EP2314954A1

EP2314954A1 - Freezer device

Info

Publication number: EP2314954A1
Application number: EP09762229A
Authority: EP
Inventors: Masaaki Takegami
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2008-06-09
Filing date: 2009-06-03
Publication date: 2011-04-27
Anticipated expiration: 2029-06-03
Also published as: EP2314954B1; EP2314954A4; WO2009150798A1; JP2009293899A

Abstract

A gas vent pipe (62) through which a gas space in a receiver (35) is communicated with an intermediate pressure chamber of a compressor (31, 32), and a gas vent valve (63) provided in the gas vent pipe (62) are provided. When the degree of subcooling of refrigerant in the outdoor heat exchanger (34) or the indoor heat exchanger (71) is greater than or equal to a predetermined value during a heating and refrigeration operation in which refrigerant discharged from the compressor (31, 32) flows into an outdoor heat exchanger (34) and an indoor heat exchanger (71), condenses, and then flows into a receiver (35), and the liquid refrigerant in the receiver (35) is supplied to a chilling heat exchanger (81) and a freezing heat exchanger (91), and evaporates, the gas vent valve (63) is opened. Consequently, the liquid refrigerant accumulated in the indoor heat exchanger (71), etc., is discharged, and flows into the receiver (35).

Description

TECHNICAL FIELD

The present invention relates to refrigeration apparatuses in which refrigerant discharged from a compressor flows into a heat source side heat exchanger and a first utilization side heat exchanger and condenses, the condensed refrigerant then flows into a receiver, and the liquid refrigerant in the receiver flows into a second utilization side heat exchanger and evaporates.

BACKGROUND ART

Conventionally, there has been known a so-called multi-type refrigeration apparatus in which a plurality of utilization units are connected in parallel to a heat source unit. For example, a refrigeration apparatus of PATENT DOCUMENT 1 includes a heat source unit which has a compressor, a heat source side heat exchanger, and a receiver, and utilization units which are used for air conditioning and cooling and each have a utilization side heat exchanger.
In such a refrigeration apparatus, the utilization units are each connected to the heat source unit through (three) connection pipes. The refrigeration apparatus enables a heating and refrigeration operation for concurrently performing heating operation of the utilization unit for air conditioning and cooling operation of the utilization unit for cooling. Specifically, in this heating and refrigeration operation, refrigerant discharged from the compressor flows into the heat source side heat exchanger and the utilization unit for air conditioning, and then condenses. The refrigerant which has condensed in the heat source side heat exchanger passes through the receiver, and then, is combined with the refrigerant which has condensed in the utilization unit for air conditioning, and the combined refrigerant evaporates in the utilization unit for cooling. That is, in the above operation, there is no balance between the cooling capacity of the utilization unit for cooling (the amount of heat of evaporation) and the heating capacity of the utilization unit for air conditioning (the amount of heat of condensation), and the surplus heat of condensation is dissipated to the outdoors by the heat source side heat exchanger.

CITATION LIST

PATENT DOCUMENT

PATENT DOCUMENT 1: Japanese Patent Publication No. 2004-44921

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

Incidentally, in the above-described heating and refrigeration operation of the refrigeration apparatus, similarly to the refrigerant which has condensed in the heat source side heat exchanger, the refrigerant which has condensed in the utilization unit for air conditioning may also pass through the receiver of the heat source unit and then be supplied to the utilization unit for cooling. Specifically, in this case, one connection pipe is further provided in order to establish communication between the utilization unit for air conditioning and the receiver.
However, for example, when the utilization unit for air conditioning is located at a higher level than the heat source unit, or when the utilization unit for air conditioning is significantly distant from the heat source unit, the pressure loss through the path allowing the refrigerant discharged from the compressor to flow through the utilization unit for air conditioning into the receiver is higher than that through the path allowing the refrigerant discharged from the compressor to flow through the heat source side heat exchanger into the receiver. In this case, the flow of refrigerant through the utilization side heat exchanger of the utilization unit for air conditioning becomes slow, and the condensed liquid refrigerant gradually accumulates in the utilization side heat exchanger. This reduces the amount of the liquid refrigerant flowing through the utilization unit for air conditioning into the receiver. By contrast, only the amount of the liquid refrigerant needed to be cooled by the utilization unit for cooling flows out of the receiver. Therefore, liquid refrigerant in the receiver gradually decreases, and finally, the receiver becomes empty. Specifically, the velocity of flow of refrigerant through one, which causes a higher pressure loss, of the path through the heat source side heat exchanger and the path through the utilization unit for air conditioning decreases, and thus, the liquid refrigerant slowly flows into the receiver. This causes a problem where the amount of refrigerant supplied to the utilization unit for cooling is not ensured, thereby reducing the cooling capacity and making cooling impossible.
The present invention has been made in view of the foregoing point, and it is an object of the present invention to ensure the amount of liquid refrigerant in a receiver and prevent a reduction in the cooling capacity of a utilization unit for cooling and the impossibility of cooling before they occur.

