JP2008064420A - Refrigerating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve COP (coefficient of performance) while securing reliability of a high stage-side compressing mechanism, in a refrigerating device comprising a low stage-side compressing mechanism and the high stage-side compressing mechanism for compressing a refrigerant in two stages. <P>SOLUTION: This refrigerating device 1 comprises an operation capacity-variable booster compressing mechanism 41, and a refrigerant circuit 10 constituted by successively connecting the operation capacity-variable high stage-side compressing mechanism 11, an outdoor heat exchanger 13, a refrigeration expansion valve 32, and a refrigeration heat exchanger 31, and performs a cooling operation by compressing the refrigerant in two stages to be condensed, and then evaporating the refrigerant by the refrigeration heat exchanger 31. A controller 100 of the refrigerating device 1 comprises a first capacity control portion 101 controlling an operation capacity of the booster compressing mechanism 41 so that an evaporation temperature in the refrigeration heat exchanger 31 is agreed with a target evaporation temperature, and a second capacity control portion 102 controlling an operation capacity of the high stage-side compressing mechanism 11 so that a discharge temperature of the booster compressing mechanism 41 is agreed with a target discharge temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

    The present invention relates to a refrigeration apparatus that includes a low-stage compression mechanism and a high-stage compression mechanism and compresses a refrigerant in two stages, and particularly relates to measures for improving COP.

    2. Description of the Related Art Conventionally, a refrigeration apparatus for a vapor compression refrigeration cycle includes a low-stage compression mechanism and a high-stage compression mechanism that compresses refrigerant in two stages (for example, Patent Document 1).

    The refrigeration apparatus of Patent Literature 1 includes a booster compressor that is a low-stage compression mechanism, an outdoor compressor that is a high-stage compression mechanism, an outdoor heat exchanger, a refrigeration expansion valve, and a refrigeration that cools the inside of the freezer. A refrigerant circuit is connected to the heat exchanger in order. In this refrigeration apparatus, the refrigerant is compressed in two stages by the booster compressor and the outdoor compressor, so that the compression ratio becomes large and the inside of the refrigerator can be cooled to a low temperature range.

In addition, such a refrigeration apparatus includes a liquid injection pipe that supplies part of the liquid refrigerant flowing through the liquid pipe between the outdoor heat exchanger and the refrigeration expansion valve to the suction side of the high-stage compression mechanism. is there. As a result, the liquid refrigerant is supplied to the suction side of the high-stage compression mechanism and the temperature of the suction refrigerant of the high-stage compression mechanism is lowered, so that the temperature of the discharge refrigerant of the high-stage compression mechanism can be lowered. . As a result, the high-stage compression mechanism can be prevented from becoming too hot, and the reliability of the high-stage compression mechanism can be improved (Japanese Patent Application No. 2005-322240).
JP 2004-325023 A

    In the conventional refrigeration apparatus described above, in order to ensure the reliability of the high-stage compression mechanism, a part of the refrigerant discharged from the high-stage compression mechanism is used for cooling in the warehouse (evaporation in the refrigeration heat exchanger). Without being used, it is injected into the suction side of the high-stage compression mechanism. For this reason, when the amount of liquid refrigerant injected is increased, the amount of refrigerant used for cooling the inside of the warehouse is reduced, so that the refrigerating capacity of the evaporator with respect to the power of the entire compression mechanism is reduced, and a desired high COP is obtained. There was a problem that it was not possible.

    The present invention has been made in view of such points, and in a refrigeration apparatus that includes a low-stage compression mechanism and a high-stage compression mechanism and compresses refrigerant in two stages, ensures the reliability of the high-stage compression mechanism. However, it aims at improving COP.

    The first aspect of the invention includes a low-stage compression mechanism (41) with variable operation capacity, a high-stage compression mechanism (11) with variable operation capacity, a condenser (13), an expansion mechanism (32), and an evaporator (31). Is a refrigeration apparatus including a refrigerant circuit (10) connected in order and compressing the refrigerant in two stages by the low-stage compression mechanism (41) and the high-stage compression mechanism (11). And the 1st capacity | capacitance control means (101) which controls the operating capacity of the said low stage side compression mechanism (41) so that the evaporation temperature in the said evaporator (31) may become target evaporation temperature, The said low stage side compression mechanism Second capacity control means (102) for controlling the operating capacity of the high-stage compression mechanism (11) so that the discharge temperature of (41) becomes the target discharge temperature.

    In the first aspect of the invention, the first capacity control means (101) controls the operating capacity of the low-stage compression mechanism (41) so that the evaporation temperature in the evaporator (31) becomes the target evaporation temperature. Then, the operation corresponding to the refrigeration load is performed. The first capacity control means (101) may perform control so that the evaporation pressure becomes a saturation pressure corresponding to the target evaporation temperature, instead of controlling the evaporation temperature.

    The second capacity control means (102) increases the operating capacity of the high-stage compression mechanism (11) when the discharge temperature of the low-stage compression mechanism (41) is higher than the target discharge temperature. Thus, the discharge temperature of the low-stage compression mechanism (41) is lowered to the target discharge temperature. And the suction | inhalation refrigerant | coolant of a high stage side compression mechanism (11) is made into a comparatively low temperature by setting the target discharge temperature of this low stage side compression mechanism (41) suitably. Thereby, when supplying a liquid refrigerant to the suction side of the high stage side compression mechanism (11) as a measure for preventing the high stage side compression mechanism (11) from becoming too hot, the amount of the liquid refrigerant is reduced.

    The second capacity control means (102) reduces the operating capacity of the high-stage compression mechanism (11) when the discharge temperature of the low-stage compression mechanism (41) is lower than the target temperature. The discharge temperature of the low-stage compression mechanism (41) is increased to the target discharge temperature. That is, when the discharge temperature of the low-stage compression mechanism (41) is lower than the target discharge temperature, the high-stage compression mechanism (11) is operated until the high-stage compression mechanism (11) does not become too high. Reduce the capacity and make the overall power of the compression mechanism (11, 41) as small as possible.

    In a second aspect based on the first aspect, the discharge pressure of the low-stage compression mechanism (41) is based on the suction pressure and suction temperature of the low-stage compression mechanism (41) and the target discharge temperature. The operating capacity of the high-stage compression mechanism (11) is controlled so as to be the derived target discharge pressure.

    Here, when the low-stage compression mechanism (41) is, for example, a scroll-type compressor, the refrigerant discharged from the compression chamber that compresses the refrigerant in the dome of the compressor is filled in the dome, and the The dome is heated and then discharged from the compressor. Therefore, when measuring the discharge temperature of the low-stage compression mechanism (41), if a temperature sensor is provided in the discharge pipe of the low-stage compression mechanism (41), the actual temperature of the refrigerant discharged from the compression chamber The discharge temperature is not measured quickly, and the response time becomes long. In addition, it is difficult to provide a temperature sensor for measuring the discharge temperature in the dome of the compressor.

    In other words, depending on the configuration of the low-stage compression mechanism (41), it may be difficult to measure the discharge temperature quickly and accurately. Therefore, in the second aspect of the invention, control for bringing the discharge temperature close to the target discharge temperature is performed. Instead, the discharge temperature is controlled by controlling the discharge pressure of the low-stage compression mechanism (41) having a short measurement response time. Specifically, the discharge pressure of the low-stage compression mechanism (41) is preliminarily determined based on the target discharge temperature of the low-stage compression mechanism (41) and the pressure and temperature of the refrigerant sucked by the low-stage compression mechanism (41). It controls so that it may become the derived | led-out target discharge pressure.

