JPWO2014064744A1 - Refrigeration equipment - Google Patents

Abstract

The high temperature side compressor 1, the high temperature side condenser 2, the high temperature side expansion valve 3, and the high temperature side evaporator 4 are sequentially connected by piping, and the high temperature side circulation circuit A in which the refrigerant circulates, the low temperature side compressor 5, the low temperature side condensation The low-temperature side flow rate adjusting valve 10 and the low-temperature side evaporator 12 are sequentially connected by pipes, and the low-temperature side circulation circuit B through which the refrigerant circulates, the high-temperature side evaporator 4 and the low-temperature side condenser 7 are configured. A cascade condenser 8 that exchanges heat between the refrigerant flowing through the side evaporator 4 and the refrigerant flowing through the low-temperature side condenser 7, and a low-temperature side second solenoid valve in a pipe between the low-temperature side condenser 7 and the low-temperature side compressor 5 A plurality of expansion tanks 18 connected via a high temperature side compressor 1, a high temperature side condenser 2, a high temperature side expansion valve 3, a high temperature side evaporator 4, a low temperature side compressor 5, and a low temperature side The condenser 7 is mounted on the outdoor unit 14, and the plurality of expansion tanks 18 are expanded tanks. Characterized in that mounted on the unit housing 31.

Description

  The present invention relates to a refrigeration apparatus including a circulation circuit (refrigeration cycle) for circulating a refrigerant.

  Conventionally, a refrigeration apparatus that performs a dual refrigeration cycle by cascade-connecting a high-temperature side circulation circuit (high-temperature side refrigeration cycle) and a low-temperature side circulation circuit (low-temperature side refrigeration cycle) via a cascade capacitor is known.

In a conventional refrigeration system, when the compressor in the low-temperature side circulation circuit is stopped, the compressor in the high-temperature side circulation circuit is operated to cool the refrigerant in the low-pressure side circulation circuit, thereby suppressing the pressure increase in the low-temperature side circulation circuit. The thing is proposed (refer patent document 1).
For example, when performing the defrosting operation of the evaporator of the low temperature side circulation circuit, the compressor of the low temperature side circulation circuit is stopped and the compressor of the high temperature side circulation circuit is operated. In addition, when the compressor of the low-temperature side circulation circuit is restarted in a state where the compressor of the low-temperature side circulation circuit is stopped (thermo-off), after the predetermined time has elapsed after starting the compressor of the high-temperature side circulation circuit, The compressor of the circulation circuit is restarted.

JP 2004-190917 A (paragraphs [0008]-[0023], FIG. 1)

However, the conventional refrigeration system has a problem that it is necessary to wastefully operate the compressor of the high-temperature side circulation circuit despite the state where the compressor of the low-temperature side circulation circuit is stopped and the cooling operation is not performed. there were.
For example, in the case where carbon dioxide is used as the refrigerant in the low-temperature side circulation circuit, in order to suppress the design pressure of the low-temperature side circulation circuit to about 3 to 4 MPa, about 30 at the time of defrosting operation of the evaporator of the low-temperature side circulation circuit. It is necessary to operate the compressor of the high-temperature side circulation circuit for about 40 minutes. This defrosting operation is performed about 4 to 5 times a day.

  Also, when the compressor of the low-temperature side circulation circuit stops (thermo-off) and the compressor of the low-temperature side circulation circuit is restarted, the compressor of the high-temperature side circulation circuit is started for a predetermined time (tens of seconds to several minutes) Since the compressor of the low temperature side circulation circuit is started after the lapse, there is a problem that the pull-down speed becomes slow.

Also, if the compressor of the high-temperature side circulation circuit is not operated when the compressor of the low-temperature side circulation circuit is stopped, and the compressor of the low-temperature side circulation circuit is stopped for a long time, the refrigerant in the low-temperature side circulation circuit will reach about the outside temperature. Warm up and pressure rises.
In order to cope with such an increase in pressure in the low temperature side circulation circuit, it is necessary to make the structure of each member constituting the low temperature side circulation circuit sturdy. For example, it is necessary to increase the thickness of the refrigerant pipe. For this reason, there existed a problem that manufacturing cost will increase.
In addition, when the pressure of the refrigerant in the low-temperature side circulation circuit rises above the design pressure, the refrigerant may be released from the safety valve. In this case, it is necessary to replenish the refrigerant in the low-temperature side circulation circuit.

The present invention was made to solve the above-described problems, and is a refrigeration apparatus that can suppress an increase in the pressure of refrigerant in the low-temperature side circulation circuit when the compressor in the low-temperature side circulation circuit is stopped. Is what you get.
In addition, when the compressor of the low-temperature side circulation circuit is stopped and restarted, a refrigeration apparatus capable of suppressing an increase in the pressure of the refrigerant in the low-temperature side circulation circuit without operating the compressor of the high-temperature side refrigerant circuit is obtained. It is.
Moreover, the freezing apparatus which can make low the design pressure of a low temperature side circulation circuit is obtained.

  The refrigeration apparatus according to the present invention includes a first circulation circuit in which a first compressor, a first condenser, a first expansion device, and a first evaporator are sequentially connected by piping to circulate a refrigerant, a second compressor, 2 condenser, a 2nd expansion device, and a 2nd evaporator are connected by piping one by one, and it comprises the 2nd circulation circuit through which a refrigerant circulates, the 1st evaporator and the 2nd condenser, and the 1st evaporation A plurality of cascade condensers that exchange heat between the refrigerant flowing through the condenser and the refrigerant flowing through the second condenser, and a pipe between the second evaporator and the second compressor via an on-off valve. An expansion tank, and the first compressor, the first condenser, the first throttling device, the first evaporator, the second compressor, and the second condenser are mounted on an outdoor unit. The plurality of expansion tanks are mounted on an expansion tank unit.

  Since the present invention includes the expansion tank connected to the pipe between the second evaporator and the second compressor via the on-off valve, the low-temperature side circulation can be performed without operating the compressor of the high-temperature side refrigerant circuit. An increase in the pressure of the refrigerant in the circuit can be suppressed.

It is a refrigerant circuit figure of the freezing apparatus in Embodiment 1 of this invention. It is a block diagram of the freezing apparatus in Embodiment 1 of this invention. It is the block diagram which looked at the outdoor unit of FIG. 2 from the A direction. It is a figure showing the relationship between the circuit internal volume and circuit internal pressure in Embodiment 1 of this invention. It is a flowchart explaining operation | movement of the freezing apparatus in Embodiment 1 of this invention. It is a block diagram of the freezing apparatus in Embodiment 2 of this invention. It is a block diagram of the freezing apparatus in Embodiment 3 of this invention. It is a block diagram of the freezing apparatus in Embodiment 4 of this invention. It is a refrigerant circuit figure of the freezing apparatus in Embodiment 5 of this invention. It is a Mollier diagram showing operation | movement of the freezing apparatus in Embodiment 5 of this invention. It is a flowchart explaining operation | movement of the freezing apparatus in Embodiment 5 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following drawings, the size relationship of each component may be different from the actual one.