SOLUTION TO THE PROBLEM

A first aspect of the invention is based on a refrigeration apparatus including: a refrigerant circuit (20) including a compressor (31, 32, 33), a heat source side heat exchanger (34), a first utilization side heat exchanger (71), a second utilization side heat exchanger (81, 91), and a receiver (35) to which a liquid-side end of the heat source side heat exchanger (34) and a liquid-side end of the first utilization side heat exchanger (71) are connected through pipes and through which liquid refrigerant flows into the second utilization side heat exchanger (81, 91), and performing a refrigeration cycle, wherein an operation in which refrigerant discharged from the compressor (31, 32, 33) flows into the heat source side heat exchanger (34) and the first utilization side heat exchanger (71), and dissipates heat, and liquid refrigerant in the receiver (35) flows into the second utilization side heat exchanger (81, 91), and absorbs heat can be performed. The refrigeration apparatus of the present invention further includes: a gas vent pipe (62) having one end communicated with a gas space in the receiver (35) and having the other end communicated with a line, which has a lower pressure than an internal pressure of the receiver (35), of the refrigerant circuit (20); an on-off valve (63) provided in the gas vent pipe (62); and a controller (100) for opening the on-off valve (63) based on indicators indicating an amount of refrigerant in the heat source side heat exchanger (34) and an amount of refrigerant in the first utilization side heat exchanger (71) during the operation.
The refrigeration apparatus of the invention can perform an operation in which heating operation of the first utilization side heat exchanger (71) and cooling operation of the second utilization side heat exchanger (81, 91) are concurrently performed. Specifically, in this operation, refrigerant discharged from the compressor (31, 32, 33) flows into the first utilization side heat exchanger (71) and the heat source side heat exchanger (34), and dissipates heat (condenses). Thus, heating operation is performed by the first utilization side heat exchanger (71). Refrigerant dissipating heat in the first utilization side heat exchanger (71) and the heat source side heat exchanger (34) flows into the receiver (35), and the liquid refrigerant in the receiver (35) flows into the second utilization side heat exchanger (81, 91), and absorbs heat (evaporates). Thus, cooling operation is performed by the second utilization side heat exchanger (81, 91). The refrigerant evaporating in the second utilization side heat exchanger (81, 91) is returned to the compressor (31, 32, 33). Here, for example, a case where the pressure loss through a path allowing refrigerant discharged from the compressor (31, 32, 33) to flow through the first utilization side heat exchanger (71) into the receiver (35) is greater than the pressure loss through a path allowing the refrigerant to flow through the heat source side heat exchanger (34) into the receiver (35) is considered. In this case, refrigerant is less likely to flow through the path through the first utilization side heat exchanger (71), and thus, the refrigerant (liquid refrigerant) tends to accumulate in the first utilization side heat exchanger (71). Thus, less refrigerant flows through the path through the first utilization side heat exchanger (71) into the receiver (35). By contrast, a necessary amount of the liquid refrigerant flows through the receiver (35) into the second utilization side heat exchanger (81, 91). Consequently, refrigerant in the receiver (35) decreases, and is finally lost. This makes it impossible to perform cooling operation in the second utilization side heat exchanger (81, 91).
Therefore, according to the present invention, when the refrigerant accumulated in the first utilization side heat exchanger (71) is increased to a predetermined amount, the on-off valve (63) opens. Here, the internal pressure of the receiver (35) is substantially identical with the discharge pressure of the compressor (31, 32, 33) (i.e., high pressure in the refrigeration cycle), and the gas vent pipe (62) is communicated with a line having a lower pressure than the high pressure. Therefore, when the on-off valve (63) opens, gas refrigerant flows through the interior of the receiver (35) into the gas vent pipe (62), and the refrigerant accumulated in the first utilization side heat exchanger (71) flows into the receiver (35) in response to the amount of the gas refrigerant. This reduces the decrease in the amount of liquid refrigerant in the receiver (35).
According to a second aspect of the invention, in the first aspect of the invention, the other end of the gas vent pipe (62) is communicated with an intermediate-pressure compression chamber of the compressor (31, 32, 33).
According to the invention, the gas vent pipe (62) is communicated with the intermediate-pressure compression chamber having a lower pressure than the receiver (35). Therefore, when the on-off valve (63) opens, gas refrigerant in the receiver (35) flows through the gas vent pipe (62) into the intermediate pressure chamber of the compressor (31, 32, 33).
According to a third aspect of the invention, in the first or second aspect of the invention, a degree of subcooling of refrigerant at a gas-side end of the heat source side heat exchanger (34) and a degree of subcooling of refrigerant at a gas-side end of the first utilization side heat exchanger (71), or a degree of subcooling of refrigerant in the heat source side heat exchanger (34) and a degree of subcooling of refrigerant in the first utilization side heat exchanger (71) are used as the indicators indicating the amounts of refrigerant.
According to the invention, the degree of subcooling of refrigerant is used as an indicator indicating the corresponding amount of refrigerant. Specifically, when refrigerant condenses in the heat source side heat exchanger (34) and the first utilization side heat exchanger (71), and the liquid refrigerant accumulates therein, the liquid refrigerant further dissipates heat, and is subcooled. Therefore, the amount of refrigerant accumulated in the heat source side heat exchanger (34) and the amount of refrigerant accumulated in the first utilization side heat exchanger (71) can be known by detecting the degrees of subcooling of refrigerant in the heat exchangers (34, 71). Furthermore, when liquid refrigerant is fully accumulated in the heat source side heat exchanger (34) and the first utilization side heat exchanger (71), the refrigerant may condense also in the vicinity of the inlets of the heat exchangers (34, 71), and may be subcooled. Therefore, the amount of the refrigerant accumulated in the heat source side heat exchanger (34) and the amount of the refrigerant accumulated in the first utilization side heat exchanger (71) can be known by detecting the degrees of subcooling of refrigerant near the inlets of the heat exchangers (34, 71).

ADVANTAGES OF THE INVENTION

As described above, according to the present invention, the gas vent pipe (62) for the receiver (35) is provided, and when the amount of refrigerant accumulated in the heat source side heat exchanger (34) and the amount of refrigerant accumulated in the first utilization side heat exchanger (71) are increased, the gas vent pipe (62) is opened. This allows liquid refrigerant accumulated in the heat source side heat exchanger (34), etc., to flow into the receiver (35). As a result, the liquid refrigerant in the receiver (35) can be prevented from decreasing and being lost. This can ensure the amount of the liquid refrigerant supplied from the receiver (35) to the second utilization side heat exchanger (81, 91), thereby avoiding a reduction in the cooling capacity of the second utilization side heat exchanger (81, 91) and the impossibility of cooling the second utilization side heat exchanger (81, 91) before they occur.
According to the second aspect of the invention, the gas vent pipe (62) is communicated with the immediate-pressure compression chamber of the compressor (31, 32, 33). This allows gas refrigerant in the receiver (35) to flow into the intermediate-pressure compression chamber. Here, for example, when the gas refrigerant in the receiver (35) is caused to flow into the suction pipe of the compressor (31, 32, 33), the amount of the refrigerant sucked into the compressor (31, 32, 33) is reduced in response to the amount of the gas refrigerant, thereby reducing the cooling capacity of the second utilization side heat exchanger (81, 91). However, according to the present invention, the gas refrigerant in the receiver (35) flows into the intermediate-pressure chamber of the compressor (31, 32, 33). This prevents the amount of the refrigerant sucked into the compressor (31, 32, 33) from decreasing. As a result, a reduction in the cooling capacity of the second utilization side heat exchanger (81, 91) can be prevented.
According to the third aspect of the invention, the amount of the refrigerant accumulated in the heat source side heat exchanger (34), etc., is detected using the degree of subcooling of refrigerant near the inlet of the heat source side heat exchanger (34), etc., and the degree of subcooling of refrigerant inside the heat source side heat exchanger (34), etc. Therefore, the amount of refrigerant accumulated in the heat source side heat exchanger (34), etc., can be easily known by utilizing a temperature sensor, a pressure sensor, etc., provided in the refrigerant circuit (20).

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a piping diagram illustrating the structure of a refrigeration apparatus according to an embodiment.
[FIG. 2] FIG. 2 is a piping diagram illustrating the flow of refrigerant during a first cooling and refrigeration operation.
[FIG. 3] FIG. 3 is a piping diagram illustrating the flow of refrigerant during a second cooling and refrigeration operation.
[FIG. 4] FIG. 4 is a piping diagram illustrating the flow of refrigerant during a first heating and refrigeration operation.
[FIG. 5] FIG. 5 is a piping diagram illustrating the flow of refrigerant during a second heating and refrigeration operation.
[FIG. 6] FIG. 6 is a flowchart illustrating control operation of a controller.
[FIG. 7] FIG. 7 is a piping diagram illustrating the flow of refrigerant when a gas vent valve is opened during the second heating and refrigeration operation.

DESCRIPTION OF EMBODIMENTS

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

A refrigeration apparatus (10) of this embodiment is installed in a convenience store, and concurrently performs cooling of a chiller and a freezer and heating or cooling of the interior of a room (the interior of the store).
As illustrated in FIG. 1, the refrigeration apparatus (10) includes an outdoor unit (11), an air conditioning unit (12), a chiller showcase (13), a freezer showcase (14), and a controller (100). The outdoor unit (11) includes an outdoor circuit (30) forming a heat source side circuit. The air conditioning unit (12), the chiller showcase (13), and the freezer showcase (14) include an air conditioning circuit (70), a chiller circuit (80), and a freezer circuit (90), respectively, and these circuits form utilization side circuits. In this embodiment, the air conditioning circuit (70) forms a first utilization system, and the chiller circuit (80) and the freezer circuit (90) form a second utilization system.
In the refrigeration apparatus (10), the plurality of utilization side circuits (70, 80, 90) are connected in parallel to the outdoor circuit (30), thereby forming a refrigerant circuit (20) for performing a vapor compression refrigeration cycle.
The outdoor circuit (30) is connected to the utilization side circuits (70, 80, 90) through a first liquid side connection pipe (25), a second liquid side connection pipe (26), a first gas side connection pipe (27), and a second gas side connection pipe (28). One end of the first liquid side connection pipe (25) is connected to a first liquid side shut-off valve (21) of the outdoor circuit (30). The other end of the first liquid side connection pipe (25) branches into two pipes, one of which is connected to the chiller circuit (80), and the other of which is connected to the freezer circuit (90). One end of the second liquid side connection pipe (26) is connected to a second liquid side shut-off valve (22) of the outdoor circuit (30), and the other end thereof is connected to the air conditioning circuit (70). One end of the first gas side connection pipe (27) is connected to a first gas side shut-off valve (23) of the outdoor circuit (30), and the other end thereof is connected to the air conditioning circuit (70). One end of the second gas side connection pipe (28) is connected to a second gas side shut-off valve (24) of the outdoor circuit (30), and the other end thereof is connected to the chiller circuit (80).

