4 functions as a condenser.

[0037] The low-temperature first refrigerant then flows out of the outdoor heat exchanger 4 and passes through the expansion valve 3, where it is reduced in pressure to become a low-temperature, low-pressure first refrigerant. The low-temperature, low-pressure first refrigerant then flows into the different-type refrigerant heat exchanger 2, where heat exchange takes place between the first refrigerant (R290) and the second refrigerant (water) circulating in the second refrigerant circuit C2.

[0038] Through heat exchange in the different-type refrigerant heat exchanger 2, the first refrigerant absorbs heat from the second refrigerant and evaporates, and the second refrigerant that has flowed into the different-type refrigerant heat exchanger 2 is cooled, and chilled water is supplied indoors by the circulation pump 6. Therefore, in chilled water production operation, the different-type refrigerant heat exchanger 2 functions as an evaporator. The first refrigerant that has absorbed heat through heat exchange in the different-type refrigerant heat exchanger 2 then flows into the compressor 1 via the switching valve 5.

[0039] The flow of the refrigerant in the hot water generating operation and the cold water generating operation, and the functions of the different-type refrigerant heat exchanger 2 and the outdoor heat exchanger 4 have been described above with reference to FIGS.

[0040] <Structure of a heat exchanger for different refrigerants> As described above, in the refrigeration cycle apparatus S according to the embodiment of the present invention, for example, R290 (propane) is used as the first refrigerant. On the other hand, for example, water is used as the second refrigerant. In this way, the first refrigerant and the second refrigerant are different types of refrigerants. In the heterogeneous refrigerant heat exchanger 2, heat is exchanged between these two types of refrigerants. As the heterogeneous refrigerant heat exchanger 2, a single-wall heat exchanger or the above-mentioned double-wall heat exchanger can be used.

[0041] Therefore, the single-wall heat exchanger and the double-wall heat exchanger will be described with reference to the drawings. Fig. 4 is an explanatory diagram illustrating the structure of a single-wall heat exchanger, which is an example of a dissimilar refrigerant heat exchanger. Fig. 5 is an explanatory diagram illustrating the structure of a double-wall heat exchanger, which is an example of a dissimilar refrigerant heat exchanger 2 used in a refrigeration cycle apparatus S according to an embodiment of the present invention.

[0042] As shown in Fig. 4, the single-wall heat exchanger SW is a type of heat exchanger in which a first refrigerant and a second refrigerant flowing inside the heat exchanger are separated by a single wall (single wall) W. For ease of explanation, the refrigerant flowing from the top to the bottom of the drawing will be referred to as the first refrigerant, and the refrigerant flowing from the bottom to the top of the drawing will be referred to as the second refrigerant.

[0043] The portion where the flow direction of the first refrigerant is indicated by a downward arrow is the first refrigerant flow path P1. On the other hand, the portion where the flow direction of the second refrigerant is indicated by an upward arrow is the second refrigerant flow path P2. In the single-wall heat exchanger SW, the first refrigerant and the second refrigerant exchange heat through the single wall W. Therefore, the heat transfer performance between the refrigerants is high.

[0044] In contrast, as described above, in the double-wall heat exchanger DW shown in Figure 5, each heat transfer plate is constructed by overlapping two metal plates, and therefore each flow path through which each refrigerant flows has its own wall (double-wall). Therefore, heat exchange occurs through the wall that forms the flow path for the first refrigerant and the wall that forms the flow path for the second refrigerant.

[0045] 5, for ease of explanation, the refrigerant flowing from the top to the bottom of the drawing is referred to as the first refrigerant, and the refrigerant flowing from the bottom to the top of the drawing is referred to as the second refrigerant. The portion where the flow direction of the first refrigerant is indicated by a downward arrow is referred to as the first refrigerant flow path P1, as in the case of the single-wall heat exchanger SW shown in FIG. 4. On the other hand, the portion where the flow direction of the second refrigerant is indicated by an upward arrow is similarly referred to as the second refrigerant flow path P2.

[0046] 5, the first refrigerant flow path P1 has a wall W1, and the first refrigerant flows in the direction of the arrow (downward) through the first refrigerant flow path P1 surrounded by the wall W1. The second refrigerant flow path P2 has a wall W2, and the second refrigerant flows in the direction of the arrow (upward) through the second refrigerant flow path P2 surrounded by the wall W2. Heat exchange occurs between the first refrigerant flowing through the first refrigerant flow path P1 and the second refrigerant flowing through the second refrigerant flow path P2, which are arranged in this manner.

[0047] In the double-wall heat exchanger DW shown in Figure 5, an air layer is provided between the wall W1 that defines the first refrigerant flow path P1 and the wall W2 that defines the second refrigerant flow path P2. The thickness of this air layer affects heat transfer performance, and the thicker the air layer, the lower the heat transfer performance.

[0048] The thickness of this air layer will be referred to as "distance d" below, as shown in Figure 5. Therefore, even in double-walled heat exchangers, the greater the distance d, the lower the heat transfer performance, and the smaller the distance d, the higher the heat transfer performance. Furthermore, this distance d can be set to any value, and there are multiple double-walled heat exchangers for each distance d.

[0049] If the distance d is zero, that is, if there is no air gap between the wall W1 of the first refrigerant flow path P1 and the wall W2 of the second refrigerant flow path P2, the first refrigerant flow path P1 and the second refrigerant flow path P2 are separated by a single wall, i.e., the heat exchanger becomes a single-wall heat exchanger SW shown in FIG.

