ES2983863T3 - Cooling device - Google Patents

Abstract

A heat source unit (10) comprising a heat source circuit (11) and connected to a use unit (50), thereby constituting a refrigeration circuit (2) that performs refrigeration cycles. The heat source unit (10) has: a switching mechanism (24) that switches between a first refrigeration cycle and a second refrigeration cycle; and a supercooling heat exchanger (40) having a first flow path (40a) and a second flow path (40b) through which a heat transfer medium that cools a refrigerant flowing through the first flow path (40a) flows. Furthermore, the heat source unit (10) comprises an adjustment mechanism (80) that performs a first operation that reduces the capacity of the second flow path (40b) to cool the refrigerant in the first flow path (40a), before switching from the first refrigeration cycle to the second refrigeration cycle. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Cooling device

Field of technology

The present invention relates to a refrigeration apparatus.

Prior art

A refrigerating apparatus having a refrigerating circuit is known. JP 201548983 A discloses a refrigerating apparatus having a refrigerating circuit. The refrigerating circuit includes a compressor, an air heat exchanger (heat source heat exchanger), an expansion valve, an internal heat exchanger (utilization heat exchanger) and a subcooler (subcooling heat exchanger). The refrigerating circuit performs a first refrigerating cycle and a second refrigerating cycle. In the first refrigerating cycle, the heat source heat exchanger serves as a radiator and the utilization heat exchanger serves as an evaporator. In the second refrigerating cycle, the heat source heat exchanger serves as an evaporator and the utilization heat exchanger serves as a radiator.

The refrigeration apparatus performs the first refrigeration cycle in a cooling operation. When the utilization heat exchanger freezes in the cooling operation, the refrigeration apparatus performs a defrosting operation. In the defrosting operation, the second refrigeration cycle is performed and the utilization heat exchanger serves as a radiator. This operation enables the refrigerant to melt the ice on the surface of the utilization heat exchanger.

Other examples of previously known refrigeration apparatus can be derived from JP 2015068571 A. JP 2010 236712 A discloses a refrigeration apparatus according to the preamble of independent claim 1.

Compendium of invention

Technical problem

When the refrigeration apparatus described above performs the first refrigeration cycle, the refrigerant that has dissipated heat in the heat source heat exchanger is cooled in the subcooling heat exchanger and then evaporated in the utilization heat exchanger. When the first refrigeration cycle is switched to the second refrigeration cycle, the refrigerant having a relatively high temperature flows into the subcooling heat exchanger from the utilization heat exchanger. This increases the thermal stress on the subcooling heat exchanger, which may cause cracks in the subcooling heat exchanger.

An objective of the present invention is to prevent the thermal stress on a subcooling heat exchanger from increasing when switching a first refrigeration cycle to a second refrigeration cycle.

Solution to the problem

This objective is solved by means of a refrigeration apparatus according to independent claim 1. Different embodiments of the invention are defined in the dependent claims.

A first aspect is directed to a refrigeration apparatus including a heat source unit (10) and a utilization unit (50) having a utilization heat exchanger (54). The heat source unit includes: a heat source circuit (11) including a compression element (20), a heat source heat exchanger (14), a subcooling heat exchanger (40) and a switching mechanism (24), the heat source unit being connected to a utilization unit (50) having a utilization heat exchanger (54) constituting a refrigerant circuit (2) performing a refrigeration cycle, wherein

The switching mechanism (24) is configured to switch the refrigeration cycle between a first refrigeration cycle in which the heat exchanger (14) of the heat source serves as a radiator and the heat exchanger (54) of utilization serves as an evaporator and a second refrigeration cycle in which the heat exchanger (54) of utilization serves as a radiator and the heat exchanger (14) of the heat source serves as an evaporator,

The subcooling heat exchanger (40) has a first channel (40a) connected to a middle portion of a liquid pipe (32, 33) through which a liquid refrigerant flows in the heat source circuit (11), and a second channel (40b) through which a heating medium for cooling the refrigerant in the first channel (40a) flows, and

The heat source unit (10) further comprises a regulating mechanism including an expansion valve (26) connected to an upstream side of the second channel (40b) and a control unit (101) configured to control an opening degree of the expansion valve (26), so that the cooling capacity is reduced in a first operation of reducing the capacity of the second channel (40b) to cool the refrigerant in the first channel (40a) before switching the first refrigeration cycle to the second refrigeration cycle.

In the first aspect, the first operation reduces the cooling capacity of the second channel (40b). As a result, the temperature of the coolant in the first channel (40a) increases.

This can prevent the thermal stress on the subcooling heat exchanger (40) from increasing even if a relatively high temperature refrigerant flows into the first channel (40a) from the utilization heat exchanger (54) in the second refrigeration cycle. In addition, controlling the opening degree of the expansion valve (26) can reduce the cooling capacity of the second channel (40b).

In a second aspect, the switching mechanism (24) is configured to switch the refrigeration cycle to the second refrigeration cycle when the temperature of the refrigerant flowing through the first channel (40a) exceeds a predetermined value in the first operation.

In the second aspect, the first refrigeration cycle is switched to the second refrigeration cycle when the temperature of the refrigerant in the first channel (40a) exceeds the predetermined value in the first operation.

In a third aspect, the heat source circuit (11) includes: an injection circuit (60) having one end branched from the liquid pipe (32, 33) and the other end communicating with an intermediate pressure portion or a suction portion of the compression element (20), and including the second channel (40b) through which a refrigerant as a heating medium flows; and the expansion valve (26) connected to the upstream side of the second channel (40b) in the injection circuit (60).

In the third aspect, the refrigerant in the second channel (40b) can be introduced into the compression element (20) through the injection circuit (60).

In a fourth aspect, the control unit (101) performs a first control in the first operation to reduce the opening degree of the expansion valve (26) so as to decrease the flow rate of the refrigerant in the second channel (40b).

In the fourth aspect, the first control reduces the flow rate of the coolant flowing into the second channel (40b). This may reduce the cooling capacity of the second channel (40b).

In a fifth aspect, the control unit (101) performs a second control in the first operation to increase the opening degree of the expansion valve (26) so as to increase the pressure of the refrigerant in the second channel (40b).

In the fifth aspect, the second control raises the pressure of the refrigerant flowing into the second channel (40b). This may reduce the cooling capacity of the second channel (40b).

In a sixth aspect, the control unit (101) performs, in the first operation, a first control to reduce the opening degree of the expansion valve (26) so that a flow rate of the refrigerant in the second channel (40b) decreases when a condition indicating that a discharge temperature, which is a temperature of the refrigerant discharged from the compression element (20), is low is met, and a second control to increase the opening degree of the expansion valve (26) so that the pressure of the refrigerant in the second channel (40b) increases when a condition indicating that the discharge temperature of the compression element (20) is high is met.

In the sixth aspect, the first control is performed when the discharge temperature is low. The second control is performed when the discharge temperature is high. The second control can reduce the temperature of the refrigerant discharged from the compression element (20).

In a seventh aspect, the heat source circuit (11) includes a flow regulating valve (28, 29) connected to a downstream side of the second channel (40b) in the injection circuit (60). The second control performed in the first operation regulates an opening degree of the flow regulating valve (28, 29) so that the discharge temperature, which is a temperature of the refrigerant discharged from the compression element (20), approaches a predetermined value.

In the seventh aspect, the amount of refrigerant introduced into the compression element (20) can be controlled by regulating the opening degree of the flow regulating valve (28, 29). This can control the discharge temperature of the compression element (20).

An eighth aspect is an embodiment of any one of the first to seventh aspects. In the eighth aspect, the heat source unit further includes:

a subcooling heat exchanger (40) having the first channel (40a) and the second channel (40b);

a bypass channel (70) configured to allow at least part of the refrigerant that has dissipated heat in the utilization heat exchanger (54) not to pass through the first channel (40a) in the second refrigeration cycle;

and

a channel switching mechanism (180) configured to regulate the refrigerant flowing through the first channel (40a) and allow the refrigerant to flow through the bypass channel (70) in the second refrigeration cycle.

In the eighth aspect, the flow rate of the refrigerant flowing through the first channel can be reduced in the second refrigeration cycle. This can prevent the thermal stress on the subcooling heat exchanger (40) from increasing.

A ninth aspect is an embodiment of any one of the first to eighth aspects. In the ninth aspect, the compression element (20) is a two-stage compression element having a first compression section (22, 23) and a second compression section (21), and is configured to compress the refrigerant in the first compression section (22, 23) and then compress the refrigerant again in the second compression section (21) in the first refrigeration cycle.

Brief description of the drawings

Figure 1 is a diagram of the piping system of a refrigeration apparatus according to one embodiment.

Figure 2 is a block diagram illustrating a relationship between a controller, various sensors, and components of a refrigerant circuit.

Figure 3 is a view corresponding to Figure 1, illustrating the flow of a coolant during a cooling operation.

Figure 4 is a view corresponding to Figure 1, illustrating the flow of a refrigerant during a defrosting operation.

Figure 5 is a flow chart of a first operation.

Figure 6 is a diagram of the piping system of a refrigeration appliance according to a first variation.

Figure 7 is a view corresponding to Figure 5, illustrating a first operation according to the first variation.

Figure 8 is a diagram of the piping system of a refrigeration appliance according to a second variation.

Figure 9 is a diagram of the piping system of a refrigeration appliance according to a third variation.

Figure 10 is a view corresponding to Figure 9, illustrating the flow of a coolant during a cooling operation.

Figure 11 is a view corresponding to Figure 9, illustrating the flow of a refrigerant during a defrosting operation.

Figure 12 is an enlarged diagram of the piping system of a subcooling heat exchanger and its peripheral components of a refrigeration apparatus according to a fourth variation.

Figure 13 is a view corresponding to Figure 12, illustrating the flow of a coolant during a cooling operation.

Figure 14 is a view corresponding to Figure 12, illustrating the flow of a refrigerant during a defrosting operation.

Figure 15 is a diagram of the piping system of a refrigerating apparatus according to a fifth variation. Figure 16 is a view corresponding to Figure 12 illustrating a refrigerating apparatus according to another embodiment. Figure 17 is a view corresponding to Figure 12 illustrating a refrigerating apparatus according to another embodiment. Figure 18 is a view corresponding to Figure 12 illustrating a refrigerating apparatus according to another embodiment. Description of the Embodiments

Embodiments of the present invention will be described below with reference to the drawings.

Realization

<General Settings>

A refrigerating apparatus (1) according to one embodiment cools air in a cooling tank. As illustrated in Fig. 1, the refrigerating apparatus (1) includes an outdoor unit (10) and an indoor unit (50). The outdoor unit (10) is a heat source unit (10) and is placed outdoors. The indoor unit (50) is a utilization unit (50).

The outdoor unit (10) includes a heat source circuit (11). The indoor unit (50) includes a utilization circuit (51). The heat source circuit (11) and the utilization circuit (51) are connected to each other by connecting pipes (3, 4) to form a refrigerant circuit (2) in the refrigeration apparatus (1). A refrigerant circulates in the refrigerant circuit (2) to perform a vapor compression refrigeration cycle.

