Refrigeration cycle equipment

Abstract

The present invention provides a refrigeration cycle device that includes a refrigerant circuit having an economizer circuit that introduces an intermediate-pressure refrigerant into the compression section, and adjusts the degree of superheating of the refrigerant downstream of the economizer circuit to an appropriate range. [Solution] The refrigeration cycle device 1 includes a control unit that performs a first control that controls the refrigerant circuit based on the difference between a first temperature, which is the refrigerant temperature downstream of the first flow path 31a of the economizer heat exchanger, and a second temperature, which is the refrigerant temperature downstream of the second flow path 31b.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration cycle device.

Background Art

[0002] The refrigerant circuit of the refrigeration cycle device disclosed in Patent Document 1 has a bypass refrigerant circuit to which an economizer is connected as an intermediate heat exchanger. The refrigerant at an intermediate pressure flowing through the bypass refrigerant circuit merges with the refrigerant during compression in the compressor. In Patent Document 1, in order to suppress the compression of the liquid refrigerant, the opening degree of the expansion valve in the bypass refrigerant circuit is adjusted based on the superheat degree of the refrigerant at an intermediate pressure on the downstream side of the economizer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The superheat degree of the refrigerant at an intermediate pressure on the downstream side of the economizer is calculated based on the temperature of the refrigerant on the upstream side and the temperature of the refrigerant on the downstream side of the economizer. However, since the refrigerant on the upstream side of the economizer is in a two-phase state, the accuracy of measuring the refrigerant temperature may decrease. In this case, there is a risk that the superheat degree of the intermediate-pressure refrigerant cannot be adjusted to an appropriate range.

[0005] An object of the present disclosure is to provide a refrigeration cycle device including a refrigerant circuit having an economizer circuit for introducing a refrigerant at an intermediate pressure into a compression section, and adjusting the superheat degree of the refrigerant on the downstream side of the economizer circuit to an appropriate range.

Means for Solving the Problems

[0006] The first aspect is A refrigeration cycle device comprising a refrigerant circuit (40) having a main refrigerant circuit (10) through which the refrigerant flows in the order of a compression section (11), a heat sink (25), a first pressure reducing mechanism (13, 14), and an evaporator (12), and an economizer circuit (30) in the main refrigerant circuit (10) that connects the space between the heat sink (25) and the first pressure reducing mechanism (13, 14) to the compression section (11), The aforementioned economizer circuit (30) A second pressure reduction mechanism (33) for reducing the pressure of a high-pressure refrigerant to an intermediate-pressure refrigerant, The system includes an economizer heat exchanger (31) in which the intermediate-pressure refrigerant and the high-pressure refrigerant between the radiator (25) and the first pressure reducing mechanism (13, 14) in the main refrigerant circuit (10) exchange heat. The economizer heat exchanger (31) has a first flow path (31a) connected to the main refrigerant circuit (10) and a second flow path (31b) connected to the economizer circuit (30), and is configured such that the refrigerant flowing through the first flow path (31a) and the refrigerant flowing through the second flow path (31b) face each other. The system includes a control unit (100) that performs a first control to control the refrigerant circuit (40) based on the difference between a first temperature, which is the refrigerant temperature downstream of the first flow path (31a), and a second temperature, which is the refrigerant temperature downstream of the second flow path (31b). It is a refrigeration cycle device.

[0007] In the first embodiment, heat exchange occurs between the high-pressure refrigerant flowing through the first channel (31a) and the intermediate-pressure refrigerant flowing through the second channel (31b) in the economizer heat exchanger (31). By executing the first control, an appropriate amount of refrigerant can be circulated through the second channel (31b). This allows the degree of superheating of the refrigerant downstream of the economizer circuit (30) to be adjusted to an appropriate range.

[0008] A second aspect is, in the first aspect, The first control is executed when the difference between the third temperature, which is the refrigerant temperature upstream of the first flow path (31a), and the second temperature is greater than or equal to a predetermined value.

[0009] In the second embodiment, the greater the difference between the third temperature and the second temperature, the more heat exchange can be performed by the refrigerant flowing through the first flow path (31a).

[0010] A third aspect is a manifestation of the first or second aspect, When the discharge temperature of the refrigerant from the compression section (11) is above a predetermined value, the difference between the first temperature and the second temperature is reduced.