[0050] In contrast, in a double-wall heat exchanger, each of the refrigerant flow paths has a wall (wall W1, wall W2). Therefore, even if one refrigerant flow path is damaged, the impact on the refrigerant flowing through the other refrigerant flow path can be minimized.

[0051] Taking the refrigerant used in the embodiment of the present invention as an example, the first refrigerant in the embodiment of the present invention is, for example, R290 (propane), and the second refrigerant is water. In this case, if the first refrigerant flows into the different-type refrigerant heat exchanger 2 at a very low temperature, there is a possibility that the second refrigerant, water, which is the heat-exchanged refrigerant, will freeze. When water freezes, its volume expands, and therefore, the freezing of the second refrigerant may damage the wall of the second refrigerant flow path P2.

[0052] In a single-wall heat exchanger, there is only one wall separating the first refrigerant flow path P1 and the second refrigerant flow path P2. If this wall is damaged, the first refrigerant (propane) may become mixed with the second refrigerant (water) because the first refrigerant (propane) has a higher pressure. If the second refrigerant circulates through the second refrigerant circuit C2 while the first refrigerant is mixed with the second refrigerant, there is an increased risk of the first refrigerant (propane) leaking into the living space via the indoor terminal 7.

[0053] On the other hand, in the case of a double-wall heat exchanger, as shown in Figure 5, a wall W1 is provided in the first refrigerant flow path P1, and a wall W2 is provided in the second refrigerant flow path P2. An air layer is formed between these walls W1 and W2, ensuring the thickness of the air layer, represented by the distance d. Therefore, with this configuration, even if the wall W of the second refrigerant flow path P2 is damaged due to freezing of the second refrigerant, immediate damage to the wall W1 of the first refrigerant flow path P1 can be prevented. Alternatively, damage to the first refrigerant flow path P1 can be delayed.

[0054] Therefore, unlike a single-wall heat exchanger, in a double-wall heat exchanger, even if the wall W2 of the second refrigerant flow path P2 is damaged, it is unlikely that the wall W1 of the first refrigerant flow path P1 will be damaged. Therefore, the first refrigerant mixes with the second refrigerant from the first refrigerant flow path P1, and the second refrigerant circulates through the second refrigerant circuit C2, thereby preventing the first refrigerant (propane) from leaking into the living space via the indoor terminal 7.

[0055] <Configuration of ice protection device> 6 is a block diagram showing the functions of the control device 9 in the refrigeration cycle apparatus S according to the embodiment of the present invention. The control device 9 includes an acquisition unit 91, a storage unit 92, a determination unit 93, and a drive control unit 94.

[0056] The acquisition unit 91 acquires information relating to a state detection value indicating the state of the first refrigerant detected by the detection sensor 81 and the temperature of water, which is the second refrigerant, detected by the heat exchanger outlet temperature sensor .

[0057] Furthermore, when detection sensor 81 is a pressure sensor, acquisition unit 91 calculates the temperature of the first refrigerant from the pressure value of the first refrigerant, which is the detected state detection value. Information about the temperature of the first refrigerant calculated by acquisition unit 91 is used by determination unit 93, which will be described later, to determine whether to start ice protection operation.

[0058] The storage unit 92 stores, for example, a threshold value used in determining whether to start the freeze protection operation executed by the determination unit 93. Furthermore, since the timing of starting the freeze protection operation differs depending on the type and specifications of the different-type refrigerant heat exchanger 2, as will be described later, the storage unit 92 stores information about the types of the different-type refrigerant heat exchangers 2 connected to the first refrigerant circuit C1 and the second refrigerant circuit C2 in the refrigeration cycle apparatus S.

[0059] The information on the type and specifications of the dissimilar refrigerant heat exchanger 2 is, for example, information that, when the dissimilar refrigerant heat exchanger 2 to be connected is a single-wall heat exchanger, the distance d between one refrigerant passage (first refrigerant passage P1) through which the first refrigerant flows and the other refrigerant passage (second refrigerant passage P2) through which the second refrigerant flows is zero. Also, when the dissimilar refrigerant heat exchanger 2 is a double-wall heat exchanger, the information is information on the length of the distance d between one refrigerant passage (first refrigerant passage P1) through which the first refrigerant flows and the other refrigerant passage (second refrigerant passage P2) through which the second refrigerant flows.

[0060] The determination unit 93 determines the timing of whether or not the refrigeration cycle apparatus S in the embodiment of the present invention starts the freeze protection operation. Here, the above-mentioned different-type refrigerant heat exchanger 2 may be damaged, for example, when the refrigeration cycle apparatus S performs a chilled water production operation. When the refrigeration cycle apparatus S performs a chilled water production operation, the first refrigerant discharged from the compressor 1 passes through the switching valve 5, the outdoor heat exchanger 4, the expansion valve 3, and the different-type refrigerant heat exchanger 2, as described with reference to FIG. 3, and is then drawn into the compressor 1.

[0061] During this chilled water production operation, if the temperature of the first refrigerant is too low when heat is exchanged with the second refrigerant in the different-type refrigerant heat exchanger 2, the second refrigerant, water, that is performing heat exchange, may freeze. That is, if the second refrigerant freezes, the refrigerant flow path through which the second refrigerant flows may be damaged in the different-type refrigerant heat exchanger 2. For example, in the case of a single-wall heat exchanger, if the refrigerant flow path is damaged, the first refrigerant may mix with the second refrigerant through the damaged area, and the first refrigerant may leak into the living space via the second refrigerant circuit C2.

