WO2008032633A1

WO2008032633A1 - Refrigeration device

Info

Publication number: WO2008032633A1
Application number: PCT/JP2007/067386
Authority: WO
Inventors: Satoru Sakae; Iwao Shinohara; Hiroto Nakajima; Ryuuji Takeuchi
Original assignee: Daikin Industries, Ltd.
Priority date: 2006-09-11
Filing date: 2007-09-06
Publication date: 2008-03-20
Also published as: JP4245023B2; JP2008064420A

Abstract

A refrigeration device (1) having a refrigeration circuit (10) formed by sequentially connecting a booster compression mechanism (41) with variable operating capacity, a high-stage side compression mechanism (11) with variable operating capacity, an outdoor heat exchanger (13), a refrigeration expansion valve (32), and a refrigeration heat exchanger (31). The refrigeration device (1) performs cooling operation in which refrigerant is condensed by being compressed in two stages and then evaporated by the refrigeration heat exchanger (31). A controller (100) for the refrigeration device (1) has a first capacity controlling section (101) and a second capacity controlling section (102). The first capacity controlling section (101) controls the operating capacity of the booster compression mechanism (41) so that the temperature of evaporation in the refrigeration heat exchanger (31) is a target evaporation temperature. The second capacity controlling section (102) controls the operating capacity of the high-stage side compression mechanism (11) so that the temperature of discharge of the booster compression mechanism (41) is a target discharge temperature.

Description

Specification

Refrigeration equipment

Technical field

TECHNICAL FIELD [0001] The present invention relates to a refrigeration apparatus that includes a low-stage compression mechanism and a high-stage compression mechanism and compresses refrigerant in two stages, and particularly relates to measures for improving COP.

Background art

[0002] Conventionally, a refrigeration apparatus for a vapor compression refrigeration cycle is known to include a low-stage compression mechanism and a high-stage compression mechanism to compress refrigerant in two stages! Patent Document 1).

[0003] The refrigeration apparatus of Patent Document 1 includes a booster compressor that is a low-stage side compression mechanism, an outdoor compressor that is a high-stage side compression mechanism, an outdoor heat exchanger, a refrigeration expansion valve, and cooling in the freezer. The refrigerant circuit is connected to a refrigeration heat exchanger that performs the above. In this refrigeration system, 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 freezing temperature range.

[0004] 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. There is something. 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, it is possible to prevent the high-stage compression mechanism from becoming too hot, and the reliability of the high-stage compression mechanism can be improved (Japanese Patent Application 2005-322240).

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-325023

Disclosure of the invention

Problems to be solved by the invention

[0005] 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 cooled in the refrigerator (in the refrigeration heat exchanger). It is injected into the suction side of the high-stage compression mechanism that is not used for evaporation. 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. Therefore, the refrigerating capacity of the evaporator with respect to the power of the entire compression mechanism is reduced, and the desired high COP cannot be obtained! /, And! /.

[0006] The present invention has been made in view of the force and the point, and in a refrigeration apparatus comprising a low-stage compression mechanism and a high-stage compression mechanism to compress refrigerant in two stages! The purpose is to improve the COP while ensuring the reliability of the high-stage compression mechanism.

Means for solving the problem

[0007] The first invention includes 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) is connected to the refrigerant circuit (10) in order, and the refrigeration apparatus compresses the refrigerant in two stages by the low-stage compression mechanism (41) and the high-stage compression mechanism (11). A 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 a target evaporation temperature; and the low-stage side Second capacity control means (102) is provided for controlling the operating capacity of the high-stage compression mechanism (11) so that the discharge temperature of the compression mechanism (41) becomes the target discharge temperature.

[0008] In the first invention, the first capacity control means (101) operates the low-stage compression mechanism (41) so that the evaporation temperature in the evaporator (31) becomes the target evaporation temperature. Operate according to the refrigeration load by controlling the capacity. Note that the first capacity control means (101) may be provided with a controller P so that the evaporation pressure becomes a saturation pressure corresponding to the target evaporation temperature, instead of controlling the evaporation temperature.

[0009] Further, 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 higher than the target discharge temperature. By increasing the discharge temperature, the discharge temperature of the low-stage compression mechanism (41) is lowered to the target discharge temperature. Then, by appropriately setting the target discharge temperature of the low-stage compression mechanism (41), the intake refrigerant of the high-stage compression mechanism (11) is set to a relatively low temperature. This reduces the amount of liquid refrigerant when supplying liquid refrigerant to the suction side of the high stage compression mechanism (11) as a measure to prevent the high stage compressor mechanism (11) from becoming too hot. .

[0010] Further, the second capacity control means (102) operates the high-stage compression mechanism (11) when the discharge temperature of the low-stage compression mechanism (41) is lower than the target temperature! Reducing capacity Thus, 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 not too hot! ) To reduce the operating capacity of the compression mechanism (11, 41) as much as possible.

