Refrigeration cycle device

Abstract

When a first compressor (11) and a second compressor (51) are in a stopped state, a control unit (100) causes the first compressor (11) to operate while keeping the second compressor (51) in a stopped state, and causes the first compressor (11) to execute a first operation in which first refrigerant is caused to dissipate heat in a refrigerant heat exchanger (52). The control unit (100) causes a second operation for operating the second compressor (51) to be executed after the first operation.

Description

Refrigeration cycle device

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

[0002] Patent Document 1 discloses a refrigeration cycle device that performs a binary refrigeration cycle. In the refrigeration cycle device, a first refrigerant circuit on the low-stage side and a second refrigerant circuit on the high-stage side are connected by a cascade heat exchanger. In the first refrigerant circuit and the second refrigerant circuit, a refrigeration cycle is performed respectively.

[0003] Japanese Patent Application Laid-Open No. 2004-132647

[0004] When the refrigeration cycle device as described in Patent Document 1 is stopped, the refrigerant may dissolve into the refrigeration machine oil inside the compressor of the second refrigerant circuit. This phenomenon is also referred to as "refrigerant infiltration". When refrigerant infiltration occurs, the substantial amount of refrigerant used in the refrigeration cycle of the second refrigerant circuit decreases. In such a state, when the compressor of the second refrigerant circuit is operated, a problem occurs in that the low-pressure pressure rapidly decreases due to the shortage of the refrigerant amount, and the compressor cannot be started stably.

[0005] An object of the present disclosure is to suppress a rapid decrease in the low-pressure pressure when the compressor of the second refrigerant circuit is started.

[0006] The first embodiment relates to a refrigeration cycle device. The refrigeration cycle device comprises a first refrigerant circuit (10) through which a first refrigerant circulates to perform a refrigeration cycle, a second refrigerant circuit (50) through which a second refrigerant circulates to perform a refrigeration cycle, a refrigerant heat exchanger (52) for heat exchange between the first refrigerant in the first refrigerant circuit (10) and the second refrigerant in the second refrigerant circuit (50), and a control unit (100) for controlling the first refrigerant circuit (10) and the second refrigerant circuit (50). The first refrigerant circuit (10) has a first compressor (11), a heat source side heat exchanger (12), and a first expansion mechanism (13, 14). The second refrigerant circuit (50) has a second compressor (51), a second expansion mechanism (53), and a utilization side heat exchanger (54). When the first compressor (11) and the second compressor (51) are stopped, the control unit (100) performs a first operation in which it operates the first compressor (11) while keeping the second compressor (51) stopped, thereby releasing heat from the first refrigerant in the refrigerant heat exchanger (52). After the first operation, the control unit (100) performs a second operation in which it operates the second compressor (51).

[0007] In the first embodiment, during the first operation, the first compressor (11) is operated while the second compressor (51) is stopped. During the first operation, the first refrigerant discharged from the first compressor (11) dissipates heat in the refrigerant heat exchanger (52). As a result, the second refrigerant in the second refrigerant circuit (50) is heated in the refrigerant heat exchanger (52), and furthermore, the inside of the second compressor (51) is heated. Consequently, the refrigerant buildup can be eliminated before starting the second compressor (51).

[0008] When the second operation is performed after the first operation, the second compressor (51) enters an operating state. At this time, since the refrigerant buildup in the second compressor (51) has been resolved, the second compressor (51) can be started stably while suppressing a rapid drop in low pressure.

[0009] In the second embodiment, the control unit (100) causes the first operation to be performed when the stopping time of the first compressor (11) and the second compressor (51) is longer than a predetermined time.

[0010] In the second embodiment, if the stopping time of the first compressor (11) and the second compressor (51) is longer than a predetermined time, the amount of refrigerant dissolved in the refrigeration oil inside the second compressor (51) increases. Therefore, if this stopping time is longer than a predetermined time, the control unit (100) performs a first operation to eliminate the refrigerant buildup.

[0011] In a third aspect, in the first or second aspect, the control unit (100) controls the rotational speed of the second compressor (51) to a low speed during the second operation. Here, "low speed" strictly means a rotational speed lower than the midpoint of the rotational speed control range of the second compressor (51).

[0012] In the third embodiment, since the rotational speed of the second compressor (51) becomes low during the second operation, a rapid decrease in the low pressure of the second refrigerant circuit (50) can be suppressed.

[0013] The fourth embodiment is one of the first to third embodiments in which the control unit (100) causes the first operation to be executed again if, during the second operation, the first condition is met in which the evaporation temperature, evaporation pressure, or low pressure of the second refrigerant circuit (50) is lower than a predetermined value.

[0014] In the fourth embodiment, if the first condition is met during the second operation, there is a possibility that the refrigerant buildup has not yet been resolved. Therefore, if the first condition is met, the control unit (100) will execute the first operation again in order to resolve the refrigerant buildup.

[0015] The fifth embodiment is one of the first to fourth embodiments, in which the control unit (100) stops the second compressor (51) if, during the second operation, the temperature difference between the first refrigerant and the second refrigerant in the refrigerant heat exchanger (52) remains greater than a predetermined value for a predetermined time or longer.

[0016] In the fifth embodiment, if the second refrigerant leaks in the second refrigerant circuit (50), the low pressure in the second refrigerant circuit (50) remains low, and the temperature difference between the first refrigerant and the second refrigerant in the refrigerant heat exchanger (52) also remains greater than a predetermined value. When these conditions are met, there is a high probability that the second refrigerant is leaking in the second refrigerant circuit. Therefore, the control unit (100) stops the second compressor (51) if the temperature difference between the first refrigerant and the second refrigerant in the refrigerant heat exchanger (52) remains greater than a predetermined value for a predetermined time or longer.