[0062] In particular, when the first refrigerant is propane, it is important to prevent the first refrigerant from leaking into the living space because the first refrigerant is flammable. To achieve this, it is necessary to prevent the second refrigerant from freezing due to heat exchange in the different refrigerant heat exchanger 2. Therefore, the refrigeration cycle apparatus S according to the embodiment of the present invention performs control to prevent the second refrigerant from freezing by transitioning from normal operation (chilled water generation operation) to ice protection operation at an appropriate timing based on the state of the first refrigerant.

[0063] The freeze protection operation prevents the temperature of the first refrigerant from decreasing too much by, for example, reducing the rotation speed of compressor 1. If the temperature of the first refrigerant does not decrease sufficiently even when the rotation speed of compressor 1 is reduced, the operation of compressor 1 may be stopped to stop cooling of the second refrigerant in different-type refrigerant heat exchanger 2.

[0064] As described above, the different refrigerant heat exchanger 2 attached to the refrigeration cycle apparatus S may be a single-wall heat exchanger or a double-wall heat exchanger. Even in the case of a double-wall heat exchanger, the distance d varies and the heat transfer performance varies.

[0065] As such, there are various types of dissimilar refrigerant heat exchangers 2 used in the refrigeration cycle device S that have different heat transfer performance. Therefore, if the judgment criteria can be changed according to the distance d when determining the timing to switch from normal operation to ice protection operation, the criteria can be used in common for various types of dissimilar refrigerant heat exchangers 2 that have different heat transfer performance.

[0066] The difference in heat transfer performance from the first refrigerant to the second refrigerant in the different-type refrigerant heat exchanger 2 due to differences in the distance d will be explained using Fig. 7. Fig. 7 is a graph showing an example of the change in temperature of the refrigerant flowing out from the outlet of the different-type refrigerant heat exchanger 2 for each different different-type refrigerant heat exchanger 2 in a refrigeration cycle apparatus S according to an embodiment of the present invention. In the graph shown in Fig. 7, the horizontal axis represents time (min), while the vertical axis represents the temperature (°C) of the first refrigerant or the second refrigerant.

[0067] The graph in Figure 7 shows three lines: a dashed-dotted line that indicates the temperature decrease of the first refrigerant (propane) over time, and a solid and dashed line that indicate the temperature decrease of the second refrigerant (water). Here, the solid line indicates the temperature change of the second refrigerant when a single-wall heat exchanger (d = 0) is used as the different refrigerant heat exchanger 2. On the other hand, the dashed line indicates the temperature change of the second refrigerant when a double-wall heat exchanger (d = d1) is used as the different refrigerant heat exchanger 2.

[0068] Figure 7 also shows times m1 and m2. The water temperature at the outlet of the single-wall heat exchanger at time m1 is Tw1s, and the water temperature at the outlet of the double-wall heat exchanger is Tw1d. The water temperature at the outlet of the single-wall heat exchanger at time m2 is Tw2s, and the water temperature at the outlet of the double-wall heat exchanger is Tw2d.

[0069] Furthermore, the temperature of the first refrigerant at time m1 is Tr1, and the temperature of the first refrigerant at time m2 is Tr2. Looking at the graph in Figure 7, the temperature of the first refrigerant changes (decreases) from temperature Tr1 to temperature Tr2 from time m1 to time m2.

[0070] (Accordingly, in FIG. 7, the solid line indicating the temperature change in the single-wall heat exchanger and the dashed line indicating the temperature change in the double-wall heat exchanger are shown partially overlapping.) As described above, when the temperature of the first refrigerant gradually decreases from time m1 to time m2, the water temperature at the outlet of the double-wall heat exchanger, indicated by the dashed line, decreases at a slower rate than the water temperature at the outlet of the single-wall heat exchanger, indicated by the solid line.

[0071] That is, looking at the dashed line showing the change in temperature of the second refrigerant in the double-wall heat exchanger and the solid line showing the change in temperature of the second refrigerant in the single-wall heat exchanger in Figure 7, the former maintains the water temperature Tw1d at time m1 for a longer period of time than the latter, and then the temperature gradually decreases.

[0072] In other words, the change in temperature of the second refrigerant in the single-wall heat exchanger begins (starts to decrease) earlier than the change in temperature of the second refrigerant in the double-wall heat exchanger. As a result, a temperature difference appears between the temperature Tw2s of the second refrigerant in the single-wall heat exchanger and the temperature Tw2d of the second refrigerant in the double-wall heat exchanger at time m2.

[0073] Next, an example of the freeze protection operation will be shown using Fig. 8. Fig. 8 is a graph showing an example of the temperature changes of the refrigerant temperature and the water temperature for each of the different refrigerant heat exchangers when the freeze protection operation is performed in the refrigeration cycle apparatus according to the embodiment of the present invention. In the graph shown in Fig. 8, the horizontal axis represents time (min), while the vertical axis represents the temperature (°C) of the first refrigerant or the second refrigerant.

[0074] The temperature of the first refrigerant, indicated by the dashed line, is calculated based on the state detection value indicating the state of the first refrigerant detected by the detection sensor 81. Furthermore, on the vertical axis, a two-dot dashed line indicates high temperature areas, and a dotted line indicates low temperature areas.

[0075] The two-dot chain line shown in the higher temperature area indicates the threshold value Tf at which the determination unit 93 determines whether to transition from normal operation to ice protection operation (decides to start ice protection operation). The threshold value Tf is, for example, 2°C. On the other hand, the dotted line shown in the lower temperature area indicates the temperature Tlim below which the second refrigerant that has undergone heat exchange in the different-type refrigerant heat exchanger 2 is more likely to freeze. The temperature Tlim is, for example, 0°C.