[0011] In a second aspect based on the first aspect, the discharge pressure of the low-stage compression mechanism (41) includes 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 that the target discharge pressure derived based on

Here, the low-stage compression mechanism (41) 1 For example, in the case of a scroll type compressor, the refrigerant discharged from the compression chamber that compresses the refrigerant in the dome of the compressor fills the end dome. The dome is heated and discharged from the compressor. Therefore, when measuring the discharge temperature of the low-stage compressor mechanism (41), if a temperature sensor is provided in the discharge pipe of the low-stage compressor 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 longer. In addition, it is difficult to provide a temperature sensor for measuring the discharge temperature in the dome of the compressor.

That is, depending on the configuration of the low-stage compression mechanism (41), it may be difficult to quickly and accurately measure the discharge temperature. Therefore, in the second invention, the discharge temperature is set to the target discharge temperature. The response time of the measurement is shorter than the control close to the degree of control, and the discharge temperature is controlled by controlling the discharge pressure of the low-stage compression mechanism (41). Specifically, the discharge pressure of the low-stage compressor mechanism (41) is determined based on the target discharge temperature of the low-stage compression mechanism (41) and the pressure and temperature of the low-stage compression mechanism (41) suction refrigerant. Control to achieve the target discharge pressure derived in advance.

In a third aspect based on the first aspect, 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. A subcooling heat exchanger (50) that cools the liquid refrigerant by exchanging heat with the branched refrigerant, and the branch refrigerant that has flowed through the supercooling heat exchanger (50) It is configured to be supplied to the suction side of (11).

[0015] Further, according to a fifth aspect based on the second aspect, the refrigerant circuit (10) is a condenser (13). A subcooling heat exchanger (50) that cools the liquid refrigerant by exchanging heat between the liquid refrigerant flowing to the expansion mechanism (32) and the branched refrigerant that is partly branched and decompressed. 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).

In the third and fifth inventions, the liquid refrigerant is cooled by the supercooling heat exchanger (50), expanded by the expansion mechanism (32), and then sent to the evaporator (31). The refrigerating capacity in the evaporator (31) is increased.

[0017] 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. On the other hand, it is provided with 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 the target cooling temperature! /

[0018] Further, in a sixth aspect based on the fifth aspect, the branch refrigerant is replaced with the supercooling heat exchanger.

The branch passage (84) supplied to (50) is provided with a pressure reducing valve (58) whose opening degree can be adjusted, while the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) is equal to the target cooling temperature. As shown, it is equipped with valve control means (103) for controlling the opening of the pressure reducing valve (58).

[0019] In the fourth and sixth inventions, when the valve control means (103) is configured such that the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) is higher than the target cooling temperature! Increases the opening of the pressure reducing valve (58) and lowers the opening of the pressure reducing valve (58) when the opening is lower than the target cooling temperature, so that the liquid refrigerant flowing through the supercooling heat exchanger (50) Let temperature be the target cooling temperature.

[0020] The target cooling temperature is set as follows, for example. That is, the branched refrigerant that cools the liquid refrigerant is supplied to the suction side of the high-stage compression mechanism (11), and therefore, when flowing through the supercooling heat exchanger (50), the high-stage compression mechanism (11) It evaporates at a saturation temperature corresponding to the suction pressure. In the second invention, since 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 be the target discharge pressure, this target discharge pressure is controlled. The saturation temperature corresponding to is 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. The invention's effect

[0021] According to the first invention, the evaporation temperature in the evaporator (31) becomes the target evaporation temperature. As described above, since the operation capacity of the low-stage compression mechanism (41) is controlled, the operation corresponding to the refrigeration load can be performed.

[0022] 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, the target discharge temperature By appropriately setting the above, the intake refrigerant of the high stage compression mechanism (11) can be set to a relatively low temperature. As a result, when supplying the liquid refrigerant to the suction side of the high-stage compression mechanism (11) as a measure to prevent the high-stage compression mechanism (11) from becoming too hot, the amount of the liquid refrigerant is reduced. be able to.

[0023] Further, in the case where the discharge temperature of the low-stage compression mechanism (41) is lower than the target discharge temperature, the high-stage compression mechanism (11) is high enough to prevent the temperature from becoming too high. Since the operating capacity of the side compression mechanism (11) can be reduced, the power of the high stage compression mechanism (11) can be reduced as much as possible. In other words, 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 that the power of both compression mechanisms (41, 11) can be reduced. This can increase the refrigeration capacity of the evaporator (31) against COP and improve the COP.

[0024] According to the second aspect of the invention, the second capacity control means (102) includes the high stage so that the discharge pressure of the low stage side compression mechanism (41) becomes the target discharge pressure. Since the operating capacity of the side compression mechanism (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 can be reduced. It can be used to control the discharge target temperature.

[0025] Further, according to the third and fifth inventions, since the liquid cooling medium is cooled by the supercooling heat exchanger (50), the cooled liquid refrigerant is supplied to the evaporator ( Therefore, the refrigerating capacity of the evaporator (31) can be increased, and the COP of the refrigerating apparatus (1) can be improved reliably.