[0011] In the third embodiment, if the refrigerant discharge temperature becomes too high, the compression unit (11) may malfunction. Therefore, by reducing the difference between the first temperature and the second temperature, the discharge temperature can be lowered, and the malfunction of the compression unit can be suppressed.

[0012] The fourth aspect is one of the first to third aspects, The compression unit (11) has a first compressor (11a) and a second compressor (11b) connected in series to the main refrigerant circuit (10). The outlet end of the refrigerant from the economizer circuit (30) is connected to a refrigerant piping that connects the discharge side of the first compressor (11a) and the suction side of the second compressor (11b).

[0013] In the fourth embodiment, the first control can also be performed in a two-stage compression type refrigerant circuit. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a piping diagram of the refrigerant circuit in the embodiment. [Figure 2] Figure 2 is a block diagram of the main components of the hot water supply system. [Figure 3] Figure 3 is a piping diagram of the hot water supply system, showing the flow of refrigerant during heating operation. [Figure 4] Figure 4 is a flowchart showing the operation when the control unit performs the first control. [Figure 5] Figure 5 is a saturated vapor curve illustrating the relationship between the first temperature TL and the temperature Tmi on the upstream side of the second flow path. [Figure 6]FIG. 6 is a piping system diagram of a refrigerant circuit corresponding to FIG. 1 of other embodiments. Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the embodiments shown below, and various modifications are possible without departing from the technical idea of the present disclosure. Since each drawing is for conceptually explaining the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for easy understanding.

[0016] (1-1) Overall Configuration The refrigeration cycle device is applied to the hot water supply device (1). The hot water supply device (1) generates hot water. The generated hot water is stored in a hot water storage tank and supplied to a predetermined target. The hot water supply device (1) of the present embodiment includes an outdoor unit (OU) installed outdoors and an indoor unit (IU) installed indoors.

[0017] As shown in FIG. 1, the hot water supply device (1) has a refrigerant circuit (40) and a water circuit (60). The refrigerant circuit (40) is filled with a first refrigerant. The first refrigerant is not particularly limited, but natural refrigerants such as carbon dioxide and hydrocarbon-based (HC) refrigerants with a low global warming potential (GWP) are preferred. When the first refrigerant is a hydrocarbon-based refrigerant, it may be a single refrigerant composed of one type of refrigerant or a mixed refrigerant composed of one or more other refrigerants.

[0018] The refrigerant circuit (40) performs a refrigeration cycle using the first refrigerant. The refrigerant circuit (40) has a main refrigerant circuit (10) and an economizer circuit (30).

[0019] (1-2) Main Refrigerant Circuit The main refrigerant circuit (10) mainly comprises a compressor (11), an outdoor heat exchanger (12), a first expansion valve (13), and a second expansion valve (14). The main refrigerant circuit (10) in this embodiment further comprises a four-way switching valve (15), a receiver (16), and a bridge circuit (20). These components are installed in the outdoor unit (OU).

[0020] The compressor (11) compresses the inhaled refrigerant and discharges the compressed refrigerant. The compressor (11) is a so-called high-pressure dome-type compressor. Specifically, the compressor (11) has a casing, a motor located inside it, and a compression mechanism driven by the motor. The inside of the casing is filled with high-pressure refrigerant discharged from the compression mechanism. An oil reservoir of refrigerant oil is formed at the bottom of the casing. This refrigerant oil is supplied to the sliding parts of the compression mechanism and bearings by an oil supply pump. The compressor (11) is an example of a compression unit of this disclosure.

[0021] The outdoor heat exchanger (12) is an air heat exchanger that exchanges heat between the outdoor air transported by the outdoor fan (17) and the first refrigerant. The outdoor heat exchanger (12) is an example of an evaporator of the present disclosure. The first expansion valve (13) and the second expansion valve (14) are examples of a first pressure reducing mechanism. The first expansion valve (13) and the second expansion valve (14) are, for example, electronic expansion valves that reduce the pressure of the refrigerant.

[0022] The four-way directional control valve (15) has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4). The four-way directional control valve (15) switches between a first state, shown by the solid line in Figure 1, and a second state, shown by the dashed line in Figure 1. In the first state, the four-way directional control valve (15) connects the first port (P1) and the second port (P2) and simultaneously connects the third port (P3) and the fourth port (P4). In the second state, the four-way directional control valve (15) connects the first port (P1) and the third port (P3) and simultaneously connects the second port (P2) and the fourth port (P4).