[0017] The sixth embodiment is one in which the second refrigerant includes propane, in any one of the first to fifth embodiments.

[0018] In the sixth embodiment, propane, a highly flammable refrigerant, is used as the second refrigerant. Propane is a highly flammable refrigerant and carries a risk of ignition. Therefore, the amount of refrigerant that can be charged into the second refrigerant circuit (50) is limited, and the amount of refrigerant used in the refrigeration cycle tends to be insufficient. Consequently, if refrigerant stagnation occurs in the second compressor (51), the problem of a decrease in low pressure becomes significant. In contrast, by performing the first operation, refrigerant stagnation can be eliminated before the second compressor (51) is started, thus suppressing the decrease in low pressure.

[0019] Figure 1 is a piping diagram of the hot water supply system according to the embodiment. Figure 2 is a block diagram of the main components of the hot water supply system. Figure 3 is a piping diagram of the hot water supply system, showing the refrigerant flow in the first heating mode and second operation of the dual heating operation. Figure 4 is a piping diagram of the hot water supply system, showing the refrigerant flow in the second heating mode of the dual heating operation. Figure 5 is a flowchart of the startup control. Figure 6 is a piping diagram of the hot water supply system, showing the refrigerant flow in the first operation. Figure 7 is a piping diagram of the hot water supply system, showing the refrigerant flow in single heating operation.

[0020] Embodiments of this disclosure will be described in detail below with reference to the drawings. This disclosure is not limited to the embodiments shown below, and various modifications are possible without departing from the technical idea of ​​this disclosure. Since the drawings are for conceptual illustration of this disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding.

[0021] (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 this embodiment has an outdoor unit (OU) installed outside and an indoor unit (IU) installed inside.

[0022] As shown in Figure 1, the hot water supply system (1) has a first refrigerant circuit (10), a second refrigerant circuit (50), and a water circuit (60). The first refrigerant circuit (10) is filled with a first refrigerant, and the second refrigerant circuit (50) is filled with a second refrigerant different from the first refrigerant. The first refrigerant is carbon dioxide, and the second refrigerant is propane (R290) as a highly flammable refrigerant. Highly flammable refrigerants have the characteristic of a high combustion rate. Highly flammable refrigerants may be, for example, methane (R50), ethane (R170), butane (R600), or isobutane (R600a). The second refrigerant may be a single refrigerant consisting of one type of highly flammable refrigerant, or it may be a mixed refrigerant consisting of a highly flammable refrigerant and one or more other refrigerants.

[0023] The hot water supply system (1) operates a dual-stage refrigeration cycle. In other words, in the hot water supply system (1), the first refrigerant circuit (10) on the low-energy side and the second refrigerant circuit (50) on the high-energy side are connected via a refrigerant heat exchanger (52), which is a so-called cascade heat exchanger. The refrigerant heat exchanger (52) has a first flow path (52a) through which the first refrigerant of the first refrigerant circuit (10) flows, and a second flow path (52b) through which the second refrigerant of the second refrigerant circuit (50) flows. In other words, the first refrigerant circuit (10) has the first flow path (52a) of the refrigerant heat exchanger (52), and the second refrigerant circuit (50) has the second flow path (52b) of the refrigerant heat exchanger (52).

[0024] (1-2) First refrigerant circuit The first refrigerant circuit (10) performs a refrigeration cycle using the first refrigerant. The first refrigerant circuit (10) mainly comprises a first compressor (11), an outdoor heat exchanger (12), a first expansion valve (13), and a second expansion valve (14). The first refrigerant circuit (10) in this embodiment further comprises a four-way switching valve (15), a receiver (16), and a bridge circuit (20). These devices are installed in the outdoor unit (OU).

[0025] The first compressor (11) compresses the inhaled refrigerant and discharges the compressed refrigerant. The first compressor (11) is a so-called high-pressure dome-type compressor. Specifically, the inside of the casing of the first compressor (11) is filled with high-pressure refrigerant discharged from the compression mechanism. An oil reservoir for 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.

[0026] The outdoor heat exchanger (12) is an example of a heat source-side heat exchanger. 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 first expansion valve (13) and the second expansion valve (14) are examples of a first pressure reduction 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.

[0027] 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).

[0028] 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 first flow path (52a) of the refrigerant heat exchanger (52).

[0029] The first refrigerant circuit (10) includes a first water heat exchanger (25) and a bypass mechanism (30). These components are installed in an indoor unit (IU).

[0030] The first water heat exchanger (25) is composed of, for example, a plate heat exchanger. The first water heat exchanger (25) has a third flow path (25a) through which the first refrigerant of the first refrigerant circuit (10) flows, and a fourth flow path (25b) through which the water of the water circuit (60) flows. The first 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 first 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.

[0031] The bypass mechanism (30) switches between a first state in which the refrigerant flows through the third flow path (25a) of the first water heat exchanger (25) and a second state in which the refrigerant bypasses the first water heat exchanger (25). The bypass mechanism (30) includes a bypass flow path (31), a first valve (32), and a second valve (33). One end of the bypass flow path (31) is connected to the gas line of the first refrigerant circuit (10). The other end of the bypass flow path (31) is connected to the piping between the first flow path (52a) and the third flow path (25a) in the first refrigerant circuit (10). The first valve (32) is, for example, an on-off valve and is provided between one end of the bypass flow path (31) in the gas line and the third flow path (25a) of the first water heat exchanger (25). The second valve (33) is, for example, an on-off valve and is provided in the bypass flow path (31). The bypass mechanism (30) may have a three-way valve instead of the first valve (32) and the second valve (33).