The connecting pipes connecting the heat source circuit (11) and the utilization circuit (51) to each other are a liquid connecting pipe (3) and a gas connecting pipe (4). One end of the liquid connecting pipe (3) is connected to a liquid-side shut-off valve (17) connected to one end of the heat source circuit (11). One end of the gas connecting pipe (4) is connected to a gas-side shut-off valve (18) connected to the other end of the heat source circuit (11).

<Outdoor unit>

The outdoor unit (10) includes an outdoor fan (15), the heat source circuit (11) and a regulating mechanism (80). The heat source circuit (11) includes a compression element (20), a four-way switching valve (24), an outdoor heat exchanger (14), a receiver (39) and a subcooling heat exchanger (40).

<Compression element and its peripheral structure>

The compression element (20) compresses a refrigerant which is a heating medium. The compression element (20) constitutes a two-stage compression element which compresses the refrigerant in the first compression sections (22, 23) to a lower pressure, and then compresses the refrigerant again in a second compression section (21) to a higher pressure. Specifically, the first compression sections (22, 23) include a first low-pressure compressor (22) and a second low-pressure compressor (23). The second compression section (21) is a high-pressure compressor (21). The first low-pressure compressor (22) and the second low-pressure compressor (23) are connected in parallel to each other. Each of the compressors (21 to 23) is a high-pressure dome-shaped hermetic scroll compressor.

A compression mechanism (not shown) and an electric motor (not shown) driving the compression mechanism are connected to each of the compressors (21 to 23). The electric motors of the high-pressure compressor (21) and the second low-pressure compressor (23) are connected to an inverter capable of freely changing the number of rotations of the electric motors within a predetermined range. The inverter can adjust the number of rotations of the electric motors, thereby increasing or decreasing the operating capacities of the high-pressure compressor (21) and the second low-pressure compressor (23). The inverter is not connected to the electric motor of the first low-pressure compressor (22). Thus, the first low-pressure compressor (22) has a fixed operating capacity. The first low-pressure compressor (22) rotates at a constant rotation speed.

A first suction pipe (44) and a first discharge pipe (41) are connected to the high-pressure compressor (21). A first check valve (CV1) is connected to the first discharge pipe (41). The first check valve (CV1) allows refrigerant to flow from a discharge end of the high-pressure compressor (21) to the four-way switching valve (24) to be described later, and prevents refrigerant from flowing in the opposite direction. A second suction pipe (45) and a second discharge pipe (42) are connected to the first low-pressure compressor (22). A second check valve (CV2) is connected to the second discharge pipe (43). The second check valve (CV2) allows refrigerant to flow from a discharge end of the first low-pressure compressor (22) to a second joining pipe (47) to be described later, and prevents refrigerant from flowing in the opposite direction. A third suction pipe (46) and a third discharge pipe (43) are connected to the second low-pressure compressor (23). A third check valve (CV3) is connected to the third discharge pipe (43). The third check valve (CV3) allows refrigerant to flow from a discharge end of the second low-pressure compressor (23) to the second joint pipe (47) to be described later, and prevents refrigerant from flowing in the opposite direction.

The second suction pipe (45) and the third suction pipe (46) are connected to a first joint pipe (48). The second discharge pipe (42) and the third discharge pipe (43) are connected to the second joint pipe (47). The heat source circuit (11) has a connecting pipe (49) having one end connected to the center of the first joint pipe (48) and the other end connected to the center of the second joint pipe (47). A sixth motor-operated valve (53) is connected to the connecting pipe (49). The sixth motor-operated valve (53) is a flow regulating valve. The sixth motor-operated valve (53) regulates the flow rate of the refrigerant in the connecting pipe (49).

<Four-way switching valve>

The four-way switching valve (24) constitutes a switching mechanism that switches the refrigerant channel. The four-way switching valve (24) has first to fourth ports (P1 to P4). The first port (P1) is connected to the first discharge pipe (41) of the high-pressure compressor (21). The second port (P2) is connected to the first suction pipe (44). The third port (P3) communicates with a gas end of the outdoor heat exchanger (14). The fourth port (P4) is connected to the second joint pipe (47).

The four-way switching valve (24) is configured to be switchable between a first state (the state indicated by solid curves in Figure 1) and a second state (the state indicated by dashed curves in Figure 1). In the first state, the second port (P2) and the fourth port (P4) communicate with each other, and the first port (P1) and the third port (P3) communicate with each other. In the second state, the second port (P2) and the third port (P3) communicate with each other, and the first port (P1) and the fourth port (P4) communicate with each other.

<Outdoor heat exchanger>

The outdoor heat exchanger (14) is a heat source heat exchanger (14). The outdoor heat exchanger (14) is a finned tube air heat exchanger. The outdoor fan (15) is arranged near the outdoor heat exchanger (14). The outdoor fan (15) transfers outdoor air. The outdoor heat exchanger (14) exchanges heat between the refrigerant flowing therethrough and the outdoor air transferred from the outdoor fan (15).

The gas end of the outdoor heat exchanger (14) communicates with the third port (P3) of the four-way switching valve (24). A liquid end of the outdoor heat exchanger (14) is connected to one end of a first pipe (31).

<Receiver, subcooling heat exchanger and peripheral structure thereof>

The receiver (39) is a container for storing the refrigerant. The receiver (39) separates the refrigerant into a gaseous refrigerant and a liquid refrigerant.

The subcooling heat exchanger (40) has a first channel (40a) and a second channel (40b). The first channel (40a) is connected to the center of a liquid pipe (32, 33) through which the liquid refrigerant flows. The refrigerant which is a heating medium flows through the second channel (40b). The second channel cools the refrigerant flowing through the first channel (40a). In the subcooling heat exchanger (40), heat exchange occurs between the refrigerant flowing through the first channel (40a) and the refrigerant flowing through the second channel (40b).

The first pipe (31) connects the liquid end of the outdoor heat exchanger (14) and the top of the receiver (39). A fourth outdoor check valve (CV4) is connected to the first pipe (31). The fourth outdoor check valve (CV4) allows refrigerant to flow from the outdoor heat exchanger (14) to the receiver (39) and prevents refrigerant from flowing in the opposite direction.

A second pipe (32) connects the bottom of the receiver (39) and one end of the first channel (40a) of the subcooling heat exchanger (40). The second pipe (32) constitutes part of the liquid pipe.

A third pipe (33) connects the other end of the first channel (40a) and the liquid side stop valve (17). The third pipe (33) constitutes a part of the liquid pipe. A fifth outer check valve (CV5) is connected to the third pipe (33). The fifth outer check valve (CV5) allows the refrigerant to flow from the first channel (40a) to an internal heat exchanger (54), and prevents the refrigerant from flowing in the opposite direction.

A fourth pipe (34) is connected to the third pipe (33). One end of the fourth pipe (34) is connected to the third pipe (33) between the fifth outdoor check valve (CV5) and the liquid side stop valve (17). The other end of the fourth pipe (34) is connected to the first pipe (31) between the fourth outdoor check valve (CV4) and the receiver (39). A sixth outdoor check valve (CV6) is connected to the fourth pipe (34). The sixth outdoor check valve (CV6) allows refrigerant to flow from the indoor heat exchanger (54) to the outdoor heat exchanger (14), and prevents refrigerant from flowing in the opposite direction.

A fifth pipe (35) is connected to the second pipe (32). One end of the fifth pipe (35) is connected to the center of the second pipe (32). The other end of the fifth pipe (35) is connected to the first pipe (31) between the fourth outdoor check valve (CV4) and the outdoor heat exchanger (14). An outdoor expansion valve (25) is connected to the fifth pipe (35). The outdoor expansion valve (25) is an electronic expansion valve having a variable opening degree. A seventh outdoor check valve (CV7) is connected to the fifth pipe (35). The seventh outdoor check valve (CV7) is provided between the junction of the first pipe (31) with the fifth pipe (35) and the outdoor expansion valve (25). The seventh outdoor check valve (CV7) allows refrigerant to flow from the indoor heat exchanger (54) to the outdoor heat exchanger (14) and prevents refrigerant from flowing in the opposite direction.

<Injection circuit>

The heat source circuit (11) includes an injection circuit (60). The injection circuit (60) introduces an intermediate pressure refrigerant into the liquid pipe (32, 33) inside the compression element (20). The injection circuit (60) has a branched end of the liquid pipe (32, 33) and the other end communicates with an intermediate pressure portion of the compression element (20). The injection circuit (60) includes the second channel (40b), a first branch pipe (61), a relay pipe (62) and three injection pipes (63, 64, 65).

An inflow end of the first branch pipe (61) is connected to the third pipe (33) between the junction of the third pipe (33) with the fourth pipe (34) and the liquid side stop valve (17). An outflow end of the first branch pipe (61) is connected to an inflow end of the second channel (40b) of the subcooling heat exchanger (40). [0049]

An injection valve (26) is connected to the first branch pipe (61). The injection valve (26) is an expansion valve (26) having a variable opening degree. The injection valve (26) is constituted by an electronic expansion valve.

An inlet flow end of the relay pipe (62) is connected to an outlet flow end of the second channel (40b). An outlet portion of the relay pipe (62) is connected to the inlet flow ends of the first injection pipe (63), the second injection pipe (64) and the third injection pipe (65).

An outlet flow end of the first injection pipe (63) communicates with a compression chamber of the high pressure compressor (21). An outlet flow end of the second injection pipe (64) communicates with a compression chamber of the first low pressure compressor (22). An outlet flow end of the third injection pipe (65) communicates with a compression chamber of the second low pressure compressor (23).

A first motor-operated valve (27) is connected to the first injection pipe (63). A second motor-operated valve (28) is connected to the second injection pipe (64). A third motor-operated valve (29) is connected to the third injection pipe (65). The first to third motor-operated valves (27 to 29) are flow regulating valves. Each of the first to third motor-operated valves (27 to 29) regulates the flow rate of the coolant in the corresponding injection pipes (63 to 65).

<Bypass channel>

The fourth pipe (34) constitutes a bypass channel (70). The bypass channel (70) may include the first pipe (31), the second pipe (32), and the fifth pipe (35). The bypass channel (70) may further include the receiver (39). The bypass channel (70) is connected in parallel with the subcooling heat exchanger (40). The refrigerant in the bypass channel (70) does not pass through the subcooling heat exchanger (40). Specifically, the refrigerant that has dissipated heat in the internal heat exchanger (54) in the second refrigeration cycle flows through the fourth pipe (34), the first pipe (31), the receiver (39), the second pipe (32), and the fifth pipe (35) in this order.

<Channel switching mechanism>

The sixth outer check valve (CV6) and the fifth outer check valve (CV5) constitute a channel switching mechanism (180). The channel switching mechanism (180) may include the fourth outer check valve (CV4) and the seventh outer check valve (CV7).