[0023] The bridge circuit (20) is composed of first to fourth pipes (21, 22, 23, 24), each having a check valve (CV). Each check valve (CV) allows the flow of refrigerant in the direction indicated by the arrow in Figure 1 and prohibits the flow of refrigerant in the opposite direction. The outlet end of the first pipe (21) and the outlet end of the second pipe (22) are connected to the inlet side of the receiver (16). The inlet end of the third pipe (23) and the inlet end of the fourth pipe (24) are connected to the outlet side of the receiver (16). The inlet end of the first pipe (21) and the outlet end of the third pipe (23) are connected to the liquid side end of the outdoor heat exchanger (12). The inlet end of the second pipe (22) and the outlet end of the fourth pipe (24) are connected to the third flow path (25a) of the water heat exchanger (25).

[0024] The water heat exchanger (25) is composed of, for example, a plate heat exchanger. The water heat exchanger (25) has a third flow path (25a) through which the first refrigerant of the main refrigerant circuit (10) flows, and a fourth flow path (25b) through which the water of the water circuit (60) flows. The water heat exchanger (25) exchanges heat between the first refrigerant in the third flow path (25a) and the water in the fourth flow path (25b). The water heat exchanger (25) is a counterflow type in which the flow of the first refrigerant in the third flow path (25a) and the flow of water in the fourth flow path (25b) are in opposite directions. The water heat exchanger (25) is an example of a heat radiator.

[0025] (1-3) Economizer Circuit The economizer circuit (30) introduces intermediate-pressure refrigerant into the compressor (11). Specifically, the economizer circuit (30) reduces the pressure of the refrigerant flowing through the main refrigerant circuit (10) to an intermediate pressure and merges the intermediate-pressure refrigerant with the refrigerant that is being compressed.

[0026] The economizer circuit (30) is positioned between the bridge circuit (20) and the receiver (16). Specifically, the economizer circuit (30) is provided to connect the water heat exchanger (25), which is a heat radiator in the main refrigerant circuit (10), and the first expansion valve (13) to the compressor (11).

[0027] The economizer circuit (30) includes an economizer heat exchanger (31), a branch pipe (32), a third expansion valve (33), and an inlet pipe (34).

[0028] The economizer heat exchanger (31) is composed of, for example, a plate heat exchanger. The economizer heat exchanger (31) exchanges heat between the intermediate-pressure refrigerant and the high-pressure refrigerant between the water heat exchanger (25) in the main refrigerant circuit (10) and the first expansion valve (13). Specifically, the economizer heat exchanger (31) has a first flow path (31a) and a second flow path (31b). The economizer heat exchanger (31) exchanges heat between the high-pressure refrigerant flowing through the first flow path (31a) and the intermediate-pressure refrigerant flowing through the second flow path (31b). The economizer heat exchanger (31) is of the counter-flow type, where the flow of refrigerant in the first flow path (31a) and the flow of refrigerant in the second flow path (31b) face each other. The first flow path (31a) constitutes part of the main refrigerant circuit (10). The second flow path (31b) constitutes part of the economizer circuit (30). In other words, the main refrigerant circuit (10) has a first flow path (31a), and the economizer circuit (30) has a second flow path (31b).

[0029] The branch pipe (32) branches off from the refrigerant piping located downstream of the bridge circuit (20) in the main refrigerant circuit (10) and connects to the upstream end of the second flow path (31b) of the economizer heat exchanger (31). The third expansion valve (33) is connected to the branch pipe (32) and reduces the pressure of the high-pressure refrigerant to an intermediate-pressure refrigerant. The third expansion valve (33) is an example of the second pressure reduction mechanism (33). The third expansion valve (33) is an electrically operated valve with adjustable opening. The inlet pipe (34) connects the downstream end of the second flow path (31b) to the compressor (11).

[0030] (1-4) Water circuit In the water circuit (60), water supplied to the target circulates. The water circuit (60) is provided with a hot water storage tank (not shown) in which water heated by the water heat exchanger (25) (hot water) is stored. The water circuit (60) is provided with a pump (61) for circulating the water. The hot water storage tank and the pump (61) are installed in the indoor unit (IU).