[0026] According to the fourth and sixth inventions, the pressure reducing valve (58) is opened so that the temperature of the liquid refrigerant flowing through the supercooling heat exchanger (50) becomes a target cooling temperature. Since the temperature is controlled, the liquid refrigerant can be cooled more reliably, so that the COP of the refrigeration apparatus (1) can be improved more reliably. Brief Description of Drawings

FIG. 1 is a piping system diagram of a refrigerant circuit of a refrigeration apparatus according to an embodiment.

FIG. 2 is a piping diagram showing the refrigerant flow during the cooling operation of the refrigeration apparatus according to the embodiment.

FIG. 3 is a flowchart showing the operation capacity control of the high-stage compression mechanism of the second capacity control unit according to the embodiment.

[FIG. 4] FIG. 4 is a flow chart showing opening control of the second expansion valve of the valve control unit according to the 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 unit (1st capacity t control means)

102 2nd capacity control unit (2nd capacity t control means)

103 Valve control unit (valve control means)

BEST MODE FOR CARRYING OUT THE INVENTION

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

[0030] As shown in FIG. 1, the embodiment of the present invention is a refrigeration apparatus (1) that cools the inside of a cabinet, and includes an outdoor unit (2), a refrigeration unit (3), and a booster unit (4). And a controller (100).

[0031] The outdoor unit (2) has an outdoor circuit (20) force S, and the refrigeration unit (3) has a refrigeration circuit ( 30) Force S, The booster unit (4) is provided with 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 ) And 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 connected in order to constitute a refrigerant circuit (10) of the vapor compression refrigeration cycle.

[0032] <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 first expansion valve (57). A two 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 shut-off valve (53), and one end of the second gas communication pipe (23) is connected to the gas-side shut-off valve (54). /!

[0033] The high stage compression mechanism (11) includes three compressors (11a, ib, 11c) connected in parallel to each other. The above three compressors (11a, l ib, 11c) are high-pressure dome type scroll compressors. In other words, each compressor (11a, ib, 11c) is not shown in the figure, but the fixed scroll and the movable scroll combine the spiral wraps to form a compression chamber.

The refrigerant compressed in the compression chamber is discharged from the compression chamber and fills the inside of the dome, and then is discharged by the compressors (11a, ib, 11c).

[0034] The first compressor (11a) is configured to have a variable operating capacity by supplying electric power to a compressor motor (not shown) via an inverter and changing the output frequency of the inverter. The second compressor (l ib) and the third compressor (11c) are configured with a fixed operating capacity. In the high-stage compression mechanism (11), the first compressor (11a) of the three compressors (11a, lib, 11c) is preferentially driven during operation of the refrigeration system (1). The second compressor (l ib) and the third compressor (11c) are sequentially driven in accordance with the cooling load in the cabinet.

A suction main pipe (55) is connected to the suction side of the high-stage compression mechanism (11). The suction main pipe (55) has one end connected to the four-way selector valve (12) and the other end connected to the third suction pipe (61c). The third inlet pipe (61c) is branched to the inlet / outlet pipe (56), and the other end of the third inlet pipe (61c) is connected to the inlet side of the third compressor (1 lc). 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 connected to the 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 (lib).

[0036] 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 end is connected to the first discharge pipe (64a), the second discharge pipe (64b), and the third discharge pipe (64c). 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 (lib), 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) that allows only the flow of the refrigerant from the compressors (11a, ib, 11c) to the four-way selector valve (12). -1, CV-2, CV-3) are provided.

[0037] The outdoor heat exchanger (13) is a cross-fin fin-and-tube heat exchanger that exchanges heat between refrigerant and outdoor air. It is configured. One end of the outdoor heat exchanger (13) is connected to the four-way switching valve (12), and the other end is 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 permits only the flow of refrigerant and the directional force 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).

[0038] The supercooling heat exchanger (50) is a plate-type heat exchanger, and performs heat exchange between the refrigerant and the first flow path (50a) and the second flow path. (50b). 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). It is connected. 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 stop valve (53). Yes.

[0039] 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) Second flow path (50b) of the supercooling heat exchanger (50) It is connected to one end. The branch passage (84) is provided with a second expansion valve (58) which is a pressure reducing valve. The second expansion valve (58) is an electronic expansion valve whose opening degree is adjustable.

[0040] The other end of the second flow path (50b) of the supercooling heat exchanger (50) is connected in the middle of the suction main pipe (55) via a gas injection pipe (85)! . The gas injection pipe (85) injects a gas refrigerant into the suction side of each of the first to third compressors (11a, ib, 11c).

[0041] 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.

[0042] Between one end of the branch passage (84) and the second expansion valve (58), one end of the fifth liquid pipe (89) is connected, and the other end of the fifth liquid pipe (89) is The first 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.

[0043] Further, one end of the 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), The other end of the communication pipe (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).