    According to a third invention, in the first or second invention, the refrigerant circuit (10) is configured such that the liquid refrigerant flowing from the condenser (13) to the expansion mechanism (32) and a part of the liquid refrigerant are branched and decompressed. The subcooled heat exchanger (50) that cools the liquid refrigerant by exchanging heat with the branched refrigerant is provided, while the branch refrigerant that has flowed through the supercooled heat exchanger (50) 11) is configured to be supplied to the suction side.

    In the third aspect of the invention, the liquid refrigerant is cooled by the supercooling heat exchanger (50) and expanded by the expansion mechanism (32) and then sent to the evaporator (31). Increases refrigeration capacity.

    In a fourth aspect based on the third aspect, the branch passage (84) for supplying the branch refrigerant to the supercooling heat exchanger (50) is provided with a pressure reducing valve (58) whose opening degree is adjustable. And a valve control means (103) for controlling the opening of the pressure reducing valve (58) so that the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) becomes a target cooling temperature.

    In the fourth aspect of the present invention, when the temperature of the liquid refrigerant that has flowed through the supercooling heat exchanger (50) is higher than the target cooling temperature, the valve control means (103) opens the opening of the pressure reducing valve (58). When the temperature is lower than the target cooling temperature, the opening degree of the pressure reducing valve (58) is decreased and the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) is set as the target cooling temperature.

    The target cooling temperature is set as follows, for example. That is, the branched refrigerant that cools this liquid refrigerant is supplied to the suction side of the high-stage compression mechanism (11), so that when the refrigerant flows through the supercooling heat exchanger (50), the high-stage compression mechanism (11) Evaporates at a saturation temperature corresponding to the suction pressure. In the second aspect of the invention, the discharge pressure of the low-stage compression mechanism (41) corresponding to the suction pressure of the high-stage compression mechanism (11) is controlled to become the target discharge pressure. The corresponding saturation temperature becomes the evaporation temperature of the branch refrigerant, and the target cooling temperature of the liquid refrigerant is set to a value slightly higher than the saturation temperature at the target discharge pressure, for example.

    According to the first aspect of the invention, since the operating capacity of the low-stage compression mechanism (41) is controlled so that the evaporation temperature in the evaporator (31) becomes the target evaporation temperature, it corresponds to the refrigeration load. Can be operated.

    Since the operating capacity of the high-stage compression mechanism (11) is controlled so that the discharge temperature of the low-stage compression mechanism (41) becomes the target discharge temperature, this target discharge temperature is set appropriately. By doing so, the suction refrigerant of the high stage side compression mechanism (11) can be set to a relatively low temperature. As a result, as a measure to prevent the high stage compression mechanism (11) from becoming too hot, the amount of liquid refrigerant should be reduced when supplying the liquid refrigerant to the suction side of the high stage compression mechanism (11). Can do.

    Further, when the discharge temperature of the low-stage compression mechanism (41) is lower than the target discharge temperature, the high-stage compression mechanism (11) to the extent that the high-stage compression mechanism (11) does not become too high. Therefore, the power of the high stage side compression mechanism (11) can be made as small as possible. That is, the flow rate of the refrigerant evaporated in the evaporator (31) can be increased, and the power of the high-stage compression mechanism (11) can be reduced as much as possible, so the power of both compression mechanisms (41, 11) The refrigerating capacity in the evaporator (31) can be increased, and COP can be improved.

    According to the second aspect of the invention, the second capacity control means (102) is configured so that the high-stage compression mechanism is configured so that the discharge pressure of the low-stage compression mechanism (41) becomes the target discharge pressure. Since the operation capacity of (11) is controlled, even if the low-stage compression mechanism (41) has a configuration in which it is difficult to measure the discharge temperature quickly and precisely, the discharge temperature is set as the discharge target temperature. Can be controlled.

    According to the third aspect of the invention, since the liquid refrigerant is cooled by the supercooling heat exchanger (50), the cooled liquid refrigerant is sent to the evaporator (31). The refrigeration capacity in the evaporator (31) can be increased, and the COP of the refrigeration apparatus (1) can be improved reliably.

    According to the fourth aspect of the invention, the opening degree of the pressure reducing valve (58) is controlled so that the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) becomes the target cooling temperature. For this reason, the liquid refrigerant can be cooled more reliably, so that the COP of the refrigeration apparatus (1) can be improved more reliably.

    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

    As shown in FIG. 1, an embodiment of the present invention is a refrigeration apparatus (1) that cools an inside of a cabinet, and includes an outdoor unit (2), a refrigeration unit (3), a booster unit (4), a controller (100 ).

    The outdoor unit (2) includes an outdoor circuit (20), the refrigeration unit (3) includes a refrigeration circuit (30), and the booster unit (4) includes a booster circuit (40). The outdoor circuit (20) and the refrigeration circuit (30) are connected via a liquid communication pipe (21), and the refrigeration circuit (30) and the booster circuit (40) are connected to a first gas communication pipe (22). The booster circuit (40) and the outdoor circuit (20) are connected via a second gas communication pipe (23). The outdoor circuit (20), the refrigeration circuit (30), and the booster circuit (40) are sequentially connected to constitute a refrigerant circuit (10) of the vapor compression refrigeration cycle.

<Outdoor unit>
The outdoor circuit (20) includes a high-stage compression mechanism (11), an outdoor heat exchanger (13), a receiver (14), a supercooling heat exchanger (50), a first expansion valve (57), and a second An expansion valve (58) and a third expansion valve (59) are provided. The outdoor circuit (20) is provided with a four-way switching valve (12), a liquid side closing valve (53), and a gas side closing valve (54). In the outdoor circuit (20), one end of the liquid communication pipe (21) is connected to the liquid side stop valve (53), and one end of the second gas communication pipe (23) is connected to the gas side stop valve (54). ing.

    The high stage compression mechanism (11) is composed of three compressors (11a, 11b, 11c) connected in parallel to each other. The three compressors (11a, 11b, 11c) are high-pressure dome type scroll compressors. In other words, each compressor (11a, 11b, 11c) is not shown in the figure, but the fixed scroll and the movable scroll mesh with each other to form a compression chamber, and a refrigerant compressed in the compression chamber. Is discharged from each compressor (11a, 11b, 11c) after being discharged from the compression chamber and filling the inside of the dome.

    The first compressor (11a) is configured such that electric power is supplied to a compressor motor (not shown) via an inverter and the output frequency of the inverter is changed to vary the operating capacity. The second compressor (11b) and the third compressor (11c) are configured to have a fixed operating capacity. In the high-stage compression mechanism (11), the first compressor (11a) of the three compressors (11a, 11b, 11c) is preferentially driven during the operation of the refrigeration apparatus (1). The second compressor (11b) and the third compressor (11c) are sequentially driven in order in accordance with the cooling load in the refrigerator.

    A suction main pipe (55) is connected to the suction side of the high-stage compression mechanism (11). One end of the suction main pipe (55) is connected to the four-way switching valve (12), and the other end is branched into a third suction pipe (61c) and a suction connection pipe (56), and the third suction pipe (61c ) Is connected to the suction side of the third compressor (11c). The suction connection pipe (56) is branched into a first suction pipe (61a) and a second suction pipe (61b), and the first suction pipe (61a) is a suction side of the first compressor (11a). On the other hand, the second suction pipe (61b) is connected to the suction side of the second compressor (11b).