Embodiment 1 FIG.
[Constitution]
FIG. 1 is a refrigerant circuit diagram of a refrigeration apparatus in Embodiment 1 of the present invention.
As shown in FIG. 1, the refrigeration apparatus includes a high temperature side circulation circuit A and a low temperature side circulation circuit (load side circuit) B.
The high temperature side circulation circuit A and the low temperature side circulation circuit B are cascade-connected via a cascade capacitor 8.
The refrigeration apparatus performs a dual refrigeration cycle by circulating a refrigerant in each of the high temperature side circulation circuit A and the low temperature side circulation circuit B.

Here, in the configuration referred to as the low temperature side and the high temperature side, the level of temperature, pressure, etc. is not particularly determined in relation to absolute values, but is relative in terms of state, operation, etc. in the refrigeration apparatus. It will be determined.
In the first embodiment, a two-stage refrigeration cycle including two refrigerant circuits will be described. However, the refrigeration apparatus according to the present invention includes three or more refrigeration cycles (multi-source refrigeration apparatus). Is included.

(High-temperature circuit A)
The high temperature side circulation circuit A includes a high temperature side compressor 1, a high temperature side condenser 2, a high temperature side expansion valve 3, and a high temperature side evaporator 4.
The high temperature side compressor 1, the high temperature side condenser 2, the high temperature side expansion valve 3, and the high temperature side evaporator 4 are connected in series by refrigerant piping.

  The high temperature side compressor 1, the high temperature side condenser 2, the high temperature side expansion valve 3, and the high temperature side evaporator 4 are accommodated in an outdoor unit 14 described later.

  As the refrigerant circulating through the high-temperature circuit A, a refrigerant having a relatively small global warming potential (GWP) (for example, R410A, R134a, R32, or HFO refrigerant) is used.

The high temperature side compressor 1 sucks the refrigerant flowing through the high temperature side circulation circuit A.
The high temperature side compressor 1 compresses the sucked refrigerant and discharges it in a high temperature and high pressure state.
The high temperature side condenser 2 performs heat exchange between the refrigerant discharged from the high temperature side compressor 1 and the air.

The high temperature side expansion valve 3 decompresses and expands the refrigerant that has flowed out of the high temperature side condenser 2.
The high temperature side evaporator 4 exchanges heat between the refrigerant decompressed by the high temperature side expansion valve 3 and the refrigerant flowing through the low temperature side condenser 7 of the low temperature side circulation circuit B.

The high temperature side evaporator 4 and the low temperature side condenser 7 constitute a cascade condenser 8.
The cascade condenser 8 is configured by, for example, a plate heat exchanger.
The cascade condenser 8 is not limited to a plate heat exchanger, and may be a shell and tube heat exchanger, a double tube heat exchanger, or the like.

The high temperature side compressor 1 corresponds to the “first compressor” in the present invention.
The high temperature side condenser 2 corresponds to a “first condenser” in the present invention.
The high temperature side expansion valve 3 corresponds to a “first throttle device” in the present invention.
The high temperature side evaporator 4 corresponds to the “first evaporator” in the present invention.

(Low-temperature circuit B)
The low temperature side circulation circuit B includes a low temperature side compressor 5, an auxiliary capacitor 6, a low temperature side condenser 7, a liquid receiver 9, a low temperature side flow rate adjustment valve 10, a low temperature side first electromagnetic valve 11, and a low temperature. The side evaporator 12, the low temperature side high pressure sensor 27, and the low temperature side low pressure sensor 28 are included.
The low temperature side compressor 5, the auxiliary capacitor 6, the low temperature side condenser 7, the liquid receiver 9, the low temperature side first electromagnetic valve 11, the low temperature side flow rate adjustment valve 10, and the low temperature side evaporator 12 are: Piping is connected in series by refrigerant piping.
An expansion tank 18 a, an expansion tank 18 b, and an expansion tank 18 c are connected to the pipe between the low temperature side condenser 7 and the low temperature side compressor 5 via a low temperature side second electromagnetic valve 17.

The low temperature side high pressure sensor 27 detects the pressure on the discharge side of the low temperature side compressor 5.
The low temperature side low pressure sensor 28 detects the pressure on the suction side of the low temperature compressor 5.

  The low temperature side compressor 5, the auxiliary capacitor 6, the low temperature side condenser 7, the liquid receiver 9, the low temperature side high pressure sensor 27, and the low temperature side low pressure sensor 28 are accommodated in an outdoor unit 14 described later. ing.

The low temperature side first solenoid valve 11, the low temperature side flow rate adjustment valve 10, and the low temperature side evaporator 12 are accommodated in a cooling unit 13.
The cooling unit 13 is used, for example, as a refrigerated freezer showcase or a unit cooler.
The cooling unit 13 is connected to the low-temperature circuit B by a liquid pipe 15 and a gas pipe 16.

Expansion tanks 18a, 18b, and 18c (hereinafter simply referred to as “expansion tank 18” when not distinguished from each other) are housed in an expansion tank unit housing 31 described later.
The expansion tank unit housing 31 corresponds to the “expansion tank unit” in the present invention.

  For example, when installing the refrigeration apparatus, the outdoor unit 14, the cooling unit 13, and the expansion tank unit housing 31 are separated and transported, and piping connection is made on site.

  For example, a carbon dioxide (CO2) refrigerant having a global warming potential (GWP) of 1 is used as the refrigerant circulating in the low-temperature side circulation circuit B.

The low temperature side compressor 5 sucks the refrigerant flowing through the low temperature side circulation circuit B.
The low temperature side compressor 5 compresses the sucked refrigerant and discharges it in a high temperature and high pressure state.
The auxiliary capacitor 6 exchanges heat between the refrigerant discharged from the low temperature side compressor 5 and the air.

The low-temperature side condenser 7 performs heat exchange between the refrigerant that has flowed out of the auxiliary capacitor 6 and the refrigerant that flows through the high-temperature side evaporator 4 of the high-temperature side circulation circuit A.
The liquid receiver 9 stores excess refrigerant out of the refrigerant flowing out of the low temperature side condenser 7.

The low-temperature-side flow rate adjustment valve 10 decompresses and expands the refrigerant flowing out of the liquid receiver 9.
The low temperature side flow rate adjustment valve 10 is constituted by a temperature type automatic expansion valve or an electronic type expansion valve.
The low temperature side evaporator 12 performs heat exchange between the refrigerant decompressed by the low temperature side flow rate adjustment valve 10 and a fluid (for example, air, water, refrigerant, brine, or the like).

The low temperature side second solenoid valve 17 is a solenoid valve that is closed when energized.
The expansion tank 18 stores refrigerant therein.
The expansion tank 18 has an outer diameter of 400 mm or less, for example.