In the second refrigeration cycle, the channel switching mechanism (180) regulates the refrigerant flowing through the first channel (40a) and allows the refrigerant to flow through the bypass channel (70). Specifically, in the second refrigeration cycle, the channel switching mechanism (180) prevents the refrigerant from flowing through the first channel (40a), and allows the refrigerant to flow through the bypass channel (70). In the first refrigeration cycle, the channel switching mechanism (180) allows the refrigerant to flow through the first channel (40a) and prevents the refrigerant from flowing through the bypass channel (70).

Specifically, in the first refrigeration cycle, the seventh outdoor check valve (CV7) prevents the refrigerant that has entered the first pipe (31) from the outdoor heat exchanger (14) from flowing through the fifth pipe (35). In the first refrigeration cycle, the sixth outdoor check valve (CV6) prevents the refrigerant that has entered the first pipe (31) from the outdoor heat exchanger (14) from flowing through the fourth pipe (34). The outdoor expansion valve (25) is fully opened in the first refrigeration cycle. Thus, the outdoor expansion valve (25) allows the refrigerant to flow into the first channel (40a).

In the second refrigeration cycle, the fifth outdoor check valve (CV5) prevents the refrigerant from flowing through the first channel (40a). In the second refrigeration cycle, the sixth outdoor check valve (CV6) allows the refrigerant to flow through the fourth pipe (34). In the second refrigeration cycle, the fourth outdoor check valve (CV4) prevents the refrigerant that has entered the first pipe (31) from the fourth pipe (34) from flowing into the outdoor heat exchanger (14). In the second refrigeration cycle, the outdoor expansion valve (25) decompresses the refrigerant. Thus, the outdoor expansion valve (25) allows the refrigerant to flow from the second pipe (32) into the fifth pipe (35). In the second refrigeration cycle, the seventh outdoor check valve (CV7) allows the refrigerant to flow through the fifth pipe (35).

The refrigerant downstream of the fifth outdoor check valve (CV5) has a higher pressure than the refrigerant upstream of the fifth outdoor check valve (CV5). This is because the pressure of the refrigerant in the first channel (40a) corresponds to the pressure of the refrigerant decompressed by the outdoor expansion valve (25). Thus, the refrigerant in the first channel (40a) does not pass through the fifth outdoor check valve (CV5).

<Sensor>

The indoor unit (10) is provided with various sensors. For example, the first to third discharge pipes (41 to 43) are respectively provided with first to third discharge temperature sensors (71 to 73). The first discharge temperature sensor (71) detects a first discharge temperature (Td1) which is the temperature of the refrigerant discharged from the high-pressure compressor (21). The second discharge temperature sensor (72) detects a second discharge temperature (Td2) which is the temperature of the refrigerant discharged from the first low-pressure compressor (22). The third discharge temperature sensor (73) detects a third discharge temperature (Td3) which is the temperature of the refrigerant discharged from the second low-pressure compressor (23). The third pipe (33) is provided with a liquid temperature sensor (74). The liquid temperature sensor (74) detects the temperature (TL) of the refrigerant flowing through the third pipe (33).

The first branch pipe (61) is provided with a first temperature sensor (75). The first temperature sensor (75) is arranged between the injection valve (26) and the second channel (40b). The first temperature sensor (75) detects the temperature (Tg1) of the coolant flowing into the second channel (40b).

The relay pipe (62) is provided with a second temperature sensor (76). The second temperature sensor (76) is arranged near the second channel (40b). The second temperature sensor (76) detects the temperature (Tg2) of the refrigerant that has just flowed into the relay pipe (62) from the second channel (40b). The relay pipe (62) is provided with a pressure sensor (77). The pressure sensor (77) detects the pressure (MP) of the refrigerant in the relay pipe (62).

<External unit>

The indoor unit (50) is a utilization unit. The indoor unit (50) includes the utilization circuit (51) and an internal fan (52).

The utilization circuit (51) is connected to the liquid connection pipe (3) and the gas connection pipe (4). The utilization circuit (51) includes a heating pipe (55), an internal expansion valve (30) and the internal heat exchanger (54) arranged in this order from the liquid end to the gas end.

The heating pipe (55) is connected to a drain pan (59) connected to a lower portion of the internal heat exchanger (54). The drain pan (59) collects condensation water dripping from the internal heat exchanger (54). The heating pipe (55) heats the drain pan (59) to prevent the drain water from freezing.

The internal expansion valve (30) is a temperature-sensitive expansion valve having a sensing bulb. When the internal heat exchanger (54) operates as an evaporator, the opening degree of the internal expansion valve (30) is adjusted according to the temperature of the refrigerant at the outlet of the internal heat exchanger (54). When the internal heat exchanger (54) operates as a radiator, the internal expansion valve (30) is completely closed.

The internal heat exchanger (54) constitutes a utilization heat exchanger. The internal heat exchanger (54) is a tube and fin heat exchanger and exchanges heat between the refrigerant and the air in the tank. The internal fan (52) is arranged near the internal heat exchanger (54). The internal fan (52) supplies the air in the tank to the internal heat exchanger (54).

The utilization circuit (51) includes an internal bypass channel (58) which bypasses the internal expansion valve (30). An internal check valve (CV8) is connected to the internal bypass channel (58). The internal check valve (CV8) allows the refrigerant to flow from the internal heat exchanger (54) to the heating pipe (55) and prevents the refrigerant from flowing in the opposite direction.

<Controller>

A controller (100), which is a control unit, includes a microcomputer mounted in a control box and a memory device (specifically, a semiconductor memory) storing software for operating the microcomputer. The controller (100) controls various components of the refrigeration apparatus (1) based on detection signals from various sensors.

As illustrated in Figure 2, the controller (100) includes an outdoor controller (101) provided in the outdoor unit (10) and an indoor controller (102) provided in the indoor unit (50). The outdoor controller (101) can communicate with the indoor controller (102).

The outdoor controller (101) serving as a control unit is connected to various sensors such as the first to third discharge temperature sensors (71 to 73), the liquid temperature sensor (74), the first and second temperature sensors (75, 76), and the pressure sensor (77) via communication lines. The outdoor controller (101) is connected to components of the refrigerant circuit (2) such as the injection valve (26), the first to third motor-driven valves (27 to 29), and the outdoor fan (15) via communication lines.

The internal controller (102) is connected to the components of the refrigerant circuit (2), such as the internal expansion valve (30) and the internal fan (52), by means of communication lines.

The outdoor controller (101) receives a signal from the indoor controller (102) and controls the four-way switching valve (24) to switch between the first refrigeration cycle and the second refrigeration cycle. When the four-way switching valve (24) is switched to the first state, the first refrigeration cycle is performed. In the first refrigeration cycle, the outdoor heat exchanger (14) serves as a radiator and the indoor heat exchanger (54) serves as an evaporator. In the first refrigeration cycle, a cooling operation is performed to cool the air in the tank. When the four-way switching valve (24) is switched to the second state, the second refrigeration cycle is performed. In the second refrigeration cycle, the indoor heat exchanger (54) serves as a radiator and the outdoor heat exchanger (14) serves as an evaporator. In the second refrigeration cycle, a defrosting operation is performed to remove ice adhered to the indoor heat exchanger (54).

<Regulatory mechanism>

The regulating mechanism (80) includes the injection valve (26) and the controller (100). Before the first refrigeration cycle is switched to the second refrigeration cycle, the regulating mechanism (80) performs a first operation of reducing the capacity of the second channel (40b) to cool the refrigerant in the first channel (40a).

In the first operation, the controller (100) controls the opening degree of the injection valve (26) to reduce the cooling capacity.

In the first operation, the reduction of the cooling capacity raises the temperature of the coolant flowing through the first channel (40a). The cooling capacity is represented, for example, by a value obtained by multiplying a difference between the specific enthalpies of the coolant at the outlet and inlet of the second channel (40b) by the flow rate of the coolant flowing through the second channel (40b).

When the temperature of the refrigerant flowing through the first channel (40a) exceeds a predetermined value, the four-way switching valve (24) switches the first state to the second state. In other words, the switching mechanism (24) switches the first refrigeration cycle to the second refrigeration cycle. The predetermined value is a target temperature (target TL) of the refrigerant coming from the first channel (40a) and flowing through the third pipe (33) in the first state. Details of the target temperature (target TL) will be described later.

-Operation-

<Cooling operation>

In the cooling operation, the compressors (21 to 23), the outdoor fan (15) and the indoor fan (52) operate. The four-way switching valve (24) is set to the first state and the outdoor expansion valve (25) is completely closed. The opening degrees of the indoor expansion valve (30), the injection valve (26) and the first to third motor-driven valves (27 to 29) are appropriately adjusted. The sixth motor-driven valve (53) is completely closed and no refrigerant flows through the connecting pipe (49).

In the cooling operation, the four-way switching valve (24) is in the first state. In the first state, the first refrigeration cycle is performed in which the outdoor heat exchanger (14) serves as a condenser (radiator) and the indoor heat exchanger (54) serves as an evaporator.

As illustrated in Figure 3, the refrigerant compressed by the first low-pressure compressor (22) and the second low-pressure compressor (23) flows through the second joint pipe (47) in the cooling operation.

This refrigerant passes through the four-way switching valve (24) and the first suction pipe (44), and is introduced into the compression chamber of the high-pressure compressor (21). The high-pressure refrigerant compressed by the high-pressure compressor (21) passes through the first discharge pipe (41) and the four-way switching valve (24) and flows to the outdoor heat exchanger (14). The refrigerant dissipates heat to the outdoor air in the outdoor heat exchanger (14). The refrigerant that has dissipated heat in the outdoor heat exchanger (14) flows through the first pipe (31). The seventh outdoor check valve (CV7) and the sixth outdoor check valve (CV6) regulate the refrigerant flowing through the fifth pipe (35) and the fourth pipe (34) that are part of the bypass channel (70). Thus, the refrigerant flows into the receiver (39) and passes through the second pipe (32) and the first channel (40a) of the subcooling heat exchanger (40).

When the injection valve (26) is opened, part of the refrigerant in the third pipe (33) flows through the first branch pipe (61). The refrigerant in the first branch pipe (61) is decompressed by the injection valve (26) and then flows through the second channel (40b) of the subcooling heat exchanger (40). In the subcooling heat exchanger (40), heat exchange occurs between the refrigerant in the second channel (40b) and the refrigerant in the first channel (40a). The refrigerant in the second channel (40b) absorbs heat from the refrigerant in the first channel (40a) and evaporates. This cools the refrigerant in the first channel (40a), which increases the degree of subcooling of the refrigerant.

The refrigerant that has flowed through the second channel is introduced into the compression chambers of the compressors (21 to 23) from the injection pipes (63 to 65) by means of the relay pipe (62).

The cooled refrigerant in the first channel (40a) flows through the third pipe (33) and the liquid connection pipe (3), and is sent to the indoor unit (50).

In the indoor unit (50), the refrigerant passes through the heating pipe (55) and is decompressed by the internal expansion valve (30). The refrigerant flows to the internal heat exchanger (54) and absorbs heat from the air in the tank to evaporate. Thus, the air in the tank is cooled.