[0044] The four-way selector valve (12) has a first port at the discharge main pipe (64), a second port at the suction main pipe (55), and a third port at one end of the outdoor heat exchanger (13). The 4th port is connected to the gas side shutoff valve (54). The four-way selector valve (12) is in the first state (the solid line in FIG. 1) 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. 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.

[0045] The outdoor circuit (20) includes an oil separator (70), a first liquid injection passage (15), First to third three oil equalizing pipes (72a, 72b, 72c) and first to third oil recovery pipes (73a, 73b, 73c) are provided.

[0046] The oil separator (70) is provided in the discharge main pipe (64) and separates the refrigerant oil from the discharged refrigerant force of the compressors (11a, ib, 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) separates the oil return pipe (71). Refrigerator oil is returned to the compressors (11a, ib, 11c) via the suction main pipe (55).

[0047] 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.

[0048] Each of the first to fourth liquid injection branch pipes (16a, 16b, 16c, 16d) is branched from the flow divider (26) of the first liquid injection main pipe (16), Each third liquid injection branch pipe (16a, 16b, 16c) is in the middle of each of the first to third suction pipes (61a, 61b, 61c), and the fourth liquid injection branch pipe (16d) is an oil return pipe. (71) The fourth solenoid valve (SV-4) is connected between the other end. In addition, 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.

[0049] In the three oil leveling pipes (72a, 72b, 72c), the first oil leveling pipe (72a) is connected between the dome of the first compressor (1 la) and the fourth liquid injection branch pipe (16d). The 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 (lib) 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 solenoid valve (SV-3). In the refrigeration system (1), the oil return pipe (71) is used for suction. The refrigeration oil returned to the main pipe (55) is configured to return in the order of the third compressor (11c), the second compressor (lib), and the first compressor (11a). Then, by the oil equalizing pipes (72a, 72b, 72c), the refrigerating machine oil of the third compressor (11c) is sequentially sent to the second compressor (lib) and the first compressor (11a), Furthermore, the excess of the refrigeration oil in the first compressor (11a) is sent to the oil return pipe (71) and is configured to equalize the oil between the compressors (11a, ib, 11c). .

[0050] 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 the second oil recovery pipe (73b) One end of each oil recovery pipe (73b) is connected to one end of the second suction pipe (61b) and one end of the third oil recovery pipe (73c) to the middle of the third suction pipe (61c). The other ends of 73b and 73c) are joined together. The oil recovery pipes (73a, 73b, 73c) are connected to the compressors (lib, 11c) when a specific compressor (lib, 11c) is stopped according to the load during operation of the refrigeration system (1). ) Refrigeration oil accumulated in the suction pipes (61b, 61c) is sent to the suction pipes (61a, 61b) of the other compressors (11a, ib) that are driven.

[0051] 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) are provided in each discharge pipe (64a, 64b, 64c). Further, in the vicinity of the outlet of the first flow path (50a) of the supercooling heat exchanger (50) in the third liquid pipe (83), the liquid that flows through the first flow path (50a) and measures the temperature of the liquid refrigerant. A refrigerant 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 selector valve (12). ing.

[0052] 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).

[0053] <Refrigeration unit>

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

[0054] The refrigeration heat exchanger (31) is a cross-fin type fin 'and' tube type heat exchanger that exchanges heat between the refrigerant and the air in the cabinet, and evaporates. Configured in a vessel Yes. 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). ! /

[0055] 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) is provided with A second refrigerant temperature sensor (34) is provided. In the refrigeration expansion valve (32), the temperature measured by the second refrigerant temperature sensor (34) is a predetermined temperature (for example, 5 ° C) higher than the vaporization temperature of the refrigerant measured by the first refrigerant temperature sensor (33). So-called superheat control is performed in which the opening degree is adjusted to be higher.

The drain pan heater (36) is disposed on the drain pan of the refrigeration heat exchanger (31) (not shown) to heat the drain pan and 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).

[0057] The refrigeration unit (3) is provided with an internal temperature sensor (35f) and an internal fan (35a). To the refrigeration heat exchanger (31), the internal air is sent by the internal fan (35a).

[0058] <Booster unit>

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

[0059] 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 composed of a high-pressure dome type scroll compressor, similarly to the high-stage compressors (11a, lib, 11c). In other words, each booster compressor (41a, 41b, 41c) is not shown in the figure, but the fixed scroll and the movable scroll are combined with each other in a spiral wrap to form a compression chamber, which is compressed in this compression chamber. Each compressor (11a, lib, 11c) force is also discharged after the refrigerant is discharged from the compression chamber and fills the inside of the dome.

[0060] The first booster compressor (41a) is supplied with electric power via an inverter to a compressor motor (not shown), and the operating capacity can be increased by changing the output frequency of the inverter. It is structured strangely. 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), during the cooling operation of the refrigeration system (1), the first booster compressor (41a) among the three booster compressors (41a, 41b, 41c) is preferentially driven. The second booster compressor (41b) and the third booster compressor (41c) are sequentially driven in accordance with the load in the storage.

[0061] 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 (44a). 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).