[0032] (1-3) Second refrigerant circuit The second refrigerant circuit (50) performs a refrigeration cycle using the second refrigerant. The second refrigerant circuit (50) mainly comprises a second compressor (51), a refrigerant heat exchanger (52), a third expansion valve (53), and a second water heat exchanger (54).

[0033] The second compressor (51) compresses the inhaled refrigerant and discharges the compressed refrigerant. The second compressor (51) is a so-called high-pressure dome-type compressor. Specifically, the inside of the casing of the second compressor (51) 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.

[0034] The refrigerant heat exchanger (52) is composed of, for example, a plate heat exchanger. The refrigerant heat exchanger (52) exchanges heat between the first refrigerant in the first flow path (52a) and the second refrigerant in the second flow path (52b). The third expansion valve (53) is an example of a second pressure reducing mechanism. The second water heat exchanger (54) is an example of a user-side heat exchanger. The second water heat exchanger (54) is composed of, for example, a plate heat exchanger. The second water heat exchanger (54) has a fifth flow path (54a) through which the second refrigerant in the second refrigerant circuit (50) flows, and a sixth flow path (54b) through which water in the water circuit (60) flows. The second water heat exchanger (54) exchanges heat between the second refrigerant in the fifth flow path (54a) and the water in the sixth flow path (54b). The second water heat exchanger (54) is a counter-flow type in which the flow of the second refrigerant in the fifth flow path (54a) and the flow of water in the sixth flow path (54b) are in opposite directions. The second water heat exchanger (54) is installed upstream of the first water heat exchanger (25) in the water circuit (60).

[0035] (1-4) Water Circuit In the water circuit (60), water supplied to the target is circulated. The water circuit (60) is provided with a hot water storage tank (not shown) in which water heated by the first water heat exchanger (25) and the second water heat exchanger (54) 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 provided in the indoor unit (IU).

[0036] (2) Sensors and pressure switches The hot water heater (1) has a plurality of sensors. As shown in Figure 1, the plurality of sensors include a first discharge pressure sensor (80), a second discharge pressure sensor (81), a discharge temperature sensor (82), an intake pressure sensor (83), and an intake temperature sensor (84). The first discharge pressure sensor (80) detects the high pressure of the first refrigerant in the first refrigerant circuit (10). The first discharge pressure sensor (80) constitutes a low-end sensor for detecting the temperature of the first refrigerant in the refrigerant heat exchanger (52). The second discharge pressure sensor (81) detects the high pressure of the second refrigerant circuit (50). The discharge temperature sensor (82) detects the temperature of the refrigerant discharged from the second compressor (51). The intake pressure sensor (83) detects the low pressure of the second refrigerant circuit (50). The intake pressure sensor (83) constitutes a high-end sensor for detecting the temperature of the second refrigerant in the refrigerant heat exchanger (52). The intake temperature sensor (84) detects the temperature of the refrigerant being drawn into the second compressor (51).

[0037] The multiple sensors include a first air temperature sensor (86) and a second air temperature sensor (87). The first air temperature sensor (86) is positioned around the first compressor (11) and detects the temperature of the outdoor air. The second air temperature sensor (87) is positioned around the second compressor (51) and detects the temperature of the indoor air.

[0038] The hot water supply system has a plurality of pressure switches. The plurality of pressure switches include a high-pressure switch (88) and a low-pressure switch (89). The high-pressure switch (88) is located on the discharge side of the second compressor (51) and operates when the high-pressure level exceeds a predetermined value. The low-pressure switch (89) is located on the suction side of the second compressor (51) and operates when the low-pressure level exceeds a predetermined value.

[0039] (3) Controller The controller (100) is an example of a control unit. The controller (100) 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 it may consist of two or more physically separated elements.

[0040] The controller (100) controls the first refrigerant circuit (10) and the second refrigerant circuit (50). Specifically, the controller (100) controls the starting and stopping of the first compressor (11), the rotational speed of the first compressor (11), the opening degree of the first expansion valve (13), the opening degree of the second expansion valve (14), the open / closed state of the first valve (32), the open / closed state of the second valve (33), the starting and stopping of the outdoor fan (17), the rotational speed of the outdoor fan (17), the starting and stopping of the second compressor (51), the rotational speed of the second compressor (51), and the opening degree of the third expansion valve (53). The controller (100) receives detection signals from the various sensors described above.

[0041] (4) Heating operation The hot water supply system (1) performs a heating operation to generate hot water in the water circuit (60). The heating operation includes dual heating operation and single heating operation. In dual heating operation, a dual refrigeration cycle is performed in which the outdoor heat exchanger (12) of the first refrigerant circuit (10) functions as an evaporator and the second water heat exchanger (54) functions as a heat radiator. The dual heating operation includes a first heating mode and a second heating mode. The first heating mode is an operating mode in which the first refrigerant flows through the first water heat exchanger (25). The second heating mode is an operating mode in which the first refrigerant bypasses the first water heat exchanger (25).

[0042] (4-1) First Heating Mode In the first heating mode shown in FIG. 3, the control unit (100) operates the first compressor (11), the second compressor (51), the outdoor fan (17), and the pump (61), sets the four-way switching valve (15) to the first state, opens the first valve (32), closes the second valve (33), and appropriately adjusts the opening degrees of the expansion valves (13, 14, 53) from the first to the third.