The outdoor circuit (30) of the outdoor unit (11) includes first through third three compressors (31, 32, 33), an outdoor heat exchanger (34), a receiver (35), an outdoor expansion valve (36), a subcooling heat exchanger (37), a subcooling expansion valve (38), and first through third three four-way selector valves (41, 42, 43).
The compressors (31, 32, 33) are formed by high-pressure dome type scroll compressors. The first compressor (31) forms a variable capacity compressor. Specifically, the first compressor (31) is configured to be variable in rotation speed by inverter control. By contrast, the second compressor (32) and the third compressor (33) form fixed capacity compressors rotating at a fixed rotation speed. The third compressor (33) may be a variable capacity compressor.
The compressors (31, 32, 33) form compression mechanisms of the refrigeration apparatus (10), and the compression mechanisms include a compression mechanism of a first utilization system and a compression mechanism of a second utilization system. Specifically, the first compressor (31) is principally routinely used for the second utilization system for chilling and freezing. The third compressor (33) is principally routinely used for the first utilization system for air conditioning. By contrast, the second compressor (32) is used while being changed between the first and second utilization systems, and the second compressor (32) forms a compressor in support of the first and second utilization systems.
The suction side of the first compressor (31) is connected through a first suction pipe (46) to the second gas side shut-off valve (24). The suction side of the second compressor (32) is connected through a second suction pipe (47) to the third four-way selector valve (43). The suction side of the third compressor (33) is connected through a third suction pipe (48) to the second four-way selector valve (42).
One end of a first discharge pipe (45a), one end of a second discharge pipe (45b), and one end of a third discharge pipe (45c) are connected to the discharge sides of the first compressor (31), the second compressor (32), and the third compressor (33), respectively. The other ends of the discharge pipes (45a, 45b, 45c) are combined together, and the combined ends are connected to one end of a discharge junction pipe (45). The other end of the discharge junction pipe (45) is connected to the first four-way selector valve (41). The discharge pipes (45a, 45b, 45c) each include a check valve (CV). The check valve (CV) allows the flow of refrigerant only in the direction of the corresponding arrow illustrated in FIG. 1. This applies to check valves (CV) described below.
The outdoor heat exchanger (34) is a cross-fin-type fin-and-tube heat exchanger, and forms a heat source side heat exchanger according to the present invention. An outdoor fan (40) is disposed in the vicinity of the outdoor heat exchanger (34). The outdoor heat exchanger (34) exchanges heat between refrigerant and outdoor air blown by the outdoor fan (40). One end of the outdoor heat exchanger (34), i.e., a gas-side end thereof, is connected to the first four-way selector valve (41). The other end of the outdoor heat exchanger (34), i.e., a liquid-side end thereof, is connected through a first liquid pipe (51) to the top of the receiver (35). The bottom of the receiver (35) is connected through a second liquid pipe (52) to the first liquid side shut-off valve (21). The first liquid pipe (51) and the second liquid pipe (52) each include a check valve (CV).
A bypass pipe (54) is disposed between the first liquid pipe (51) and the second liquid pipe (52). Specifically, one end of the bypass pipe (54) is connected upstream of the check valve (CV) in the first liquid pipe (51), and the other end thereof is connected upstream of the check valve (CV) in the second liquid pipe (52). The outdoor expansion valve (36) is disposed at any location along the bypass pipe (54). The outdoor expansion valve (36) is formed by an electronic expansion valve having an adjustable opening.
The four-way selector valves (41, 42, 43) each include first through fourth four ports. The first, second, third, and fourth ports of the first four-way selector valve (41) are connected to the discharge junction pipe (45), the fourth port of the second four-way selector valve (42), the outdoor heat exchanger (34), and the first gas side shut-off valve (23), respectively. While the first and second ports of the second four-way selector valve (42) are connected to the discharge junction pipe (45) and the third suction pipe (48), respectively, the third port of the second four-way selector valve (42) is closed.
The first four-way selector valve (41) and the second four-way selector valve (42) are each switchable between a first position in which the first and third ports are communicated with each other and the second and fourth ports are communicated with each other (the position illustrated by the solid lines in FIG. 1), and a second position in which the first and fourth ports are communicated with each other and the second and third ports are communicated with each other (the position illustrated by the broken lines in FIG. 1).
The first port of the third four-way selector valve (43) is communicated with the discharge junction pipe (45) through a first connection pipe (49a), the second port thereof is connected to the second suction pipe (47), the third port thereof is connected to the third suction pipe (48) through a second connection pipe (49b), and the fourth port thereof is connected to the first suction pipe (46) through a third connection pipe (49c). The second connection pipe (49b) and the third connection pipe (49c) each include a check valve (CV). Specifically, while the discharge pressure of each compressor (31, 32, 33) is always exerted on the first port of the third four-way selector valve (43), the suction pressures of the second compressor (32), the third compressor (33), and the first compressor (31) are exerted on the second, third, and fourth ports, respectively, thereof.
The third four-way selector valve (43) is switchable between a first position in which the first and third ports are communicated with each other and the second and fourth ports are communicated with each other (the position illustrated by the solid lines in FIG. 1), and a second position in which the first and fourth ports are communicated with each other and the second and third ports are communicated with each other (the position illustrated by the broken lines in FIG. 1). In this embodiment, the above-described third four-way selector valve (43) and the connection pipes (49a, 49b, 49c) form a compressor selector.
The second liquid pipe (52) includes the subcooling heat exchanger (37). The subcooling heat exchanger (37) includes a high-pressure channel (37a) and a low-pressure channel (37b). The subcooling heat exchanger (37) is configured so that heat is exchanged between refrigerant flowing through the high-pressure channel (37a) and refrigerant flowing through the low-pressure channel (37b) to subcool the refrigerant through the high-pressure channel (37a). For example, the subcooling heat exchanger (37) is formed by a plate heat exchanger.
The high-pressure channel (37a) is connected upstream of the junction of the second liquid pipe (52) with the bypass pipe (54). Specifically, one end of the high-pressure channel (37a), i.e., the inflow end thereof, is communicated with the bottom of the receiver (35), and the other end thereof, i.e., the outflow end thereof, is communicated with the first liquid side shut-off valve (21). By contrast, a first branch pipe (55) serving as a subcooling passage is connected to one end of the low-pressure channel (37b), i.e., the inflow end thereof. The first branch pipe (55) branches from the downstream side of the check valve (CV) in the second liquid pipe (52). The first branch pipe (55) includes the subcooling expansion valve (38). The subcooling expansion valve (38) is formed by an electronic expansion valve having an adjustable opening. One end of an injection pipe (61) described below is connected to the other end of the low-pressure channel (37b), i.e., the outflow end thereof.
A second branch pipe (56) is disposed between the first branch pipe (55) and the first connection pipe (49a). Specifically, one end of the second branch pipe (56) is connected upstream of the subcooling expansion valve (38) in the first branch pipe (55), and the other end thereof is connected at any location along the first connection pipe (49a). The second branch pipe (56) includes a check valve (CV).
The second branch pipe (56) is provided with a third branch pipe (57). Specifically, one end of the third branch pipe (57) is connected upstream of the check valve (CV) in the second branch pipe (56), and the other end thereof is connected to the top of the receiver (35). The second branch pipe (56) is connected in the vicinity of one end of the third branch pipe (57), which is connected to the second liquid side shut-off valve (22). The third branch pipe (57) includes a solenoid valve (SV) and a check valve (CV) in a sequential order from the end of the third branch pipe (57) close to the second branch pipe (56).
The liquid-side end of the outdoor heat exchanger (34) and the liquid-side end of an indoor heat exchanger (71) of the air conditioning circuit (70) described below are each connected to the top of the receiver (35) through a pipe. The receiver (35) is configured so that liquid refrigerant in the receiver (35) flows through the second liquid pipe (52) and the first liquid side connection pipe (25) to the chiller circuit (80) and the freezer circuit (90).
A third liquid pipe (53) is connected between the second liquid pipe (52) and the third branch pipe (57). Specifically, one end of the third liquid pipe (53), i.e., the inflow end thereof, is connected to the second liquid pipe (52) upstream of the subcooling heat exchanger (37), and the other end thereof, i.e., the outflow end thereof, is connected to the third branch pipe (57) upstream of the solenoid valve (SV). The third liquid pipe (53) includes a check valve (CV).
The other end (outflow end) of the injection pipe (61) branches into three branch injection pipes (61a, 61b, 61c). These three branch injection pipes (61a, 61b, 61c) are connected to intermediate ports of the corresponding compressors (31, 32, 33). The intermediate ports of the compressors (31, 32, 33) are communicated with corresponding compression chambers at intermediate pressure (hereinafter referred to as the intermediate pressure chambers). Specifically, these injection pipes (61, 61a, 61b, 61c) form an injection circuit for injecting gas refrigerant from the subcooling heat exchanger (37) into the intermediate pressure chambers of the compressors (31, 32, 33). The injection circuit is configured as a so-called economizer system. The branch injection pipes (61a, 61b, 61c) each include a solenoid valve (SV).
Oil separators (39) are each disposed upstream of the check valve (CV) in the corresponding discharge pipe (45a, 45b, 45c). The oil separators (39) are each configured to separate refrigerant oil from refrigerant discharged from the corresponding compressor (31, 32, 33). Oil return pipes (65a, 65b, 65c) are connected to the corresponding oil separators (39). These three oil return pipes (65a, 65b, 65c) are connected in the vicinity of the inflow end of an oil return junction pipe (65). The outflow end of the oil return junction pipe (65) is connected at any location along the injection pipe (61). Specifically, the oil return junction pipe (65) is communicated with the intermediate pressure chambers of the compressors (31, 32, 33). The oil return pipe (65a) corresponding to the first compressor (31) includes a capillary tube (CP). The oil return pipes (65b, 65c) corresponding to the second compressor (32) and the third compressor (33) each include a check valve (CV) and a capillary tube (CP) in a sequential order from the end of the oil return pipe (65b, 65c) close to the corresponding oil separator (39).
The oil return pipes (65a, 65b, 65c) and the oil return junction pipe (65) form an oil return passage for returning the refrigerant oil separated by the oil separators (39) into the intermediate pressure chambers of the compressors (31, 32, 33). As such, the refrigerant oil from the oil separators (39) is returned not into the suction pipes (46, 47, 48) but into the intermediate pressure chambers, and thus, is not cooled by low-pressure refrigerant, thereby preventing the viscosity of the refrigerant oil from increasing.
One of the features of the present invention is that the refrigerant circuit (20) includes a gas vent pipe (62). One end of the gas vent pipe (62) forms an inflow end, and is connected to the top (gas space) of the receiver (35). The other end of the gas vent pipe (62) forms an outflow end, and is connected to the injection pipe (61) upstream of the oil return junction pipe (65). Therefore, the gas space of the receiver (35) is communicated with the intermediate pressure chambers of the compressors (31, 32, 33). Specifically, the other end (outflow end) of the gas vent pipe (62) is communicated with a line having a lower pressure than the pressure of the receiver (35) (the discharge pressure of each compressor (31, 32, 33), i.e., high pressure). The gas vent pipe (62) includes a gas vent valve (63) formed by an on-off valve (solenoid valve).
The outdoor circuit (30) includes various sensors and pressure switches. Specifically, a discharge temperature sensor (111, 112, 113) and a high pressure switch (114, 115, 116) are disposed upstream of the check valve (CV) in each discharge pipe (45a, 45b, 45c). The discharge temperature sensor (111, 112, 113) serves to sense the temperature of the corresponding discharge pipe (45a, 45b, 45c), and the high pressure switch (114, 115, 116) serves to sense the corresponding discharge pressure and provide an emergency stop of the refrigeration apparatus (1) under abnormally high pressure. The discharge junction pipe (45) includes a discharge pressure sensor (117) for sensing the discharge pressures of the compressors (31, 32, 33). The first suction pipe (46) and the third suction pipe (48) each include a suction temperature sensor (118, 119) and a suction pressure sensor (120, 121). The suction temperature sensor (118, 119) serves to sense the temperature of the corresponding suction pipe (46, 48), and the suction pressure sensor (120, 121) serves to sense the suction pressure of the corresponding compressor (31, 32, 33). The second liquid pipe (52) includes a liquid temperature sensor (123) downstream of the subcooling heat exchanger (37). The liquid temperature sensor (123) serves to sense the temperature of liquid refrigerant flowing out of the subcooling heat exchanger (37) into the second liquid pipe (52).
An outdoor temperature sensor (122) is disposed in the vicinity of the outdoor heat exchanger (34) to sense the temperature of outdoor air. The gas-side end (inlet end) of the outdoor heat exchanger (34) is provided with a first refrigerant temperature sensor (125), and a heat transfer tube of the outdoor heat exchanger (34) is provided with a second refrigerant temperature sensor (126).