The refrigerant evaporated in the indoor heat exchanger (54) is sent to the outdoor unit (10) through the gas connection pipe (4). This refrigerant flows through the first connection pipe (48) and is sucked into the first low-pressure compressor (22) and the second low-pressure compressor (23). This circulation of the refrigerant achieves cooling operation to maintain the temperature in the cooling tank at a set temperature.

<Deicing operation>

In the defrosting operation, the high-pressure compressor (21) and the outdoor fan (15) operate and the indoor fan (52) stops. The four-way switching valve (24) is set to the second state and the indoor expansion valve (30) is completely closed. The sixth motor-driven valve (53) is fully opened.

In the defrosting operation, the coolant may flow through the injection circuit (60) as in the cooling operation. The injection valve (26) may be completely closed so that no coolant flows through the injection circuit (60).

In the defrosting operation, the four-way switching valve (24) is in the second state. In the second state, the second refrigeration cycle is performed in which the outdoor heat exchanger (14) serves as an evaporator and the indoor heat exchanger (54) serves as a condenser (radiator).

As illustrated in Figure 4, the refrigerant compressed in the high-pressure compressor (21) flows through the first discharge pipe (41), the four-way switching valve (24), the second joint pipe (47), the connecting pipe (49), and the first joint pipe (48) in this order in the defrosting operation. This refrigerant is sent to the indoor unit (50) through the gas connecting pipe (4). The refrigerant flows through the indoor heat exchanger (54) in the indoor unit (50). The refrigerant melts the ice on the surface of the indoor heat exchanger (54). The refrigerant that has dissipated heat in the indoor heat exchanger (54) flows through the indoor bypass channel (58) and the heating pipe (55). This refrigerant flows through the liquid connecting pipe (3) and is sent to the outdoor unit (10).

The refrigerant in the outdoor unit (10) enters the fourth pipe (34) from the third pipe (33). The refrigerant then flows through the first pipe (31), the receiver (39) and the second pipe (32) in this order. This refrigerant enters the fifth pipe (35), and is then decompressed by the outdoor expansion valve (25). The flow of this refrigerant to the first channel (40a) is regulated. This is because, as described above, the differential pressure across the fifth outdoor check valve (CV5) prevents the refrigerant from flowing through the fifth outdoor check valve (CV5). The refrigerant flowing through the fifth pipe (35) passes through the first pipe (31) and then flows to the outdoor heat exchanger (14).

In the outdoor heat exchanger (14), the low-pressure refrigerant exchanges heat with the outdoor air to evaporate. The evaporated refrigerant in the outdoor heat exchanger (14) passes through the four-way switching valve (24) and the first suction pipe (44), and is introduced into the compression chamber of the high-pressure compressor (21). This circulation of the refrigerant achieves the defrosting operation to remove ice adhered to the indoor heat exchanger (54).

-Problem when switching from the second cooling cycle to the first cooling cycle-

The direction of the refrigerant flowing in the first refrigeration cycle and the direction of the refrigerant flowing in the second refrigeration cycle are opposite to each other. Thus, when the refrigeration apparatus (1) including the subcooling heat exchanger (40) connected between the channel of the outdoor heat exchanger (14) and the channel of the indoor heat exchanger (54) switches the first refrigeration cycle to the second refrigeration cycle, a relatively high-temperature refrigerant flows from the indoor heat exchanger (54) to the channel (first channel (40a)) of the subcooling heat exchanger (40). If the high-temperature refrigerant suddenly flows into the first channel (40a) that has been cooled in the first refrigeration cycle, the thermal stress on the subcooling heat exchanger (40) increases due to the temperature difference. This may cause damage to the subcooling heat exchanger (40).

Strictly speaking, the refrigerant does not flow continuously through the first channel (40a) in the defrosting operation (second refrigeration cycle). Since the refrigerant has a higher pressure at the outlet of the fifth outdoor check valve (CV5) than at the inlet of the fifth outdoor check valve (CV5), the refrigerant is prevented from flowing continuously from the first channel (40a) to the third pipe (33). This is because the pressure of the refrigerant in the first channel (40a) corresponds to the pressure of the refrigerant decompressed by the outdoor expansion valve (25).

However, as illustrated in Figure 4, part of the refrigerant flowing from the receiver (39) to the second pipe (32) enters the first channel (40a) at the start of the defrosting operation. If the high-temperature refrigerant suddenly flows into the first channel (40a) that has been cooled in the first refrigeration cycle, the thermal stress on the subcooling heat exchanger (40) increases and the subcooling heat exchanger (40) may be damaged.

In consideration of such a problem, the refrigeration apparatus (1) of the present embodiment performs the following operation before switching the first refrigeration cycle to the second refrigeration cycle to prevent the thermal stress in the first channel (40a) from increasing.

<First operation>

A first operation will be described in detail below. When a condition for starting the defrosting operation in the cooling operation is met, the indoor controller (102) transmits a defrosting request signal. The outdoor controller (101) receives the defrosting operation request. The outdoor controller (101) serving as the regulating mechanism (80) performs the first operation. Specifically, in the first operation, the outdoor controller (101) controls the injection valve (26) and the second and third motor-driven valves (28, 29).

As illustrated in Figure 5, upon receiving a command to execute the first operation, the outdoor controller (101) stores the current opening degree (Pls1) of the injection valve (26) in step ST1.

In step ST2, the outdoor controller (101) determines whether a condition indicating that the discharge temperature of the compression element (20) is high is met. Specifically, the outdoor controller (101) determines whether a condition indicating that the second discharge temperature (Td2) of the first low-pressure compressor (22) and the third discharge temperature (Td3) of the second low-pressure compressor (23) are both high is met. More specifically, the outdoor controller (101) determines whether the following conditions a) and b) are met in step ST2.

a) The second discharge temperature (Td2) of the first low pressure compressor (22) is lower than a predetermined value. The predetermined value is, for example, 95 °C.

b) The third discharge temperature (Td3) of the second low pressure compressor (23) is lower than a predetermined value. The predetermined value is, for example, 95 °C.

If both conditions a) and b) are met in step ST2, the process continues with step ST3. If at least one of conditions a) or b) is not met in step ST2, the process continues with steps ST4 to ST6.

In step ST3, the outdoor controller (101) performs a first control to reduce the opening degree of the injection valve (26) so that the flow rate of the refrigerant in the second channel (40b) decreases. The first control reduces the flow rate of the refrigerant flowing through the second channel (40b). Thus, the amount of heat exchanged between the refrigerant in the second channel (40b) and the refrigerant in the first channel (40a) decreases. This reduces the ability of the second channel (40b) to cool the refrigerant in the first channel (40a). As a result, the temperature of the refrigerant flowing through the first channel (40a) increases and the temperature (TL) of the refrigerant in the third pipe (33) increases.

The outdoor controller (101) performs the first control until the temperature of the refrigerant (TL) in the third pipe (33) detected by the liquid temperature sensor (74) reaches the target temperature (target TL). A thermal stress is applied to the subcooling heat exchanger (40) because of the difference in refrigerant temperature before and after switching from the cooling operation (first refrigeration cycle) to the defrosting operation (second refrigeration cycle). The outdoor controller (101) sets the target temperature (target TL) to a temperature at which the subcooling heat exchanger (40) can withstand the thermal stress. Specifically, the outdoor controller (101) sets the target temperature (target TL) to the lower of temperature A or temperature B. Temperature A is calculated based on a target temperature of the refrigerant discharged from the compression element (20) during defrosting operation. Temperature A is also calculated by taking into account the number of times of defrosting operation and the temperature of liquid refrigerant during cooling operation. Temperature B is a saturation temperature corresponding to the high pressure during cooling operation.

In the first control, the outdoor controller (101) sets an upper limit value of a control range of the opening degree of the injection valve (26). This upper limit value is the opening degree (Pls1) stored in step ST1. Thus, in the first control, the outdoor controller (101) adjusts the opening degree of the injection valve (26) within a range not exceeding the upper limit opening degree (Pls1).

In step ST4, the outdoor controller (101) performs a second control to increase the opening degree of the injection valve (26) so that the pressure of the refrigerant in the second channel (40b) increases. The second control raises the evaporation temperature of the refrigerant in the second channel (40b). This reduces the ability of the second channel (40b) to cool the refrigerant in the first channel (40a). As a result, the temperature of the refrigerant flowing through the first channel (40a) increases and the temperature (TL) of the refrigerant in the third pipe (33) increases.

The outdoor controller (101) performs the second control until the pressure (MP) detected by the pressure sensor (77) reaches a target intermediate pressure (target MP). The target intermediate pressure (target MP) is calculated based on the saturation pressure corresponding to the target temperature (target TL) of the refrigerant in the third pipe (33).

In step ST5, the outdoor controller (101) adjusts the opening degree of the second motor-driven valve (28) so that the second discharge temperature (Td2) approaches a predetermined value. Specifically, the outdoor controller (101) adjusts the amount of refrigerant introduced into an intermediate pressure portion of the first low-pressure compressor (22). The predetermined value is, for example, 95 °C.

In step ST6, the outdoor controller (101) adjusts the opening degree of the third motor-driven valve (29) so that the third discharge temperature (Td3) approaches a predetermined value. Specifically, the outdoor controller (101) adjusts the amount of refrigerant introduced into an intermediate pressure portion of the second low-pressure compressor (23). The predetermined value is, for example, 95 °C.

In step ST7, the outdoor controller (101) determines whether the temperature (TL) of the refrigerant in the third pipe (33) is higher than the target temperature (Target TL). If the temperature (TL) of the refrigerant in the third pipe (33) is higher than the target temperature (Target TL), the outdoor controller (101) ends the first operation and the process continues with step ST8. If the temperature (TL) of the refrigerant in the third pipe (33) is equal to or lower than the target temperature (Target TL), the process continues with step ST2.

In step ST8, the outdoor controller (101) switches the first state of the four-way switching valve (24) to the second state to switch the first refrigeration cycle to the second refrigeration cycle (start the defrosting operation).

-Advantages of realization-

The heat source unit of the embodiment includes: a heat source circuit (11) including a compression element (20), a heat source heat exchanger (14), a subcooling heat exchanger (40) and a switching mechanism (24), the heat source unit being connected to a utilization unit (50) having a utilization heat exchanger (54) constituting a refrigerant circuit (2) performing a refrigeration cycle. The switching mechanism (24) is configured to switch the refrigeration cycle between a first refrigeration cycle in which the heat source heat exchanger (14) serves as a radiator and the utilization heat exchanger (54) serves as an evaporator and a second refrigeration cycle in which the utilization heat exchanger (54) serves as a radiator and the heat source heat exchanger (14) serves as an evaporator. The subcooling heat exchanger (40) has a first channel (40a) connected to a middle portion of a liquid pipe (32, 33) through which a liquid refrigerant flows in the heat source circuit (11), and a second channel (40b) through which a heating medium flows for cooling the refrigerant in the first channel (40a). The heat source unit further comprises a regulating mechanism configured to perform a first operation of reducing the capacity of the second channel (40b) for cooling the refrigerant in the first channel (40a) before switching the first refrigeration cycle to the second refrigeration cycle.