The low temperature side compressor 5 corresponds to the “second compressor” in the present invention.
The low temperature side condenser 7 corresponds to a “second condenser” in the present invention.
The low temperature side flow rate adjustment valve 10 corresponds to a “second throttle device”.
The low temperature side evaporator 12 corresponds to the “second evaporator” in the present invention.
The low temperature side second electromagnetic valve 17 corresponds to an “open / close valve” in the present invention.

(Operation of high-temperature side circulation circuit A)
The high-temperature and high-pressure gas-phase refrigerant discharged from the high-temperature side compressor 1 flows into the high-temperature side condenser 2.
The refrigerant flowing into the high temperature side condenser 2 is condensed and liquefied by heat exchange with air, and becomes a refrigerant in a liquid phase state at a high pressure.
The high-pressure and liquid-phase refrigerant that has flowed out of the high-temperature side condenser 2 is decompressed by the high-temperature side expansion valve 3 and becomes a refrigerant in a gas-liquid two-phase state at a low temperature and low pressure.
This low-temperature low-pressure gas-liquid two-phase refrigerant evaporates by exchanging heat with the refrigerant flowing through the low-temperature side condenser 7 of the low-temperature side circulation circuit B in the high-temperature side evaporator 4 constituting the cascade condenser 8. It becomes a gas-phase refrigerant at low pressure.
At this time, the refrigerant flowing through the low temperature side condenser 7 of the low temperature side circulation circuit B is cooled.
The refrigerant flowing out from the high temperature side evaporator 4 is sucked into the high temperature side compressor 1 again.

(Operation of low-temperature circuit B)
The high-temperature and high-pressure gas-phase refrigerant discharged from the low-temperature side compressor 5 flows into the auxiliary capacitor 6.
In the auxiliary capacitor 6, the refrigerant in the gas phase at high temperature and high pressure exchanges heat with the air, and the refrigerant is cooled and the temperature is slightly lowered.
The refrigerant cooled by the auxiliary condenser 6 flows into the low temperature side condenser 7 constituting the cascade condenser 8.
This low-temperature low-pressure gas-liquid two-phase refrigerant evaporates by exchanging heat with the refrigerant flowing through the low-temperature side condenser 7 of the low-temperature side circulation circuit B in the high-temperature side evaporator 4 constituting the cascade condenser 8. It becomes a gas-phase refrigerant at low pressure.
The refrigerant flowing into the low-temperature side condenser 7 is condensed by exchanging heat with the refrigerant flowing through the high-temperature side evaporator 4 of the high-temperature side circulation circuit A to become a low-temperature high-pressure liquid-phase refrigerant.
At this time, the refrigerant flowing through the high temperature side evaporator 4 of the high temperature side circulation circuit A is heated.

The low-temperature and high-pressure liquid phase refrigerant that has flowed out of the low-temperature side condenser 7 flows into the liquid receiver 9.
A part of the refrigerant flowing into the liquid receiver 9 is stored as surplus refrigerant, and the rest flows into the low-temperature side flow rate adjustment valve 10.
The high-pressure and liquid-phase refrigerant that has flowed into the low-temperature-side flow rate adjustment valve 10 is decompressed and becomes a gas-liquid two-phase refrigerant.
This low-temperature, low-pressure, gas-liquid two-phase refrigerant flows into the low-temperature side evaporator 12.
In the low temperature side evaporator 12, the refrigerant exchanges heat with a fluid (for example, air) and evaporates to become a high temperature and low pressure gas phase refrigerant.
At this time, the cooling target space is cooled in the cooling unit 13.
The low-pressure gas-phase refrigerant that has flowed out of the low-temperature side evaporator 12 is again sucked into the low-temperature side compressor 5.

In the first embodiment, the liquid receiver 9 is connected as one of the components of the low temperature side circulation circuit B. However, the present invention is not limited to this, and the liquid receiver 9 is not connected. Also good.
Further, a liquid receiver such as an accumulator may be connected to the suction side of the low temperature side compressor 5 instead of the liquid receiver 9.
That is, the liquid receiver 9 may determine the connection and the type of the connection depending on the use of the refrigeration apparatus and the refrigerant used.

  Next, arrangement of devices in each unit and details of the devices will be described.

(Outdoor unit 14)
FIG. 2 is a configuration diagram of the refrigeration apparatus according to Embodiment 1 of the present invention.
As shown in FIG. 2, the outdoor unit 14 includes a high temperature side housing 19 and a low temperature side housing 20.
The high temperature side casing 19 and the low temperature side casing 20 are configured by casings having the same outer shape.
The high temperature side casing 19 and the low temperature side casing 20 share a bottom plate with a common base 21.
The high temperature side casing 19 and the low temperature side casing 20 are installed adjacent to each other on the common mount 21.

The high temperature side housing 19 is provided with a high temperature side compressor 1, a high temperature side condenser 2, a high temperature side expansion valve 3, a high temperature side blower 22, and a high temperature side controller 24.
The high temperature side blower 22 is installed on the upper portion of the high temperature side casing 19 and supplies air to the high temperature side condenser 2.
The high temperature side controller 24 executes various controls of the high temperature side equipment.

The low temperature side housing 20 is provided with a low temperature side compressor 5, an auxiliary capacitor 6, a liquid receiver 9, a cascade capacitor 8, a low temperature side blower 23, and a low temperature side controller 26.
The low temperature side blower 23 is installed in the upper part of the low temperature side housing 20 and supplies air to the high temperature side condenser 2.
The low temperature side controller 26 executes various controls of the low temperature side equipment.
The low temperature side controller 26 controls the low temperature side second electromagnetic valve 17.

  Note that the cascade capacitor 8 extending over both the high temperature side and the low temperature side may be arranged in either the high temperature side casing 19 or the low temperature side casing 20 in consideration of the arrangement condition or the like.

  The low temperature side controller 26 corresponds to a “control unit” in the present invention.

(Expansion tank unit housing 31)
FIG. 3 is a configuration diagram of the outdoor unit of FIG. 2 viewed from the A direction.
As shown in FIG. 3, the expansion tank unit housing 31 is arranged with a space beside the high temperature side housing 19 and the low temperature side housing 20.
The expansion tanks 18a, 18b, 18c are accommodated in the expansion tank unit housing 31.
The expansion tank unit housing 31 includes an expansion tank unit mount 30, a support 31b, and a support 31c.
An expansion tank 18 a is mounted on the expansion tank unit mount 30.
The expansion tank 18b is mounted on the support 31b.
The expansion tank 18c is mounted on the support 31c.
That is, the expansion tanks 18a, 18b, and 18c are mounted on the expansion tank unit housing 31 side by side in the vertical direction.