[0076] When the temperature of the first refrigerant falls below the threshold value Tf, the control device 9 starts the ice protection operation and reduces the rotation speed of the compressor, thereby suppressing a decrease in the temperature of the first refrigerant and preventing the refrigerant temperature from falling below the temperature Tlim.

[0077] 8, the change in the temperature of the first refrigerant after it falls below the threshold Tf is shown by a dashed-dotted line, and the change in the temperature of the second refrigerant is shown by a solid and dashed lines. The horizontal axis also shows time m3 (hereinafter, this time may be referred to as "reference time m3" as appropriate) and time m4.

[0078] These times indicate the control timings at which the control device 9 controls the refrigeration cycle device S. That is, at reference time m3, the temperature of the first refrigerant is detected by instruction from the control device 9 and compared with the threshold value Tf. When it is determined that the temperature of the first refrigerant is lower than the threshold value Tf, the control device 9 starts the ice protection operation.

[0079] As described above, it takes time from when the ice protection operation is started (time m3) until the first refrigerant temperature, which has once decreased, starts to rise (time m4).

[0080] Next, we will explain the temperature change of the second refrigerant. In the case of a single-wall heat exchanger, heat exchange occurs between the first refrigerant and the second refrigerant separated by a single wall. In contrast, in the case of a double-wall heat exchanger, a wall is provided for each refrigerant flow path, making heat exchange more difficult than in a single-wall heat exchanger. In other words, the amount of energy imparted by the first refrigerant to the second refrigerant is less in a double-wall heat exchanger than in a single-wall heat exchanger.

[0081] Therefore, when the dissimilar refrigerant heat exchanger 2 is a double-wall heat exchanger, the temperature of the second refrigerant flowing out of the dissimilar refrigerant heat exchanger 2 decreases more slowly than the temperature of the second refrigerant flowing out of a single-wall heat exchanger. Therefore, as shown in Figure 8, the dashed line representing the temperature change of the second refrigerant in the double-wall heat exchanger has a gentler slope than the solid line representing the temperature change of the second refrigerant in the single-wall heat exchanger. At time m4, when the temperature of the first refrigerant begins to rise, there is a temperature difference Td between the temperature of the second refrigerant flowing out of the single-wall heat exchanger and the temperature of the second refrigerant flowing out of the double-wall heat exchanger.

[0082] Therefore, based on the temperature of the second refrigerant flowing out of the double-wall heat exchanger at time m4, the second refrigerant is less likely to freeze in the double-wall heat exchanger, which is the heterogeneous refrigerant heat exchanger 2, and there is a possibility that excessive protective operation is occurring.

[0083] Therefore, for example, even if a double-wall heat exchanger is used as the different refrigerant heat exchanger 2, if the freeze protection operation is started in the same way as in the case of a single-wall heat exchanger, the freeze protection operation will be performed even though there is no risk of freezing of the second refrigerant that exchanges heat with the first refrigerant.

[0084] When the freeze protection operation is started, as described above, measures are taken, such as reducing the rotation speed of the compressor 1. Therefore, even though there is no risk of freezing, the chilled water production operation is stopped, and for example, the temperature of the supplied chilled water gradually increases, which may cause discomfort to the user.

[0085] Therefore, even if the heat transfer performance differs depending on the type of the heterogeneous refrigerant heat exchanger 2, it is necessary to determine whether or not anti-freeze operation is necessary depending on the type of the heterogeneous refrigerant heat exchanger 2, avoid stopping the cold water generation operation as much as possible, and perform anti-freeze operation only when necessary for safety reasons to avoid freezing of the second refrigerant.

[0086] <Ice protection operation start determination> Therefore, in the embodiment of the present invention, the determination unit 93 determines the timing to start the ice protection operation using an appropriate determination method according to the distance d, as described below. This allows reliable prevention of freezing in the refrigeration cycle apparatus S according to the type and specifications of the refrigerant heat exchanger 2.

[0087] <<Ice protection operation start determination (first determination method)>> A first determination method for transitioning from normal operation (chilled water generating operation) to freeze protection operation by the determination unit 93 will be described. Fig. 9 is a graph illustrating the first determination method for controlling the start of freeze protection operation in the refrigeration cycle apparatus S according to an embodiment of the present invention.

[0088] In the graph shown in Fig. 9, the vertical axis indicates the temperature (°C) of the first refrigerant, the horizontal axis indicates time (min), and the threshold value Tf and temperature Tlim are shown, similar to Fig. 8. In Fig. 9, the solid line indicates how the first refrigerant temperature gradually decreases during the chilled water production operation when the different-type refrigerant heat exchanger 2 is a single-wall heat exchanger.

[0089] Similarly, the dashed line shows how the temperature of the first refrigerant gradually decreases during the chilled water production operation when the different-type refrigerant heat exchanger 2 is a double-wall heat exchanger. However, in the first determination method for controlling the start of the freeze protection operation described below, the temperature of the first refrigerant in a single-wall heat exchanger shown by the solid line will be used as an example.

[0090] The first determination method shown in Figure 9 is a method in which the determination cycle used by the determination unit 93 to determine the timing to start ice protection operation is changed depending on the distance d. The graph in Figure 9 shows solid and dashed lines parallel to the vertical axis. These lines indicate the timing of the determination process by the determination unit 93. Therefore, adjacent solid lines or adjacent dashed lines indicate the determination cycle by the determination unit 93, respectively.