One end (liquid-side end) of the air conditioning circuit (70) of the air conditioning unit (12) is connected to the second liquid side connection pipe (26), and the other end (gas-side end) thereof is connected to the first gas side connection pipe (27). The air conditioning circuit (70) includes the indoor heat exchanger (71) and an indoor expansion valve (72) in a sequential order from the gas-side end. The indoor heat exchanger (71) is a cross-fin-type fin-and-tube heat exchanger, and forms a first utilization side heat exchanger according to the present invention. An indoor fan (73) is disposed in the vicinity of the indoor heat exchanger (71). The indoor heat exchanger (71) exchanges heat between refrigerant and indoor air blown by the indoor fan (73). An indoor expansion valve (72) is formed by an electronic expansion valve having an adjustable opening.
In the air conditioning circuit (70), the gas-side end of the indoor heat exchanger (71) is provided with a first refrigerant temperature sensor (131), and a heat transfer tube of the indoor heat exchanger (73) is provided with a second refrigerant temperature sensor (132). An indoor temperature sensor (133) is disposed in the vicinity of the indoor heat exchanger (71) to sense the temperature of the internal air of the store.

One end (liquid-side end) of the chiller circuit (80) of the chiller showcase (13) is connected to the branching end of the first liquid side connection pipe (25), and the other end (gas-side end) thereof is connected to the second gas side connection pipe (28). The chiller circuit (80) includes a chilling heat exchanger (81) and a chilling expansion valve (82) in a sequential order from the gas-side end. The chilling heat exchanger (81) is a cross-fin-type fin-and-tube heat exchanger, and forms a second utilization side heat exchanger according to the present invention. A chilling fan (83) is disposed in the vicinity of the chilling heat exchanger (81). The chilling heat exchanger (81) exchanges heat between refrigerant and the internal air of the chiller showcase blown by the chilling fan (83).
An outlet refrigerant temperature sensor (134) is disposed at the outflow side of the chilling heat exchanger (81) of the chiller circuit (80). The chilling expansion valve (82) is formed by a thermostatic expansion valve having an opening controlled based on the temperature sensed by the outlet refrigerant temperature sensor (134). An openable and closable solenoid valve (SV) is disposed in the vicinity of the upstream side of the chilling expansion valve (82). An internal chiller showcase temperature sensor (135) is disposed in the vicinity of the chilling heat exchanger (81) to sense the temperature of the air in the chiller showcase (13).