[0043] In the first refrigerant circuit (10), the first refrigerant compressed by the first compressor (11) dissipates heat to the water in the water circuit (60) in the first water-to-heat exchanger (25). The first refrigerant that has dissipated heat dissipates heat to the second refrigerant in the second refrigerant circuit (50) in the refrigerant heat exchanger (52). As a result, the degree of subcooling of the first refrigerant increases. The first refrigerant that has passed through the refrigerant heat exchanger (52) is decompressed by the first expansion valve (13), then passes through the receiver (16), and is further decompressed by the second expansion valve (14). Thereafter, the first refrigerant absorbs heat from the outdoor air and evaporates in the outdoor heat exchanger (12), and is sucked into the first compressor (11).

[0044] In the second refrigerant circuit (50), the second refrigerant compressed by the second compressor (51) dissipates heat to the water in the water circuit (60) in the second water-to-heat exchanger (54). The second refrigerant that has dissipated heat is decompressed by the third expansion valve (53). Thereafter, the second refrigerant absorbs heat from the first refrigerant and evaporates in the refrigerant heat exchanger (52), and is sucked into the second compressor (51).

[0045] In the water circuit (60), the water conveyed by the pump (61) is heated in the second water-to-heat exchanger (54) and the first water-to-heat exchanger (25), and is used for generating hot water in the hot water storage tank.

[0046] (4-2) Second Heating Mode In the second heating mode shown in FIG. 4, the control unit (100) operates the first compressor (11), the second compressor (51), the outdoor fan (17), and the pump (61), sets the four-way switching valve (15) to the first state, closes the first valve (32), opens the second valve (33), and appropriately adjusts the opening degrees of the expansion valves (13, 14, 53) from the first to the third.

[0047] In the first refrigerant circuit (10), the first refrigerant compressed by the first compressor (11) dissipates heat to the second refrigerant in the second refrigerant circuit (50) in the refrigerant heat exchanger (52) after bypassing the first water heat exchanger (25). The first refrigerant that has passed through the refrigerant heat exchanger (52) is decompressed by the first expansion valve (13), then passes through the receiver (16), and is further decompressed by the second expansion valve (14). Thereafter, the first refrigerant absorbs heat from the outdoor air and evaporates in the outdoor heat exchanger (12), and is inhaled into the first compressor (11).

[0048] In the second refrigerant circuit (50), the second refrigerant compressed by the second compressor (51) dissipates heat to the water in the water circuit (60) in the second water heat exchanger (54). The second refrigerant that has dissipated heat is decompressed by the third expansion valve (53). Thereafter, the second refrigerant absorbs heat from the first refrigerant and evaporates in the refrigerant heat exchanger (52), and is inhaled into the second compressor (51). In the water circuit (60), the water conveyed by the pump (61) is heated in the second water heat exchanger (54) and used for generating hot water in the hot water storage tank.

[0049] (5-1) Regarding the refrigerant and the refrigeration oil, the first refrigerant in the first refrigerant circuit (10) is carbon dioxide. The first refrigerant circuit (10) contains the first refrigeration oil for lubricating the sliding part of the first compressor (11). The first refrigeration oil is mainly composed of, for example, PAG (polyalkylene glycol). The second refrigerant in the second refrigerant circuit (50) is a strongly flammable refrigerant, specifically propane. The second refrigerant circuit (50) contains the second refrigeration oil for lubricating the sliding part of the first compressor (11). The second refrigeration oil in the second refrigerant circuit (50) is mainly composed of, for example, PAG (polyalkylene glycol). The second refrigeration oil may be mainly composed of POE (polyester) or PVE (polyvinyl ether).

[0050] The second refrigerant circuit (50) uses a highly flammable refrigerant. Highly flammable refrigerants have the potential to ignite. For example, if propane is used as the refrigerant to fill the second refrigerant circuit (50) and it is installed indoors, according to IEC60335-2-40 Ed.7, if the amount of refrigerant exceeds 152g, there will be restrictions on the floor area of ​​the room where the equipment is installed, and safety measures in case of leakage will need to be taken. In this embodiment, since the second refrigerant circuit (50) is installed in an indoor unit (IU), the amount of refrigerant that can be filled into the second refrigerant circuit (50) is limited. For this reason, the amount of refrigerant that can be filled into the second refrigerant circuit (50) is less than the amount of refrigerant that can be filled into the first refrigerant circuit (10). For example, the amount of refrigerant that can be filled into the first refrigerant circuit (10) is between 15 and 25 times the amount of refrigerant that can be filled into the second refrigerant circuit (50). For example, if the refrigerant charge amount for the second refrigerant circuit (50) is 152g or less, the refrigerant charge amount for the first refrigerant circuit (10) is 2500g or more and 3500g or less.

[0051] Propane is a hydrocarbon refrigerant and has the property of being highly compatible with refrigeration oil. For this reason, the compatibility of the second refrigerant with the second refrigeration oil (e.g., PAG) is higher than the compatibility of the first refrigerant with the first refrigeration oil (e.g., PAG).

[0052] (5-2) Low-pressure issues due to refrigerant stagnation When the hot water supply system (1) is stopped, the temperature of the first compressor (11) and the second compressor (51) drops. As a result, the refrigerant inside the first compressor (11) and the second compressor (51) is prone to dissolving into the refrigerant oil, a phenomenon known as refrigerant stagnation.