[0031] (2) Sensor The hot water supply device (1) has multiple sensors. As shown in Figure 1, the multiple sensors include an intake pressure sensor (89), a discharge pressure sensor (88), a discharge temperature sensor (80), a first temperature sensor (91), a second temperature sensor (92), and a third temperature sensor (93).

[0032] The suction pressure sensor (89) is installed in the refrigerant piping on the suction side of the compressor (11). The suction pressure sensor (89) detects the low pressure PS of the refrigerant circuit (40).

[0033] The discharge pressure sensor (88) is installed in the refrigerant piping on the discharge side of the compressor (11). The discharge pressure sensor (88) detects the high pressure Pd of the refrigerant circuit (40).

[0034] The discharge temperature sensor (80) is installed in the refrigerant piping on the discharge side of the compressor (11). The discharge temperature sensor (80) detects the temperature Td of the high-pressure discharge refrigerant discharged from the compressor (11).

[0035] The first temperature sensor (91) is installed in the refrigerant piping downstream of the bridge circuit (20) and upstream of the first flow path (31a). The first temperature sensor (91) detects the temperature Ti of the refrigerant immediately before it flows into the first flow path (31a).

[0036] The second temperature sensor (92) is installed in the refrigerant piping downstream of the first flow path (31a). The second temperature sensor (92) detects the temperature TL of the refrigerant that has undergone heat exchange in the first flow path (31a).

[0037] The third temperature sensor (93) is installed in the inlet pipe (34). The third temperature sensor (93) detects the temperature Tmo of the refrigerant downstream of the second flow path (31b). The temperature Tmo is the temperature of the refrigerant that has undergone heat exchange in the second flow path (31b).

[0038] The hot water supply system has a pressure switch. The pressure switch includes a high-pressure switch (87). The high-pressure switch (87) is located on the discharge side of the compressor (11) and operates when the high-pressure pressure exceeds a predetermined value.

[0039] (3) Control Unit The control unit (100) shown in Figure 2 includes an MCU (Micro Control Unit), electrical circuits, and electronic circuits. The MCU includes a CPU (Central Processing Unit), memory, and a communication interface. The memory stores various programs for the CPU to execute. The controller (100) may consist of one physically independent element or two or more physically separated elements.

[0040] The control unit (100) controls the refrigerant circuit (40). Specifically, the control unit (100) controls the starting and stopping of the compressor (11), the rotational speed of the compressor (11), the opening degree of the first to third expansion valves (13, 14, 33), the starting and stopping of the outdoor fan (17), and the rotational speed of the outdoor fan (17). The control unit (100) receives detection signals from the various sensors mentioned above.

[0041] (4) Heating operation The hot water supply unit (1) performs a heating operation to generate hot water in the water circuit (60). During the heating operation, a refrigeration cycle is performed in which the outdoor heat exchanger (12) of the refrigerant circuit (40) functions as an evaporator and the water heat exchanger (25) functions as a heat radiator.

[0042] In the heating operation shown in Figure 3, the control unit (100) operates the compressor (11), the outdoor fan (17), and the pump (61), sets the four-way switching valve (15) to the first state, and adjusts the opening degrees of the first to third expansion valves (13, 14, 33) as appropriate.

[0043] In the main refrigerant circuit (10), the first refrigerant compressed by the compressor (11) dissipates heat to the water in the water circuit (60) in the water heat exchanger (25). The dissipated first refrigerant flows through the first channel (31a) of the economizer heat exchanger (31) and is cooled by heat exchange with the intermediate-pressure refrigerant in the second channel (31b). The refrigerant cooled in the economizer heat exchanger (31) is depressurized in the first expansion valve (13), then passes through the receiver (16), and is further depressurized in the second expansion valve (14). After that, the first refrigerant absorbs heat from the outside air in the outdoor heat exchanger (12), evaporates, and is drawn into the compressor (11).

[0044] In the economizer circuit (30), a portion of the refrigerant flowing through the main refrigerant circuit (10) flows into the branch pipe (32) and is depressurized by the third expansion valve (33). The depressurized refrigerant flows into the second flow path (31b) of the economizer circuit (30) as intermediate-pressure refrigerant. In the economizer circuit (30), the refrigerant in the second flow path (31b) is heated by heat exchange with the refrigerant in the first flow path (31a). The heated refrigerant is introduced to the compressor (11) via the introduction pipe (34). The refrigerant introduced into the compressor (11) merges with the refrigerant that is being compressed.