A pipe 32a is connected to the lower part of the expansion tank 18a.
A pipe 32b is connected to the lower part of the expansion tank 18b.
A pipe 32c is connected to the lower part of the expansion tank 18c.
The pipe 32 a, the pipe 32 b, and the pipe 32 c gather in the pipe 32 and are connected to the low temperature side second electromagnetic valve 17.
The reason for connecting the pipes 32a, 32b, and 32c to the lower portions of the expansion tanks 18a, 18b, and 18c is to reliably collect the refrigerating machine oil.

In the first embodiment, the case where the number of the low temperature side second electromagnetic valve 17 is one will be described. However, the present invention is not limited to this and may be provided in each of the expansion tanks 18a, 18b, and 18c.
The expansion tanks 18a, 18b, and 18c are housed in the expansion tank unit housing 31, but the expansion tanks 18a, 18b, and 18c may be stacked.

As will be described later, the expansion tanks 18a, 18b, 18c have an outer diameter of 270 mm (wall thickness: 8 mm) and a length of about 1500 mm.
By arranging the expansion tanks 18a, 18b, and 18c side by side in the vertical direction, the depth of the expansion tank unit housing 31 is about 400 mm.
The depth of the high temperature side housing 19 and the low temperature side housing 20 is about 800 mm.
The suction space for the high-temperature side condenser 2 and the auxiliary condenser 6 is secured to 300 mm.
For this reason, the expansion tank unit housing | casing 31 and the outdoor unit 14 can be installed in the space of about 1500 mm.

  Next, the capacity of the expansion tank 18 will be described.

FIG. 4 is a diagram showing the relationship between the circuit internal volume and the circuit internal pressure in Embodiment 1 of the present invention.
In FIG. 4, the refrigerant pressure in the low-temperature side circulation circuit B when the refrigerant circulation in the high-temperature side circulation circuit A and the low-temperature side circulation circuit B stops and the refrigerant temperature rises to the ambient temperature under the following conditions: The relationship with the circuit internal volume of the low temperature side circulation circuit B is shown.
The refrigerant of the low temperature side circulation circuit B is carbon dioxide.
The ambient temperature (outside air temperature) of the outdoor unit 14 is 46 ° C.
The nominal output of the low temperature side compressor 5 of the low temperature side circulation circuit B is about 28 kW (about 10 horsepower).
The internal volume of the low temperature side evaporator 12 is about 72 liters.
The internal volume of the low temperature side compressor 5, the auxiliary capacitor 6, the low temperature side condenser 7, and the liquid receiver 9 is about 40 liters.
When the length of the liquid pipe 15 and the gas pipe 16 (hereinafter also referred to as “extended pipe”) connecting the cooling unit 13 and the outdoor unit 14 is 70 m, the internal volume is about 48 liters.
That is, when the length of the extension pipe is 70 m, a value obtained by adding the internal volumes of the expansion tanks 18a, 18b, 18c to about 160 liters is the circuit internal volume of the low temperature side circulation circuit B.

As shown in FIG. 4, the larger the circuit volume of the low temperature side circulation circuit B, the smaller the pressure rise.
For example, when the design pressure of the low-temperature side circulation circuit B is 4.15 MPa, which is equivalent to the case where R410A is used, the required circuit internal volume (marked in the figure) is about 400 liters.
Under the conditions described above, the total internal volume of the expansion tank 18 needs to be 240 liters, which is the difference between 400 liters and 160 liters.
Therefore, when three tanks of the expansion tanks 18a, 18b, and 18c are provided, the outer diameter is 270 mm (wall thickness 8 mm) and the length is about 1500 mm.

Further, when the length of the extension pipe is 35 m, the required circuit internal volume (♦ in FIG. 4) is about 300 liters.
Under the conditions described above, the total internal volume of the expansion tank 18 needs to be 140 liters, which is the difference between 300 liters and 160 liters.
In this case, two expansion tanks 18 having an outer diameter of 270 mm (wall thickness: 8 mm) and a length of about 1500 mm may be used.

  The internal volume and number of the expansion tanks 18 are not limited to the above-described configuration, and can be appropriately selected according to the required internal volume.

Here, when carbon dioxide is used as the refrigerant of the low-temperature side circulation circuit B, since the pressure loss is small, the pipe diameter of the gas pipe 16 can be made smaller than that of the HFC refrigerant.
For example, in a refrigeration system having a refrigeration capacity of 28 kW, the pipe diameter of the gas pipe 16 is φ31.75 mm when using R410A, whereas the pipe diameter of the gas pipe 16 is set when using carbon dioxide. It can be set to φ19.05 mm.
However, even if carbon dioxide is used to secure the pipe internal volume, if the pipe diameter (φ31.75 mm) is the same as the pipe when HFC refrigerant is used, the internal volume of the extension pipe is increased. Can be made.
For example, when the length of the extension pipe is 70 m, the internal volume increases by about 40 liters when the pipe diameter of the gas pipe 16 is changed from φ19.05 mm to φ31.75 mm.
Therefore, the internal volume of the expansion tank 18 can be reduced.

In the above-described conditions, the capacity of the expansion tank 18 was calculated assuming that the ambient temperature was 46 ° C. However, the internal volume and number of the expansion tanks 18 can be appropriately selected according to the temperature environment in which the refrigeration apparatus is used. .
For example, if the ambient temperature is about 32 ° C., the capacity or number of the expansion tanks 18 can be reduced.

Thus, by providing the expansion tank 18, the pressure rise of the refrigerant in the low-temperature side circulation circuit B can be suppressed, and the design pressure of the low-temperature side circulation circuit B can be lowered.
Therefore, the manufacturing cost of each member which comprises the low temperature side circulation circuit B can be reduced.
For example, when the design pressure of the low temperature side circulation circuit B is set to 8.5 MPa without providing the expansion tank 18, the specification of the copper pipe (hairpin) passing through the inside of the plate fin tube type low temperature evaporator 12 is, for example, It becomes about φ9.52 mm (wall thickness 0.8 mm).
On the other hand, when the expansion tank 18 is provided and the design pressure is 4.15 MPa, the specification of the hairpin of the low temperature side evaporator 12 is about φ9.52 mm (thickness 0.35 mm).
Thus, the thickness of the hairpin can be halved, and the material cost alone is halved.
Similarly, the wall thickness of the low temperature side compressor 5, the auxiliary capacitor 6, the cascade capacitor 8, the liquid receiver 9, the liquid pipe 15, the gas pipe 16, and the expansion tank 18 can be reduced.
In other words, the refrigeration apparatus in which the design pressure of the low-temperature side circulation circuit B is 4.15 MPa or less can reduce the manufacturing cost to half or less compared to the refrigeration apparatus in which the design pressure of the low-temperature side circulation circuit B is 8.5 MPa. it can.

  Next, the control operation of the low temperature side second electromagnetic valve 17 communicating with the expansion tank 18 will be described.

FIG. 5 is a flowchart illustrating the operation of the refrigeration apparatus in Embodiment 1 of the present invention.
Hereinafter, description will be given based on each step of FIG.