[0091] In FIG. 9, the period P is the period indicated by the double-headed arrow P of the solid line. In FIG. 9, the timing of the determination process closest to the origin is designated as "time P1", and the timings of the determinations that appear as time passes are represented as "time P2" and "time P3".

[0092] Based on the state detection value of the first refrigerant detected by the detection sensor 81 at the timing of the first determination process by the determination unit 93 (the portion indicated by the arrow of the solid line shown at time P1), the temperature of the first refrigerant calculated by the acquisition unit 91 is set as temperature T1. When the temperature T1 of the first refrigerant is compared with the threshold value Tf, it is in the relationship of T 1 > Tf and has not yet fallen below the threshold value Tf. Therefore, in this case, the determination to start the ice protection operation is not made, and the normal operation (chilled water generation operation) is continued.

[0093] Next, at the timing of the second determination process (the portion indicated by the arrow of the solid line shown at time P2), although the temperature T2 of the first refrigerant obtained by the above-described calculation process is closer to the threshold value Tf than the temperature T1, it has not yet fallen below the threshold value Tf. Therefore, the normal operation (chilled water generation operation) is continued.

[0094] Then, at the timing of the third determination process (the portion indicated by the arrow of the solid line shown at time P3), the temperature T3 of the first refrigerant falls below the threshold value Tf and is in the relationship of T 3 < Tf with respect to the threshold value Tf. Therefore, in this determination process, the determination unit 93 determines the timing to start the ice protection operation.

[0095] However, the temperature T3 of the first refrigerant in this third determination process is a temperature close to the temperature Tlim which is the temperature at which the second refrigerant that exchanges heat in the different-kind refrigerant heat exchanger 2 freezes. Therefore, even if the operation is switched from the chilled water generation operation to the ice protection operation and the ice protection operation is started at this time point of time P3, there is a possibility that it may not be in time to avoid the freezing of the second refrigerant.

[0096] Therefore, by adjusting the cycle of the determination process by the determination unit 93, it is possible to reliably prevent the second refrigerant from freezing by the freeze protection operation. For example, the timing at which the determination unit 93 starts the freeze protection operation is inversely proportional to the length of the distance d. In this case, when the distance d is short, the cycle of the determination process is shorter than when the distance d is long. Note that the cycles of the determination process (hereinafter also referred to as cycle p) that can be selected by the determination unit 93 may be stored in advance in the storage unit 92, for example, by associating the distance d with the cycle of the determination process.

[0097] The cycle p of the new determination process selected by the determination unit 93 is indicated by a dashed line in the graph of Fig. 9. For ease of explanation, in Fig. 9, the timing of the new first determination process (time p1) is aligned with the timing of the first determination process described above (time P1).

[0098] This new determination cycle is the period indicated by the dashed double-headed arrow p between adjacent dashed lines. For ease of explanation, in Fig. 9, the determination process timing closest to the origin is designated as "time p1," and the determination times that appear over time are designated as "time p2" through "time p6."

[0099] Next, the new determination process cycle p will be described. As shown in Fig. 9, the new determination process cycle p is shorter than the determination process cycle P described above. In other words, when the distance d is short, the determination cycle is set shorter than when the distance d is long. Therefore, when the distance d is short, the determination process by the determination unit 93 is performed more frequently.

[0100] In the embodiment of the present invention, while two determination processes (times P1 and P2) are performed in a determination process cycle P, three determination processes (times p1 to p3) are performed in a new determination process cycle p.

[0101] At the timing of the first determination process by the determination unit 93 (the part indicated by the dashed arrow shown at time p1), the temperature of the first refrigerant calculated by the acquisition unit 91 based on the state detection value of the first refrigerant detected by the detection sensor 81 is set as temperature t1. When the temperature t1 of the first refrigerant is compared with the threshold value Tf, it is in the relationship of t1 > Tf and has not yet fallen below the threshold value Tf. Therefore, in this case, as a result of determining whether to start the ice protection operation, it is not determined to start the ice protection operation, and normal operation (chilled water generation operation) is continued.

[0102] Also, at the timings of the second and third determination processes (times p2 and p3), although the temperatures t2 and t3 of the first refrigerant both approach the threshold value Tf more than the temperature t1, they have not yet fallen below the threshold value Tf. Therefore, normal operation (chilled water generation operation) is continued.

[0103] The temperature t4 of the first refrigerant at the timing of the next fourth determination process (time p4) is below the threshold value Tf. Therefore, the determination unit 93 determines to start the ice protection operation at the timing of time p4 (the temperature t4 of the first refrigerant).

[0104] The start of the ice protection operation in the original determination process cycle P by the determination unit 93 is at time P3, and the start of the ice protection operation in the new determination process cycle p is at time p4. Also, the temperature of the first refrigerant at each time is "T3" for the former and "t4" for the latter.

[0105] When comparing the temperature difference between the temperature T3 of the first refrigerant and the temperature Tlim as "Td1" and the temperature difference between the temperature t4 of the first refrigerant and the temperature Tlim as "Td2", they are in the relationship of Td1 < Td2. That is, because the new determination process cycle p has a shorter cycle than the original determination process cycle P, it is possible to grasp that the temperature of the first refrigerant has fallen below the threshold value Tf at the timing immediately after the temperature of the first refrigerant has fallen below the threshold value Tf.