    A discharge main pipe (64) is connected to the discharge side of the high-stage compression mechanism (11). One end of the discharge main pipe (64) is connected to the four-way switching valve (12), while the other ends are the first discharge pipe (64a), the second discharge pipe (64b), and the third discharge pipe (64c). It is branched to. The first discharge pipe (64a) is on the discharge side of the first compressor (11a), the second discharge pipe (64b) is on the discharge side of the second compressor (11b), and the third discharge pipe (64c) Are connected to the discharge side of the third compressor (11c). Each discharge pipe (64a, 64b, 64c) has a check valve (CV-1, CV that allows only the refrigerant flow from each compressor (11a, 11b, 11c) to the four-way selector valve (12). -2, CV-3) are provided.

    The outdoor heat exchanger (13) is a cross fin type fin-and-tube heat exchanger that exchanges heat between refrigerant and outdoor air, and is configured as a condenser. . The outdoor heat exchanger (13) has one end connected to the four-way switching valve (12) and the other end connected to the top of the receiver (14) via the first liquid pipe (81). The first liquid pipe (81) is provided with a check valve (CV-4) that allows only the refrigerant to flow from the outdoor heat exchanger (13) to the receiver (14). One end of the second liquid pipe (82) is connected to the bottom of the receiver (14).

    The supercooling heat exchanger (50) is a plate heat exchanger, and performs heat exchange between the refrigerant and the first flow path (50a) and the second flow path (50b). And. The first flow path (50a) of the supercooling heat exchanger (50) has one end connected to the other end of the second liquid pipe (82) and the other end connected to one end of the third liquid pipe (83). Has been. The other end of the third liquid pipe (83) is connected to one end of the liquid communication pipe (21) via the liquid side closing valve (53). The third liquid pipe (83) is provided with a check valve (CV-5) that allows only the refrigerant to flow from the other end of the first flow path (50a) to the liquid side shut-off valve (53). Yes.

    One end of a branch passage (84) is connected to the third liquid pipe (83) on the upstream side of the check valve (CV-5), and the other end of the branch passage (84) is connected to the subcooling heat. It is connected to one end of the second flow path (50b) of the exchanger (50). The branch passage (84) is provided with a second expansion valve (58) that is a pressure reducing valve. The second expansion valve (58) is an electronic expansion valve whose opening degree is adjustable.

    The other end of the second flow path (50b) of the supercooling heat exchanger (50) is connected to the suction main pipe (55) through a gas injection pipe (85). The gas injection pipe (85) is for injecting a gas refrigerant into the suction side of the first to third compressors (11a, 11b, 11c).

    In the third liquid pipe (83), one end of a fourth liquid pipe (88) is connected between the check valve (CV-5) and the liquid side shut-off valve (53). The other end of the fourth liquid pipe (88) is connected between the check valve (CV-4) and the receiver (14) in the first liquid pipe (81). The fourth liquid pipe (88) is provided with a check valve (CV-6) that allows only the refrigerant to flow from one end to the other end.

    One end of the fifth liquid pipe (89) is connected between one end of the branch passage (84) and the second expansion valve (58), and the other end of the fifth liquid pipe (89) is The liquid pipe (81) is connected between the outdoor heat exchanger (13) and the check valve (CV-4). The fifth liquid pipe (89) is provided with a first expansion valve (57). The first expansion valve (57) is an electronic expansion valve whose opening degree is adjustable.

    In addition, one end of a communication pipe (78) is connected between the check valve (CV-4) and the connection part of the fourth liquid pipe (88) in the first liquid pipe (81), and the communication pipe The other end of (78) is connected to the discharge main pipe (64). The communication pipe (78) is provided with a check valve (CV-7) that allows only the refrigerant to flow from the first liquid pipe (81) to the discharge main pipe (64).

    The four-way switching valve (12) has a first port at the discharge main pipe (64), a second port at the suction main pipe (55), a third port at one end of the outdoor heat exchanger (13), and a fourth port. Are respectively connected to the gas-side shutoff valves (54). The four-way switching valve (12) is in a first state in which the first port and the third port communicate with each other and the second port and the fourth port communicate with each other (state indicated by a solid line in FIG. 1). ) And a second state (state indicated by a broken line in FIG. 1) in which the first port and the fourth port communicate with each other and the second port and the third port communicate with each other.

    The outdoor circuit (20) includes an oil separator (70), a first liquid injection passage (15), first to third oil equalizing pipes (72a, 72b, 72c), and first to first Three three oil recovery pipes (73a, 73b, 73c) are provided.

    The oil separator (70) is provided in the discharge main pipe (64) and separates refrigeration oil from refrigerant discharged from the compressors (11a, 11b, 11c). One end of an oil return pipe (71) is connected to the oil separator (70), and the other end of the oil return pipe (71) is connected to a connection portion of the gas injection pipe (85) in the suction main pipe (55). Connected downstream. The oil return pipe (71) is provided with a fourth solenoid valve (SV-4) that can be freely opened and closed. When the fourth solenoid valve (SV-4) is opened, the oil separator (70) is separated. Refrigerator oil is returned to the compressors (11a, 11b, 11c) via the suction main pipe (55).

    The first liquid injection passage (15) includes a first liquid injection main pipe (16) and first to fourth liquid injection branch pipes (16a, 16b, 16c, 16d). One end of the first liquid injection main pipe (16) is connected between one end of the branch passage (84) and a connection portion of the fifth liquid pipe (89), and a shunt (26) is provided at the other end. ing. A third expansion valve (59) is provided in the middle of the first liquid injection main pipe (16). The third expansion valve (59) is an electronic expansion valve whose opening degree is adjustable.

    The first to fourth liquid injection branch pipes (16a, 16b, 16c, 16d) are branched from the flow divider (26) of the first liquid injection main pipe (16), and the first to third liquid injection branch pipes (16a, 16b, 16c, 16d) are branched. Each liquid injection branch pipe (16a, 16b, 16c) is in the middle of each of the first to third suction pipes (61a, 61b, 61c), and a fourth liquid injection branch pipe (16d) is an oil return pipe (71). The fourth solenoid valve (SV-4) is connected between the other end. Each of the first to fourth liquid injection branch pipes (16a, 16b, 16c, 16d) is provided with a capillary tube (17a, 17b, 17c, 17d) in the middle.

    In the three oil leveling pipes (72a, 72b, 72c), the first oil leveling pipe (72a) is connected to the dome of the first compressor (11a) and the middle of the fourth liquid injection branch pipe (16d), A first solenoid valve (SV-1) is provided on the way. The second oil leveling pipe (72b) is connected to the dome of the second compressor (11b) and the middle of the first suction pipe (61a), and includes a second electromagnetic valve (SV-2). The third oil equalizing pipe (72c) is connected to the dome of the third compressor (11c) and the suction connecting pipe (56), and includes a third electromagnetic valve (SV-3). In the refrigeration apparatus (1), the refrigeration oil returned to the suction main pipe (55) by the oil return pipe (71) is supplied to the third compressor (11c), the second compressor (11b), and the first compressor ( It is configured to return in the order of 11a). Then, through the oil equalizing pipes (72a, 72b, 72c), the refrigerating machine oil of the third compressor (11c) is sequentially sent to the second compressor (11b) and the first compressor (11a). The surplus of the refrigerating machine oil of one compressor (11a) is sent to the oil return pipe (71) so that the compressors (11a, 11b, 11c) are oil-equalized with each other.