(S1)
The low temperature side controller 26 detects the pressure on the discharge side of the low temperature side compressor 5 detected by the low temperature side high pressure sensor 27 and the low temperature side low pressure sensor 28 when the low temperature side compressor 5 is stopped. The pressure on the suction side of the low-temperature compressor 5 thus obtained is acquired.
Then, it is determined whether at least one of the suction-side pressure and the discharge-side pressure of the low-temperature side compressor 5 is equal to or higher than a preset pressure value P1.
If at least one of the suction-side pressure and the discharge-side pressure of the low-temperature side compressor 5 is not equal to or higher than the preset pressure value P1, step S1 is repeated.

Here, the pressure value P1 is set according to the design pressure of the low temperature side circulation circuit B, for example. For example, when the design pressure is 4.15 MPa, the pressure is set to 4 MPa in consideration of the measurement error of the sensor and the operation time of the solenoid valve.
The pressure value P1 corresponds to the “first pressure value” in the present invention.

(S2)
When at least one of the suction-side pressure and the discharge-side pressure of the low-temperature side compressor 5 is equal to or higher than the preset pressure value P1, the low-temperature side controller 26 opens the low-temperature side second electromagnetic valve 17. .
Thereby, the refrigerant of the low temperature side circulation circuit B flows into each of the expansion tanks 18a, 18b, 18c. That is, the circuit volume of the low-temperature side circulation circuit B increases and the refrigerant pressure decreases.

(S3)
The low temperature side controller 26 determines whether the suction side pressure or the discharge side pressure of the low temperature side compressor 5 is equal to or less than a preset pressure value P2.
When the pressure on the suction side or the pressure on the discharge side of the low temperature side compressor 5 is not equal to or lower than the preset pressure value P2, the process returns to step S2 and the open state of the low temperature side second electromagnetic valve 17 is maintained.
Here, the pressure value P2 is set to a value lower than the pressure value P1.
The pressure value P2 corresponds to the “second pressure value” in the present invention.

(S4)
When the suction-side pressure or the discharge-side pressure of the low-temperature side compressor 5 is equal to or lower than the preset pressure value P2, the low-temperature side controller 26 closes the low-temperature side second electromagnetic valve 17 and performs step S1. Return to.
As described above, when the pressure of the refrigerant decreases, the low temperature side second electromagnetic valve 17 is closed to stop the flow of the refrigerant into the expansion tank 18. Thus, the refrigerant can be collected in a short time when the low temperature side compressor 5 is restarted.

Note that the power supply to the refrigeration apparatus may be stopped for a long time due to, for example, a power failure.
The low temperature side second solenoid valve 17 in the first embodiment is a solenoid valve that is closed when energized. For this reason, even when the low temperature side compressor 5 is stopped due to a power failure or the like, the low temperature side second electromagnetic valve 17 is opened, the internal volume of the low temperature side circulation circuit B is increased, and the refrigerant pressure is increased. descend.

(When restarting the low-temperature compressor 5)
The low temperature side controller 26 opens the low temperature side second electromagnetic valve 17 for a preset time when the low temperature side compressor 5 is restarted.
That is, when the low temperature side compressor 5 is started, the low temperature side second electromagnetic valve 17 is opened, and after the preset time has elapsed, the low temperature side second electromagnetic valve 17 is closed.
Thereby, the refrigerant in the expansion tank 18 can be recovered in the low temperature side circulation circuit B.

  In addition, the operation | movement of step S3 and S4 mentioned above may be abbreviate | omitted, and the low temperature side 2nd solenoid valve 17 may be maintained in an open state. The low temperature side second electromagnetic valve 17 may be closed after a preset time has elapsed since the low temperature side compressor 5 was restarted.

As described above, the first embodiment includes the expansion tank 18 connected to the pipe between the low temperature side evaporator 12 and the low temperature side compressor 5 via the low temperature side second electromagnetic valve 17.
For this reason, when the low temperature side compressor 5 of the low temperature side circulation circuit B has stopped, the pressure rise of the refrigerant | coolant of the low temperature side circulation circuit B can be suppressed.
Further, when the low temperature side compressor 5 of the low temperature side circulation circuit B is stopped and restarted, the increase in the pressure of the refrigerant in the low temperature side circulation circuit B is suppressed without operating the high temperature side compressor 1 of the high temperature side circulation circuit A. can do.
Moreover, the design pressure of the low temperature side circulation circuit B can be lowered.

Further, when carbon dioxide is used as the refrigerant of the low-temperature side circulation circuit B, the design pressure of the low-temperature side circulation circuit B can be set to 4.15 MPa equivalent to that when the R410A refrigerant is used.
For this reason, the low temperature side compressor 5, the auxiliary capacitor 6, the cascade capacitor 8, the liquid receiver 9, the low temperature side evaporator 12 (showcase, unit cooler), the liquid pipe 15, The gas pipe 16 and the expansion tank 18 can be made of a general-purpose HFC refrigerant.
Therefore, the cost increase from the model of HFC refrigerant | coolant can be suppressed significantly using the carbon dioxide refrigerant | coolant which can respond to global warming.

Further, when the low temperature side compressor 5 of the low temperature side circulation circuit B is stopped and restarted, it is not necessary to wastefully operate the high temperature side compressor 1 of the high temperature side circulation circuit A.
Further, at the time of restart after the low temperature side compressor 5 of the low temperature side circulation circuit B is stopped (thermo-off), after the high temperature side compressor 1 of the high temperature side circulation circuit A is started, the low temperature side There is no need to restart the compressor 5. For this reason, the pull-down speed does not become slow.

  Further, since the low temperature side second electromagnetic valve 17 is a solenoid valve that is closed when energized, the refrigerant of the low temperature side circulation circuit B can be used even when the power supply to the refrigeration apparatus is stopped for a long time due to a power failure or the like. The pressure rise can be suppressed.

Embodiment 2. FIG.
FIG. 6 is a configuration diagram of a refrigeration apparatus in Embodiment 2 of the present invention.
As shown in FIG. 6, the pipe 33a is inserted into the expansion tank 18a from the upper part of the expansion tank 18a. The end of the pipe 33a is disposed at a position close to the bottom of the expansion tank 18a.
The pipe 33b is inserted into the expansion tank 18b from the upper part of the expansion tank 18b. The end of the pipe 33b is arranged at a position close to the bottom of the expansion tank 18b.
The piping 33c is inserted into the expansion tank 18c from the upper part of the expansion tank 18c. The end of the pipe 33c is arranged at a position close to the bottom of the expansion tank 18c.
The pipe 33 a, the pipe 33 b, and the pipe 33 c are gathered in the pipe 33 and connected to the low temperature side second electromagnetic valve 17.
The reason why the ends of the pipes 33a, 33b, and 33c are arranged at positions close to the bottoms of the expansion tanks 18a, 18b, and 18c is to reliably collect the refrigerating machine oil.