[0106] Thus, the shorter the determination process cycle, the more frequently determination unit 93 executes the determination process, and so even if it is determined that the temperature, such as first refrigerant temperature t3, is slightly higher than threshold Tf and will not fall below threshold Tf, the next determination process cycle will arrive soon. Therefore, a long determination process cycle can prevent the determination process from being executed when the first refrigerant temperature has significantly dropped below threshold Tf, as in the case of first refrigerant temperature T3.

[0107] In other words, the shorter the cycle of the determination process, the more likely it is that the temperature of the first refrigerant used to determine whether to start the ice protection operation will fall significantly below the threshold Tf, and the sooner the timing to start the ice protection operation will be determined after the temperature of the first refrigerant falls below the threshold Tf. By performing such a determination, the ice protection operation can reliably prevent freezing.

[0108] The cycle of the process for determining whether to start the freeze protection operation by the determination unit 93, as explained above, can be applied to both single-wall and double-wall heat exchangers. In other words, it is possible to determine whether to perform freeze protection even when the heat transfer performance differs depending on the type of heat exchanger.

[0109] The determination unit 93 determines whether the second refrigerant temperature is equal to or higher than the threshold value Tf. If the second refrigerant temperature falls below the threshold value Tf, the determination unit 93 determines to transition from normal operation (chilled water generation operation) to freeze protection operation (start of freeze protection operation), and the refrigeration cycle apparatus S stops the normal operation and starts the freeze protection operation.

[0110] Specifically, the decision made by the determination unit 93 is transmitted to the drive control unit 94, and the drive control unit 94, for example, stops the operation of the compressor 1. Note that the ice protection operation is not limited to stopping the operation of the compressor 1, and the ice protection operation may be performed by controlling the rotation speed of the compressor 1, for example.

[0111] When the freeze protection operation is started and the temperature of the first refrigerant becomes equal to or higher than the threshold value Tf, the risk of the second refrigerant freezing is avoided, and the judgment unit 93 terminates the freeze protection operation and transitions to normal operation (chilled water generation operation).

[0112] If the temperature of the first refrigerant does not reach or exceed the threshold value Tf after a predetermined time has elapsed, the determination unit 93 finally forcibly stops the entire refrigeration cycle apparatus S and performs a fault determination. Note that the slope from when the freeze protection operation is started until the temperature exceeds the threshold value Tf is known in advance. Therefore, the time from when the freeze protection operation is started until the temperature exceeds the threshold value Tf is also known, and the preset time is set based on this known time.

[0113] This preset time is measured by, for example, a timer unit not shown in Fig. 6. That is, the timer unit receives a timing start instruction from the determination unit 93 when ice protection operation is started, which determines the timing to start timing, and starts measuring the preset time.

[0114] <Operation of Refrigeration Cycle Device According to First Determination Method> Next, the control flow in the control device 9 when transitioning from the above-mentioned normal operation (chilled water generating operation) to the start of the freeze protection operation and then transitioning back to the normal operation will be described with reference to Fig. 10. Fig. 10 is a flowchart showing the processing flow in the above-mentioned first determination method regarding control of the start of the freeze protection operation in the refrigeration cycle apparatus S according to the embodiment of the present invention.

[0115] As described above, in the embodiment of the present invention, it is assumed that the chilled water generating operation, which is a normal operation, is being performed. Therefore, the chilled water generating operation is started first (ST1). After that, the acquisition unit 91 of the control device 9 acquires the state detection value of the first refrigerant detected by the detection sensor 81 (ST2), and calculates the temperature of the first refrigerant based on the state detection value (ST3).

[0116] Using the calculated temperature of the first refrigerant, the determination unit 93 compares the temperature of the first refrigerant with the threshold value Tf (ST4). As described above, the determination unit 93 determines whether the temperature of the first refrigerant is lower than the threshold value Tf (ST5).

[0117] As a result, if the temperature of the first refrigerant is equal to or higher than the threshold value Tf (NO in ST5), the process returns to step ST2, and the judgment unit 93 waits for the timing of the next judgment process and again uses the temperature of the first refrigerant to make a judgment as to whether or not to start ice protection operation.

[0118] Conversely, if the temperature of the first refrigerant falls below the threshold value Tf (YES in ST5), the determination unit 93 determines the timing to start the freeze protection operation depending on the type of different-type refrigerant heat exchanger 2 installed in the refrigeration cycle apparatus S (ST6). Then, in order to perform the process defined as the freeze protection operation, the drive control unit 94 outputs a signal to the compressor 1 to control the rotation speed of the compressor 1, and the freeze protection operation is started (ST7).

[0119] Specifically, based on an instruction from the determination unit 93, the drive control unit 94 controls the rotation speed of the compressor 1 to be reduced to a predetermined rotation speed (for example, the lowest rotation speed at which the compressor 1 can operate (for example, 20 rps)) (ST8). While the ice protection operation is being performed and the rotation speed of the compressor 1 is being reduced, the determination unit 93 determines whether the temperature of the first refrigerant has become equal to or higher than the threshold value Tf (ST9).

[0120] If the temperature of the first refrigerant is equal to or higher than the threshold value Tf (YES in ST9), the determination unit 93 ends the freeze protection operation and transitions to normal operation (chilled water generation operation) (ST10).

[0121] On the other hand, if the temperature of the first refrigerant does not become equal to or higher than the threshold value Tf (NO in ST9), the determination unit 93 further checks the time since the temperature of the first refrigerant fell below the threshold value Tf and determines whether a predetermined time has elapsed (ST11). If the predetermined time has not elapsed (NO in ST11), the process returns to step ST8, and the drive control unit 94 controls the rotation speed of the compressor 1 to be reduced.