[0062] 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 Branch to the booster discharge pipe (45b) and the 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) that allows only the flow of refrigerant from the booster compressor (41a, 41b, 41c) to the booster discharge main pipe (45). -8, CV-9, and CV-10).

[0063] 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 fourth Two oil leveling pipes (74a, 74b) of No. 5 and three oil recovery pipes (75a, 75b, 75c) of No. 4 to No. 6 are provided.

[0064] 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). To do It is. One end of a first bypass pipe (47) is connected to the oil separator (46), and the other end of the first binose 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 boosted during the defrosting operation of the refrigeration apparatus (1). This is to bypass the compression mechanism (41). Also, one end of an 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).

[0065] 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 to the middle of the liquid communication pipe (21), and the other end of the second liquid injection main pipe (28) is connected to the second liquid injection main pipe (28). 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 liquid injection branch pipes (28a, 28b, 28c). Each booster suction pipe (41a, 41b, 4 lc) is connected to each.

[0066] The second liquid injection main pipe (28) is provided with a fourth expansion valve (38), which is provided in the middle of the fifth to seventh liquid injection branch pipes (28a, 28b, 28c). Each is provided with a capillary tube (37a, 37b, 37c). 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 of the booster discharge main pipe (45). It is connected between the oil separator (46) and the closing valve (51). A fifth expansion valve (39) is provided in the third liquid injection passage (29). The fourth and fifth expansion valves (38, 39) are electronic expansion valves whose degree of opening is adjustable.

[0067] 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 can be opened and closed in the middle of the seventh solenoid valve (SV-7) And a check 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). On the way Equipped with 8 solenoid valves (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 solenoid valve (SV-9).

[0068] In the refrigeration system (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) and the second booster compressor (41b). The first booster compressor (41a) is configured to return in order. The refrigerating machine oil of the third booster compressor (41c) is transferred to the second booster compressor (41b) and the first booster compressor (41a) through the fourth and fifth oil equalizing pipes (74a, 74b). The refrigeration oil surplus of the first booster compressor (41a) is sent to the compressors (11a, l ib, 11c) of the outdoor circuit (20) through the oil feed pipe (76). Has been.

[0069] 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). Are connected in the middle of the second booster suction pipe (44b) and one end of the sixth oil recovery pipe (75c) is connected in the middle of the third booster suction pipe (44c), respectively, while the oil recovery pipes (75a, 75b, The other ends of 75c) 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 the operation of the refrigeration system (1). ) Of the refrigerating machine oil stored in the suction pipes (44b, 44c) of the other booster compressors (41a, 41b).

Furthermore, the booster circuit (40) is provided with a second bypass pipe (49) that connects the booster suction main pipe (42) and the booster discharge main pipe (45). When the booster compression mechanism (41) is stopped, 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). There is a check valve (CV-12) that allows only the refrigerant to flow from the booster suction main pipe (42) to the booster discharge main pipe (45).

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 the booster discharge pressure sensor (144) and the booster discharge main temperature sensor (145) are provided. Each booster discharge sub-temperature sensor (45) 148, 149, 150) and each pressure switch (155, 156, 157) are provided in each booster discharge pipe (45a, 45b, 45c).

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

[0073] The first capacity control unit (101) is configured to increase the evaporating temperature in the refrigeration heat exchanger (31) to a target evaporating temperature suitable for maintaining the interior at a set temperature. 41) is used to control the operating capacity, and is configured as a first capacity control means.

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. Yes, it is configured as the second capacity control means. Here, since each of the compressors (4 la, 41b, 41c) of the booster compression mechanism (41) is a high-pressure dome type scroll compressor, it is the temperature of the refrigerant discharged from the compression chamber in the dome. When measuring the discharge temperature, if the booster discharge main temperature sensor (145) or the discharge sub temperature sensor (148, 149, 150) is used, it takes a long response time and cannot be measured quickly. Therefore, the discharge temperature of 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. The target discharge pressure is controlled.

[0075] The valve control unit (103) includes the second expansion valve (103) so that the temperature of the liquid refrigerant flowing through the first flow path (50a) of the supercooling heat exchanger (50) becomes a target cooling temperature. 58), and is configured as a valve control means.

[0076] Driving action

Next, the operation of the refrigeration apparatus (1) of the present embodiment will be described with reference to FIGS. The refrigeration apparatus (1) performs a cooling operation for cooling the inside of the refrigerator and a defrosting operation for removing frost formation on the refrigeration heat exchanger (31).

[0077] In the cooling operation, as shown in Fig. 2, the four-way selector valve (12) of the outdoor circuit (20) is in the first state. The first expansion valve (57) is set to the fully closed state, and the first to third compressors (11a, l ib, 11c) of the high-stage compression mechanism (11) are driven to booster compression The first to third booster compressors (41a, 41b, 41c) of the mechanism (41) are 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 The solenoid valve (SV-5) is set to the normally closed state, and the sixth to ninth solenoid valves (SV-6, 7, 8, 9) are intermittently controlled to open and close appropriately.