In this configuration, the first operation is performed before the first refrigeration cycle switches to the second refrigeration cycle, which reduces the ability of the second channel (40b) to cool the refrigerant in the first channel (40a). As a result, the temperature of the refrigerant in the first channel (40a) increases. This can reduce the increase in thermal stress on the subcooling heat exchanger (40) caused by the high-temperature refrigerant flowing into the first channel (40a). This can protect the subcooling heat exchanger (40) from damage.

According to the embodiment, the switching mechanism (24) switches to the second refrigeration cycle when the temperature of the refrigerant in the first channel (40a) exceeds a predetermined value in the first operation.

In this configuration, the second refrigeration cycle starts when the temperature of the refrigerant in the first channel (40a) is higher than the predetermined value. The predetermined value is the target temperature (TL target) of the refrigerant flowing from the first channel (40a) to the third pipe (33). The target temperature (TL) is a temperature at which the subcooling heat exchanger (40) can withstand the thermal stress caused by the high-temperature refrigerant flowing from the internal heat exchanger (54) into the first channel (40a) in the defrosting operation (second refrigeration cycle). This can reliably protect the subcooling heat exchanger (40) from damage even if the high-temperature refrigerant flows into the first channel (40a) just after the start of the defrosting operation (second refrigeration cycle).

According to the embodiment, the heat source circuit (11) includes: an injection circuit (60) having one end branched from the liquid pipe (32, 33) and the other end communicating with an intermediate pressure portion of the compression element (20), and including the second channel (40b) through which a refrigerant as a heating medium flows; and an expansion valve (26) connected to an upstream side of the second channel (40b) in the injection circuit (60). The regulating mechanism (80) includes the expansion valve (26) and a control unit (101) configured to control an opening degree of the expansion valve (26) so that the cooling capacity is reduced in the first operation.

In this configuration, the outdoor controller (101) controls the opening degree of the expansion valve (26). The expansion valve (26) regulates the pressure and flow rate of the refrigerant flowing into the second channel (40b). This can reliably reduce the cooling capacity of the second channel (40b).

Furthermore, the injection circuit (60) communicates with the intermediate pressure portion of each of the compressors (21 to 23). Thus, the refrigerant flowing through the injection circuit (60) can be injected into each of the compressors (21 to 23).

The injected refrigerant can lower the temperatures (Td2, Td3) of the refrigerant discharged from the first and second low-pressure compressors (21, 22).

According to the embodiment, the control unit (101) performs the first control in the first operation to reduce the opening degree of the expansion valve (26) so that the flow rate of the refrigerant in the second channel (40b) decreases.

In this configuration, the first control reduces the flow rate of the coolant flowing into the second channel (40b).

Thus, the amount of heat exchanged between the refrigerant in the second channel (40b) and the refrigerant in the first channel (40a) can be reduced. This can reliably reduce the cooling capacity of the second channel (40b).

According to the embodiment, the control unit (101) performs the second control in the first operation to increase the opening degree of the expansion valve (26) so as to increase the pressure of the refrigerant in the second channel (40b).

In this configuration, the second control raises the evaporation temperature of the refrigerant in the second channel (40b). This reduces the ability of the second channel (40b) to cool the refrigerant in the first channel (40a).

The larger opening degree of the injection valve (26) (expansion valve) can introduce the refrigerant from the injection circuit (60) to the first low-pressure compressor (22) and the second low-pressure compressor (23). This can control the second discharge temperature (Td2) of the first low-pressure compressor (22) and the third discharge temperature (Td3) of the second low-pressure compressor (23).

According to the embodiment, the control unit (101) performs, in the first operation, a first control to reduce the opening degree of the expansion valve (26) so that a flow rate of the refrigerant in the second channel (40b) decreases when a condition indicating that a discharge temperature, which is a temperature of the refrigerant discharged from the compression element (20), is low is met, and a second control to increase the opening degree of the expansion valve (26) so that the pressure of the refrigerant in the second channel (40b) increases when a condition indicating that the discharge temperature of the compression element (20) is high is met.

In this configuration, the first control reduces the opening degree of the injection valve (26), thereby rapidly reducing the cooling capacity of the second channel (40b). The temperature of the refrigerant in the first channel (40a) can be easily raised without regulating the discharge temperatures (Td2, Td3) of the first and second low-pressure compressors (22, 23). The second control increases the opening degree of the injection valve (26), thereby reducing the cooling capacity of the second channel (40b). The refrigerant is introduced into the first and second low-pressure compressors (22, 23), and thus the discharge temperatures (Td2, Td3) of the first and second low-pressure compressors (22, 23) can be reliably reduced.

According to the embodiment, the heat source circuit (11) includes a flow regulating valve (28, 29) connected to a downstream side of the second channel (40b) in the injection circuit (60), and the second control is performed in the The first operation regulates an opening degree of the flow regulating valve (28, 29) so that the discharge temperature of the refrigerant discharged from the compression element (20) approaches a predetermined value.

In this configuration, adjusting the opening degrees of the second motor-driven valve (28) and the third motor-driven valve (29), which are the flow regulating valves, can regulate the amount of refrigerant introduced into the first and second low-pressure compressors (22, 23). This can control the discharge temperatures (Td2, Td3) of the first and second low-pressure compressors (22, 23). As a result, the temperature rise of the refrigerant flowing into the high-pressure compressor (21) is reduced, thereby preventing the superheat degree of the refrigerant discharged from the high-pressure compressor (21) from increasing excessively.

The heat exchange unit of the embodiment includes: a subcooling heat exchanger (40) having the first channel (40a) and the second channel (40b); a bypass channel (70) configured to allow at least part of the refrigerant that has dissipated heat in the utilization heat exchanger (54) not to pass through the first channel (40a) in the second refrigeration cycle; and a channel switching mechanism (180) configured to regulate the refrigerant flowing through the first channel (40a) and allow the refrigerant to flow through the bypass channel (70) in the second refrigeration cycle.

In this configuration, all or part of the refrigerant flows through the bypass channel (70) when the second refrigeration cycle starts. Thus, the refrigerant flowing through the first channel (40a) can be regulated in the second refrigeration cycle. Thus, the thermal stress on the subcooling heat exchanger (40) can be prevented from increasing even if a relatively high-temperature refrigerant flows into the outdoor unit (10) immediately after the first refrigeration cycle is switched to the second refrigeration cycle. This can prevent damage to the subcooling heat exchanger (40).

Furthermore, the refrigerant flowing through the bypass channel (70) is regulated in the first refrigeration cycle. Thus, a sufficient amount of refrigerant can flow through the first channel (40a) of the subcooling heat exchanger (40) during the first refrigeration cycle. This can improve the cooling capacity of the indoor unit (50).

According to the embodiment, the compression element (20) is a two-stage compression element having a first compression section (22, 23) and a second compression section (21), and is configured to compress the refrigerant in the first compression section (22, 23) and then compress the refrigerant again in the second compression section (21) in the first refrigeration cycle.

In this configuration, the evaporation pressure in the first refrigeration cycle is lower than that of a single-stage compressor. Thus, the refrigerant is cooled in the first channel (40a) to a relatively low temperature (e.g., -35 °C) in the first refrigeration cycle. When the first refrigeration cycle is switched to the second refrigeration cycle, the relatively high-temperature refrigerant that has received heat in the internal heat exchanger (54) flows into the heat source circuit (11). Thus, the two-stage compression element has a major problem of high thermal stress on the subcooling heat exchanger (40) due to the temperature difference. However, the heat source circuit (11) of the present embodiment having the regulating mechanism (80) can reduce the refrigeration capacity of the second channel (40b) in the first operation. Thus, the outdoor unit (10) including the compression element configured as a two-stage compression element can reduce an increase in the thermal stress in the first channel (40a) due to the switching of the first refrigeration cycle to the second refrigeration cycle.

«First variation»

A first variation has been made by partially modifying the configuration of the heat source unit (10) of the embodiment. Thus, the following description will focus on the differences with the embodiment.

<Injection circuit>

As illustrated in Fig. 6, one end of the relay pipe (62) in the injection circuit (60) is connected to an outflow end of the second channel (40b). The other end of the relay pipe (62) communicates with the suction portion of the first low-pressure compressor (22) and the suction portion of the second low-pressure compressor. Specifically, the relay pipe (62) has one end connected to one end of the second channel (40b), and the other end connected to the center of the first joint pipe (48).

The relay pipe (62) is provided with a fourth motor-operated valve (68). The fourth motor-operated valve (68) is a flow regulating valve which regulates the flow rate of the refrigerant introduced into the first low-pressure compressor (22) and into the second low-pressure compressor (23).

One end of the first injection pipe (63) is connected to an intermediate pressure portion of the high-pressure compressor (21). The other end of the first injection pipe (63) is connected to one end of the second injection pipe (64) and to one end of the third injection pipe (65). The other end of the second injection pipe (64) is connected to an intermediate pressure portion of the first low-pressure compressor (22), and the other end of the third injection pipe (65) is connected to an intermediate pressure portion of the second low-pressure compressor (23).

The injection circuit includes a second branch pipe (66). One end of the second branch pipe (66) is connected to the first branch pipe (61) between the junction of the first branch pipe (61) with the third pipe (33) and the injection valve (26). The other end of the second branch pipe (66) is connected to the first injection pipe (63) between the junction of the second injection pipe (64) and the third injection pipe (65) and the first motor-operated valve (27).

-Operation-

According to the first variation, as in the previous embodiment, the refrigerant from the outdoor heat exchanger (14) passes through the first channel (40a) and flows into the third pipe (33) in the cooling operation. Part of the refrigerant in the third pipe (33) flows into the first branch pipe (61). The rest of the refrigerant in the third pipe (33) flows into the indoor heat exchanger (54).

Part of the refrigerant in the first branch pipe (61) flows into the second branch pipe (66). The refrigerant in the second branch pipe (66) diverges into the first to third injection pipes (63 to 65). The refrigerant in each of the first to third injection pipes (63 to 65) has its flow rate appropriately regulated by a corresponding one of the first to third motor-operated valves (27 to 29), and is introduced into the intermediate pressure portion of the corresponding one of the compressors (21 to 23).

The remaining refrigerant in the first branch pipe (61) is decompressed by the injection valve (26) and flows into the second channel (40b). Heat exchange between the refrigerant in the second channel (40b) and the refrigerant in the first channel (40a) cools the refrigerant in the first channel (40a).

The refrigerant which has passed through the second channel (40b) flows through the relay pipe (62) and the first joint pipe (48) in this order. This refrigerant diverges into the second suction pipe (45) and the third suction pipe (46). The diverging flows of the refrigerant are introduced into the suction portion of the first low-pressure compressor (22) and the suction portion of the second low-pressure compressor (23).

Specifically, according to the first variation, the outdoor controller (101) controls the injection valve (26) and the fourth motor-driven valve (68) in the first operation.