[0122] On the other hand, if a predetermined time has elapsed since the temperature of the first refrigerant fell below the threshold value Tf (YES in ST11), the judgment unit 93 performs control to forcibly stop the entire refrigeration cycle device S from a safety standpoint (fault judgment) (ST12).

[0123] By adopting the control method of the refrigeration cycle device S described above, it is possible to determine whether or not the heat exchanger has been frozen, even if the heat transfer performance of the heat exchanger is different. Furthermore, by ensuring reliable freezing prevention, it is possible to prevent refrigerant from leaking into the living space, thereby improving safety for users.

[0124] Furthermore, various heat exchangers, such as single-wall heat exchangers and double-wall heat exchangers, can be used as the heterogeneous refrigerant heat exchanger 2. However, with the control method described above, it is not necessary to change the judgment method depending on the type of heat exchanger, and it is possible to standardize the method. Therefore, the development cost of the judgment method can be reduced.

[0125] <<Ice protection operation start determination (second determination method)>> Next, a second determination method according to the present invention will be described. In the second determination method, the same components as those described in the first determination method are denoted by the same reference numerals, and redundant descriptions of the same components will be omitted.

[0126] In the first determination method, the control of the start of ice protection operation has been described, which enables the ice protection operation to be started at an appropriate time by changing the cycle of the process for determining the start of ice protection operation in accordance with the distance d.

[0127] In the refrigeration cycle apparatus S in the second determination method of the present invention, a second control method will be described in which a determination process is performed using a method different from the first determination method described above, and the freeze protection operation is started at an appropriate timing. Figures 11 and 12 are graphs illustrating the second determination method in controlling the start of the freeze protection operation in the refrigeration cycle apparatus S according to the embodiment of the present invention.

[0128] The graphs shown in Figures 11 and 12 are similar to Figures 8 and 9 in that the vertical axis shows temperature (°C) and the horizontal axis shows time (min), and that the threshold value Tf and the temperature Tlim at which the second refrigerant, water, may freeze are shown.

[0129] 11 and 12, the graphs show dashed lines that indicate the temperature decrease of the first refrigerant over time, as shown in Fig. 8. Here, the solid line in Fig. 11 shows the temperature change of the first refrigerant when a single-wall heat exchanger is used as the different refrigerant heat exchanger 2. On the other hand, the dashed line in Fig. 12 shows the temperature change of the first refrigerant when a double-wall heat exchanger is used as the different refrigerant heat exchanger 2.

[0130] As described above, the reference time m3 is the time when it is determined that the temperature of the first refrigerant discharged from the different-type refrigerant heat exchanger 2 and detected by the detection sensor 81 has fallen below the threshold value Tf. In the case of a single-wall heat exchanger, the temperature of the second refrigerant decreases at a slope indicated by the solid line in FIG.

[0131] Therefore, in the refrigeration cycle device S of an embodiment of the present invention, when a single-wall heat exchanger is used as the heterogeneous refrigerant heat exchanger 2 and the judgment unit 93 determines that the temperature of the first refrigerant has fallen below the threshold value Tf, control is performed to start ice protection operation when time J has elapsed since the judgment.

[0132] 11, time J is set to a short time after the temperature of the first refrigerant falls below threshold Tf. If the ice protection operation is started shortly after the determination by determination unit 93, the temperature of the first refrigerant decreases only slightly from threshold Tf, and the temperature of the first refrigerant can be raised to or above threshold Tf before it reaches temperature Tlim. This also prevents the second refrigerant from freezing.

[0133] On the other hand, when a double-wall heat exchanger is used as the heterogeneous refrigerant heat exchanger 2, control is performed to start the ice protection operation after a time K different from that in the case of a single-wall heat exchanger has elapsed after the judgment unit 93 determines that the temperature of the first refrigerant has fallen below the threshold value Tf.

[0134] Furthermore, when comparing the ``time J'' from when it is determined that the temperature of the first refrigerant has fallen below the threshold value Tf in the case of a single-wall heat exchanger to when the anti-freeze operation is started with the ``time K'' from when it is determined that the temperature of the first refrigerant has fallen below the threshold value Tf in the case of a double-wall heat exchanger to when the anti-freeze operation is started, the latter is longer than the former.

[0135] That is, in the case of a double-wall heat exchanger, the time from when it is determined that the temperature of the first refrigerant has fallen below the threshold Tf until the freeze protection operation is started is set longer than in the case of a single-wall heat exchanger. In the case of a double-wall heat exchanger, the freeze protection operation is started after the elapse of time K from the reference time m3.

[0136] The above description focuses on a single-wall heat exchanger and a double-wall heat exchanger as the dissimilar refrigerant heat exchanger 2. As described above, heat transfer performance differs depending on the value of the distance d, and therefore the time from when it is determined that the temperature of the first refrigerant has fallen below the threshold value Tf until the freeze protection operation is started is adjusted according to the distance d.

[0137] The second determination method described above is a second control method that changes the time from when it is determined that the temperature of the first refrigerant has fallen below the threshold value Tf to when the ice protection operation is started, depending on the type of heat exchanger used as the heterogeneous refrigerant heat exchanger 2. As a method for determining the timing of when to start the ice protection operation, the threshold value Tf may be made variable depending on the distance d.