[0053] As mentioned above, the second refrigerant circuit (50) uses a highly flammable refrigerant, and the amount of refrigerant charged is small. In addition, as mentioned above, propane has high compatibility with refrigeration oil, so a large amount of refrigerant dissolves into the refrigeration oil in the second compressor (51). For example, in the second refrigerant circuit (50), the amount of refrigerant charged is between 0.5 and 0.8 relative to the amount of refrigeration oil charged. In the second refrigerant circuit (50), the required amount of refrigeration oil is determined by the second compressor (51). Therefore, even if the amount of refrigerant charged is small, it is difficult to reduce the amount of refrigeration oil charged to match the amount of refrigerant charged. Consequently, if refrigerant stagnation occurs in the second compressor (51), the amount of refrigerant relative to the refrigeration oil is small, and the effective absolute amount of second refrigerant in the second refrigerant circuit (50) decreases. When the second compressor (51) is started from this state, the low pressure in the second refrigerant circuit (50) drops sharply. As a result, there is a possibility that the second compressor (51) cannot be started stably. Specifically, the low pressure in the second refrigerant circuit (50) may fall below a threshold, causing protective control of the second compressor (51) to be executed or the low pressure switch (89) to be activated. Therefore, in this embodiment, a start control is performed to solve this problem.

[0054] (5-3) Start-up control Details of the start-up control will be explained. Start-up control is performed when starting dual heating operation from the time the hot water supply system (1) is stopped. When the hot water supply system (1) is stopped, the first compressor (11) and the second compressor (51) are in a stopped state. Figure 5 is a flowchart of the start-up control.

[0055] For example, when a user operates a remote controller, a command for dual heating operation is input to the controller (100) (YES in step ST11). Then, in step ST12, the controller (100) determines whether the downtime of the hot water heater (1) is greater than or equal to the first time ΔT1. Here, the downtime is the time from the time the hot water heater (1) was last stopped until the present time. In this embodiment, the first time ΔT1 is a fixed value and is set to, for example, 3 hours. In step ST12, if the downtime is less than the first time ΔT1, the possibility of refrigerant buildup in the second compressor (51) is low. Therefore, in step ST12, if the downtime is less than the first time ΔT1, the controller (100) executes the dual heating operation as usual in step ST23. In step ST23, the controller (100) operates the first compressor (11) and the second compressor (51) at the same time.

[0056] In step ST12, if the stop time is 1 hour ΔT1 or longer, there is a high probability that refrigerant buildup will occur in the second compressor (51). Therefore, in step ST12, if the stop time is 1 hour ΔT1 or longer, the controller (100) will execute the first operation in step ST13.

[0057] In the first operation, the controller (100) operates the first compressor (11) while keeping the second compressor (51) in a stopped state. The controller (100) controls the rotational speed of the first compressor (11) to a first rotational speed R1. Specifically, in the first operation, the controller (100) operates the first compressor (11), sets the four-way switching valve (15) to the first state, adjusts the opening of the first expansion valve (13) and the second expansion valve (14), and operates the outdoor fan (17). As a result, as shown in Figure 6, in the first refrigerant circuit (10), a refrigeration cycle is performed in which the first refrigerant dissipates heat in the refrigerant heat exchanger (52) and the first refrigerant evaporates in the outdoor heat exchanger (12). In other words, in the first operation, a refrigeration cycle is performed in which the first flow path (52a) of the refrigerant heat exchanger (52) functions as a heat radiator and the outdoor heat exchanger (12) functions as an evaporator. In this embodiment, the controller (100) sets the bypass mechanism (30) to the second state in the first operation. As a result, the first refrigerant bypasses the first water heat exchanger (25).

[0058] During the first operation, when the first refrigerant in the first flow path (52a) dissipates heat in the refrigerant heat exchanger (52), this heat is transferred to the second compressor (51) via the refrigerant heat exchanger (52) (see the dashed arrow in Figure 6). As a result, the second compressor (51) is heated, and the refrigerant dissolved in the second refrigerant oil evaporates. Therefore, refrigerant stagnation in the second compressor (51) can be eliminated. In the first operation, the first refrigerant bypasses the first water heat exchanger (25), which suppresses heat dissipation from the first refrigerant to the water circuit (60), thus improving the heating capacity of the second compressor (51).

[0059] In the first operation of step ST13, the controller (100) of this embodiment determines the first rotational speed R1 based on the ambient temperature of the first compressor (11), specifically, the outside air temperature detected by the first air temperature sensor (86). When the outside air temperature is relatively low, it takes time for the first refrigerant to reach a temperature sufficient to heat the second refrigerant. In addition, when the outside air temperature is low, the density of the low-pressure gas refrigerant of the first refrigerant decreases, so the amount of refrigerant circulated in the first refrigerant circuit (10) in the first operation decreases. Therefore, the controller (100) increases the first rotational speed R1 as the outside air temperature decreases. This allows the second refrigerant to be heated quickly even under conditions of low outside air temperature.

[0060] In step ST14, when two time intervals ΔT2 have elapsed since the start of the first operation, in step ST15, the controller (100) executes a second operation to operate the second compressor (51). Specifically, in the second operation, the controller (100) maintains the operation of the first compressor (11) and operates the second compressor (51). In the second operation, the controller (100) adjusts the opening degree of the third expansion valve (53). As a result, in the second refrigerant circuit (50), a refrigeration cycle is performed in which the second refrigerant evaporates in the refrigerant heat exchanger (52) and the second refrigerant dissipates heat in the second water heat exchanger (54). In other words, in the second operation, a refrigeration cycle is performed in which the second flow path (52b) of the refrigerant heat exchanger (52) functions as an evaporator and the fifth flow path (54a) of the second water heat exchanger (54) functions as a heat radiator. Before the second operation, the refrigerant buildup is mitigated by the first operation, so when starting the second compressor (51), a rapid drop in the low pressure of the second refrigerant circuit (50) can be suppressed.