    In the three oil recovery pipes (73a, 73b, 73c), one end of the first oil recovery pipe (73a) is in the middle of the first suction pipe (61a) and one end of the second oil recovery pipe (73b) is One end of the third oil recovery pipe (73c) is connected to the middle of the third suction pipe (61c) in the middle of the second suction pipe (61b), while each oil recovery pipe (73a, 73b, 73c) The other ends of the two are joined together. The oil recovery pipe (73a, 73b, 73c) is connected to the compressor (11b, 11c) when a specific compressor (11b, 11c) is stopped according to the load during operation of the refrigeration system (1). The refrigeration oil staying in the suction pipes (61b, 61c) is sent to the suction pipes (61a, 61b) of the other compressors (11a, 11b) being driven.

    The outdoor circuit (20) is provided with various sensors and pressure switches. Specifically, a suction pressure sensor (135) and a suction temperature sensor (136) are provided in the suction main pipe (55), a discharge pressure sensor (137) is provided in the discharge main pipe (64), and each discharge temperature sensor (138, 139, 140) is provided in each discharge pipe (64a, 64b, 64c). Further, a liquid refrigerant that measures the temperature of the liquid refrigerant flowing through the first flow path (50a) near the outlet of the first flow path (50a) of the supercooling heat exchanger (50) in the third liquid pipe (83). A temperature sensor (141) is provided. In addition, pressure switches (151, 152, 153, 154) are provided in the discharge pipes (64a, 64b, 64c) and pipes between the gas side shut-off valve (54) and the four-way switching valve (12). ing.

    The outdoor unit (2) is provided with an outdoor air temperature sensor (13a) and an outdoor fan (13f). Outdoor air is sent to the outdoor heat exchanger (13) by the outdoor fan (13f).

<Refrigeration unit>
The refrigeration circuit (30) includes a refrigeration heat exchanger (31), a drain pan heater (36), and a refrigeration expansion valve (32).

    The refrigeration heat exchanger (31) is a cross-fin fin-and-tube heat exchanger that exchanges heat between the refrigerant and the air in the cabinet, and is configured as an evaporator. ing. The refrigeration heat exchanger (31) has one end connected to one end of the drain pan heater (36) via the refrigeration expansion valve (32), and the other end connected to one end of the first gas communication pipe (22). Yes.

    The refrigeration expansion valve (32) is an electronic expansion valve whose opening degree can be adjusted, and is configured as an expansion mechanism. The refrigeration heat exchanger (31) is provided with a first refrigerant temperature sensor (33) for measuring the evaporation temperature of the refrigerant in the heat transfer tube, while the other end of the refrigeration heat exchanger (31) A second refrigerant temperature sensor (34) is provided. The refrigeration expansion valve (32) is configured such that the temperature measured by the second refrigerant temperature sensor (34) is higher by a predetermined temperature (for example, 5 ° C.) than the refrigerant evaporation temperature measured by the first refrigerant temperature sensor (33). The so-called superheat control is performed in which the opening degree is adjusted.

    The drain pan heater (36) is disposed on the drain pan of the refrigeration heat exchanger (31) (not shown) and heats the drain pan to prevent frost formation and ice formation. The other end of the drain pan heater (36) is connected to the other end of the liquid communication pipe (21).

    The refrigeration unit (3) is provided with an internal temperature sensor (35f) and an internal fan (35a). The internal air is sent to the refrigeration heat exchanger (31) by the internal fan (35a).

<Booster unit>
The booster circuit (40) includes a booster compression mechanism (41) that is a low-stage side compression mechanism, a fourth expansion valve (38), and a fifth expansion valve (39).

    The booster compression mechanism (41) includes first to third booster compressors (41a, 41b, 41c) connected in parallel to each other. Each of the booster compressors (41a, 41b, 41c) is configured by a high-pressure dome type scroll compressor, like the compressors (11a, 11b, 11c) on the higher stage side. In other words, each booster compressor (41a, 41b, 41c) is not shown in the figure, but the fixed scroll and the movable scroll mesh with each other to form a compression chamber, and are compressed in this compression chamber. The refrigerant is discharged from each compressor (11a, 11b, 11c) after being discharged from the compression chamber and filling the dome.

    The first booster compressor (41a) is configured such that electric power is supplied to a compressor motor (not shown) via an inverter, and the output frequency of the inverter is changed to vary the operating capacity. On the other hand, the second booster compressor (41b) and the third booster compressor (41c) have a fixed operating capacity. In the booster compression mechanism (41), the first booster compressor (41a) among the three booster compressors (41a, 41b, 41c) is preferentially driven during the cooling operation of the refrigeration apparatus (1). The second booster compressor (41b) and the third booster compressor (41c) are sequentially driven in accordance with the load in the cabinet.

    A booster suction main pipe (42) is connected to the suction side of the booster compression mechanism (41). The suction main pipe (42) has one end connected to the other end of the first gas communication pipe (22) and the other end branched to a third booster suction pipe (44c) and a booster suction connection pipe (43). The other end of the third booster suction pipe (44c) is connected to the suction side of the third booster compressor (41c). The booster suction connection pipe (43) is branched into a first booster suction pipe (44a) and a second booster suction pipe (44b), and the first booster suction pipe (44a) is connected to the first booster compressor (44). The second booster suction pipe (44b) is connected to the suction side of the second booster compressor (41b) while being connected to the suction side of 41a).

    A booster discharge main pipe (45) is connected to the discharge side of the booster compression mechanism (41). One end of the booster discharge main pipe (45) is connected to one end of the second gas communication pipe (23) via the closing valve (51), while the other end is connected to the first booster discharge pipe (45a) and the second It is branched into a booster discharge pipe (45b) and a third booster discharge pipe (45c). The first booster discharge pipe (45a) is connected to the discharge side of the first booster compressor (41a), and the second booster discharge pipe (45b) is connected to the discharge side of the second booster compressor (41b). The third booster discharge pipe (45c) is connected to the discharge side of the third booster compressor (41c). Each booster discharge pipe (45a, 45b, 45c) has a check valve (CV-8, which allows only the refrigerant flow from each of the booster compressors (41a, 41b, 41c) to the booster discharge main pipe (45). CV-9 and CV-10) are provided respectively.

    The booster circuit (40) includes an oil separator (46), two second and third liquid injection passages (27, 29), an oil feed pipe (76), a fourth and a fifth two. An oil equalizing pipe (74a, 74b) and fourth to sixth oil recovery pipes (75a, 75b, 75c) are provided.

    The oil separator (46) is provided in the booster discharge main pipe (45), and separates the refrigerating machine oil from the refrigerant discharged from the first to third booster compressors (41a, 41b, 41c). Is. One end of a first bypass pipe (47) is connected to the oil separator (46), and the other end of the first bypass pipe (47) is connected to the booster suction main pipe (42). The first bypass pipe (47) has a fifth solenoid valve (SV-5), and the refrigerant discharged from the high-stage compression mechanism (11) is booster-compressed during the defrosting operation of the refrigeration apparatus (1). This is for bypassing the mechanism (41). Also, one end of the oil return pipe (48) is connected between the fifth solenoid valve (SV-5) and one end of the first bypass pipe (47), and the other end of the oil return pipe (48) It is connected in the middle of the booster suction main pipe (42). The oil return pipe (48) is provided with a sixth solenoid valve (SV-6) that can be freely opened and closed. When the sixth solenoid valve (SV-6) is opened, the oil separator (46) is refrigerated. Machine oil is returned to each booster compressor (41a, 41b, 41c) via the booster suction main pipe (42).