As illustrated in Figure 7, when the outdoor controller (101) receives a command to execute the first operation, the second discharge temperature sensor (72) and the third discharge temperature sensor (73) detect the discharge temperatures (Td2, Td3) of the first and second pressure compressors (22, 23) in step ST11.

Specifically, the outdoor controller (101) determines whether a condition is met that indicates that the second discharge temperature (Td2) of the first low-pressure compressor (22) and the third discharge temperature (Td3) of the second low-pressure compressor (23) are both high. More specifically, the outdoor controller (101) determines whether the following conditions a) and b) are met.

a) The second discharge temperature (Td2) of the first low pressure compressor (22) is lower than a predetermined value. The predetermined value is, for example, 95 °C.

b) The third discharge temperature (Td3) of the second low pressure compressor (23) is lower than a predetermined value. The predetermined value is, for example, 95 °C.

If both conditions a) and b) are met in step ST11, the process continues with step ST12. If at least one of the conditions a) or b) is not met in step ST11, the process continues with step ST 13.

In step ST12, the outdoor controller (101) performs the first control to completely close the injection valve (26). In the first control, no coolant flows into the second channel (40b). This reduces the ability of the second channel (40b) to cool the coolant in the first channel (40a). As a result, the temperature of the coolant in the first channel (40a) increases.

In step ST13, the outdoor controller (101) performs the second control to fully open the injection valve (26). In the second control, the refrigerant that has entered the first branch pipe (61) flows into the second channel (40b) without being decompressed by the injection valve (26). This reduces the ability of the second channel (40b) to cool the refrigerant in the first channel (40a). As a result, the temperature of the refrigerant in the first channel (40a) increases.

In step ST 14, the outdoor controller (101) adjusts the opening degree of the fourth motor-operated valve (68) so that each of the second discharge temperature (Td2) and the third discharge temperature (Td3) reaches the target discharge temperature. The refrigerant that has passed through the second channel (40b) passes through the relay pipe (62) and diverges into the second suction pipe (45) and the third suction pipe (46). The divided flows of the refrigerant are respectively introduced into the suction portions of the first low-pressure compressor (22) and the second low-pressure compressor (23). The outdoor controller (101) controls the fourth motor-operated valve (68) of the relay pipe (62) to regulate the flow rate of the refrigerant introduced into the first low-pressure compressor (22) and the second low-pressure compressor (23). Thus, the second discharge temperature (Td2) and the third discharge temperature (Td3) are controlled to the target discharge temperature. The target discharge temperature is, for example, 95 °C.

In step ST15, the outdoor controller (101) determines whether the temperature (TL) of the refrigerant in the third pipe (33) is higher than a target temperature (target TL). If the temperature (TL) of the refrigerant in the third pipe (33) is higher than the target temperature (target TL), the outdoor controller (101) ends the first operation and the process continues with step ST 16. If the temperature (TL) of the refrigerant in the third pipe (33) is equal to or lower than the target temperature (target TL), the process continues with step ST11.

In step ST 16, the outdoor controller (101) switches the first state of the four-way switching valve (24) to the second state to switch the first refrigeration cycle to the second refrigeration cycle (start the defrosting operation).

In the first variation, the injection valve (26) is fully opened in the first control and fully closed in the second control. This can reliably reduce the ability of the second channel (40b) to cool the coolant in the first channel (40a).

In the first check it is only necessary to completely close the injection valve (26). In the second check it is only necessary to completely open the injection valve (26). This can facilitate the control of the first operation.

In the second control, the refrigerant flowing through the injection circuit (60) is introduced into the suction portions of the first low-pressure compressor (22) and the second low-pressure compressor (23). Also in the first variation, the discharge temperatures (Td2, Td3) of the first and second low-pressure compressors (22, 23) can be lowered.

«Second variation»

A second variation has been made by partially modifying the configuration of the heat source unit (10) of the embodiment. Thus, the following description will focus on the differences with the embodiment.

<Injection circuit>

As illustrated in Figure 8, the injection circuit (60) includes a third branch pipe (67). One end of the third branch pipe (67) is connected to the first branch pipe (61) between the junction of the first branch pipe (61) with the third pipe (33) and the injection valve (26). An outlet portion of the third branch pipe (67) is connected to the inlet flow ends of the first to third injection pipes (63 to 65).

The third branch pipe (67) is provided with a fifth motor-operated valve (69). The fifth motor-operated valve (69) is a flow regulating valve that regulates the flow rate of the refrigerant in the third branch pipe (67).

-Operation-

According to the second variation, as in the previous embodiment, the refrigerant from the outdoor heat exchanger (14) passes through the first channel (40a) and flows into the third pipe (33) in the cooling operation. Part of the refrigerant in the third pipe (33) flows into the first branch pipe (61). The rest of the refrigerant in the third pipe (33) flows into the indoor heat exchanger (54).

Part of the refrigerant in the first branch pipe (61) flows into the third branch pipe (67). The refrigerant in the third branch pipe (67) diverges into the first to third injection pipes (63 to 65). The refrigerant in each of the first to third injection pipes (63 to 65) has its flow rate appropriately regulated by a corresponding one of the first to third motor-operated valves (27 to 29), and is introduced into the intermediate pressure portion of the corresponding one of the compressors (21 to 23).

The remaining refrigerant in the first branch pipe (61) is decompressed by the injection valve (26) and flows into the second channel (40b). Heat exchange between the refrigerant in the second channel (40b) and the refrigerant in the first channel (40a) cools the refrigerant in the first channel (40a).

The refrigerant which has passed through the second channel (40b) flows through the relay pipe (62) and the first joint pipe (48) in this order. This refrigerant diverges into the second suction pipe (45) and the third suction pipe (46). The diverging flows of the refrigerant are introduced into the suction portion of the first low-pressure compressor (22) and the suction portion of the second low-pressure compressor (23).

According to the second variation, the controller (100) controls the injection valve (26) and the fifth motor-driven valve (69) in the first operation.

Specifically, the controller (100) completely closes the injection valve (26) in the first operation. Thus, no coolant flows into the second channel (40b). This reduces the ability of the second channel (40b) to cool the coolant in the first channel (40a).

Reducing the cooling capacity of the second channel (40b) raises the temperature of the refrigerant in the first channel (40a). When the temperature detected by the liquid temperature sensor (74) reaches the target temperature, the first operation ends and the defrosting operation begins. The target temperature referred to herein is the same as the target temperature described in the previous embodiment.

In the first operation, the amounts of refrigerant introduced into the first and second low-pressure compressors (21, 22) are adjusted so that each of the second and third discharge temperatures reaches the target discharge temperature. Specifically, the fifth motor-operated valve (69) regulates the flow rate of the refrigerant flowing through the third branch pipe (67). This refrigerant diverges into the second injection pipe (64) and the third injection pipe (65). Next, the second motor-operated valve (28) and the third motor-operated valve (29) regulate the flow rates of the diverging refrigerant flows. The refrigerant flows are introduced into the intermediate pressure portions of the first and second low-pressure compressors (21, 22).

Also in the second variation, the first operation may reduce the capacity of the second channel (40b) to cool the refrigerant in the first channel (40a). This may prevent the thermal stress on the subcooling heat exchanger (40) from increasing.

According to the second variation, the injection valve (26) is completely closed and the flow rate of the refrigerant introduced into each of the first and second low-pressure compressors (21, 22) is regulated by the fifth motor-driven valve (69) in the first operation, regardless of the discharge temperatures (Td2, Td3) of the first and second low-pressure compressors (22, 23). This can facilitate control of the first operation.

«Third variation»

As illustrated in Figure 9, a third variation has been made by partially modifying the configuration of the outdoor unit (10) of the embodiment. Thus, the following description will focus on the differences with the embodiment.

<Bypass channel>

The heat source circuit (11) according to the third variation includes a sixth pipe (36). The sixth pipe (36) is a bypass channel (70) which does not pass through the first channel (40a). The sixth pipe (36) is connected to the liquid pipes (32, 33) in parallel with the subcooling heat exchanger (40). Specifically, one end of the sixth pipe (36) is connected to the second pipe (32). The other end of the sixth pipe (36) is connected to the third pipe (33) located downstream of the fifth outdoor check valve (CV5). An eighth outdoor check valve (CV9) is connected to the sixth pipe (36). The eighth outdoor check valve (CV9) allows the refrigerant to flow from the indoor heat exchanger (54) to the outdoor heat exchanger (14) and prevents the refrigerant from flowing in the opposite direction in the second refrigeration cycle.

<Channel switching mechanism>

The channel switching mechanism (180) includes the eighth outdoor check valve (CV9) and the fifth outdoor check valve (CV5). The fifth outdoor check valve (CV5) is connected to the third pipe (33) between the junction of the third pipe (33) with the sixth pipe (36) and one end of the first channel (40a) to the indoor heat exchanger (54). The fifth outdoor check valve (CV5) allows the refrigerant to flow from the outdoor heat exchanger (14) to the indoor heat exchanger (54) and prevents the refrigerant from flowing in the opposite direction.

<Injection circuit, other pipes>

An inflow end of the first branch pipe (61) of the injection circuit (60) is connected to the third pipe (33) between the junction of the third pipe (33) with the sixth pipe (36) and the liquid side stop valve (17). An outlet portion of the first branch pipe (61) is connected to the first to third injection pipes (63 to 65).

One end of the fourth pipe (34) is connected to the second pipe (32) between the junction with the sixth pipe (36) and the junction with the fifth pipe (35). The other end of the fourth pipe (34) is connected to the first pipe (31) located downstream of the fourth outer check valve (CV4).

-Operation

<Cooling operation>

As illustrated in Figure 10, the refrigerant compressed in the low-pressure compressors (22, 23) and compressed again in the high-pressure compressor (21) dissipates heat to the outside air in the outdoor heat exchanger (14). The refrigerant that has dissipated heat in the outdoor heat exchanger (14) flows through the first pipe (31). The refrigerant flows to the receiver (39) and then flows through the second pipe (32) to the subcooling heat exchanger (40). The refrigerant in the second pipe (32) flows through the first channel (40a) of the subcooling heat exchanger (40). The eighth outdoor check valve (CV9) prevents the refrigerant from flowing into the sixth pipe (36) serving as a bypass channel (70).

The refrigerant flowing through the first channel (40a) exchanges heat with the refrigerant flowing through the second channel (40b) and is cooled. Part of the refrigerant that has entered the third pipe (33) flows into the first branch pipe (61), and the rest of the refrigerant flows into the internal heat exchanger (54).

The refrigerant that has entered the first branch pipe (61) is introduced from the injection pipes (63 to 65) into the compression chambers of the compressors (21 to 23).

The refrigerant flowing into the indoor unit (50) is sent to the indoor unit (50) through the liquid connection pipe (3).

<Deicing operation>

As illustrated in Figure 11, the injection valve (26) is completely closed in the defrosting operation. Thus, no refrigerant flows into the second channel (40b).