One end (liquid-side end) of the freezer circuit (90) of the freezer showcase (14) is connected to the branching end of the first liquid side connection pipe (25), and the other end (gas-side end) thereof is connected at any location along the second gas side connection pipe (28). The freezer circuit (90) includes a freezing expansion valve (92), a freezing heat exchanger (91), and a booster compressor (94) in a sequential order from the liquid-side end. The freezing heat exchanger (91) is a cross-fin-type fin-and-tube heat exchanger, and forms a second utilization side heat exchanger according to the present invention together with the chilling heat exchanger (81). A freezing fan (93) is disposed in the vicinity of the freezing heat exchanger (91). The freezing heat exchanger (91) exchanges heat between refrigerant and the internal air of the freezer showcase blown by the freezing fan (93).
An outlet refrigerant temperature sensor (136) is disposed at the outflow side of the freezing heat exchanger (91) of the freezer circuit (90). The freezing expansion valve (92) is formed by a thermostatic expansion valve having an opening controlled based on the temperature sensed by the outlet refrigerant temperature sensor (136). An openable and closable solenoid valve (SV) is disposed in the vicinity of the upstream side of the freezing expansion valve (92). An internal freezer showcase temperature sensor (137) is disposed in the vicinity of the freezing heat exchanger (91) to sense the temperature of the air in the freezer showcase (14).
The booster compressor (94) is a high-pressure dome type scroll compressor, and forms a variable capacity compressor. A discharge pipe (95) for the booster compressor (94) is connected to the second gas side connection pipe (28), and a suction pipe (96) for the booster compressor (94) is connected to the freezing heat exchanger (91). The discharge pipe (95) includes a high pressure switch (138), an oil separator (97), and a check valve (CV) in a sequential order from the end of the discharge pipe (95) close to the booster compressor (94). The suction pipe (96) is provided with a suction pressure sensor (139) for sensing the suction pressure of the booster compressor (94). An oil return pipe (98) is connected to the oil separator (97) to return refrigerant oil separated from refrigerant into the suction side of the booster compressor (94) (a suction pipe (96)). The oil return pipe (98) includes a capillary tube (CP).
The freezer circuit (90) also includes a bypass pipe (99) providing connection between the suction pipe (96) and the discharge pipe (95). The bypass pipe (99) includes a check valve (CV). The bypass pipe (99) is configured so that, during fault conditions, etc., of the booster compressor (94), refrigerant flowing through the suction pipe (96) bypasses the booster compressor (94) and flows into the discharge pipe (95).
In the refrigerant circuit (20) of this embodiment, the evaporation temperatures of refrigerant in the air conditioning circuit (70), the chiller circuit (80), and the freezer circuit (90) are different. The evaporation pressures of refrigerant in the air conditioning circuit (70), the chiller circuit (80), and the freezer circuit (90) are different.

The controller (100) serves to control various devices and valves described above and control the operation of the refrigeration apparatus (10), and forms a control section according to the present invention. Values sensed by various sensors described above are entered into the controller (100).
One of the features of the present invention is that the controller (100) controls the opening and closing of the gas vent valve (63) based on the refrigerant amount in the outdoor heat exchanger (34) and the refrigerant amount in the indoor heat exchanger (71) during a second heating and refrigeration operation described below. The detailed operation of the control of the opening and closing will be described below.

-Operational Behavior-

Next, the operational behavior of the refrigeration apparatus (10) in each operation mode will be described. Here, as typical operation modes, <i> a first cooling and refrigeration operation for concurrently performing the room cooling of the air conditioning unit (12) and the cooling of the showcases (13, 14), <ii> a second cooling and refrigeration operation performed when the air conditioning unit (12) lacks the cooling capacity during the first cooling and refrigeration operation, <iii> a first heating and refrigeration operation for performing the room heating of the air conditioning unit (12) and the cooling of the showcases (13, 14) in a 100% heat recovery operation without using the outdoor heat exchanger (34), and <iv> a second heating and refrigeration operation performed when the air conditioning unit (12) has too much heating capacity during the first heating and refrigeration operation will be specifically described.

As illustrated in FIG. 2, in the first cooling and refrigeration operation, the first compressor (31) and the second compressor (32) form compression mechanisms of the second utilization system, and the third compressor (33) forms a compression mechanism of the first utilization system. The first compressor (31), the second compressor (32), and the third compressor (33) are driven, and the booster compressor (94) is also driven.
All of the four-way selector valves (41, 42, 43) are set to the first positions. Furthermore, the outdoor expansion valve (36) is fully closed, and the solenoid valves (SV) of the chiller circuit (80) and the freezer circuit (90) are set to open positions. The openings of the indoor expansion valve (72), the chilling expansion valve (82), the freezing expansion valve (92), and the subcooling expansion valve (38) are appropriately adjusted. While the solenoid valves (SV) of the branch injection pipes (61a, 61b, 61c) are set to open positions, the solenoid valve (SV) of the third branch pipe (57) and the gas vent valve (63) of the gas vent pipe (62) are set to the closed positions.
The refrigerant compressed by the compressors (31, 32, 33) is combined together in the discharge junction pipe (45), and then flows through the first four-way selector valve (41) into the outdoor heat exchanger (34). In the outdoor heat exchanger (34), the refrigerant dissipates heat to outdoor air, and condenses. The liquid refrigerant condensed in the outdoor heat exchanger (34) flows through the first liquid pipe (51) into the receiver (35). The liquid refrigerant in the receiver (35) flows into the second liquid pipe (52).
Part of the liquid refrigerant flowing into the second liquid pipe (52) flows into the high-pressure channel (37a) of the subcooling heat exchanger (37), and the rest of the liquid refrigerant flows through the third liquid pipe (53) and the third branch pipe (57) into the second liquid side connection pipe (26). By contrast, the branching refrigerant branching from the second liquid pipe (52) into the first branch pipe (55) is decompressed by the subcooling expansion valve (38), and then flows into the low-pressure channel (37b) of the subcooling heat exchanger (37). The subcooling heat exchanger (37) exchanges heat between the branching refrigerant through the low-pressure channel (37b) and the liquid refrigerant through the high-pressure channel (37a), thereby allowing the branching refrigerant through the low-pressure channel (37b) to evaporate and enabling the subcooling of the liquid refrigerant through the high-pressure channel (37a). The subcooled liquid refrigerant flows through the second liquid pipe (52) into the first liquid side connection pipe (25). By contrast, the evaporated refrigerant through the low-pressure channel (37b) flows into the injection pipe (61).
The refrigerant flowing into the injection pipe (61) is injected through the branch injection pipes (61a, 61 b, 61 c) into the intermediate pressure chambers of the compressors (31, 32, 33). This reduces the discharge gas temperatures of the compressors (31, 32, 33). The refrigerant oil separated by the oil separator (39) is returned through the oil return junction pipe (65) into the injection pipe (61), and is injected into the intermediate pressure chambers of the compressors (31, 32, 33) together with refrigerant.
The liquid refrigerant flowing into the second liquid side connection pipe (26) flows into the air conditioning circuit (70). The refrigerant flowing into the air conditioning circuit (70) is decompressed by the indoor expansion valve (72), then absorbs heat from indoor air in the indoor heat exchanger (71), and evaporates. This enables the cooling of the indoor air, thereby performing the air cooling of the store. The refrigerant evaporating in the indoor heat exchanger (71) sequentially passes through the first gas side connection pipe (27), the first four-way selector valve (41), and the second four-way selector valve (42), and then is sucked through the third suction pipe (48) into the third compressor (33).
By contrast, the liquid refrigerant flowing into the first liquid side connection pipe (25) flows into the chiller circuit (80) and the freezer circuit (90). The refrigerant flowing into the chiller circuit (80) is decompressed by the chilling expansion valve (82), then absorbs heat from the internal air of the chiller in the chilling heat exchanger (81), and evaporates. This enables the cooling of the interior of the chiller showcase (13). The internal temperature of the chiller showcase (13) is kept at, e.g., 5°C. The refrigerant evaporating in the chilling heat exchanger (81) flows into the second gas side connection pipe (28). The refrigerant flowing into the freezer circuit (90) is decompressed by the freezing expansion valve (92), then absorbs heat from the internal air of the freezer in the freezing heat exchanger (91), and evaporates. This enables the cooling of the interior of the freezer showcase (14). The internal temperature of the freezer showcase (14) is kept at, e.g., -10°C. The refrigerant evaporating in the freezing heat exchanger (91) is compressed by the booster compressor (94), and then is combined with the refrigerant from the chiller circuit (80) in the second gas side connection pipe (28). The combined refrigerant flows into the first suction pipe (46). Then, part of the combined refrigerant is sucked into the first compressor (31), and the rest thereof is sucked through the third four-way selector valve (43) and the second suction pipe (47) into the second compressor (32).
Refrigerant repeats circulating as described above, thereby concurrently performing the air cooling of the store and the cooling of the interiors of the chiller showcase (13) and the freezer showcase (14).