    The second liquid injection passage (27) includes a second liquid injection main pipe (28) and fifth to seventh liquid injection branch pipes (28a, 28b, 28c). In the second liquid injection passage (27), one end of the second liquid injection main pipe (28) is connected in the middle of the liquid communication pipe (21), and the other end of the second liquid injection main pipe (28) is the first. The fifth to seventh liquid injection branch pipes (28a, 28b, 28c) are branched, and the fifth to seventh liquid injection branch pipes (28a, 28b, 28c) are connected to the first to third boosters. The suction pipes (41a, 41b, 41c) are connected respectively.

    The second liquid injection main pipe (28) is provided with a fourth expansion valve (38), and each of the fifth to seventh liquid injection branch pipes (28a, 28b, 28c) has a capillary in the middle thereof. Tubes (37a, 37b, 37c) are provided. One end of the third liquid injection passage (29) is connected between one end of the second liquid injection main pipe (28) and the fourth expansion valve (38), and the other end is oil of the booster discharge main pipe (45). It is connected between the separator (46) and the closing valve (51). A fifth expansion valve (39) is provided in the third liquid injection passage (29). Each of the fourth and fifth expansion valves (38, 39) is an electronic expansion valve whose opening degree is adjustable.

    The oil feed pipe (76) is connected to the dome of the first booster compressor (41a) and the middle of the booster discharge main pipe (45), and is non-returnable with the seventh solenoid valve (SV-7) that can be opened and closed halfway. And a valve (CV-11). In the two oil leveling pipes (74a, 74b), the fourth oil leveling pipe (74a) is connected to the dome of the second booster compressor (41b) and the middle of the first booster suction pipe (44a). Is equipped with an eighth solenoid valve (SV-8). The fifth oil equalizing pipe (74b) is connected to the dome of the third booster compressor (41c) and the middle of the booster suction connecting pipe (43), and includes a ninth electromagnetic valve (SV-9).

    In the refrigeration apparatus (1), the refrigeration oil returned to the booster suction main pipe (42) by the oil return pipe (48) is supplied to the third booster compressor (41c), the second booster compressor (41b), the first The booster compressor (41a) is configured so as to return in order. The refrigerating machine oil of the third booster compressor (41c) is supplied to the second booster compressor (41b) and the first booster compressor (41a) through the fourth and fifth oil equalizing pipes (74a, 74b). The surplus of the refrigeration oil in the first booster compressor (41a) is sent to each compressor (11a, 11b, 11c) in the outdoor circuit (20) through the oil feed pipe (76). Yes.

    The three oil recovery pipes (75a, 75b, 75c) have one end of the fourth oil recovery pipe (75a) in the middle of the first booster suction pipe (44a) and one end of the fifth oil recovery pipe (75b) being the second. One end of the sixth oil recovery pipe (75c) is connected to the middle of the third booster suction pipe (44c) in the middle of the booster suction pipe (44b), while each oil recovery pipe (75a, 75b, 75c) The other ends are joined together. The oil recovery pipe (75a, 75b, 75c) is connected to the booster compressor (41b, 41c) when a specific booster compressor (41b, 41c) is stopped according to the load during operation of the refrigeration apparatus (1). ) Is sucked into the booster suction pipes (44a, 44b) of the other booster compressors (41a, 41b) that are driven.

    Further, the booster circuit (40) is provided with a second bypass pipe (49) for connecting the booster suction main pipe (42) and the booster discharge main pipe (45). The second bypass pipe (49) bypasses the booster compression mechanism (41) and sends the refrigerant flowing through the booster suction main pipe (42) to the booster discharge main pipe (45) when the booster compression mechanism (41) is stopped. A check valve (CV-12) that allows only the flow of refrigerant from the booster suction main pipe (42) to the booster discharge main pipe (45) is provided.

    The booster circuit (40) is provided with various sensors and pressure switches. Specifically, a booster suction pressure sensor (142) and a booster suction temperature sensor (143) are provided in the booster suction main pipe (42), and a booster discharge pressure sensor (144) and a booster discharge main temperature sensor (145) are provided in the booster discharge main pipe. (45), each booster discharge sub temperature sensor (148, 149, 150) and each pressure switch (155, 156, 157) are provided in each booster discharge pipe (45a, 45b, 45c).

<controller>
The controller (100) performs switching and opening adjustment of various valves provided in the refrigerant circuit (10), as well as compressors (11a, 11b, 11c, 41a, 41b, 41c) and fans (13f). , 35f) to control the operation of the refrigeration apparatus (1). The controller (100) includes a first capacity control unit (101), a second capacity control unit (102), and a valve control unit (103) as a feature of the present invention.

    The first capacity control unit (101) is configured to control the booster compression mechanism (41) so that the evaporation temperature in the refrigeration heat exchanger (31) becomes a target evaporation temperature suitable for maintaining the interior at a set temperature. The operation capacity is controlled, and the first capacity control means is configured.

    The second capacity control unit (102) controls the operating capacity of the high stage compression mechanism (11) so that the discharge temperature of the booster compression mechanism (41) becomes a target discharge temperature. It is comprised by the capacity | capacitance control means. Here, since each compressor (41a, 41b, 41c) of the booster compression mechanism (41) is a high-pressure dome type scroll compressor, the discharge is the temperature of the refrigerant discharged from the compression chamber in the dome. If the booster discharge main temperature sensor (145) or the discharge sub temperature sensor (148, 149, 150) is used for measuring the temperature, it takes a long response time and cannot be measured quickly. Accordingly, the target discharge temperature determined by the booster compression mechanism (41) measured by the booster discharge pressure sensor (144) is derived in advance based on the suction pressure and suction temperature of the booster compression mechanism (41) and the target discharge temperature. Control to be pressure.

    The valve control unit (103) controls the second expansion valve (58) so that the temperature of the liquid refrigerant flowing through the first flow path (50a) of the supercooling heat exchanger (50) becomes the target cooling temperature. The opening degree is controlled, and is configured as a valve control means.

-Driving action-
Next, the operation | movement operation | movement of the freezing apparatus (1) of this embodiment is demonstrated based on FIGS. The said refrigeration apparatus (1) performs the cooling operation which cools the inside of a store | warehouse | chamber, and the defrost operation which removes frost formation of a freezing heat exchanger (31).

    In the cooling operation, as shown in FIG. 2, the four-way switching valve (12) of the outdoor circuit (20) is set to the first state, the first expansion valve (57) is set to the fully closed state, and the high stage side is set. The first to third compressors (11a, 11b, 11c) of the compression mechanism (11) are driven, and the first to third booster compressors (41a, 41b, 41c) of the booster compression mechanism (41) are driven. Is driven, and the refrigerant circulates in the direction indicated by the arrow in FIG. Each fan (13f, 35f) is driven. The opening degrees of the refrigeration expansion valve (32) and the second to fifth expansion valves (58, 59, 38, 39) are adjusted as appropriate. In the outdoor circuit (20), the first to fourth solenoid valves (SV-1, 2, 3, 4) are intermittently controlled to be opened and closed appropriately, while in the booster circuit (40), the fifth electromagnetic valve is controlled. The valve (SV-5) is set to a normally closed state, and the sixth to ninth solenoid valves (SV-6, 7, 8, 9) are intermittently controlled appropriately.