In the second refrigeration cycle, the refrigerant from the indoor unit (50) passes through the liquid connection pipe (3) and flows into the third pipe (33). The fifth outdoor check valve (CV5) blocks the flow of the refrigerant in the third pipe (33) into the first channel (40a) and passes through the sixth pipe (36) serving as a bypass channel (70). The refrigerant that has passed through the sixth pipe (36) flows through the second pipe (32), the fourth pipe (34), the first pipe (31), the receiver (39) and the second pipe (32) in this order. The refrigerant is decompressed by the outdoor expansion valve (25) and then passes through the fifth pipe (35) and the first pipe (31) to flow into the outdoor heat exchanger (14). The refrigerant that flows into the second pipe (32) from the sixth pipe (36) does not pass through the first channel (40a). This is because the differential pressure across the fifth outdoor check valve (CV5) does not allow the refrigerant to flow through the fifth outdoor check valve (CV5). Also, the pressure difference across the fourth outdoor check valve (CV4) does not allow the refrigerant that has entered the first pipe (31) to flow to the receiver (39).

In the third variation, the fifth outdoor check valve (CV5) and the eighth outdoor check valve (CV9) prevent the refrigerant from flowing through the first channel (40a) and allow the refrigerant to flow through the bypass channel (70) in the second refrigeration cycle. Thus, in the second refrigeration cycle, the refrigerant from the indoor unit (50) passes through the sixth pipe (36) serving as the bypass channel (70), and the flow of the refrigerant through the first channel (40a) is regulated. Thus, also in the first variation, a flow of a relatively high-temperature refrigerant into the first channel (40a) can be regulated immediately after the first refrigeration cycle is switched to the second refrigeration cycle. This can prevent the thermal stress on the subcooling heat exchanger (40) from increasing.

Furthermore, the channel through which the coolant flows can be automatically switched when switching between the first cooling cycle and the second cooling cycle. Thus, even in the first variation, an increase in the thermal stress on the subcooling heat exchanger (40) immediately after switching from the first cooling cycle to the second cooling cycle can be reliably prevented.

In the first refrigeration cycle, the entire amount of refrigerant flows through the first channel (40a), and no refrigerant is allowed to pass through the bypass channel. Thus, the subcooling heat exchanger (40) can cool the entire amount of refrigerant in the first refrigeration cycle.

«Fourth variation»

A fourth variation has been made by partially modifying the configuration of the channel switching mechanism (180) of the third variation. Thus, the following description will focus on the differences with the third variation.

<Channel switching mechanism>

As illustrated in Figure 12, a channel switching mechanism (180) according to the second variation includes a first three-way switching valve (81) and a second three-way switching valve (82).

The first three-way switching valve (81) is connected to the junction of the second pipe (32) with the sixth pipe (36). Specifically, the third port (P3) of the first three-way switching valve (81) is connected to the second pipe (32) extending from the outdoor heat exchanger (14). The second port (P2) is connected to one end of the sixth pipe (36). The first port (P1) is connected to the second pipe (32) extending from the first channel (40a).

The second three-way switching valve (82) is connected to the junction of the third pipe (33) with the sixth pipe (36). Specifically, the first port (P1) of the second three-way switching valve (82) is connected to the third pipe (33) extending from the internal heat exchanger (54). The second port (P2) is connected to the other end of the sixth pipe (36). The third port (P3) is connected to the third pipe (33) extending from the first channel (40a).

The controller (100) controls the channel switching mechanism (180). In the first state (the state indicated by the solid curves in Fig. 12), the first port (P1) and the third port (P3) are connected to each other in each of the first three-way switching valve (81) and the second three-way switching valve (82). In the second state (the state indicated by the dashed curves in Fig. 12), the first port (P1) and the second port (P2) are connected to each other in each of the first three-way switching valve (P1) and the second three-way switching valve (P2).

As illustrated in Fig. 13, the channel switching mechanism (180) is in the first state of the first refrigeration cycle. In the first state, the refrigerant does not flow into the sixth pipe (36) serving as the bypass channel (70), but flows through the first channel (40a). Thus, in the first refrigeration cycle, no refrigerant is allowed to enter the bypass channel (70), and the entire amount of refrigerant can flow through the first channel (40a).

As illustrated in Fig. 14, the channel switching mechanism (180) is in the second state of the second refrigeration cycle. In the second state, the refrigerant does not flow into the first channel (40a), but flows through the sixth pipe (36) serving as the bypass channel (70). Thus, in the second refrigeration cycle, refrigerant is not allowed to enter the first channel (40a), and the entire amount of refrigerant can flow through the bypass channel (70).

Also in the fourth variation, the refrigerant flowing from the internal heat exchanger (54) does not pass through the first channel (40a) in the second cooling cycle. Thus, the thermal stress on the subcooling heat exchanger (40) can be prevented from increasing immediately after the first cooling cycle is switched to the second cooling cycle.

«Fifth variation»

A fifth variation has been made by partially modifying the configuration of the subcooling heat exchanger (40) of the third and fourth variations. Thus, the following description will focus on the differences with the third and fourth variations.

<Subcooling circuit>

As illustrated in Figure 15, an outdoor unit (10) of the fifth variation includes a subcooling unit (90). The subcooling unit (90) includes a subcooling circuit (91) and a subcooling fan (94).

The subcooling circuit (91) includes a subcooling compressor (92), a subcooling heat exchanger (93), a subcooling expansion valve (26) and a second channel (40b). The subcooling circuit (91) is a refrigerant circuit independent of the heat source circuit (11). The subcooling circuit (91) is configured to allow the refrigerant as a heating medium to flow through the subcooling compressor (92), the subcooling heat exchanger (93), the subcooling expansion valve (26) and the second channel (40b) in this order.

The subcooling compressor (92) is a high-pressure dome-shaped hermetic scroll compressor. A compressor section (not shown) and an electric motor (not shown) driving the compressor section are connected to the subcooling compressor (92). The electric motor of the subcooling compressor (92) is connected to an inverter capable of freely changing the number of rotations of the electric motor within a predetermined range. The number of revolutions of the electric motor can be adjusted by the inverter, thereby increasing or decreasing the operating capacity of the subcooling compressor (92).

The subcooling heat exchanger (93) is a tube-and-fin air heat exchanger. The subcooling fan (94) is arranged near the subcooling heat exchanger (93). The subcooling fan (94) transfers outside air. The subcooling heat exchanger (93) exchanges heat between the high-pressure refrigerant flowing therethrough and the outside air transferred from the subcooling fan (94).

The subcooling expansion valve (26) is an electronic expansion valve having a variable opening degree. Adjusting the opening degree of the subcooling expansion valve (26) controls the temperature of the refrigerant flowing through the second channel (40b).

The refrigerant whose pressure is reduced by the subcooling expansion valve (26) flows through the second channel (40b). The refrigerant flowing through the second channel (40b) absorbs heat from the refrigerant flowing through the first channel (40a) and evaporates.

-Operation-

<Cooling operation>

The subcooling compressor (92) and the subcooling fan (94) of the subcooling unit (90) operate in the cooling operation. The opening degree of the subcooling expansion valve (26) is adjusted appropriately.

In the subcooling circuit (91), the refrigerant compressed by the subcooling compressor (92) dissipates heat to the outside air in the subcooling heat exchanger (93). The refrigerant that has dissipated heat is decompressed by the subcooling expansion valve (26) and flows into the second channel (40b). The refrigerant in the second channel (40b) exchanges heat with the refrigerant flowing through the first channel (40a) and is then sucked back into the subcooling compressor (92).

In the heat source circuit, as in the third and fourth variations, the refrigerant compressed in the low-pressure compressors (22, 23) and the high-pressure compressor (21) dissipates heat to the outside air in the outdoor heat exchanger (14). The refrigerant that has dissipated heat flows through the first pipe (31). The refrigerant flows to the receiver (39), passes through the second pipe (32) and flows through the first channel (40a) of the subcooling heat exchanger (40).

The refrigerant flowing through the first channel (40a) exchanges heat with the refrigerant flowing through the second channel (40b) and is cooled. Part of the refrigerant that has entered the third pipe (33) flows into the first branch pipe (61), and the rest of the refrigerant flows into the internal heat exchanger (54).

<Deicing operation>

The subcooling compressor (92) stops operating in the defrost operation. Thus, no refrigerant flows into the second channel (40b).

As in the third and fourth variations, the refrigerant from the indoor unit (50) passes through the liquid connection pipe (3) and flows into the third pipe (33). The fifth outdoor check valve (CV5) blocks the flow of the refrigerant in the third pipe (33) into the first channel (40a) and passes through the sixth pipe (36) serving as a bypass channel (70). The refrigerant that has passed through the sixth pipe (36) flows through the second pipe (32), the fourth pipe (34), the first pipe (31), the receiver (39) and the second pipe (32) in this order. The refrigerant is decompressed by the outdoor expansion valve (25) and then passes through the fifth pipe (35) and the first pipe (31) to flow into the outdoor heat exchanger (14). Note that the pressure difference across the fifth outdoor check valve (CV5) does not allow the refrigerant that has entered the second pipe (32) from the sixth pipe (36) to flow through the first channel (40a). Also, the pressure difference across the fourth outdoor check valve (CV4) does not allow the refrigerant that has entered the first pipe (31) from the fifth pipe (35) to flow to the receiver (39).

Also in the fifth variation, the refrigerant flowing from the internal heat exchanger (54) does not pass through the first channel (40a) in the second cooling cycle. Thus, the thermal stress on the subcooling heat exchanger (40) can be prevented from increasing immediately after the first cooling cycle is switched to the second cooling cycle.

Furthermore, the subcooling unit (90) includes the subcooling circuit (91) which is a refrigerant circuit independent of the heat source circuit (11). Thus, the temperature of the refrigerant flowing through the second channel (40b) can be controlled independently.

<<Other achievements»

The embodiment described above may be modified as follows.

The second refrigeration cycle may be a heating operation in which the indoor heat exchanger (54) serves as a radiator and the outdoor heat exchanger (14) serves as an evaporator. When the controller (100) receives an instruction to perform the heating operation during the cooling operation, the refrigeration apparatus (1) performs the first operation. When the temperature of the refrigerant in the first channel (40a) reaches the target temperature (target TL), the heating operation starts. After switching to the heating operation, the refrigerant flowing from the indoor heat exchanger (54) to the outdoor heat exchanger (14) does not pass through the first channel (40a). In this case too, the thermal stress on the subcooling heat exchanger (40) can be prevented from increasing.

The compression element (20) may be a single-stage compression element. In this case, the high-pressure compressor (21) operates and the first low-pressure compressor (22) and the second low-pressure compressor (23) stop operating in the first refrigeration cycle (cooling operation) of the above embodiment. The sixth motor-driven valve (53) is fully opened. The refrigerant that has entered the first connection pipe (48) from the indoor heat exchanger (54) flows through the connection pipe (49) and is sucked into the high-pressure compressor (21). The refrigerant compressed by the high-pressure compressor (21) flows through the outdoor heat exchanger (14), the receiver (39) and the subcooling heat exchanger (40), as in the above embodiment. In this way, the refrigerant flows through the refrigerant circuit (2).