[0045] In the water circuit (60), water transported by the pump (61) is heated in the water heat exchanger (25) and used to generate hot water in the hot water storage tank.

[0046] (5) Superheating degree of intermediate pressure refrigerant In a refrigeration cycle system having an economizer circuit, it is preferable that the intermediate-pressure refrigerant introduced into the compressor is in a saturated state. If the intermediate-pressure refrigerant is in a two-phase state, the compressor will compress the liquid refrigerant, reducing the reliability of the compressor. Therefore, it is preferable to ensure the superheating degree of the intermediate-pressure refrigerant.

[0047] In this embodiment, the control unit (100) performs a first control that controls the refrigerant circuit (40) based on the difference between a first temperature TL, which is the temperature downstream of the first flow path (31a) of the economizer heat exchanger (31), and a second temperature Tmo, which is the temperature downstream of the second flow path (31b). The first control is a control that adjusts the intermediate pressure refrigerant to an appropriate range. This suppresses liquid compression and prevents a decrease in the reliability of the compressor (11). The operation of the control unit (100), including the first control, will be described below with reference to Figure 4.

[0048] (6) First control In step ST01, the control unit (100) obtains the high-pressure pressure Pd, suction pressure Ps, first temperature TL, second temperature Tmo, third temperature Ti, and discharge temperature Td.

[0049] In step ST02, the control unit (100) determines whether the discharge temperature Td is higher than the first temperature T1. The first temperature T1 is, for example, 80°C. If the discharge temperature Td is lower than the first temperature T1, the temperature of the refrigerant after heat exchange in the second flow path (31b) is relatively low. Therefore, if the temperature of the intermediate pressure refrigerant introduced into the compressor (11) is low, the discharge temperature in the cold zone decreases, and the operating efficiency deteriorates. Thus, in step ST02, it is determined whether the discharge temperature Td is higher than a predetermined first temperature T1. The refrigerant flowing through the first channel (31a) of the economizer heat exchanger (31) does not reach a high temperature, and the refrigerant in the second channel (31b) that exchanges heat with the refrigerant in the first channel (31a) is not sufficiently heated. Therefore, the control unit (100) determines whether the discharge temperature Td is higher than the first temperature T1. If it is determined that the discharge temperature Td is higher than the first temperature T1 (YES in step ST02), step ST04 is executed. If it is determined that the discharge temperature Td is less than or equal to the first temperature T1 (NO in step ST02), step ST03 is executed.

[0050] In step ST03, the control unit (100) completely closes the third expansion valve (33). As a result, the refrigerant flowing through the main refrigerant circuit (10) does not flow into the economizer circuit (30). After that, step ST01 is executed. If the third expansion valve (33) is already open to a predetermined degree, the control unit (100) lowers the first temperature T1 to, for example, 70°C in step ST02.

[0051] In step ST04, the control unit (100) determines whether ΔT1, which represents the difference (Ti-Tmo) between the third temperature Ti and the second temperature Tmo, is higher than the second temperature T2. The second temperature T2 is, for example, 2°C. If it is determined that ΔT1 is higher than the second temperature T2 (YES in step ST04), it can be assumed that sufficient heat exchange is occurring in the refrigerant flowing through the first channel (31a), and then step ST06 is executed. If it is determined that ΔT1 is less than or equal to the second temperature T2 (NO in step ST04), it can be assumed that sufficient heat exchange is not occurring in the refrigerant flowing through the second channel (31b), and then step ST05 is executed.

[0052] In step ST05, the control unit (100) increases the opening of the third expansion valve (33) by a predetermined value. This increases the flow rate of the refrigerant flowing through the second flow path (31b). Then step ST01 is executed again.