[0061] In the second operation, the controller (100) controls the rotational speed of the second compressor (51) to the second rotational speed R2. In this embodiment, the controller (100) controls the second compressor (51) at a low speed. Here, "low speed" means a rotational speed lower than the midpoint of the control range for the rotational speed of the second compressor (51). In this embodiment, the second rotational speed R2 is a fixed value within the range of, for example, 25 rps to 58 rps. It is preferable that the second rotational speed R2 is the lowest rotational speed of the second compressor (51) (for example, 25 rps). In the second operation, by controlling the rotational speed of the second compressor (51) to a low speed or the lowest rotational speed, a rapid decrease in the low pressure of the second refrigerant circuit (50) can be suppressed.

[0062] Next, in step ST16, the controller (100) determines whether a first condition indicating low low pressure is met. In this embodiment, the first condition is that the evaporation temperature Te of the second refrigerant circuit (50) is lower than a predetermined temperature (for example, -15°C). The controller (100) determines the evaporation temperature Te as the gas saturation temperature corresponding to the low low pressure detected by, for example, the suction pressure sensor (83). If the first condition is met, there is a possibility that the refrigerant buildup has not yet been sufficiently resolved. Therefore, if the first condition in step ST16 is met, in step ST19, the controller (100) stops the second compressor (51). The first condition may also be that the low pressure or evaporation pressure of the second refrigerant circuit (50) is lower than a predetermined value.

[0063] Next, in step ST20, the controller (100) adds 1 to flag N. This flag N represents the number of times the first condition has been met after the first operation by the startup control. If flag N is less than 3 in step ST21, the process returns to step ST14. After that, the controller (100) executes the second operation again after the second time ΔT2 has elapsed. If the first condition is met again (YES in step ST16) and the first operation is repeated, and flag N becomes greater than 3 (YES in step ST21), there is a possibility that the second refrigerant is leaking from the second refrigerant circuit (50). This is because, normally, the refrigerant buildup in the second compressor (51) is resolved by repeatedly executing the first operation. Therefore, if the condition in step ST21 is met, in step S22, the controller (100) determines that there is a suspicion of a leak of the second refrigerant in the second refrigerant circuit (50). In this case, the controller (100) executes the unit heating operation in step ST24. Details of the unit heating operation will be described later.

[0064] In step ST16, if the first condition is not met, in step ST17, the second operation is continuously executed for a third time ΔT3. The third time ΔT3 is, for example, 15 minutes. Next, in step ST18, the controller (100) determines whether the state in which α is greater than 5°C has continued for a fourth time ΔT4 or longer. Here, α is the difference (Tr1-Tr2) between the temperature Tr1 of the first refrigerant in the refrigerant heat exchanger (52) and the temperature Tr2 of the second refrigerant in the refrigerant heat exchanger (52). As the temperature Tr1 of the first refrigerant, the saturation temperature based on the high pressure of the first refrigerant detected by the first discharge pressure sensor (80) is used. As the temperature Tr2 of the second refrigerant, the saturation temperature based on the low pressure of the second refrigerant detected by the suction pressure sensor (83) is used.

[0065] Pressure sensors may be provided near the first flow path (52a) and the second flow path (52b) of the refrigerant heat exchanger (52), and the temperature Tr1 of the first refrigerant and the temperature Tr2 of the second refrigerant may be determined as saturation temperatures corresponding to the pressure detected by these pressure sensors. Alternatively, temperature sensors that directly detect the temperature Tr1 of the first refrigerant and the temperature of the second refrigerant may be provided on the refrigerant heat exchanger (52). If the second refrigerant leaks from the second refrigerant circuit (50), the low pressure in the second refrigerant circuit (50) does not rise easily. As a result, the temperature Tr2 of the second refrigerant remains low, and a relatively large α (= T1-T2) continues. Therefore, in step ST18, if the state in which α is greater than 5°C continues for four hours ΔT4 or more, the controller (100) determines in step ST22 that there is a suspicion of leakage of the second refrigerant from the second refrigerant circuit (50). Fourth hours ΔT4 is, for example, four minutes.

[0066] In step ST18, if the absolute value of the temperature Tr2 of the second refrigerant is used to determine refrigerant leakage, the accuracy of the refrigerant leakage determination will decrease due to the influence of the ambient temperature of the refrigerant heat exchanger (52). In contrast, by using the temperature difference α between the first and second refrigerants in the refrigerant heat exchanger (52), the decrease in the accuracy of refrigerant leakage determination due to the influence of ambient temperature can be suppressed.

[0067] If the conditions in step ST18 are not met and there is no suspicion of refrigerant leakage, then in step ST23, the operation of the first compressor (11) and the second compressor (51) continues, and the system transitions to normal dual heating operation.

[0068] (5-4) The unit heating operation of step ST24 will be explained. In the unit heating operation shown in Figure 7, the controller (100) operates the first compressor (11), operates the outdoor fan (17), sets the four-way switching valve (15) to the first state, sets the bypass mechanism (30) to the first state, and adjusts the opening of the first expansion valve (13) and the second expansion valve (14). The controller (100) stops the second compressor (51), so the refrigeration cycle does not occur in the second refrigerant circuit (50).

[0069] In the first refrigerant circuit (10), a refrigeration cycle is performed in which the first refrigerant dissipates heat in the first water heat exchanger (25) and the first refrigerant evaporates in the outdoor heat exchanger (12). In the second refrigerant circuit (50), the risk of refrigerant leakage can be reduced because the second compressor (51) is stopped. In the first water heat exchanger (25), the first refrigerant dissipates heat into the water in the water circuit (60). Therefore, hot water can be generated in the water circuit (60) while the second compressor (51) is stopped.

[0070] (6) Effects of the Embodiment (6-1) When the first compressor (11) and the second compressor (51) are stopped, the controller (100) operates the first compressor (11) while keeping the second compressor (51) stopped, and performs a first operation in which the first refrigerant is released into the refrigerant heat exchanger (52). After the first operation, the controller (100) performs a second operation in which the second compressor (51) is operated.

