JP3082560B2 - Dual cooling system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual cooling device,
More specifically, the present invention relates to a dual cooling device that can reduce the time required for a defrost operation performed by a low-temperature unit provided inside a refrigerator.

[0002]

2. Description of the Related Art A plurality of low-temperature units and one high-temperature unit are cascade-connected by a cascade condenser, and the latent heat of condensation generated at the low-temperature unit and the latent heat of evaporation at the high-temperature unit are converted into heat. The cascade freeze multi that is replaced is commonly used because it is easy to obtain a low temperature under a simple structure, and frost often occurs because the evaporator of the low-temperature side unit has a low evaporation temperature of -70 ° C etc. It is known that defrosting needs to be performed repeatedly in order to do so.

As a technique for performing defrost in a dual cooling device, there is a prior art disclosed in, for example, Japanese Patent Application Laid-Open No. 2-192559. In this prior art, a low-temperature side unit of a dual cooling device is defrosted by using a hot gas of a refrigeration cycle of the unit itself by a hot gas bypass method.

[0004]

According to this prior art, when frost grows and defrosting is required, defrosting is performed by a hot gas bypass system, and high-temperature gas is supplied to a high-temperature side heat-absorbing side passage in the cascade condenser. It is said that by flowing a refrigerant to form a gas-filled state in which no liquid is stored on the low temperature side, it is possible to prevent a decrease in the amount of hot gas. However, in this case, when the defrost cycle arrives or a defrost command is issued, the defrost is performed based on the command regardless of the operation state before the defrost. This does not cause a problem in normal refrigeration operation, but immediately before defrost, the internal temperature is low, and the dual cooling device is operated in a state where the pressure difference is small at the intermediate pressure, that is, in a state where the compression ratio is small. In particular, when the outside air temperature is low, this operation state is often performed, so when switching to the defrost operation, the defrost capacity is reduced, and as a result, the defrost time becomes longer. There is.

[0005] An object of the present invention is to provide a dual refrigeration system of this type by positively increasing the pressure and temperature of the refrigerant in the low-temperature side unit without being affected by the operation state immediately before defrost. It is intended to reduce the time required for defrosting by causing the refrigerant to store heat and then performing defrosting.

[0006]

SUMMARY OF THE INVENTION The present invention provides a compressor 13,
A high-temperature side unit 1 including a series refrigerant circuit including a condenser 14 and a low-pressure refrigerant that forms a refrigeration cycle including a compressor 3n, a cascade condenser 4n, a decompressor 5n, and an evaporator 6n and is a cooling-side path of the cascade condenser 4n The coil 40n includes at least one low-temperature unit 2n connected in parallel to the series refrigerant circuit of the high-temperature unit 1 via the expansion valve 10n in series, and each low-temperature unit 2n has its own A binary cooling device provided with a defrost means 7n for defrosting the evaporator 6n by a refrigerant of a refrigeration cycle, wherein the defrost means 7n
Prior to the defrosting by the low-pressure refrigerant coil 40 of the cascade condenser 4n in the corresponding low-temperature side unit 2n
n, which shuts off the supply of the refrigerant from the high-temperature side unit 1 to the n.
The low-temperature unit 2n is provided with defrost starting means 35n for operating the defrost means 7n in response to the temperature or pressure of the high-pressure refrigerant of the low-temperature unit 2n rising to the constant value. It is a former cooling device.

According to the present invention, the defrost means 7n supplies the discharge gas from the compressor 3n to the cascade condenser 4n.
This is a dual cooling device that performs hot gas bypass leading to the evaporator 6n by bypassing the high-pressure refrigerant coil 41A and the pressure reducer 5n.

According to the present invention, the defrost means 7n converts the gas discharged from the compressor 3n from the evaporator 6n to the decompressor 5n.
Through the high-pressure refrigerant coil 41 of the cascade condenser 4n
This is a binary cooling device that performs a reverse refrigeration cycle led to A.

According to the present invention, the defrost means 7n supplies the gas discharged from the compressor 3n to the cascade condenser 4n.
From the high-pressure refrigerant coil 41A through the pressure reducer 5n to the evaporator 6
This is a binary cooling device that performs a normal refrigeration cycle led to n.