[0053] In step ST06, the control unit (100) executes the first control. In this embodiment, the first control unit corresponds to the control in steps ST06 to ST09. The control unit (100) determines whether ΔT2, which represents the difference (TL-Tmo) between the first temperature TL and the second temperature Tmo, is within a predetermined temperature range. Here, in step ST06, the refrigerant in the first flow path (31a) is sufficiently heat-exchanged. In other words, since the refrigerant in the first flow path (31a) is sufficiently cooled, the first refrigerant temperature TL, which is the refrigerant temperature after outflow, becomes sufficiently lower than the third temperature Ti, which is the refrigerant temperature before inflow into the first flow path (31a). In this case, the temperature Tmi of the intermediate-pressure refrigerant upstream of the second flow path (31b), which has been depressurized by the third expansion valve (33) of the economizer circuit (30), becomes approximately equal to the first temperature TL. This indicates that temperature Tmi and the first temperature TL lie on approximately the same isotherm, as shown in Figure 5, and the first temperature TL can be considered as the refrigerant temperature Tmi upstream of the second flow path (31b). Therefore, the degree of superheating (ΔT2) of the intermediate-pressure refrigerant can be determined by the difference between the first temperature TL and the second temperature Tmo without measuring temperature Tmi. The predetermined temperature range indicates the range in which the degree of superheating is normal. The predetermined temperature range is, for example, ±2℃. When ΔT2 is within the ±2℃ range (YES in step ST06), this control is terminated. When ΔT2 is outside the ±2℃ range, step ST07 is executed.

[0054] In step ST07, the control unit (100) determines whether ΔT2 is above a predetermined range. In this embodiment, the control unit (100) determines whether ΔT2 is above 2°C. If ΔT2 is above 2°C (YES in step ST07), step ST08 is executed. If ΔT2 is not above 2°C (NO in step ST07), it is determined that ΔT2 is below -2°C, and step ST09 is executed.

[0055] In step ST08, the control unit (100) increases the opening of the third expansion valve (33). This increases the refrigerant flow rate in the second flow path (31b). When the refrigerant flow rate in the second flow path (31b) increases, the refrigerant flow rate in the second flow path (31b) that cannot exchange heat with the refrigerant in the first flow path (31a) increases, so the second temperature Tmo decreases. As a result, ΔT2 becomes smaller and the degree of superheating of the intermediate pressure refrigerant decreases. After step ST08, step ST01 is executed again.

[0056] In step ST09, the control unit (100) reduces the opening of the third expansion valve (33). This reduces the refrigerant flow rate in the second flow path (31b). When the refrigerant flow rate in the second flow path (31b) decreases, the refrigerant at the second flow rate can completely exchange heat with the refrigerant in the first flow path (31a), causing the second temperature Tmo to rise. As a result, ΔT2 increases and the degree of superheating of the intermediate-pressure refrigerant increases. After step ST09, step ST01 is executed again.

[0057] (7) Characteristics (7-1) Feature 1 The hot water supply device (1) of this embodiment includes a main refrigerant circuit (10) through which refrigerant flows in the order of compressor (11), radiator (25), first pressure reducing mechanism (13, 14), and evaporator (12), and a refrigerant circuit (40) having an economizer circuit (30) that connects the space between the radiator (25) and the first pressure reducing mechanism (13, 14) and the compression section (11) in the main refrigerant circuit (10). The control unit (100) of the hot water supply device (1) performs a first control that controls the refrigerant circuit (40) based on the difference between a first temperature TL, which is the refrigerant temperature downstream of the first flow path (31a), and a second temperature Tmo, which is the refrigerant temperature downstream of the second flow path (31b).

[0058] The degree of superheating of the intermediate-pressure refrigerant introduced from the economizer circuit (30) to the compressor (11) corresponds to the temperature difference between the refrigerant temperature Tmi before inflow and the refrigerant temperature Tmo after outflow in the second flow path (31b). If the flow rate of the refrigerant flowing through the second flow path (31b) is excessive, the amount of heat exchange will be insufficient, and unsaturated refrigerant will be drawn into the compression section (11), potentially reducing the reliability of the compression section (11). On the other hand, if the flow rate of the refrigerant flowing through the second flow path (31b) is relatively low, the amount of intermediate-pressure refrigerant introduced into the compression section (11) will be small, and the effect of the economizer circuit (30) will not be fully obtained.

[0059] Therefore, in this embodiment, by executing the first control, an appropriate amount of refrigerant, sufficient for heat exchange between the refrigerant flowing through the first channel (31a) and the second channel (31b), is circulated. As a result, the refrigerant temperature TL downstream of the first channel (31a) can be considered equal to the refrigerant temperature Tmi upstream of the second channel (31b). In this way, by considering the first temperature TL to be equal to the temperature Tmi upstream of the second channel (31b), the degree of superheating can be determined based on the first temperature TL and the second temperature Tmi. Therefore, it becomes unnecessary to detect the temperature Tmi upstream of the second channel (31b). Furthermore, by controlling at least the third expansion valve (33) among the expansion valves based on the determined degree of superheating, the degree of superheating can be adjusted to an appropriate temperature range.