As illustrated in FIG. 3, the second cooling and refrigeration operation is an operation in which the system of the second compressor (32) in the first cooling and refrigeration operation is changed to the first utilization system. The settings of the second cooling and refrigeration operation are basically similar to those of the first cooling and refrigeration operation except that the third four-way selector valve (43) is set to the second position.
Therefore, during the second cooling and refrigeration operation, similarly to the first cooling and refrigeration operation, refrigerant discharged from the first compressor (31), the second compressor (32), and the third compressor (33) condenses in the outdoor heat exchanger (34), and evaporates in the indoor heat exchanger (71), the chilling heat exchanger (81), and the freezing heat exchanger (91).
The refrigerant evaporating in the indoor heat exchanger (71) is sucked into the second compressor (32) and the third compressor (33), and the refrigerant evaporating in the chilling heat exchanger (81) and the freezing heat exchanger (91) is sucked into the first compressor (31). Specifically, when the two compressors (32, 33) are used for the first utilization system for air conditioning, this enables compensation for the lack of the capacity to cool the interior of the store.

The first heating and refrigeration operation is performed without using the outdoor heat exchanger (34). As illustrated in FIG. 4, in the first heating and refrigeration operation, while the first compressor (31), and the second compressor (32), and the booster compressor (94) are driven, the third compressor (33) is stopped.
The first four-way selector valve (41) is set to the second position, and the second four-way selector valve (42) and the third four-way selector valve (43) are set to the first positions. Furthermore, the outdoor expansion valve (36) is fully closed, and the solenoid valves (SV) of the chiller circuit (80) and the freezer circuit (90) are set to open positions. While the indoor expansion valve (72) is set to a fully-open position, the openings of the chilling expansion valve (82) and the freezing expansion valve (92) are appropriately adjusted. The subcooling expansion valve (38) is set to a fully-closed position. The solenoid valve (SV) of the third branch pipe (57) is set to an open position, and the gas vent valve (63) of the gas vent pipe (62) is set to a closed position. The solenoid valves (SV) of the branch injection pipes (61a, 61b, 61c) are set to open positions, and the refrigerant oil is injected through the oil separator (39) into the intermediate pressure chambers of the compressors (31, 32, 33).
Under such conditions, the refrigerant compressed by the first compressor (31) and the second compressor (32) flows through the first four-way selector valve (41) and the first gas side connection pipe (27) into the air conditioning circuit (70). The refrigerant flowing into the air conditioning circuit (70) dissipates heat to indoor air in the indoor heat exchanger (71), and condenses. This enables the heating of the indoor air, thereby performing the heating of the interior of the store. The liquid refrigerant condensing in the indoor heat exchanger (71) flows through the second liquid side connection pipe (26) and the third branch pipe (57) into the receiver (35).
The liquid refrigerant in the receiver (35) flows into the second liquid pipe (52), and then flows through the high-pressure channel (37a) of the subcooling heat exchanger (37) into the first liquid side connection pipe (25). The liquid refrigerant passing through the high-pressure channel (37a) of the subcooling heat exchanger (37) is not subcooled.
The liquid refrigerant flowing into the first liquid side connection pipe (25) flows into the chiller circuit (80) and the freezer circuit (90). The refrigerant flows through the chiller circuit (80) and the freezer circuit (90) in the same manner as in the first cooling and refrigeration operation. Specifically, in the chiller circuit (80), refrigerant evaporates in the chilling heat exchanger (81), and thus, the interior of the chiller showcase (13) is cooled. In the freezer circuit (90), refrigerant evaporates in the freezing heat exchanger (91), and thus, the interior of the freezer showcase (14) is cooled. The refrigerant evaporating in the chilling heat exchanger (81) and the refrigerant evaporating in the freezing heat exchanger (91) are combined together in the second gas side connection pipe (28), and then the combined refrigerant is sucked into the first compressor (31) and the second compressor (32) separately. Refrigerant repeats circulating as described above, thereby concurrently performing the heating of the interior of the store and the cooling of the interiors of the chiller showcase (13) and the freezer showcase (14).
In the first heating and refrigeration operation, there is a balance between the cooling capacity of the chiller showcase (13) and the freezer showcase (14) (the amount of heat of evaporation) and the heating capacity of the air conditioning unit (12) (the amount of heat of condensation), thereby performing a 100% heat recovery. As such, in the first heating and refrigeration operation, the refrigerant condensing in the air conditioning unit (12) flows directly into the chiller showcase (13) and the freezer showcase (14) without being returned to the outdoor unit (10).

As illustrated in FIG. 5, in the second heating and refrigeration operation, the settings of the valves, etc., are identical with those in the first heating and refrigeration operation except that the second four-way selector valve (42) is set to the second position.
Part of refrigerant compressed by the first compressor (31) and the second compressor (32) flows into the indoor heat exchanger (71), and condenses in the same manner as in the first heating and refrigeration operation. The condensed liquid refrigerant flows through the second liquid side connection pipe (26) and the third branch pipe (57) into the receiver (35). By contrast, the rest of the refrigerant compressed by the first compressor (31) and the second compressor (32) flows sequentially through the second four-way selector valve (42) and the first four-way selector valve (41) into the outdoor heat exchanger (34). In the outdoor heat exchanger (34), the refrigerant absorbs heat from outdoor air, and condenses. The condensed liquid refrigerant flows through the first liquid pipe (51) into the receiver (35).
The liquid refrigerant in the receiver (35) flows through the second liquid pipe (52) and the first liquid side connection pipe (25) into the chiller circuit (80) and the freezer circuit (90) in the same manner as in the first heating and refrigeration operation. Similarly, refrigerant evaporating in the chiller circuit (80) and refrigerant evaporating in the freezer circuit (90) are combined together in the second gas side connection pipe (28), and then the combined refrigerant is sucked into the first compressor (31) and the second compressor (32) separately. Refrigerant repeats circulating as described above, thereby concurrently performing the heating of the interior of the store and the cooling of the interiors of the chiller showcase (13) and the freezer showcase (14).
As described above, the second heating and refrigeration operation is an operation in which refrigerant discharged from the compressors (31, 32) flows into the outdoor heat exchanger (34) and the indoor heat exchanger (71), dissipates heat, and then flows into the receiver (35), and the liquid refrigerant in the receiver (35) flows into the chilling heat exchanger (81) and the freezing heat exchanger (91), and absorbs heat. In the second heating and refrigeration operation, there is no balance between the cooling capacity of the chiller showcase (13) and the freezer showcase (14) (the amount of heat of evaporation) and the heating capacity of the air conditioning unit (12) (the amount of heat of condensation), and thus, the surplus heat of condensation is dissipated to outdoor air by the outdoor heat exchanger (34).