[0010]

According to the present invention, each low-temperature side unit 2n is provided with the refrigerant shut-off means 9n and the defrost starting means 35n in relation to the defrost means 7n. Refrigerant shut-off means 9n
Prior to the start of defrosting, the supply of the refrigerant from the high temperature side unit 1 to the low pressure refrigerant coil 40n of the cascade condenser 4n is shut off. Since the supply of the low-pressure refrigerant is cut off, heat exchange between the high-pressure and low-pressure refrigerant in the cascade condenser 4n is not performed, and the pressure and temperature of the high-pressure refrigerant in the refrigeration cycle of the low-temperature unit 2n increase. Then, heat storage is performed. When this pressure or temperature rises to the constant value, the defrost starting means 35n operates, and defrosting by the defrost means 7n is started. As a result, the defrost of the evaporator 6n is performed with a sufficient amount of the refrigerant circulated by the high-temperature refrigerant that has been sufficiently stored and gasified, so that the defrost is completed in a short time.

According to the present invention, the defrost means 7n performs hot gas bypass. In the hot gas bypass system, control valves such as a four-way switching valve 7n are provided in association with the discharge side and the suction side of the compressor 3n, the high-pressure refrigerant coil 41A of the cascade condenser 4n, the evaporator 6n, and the resistance pipe. It is possible to adopt a configuration in which a bypass circuit is provided. In the present invention, the defrost means 7n performs a reverse refrigeration cycle or a normal refrigeration cycle. As the reverse refrigeration cycle system, the four-way switching valve 7n
It is possible to adopt a configuration in which a control valve is provided, and as a normal refrigeration cycle system, it is possible to adopt a configuration in which the degree of decompression of the decompressor 5n is reduced. In each case, a simple structure and a simple Switching between cooling and defrosting can be performed by the operation.

[0012]

FIG. 1 is a refrigeration circuit diagram according to a first embodiment of the present invention. The illustrated embodiment includes an outdoor unit 1 which is one high-temperature side unit installed outdoors or in a machine room;
Indoor units 2A, 2B,..., Which are a plurality of low-temperature units installed inside a freezer or the like. The outdoor unit 1 includes a compressor 13, a condenser 14, an accumulator 17, and a receiver 18 as main devices, and a serial refrigerant circuit is formed by the receiver 18, the condenser 14, the compressor 13, and the accumulator 17. ,
This series refrigerant circuit is composed of a high-pressure liquid line 25 and a low-pressure gas line 26.
Are connected in series. In addition, a bypass pipeline provided by connecting the solenoid valve 19 and the capillary tube 16 in series is connected in parallel to the series refrigerant circuit.

As the compressor 13, for example, a scroll compressor is used. The discharge port and the intermediate pressure port inside the cylinder are connected by a resistance line having a capillary tube 20, and the intermediate pressure port and the suction port are unloaded. They are connected by a bypass line having an electromagnetic valve 21. On the other hand, a discharge port of the compressor 13 and a refrigerant inlet of the accumulator 17 are connected by a pipe having a constant-pressure expansion valve 22, and a discharge port and a suction port of the compressor 13 are connected by a pipe having an electromagnetic valve 23. Connected.

The compressor 13 operates at a rated output by closing the unload solenoid valve 21 and operates at a low output by opening the solenoid valve 21.
The output is adjusted in accordance with the total operation cooling capacity of B,. In addition, the outdoor unit 1 controls the pressure of the suction gas pipe of the compressor 13 to be constant by the valve opening adjustment operation of the constant pressure expansion valve 22, depressurizes the liquid refrigerant with the capillary tube 16, and draws the suction of the compressor 13. The gas temperature is controlled to be constant.

Since the indoor units 2A, 2B,... Have the same configuration of the refrigeration circuit, the indoor unit 2A will be described below. Items common to each unit are "A",
In some cases, "n" is added instead of "B". The indoor unit 2A includes a compressor 3A, a four-way switching valve 7A, a cascade condenser 4A, and a decompressor 5 realized by a temperature-sensitive expansion valve.
A, an evaporator 6A and a compressor accumulator 8A are provided, a discharge port of the compressor 3A, a four-way switching valve 7A, a high-pressure refrigerant coil 41A of a cascade condenser 4A, and a decompressor 5
A, evaporator 6A, compressor accumulator 8A, compressor 3
A well-known refrigeration cycle is constituted by the inlet of A.