[0060] Furthermore, the refrigerant at temperature Tmi is in a two-phase state, and the accuracy of temperature sensor detection may not be high. In such cases, the degree of superheating of the intermediate-pressure refrigerant can be easily controlled by using the first temperature TL. By performing this first control, liquid compression of the compressor (11) can be suppressed. In addition, since it is not necessary to detect the refrigerant temperature upstream of the second flow path (31b), such a temperature sensor can be eliminated. Moreover, an intermediate-pressure sensor for detecting the intermediate-pressure refrigerant downstream of the second flow path (31b) becomes unnecessary.

[0061] (7-2) Feature 2 In the hot water supply system (1) of this embodiment, the control unit (100) executes the first control when it determines that the difference between the third temperature Ti, which is the refrigerant temperature upstream of the first flow path (31a), and the second temperature Tmo is greater than or equal to a predetermined value. The larger the difference between the second temperature Tmo and the third temperature Ti, the more heat exchange can be performed by the refrigerant flowing through the first flow path (31a). Therefore, by setting a predetermined value such that the heat exchange of the refrigerant in the first flow path (31a) is sufficient, and executing the first control when the control unit (100) determines that the difference between the second temperature Tmo and the third temperature Ti is greater than or equal to the predetermined value, the accuracy of estimating the degree of superheating of the refrigerant at intermediate pressure is improved.

[0062] (8) Other embodiments The above embodiment may be configured as follows.

[0063] When the control unit (100) performs the above-mentioned first operation, if the discharge temperature of the refrigerant from the compressor (11) is above a predetermined value, it may control the refrigerant circuit (10) to reduce the difference between the first temperature TL and the second temperature Tmo. In this case, the opening degree of the third expansion valve (33) is controlled as appropriate. If the discharge temperature of the refrigerant becomes too high, the compressor (11) may fail. By reducing the difference between the first temperature TL and the second temperature Tmo, the discharge temperature is reduced, and the decrease in the reliability of the compressor (11) can be suppressed.

[0064] In the first control described above, the value of ΔT(TL-Tmo) in step ST06 may be controlled based on the refrigerant discharge temperature, the water heat exchange capacity of the water heat exchanger (25), and the temperature on the upstream (inlet) or downstream (outlet) side of the water heat exchanger (25) in the water circuit (60). For example, if the discharge temperature is relatively high, the refrigerant circuit (40) is controlled to decrease the value of ΔT. This increases the flow rate of the refrigerant in the second flow path (31b), and also increases the flow rate of refrigerant introduced from the economizer circuit (30) to the compressor (11). As a result, the discharge temperature decreases, and the decrease in the reliability of the compressor (11) can be suppressed. On the other hand, if the discharge temperature is relatively low, the refrigerant circuit (40) may be controlled to increase the value of ΔT. Also, if the heat exchange load on the water heat exchanger (25) is relatively large, the refrigerant circuit (40) may be controlled to increase the value of ΔT. When the load on the water heat exchanger (25) increases, the temperature difference between TL and Tmi also increases, so it is necessary to increase the value of ΔT. On the other hand, when the load on the water heat exchanger (25) is relatively small, the refrigerant circuit (40) may be controlled to decrease the value of ΔT. The load on the water heat exchanger (25) is determined based on the temperature difference between the water temperature Tw1 on the upstream side of the fourth flow path (25b) and the water temperature Tw2 on the downstream side, as well as the flow rate of water flowing through the fourth flow path (25b). In this case, a water temperature sensor that detects water temperatures Tw1 and Tw2 is provided in the water circuit (60). Also, if the temperature on the upstream side or downstream side of the water heat exchanger (25) in the water circuit (60) is high, the refrigerant circuit (40) may be controlled to decrease ΔT. The temperature on the upstream side of the water heat exchanger (25) is water temperature Tw1, and the temperature on the downstream side of the water heat exchanger (25) is water temperature Tw2. When the heat exchanger (25), which is a heat sink, is at a relatively high temperature, the discharge temperature is reduced by increasing the amount of refrigerant introduced from the economizer circuit (30) to the compressor (11).