During the second heating and refrigeration operation, the controller (100) controls the opening and closing of the gas vent valve (63) based on the flow illustrated in FIG. 6.
Here, a case in which the air conditioning unit (12) is located at a higher level than the outdoor unit (11), and a case in which the first gas side connection pipe (27) and the second liquid side connection pipe (26) are long are considered. In such a case, in the second heating and refrigeration operation, the pressure loss through the path allowing the refrigerant discharged from the compressors (31, 32) to flow through the air conditioning unit (12) into the receiver (35) (hereinafter referred to as the air conditioning unit side path) is higher than that through the path allowing the refrigerant discharged from the compressors (31, 32) to flow through the outdoor heat exchanger (34) into the receiver (35) (hereinafter referred to as the outdoor heat exchanger side path). Therefore, the flow of the refrigerant through the air conditioning unit side path is slower than that of the refrigerant through the outdoor heat exchanger side path. This makes it difficult even for the condensed refrigerant to flow through the indoor heat exchanger (71), and thus, the liquid refrigerant gradually accumulates. As a result, the amount of the liquid refrigerant flowing into the receiver (35) through the air conditioning unit side path decreases. By contrast, the amount of the liquid refrigerant required to cool the showcases (13, 14) flows out of the receiver (35) into the second liquid pipe (52). Therefore, in the second heating and refrigeration operation, the liquid refrigerant in the receiver (35) gradually decreases, and is finally lost, thereby making it impossible to cool the showcases (13, 14). This result applies also to the case in which the pressure loss through the outdoor heat exchanger side path is higher than that through the air conditioning unit side path. Therefore, in the second heating and refrigeration operation of this embodiment, the gas vent valve (63) is controlled by the controller (100).
First, upon the start of the flow in FIG. 6, a determination is made whether or not a large amount of refrigerant accumulates in the indoor heat exchanger (71) or in the outdoor heat exchanger (34) in step S1.
Specifically, in step S1, the temperature differences "Pc - Th1" and "Pc - Th2" between the equivalent saturation temperature Pc of high-pressure refrigerant determined based on the values sensed by the discharge temperature sensors (111, 112) and the discharge pressure sensor (117), and the refrigerant temperature Th1 sensed by the first refrigerant temperature sensor (131) of the indoor heat exchanger (71) and the refrigerant temperature Th2 sensed by the first refrigerant temperature sensor (125) of the outdoor heat exchanger (34) are calculated. Specifically, in step S1, the degree of subcooling "Pc - Th1" of refrigerant in the vicinity of the inlet of the indoor heat exchanger (71) and the degree of subcooling "Pc - Th2" of refrigerant in the vicinity of the inlet of the outdoor heat exchanger (34) are calculated.
Here, when the interior of the indoor heat exchanger (71) and the interior of the outdoor heat exchanger (34) are filled with liquid refrigerant, refrigerant near the inlet of the indoor heat exchanger (71), etc., is also subcooled, and thus, the degrees of subcooling "Pc - Th1" and "Pc - Th2" of such refrigerant also increases. Specifically, the degrees of subcooling "Pc - Th1" and "Pc - Th2" of such refrigerant as described above are indicators indicating the amount of refrigerant in the indoor heat exchanger (71) and the amount of refrigerant in the outdoor heat exchanger (34). Therefore, when, in step S1, the degrees of subcooling are greater than T1°C (e.g., 2°C), a determination is made that a large amount of refrigerant accumulates in one of the indoor heat exchanger (71) and the outdoor heat exchanger (34) in which the degree of subcooling of refrigerant is greater, and this process proceeds to step S2.
In step S2, the gas vent valve (63) of the gas vent pipe (62) is changed to an open position. This provides communication between the air space in the receiver (35) and the intermediate pressure chambers of the compressors (31, 32) as illustrated in FIG. 7. Since the internal pressure of the receiver (35) is high, and the internal pressures of the intermediate pressure chambers are intermediate, such pressure differences allow gas refrigerant in the receiver (35) to flow out into the gas vent pipe (62). The gas refrigerant flowing out into the gas vent pipe (62) flows through the injection pipe (61) and the branch injection pipes (61 a, 61b) into the intermediate pressure chambers of the compressors (31, 32). Thus, the internal pressure of the receiver (35) is reduced in response to the amount of the gas refrigerant flowing out, and therefore, liquid refrigerant flows through one of the indoor heat exchanger (71) and the outdoor heat exchanger (34) filled with the liquid refrigerant into the receiver (35). This eliminates accumulation of liquid refrigerant in the indoor heat exchanger (71), etc., and prevents liquid refrigerant in the receiver (35) from decreasing.
Such discharge of the refrigerant accumulated in the indoor heat exchanger (71), etc., also gradually decreases the degrees of subcooling "Pc - Th1" and "Pc - Th2." Then, when, in step S1, the degrees of subcooling of refrigerant are less than or equal to T1°C, this process proceeds to step S3.
In step S3, a determination is made to check whether or not accumulation of refrigerant in the indoor heat exchanger (71), etc., has been eliminated. Specifically, when, in step S3, e.g., the degree of subcooling "Pc - Th1"of refrigerant near the inlet of the indoor heat exchanger (71) is continuously less than or equal to T1°C for t1 minutes (e.g., three minutes) or more, a determination is made that refrigerant is hardly accumulated in the indoor heat exchanger (71), and this process proceeds to step S4. In step S4, the position of the gas vent valve (63) is changed to a closed position.
In step S3, the temperature differences "Pc - Th3" and "Pc - Th4" between the equivalent saturation temperature Pc of high-pressure refrigerant, and the refrigerant temperature Th3 sensed by the second refrigerant temperature sensor (132) of the indoor heat exchanger (71) and the refrigerant temperature Th4 sensed by the second refrigerant temperature sensor (126) of the outdoor heat exchanger (34) are also calculated. Specifically, in step S3, the degree of subcooling "Pc - Th3" of refrigerant immediately forward of the outlet of the indoor heat exchanger (71) and the degree of subcooling "Pc - Th4" of refrigerant immediately forward of the outlet of the outdoor heat exchanger (34) are also calculated. Also when the degree of subcooling "Pc - Th3," etc., is continuously less than T2°C (e.g., 5°C) for t2 minutes (e.g., two minutes) or more, a determination is made that liquid refrigerant is hardly accumulated in the indoor heat exchanger (71), etc., and this process proceeds to step S4. As a result, the gas vent valve (63) is closed. By contrast, when neither of the above-described two conditions is satisfied, the gas vent valve (63) is kept open.
As described above, in control operation corresponding to the flow in FIG. 6, when the amount of refrigerant accumulated in the indoor heat exchanger (71) or the outdoor heat exchanger (34) increases, the position of the gas vent valve (63) is changed to an open position before liquid refrigerant in the receiver (35) is lost. This allows the liquid refrigerant accumulated in the indoor heat exchanger (71), etc., to flow into the receiver (35) before liquid refrigerant in the receiver (35) is lost.