    In the outdoor circuit (20), the refrigerant discharged from the first to third compressors (11a, 11b, 11c) flows through the discharge pipes (64a, 64b, 64c) and joins in the discharge main pipe (64). And flows through the outdoor heat exchanger (13) through the four-way switching valve (12). In the outdoor heat exchanger (13), the refrigerant dissipates heat to the outdoor air and condenses. The condensed liquid refrigerant flows through the first liquid pipe (81), passes through the receiver (14), flows through the second liquid pipe (82), and passes through the first flow path (50a) of the supercooling heat exchanger (50). Flowing. The liquid refrigerant that has flowed through the first flow path (50a) flows through the third liquid pipe (83). A part of the liquid refrigerant flowing through the third liquid pipe (83) is branched into the branch passage (84) to become a branch refrigerant, and is depressurized by the second expansion valve (58), and the supercooling heat exchanger (50). Into the second flow path (50b). In the supercooling heat exchanger (50), the branched refrigerant flowing through the second flow path (50b) absorbs heat from the liquid refrigerant flowing through the first flow path (50a) and evaporates, whereby the first flow path The liquid refrigerant flowing through (50a) is cooled to the target cooling temperature, as will be described later. The refrigerant evaporated in the second flow path (50b) is supplied to the suction main pipe (55) through the gas injection pipe (85). Then, the cooled liquid refrigerant flows from the third liquid pipe (83) to the liquid communication pipe (21) and is introduced into the refrigeration circuit (30).

    The liquid refrigerant introduced into the refrigeration circuit (30) flows through the drain pan heater (36), expands at the refrigeration expansion valve (32), and flows through the refrigeration heat exchanger (31). In the refrigeration heat exchanger (31), the refrigerant absorbs heat from the air in the warehouse and evaporates, whereby the interior is cooled. The gas refrigerant evaporated in the refrigeration heat exchanger (31) flows through the first gas communication pipe (22) and is introduced into the booster circuit (40).

    The gas refrigerant introduced into the booster circuit (40) flows through the booster suction main pipe (42), branches into a third booster suction pipe (44c) and a booster suction connection pipe (43), and the third booster suction pipe ( The refrigerant flowing through 44c) is sucked into the third booster compressor (41c) and compressed. On the other hand, the refrigerant flowing through the booster suction connection pipe (43) branches into a first booster suction pipe (44a) and a second booster suction pipe (44b), and the first and second booster compressors (41a, 41b) is inhaled and compressed. Refrigerant discharged from each compressor (41a, 41b, 41c) of the booster compression mechanism (41) flows through each booster discharge pipe (45a, 45b, 45c), joins in the booster discharge main pipe (45), and is supplied with the second gas. It flows through the connecting pipe (23) and is introduced into the outdoor circuit (20).

    The refrigerant introduced into the outdoor circuit (20) flows through the suction main pipe (55) through the four-way switching valve (12). The refrigerant flowing through the suction main pipe (55) branches into the third suction pipe (61c) and the suction connection pipe (56), and the refrigerant flowing through the third suction pipe (61c) is transferred to the third compressor (11c). ) Is inhaled and compressed. On the other hand, the refrigerant flowing through the suction connection pipe (56) branches to the first suction pipe (61a) and the second suction pipe (61b), and is sucked into the first and second compressors (11a, 11b). And compressed.

    In the refrigeration apparatus (1), as described later, the second capacity control unit (102) controls the capacity of the high stage compression mechanism (11), so that the high stage compression mechanism (11) Although it is prevented from becoming high temperature, the opening degree of each of the third to fifth expansion valves (59, 38, 39) is changed from the fully closed state to the open state, and the opening degree is adjusted appropriately so that the high stage side It can prevent that a compression mechanism (11) becomes high temperature. That is, a part of the refrigerant flowing through the branch passage (84) is appropriately supplied to the suction side of the high-stage compression mechanism (11) via the first liquid injection passage (15), and the second and third liquid injection passages. The liquid refrigerant is appropriately supplied to the suction side and the discharge side of the booster compression mechanism (41) via (27, 29).

    Although detailed description and illustration are omitted for the operation during the defrosting operation, reverse cycle defrosting is performed in which the refrigerant circulates in the refrigerant circuit (10) in the opposite direction to that during the cooling operation. Specifically, the first and second compressors (11a, 11b) of the high-stage compression mechanism (11) are driven, and the other compressors (11c, 41a, 41b, 41c) are stopped. And the refrigerant | coolant discharged from the 1st and 2nd compressor (11a, 11b) flows through the 1st bypass pipe (47) of a booster circuit (40), bypasses a booster compression mechanism (41), and refrigeration heat exchange The refrigeration heat exchanger (31) is defrosted by condensing in the condenser (31), expanded by the first expansion valve (57), evaporated in the outdoor heat exchanger (13), and again the first and second It is sucked into the compressor (11a, 11b).

<Operation capacity control of each compression mechanism>
Next, control of the operating capacity of the booster compression mechanism (41) and the high stage compression mechanism (11) will be described.

    The operating capacity of the booster compression mechanism (41) is determined by the first capacity control unit (101) so that the evaporation temperature in the refrigeration heat exchanger (31) maintains the inside of the chamber at a set temperature (for example, −30 ° C.). The target evaporation temperature (for example, −40 ° C.) suitable for the temperature is controlled. That is, the first capacity control unit (101) performs control so as to increase the operating capacity of the booster compression mechanism (41) when the evaporation temperature in the refrigeration heat exchanger (31) is higher than the target evaporation temperature. As a result, the flow rate of the refrigerant flowing through the refrigeration heat exchanger (31) increases, and the evaporation temperature gradually decreases to the target evaporation temperature. On the other hand, when the evaporation temperature in the refrigeration heat exchanger (31) is lower than the target evaporation temperature, control is performed to reduce the operating capacity of the booster compression mechanism (41). Thereby, the flow volume of the refrigerant | coolant which flows through a freezing heat exchanger (31) becomes small, evaporation temperature rises gradually, and it becomes target evaporation temperature. In this way, an operation suitable for the cooling load in the warehouse is performed.

    Further, the operating capacity of the high-stage compression mechanism (11) is controlled so that the discharge temperature of the booster compression mechanism (41) becomes the target discharge temperature TM based on the flowchart of FIG. The target discharge temperature TM is set to, for example, 80 ° C. or higher and 90 ° C. or lower. That is, when the discharge temperature is higher than 90 ° C., each compressor (11a, 11b, 11c) of the high stage side compression mechanism (11) may become too high, so the target discharge temperature TM is set to 90 ° C. or less. And when discharge temperature is less than 80 degreeC, even if discharge temperature raises a little by reducing the operating capacity of a high stage side compression mechanism (11), each compressor (11) of this high stage side compression mechanism (11) 11a, 11b, 11c) is not likely to become too hot. In such a case, the operating capacity of the high-stage compression mechanism (11) is reduced to reduce the power of the compression mechanism (11, 41) as a whole. Since it is better to make it smaller, the discharge temperature is set to 80 ° C. or higher.

    First, when the operation capacity control of the high-stage compression mechanism (11) starts, the target discharge pressure PMs of the booster compression mechanism (41) is set in step ST1. Specifically, the state equation of polytropic change shown in Step 1 includes the target discharge temperature TM of the booster compression mechanism (41), the suction temperature TL measured by the booster suction temperature sensor (143), and the booster suction pressure sensor (142). The target suction pressure PMs is calculated by substituting the suction pressure PL measured in step (1). Note that κ used in the equation of step ST1 is a polytropic index.

    In step ST2, the discharge pressure PMr of the booster compression mechanism (41) measured by the booster discharge pressure sensor (144) approximates the target discharge pressure PMs set in step ST1 (the difference between the target discharge pressure PMs is ± a value that is within the range of α and can be regarded as the target discharge pressure PMs, α is a predetermined allowable value), or the actual discharge pressure PMr is not a value that approximates the target discharge pressure PMs. It is determined whether the pressure PMs is larger or smaller.