[0065] As shown in Figure 6, the main refrigerant circuit (10) may be a two-stage compressor type refrigerant circuit. The compression section (11) has a first compressor (11a) and a second compressor (11b) connected in series to the main refrigerant circuit (10). The economizer circuit (30) is connected to refrigerant piping that connects the discharge side of the first compressor (11a) and the suction side of the second compressor (11b). Specifically, the inlet pipe (34) of the economizer circuit (30) is connected to refrigerant piping that connects the first compressor (11a) and the second compressor (11b) in series. This refrigerant piping is the discharge side piping of the first compressor (11a) and the suction side piping of the second compressor (11b). In the compression section (11), the low-pressure refrigerant drawn in by the first compressor (11a) is compressed to an intermediate pressure, and the intermediate-pressure refrigerant is compressed to a high pressure by the second compressor (11b) before being discharged. As a result, the refrigerant at the intermediate pressure in the economizer circuit (30) merges with the refrigerant at the intermediate pressure on the discharge side of the first compressor (11a) (the suction side of the second compressor (11b)).

[0066] The sensor does not necessarily have to include a discharge pressure sensor (88), an intake pressure sensor (89), and a discharge temperature sensor (80).

[0067] While embodiments and modifications have been described above, it will be understood that a variety of changes in form and details are possible without departing from the spirit and scope of the claims. Furthermore, these embodiments and modifications may be combined or substituted as appropriate, as long as they do not impair the functions of the subject matter of this disclosure. The terms “First,” “Second,” etc., used above are used to distinguish the phrases to which these terms are attached, and do not limit the number or order of such phrases. [Industrial applicability]

[0068] As explained above, this disclosure is useful for refrigeration cycle systems. [Explanation of Symbols]

[0069] 1. Hot water supply system (refrigeration cycle system) 10 Main refrigerant circuit 11 Compressor (Compression Section) 11a First Compressor (Compression Section) 11b Second Compressor (Compression Section) 12. Outdoor heat exchanger (evaporator) 13,14 Pressure reduction mechanism (First pressure reduction mechanism) 25 Water heat exchanger (radiator) 30 Economizer Circuit 31 Economizer Heat Exchanger 31a First channel 31b Second channel 33. Third expansion valve (second pressure reducing mechanism) 100 Control Unit

Claims

1. A refrigeration cycle device comprising a main refrigerant circuit (10) through which the refrigerant flows in the order of a compression unit (11), a heat sink (25), first pressure reducing mechanisms (13, 14), and an evaporator (12), and a refrigerant circuit (40) having an economizer circuit (30) in the main refrigerant circuit (10) that connects the space between the heat sink (25) and the first pressure reducing mechanisms (13, 14) to the compression unit (11), The aforementioned economizer circuit (30) A second pressure reduction mechanism (33) that reduces the pressure of the high-pressure refrigerant to an intermediate-pressure refrigerant, The system includes an economizer heat exchanger (31) in which the intermediate-pressure refrigerant and the high-pressure refrigerant between the radiator (25) and the first pressure reducing mechanism (13, 14) in the main refrigerant circuit (10) exchange heat. The economizer heat exchanger (31) has a first flow path (31a) connected to the main refrigerant circuit (10) and a second flow path (31b) connected to the economizer circuit (30), and is configured such that the refrigerant flowing through the first flow path (31a) and the refrigerant flowing through the second flow path (31b) face each other. The system includes a control unit (100) that performs a first control to control the refrigerant circuit (40) based on the difference between a first temperature, which is the refrigerant temperature downstream of the first flow path (31a), and a second temperature, which is the refrigerant temperature downstream of the second flow path (31b). Refrigeration cycle device.

2. The first control is executed when the difference between the third temperature, which is the refrigerant temperature upstream of the first flow path (31a), and the second temperature is greater than or equal to a predetermined value. The refrigeration cycle apparatus according to claim 1.

3. When the discharge temperature of the refrigerant from the compression section (11) is above a predetermined value, the difference between the first temperature and the second temperature is reduced. A refrigeration cycle apparatus according to claim 1 or 2.

4. The compression unit (11) has a first compressor (11a) and a second compressor (11b) connected in series to the main refrigerant circuit (10). The refrigerant outlet end of the economizer circuit (30) is connected to a refrigerant piping that connects the discharge side of the first compressor (11a) and the suction side of the second compressor (11b). A refrigeration cycle apparatus according to claim 1 or 2.

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