[0071] In this configuration, the first refrigerant discharged from the first compressor (11) by the first operation dissipates heat in the refrigerant heat exchanger (52). As a result, the second refrigerant in the second refrigerant circuit (50) is heated in the refrigerant heat exchanger (52), and furthermore, the inside of the second compressor (51) is heated. Consequently, any refrigerant buildup can be eliminated before starting the second compressor (51).

[0072] When the second operation is performed after the first operation, the second compressor (51) enters an operating state. At this time, since the refrigerant buildup in the second compressor (51) has been resolved, the second compressor (51) can be started stably while suppressing a rapid drop in low pressure.

[0073] (6-2) The controller (100) executes the first operation when the downtime of the first compressor (11) and the second compressor (51) is longer than the first time ΔT1. This eliminates the refrigerant buildup in the second compressor (51) under conditions where the downtime of the first compressor (11) and the second compressor (51) is long and the refrigerant is prone to buildup. The controller (100) does not execute the first operation when the downtime of the first compressor (11) and the second compressor (51) is shorter than the first time ΔT1, and instead performs a dual heating operation in which the first compressor (11) and the second compressor (51) are operated. This allows for the rapid commencement of dual heating operation under conditions where the possibility of refrigerant buildup in the second compressor (51) is low.

[0074] (6-3) In the second operation, the controller (100) controls the rotational speed of the second compressor (51) to a low speed. This prevents a rapid drop in the low pressure of the second refrigerant circuit (50) during the second operation. In particular, by setting the rotational speed of the second compressor (51) to the lowest speed, a rapid drop in the low pressure of the second refrigerant circuit (50) can be effectively prevented.

[0075] (6-4) The controller (100) repeats the first operation if the first condition is met during the second operation, in which the evaporation temperature, evaporation pressure, or low pressure of the second refrigerant circuit (50) is lower than a predetermined value. This allows the refrigerant to be eliminated under conditions where the low pressure of the second refrigerant circuit (50) is low and there is a possibility that the refrigerant has not yet been eliminated. As a result, it is possible to prevent the low pressure of the second refrigerant circuit (50) from becoming excessively low.

[0076] (6-5) The controller (100) stops the second compressor (51) if, during the second operation, the temperature difference α between the first refrigerant and the second refrigerant in the refrigerant heat exchanger (52) remains greater than a predetermined value for a fourth time ΔT4 or longer. If this condition is met, there is a possibility that refrigerant is leaking from the second refrigerant circuit (50). Stopping the second compressor (51) at this time can prevent the refrigerant leakage from being exacerbated. By using the temperature difference α as a judgment value, it is possible to prevent misjudgments due to the influence of the ambient temperature of the refrigerant heat exchanger (52).

[0077] (6-6) Since propane, a highly flammable refrigerant, is used as the second refrigerant, the amount of refrigerant charged into the second refrigerant circuit (50) is particularly reduced. This makes the problem of refrigerant stagnation in the second compressor (51) more pronounced. In contrast, by performing the first operation, refrigerant stagnation can be eliminated before the second compressor (51) is started.

[0078] Since carbon dioxide, used as the first refrigerant, is not a highly flammable refrigerant, the amount of refrigerant charged in the first refrigerant circuit (10) is greater than the amount of the second refrigerant charged in the second refrigerant circuit (50). In addition, carbon dioxide has lower compatibility with refrigerant oil compared to propane. For this reason, the amount of refrigerant in the first refrigerant circuit (10) is less likely to be insufficient when the first compressor (11) is started. Therefore, even when the first compressor (11) is started in the first operation, the low pressure in the first refrigerant circuit (10) is less likely to drop sharply. Thus, by performing the first and second operations of this embodiment, a sharp drop in low pressure can be suppressed in both the first refrigerant circuit (10) and the second refrigerant circuit (50).

[0079] (7) Modified Forms The above embodiment may also have the following modified configuration. The differences from the above embodiment will be explained below.

[0080] (7-1) Modification 1 The controller (100) may determine whether or not to perform the first operation based on other conditions under which it is presumed that refrigerant buildup has occurred when the first compressor (11) and the second compressor (51) are stopped. For example, the controller (100) may perform the first operation when the ambient temperature of the second compressor (51) is lower than a predetermined temperature, and perform dual heating operation without performing the first operation when the ambient temperature of the second compressor (51) is higher than the predetermined temperature.

[0081] (7-2) Modified Example 2 In the first operation of step ST13 in Figure 5, the controller (100) may control the first rotational speed R1 of the first compressor (11) to a predetermined fixed value. This fixed value may be a predetermined rotational speed greater than the minimum rotational speed of the first compressor (11), or it may be the maximum rotational speed of the first compressor (11).

[0082] (7-3) Modification 3 The controller (100) may determine the execution time of the first operation (second time ΔT2 in step SST14) based on the stop time of the first compressor (11) and the second compressor (51) before the first operation. If the stop time is long, a large amount of the second refrigerant dissolves into the refrigeration oil. Therefore, the controller (100) lengthens the second time ΔT2 when the stop time is long. This allows the refrigerant to settle sufficiently during the first operation. If the stop time is short, a small amount of the second refrigerant dissolves into the refrigeration oil. Therefore, the controller (100) shortens the second time ΔT2 when the stop time is short. This prevents the first operation from becoming excessively long and shortens the time until normal dual heating operation is reached.