[0078] In the outdoor circuit (20), the refrigerant discharged from the first to third compressors (11a, ib, 11c) flows through the discharge pipes (64a, 64b, 64c) and discharge main pipes ( 64) and flows through the four-way selector valve (12) and the outdoor heat exchanger (13). 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). ). 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) branches into the branch passage (84) to become a branch refrigerant, and is depressurized by the second expansion valve (58), so that the supercooling heat exchanger (50 ) Into the second flow path (50b). In the supercooling heat exchanger (50), the branching refrigerant flowing through the second flow path (50b) absorbs heat from the liquid refrigerant flowing through the first flow path (50a) and evaporates. The liquid refrigerant flowing through the passage (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) via the gas induction 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).

[0079] 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).

[0080] The gas refrigerant introduced into the booster circuit (40) flows through the booster suction main pipe (42) and branches into the third booster suction pipe (44c) and the booster suction connection pipe (43). 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 the first booster suction pipe (44a) and the second booster suction pipe (44b), and the first and second booster compressors (41a , 41b) and compressed. The refrigerant discharged from the compressors (41a, 41b, 41c) of the booster compression mechanism (41) flows through the booster discharge pipes (45a, 45b, 45c), joins in the booster discharge main pipe (45), and then enters the second gas. It flows through the connecting pipe (23) and is introduced into the outdoor circuit (20).

[0081] The refrigerant introduced into the outdoor circuit (20) flows through the suction main pipe (55) via 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) passes through the third compressor (11c). ) Is inhaled and compressed. On the other hand, the refrigerant flowing through the suction connection pipe (56) is branched into the first suction pipe (61a) and the second suction pipe (61b), and the first and second compressors (11a, ib) Inhaled 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) is prevented from reaching a high temperature, but the degree of opening of each of the third to fifth expansion valves (59, 38, 39) is adjusted from the fully closed state to the open state as appropriate. In addition, the high-stage compression mechanism (11) can prevent the temperature from becoming high. 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 injections. Liquid refrigerant is appropriately supplied to the suction side and the discharge side of the booster compression mechanism (41) via the passages (27, 29).

[0083] Although detailed description and illustration are omitted for the operation during the defrosting operation, a reverse cycle defrost is performed in which the refrigerant circulates in the refrigerant circuit (10) in the direction opposite to that during the cooling operation. Specifically, the first and second compressors (11a, ib) of the high stage compression mechanism (11) are driven, and the other compressors (11c, 41a, 41b, 41c) are stopped. Then, it flows through the first bypass pipe (47) of the refrigerant booster circuit (40) discharged from the first and second compressors (11a, ib), bypasses the booster compression mechanism (41), and performs refrigeration heat exchange. The refrigeration heat exchanger (31) is defrosted by the condenser (31), expanded by the first expansion valve (57), evaporated by the outdoor heat exchanger (13), and again the first and second 2 Sucked into the compressor (11a, l ib).

<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.

[0085] The operating capacity of the booster compression mechanism (41) is determined by the first capacity control unit (101) by setting the evaporation temperature in the refrigeration heat exchanger (31) to a set temperature (for example, 30 ° C). The target evaporation temperature (for example, 40 ° C) suitable for maintaining the temperature is controlled. That is, the first capacity control unit (101) performs control 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 so as to reduce the operating capacity of the booster compression mechanism (41). As a result, the flow rate of the refrigerant flowing through the refrigeration heat exchanger (31) decreases, and the evaporation temperature gradually rises to the target evaporation temperature. In this way, an operation suitable for the cooling load in the warehouse is performed.

[0086] 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 more and 90 ° C or less. In other words, if the discharge temperature is higher than 90 ° C, the compressor (11a, ib, 11c) of the high-stage compression mechanism (11) may become too hot, so the target discharge temperature TM should be 90 ° C. The following. If the discharge temperature is less than 80 ° C, even if the discharge temperature rises slightly by reducing the operating capacity of the high-stage compression mechanism (11), each compression of the high-stage compression mechanism (11) In such a case, the operating capacity of the high-stage compression mechanism (11) can be reduced to reduce the compression mechanism (11, 41). Since it is better to reduce the overall power, the discharge temperature should be 80 ° C or higher.

First, when the operation capacity control of the high stage compression mechanism (11) is started, the target discharge pressure PMs of the booster compression mechanism (41) is set in step ST1. Specifically, the polytrope change equation of state 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. The suction pressure PL measured in (142) is substituted, and the target discharge pressure PMs is calculated. Note that _κ used in the equation of step ST1 is a polytropic index. [0088] 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 target discharge pressure PMs and Is within the range of soil α, a value that can be regarded as the target discharge pressure PMs, α is a force that is a predetermined allowable value), and the actual discharge pressure PMr approximates the target discharge pressure PMs It is judged whether it is larger or smaller than the target discharge pressure PMs.