As the compressor 3A, for example, a rotary compressor is used, and the discharge port has a four-way switching valve 7A through a gas line.
And connected to the refrigerant inlet of the compressor accumulator 8A via the solenoid valve 30A and the capillary tube 29A in series. The compressor 3A has a high-pressure refrigerant coil 41 through an intermediate pressure port provided with a capillary tube 11A and a solenoid valve 12A in series.
A is connected to the refrigerant liquid side end. The four-way switching valve 7A has a low-pressure side port connected to the refrigerant inlet of the compressor accumulator 8A by a gas line having a check valve 24, and one switching port communicating with the high-pressure side port during the cooling operation has a gas switching port. The high-pressure refrigerant coil 41A is connected to the refrigerant gas flow side end of the high-pressure refrigerant coil 41A by a conduit.

The indoor unit 2A is further provided with a hot gas bypass circuit. This hot gas bypass circuit includes a check valve 27A, a capillary tube 28A,
A refrigerant circuit in which a drain pan heater 15A is connected in series by a pipe line, and when the four-way switching valve 7A performs a defrost operation, the other switching port communicating with the high pressure side port and the low pressure fluid of the pressure reducing device 5A It is connected across the flow end.

The cascade condenser 4A includes a high-pressure refrigerant coil 41A into which a high-temperature and high-pressure refrigerant gas discharged from the compressor 3A is introduced during a cooling operation, and a low-pressure refrigerant as a cooling-side passage through which the low-pressure refrigerant in the outdoor unit 1 is introduced. Coil 40
A is formed by a heat exchanger provided so as to be able to exchange heat. An expansion valve 10A realized by a temperature-sensitive expansion valve is connected in series to the low-pressure refrigerant coil 40A to form a serial refrigerant circuit. This series refrigerant circuit is connected in series between the low-pressure gas line 26 and the high-pressure liquid line 25. With such a refrigerant circuit configuration, the compressor 13 and the condenser 1
4, high-pressure liquid line 25, expansion valve 10A, low-pressure refrigerant coil 40A of cascade condenser 4A, low-pressure gas line 26,
A refrigerant cycle including the accumulator 17 is formed.

On the other hand, the temperature-sensitive expansion valve 10A is provided with a three-way valve 9A realized by a three-way solenoid valve. The three-way solenoid valve 9A has a pressure port, a first switching port that communicates with the pressure port when the electromagnetic coil is de-energized (off), and a second switching port that communicates with the pressure port when energized (on).
A pressure port connected to a pressure equalizing chamber acting on a valve of the temperature-sensitive expansion valve 10A;
The switching port is branched and connected to a low-pressure gas pipe attached to the temperature-sensitive cylinder 39A of the temperature-sensitive expansion valve 10A, and the second switching port is branched to a high-pressure liquid pipe connected to the inlet of the temperature-sensitive expansion valve 10A. Connected. By turning off the three-way solenoid valve 9A connected in this manner, the temperature-sensitive expansion valve 10A is maintained in the pressure-equalizing operation state, so that the normal pressure-reducing expansion function is exhibited, and the three-way solenoid valve 9A is turned on. As a result, a high pressure is applied to the pressure equalizing chamber, the valve is forcibly closed, and the pressure equalizing chamber operates as a refrigerant shutoff unit.

When the compressor 3A is driven, the indoor unit 2A exchanges heat between the high-temperature and high-pressure gas refrigerant discharged from the compressor 3A and the low-pressure refrigerant guided into the low-pressure refrigerant coil 40A in the cascade condenser 4A. After being condensed and liquefied, the pressure is reduced by the temperature-sensitive expansion valve 5A and becomes a low-pressure low-temperature liquid refrigerant, which is guided to the evaporator 6A. And evaporator 6A
Then, the refrigerant evaporates by exchanging heat with the air in the refrigerator circulated and blown by the evaporator fan 31A, becomes a low-pressure gas refrigerant, and is sucked into the compressor 3A via the accumulator 8A. As described above, the cooling operation for cooling the inside air is performed by performing the circulation accompanied by the condensation and evaporation of the refrigerant. During the cooling operation, the four-way switching valve 7A is in the valve switching state shown by the solid line in FIG. 1, the solenoid valve 12A is opened, and the three-way solenoid valve 9A is opened.
Is turned off. The flow state of the refrigerant is indicated by solid arrows.