[0138] It should be noted that the present invention is not limited to the above-described embodiment, but is merely an example of the present invention. In the implementation stage, the components can be modified and embodied without departing from the spirit of the invention, and various changes and improvements can be made to the above-described embodiment. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiment. [Explanation of symbols]

[0139] 1···Compressor, 2···Different refrigerant heat exchanger, 3···Expansion valve, 4···Outdoor heat exchanger, 5···Switching valve, 6···Circulation pump, 7···Indoor terminal, 8···Sensor, 81···Detection sensor, 82···Heat exchanger outlet temperature sensor, 9···Control device, 90···Ice protection device, 91···Acquisition unit, 92···Memory unit, 93···Determination unit, 94···Drive control unit, C···Refrigerant circuit, S···Refrigeration cycle device, Tf, Tf'··Threshold value

Claims

1. a refrigerant circuit for circulating a first refrigerant; a compressor that compresses the first refrigerant; an outdoor heat exchanger that exchanges heat between outdoor air and the first refrigerant; An expansion valve; a different-type refrigerant heat exchanger that exchanges heat between the first refrigerant and the second refrigerant; a detection sensor that detects a refrigerant state quantity that indicates a state of the first refrigerant flowing between the different-type refrigerant heat exchanger and the compressor; a control device that determines whether to start an ice protection operation based on the refrigerant state quantity detected by the detection sensor in accordance with the heat transfer performance of the different-type refrigerant heat exchanger; A refrigeration cycle device comprising:

2. 2. The refrigeration cycle device according to claim 1, wherein the heat transfer performance is determined based on a distance d between one refrigerant passage through which the first refrigerant flows and the other refrigerant passage through which the second refrigerant flows, and the heat transfer performance is determined to be lower as the distance d increases.

3. The control device an acquisition unit that acquires the refrigerant state quantity detected by the detection sensor; a determination unit that calculates a temperature of the first refrigerant from the refrigerant state quantity acquired by the acquisition unit, compares the temperature of the first refrigerant with a preset threshold, and determines whether the temperature of the first refrigerant has fallen below the threshold; a drive control unit that performs the ice protection operation by controlling a rotation speed of the compressor when the determination unit determines that the temperature of the first refrigerant has fallen below the threshold value; The refrigeration cycle device according to claim 1, further comprising:

4. 4. The refrigeration cycle device according to claim 3, wherein a cycle of judgment in the judgment unit is set in accordance with the distance d.

5. 5. The refrigeration cycle apparatus according to claim 4, wherein the determination cycle is set shorter for the shorter distance d than for the longer distance d.

6. The refrigeration cycle device described in claim 3, characterized in that, for the judgment by the judgment unit, the time when the temperature of the first refrigerant falls below the threshold is set as a reference time, and the time from the reference time to the start time of the ice protection operation is set according to the distance d.

7. 7. The refrigeration cycle apparatus according to claim 6, wherein the time from the reference time to the start time of the ice protection operation is set so that the shorter distance d is shorter than the longer distance d.

8. 2. The refrigeration cycle device according to claim 1, wherein the different refrigerant heat exchanger is connected to an indoor terminal of the circulating pump by a refrigerant piping, and is connected to an indoor refrigerant circuit through which the second refrigerant circulates by operation of the circulating pump.

9. 9. The refrigeration cycle device according to claim 1, wherein the second refrigerant is water.

10. a refrigerant circuit for circulating a first refrigerant; a compressor that compresses the first refrigerant; an outdoor heat exchanger that exchanges heat between outdoor air and the first refrigerant; An expansion valve; a different-type refrigerant heat exchanger that exchanges heat between the first refrigerant and the second refrigerant; a detection sensor that detects a state detection value that indicates a state of the first refrigerant flowing between the different-type refrigerant heat exchanger and the compressor; a control device that determines whether to start an ice protection operation based on the state detection value detected by the detection sensor in accordance with the heat transfer performance of the different-type refrigerant heat exchanger, The heat transfer performance is determined based on a distance d between one refrigerant passage through which the first refrigerant flows and the other refrigerant passage through which the second refrigerant flows, and the control method for controlling a refrigeration cycle device is characterized in that the criteria for determining whether to start the ice protection operation are varied depending on the distance d.

11. After the refrigeration cycle device starts the cold water generation operation, calculating a temperature of the first refrigerant from the state detection value detected by the detection sensor; comparing the calculated temperature of the first refrigerant with a preset threshold value to determine whether the temperature of the first refrigerant is lower than the threshold value; starting the ice protection operation by controlling the rotation speed of the compressor when it is determined that the temperature of the first refrigerant is lower than the threshold value; The method for controlling a refrigeration cycle apparatus according to claim 10, further comprising:

12. 12. The method for controlling a refrigeration cycle apparatus according to claim 10, wherein a cycle of determination in the control device is set in accordance with the distance d.

13. The control method for a refrigeration cycle device according to claim 12, characterized in that, in the judgment step in the control device, when the time when the temperature of the first refrigerant falls below the threshold value is set as a reference time, the time from the reference time to the start time of the ice protection operation is set according to the distance d.

14. After the step of controlling the rotation speed of the compressor, determining whether the temperature of the first refrigerant is equal to or greater than the threshold; a step of determining whether a predetermined time has elapsed when it is determined that the temperature of the first refrigerant is not equal to or higher than the threshold value; When it is determined that the temperature of the first refrigerant is not equal to or higher than the threshold value and the predetermined time has elapsed, performing a failure determination and forcibly stopping the refrigeration cycle device; The method for controlling a refrigeration cycle apparatus according to claim 12, further comprising:

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