[0089] In step ST2, if the actual discharge pressure PMr is not a value approximate to the target discharge pressure PMs but is larger than the target discharge pressure PMs, the process proceeds to step ST3, where the second capacity control unit (102) force S, high Control is performed to increase the operating capacity of the stage side compression mechanism (11). As a result, the suction pressure of the high-stage compression mechanism (11) decreases, so that the discharge pressure PMr of the booster compression mechanism (41) decreases and 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 go from step 3 to return and start again.

[0090] In step ST2, when it is determined that the actual discharge pressure PMr is a value approximate to the target discharge pressure PMs, the process proceeds to return, and then returns to 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.

[0091] In step ST2, when the actual discharge pressure PMr is not a value approximate to the target discharge pressure PMs but smaller than the target discharge pressure PMs, the process proceeds to step ST4, where the second capacity control unit (102) force S, high Control is performed to reduce the operating capacity of the stage side compression mechanism (11). Thereby, the power of the high stage side compression mechanism (11) can be reduced. In addition, if 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 force S, which increases the discharge temperature of the booster compression mechanism (41), The high-stage compression mechanism (11) does not become too hot until it reaches a value that approximates the target discharge pressure PMs, so that the high-stage compression mechanism (11) is secured while ensuring its reliability. The power of the side compression mechanism (11) can be made as small as possible. Then move from step ST4 to return and start again. Return.

[0092] In this way, since the discharge pressure PMr of the booster compression mechanism (41) is controlled to be the target discharge pressure PMs, as a measure for preventing the high-stage compression mechanism (11) from becoming high temperature, When supplying liquid refrigerant to the suction side of the stage-side compression mechanism (11), the amount of this liquid refrigerant can be reduced, and the operating capacity of the high-stage side compression mechanism (11) can be reduced as much as possible. S can. 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. COP is improved.

[0093] <Opening control of second expansion valve>

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

[0094] First, when the opening control of the second expansion valve (58) starts, in step ST11, the target cooling temperature Ts of the liquid refrigerant that has flowed through the first flow path (50a) of the supercooling heat exchanger (50). Is set. The target cooling temperature Ts is set as follows. That is, the branching 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 stage side compression mechanism (11). Then, the discharge pressure of the booster compression mechanism (41) corresponding to the suction pressure of the high-stage compression mechanism (11) is controlled to be the target discharge pressure PMs! /, So the evaporation temperature of the branching refrigerant is The saturation temperature Tm corresponds to the target discharge pressure PMs. Then, the liquid refrigerant flowing through the first flow path (50a) is cooled by the branched refrigerant that evaporates at this saturation temperature Tm, and is not cooled to this saturation temperature Tm! /, So the target cooling temperature Ts is targeted. Set the temperature slightly higher than the saturation temperature Tm (Tm + ΔΤ) at the discharge pressure PMs.

[0095] Then, 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) is the target cooling temperature Ts. A force that is a value that approximates to (the difference from the target cooling temperature Ts is within the range of soil / 3 and can be regarded as the target cooling temperature Ts, / 3 is a predetermined allowable value), the actual It is determined whether the temperature Tr of the liquid refrigerant is greater or less than the target cooling temperature Ts that is less than the target cooling temperature Ts.

[0096] In step ST12, the actual temperature Tr of the liquid refrigerant approximates the target cooling temperature Ts. If it is higher than the target cooling temperature Ts, move to step ST13. In step ST13, a determination is made as to whether or not the actual temperature of the liquid refrigerant Tr is 10 ° C or higher, and a determination is made as to whether or not the superheat degree SH of the suction refrigerant of the high-stage compression mechanism (11) is 5 ° C or higher. The In other words, if the liquid refrigerant is cooled too much, the supercooling heat exchanger (50) may freeze, so it is overcooled at the appropriate lower limit of 10 ° C! /, N! /, If the branch refrigerant flowing through the second flow path (50b) does not completely evaporate and becomes wet, the high-stage compression mechanism (11) may suck the wet refrigerant and compress the liquid. Then, it is determined whether the suction refrigerant of the high-stage compression mechanism (11) is in a wet state! / ,!

Note that 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). In addition, the lower limit value of the temperature for preventing freezing of the supercooling heat exchanger (50) may be set to 5 ° C or 15 ° C, for example. When at least one of these conditions is satisfied, the process proceeds to step ST14, and when neither is satisfied, the process proceeds to return and returns to the start. In Step ST14, the valve control unit (103) controls the second expansion valve (58) so that the opening degree is increased. As a result, the amount of refrigerant in the second flow path (50b) increases, so that the temperature of the liquid coolant 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 close 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 in the high-stage compression mechanism (11) is less than 5 ° C. If at least one of these conditions is met, the process moves to step ST16. If neither of these conditions is met, the process moves to return and returns to start. In step ST16, the opening of the second expansion valve (58) is controlled to be small by the valve control unit (103). As a result, the temperature Tr of the liquid refrigerant increases.