On the other hand, in the outdoor unit 1, when the compressor 13 is driven, the high-temperature and high-pressure gas refrigerant discharged from the compressor 13 is exchanged with the outside air circulated and blown by the condenser fan 32 in the condenser 14. After being exchanged and condensed and liquefied, the pressure is reduced by the temperature-sensitive expansion valve 10A through the receiver 18 and the high-pressure liquid line 25 to become a low-pressure low-temperature liquid refrigerant, which is guided to the low-pressure refrigerant coil 40A, and the high-temperature high-pressure The refrigerant exchanges heat with the gas refrigerant and evaporates to become a low-pressure gas refrigerant, which passes through the low-pressure gas line 26 and the accumulator 17 to reach the compressor 1.
Inhaled in 3. In this way, by performing the circulation accompanied by the condensation and evaporation of the refrigerant, each of the indoor units 2A, 2B,
, And a refrigeration operation is performed in which the latent heat of condensation generated in ... is released to the outdoors using a refrigerant as a medium. In this case, the temperature-sensitive expansion valve 10A
The valve opening is adjusted by the low-pressure gas refrigerant temperature detected by the temperature-sensitive cylinder 39A to control the degree of superheat constant. The flow of the refrigerant is as shown by the solid line arrow.

In the first embodiment shown in FIG. 1, the outdoor unit 1 is provided with a high-voltage protection pressure switch 33 and a low-pressure control pressure switch 34 as control members, and the indoor unit 2A is provided with a defroster. A start high-pressure switch 35, a high-pressure protection pressure switch 36, a hot gas bypass high-pressure switch 37, and a defrost ending high-pressure switch 38 are provided as control members.

FIG. 2 is a flow chart showing the mode of operation control in the first embodiment shown in FIG. In the first embodiment, each of the indoor units 2A, 2B,... Individually performs the cooling operation and the defrost operation, and some or all of the indoor units 2A, 2B,... May perform the cooling operation, and some may perform the defrost operation. The output is adjusted on the outdoor unit 1 side according to the operation state at that time, and the indoor units 2A, 2B,
The individual capacity control is performed by controlling the opening degree of the expansion valves 10A, 10B,. For example, outdoor unit 2A
When the cooling operation is being performed in step m1 and frost is formed on the evaporator 6A, the process proceeds to step m2, and the necessity of starting defrost is checked by a frost detector or a defrost timer (not shown). Then, when the defrost start command is output, the flow proceeds to the next step m3 to operate the refrigerant shut-off means. This refrigerant shut-off means is performed as follows. That is, the three-way solenoid valve 9A
Is supplied with an ON output for energizing the electromagnetic coil. Since the three-way solenoid valve 9A applies a high pressure on the inlet side of the expansion valve 10A to the pressure equalizing chamber of the temperature-sensitive expansion valve 10A by being turned on, the temperature-sensitive expansion valve 10A is forcibly closed. With this valve closing, the cascade condenser 4A becomes
Since the supply of the low-pressure low-temperature liquid refrigerant to the low-pressure refrigerant coil 40A is cut off, the condensing pressure increases. About 10 seconds after the closing of the temperature-sensitive expansion valve 10A, the defrost starting means realized by the high-pressure switch 35 in step m4, for example, at a pressure of 11 kg / c
Detects m ² · G and operates to output a defrost start command. With the operation of the defrost starting means, the process proceeds to the next step m5, and the indoor unit 2A performs the defrost operation. In this case, the defrost operation is performed by stopping the evaporator fan 31A and setting the four-way switching valve 7A to the valve switching state indicated by the broken line, and the refrigerant flows as indicated by the broken arrow. The hot gas exiting the compressor 3A is supplied to the check valve 27.
A, capillary tube 28A, drain pan heater 15
A through the hot gas bypass circuit made of evaporator 6A
After flowing through the coil and exchanging heat with the frost adhering to the coil to perform defrost, via the accumulator 8A,
It is led to the compressor 3A.