Other configurations and operations are the same as those in the first embodiment.
Also in the second embodiment, the same effect as in the first embodiment can be obtained.

Embodiment 3 FIG.
FIG. 7 is a configuration diagram of a refrigeration apparatus according to Embodiment 3 of the present invention.
As shown in FIG. 7, an expansion tank frame 35 is provided below the common frame 21 of the high temperature side case 19 and the low temperature side case 20.
The expansion tanks 18a, 18b, and 18c are mounted on the expansion tank mount 35.
That is, the expansion tank mount 35 is disposed adjacent to the lower side of the high temperature side casing 19 and the low temperature side casing 20, and the expansion tanks 18a, 18b, and 18c are mounted on the expansion tank mount 35 side by side in the horizontal direction. ing.
The expansion tank mount 35 corresponds to the “expansion tank unit” in the present invention.

A pipe 34a is connected to the lower part of the expansion tank 18a.
A pipe 34b is connected to the lower part of the expansion tank 18b.
A pipe 34c is connected to the lower part of the expansion tank 18c.
The pipe 34 a, the pipe 34 b, and the pipe 34 c are collected in the pipe 34 and connected to the low temperature side second electromagnetic valve 17.
The reason why the pipes 34a, 34b, 34c are connected to the lower portions of the expansion tanks 18a, 18b, 18c is to reliably collect the refrigerating machine oil.

Other configurations and operations are the same as those in the first embodiment.
Also in the third embodiment, the same effect as in the first embodiment can be obtained.
Further, since the expansion tank frame 35 is provided below the common frame 21 of the high temperature side case 19 and the low temperature side case 20, compared with the first embodiment, the expansion tank 18 and the outdoor unit 14 are separated from each other. The installation width (depth) can be reduced.
For example, if the outer diameter of the expansion tank 18 is 300 mm or less, the depth of the outdoor unit 14 can be 1000 mm or less.
Therefore, a compact refrigeration apparatus can be provided despite the presence of the expansion tank 18.

Embodiment 4 FIG.
FIG. 8 is a block diagram of a refrigeration apparatus in Embodiment 4 of the present invention.
As shown in FIG. 8, the pipe 36a is inserted into the expansion tank 18a from the upper part of the expansion tank 18a. The end of the pipe 36a is disposed at a position close to the bottom of the expansion tank 18a.
The pipe 36b is inserted into the expansion tank 18b from the upper part of the expansion tank 18b. The end of the pipe 36b is disposed at a position close to the bottom of the expansion tank 18b.
The pipe 36c is inserted into the expansion tank 18c from the upper part of the expansion tank 18c. The end of the pipe 36c is disposed at a position close to the bottom of the expansion tank 18c.
The pipe 36 a, the pipe 36 b, and the pipe 36 c are collected in the pipe 36 and connected to the low temperature side second electromagnetic valve 17.
The reason why the ends of the pipes 36a, 36b, and 36c are arranged at positions close to the bottoms of the expansion tanks 18a, 18b, and 18c is to reliably collect the refrigerating machine oil.

Other configurations and operations are the same as those in the fourth embodiment.
Also in the fourth embodiment, the same effect as in the third embodiment can be obtained.

Embodiment 5 FIG.
In the first to fourth embodiments, the refrigeration apparatus in which the high-temperature side circulation circuit A and the low-temperature side circulation circuit B are cascade-connected has been described. In the fifth embodiment, a refrigeration apparatus that performs two-stage compression will be described.

FIG. 9 is a refrigerant circuit diagram of the refrigeration apparatus in Embodiment 5 of the present invention.
As shown in FIG. 9, the refrigerating apparatus of the fifth embodiment includes a low stage compressor 55, a high stage compressor 51, an intermediate cooler 54, a low stage first solenoid valve 57, and a low stage side first. A flow rate adjusting valve 56 and a low-stage evaporator 58 are sequentially connected by piping, and a circulation circuit for circulating the refrigerant is provided.
In addition, the refrigerant branched from the outlet side of the gas cooler 52 and passed through the intermediate cooling flow rate adjustment valve 53 and the intermediate cooler 54 is supplied between the low-stage compressor 55 and the high-stage compressor 51. An intermediate pressure circuit is provided.
An expansion tank 63a, an expansion tank 63b, and an expansion tank 63c are connected to the pipe between the low-stage evaporator 58 and the low-stage compressor 55 via a low-stage second electromagnetic valve 62. .

  Carbon dioxide (CO2) refrigerant having a global warming potential (GWP) of 1 is used as the refrigerant circulating in the circulation circuit and the intermediate pressure circuit of the refrigeration apparatus in the fifth embodiment.

The low stage high pressure sensor 64 detects the pressure on the discharge side of the low stage compressor 55.
The low stage low pressure sensor 65 detects the pressure on the suction side of the low stage compressor 55.

The low-stage first flow rate adjusting valve 56, the low-stage first electromagnetic valve 57, and the low-stage evaporator 58 are housed in the low-stage cooling unit 59.
The low-stage cooling unit 59 is used as, for example, a refrigerated freezer showcase or a unit cooler.
The low-stage cooling unit 59 is connected to the circulation circuit by a low-stage liquid pipe 60 and a low-stage gas pipe 61.

The low-stage second electromagnetic valve 62 is an electromagnetic valve that is closed when energized.
The low-stage second electromagnetic valve 62 is controlled by the controller 66.

  The internal volume and the number of expansion tanks 63a, 63b, 63c (hereinafter simply referred to as “expansion tank 63” if not distinguished from each other) are based on the relationship between the circuit internal volume and the circuit internal pressure, and the design pressure. Appropriate selection can be made by applying the technical idea described in 1.

The low stage compressor 55 corresponds to the “first stage compressor” in the present invention.
The high stage compressor 51 corresponds to the “second stage compressor” in the present invention.
The gas cooler 52 corresponds to a “heat radiator” in the present invention.
The low-stage-side first flow rate adjustment valve 56 corresponds to the “throttle device” in the present invention.
The low-stage evaporator 58 corresponds to the “evaporator” in the present invention.
The low-stage second electromagnetic valve 62 corresponds to the “open / close valve” in the present invention.
The controller 66 corresponds to a “control unit” in the present invention.

  Next, operation | movement of the freezing apparatus in this Embodiment 5 is demonstrated.

FIG. 10 is a Mollier diagram representing the operation of the refrigeration apparatus in Embodiment 5 of the present invention.
The low-pressure gas-phase refrigerant (point F in FIG. 10) that has flowed out of the low-stage evaporator 58 is sucked into the low-stage compressor 55 and compressed to an intermediate pressure.
The superheated steam (point G in FIG. 10) discharged from the low-stage compressor 55 merges with the intermediate-pressure refrigerant that has flowed out of the intermediate cooler 54 (point H in FIG. 10), and enters the high-stage compressor 51. enter.