    In step ST2, when the actual discharge pressure PMr is not a value approximate to the target discharge pressure PMs and is larger than the target discharge pressure PMs, the process proceeds to step ST3, where the second capacity control unit (102) moves the high-stage compression mechanism. Control to increase the operating capacity of (11). As a result, the suction pressure of the high-stage compression mechanism (11) decreases, and the discharge pressure PMr of the booster compression mechanism (41) decreases to a value that approximates the target discharge pressure PMs. The discharge temperature of 41) becomes the target discharge temperature TM. In this way, since the intake refrigerant of the high stage compression mechanism (11) can be set to a relatively low temperature, the high stage compression mechanism (11) can be prevented from becoming too high. Then, the process proceeds from step 3 to return and returns to the start again.

    If it is determined in step ST2 that the actual discharge pressure PMr is a value that approximates the target discharge pressure PMs, the process proceeds to return and returns to the start. That is, if the value approximates the target discharge pressure PMs, the discharge temperature is substantially the target discharge temperature TM, so the operating capacity of the high-stage compression mechanism (11) is maintained as it is.

    In step ST2, when the actual discharge pressure PMr is not a value approximate to the target discharge pressure PMs and is smaller than the target discharge pressure PMs, the process proceeds to step ST4, where the second capacity control unit (102) performs the high-stage compression mechanism. Control to reduce the operating capacity of (11). Thereby, the motive power of this high stage side compression mechanism (11) can be made small. Further, when the operating capacity of the high-stage compression mechanism (11) is reduced, the discharge pressure PMr of the booster compression mechanism (41) increases, so the discharge temperature of the booster compression mechanism (41) also increases, but the target discharge pressure Until the value approximates to PMs, the high-stage compression mechanism (11) does not become too hot, so that the high-stage compression mechanism (11) is secured while ensuring the reliability. The power of (11) can be made as small as possible. Then, the process proceeds from step ST4 to return, and then returns to start.

    In this way, since the discharge pressure PMr of the booster compression mechanism (41) is controlled to the target discharge pressure PMs, the high-stage compression is used as a measure for preventing the high-stage compression mechanism (11) from becoming high temperature. When supplying the liquid refrigerant to the suction side of the mechanism (11), the amount of the liquid refrigerant can be reduced, and the operating capacity of the high stage compression mechanism (11) can be made as small as possible. That is, the amount of refrigerant sent to the refrigeration heat exchanger (31) can be increased and the power of the compression mechanism (11, 41) as a whole can be reduced, so that the COP of the refrigeration apparatus (1) can be reduced. improves.

<Opening control of second expansion valve>
Next, the opening degree control of the second expansion valve (58) will be described based on the flowchart of FIG.

    First, when the opening degree control of the second expansion valve (58) is started, in step ST11, the target cooling temperature Ts of the liquid refrigerant flowing through the first flow path (50a) of the supercooling heat exchanger (50) is set. The The target cooling temperature Ts is set as follows. That is, the branch refrigerant that cools the liquid refrigerant by flowing through the second flow path (50b) of the supercooling heat exchanger (50) is supplied to the suction side of the high-stage compression mechanism (11). It evaporates at a saturation temperature Tm corresponding to the suction pressure of the side compression mechanism (11). And since the discharge pressure of the booster compression mechanism (41) corresponding to the suction pressure of the high stage side compression mechanism (11) is controlled to become the target discharge pressure PMs, the evaporation temperature of the branched refrigerant is the target discharge pressure. A saturation temperature Tm corresponding to PMs is obtained. The liquid refrigerant flowing through the first flow path (50a) is cooled by the branching refrigerant that evaporates at the saturation temperature Tm, but is not cooled to the saturation temperature Tm, so the target cooling temperature Ts is set to the target discharge pressure PMs. Is set to a temperature (Tm + ΔT) slightly higher than the saturation temperature Tm.

    In step ST12, the temperature Tr of the liquid refrigerant flowing through the first flow path (50a) of the supercooling heat exchanger (50) measured by the liquid refrigerant temperature sensor (141) approximates the target cooling temperature Ts. Value (the difference from the target cooling temperature Ts is within a range of ± β, a value that can be regarded as the target cooling temperature Ts, β is a predetermined allowable value), or the actual liquid refrigerant temperature Tr is It is determined whether the value is not a value that approximates the target cooling temperature Ts but is larger or smaller than the target cooling temperature Ts.

    In step ST12, when the actual temperature Tr of the liquid refrigerant is not a value approximate to the target cooling temperature Ts but higher than the target cooling temperature Ts, the process proceeds to step ST13. In step ST13, it is determined whether or not the actual liquid refrigerant temperature Tr is 10 ° C. or higher, and whether or not the superheat degree SH of the suction refrigerant in the high-stage compression mechanism (11) is 5 ° C. or higher. That is, if the liquid refrigerant is cooled too much, the supercooling heat exchanger (50) may be frozen. Therefore, it is determined whether the cooling medium is not cooled too much because the lower limit is set to 10 ° C. or more. If the branched refrigerant flowing in the passage (50b) does not completely evaporate and becomes wet, the high stage compression mechanism (11) may suck the wet refrigerant and compress the liquid, so the high stage compression mechanism (11) It is determined whether the suction refrigerant is not wet.

    The superheat degree SH of the suction refrigerant of the high-stage compression mechanism (11) is determined by the measured values of the suction pressure sensor (135) and the suction temperature sensor (136) of the suction main pipe (55). Moreover, you may set the lower limit of the temperature for preventing freezing of a supercooling heat exchanger (50), for example to 5 degreeC or 15 degreeC. If at least one of these conditions is satisfied, the process proceeds to step ST14. If none of these conditions is satisfied, the process proceeds to return and returns to the start. In step ST14, the valve control unit (103) controls the opening of the second expansion valve (58) to be increased. As a result, the amount of refrigerant in the second flow path (50b) increases, so that the temperature of the liquid refrigerant flowing through the first flow path (50a) decreases to the target cooling temperature Ts.

    If it is determined in step ST12 that the actual liquid refrigerant temperature Tr is a value approximate to the target cooling temperature Ts, the process proceeds to step ST15. In step ST15, it is determined whether or not the actual liquid refrigerant temperature Tr is less than 10 ° C. and whether or not the superheat degree SH of the suction refrigerant of the high-stage compression mechanism (11) is less than 5 ° C. If at least one of the conditions is satisfied, the process proceeds to step ST16, and if neither is satisfied, the process returns to the start and returns to the start. In step ST16, the valve control unit (103) controls the opening of the second expansion valve (58) to be small. As a result, the temperature Tr of the liquid refrigerant increases.

    In other words, even when the temperature Tr of the liquid refrigerant is a value that approximates the target cooling temperature Ts, the liquid refrigerant temperature Tr is less than 10 ° C. and is too cooled, or the high-stage compression mechanism (11). When the superheat degree SH of the suction refrigerant is low, the opening degree of the second expansion valve (58) is controlled to be small, and the supercooling heat exchanger (50) is frozen or the high stage side compression mechanism (11 ) Prevents inhalation of wet refrigerant and liquid compression. And when none of the conditions determined in step ST15 are satisfied, there is no possibility that the supercooling heat exchanger (50) freezes or the high stage compression mechanism (11) is liquid compressed. The opening degree of the second expansion valve (58) is maintained as it is, and is maintained at a temperature that approximates the target cooling temperature Ts.