[0083] (7-4) Modification 4 In the second operation of step ST15 in Figure 5, the controller (100) may control the second rotation speed R2 to decrease as the indicators showing the low pressure of the second refrigerant circuit (50) (low pressure, evaporation temperature, evaporation pressure) decrease. This makes it possible to suppress the low pressure of the second refrigerant circuit (50) from becoming excessively low in the second operation.

[0084] In the second operation, the controller (100) may stop the first compressor (11) and operate the second compressor (51).

[0085] (7-5) Modification 5 The controller (100) may immediately execute the second operation in step ST15 after stopping the second compressor (51) if the first condition in step ST16 is met. In other words, the controller (100) may execute the second operation even if the second time ΔT2 has not elapsed if the first condition is met.

[0086] (7-6) Modification 6 The hot water supply system (1) may have an alarm unit, a ventilation system, a shut-off valve, etc., as a countermeasure device for refrigerant leakage. The alarm unit informs the user of information regarding refrigerant leakage by sound, light, display, etc. The ventilation system ventilates the air in the room. The shut-off valve closes a predetermined flow path in the refrigerant circuit. The controller (100) activates such countermeasure devices when it determines, for example, in step ST22 of Figure 5 that there is a suspicion of refrigerant leakage. The controller (100) may stop the hot water supply system (1) without performing unit operation when it determines in step ST22 of Figure 5 that there is a suspicion of refrigerant leakage.

[0087] (7-7) Modification 7 The controller (100) may set the bypass mechanism (30) to a first state in the first operation. In this case, in the first operation, the water in the water circuit (60) can be heated before the dual heating operation. The controller (100) may operate the first compressor (11) with the first expansion valve (13) and the second expansion valve (14) fully open in the first operation.

[0088] (7-8) Modification 8 The controller (100) may perform the above-described start control when a thermo-on command is received after the indoor unit (IU) has entered the thermo-off state during dual heating operation. When the indoor unit (IU) enters the thermo-off state, refrigerant buildup in the second compressor (51) is more likely to occur. Therefore, the controller (100) performs start control in the same manner as in the embodiment when a thermo-on command is received while the thermo-off state is in effect. It is preferable for the controller (100) to perform the first operation when the indoor unit (IU) enters the thermo-off state and the stopping time of the first compressor (11) and the second compressor (51) is longer than a predetermined time.

[0089] (8) Other embodiments The refrigeration cycle device does not have to be a hot water supply device. The refrigeration cycle device may be an air conditioning device that adjusts the temperature of the indoor air or a cooling device that cools the air inside the storage room.

[0090] The first refrigerant circuit (10) may be configured without a first water heat exchanger (25).

[0091] The first and second expansion mechanisms do not necessarily have to be expansion valves; they may be capillary tubes or expansion machines. The first expansion mechanism has two expansion valves (13, 14), but may also consist of one expansion valve that reduces the pressure of the high-pressure refrigerant to a low-pressure level.

[0092] 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, the embodiments, modifications, and other embodiments described above may be combined or substituted as appropriate, as long as they do not impair the functions covered by this disclosure.

[0093] The designations "first," "second," "third," etc., mentioned above are used to distinguish between the terms to which these designations are attached, and do not limit the number or order of those terms.

[0094] As described above, this disclosure is useful for refrigeration cycle systems.

[0095] 1 Hot water supply system (refrigeration cycle system) 10 First refrigerant circuit 11 First compressor 12 Outdoor heat exchanger (heat source side heat exchanger) 50 Second refrigerant circuit 51 Second compressor 52 Refrigerant heat exchanger 53 Third expansion valve (second expansion mechanism) 54 Second water heat exchanger (utilization side heat exchanger) 100 Controller (control unit)

Claims

1. The system comprises: a first refrigerant circuit (10) through which a first refrigerant circulates to perform a refrigeration cycle; a second refrigerant circuit (50) through which a second refrigerant circulates to perform a refrigeration cycle; a refrigerant heat exchanger (52) for heat exchange between the first refrigerant in the first refrigerant circuit (10) and the second refrigerant in the second refrigerant circuit (50); and a control unit (100) for controlling the first refrigerant circuit (10) and the second refrigerant circuit (50), wherein the first refrigerant circuit (10) includes a first compressor (11), a heat source side heat exchanger (12), and a first expansion mechanism (13, 14); the second refrigerant circuit (50) includes a second compressor (51), a second expansion mechanism (53), and a utilization side heat exchanger (54); and the control unit (100) controls the first refrigerant circuit (10) and the second refrigerant circuit (50). A refrigeration cycle device that, when the first compressor (11) and the second compressor (51) are stopped, operates the first compressor (11) while the second compressor (51) is stopped, performing a first operation in which the first refrigerant is released into the refrigerant heat exchanger (52) to dissipate heat, and then performs a second operation in which the second compressor (51) is operated after the first operation.

2. The refrigeration cycle apparatus according to claim 1, wherein the control unit (100) causes the first operation to be performed when the stopping time of the first compressor (11) and the second compressor (51) is longer than a predetermined time.

3. The refrigeration cycle apparatus according to claim 1 or 2, wherein the control unit (100) controls the rotational speed of the second compressor (51) to a low speed in the second operation.

4. The refrigeration cycle apparatus according to any one of claims 1 to 3, wherein the control unit (100) causes the first operation to be executed again if, during the second operation, the first condition is met in which the evaporation temperature, evaporation pressure, or low pressure of the second refrigerant circuit (50) is lower than a predetermined value.

5. The refrigeration cycle apparatus according to any one of claims 1 to 4, wherein the control unit (100) stops the second compressor (51) if, during the second operation, the temperature difference between the first refrigerant and the second refrigerant in the refrigerant heat exchanger (52) remains greater than a predetermined value for a predetermined time or longer.

6. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the second refrigerant includes propane.

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