The compression element (20) may be a single-stage compression element having a plurality of compressors connected in parallel.

In the above embodiment, the first control in the first operation (step ST3 in Fig. 5) may completely close the injection valve (26). In this case, no coolant flows into the second channel (40b), which reduces the ability of the second channel (40b) to cool the coolant in the first channel (40a).

In the above embodiment, the second control in the second operation (step ST4 in Fig. 5) may fully open the injection valve (26). In this case, the injection valve (26) does not decompress the refrigerant, which reduces the ability of the second channel (40b) to cool the refrigerant in the first channel (40a).

In the above embodiment, the temperature value (Tg1) of the refrigerant flowing into the second channel (40b) detected by the first temperature sensor (75) can be replaced with a value of the pressure sensor (77) converted to a temperature of the saturated liquid.

The pressure value (MP) of the refrigerant in the relay pipe (62) detected by the pressure sensor (77) can be replaced with a value from the first temperature sensor (75) converted to a saturated liquid pressure.

In the above embodiment and variations, the heat source unit (10) may not have a bypass channel (70). Also, the heat source unit (10) may not have any channel switching mechanism (180).

In the above embodiment, the utilization circuit (51) may not have an internal bypass channel (58). In this case, the internal expansion valve (30) is an electronic expansion valve having a variable opening degree. When the internal heat exchanger (54) functions as a radiator, the internal expansion valve (30) is fully opened.

The channel switching mechanism (180) may be a motor-operated valve having a variable opening degree. Specifically, the fifth outer check valve (CV5) and the sixth outer check valve (CV6) of the previous embodiment and the fifth outer check valve (CV5) and the eighth outer check valve (CV9) of the third variation may be motor-operated valves. In the first and second refrigeration cycles, adjusting the opening degrees of the motor-operated valves can regulate the flow rate of the refrigerant in the first channel (40a) and the flow rate of the refrigerant in the bypass channel (70). This allows at least part of the refrigerant to flow through the bypass channel (70) in the second refrigeration cycle. Thus, regulating the flow rate of the refrigerant in the bypass channel (70) can prevent the thermal stress on the subcooling heat exchanger (40) from increasing in the second refrigeration cycle. Also in the first cooling cycle, the regulation allows at least part of the refrigerant to flow through the bypass channel (70). This can control the amount of refrigerant that exchanges heat in the first channel (40a) in the first cooling cycle.

The channel switching mechanism (180) may be an on-off valve that is simply opened and closed. Specifically, the fifth outer check valve (CV5) and the sixth outer check valve (CV6) of the previous embodiment and the fifth outer check valve (CV5) and the eighth outer check valve (CV9) of the third variation may be on-off valves that are simply opened and closed. In the first refrigeration cycle, one of the valves is opened to allow the refrigerant to flow through the first channel (40a), and the other is closed to prevent the refrigerant from flowing through the bypass channel (70). Thus, the entire amount of refrigerant can flow through the first channel (40a). In the second refrigeration cycle, one of the valves is closed to prevent the refrigerant from flowing through the first channel (40a), and the other is opened to allow the refrigerant to flow through the bypass channel (70). This allows the entire amount of coolant to flow through the bypass channel (70).

As illustrated in Fig. 16, the channel switching mechanism (180) of the third and fourth variations may include the first three-way switching valve (81) and the fifth outer check valve (CV5). In the first refrigeration cycle, the first port (P1) and the third port (P3) of the first three-way switching valve (81) are connected to each other. Thus, the refrigerant is prevented from flowing into the sixth pipe (36) in the first refrigeration cycle. This allows the entire amount of refrigerant to flow through the first channel (40a) in the first refrigeration cycle.

In the second refrigeration cycle, the first port (P1) and the second port (P2) of the first three-way switching valve (81) are connected to each other. Thus, the refrigerant is prevented from flowing into the first channel (40a) in the second refrigeration cycle. This allows the entire amount of refrigerant to flow through the sixth pipe (36) in the second refrigeration cycle.

As illustrated in Fig. 17, the channel switching mechanism (180) of the third and fourth variations may include the second three-way switching valve (82) and the eighth outer check valve (CV9). In the first refrigeration cycle, the first port (P1) and the third port (P3) of the second three-way switching valve (82) are connected to each other. Thus, the refrigerant is prevented from flowing into the sixth pipe (36) in the first refrigeration cycle.

This allows the entire amount of refrigerant to flow through the first channel (40a) in the first refrigeration cycle.

In the second refrigeration cycle, the first port (P1) and the second port (P2) of the second three-way switching valve (82) are connected to each other. Thus, the refrigerant is prevented from flowing into the first channel (40a) in the second refrigeration cycle. This allows the entire amount of refrigerant to flow through the sixth pipe (36) in the second refrigeration cycle.

As illustrated in Fig. 18, the channel switching mechanism (180) of the third and fourth variations may include only the second three-way switching valve (82). In the first refrigeration cycle, the first port (P1) and the third port (P3) of the second three-way switching valve (82) are connected to each other. In the second refrigeration cycle, the first port (P1) and the second port (P2) of the second three-way switching valve (82) are connected to each other.

The injection circuit (60) is not limited to that described in the previous embodiment. The injection circuit (60) may be modified as appropriate without deteriorating the intended functions described in the previous embodiment.

In the above embodiment, the utilization circuit (51) may not have an internal bypass channel (58). In this case, the internal expansion valve (30) is an electronic expansion valve having a variable opening degree. When the internal heat exchanger (54) functions as a radiator, the internal expansion valve (30) is fully opened.

The outer expansion valve (25) of the previous embodiment can be connected to the second pipe (32) between the receiver (39) and the end of the fifth pipe (35) connected to the second pipe (32).

Industrial applicability

As can be seen from the above paragraphs, the present invention is useful for a refrigeration apparatus.

Description of reference characters

1 Refrigeration device

2 Refrigerant circuit

10 Outdoor unit (heat source unit)

11 Heat source circuit

14 Outdoor heat exchanger (heat source heat exchanger)

20 Compression element

21 High pressure compressor (second compression section)

First low-pressure compressor (first compression section) Second low-pressure compressor (first compression section) Four-way switching valve (switching mechanism) Injection valve (expansion valve)

Second motor-operated valve (flow control valve) Third motor-operated valve (flow control valve) Second pipe (liquid pipe)

Third pipe (liquid pipe)

Subcooling heat exchanger

a First channel

b Second channel

Internal unit (unit of use)

Internal heat exchanger (utilization heat exchanger) Injection circuit

Bypass channel

Regulatory mechanism

1 Outdoor controller (control unit)

0 Channel switching mechanism

Claims (9)

1. A refrigerating apparatus, comprising: a utilization unit (50) having a utilization heat exchanger (54), and a heat source unit (10), wherein the heat source unit (10) comprises: a heat source circuit (11) including a compression element (20), a heat source heat exchanger (14), a subcooling heat exchanger (40) and a switching mechanism (24), the heat source unit being connected to the utilization unit (50) having the utilization heat exchanger (54) constituting a refrigerant circuit (2) performing a refrigeration cycle, wherein the switching mechanism (24) is configured to switch the refrigeration cycle between a first refrigeration cycle in which the heat source heat exchanger (14) serves as a radiator and the utilization heat exchanger (54) serves as an evaporator, and a second refrigeration cycle in which the utilization heat exchanger (54) serves as a radiator and the heat source heat exchanger (14) serves as an evaporator, The subcooling heat exchanger (40) has a first channel (40a) connected to a middle portion of a liquid pipe (32, 33) through which a liquid refrigerant flows in the heat source circuit (11), and a second channel (40b) through which a heating medium for cooling the refrigerant in the first channel (40a) flows, The heat source unit (10) further comprises a regulating mechanism including an expansion valve (26) connected to an upstream side of the second channel (40b) and a control unit (101), characterized in that The control unit (101) is configured to control an opening degree of the expansion valve (26) so that the cooling capacity is reduced in a first operation of reducing the capacity of the second channel (40b) to cool the refrigerant in the first channel (40a) before switching the first refrigeration cycle to the second refrigeration cycle. 2. The refrigeration apparatus of claim 1, wherein The switching mechanism (24) is configured to switch the refrigeration cycle to the second refrigeration cycle when the temperature of the refrigerant flowing through the first channel (40a) exceeds a predetermined value in the first operation. 3. The refrigerating apparatus of claim 1 or 2, wherein the heat source circuit (11) includes: an injection circuit (60) having one end branched from the liquid pipe (32, 33) and the other end communicating with an intermediate pressure portion or a suction portion of the compression element (20), and includes the second channel (40b) through which a refrigerant as a heating medium flows; and the expansion valve (26) is connected to the upstream side of the second channel (40b) in the injection circuit (60). 4. The refrigeration apparatus of any one of claims 1 to 3, wherein: The control unit (101) performs a first control in the first operation to reduce the opening degree of the expansion valve (26) so as to decrease the flow rate of the refrigerant in the second channel (40b). 5. The refrigeration apparatus of any one of claims 1 to 4, wherein: The control unit (101) performs a second control in the first operation to increase the opening degree of the expansion valve (26) so that the pressure of the refrigerant in the second channel (40b) increases. 6. The refrigeration apparatus of any of the preceding claims, wherein The control unit (101) performs, in the first operation, first control to reduce the opening degree of the expansion valve (26) so that the flow rate of the refrigerant in the second channel (40b) decreases when a condition indicating that a discharge temperature, which is a temperature of the refrigerant discharged from the compression element (20), is low is met, and second control to increase the opening degree of the expansion valve (26) so that the pressure of the refrigerant in the second channel (40b) increases when a condition indicating that the discharge temperature of the compression element (20) is high is met. 7. The refrigeration apparatus of claim 5 or 6, wherein The heat source circuit (11) includes a flow regulating valve (28, 29) connected to a downstream side of the second channel (40b) in the injection circuit (60), and The second control performed in the first operation regulates an opening degree of the flow regulating valve (28, 29) so that the discharge temperature, which is a temperature of the refrigerant discharged from the compression element (20), approaches a predetermined value. 8. The refrigeration apparatus of any one of claims 1 to 7 further comprising: a subcooling heat exchanger (40) having the first channel (40a) and the second channel (40b); a bypass channel (70) configured to allow at least part of the refrigerant that has dissipated heat in the utilization heat exchanger (54) not to pass through the first channel (40a) in the second refrigeration cycle; and a channel switching mechanism (180) configured to regulate the refrigerant flowing through the first channel (40a) and allow the refrigerant to flow through the bypass channel (70) in the second refrigeration cycle. 9. The refrigeration apparatus of any one of claims 1 to 8, wherein: The compression element (20) is a two-stage compression element having a first compression section (22, 23) and a second compression section (21), and is configured to compress the refrigerant in the first compression section (22, 23) and then compress the refrigerant again in the second compression section (21) in the first refrigeration cycle.