    When it is determined in step ST12 that the actual liquid refrigerant temperature Tr is not a value approximate to the target cooling temperature Ts and is lower than the target liquid refrigerant temperature Tr, the process proceeds to step ST16 and the valve control unit (103). Thus, the opening of the second expansion valve (58) is controlled to be small. As a result, the amount of refrigerant in the second flow path (50b) decreases, so that the temperature of the liquid refrigerant flowing through the first flow path (50a) rises to the target cooling temperature Ts. Then, return to return and start again.

    In this way, the liquid refrigerant flowing through the first flow path (50a) of the supercooling heat exchanger (50) can be set to the target cooling temperature Ts, so the liquid refrigerant sent to the refrigeration heat exchanger (31). Can be reliably cooled, and the refrigeration capacity of the refrigeration heat exchanger (31) can be increased. In addition, in this way, while cooling the liquid refrigerant flowing through the first flow path (50a) of the supercooling heat exchanger (50), this cooling causes the supercooling heat exchanger (50) to freeze, The side compression mechanism (11) can be prevented from liquid compression.

-Effect of the embodiment-
In the refrigeration apparatus (1), the first capacity control unit (101) controls the operating capacity of the booster compression mechanism (41) so that the evaporation temperature in the refrigeration heat exchanger (31) becomes the target evaporation temperature. Therefore, the operation corresponding to the cooling load of the refrigeration apparatus (1) can be performed. In addition, the second capacity control unit (102) controls the operating capacity of the high-stage compression mechanism (11) so that the discharge temperature of the booster compression mechanism (41) becomes the target discharge temperature. By appropriately setting the target discharge temperature, the intake refrigerant of the high stage side compression mechanism (11) can be set to a relatively low temperature. Thus, as a measure for preventing the high stage compression mechanism (11) from becoming high temperature, the amount of the liquid refrigerant can be reduced when supplying the liquid refrigerant to the suction side of the high stage compression mechanism (11). Therefore, the amount of refrigerant evaporated in the refrigeration heat exchanger (31) can be increased.

    Furthermore, when the discharge temperature of the booster compression mechanism (41) is lower than the target discharge temperature, the operation of the high stage compression mechanism (11) is performed until the high stage compression mechanism (11) does not become too high. Since the capacity can be reduced, the power of the high stage compression mechanism (11) can be made as small as possible. That is, the flow rate of the refrigerant evaporated in the refrigeration heat exchanger (31) can be increased, and the power of the high stage compression mechanism (11) can be reduced as much as possible, so both compression mechanisms (41, 11) The refrigeration capacity in the refrigeration heat exchanger (31) for the power of the power can be increased, and COP can be improved.

    The second capacity control unit (102) controls the operating capacity of the high-stage compression mechanism (11) so that the discharge pressure of the booster compression mechanism (41) becomes the target discharge pressure. Each booster compressor (41a, 41b, 41c) of (41) is a high-pressure dome type scroll compressor, and even if it is difficult to measure the discharge temperature quickly and precisely, the discharge temperature is discharged. Control to the target temperature can be reliably performed.

    Further, in the refrigeration apparatus (1), the valve control unit (103) controls the opening degree of the second expansion valve (58), and the first flow path (50a) of the supercooling heat exchanger (50) is controlled. Since the flowing liquid refrigerant is cooled to the target cooling temperature Ts, the refrigerant sent to the refrigeration heat exchanger (31) is reliably cooled to increase the refrigeration capacity in the refrigeration heat exchanger (31). Therefore, the COP of the refrigeration apparatus (1) can be improved more reliably.

<< Other Embodiments >>
About the said embodiment, it is good also as the following structures.

    In the refrigeration apparatus (1) of the above embodiment, each compression mechanism (11, 41) is configured by connecting three compressors in parallel. For example, each compression mechanism (11, 41) is configured as one unit. You may make it comprise with a compressor. Moreover, although the refrigerating apparatus (1) of the said embodiment was one refrigeration heat exchanger (31), the structure by which a some freezing heat exchanger (31) is connected in parallel may be sufficient.

    Further, in the refrigeration apparatus (1) of the above embodiment, scroll type compressors are used as the compressors (41a, 41b, 41c) of the booster compression mechanism (41), and the response time of the discharge temperature measurement is long. Therefore, the discharge pressure is controlled to become the target discharge pressure. However, if the compressor has a short response time of the discharge temperature (for example, a rotary type compressor), the control directly sets the discharge temperature to the target discharge temperature. May be performed. Further, even when a scroll type compressor is used, the discharge temperature may be estimated and controlled from the temperature of the refrigerant flowing through the discharge pipe.

    In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

    As described above, the present invention is useful for a refrigeration apparatus that includes a low-stage compression mechanism and a high-stage compression mechanism and compresses refrigerant in two stages.

It is a piping system diagram of the refrigerant circuit of the refrigerating device concerning an embodiment. It is a piping system diagram showing the flow of the refrigerant during the cooling operation of the refrigeration apparatus according to the embodiment. It is a flowchart which shows the operation capacity control of the high stage side compression mechanism of the 2nd capacity | capacitance control part which concerns on embodiment. It is a flowchart which shows the opening degree control of the 2nd expansion valve of the valve control part which concerns on embodiment.

Explanation of symbols

1 Refrigeration equipment
10 Refrigerant circuit
11 High-stage compression mechanism
13 Outdoor heat exchanger (condenser)
31 Refrigeration heat exchanger (evaporator)
32 Refrigeration expansion valve (expansion mechanism)
41 Booster compression mechanism (low-stage compression mechanism)
50 Supercooling heat exchanger
58 Second expansion valve (pressure reducing valve)
84 Branch passage
101 1st capacity control part (1st capacity control means)
102 Second capacity control unit (second capacity control means)
103 Valve control unit (valve control means)

Claims (4)

A refrigerant in which a low-stage compression mechanism (41) with variable operating capacity, a high-stage compression mechanism (11) with variable operating capacity, a condenser (13), an expansion mechanism (32), and an evaporator (31) are connected in order. A refrigeration apparatus comprising a circuit (10), wherein the refrigerant is compressed in two stages by the low-stage compression mechanism (41) and the high-stage compression mechanism (11),
First capacity control means (101) for controlling the operating capacity of the low-stage compression mechanism (41) so that the evaporation temperature in the evaporator (31) becomes the target evaporation temperature;
Second capacity control means (102) for controlling the operating capacity of the high stage compression mechanism (11) so that the discharge temperature of the low stage compression mechanism (41) becomes the target discharge temperature. Refrigeration equipment characterized. In claim 1,
The second capacity control means (102) derives the discharge pressure of the low-stage compression mechanism (41) based on the suction pressure and suction temperature of the low-stage compression mechanism (41) and the target discharge temperature. A refrigeration apparatus that controls the operating capacity of the high-stage compression mechanism (11) so as to achieve the target discharge pressure. In claim 1 or 2,
The refrigerant circuit (10) cools the liquid refrigerant by exchanging heat between the liquid refrigerant flowing from the condenser (13) to the expansion mechanism (32) and the branched refrigerant partially branched and decompressed. The subcooling heat exchanger (50) is provided, and the branched refrigerant that has flowed through the supercooling heat exchanger (50) is supplied to the suction side of the high-stage compression mechanism (11). A refrigeration apparatus characterized by that. In claim 3,
The branch passage (84) for supplying the branch refrigerant to the supercooling heat exchanger (50) is provided with a pressure reducing valve (58) whose opening degree is adjustable,
Characterized by comprising valve control means (103) for controlling the opening of the pressure reducing valve (58) so that the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) becomes a target cooling temperature. Refrigeration equipment.

Images