The gas refrigerant compressed by the high-stage compressor 51 (point J in FIG. 10) is cooled by the gas cooler 52 and slightly subcooled (point K in FIG. 10).
Most of the refrigerant that has flowed out of the gas cooler 52 passes through the high-pressure side of the intercooler 54, further increases supercooling (point M in FIG. 10), and flows into the low-stage first flow rate adjustment valve 56. .

The supercooled liquid refrigerant that has flowed into the low-stage-side first flow rate adjustment valve 56 is decompressed and becomes a gas-liquid two-phase refrigerant (point Q in FIG. 10).
This low-temperature and low-pressure gas-liquid two-phase refrigerant flows into the low-stage evaporator 58.
In the low-stage evaporator 58, the refrigerant exchanges heat with a fluid (for example, air) and evaporates to become a high-temperature and low-pressure gas-phase refrigerant.
At this time, the space to be cooled is cooled in the low-stage cooling unit 59.
The low-pressure gas-phase refrigerant (point F in FIG. 10) that has flowed out of the low-stage evaporator 58 is again sucked into the low-stage compressor 55.

On the other hand, the refrigerant branched on the outlet side of the gas cooler 52 becomes a refrigerant (N point in FIG. 10) whose pressure is reduced to the intermediate pressure by the intermediate cooling flow rate adjustment valve 53. The intermediate pressure refrigerant flows into the intermediate pressure side of the intermediate cooler 54.
The refrigerant that has flowed into the intermediate pressure side of the intermediate cooler 54 exchanges heat with the refrigerant that flows through the high pressure side of the intermediate cooler 54, and excessively passes high pressure gas (point K in FIG. 10) toward the low-stage first electromagnetic valve 57. Increase the degree of cooling (point M in FIG. 10).
The intermediate pressure side of the intermediate cooler 54 is in a state where the refrigerant liquid and the steam coexist, but from here the steam (point H in FIG. 10) close to the saturated state is sucked into the high stage compressor 51.

Next, the control operation of the low-stage second electromagnetic valve 62 communicating with the expansion tank 63 will be described.
The same technical idea as the control operation of the low temperature side second electromagnetic valve 17 in the first embodiment described above can be applied to the control operation of the low stage side second electromagnetic valve 62.

FIG. 11 is a flowchart for explaining the operation of the refrigeration apparatus in Embodiment 5 of the present invention.
Hereinafter, a description will be given based on each step of FIG.

(S11)
The controller 66 uses the discharge pressure of the low-stage compressor 55 detected by the low-stage high pressure sensor 64 and the low-stage low-pressure sensor 65 when the low-stage compressor 55 is stopped. The detected pressure on the suction side of the low stage compressor 55 is acquired.
Then, it is determined whether at least one of the suction-side pressure and the discharge-side pressure of the low-stage compressor 55 is equal to or higher than a preset pressure value P1.
If at least one of the suction-side pressure and the discharge-side pressure of the low-stage compressor 55 is not greater than or equal to the preset pressure value P1, step S11 is repeated.

Here, the pressure value P1 is set according to the design pressure of the circulation circuit, for example. For example, when the design pressure is 4.15 MPa, the pressure is set to 4 MPa in consideration of the measurement error of the sensor and the operation time of the solenoid valve.
The pressure value P1 corresponds to the “first pressure value” in the present invention.

(S12)
When at least one of the suction-side pressure and the discharge-side pressure of the low-stage compressor 55 is equal to or higher than a preset pressure value P1, the controller 66 opens the low-stage second electromagnetic valve 62.
As a result, the refrigerant in the circulation circuit flows into the expansion tanks 63a, 63b, and 63c. That is, the circuit volume of the circulation circuit increases and the pressure of the refrigerant decreases.

(S13)
The controller 66 determines whether the suction-side pressure or the discharge-side pressure of the low-stage compressor 55 is equal to or less than a preset pressure value P2.
When the suction-side pressure or the discharge-side pressure of the low-stage compressor 55 is not less than or equal to the preset pressure value P2, the process returns to step S12 and the open state of the low-stage second electromagnetic valve 62 is maintained.
Here, the pressure value P2 is set to a value lower than the pressure value P1.
The pressure value P2 corresponds to the “second pressure value” in the present invention.

(S14)
When the suction-side pressure or the discharge-side pressure of the low-stage compressor 55 is equal to or lower than the preset pressure value P2, the controller 66 closes the low-stage second electromagnetic valve 62 and proceeds to step S11. Return.
As described above, when the pressure of the refrigerant decreases, the low-stage second electromagnetic valve 62 is closed to stop the inflow of the refrigerant into the expansion tank 63. Thus, the refrigerant can be collected in a short time when the low-stage compressor 55 is restarted.

Note that the power supply to the refrigeration apparatus may be stopped for a long time due to, for example, a power failure.
The low-stage second electromagnetic valve 62 in the fifth embodiment is an electromagnetic valve that is closed when energized. For this reason, even when the low-stage compressor 55 is stopped due to a power failure or the like, the low-stage second electromagnetic valve 62 is opened, the circuit volume of the circulation circuit increases, and the refrigerant pressure decreases. To do.

(When the low-stage compressor 55 is restarted)
When the low-stage compressor 55 is restarted, the controller 66 opens the low-stage second electromagnetic valve 62 for a preset time.
That is, when the low-stage compressor 55 is started, the low-stage second electromagnetic valve 62 is opened, and after the preset time has elapsed, the low-stage second electromagnetic valve 62 is closed.
Thereby, the refrigerant in the expansion tank 63 can be recovered in the circulation circuit.

  In addition, the operation | movement of step S13 and S14 mentioned above may be abbreviate | omitted, and the low stage 2nd solenoid valve 62 may be maintained in an open state. The low-stage second electromagnetic valve 62 may be closed after a preset time has elapsed since the low-stage compressor 55 was restarted.

As described above, the fifth embodiment includes the expansion tank 63 connected to the pipe between the low-stage evaporator 58 and the low-stage compressor 55 via the low-stage second electromagnetic valve 62. ing.
For this reason, it is possible to suppress an increase in refrigerant pressure in the circulation circuit when the low-stage compressor 55 of the circulation circuit is stopped.
Moreover, the design pressure of the circulation circuit can be lowered. Therefore, the manufacturing cost of each member which comprises the low temperature side circulation circuit B can be reduced.

  In addition, since the low-stage second electromagnetic valve 62 is an electromagnetic valve that is closed when energized, even if the power supply to the refrigeration apparatus is stopped for a long time due to a power failure or the like, the refrigerant pressure in the circulation circuit The rise can be suppressed.