[0099] That is, even if the temperature Tr of the liquid refrigerant is a value that approximates the target cooling temperature Ts, the temperature Tr of the liquid refrigerant is less than 10 ° C and it is overcooled, or the high-stage compression When the superheat degree SH of the suction refrigerant of the mechanism (11) is low, the opening of the second expansion valve (58) is controlled to be small, and the supercooling heat exchanger (50) is frozen or It prevents the stage-side compression mechanism (11) from sucking wet refrigerant and compressing it. And all the conditions judged in step ST15 If not, there is no risk of the supercooling heat exchanger (50) freezing or the high-stage compression mechanism (11) liquid compressing. The temperature is maintained at a temperature that approximates the target cooling temperature Ts.

[0100] When it is determined in step ST12 that the actual liquid refrigerant temperature Tr is not close to the target cooling temperature Ts and is lower than the target liquid refrigerant temperature Tr, the process proceeds to step ST16 and valve control is performed. The opening of the second expansion valve (58) is controlled by the portion (103) 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 move on to return and start again.

[0101] In this way, since 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, the refrigeration heat exchanger (31) The liquid refrigerant to be sent 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 or It is possible to prevent the step-side compression mechanism (11) from compressing liquid.

[0102] Effects of one embodiment

In the refrigeration system (1), the operating capacity of the booster compression mechanism (41) is controlled by the first capacity control unit (101) so that the evaporation temperature in the refrigeration heat exchanger (31) becomes the target evaporation temperature. Therefore, an 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. Thus, 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. This reduces the amount of liquid refrigerant when supplying liquid refrigerant to the suction side of the high stage compression mechanism (11) as a measure to prevent the high stage compression mechanism (11) from becoming hot. Therefore, the amount of refrigerant evaporated in the refrigeration heat exchanger (31) can be increased.

[0103] Further, when the discharge temperature of the booster compression mechanism (41) is lower than the target discharge temperature, the high-stage compression mechanism (11 ) Therefore, it is possible to reduce the power of the high-stage compression mechanism (11) as much as possible. In other words, it is possible to increase the flow rate of the refrigerant that evaporates in the refrigeration heat exchanger (31), and to reduce the power of the high-stage compression mechanism (11) as much as possible. , 11) The refrigeration capacity in the refrigeration heat exchanger (31) can be increased, and the COP can be improved.

[0104] Further, 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. Even if the booster compressors (41a, 41b, 41c) of the booster compression mechanism (41) are high-pressure dome type scroll compressors and it is difficult to measure the discharge temperature quickly and accurately. In addition, it is possible to reliably control the discharge temperature as the discharge target temperature.

[0105] In the refrigeration system (1), the valve control unit (103) controls the opening of the second expansion valve (58), and the first flow path of the supercooling heat exchanger (50) ( Since the liquid refrigerant flowing through 50a) is cooled to the target cooling temperature T s, the refrigerant sent to the refrigeration heat exchanger (31) is reliably cooled, and the refrigeration capacity in the refrigeration heat exchanger (31) is Therefore, the COP of the refrigeration apparatus (1) can be improved more reliably.

<< Other Embodiments >>

According to the above embodiment, the following configuration is possible.

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) You may make it comprise with one compressor. Further, although the refrigeration apparatus (1) of the above embodiment has one refrigeration heat exchanger (31), it may have a configuration in which a plurality of refrigeration heat exchangers (31) are connected in parallel.

[0108] Further, in the refrigeration apparatus (1) of the above embodiment, a scroll type compressor is used as each compressor (41a, 41b, 41c) of the booster compression mechanism (41), and the discharge temperature is measured. Force that controls the discharge pressure to the target discharge pressure due to the long response time If the compressor has a short response time of the discharge temperature (for example, a rotary compressor), the target discharge temperature is directly discharged. Control of temperature may be performed. Further, even when a scroll compressor is used, the discharge temperature may be estimated and controlled from the temperature of the refrigerant flowing through the discharge pipe. [0109] It should be noted that the above embodiments are essentially preferable examples, and are not intended to limit the scope of the present invention, its application, or its use.

Industrial applicability

[0110] 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 the refrigerant in two stages.

Claims

The scope of the claims

[1] Low-stage compression mechanism (41) with variable operating capacity, high-stage compression mechanism (11) with variable operating capacity, condenser (13), expansion mechanism (32), and evaporator (31) in sequence A refrigeration apparatus comprising a refrigerant circuit (10) configured to compress the refrigerant 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! A refrigeration apparatus characterized by the above.

[2] In claim 1,

In the second capacity control means (102), 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! Control the operating capacity of the high-stage compression mechanism (11) so that the target discharge pressure derived from

A refrigeration apparatus characterized by that.

[3] In claim 1,

The refrigerant circuit (10) exchanges heat between the liquid refrigerant flowing from the condenser (13) to the expansion mechanism (32) and the branched refrigerant in which a part of the liquid cooling medium is branched and depressurized. A subcooling heat exchanger (50) for cooling 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 system characterized by that.

[4] 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,

Provided with 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 the target cooling temperature.

A refrigeration apparatus characterized by that.

[5] In claim 2,

[6] In claim 5,

A refrigeration apparatus characterized by that.