-Advantages of Embodiment-

In this embodiment, the gas vent pipe (62) is disposed to provide communication between the gas space in the receiver (35) and the intermediate pressure chambers, which each have a lower pressure than the gas space, of the compressors (31, 32, 33). Furthermore, in this embodiment, in the second heating and refrigeration operation, the gas vent valve (63) in the gas vent pipe (62) is opened based on the indicators indicating the amount of refrigerant accumulated in the indoor heat exchanger (71) and the amount of refrigerant accumulated in the outdoor heat exchanger (34) (the degrees of subcooling of refrigerant). Specifically, when the amount of refrigerant accumulated in the indoor heat exchanger (71), etc., increases, the gas vent valve (63) is opened. This allows the liquid refrigerant accumulated in the indoor heat exchanger (71), etc., to flow into the receiver (35) before liquid refrigerant in the receiver (35) is lost, i.e., before all the liquid refrigerant flows out of the receiver (35) into the second liquid pipe (52). This can prevent liquid refrigerant in the receiver (35) from being lost in the second heating and refrigeration operation. As a result, in the second heating and refrigeration operation, the amount of the liquid refrigerant supplied from the receiver (35) to each showcase (13, 14) can be always ensured, thereby avoiding the impossibility of cooling the showcase and a reduction in the cooling capacity of the showcase before they occur. This can improve the reliability of the refrigeration apparatus (10).
The gas vent valve (63) is controlled such that even when the degree of subcooling of refrigerant in the vicinity of the inlet of the indoor heat exchanger (71), etc., is less than or equal to a predetermined value, the gas vent valve (63) is not immediately closed, and when the degree of subcooling of the refrigerant is continuously less than or equal to the predetermined value for a fixed time period, the gas vent valve (63) is closed. This can certainly eliminate accumulation of refrigerant in the indoor heat exchanger (71), etc. As a result, liquid refrigerant in the receiver (35) can be reliably prevented from being lost.
In this embodiment, the amount of the refrigerant accumulated in the outdoor heat exchanger (34) and the amount of refrigerant accumulated in the indoor heat exchanger (71) are detected using the degree of subcooling of the refrigerant near the inlet of the indoor heat exchanger (71) and the degree of subcooling of the refrigerant inside the indoor heat exchanger (71). Therefore, the accumulation of liquefied refrigerant in the indoor heat exchanger (71), etc., can be relatively easily known.
When a large amount of liquid refrigerant accumulates in the indoor heat exchanger (71), the refrigerant cannot condense in the heat exchanger (71) very much, thereby reducing the heating capacity. However, when, as described in this embodiment, liquid refrigerant accumulated in the indoor heat exchanger (71) is discharged by opening the gas vent valve (63), this can prevent a reduction in the heating capacity.
In this embodiment, the gas vent pipe (62) is communicated with the intermediate-pressure compression chambers of the compressors (31, 32, 33), thereby allowing gas refrigerant in the receiver (35) to flow into the intermediate-pressure compression chambers. Here, for example, when gas refrigerant in the receiver (35) flows into the suction pipes of the compressors (31, 32), the amount of refrigerant sucked through the chiller showcase (13) into the compressors (31, 32) and the amount of refrigerant sucked through the freezer showcase (14) thereinto are reduced in response to the amounts of the gas refrigerant flowing into the corresponding suction pipes. Therefore, the amount of refrigerant circulating through each of the chilling heat exchanger (81) and the freezing heat exchanger (91) decreases, thereby decreasing the cooling capacity. However, since, in this embodiment, gas refrigerant in the receiver (35) flows into the intermediate pressure chambers of the compressors (31, 32), this prevents a reduction in the amount of the refrigerant circulating through each of the chilling heat exchanger (81) and the freezing heat exchanger (91) and a reduction in the cooling capacity.

«Other Embodiments»

The embodiment may be configured as described below.
For example, in the embodiment, the amount of refrigerant accumulated in the indoor heat exchanger (71), etc., is determined based on the degree of subcooling of refrigerant near the inflow side of the indoor heat exchanger (71), etc., and the degree of subcooling of refrigerant inside the indoor heat exchanger (71), etc. However, it may be determined using any other methods.
In the embodiment, gas refrigerant in the receiver (35) flows through the gas vent pipe (62) into the intermediate pressure chambers of the compressors (31, 32, 33). However, also when the gas refrigerant is alternatively returned to the suction sides of the compressors (31, 32, 33), the object of the present invention can be achieved.
A plurality of air conditioning circuits (70) may be provided as the first utilization side heat exchangers, and only the chiller circuit (80) or only the freezer circuit (90) may be provided as the second utilization side heat exchanger.
The foregoing embodiments have been set forth merely for purposes of preferred examples in nature, and are not intended to limit the scope, applications, and use of the invention.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful for refrigeration apparatuses each configured such that refrigerant condenses in both of a heat source side heat exchanger and a first utilization side heat exchanger, and then flows into a receiver, and the liquid refrigerant in the receiver is supplied to a second utilization side heat exchanger, and evaporates.

DESCRIPTION OF REFERENCE CHARACTERS

10: Refrigeration Apparatus
20: Refrigerant Circuit
31: First Compressor (Compressor)
32: Second Compressor (Compressor)
33: Third Compressor (Compressor)
34: Outdoor Heat Exchanger (Heat Source Side Heat Exchanger)
35: Receiver
62: Gas Vent Pipe
63: Gas Vent Valve (On-Off Valve)
71: Indoor Heat Exchanger (First Utilization Side Heat Exchanger)
81: Chilling Heat Exchanger (Second Utilization Side Heat Exchanger)
91: Freezing Heat Exchanger (Second Utilization Side Heat Exchanger)
100: Controller (Control Section)

Claims

A refrigeration apparatus comprising:
a refrigerant circuit (20) including a compressor (31, 32, 33), a heat source side heat exchanger (34), a first utilization side heat exchanger (71), a second utilization side heat exchanger (81, 91), and a receiver (35) to which a liquid-side end of the heat source side heat exchanger (34) and a liquid-side end of the first utilization side heat exchanger (71) are connected through pipes and through which liquid refrigerant flows into the second utilization side heat exchanger (81,91), and performing a refrigeration cycle,

wherein an operation in which refrigerant discharged from the compressor (31, 32, 33) flows into the heat source side heat exchanger (34) and the first utilization side heat exchanger (71), and dissipates heat, and liquid refrigerant in the receiver (35) flows into the second utilization side heat exchanger (81, 91), and absorbs heat can be performed, and

the refrigeration apparatus further includes:
a gas vent pipe (62) having one end communicated with a gas space in the receiver (35) and having the other end communicated with a line, which has a lower pressure than an internal pressure of the receiver (35), of the refrigerant circuit (20);

an on-off valve (63) provided in the gas vent pipe (62); and

a controller (100) for opening the on-off valve (63) based on indicators indicating an amount of refrigerant in the heat source side heat exchanger (34) and an amount of refrigerant in the first utilization side heat exchanger (71) during the operation.
The refrigeration apparatus of claim 1, wherein
the other end of the gas vent pipe (62) is communicated with an intermediate-pressure compression chamber of the compressor (31, 32, 33).
The refrigeration apparatus of claim 1 or 2, wherein
a degree of subcooling of refrigerant at a gas-side end of the heat source side heat exchanger (34) and a degree of subcooling of refrigerant at a gas-side end of the first utilization side heat exchanger (71), or a degree of subcooling of refrigerant in the heat source side heat exchanger (34) and a degree of subcooling of refrigerant in the first utilization side heat exchanger (71) are used as the indicators indicating the amounts of refrigerant.