On the other hand, the refrigerant present in the high-pressure refrigerant coil 41A of the cascade condenser 4A and in the pipeline connected to the inlet side of the temperature-sensitive expansion valve 5A is in a state of a high-pressure gas stored as the condensing pressure increases. After being filled and passing through the four-way switching valve 7A and the check valve 24A due to the pressure difference, the refrigerant merges with the refrigerant that has passed through the evaporator 6A and is sucked into the compressor 3A through the accumulator 8A. As a result, defrost is quickly performed by the refrigerant of the low-temperature side refrigeration cycle that has been sufficiently stored. In this case, since the refrigerant exists in a gaseous state on the high-temperature refrigerant coil 41A side, the circulation amount of the refrigerant necessary for defrost is sufficiently ensured.

In the state where the defrost operation is being performed, the end of the defrost is checked in step m6, and a defrost end command is output in accordance with the operation of the high pressure switch 38. Is returned to.

In the embodiment shown in FIG. 1, the refrigerant pressure is detected by using a high pressure switch 35 as the defrost starting means. The defrost starting means utilizes the temperature or time of the refrigerant. For example, in the case of the temperature of the refrigerant, the temperature of the discharge pipe may be detected and the defrost may be started by increasing the temperature from 60 ° C. to 80 ° C. in the normal cooling operation, On the other hand, in the case of time, the low-pressure refrigerant coil 4
The time from when the supply of refrigerant to 0n is cut off may be detected by a timer, and the defrost may be started when 10 to 20 seconds have elapsed. These modifications are also included in the scope of the present invention. You.

FIG. 3 shows a refrigeration circuit of an indoor unit 2A according to a second embodiment of the present invention. This second embodiment is similar to the first embodiment shown in FIG. 1, and corresponding members have the same reference numerals. What should be noted in the second embodiment is that a two-way valve 42A is used instead of the three-way solenoid valve 9A in the first embodiment. The two-way valve 42A uses a general-purpose solenoid valve 42A, and is provided in the refrigerant line in series with the temperature-sensitive expansion valve 10A. Then, the same function as the three-way solenoid valve 9A can be exhibited by opening the solenoid valve 42A in the off operation during the normal cooling operation and closing it in the on operation during the defrost operation. Since the outdoor unit 1 has the same structure as that of the first embodiment, the illustration is omitted.

Although not shown, an electric expansion valve may be used instead of connecting the temperature-sensitive expansion valve 10A and the solenoid valve 42A in series. The same function as in the first and second embodiments can be exhibited by adjusting the temperature in accordance with the evaporation temperature and forcibly closing the valve during the defrost operation.

FIG. 4 shows a refrigeration circuit of an indoor unit 2A according to a third embodiment of the present invention. This third embodiment is similar to the first embodiment shown in FIG. With the same reference numbers. It should be noted in the third embodiment that the defrost operation in the indoor unit 2A is performed by the reverse refrigeration cycle. Indoor unit 2
A, a capillary tube 43 for defrost is provided in series with the temperature-sensitive expansion valve 5A in the high-pressure liquid pipe, a check valve 44 is connected in parallel to the capillary tube 43, and the temperature-sensitive expansion A check valve 45 is provided in parallel with the valve 5A. Furthermore, drain pan heater 15
A check valve 46 is connected in series with A, and a check valve 47 is connected in parallel to a series refrigerant circuit of the drain pan heater 15A and the check valve 46.

In the third embodiment, during the cooling operation, the refrigerant flows as indicated by the solid line arrow in FIG. 4, while during the defrost operation, the refrigerant flows as indicated by the broken line arrow and defrosting is performed by the reverse refrigeration cycle. The point that the defrost operation is performed by storing heat in the refrigerant is the same as in the first embodiment. Note that the outdoor unit 1 has the same structure as that of the first embodiment and is not shown.

FIG. 5 shows a refrigeration circuit of an indoor unit 2A according to a fourth embodiment of the present invention. This fourth embodiment is similar to the first embodiment shown in FIG. 1 and corresponding members are denoted by the same reference numerals. In the illustrated fourth embodiment, the indoor unit 2A is provided with a solenoid valve 48 with respect to the temperature-sensitive expansion valve 5A.
It is noted that the refrigerant pipes provided by connecting the refrigerant tube 43 and the defrost capillary tube 43 in series have a circuit structure connected in parallel. In the fourth embodiment, during the cooling operation, the refrigerant flows as indicated by the solid line arrow in FIG. 5, while during the defrost operation, the refrigerant flows as indicated by the broken arrow and defrost is performed by the normal refrigeration cycle. As in the example, a defrost operation is performed by storing heat in the refrigerant.