  DESCRIPTION OF SYMBOLS 1 High temperature side compressor, 2 High temperature side condenser, 3 High temperature side expansion valve, 4 High temperature side evaporator, 5 Low temperature side compressor, 6 Auxiliary capacitor, 7 Low temperature side condenser, 8 Cascade capacitor, 9 Receiver, 10 Low temperature side flow control valve, 11 Low temperature side first solenoid valve, 12 Low temperature side evaporator, 13 Cooling unit, 14 Outdoor unit, 15 liquid piping, 16 gas piping, 17 Low temperature side second electromagnetic valve, 18a Expansion tank, 18b Expansion Tank, 18c Expansion tank, 19 High temperature side casing, 20 Low temperature side casing, 21 Common mount, 22 High temperature side blower, 23 Low temperature side blower, 24 High temperature side controller, 26 Low temperature side controller, 27 Low temperature side high pressure sensor 28 Low temperature side low pressure sensor, 30 Expansion tank unit mount, 31 Expansion tank unit housing, 31b Support, 31c Support, 32 Piping, 32a piping, 32b piping, 32c piping, 33 piping, 33a piping, 33b piping, 33c piping, 34 piping, 34a piping, 34b piping, 34c piping, 35 expansion tank mount, 36 piping, 36a piping, 36b piping, 36c Piping, 51 High-stage compressor, 52 Gas cooler, 53 Intermediate cooling flow adjustment valve, 54 Intermediate cooler, 55 Low-stage compressor, 56 Low-stage first flow adjustment valve, 57 Low-stage first solenoid valve 58 Low stage evaporator, 59 Low stage cooling unit, 60 Low stage liquid piping, 61 Low stage gas piping, 62 Low stage second solenoid valve, 63 Expansion tank, 63a Expansion tank, 63b Expansion tank, 63c Expansion tank, 64 Low stage high pressure sensor, 65 Low stage low pressure sensor, 66 Controller, A High temperature side circulation circuit, B Low temperature side circulation circuit .

The refrigeration apparatus according to the present invention includes a first circulation circuit in which a first compressor, a first condenser, a first expansion device, and a first evaporator are sequentially connected by piping to circulate a refrigerant, a second compressor, 2 condenser, a 2nd expansion device, and a 2nd evaporator are connected by piping one by one, and it comprises the 2nd circulation circuit through which a refrigerant circulates, the 1st evaporator and the 2nd condenser, and the 1st evaporation A plurality of cascade condensers that exchange heat between the refrigerant flowing through the condenser and the refrigerant flowing through the second condenser, and a pipe between the second evaporator and the second compressor via an on-off valve. An expansion tank; and a control unit that controls the on-off valve , the first compressor, the first condenser, the first throttling device, the first evaporator, the second compressor, and the first The two condensers are mounted on an outdoor unit, and the plurality of expansion tanks are expanded tank units. Is mounted, wherein, when the second compressor is stopped, at least one of the pressure of the pressure and the discharge side of the suction side of the second compressor, when the above first pressure value, the When the on-off valve is opened, and the suction-side pressure and the discharge-side pressure of the second compressor are equal to or lower than the second pressure value, which is lower than the first pressure value, the on-off valve is closed; When the second compressor is restarted, the on-off valve is opened for a preset time .

Claims (15)

A first circulation circuit in which a first compressor, a first condenser, a first throttling device, and a first evaporator are sequentially connected by piping and the refrigerant circulates;
A second compressor, a second condenser, a second expansion device, and a second evaporator are sequentially connected by piping, and a second circulation circuit in which the refrigerant circulates;
A cascade condenser composed of the first evaporator and the second condenser, wherein the refrigerant flowing through the first evaporator and the refrigerant flowing through the second condenser exchange heat;
A plurality of expansion tanks connected to a pipe between the second evaporator and the second compressor via an on-off valve;
The first compressor, the first condenser, the first throttling device, the first evaporator, the second compressor, and the second condenser are mounted on an outdoor unit,
The refrigeration apparatus, wherein the plurality of expansion tanks are mounted on an expansion tank unit. The expansion tank unit is arranged with a space beside the outdoor unit,
The refrigeration apparatus according to claim 1, wherein the plurality of expansion tanks are mounted on the expansion tank unit side by side in the vertical direction. The expansion tank unit is disposed adjacent to and below the outdoor unit;
The refrigeration apparatus according to claim 1, wherein the plurality of expansion tanks are mounted on the expansion tank unit side by side in the horizontal direction. 3. The refrigeration according to claim 1, wherein ends of the pipes connected to the plurality of expansion tanks and the on-off valves on the side of the plurality of expansion tanks are connected to lower portions of the plurality of expansion tanks. apparatus. Ends on the side of the plurality of expansion tanks of pipes connected to the plurality of expansion tanks and the on-off valves are inserted from the top of the plurality of expansion tanks and arranged at the bottom of the plurality of expansion tanks. The refrigeration apparatus according to claim 1 or 2, characterized in that: A control unit for controlling the on-off valve;
The controller is
When at least one of the suction side pressure and the discharge side pressure of the second compressor is equal to or higher than the first pressure value when the second compressor is stopped, the on-off valve is opened. The refrigeration apparatus according to any one of claims 1 to 5, wherein: The controller is
The on-off valve is closed when a suction-side pressure and a discharge-side pressure of the second compressor are equal to or lower than a second pressure value that is lower than the first pressure value. 6. The refrigeration apparatus according to 6. The controller is
The refrigerating apparatus according to claim 6 or 7, wherein the on-off valve is opened for a preset time when the second compressor is restarted. The refrigeration apparatus according to any one of claims 1 to 8, wherein the on-off valve is an electromagnetic valve that is closed when energized. The refrigerating apparatus according to any one of claims 1 to 9, wherein the refrigerant circulating in the second circulation circuit is carbon dioxide. The refrigerant circulating in the second circulation circuit is carbon dioxide,
The diameter of the pipe between the second evaporator and the second compressor is
The refrigeration apparatus according to any one of claims 1 to 9, wherein the refrigeration apparatus has the same diameter as a pipe when HFC is used as a refrigerant circulating in the second circulation circuit. A circulation circuit in which a first stage compressor, a second stage compressor, a radiator, a throttling device, and an evaporator are sequentially connected by piping, and the refrigerant circulates;
An intermediate pressure circuit that branches the outlet side of the radiator, depressurizes the refrigerant, and supplies the refrigerant between the first stage compressor and the second stage compressor;
A refrigerating apparatus comprising: an expansion tank connected to a pipe between the evaporator and the second stage compressor via an on-off valve. A control unit for controlling the on-off valve;
The controller is
When at least one of the suction side pressure and the discharge side pressure of the second stage compressor is equal to or higher than the first pressure value when the second stage compressor is stopped, the on-off valve is opened. The refrigeration apparatus according to claim 12, wherein: The controller is
The on-off valve is closed when a suction-side pressure and a discharge-side pressure of the second-stage compressor are equal to or lower than a second pressure value that is lower than the first pressure value. Item 14. A refrigeration apparatus according to item 13. The controller is
The refrigerating apparatus according to claim 13 or 14, wherein the on-off valve is opened for a preset time when the second stage compressor is restarted.

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