[0032]

As described above, according to the present invention, the supply of refrigerant to the low-pressure refrigerant coil 40n of the cascade condenser 4n is cut off when performing defrosting in the dual cooling device, and the low-temperature side unit 2n By starting the defrost after the refrigerant pressure has been increased and the heat has been sufficiently stored, the defrost operation can be performed with the high-temperature refrigerant, so that it is affected by the state of the cooling operation immediately before the defrost. In addition, sufficient defrosting ability can be ensured to shorten the defrosting time. Further, in the invention of claim 2, the refrigerant can be prevented from staying in the high-pressure refrigerant coil 41n of the cascade condenser 4n at the time of defrosting, and the defrost time can be shortened by increasing the refrigerant circulation amount.

[Brief description of the drawings]

FIG. 1 is a refrigeration circuit diagram of a two-way cooling device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a mode of operation control according to the first embodiment shown in FIG. 1;

FIG. 3 is a refrigeration circuit diagram of an indoor unit 2A of a dual cooling device according to a second embodiment of the present invention.

FIG. 4 is a refrigeration circuit diagram of an indoor unit 2A of a dual cooling device according to a third embodiment of the present invention.

FIG. 5 is a refrigeration circuit diagram of an indoor unit 2A of a dual cooling device according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High-temperature side unit 2A, B, n Low-temperature side unit 3A, B, n Compressor 4A, B, n Cascade condenser 5A, B, n Pressure reducer 6A, B, n Evaporator 7A, B, n Four-way switching valve 9A , B, n Three-way valve 10A, B, n Expansion valve 13 Compressor 14 Condenser 15A, B, n Drain pan heater 27A, B, n Check valve 28A, B, n Capillary tube 35A, B, n High pressure switch 40A, B, n Solenoid valve 41A, B, n Capillary tube for defrost

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-192559 (JP, A) JP-A-4-369368 (JP, A) Fully open sho 51-83851 (JP, U) Really open sho 51- 106349 (JP, U) Japanese Utility Model Showa 64-19877 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F25B 47/02 570 F25B 7/00

Claims (4)

(57) [Claims] 1. A refrigeration cycle including a high-temperature side unit 1 including a series refrigerant circuit including a compressor 13 and a condenser 14, a compressor 3n, a cascade condenser 4n, a decompressor 5n, and an evaporator 6n is formed. The low pressure refrigerant coil 40n, which is a 4n cooling side path, is provided with an expansion valve 10n.
And at least one low-temperature unit 2n connected in parallel to the series refrigerant circuit of the high-temperature unit 1 through the respective series, and each low-temperature unit 2n is evaporated by the refrigerant of its own refrigeration cycle. A defrosting means 7n for defrosting the vessel 6n, which is provided to the low-pressure refrigerant coil 40n of the cascade condenser 4n in the corresponding low-temperature side unit 2n prior to the defrosting by the defrosting means 7n. A coolant shut-off means 9n for shutting off the supply of the refrigerant from the high-temperature side unit 1; and, according to the temperature or pressure of the high-pressure refrigerant of the low-temperature side unit 2n rising to the constant value after the operation of the coolant cut-off means 9n. And a defrost starting means 35n for operating the defrost means 7n is provided in each low-temperature side unit 2n. Apparatus. 2. A defrost means 7n performs a hot gas bypass that guides the discharge gas from the compressor 3n to the evaporator 6n by bypassing the high-pressure refrigerant coil 41A of the cascade condenser 4n and the decompressor 5n. The dual cooling device according to claim 1, wherein 3. A reverse refrigeration cycle in which the defrost means 7n guides the discharge gas from the compressor 3n from the evaporator 6n to the high-pressure refrigerant coil 41A of the cascade condenser 4n via the decompressor 5n. Item 2. The dual cooling device according to Item 1. 4. A normal refrigeration cycle in which the defrost means 7n conducts a discharge gas from the compressor 3n from the high-pressure refrigerant coil 41A of the cascade condenser 4n to the evaporator 6n via the pressure reducer 5n. Item 2. The dual cooling device according to Item 1.