JPH07243726A - Two-stage cooler - Google Patents

Abstract

PURPOSE:To shorten a required time by storing beat in refrigerant of a refrigerating cycle of a low-temperature side unit of a two-stage cooler and then defrosting it. CONSTITUTION:A high-temperature side unit 1 is cascade connected to a low- temperature side unit 2n via a cascade condenser 4n to form a two-stage cooler. When an evaporator 6n is defrosted by hot gas of a refrigerating cycle of the unit 2n itself, refrigerant supply to a low-temperature refrigerant coil 40n of the condenser 4n is shut OFF by closing an expansion valve 10A thereby to enhance high-pressure side refrigerant pressure and temperature for thermal storing. Thereafter, a four-way switching valve 7n is switched, thereby defrosting with the hot gas.

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 in a low temperature unit provided inside a refrigerator.

[0002]

2. Description of the Related Art A plurality of low temperature side units and one high temperature side unit are cascade-connected by a cascade condenser to heat the condensation latent heat generated in the low temperature side unit and the evaporation latent heat in the high temperature side unit. The cascade freeze mulch that is exchanged is commonly used because it is easy to obtain a low temperature under a simple structure. In the evaporator of the low temperature side unit, the evaporation temperature is as low as -70 ° C and so frost frequently occurs. To do this, it is known that defrosting must be repeated.

There is a prior art disclosed in, for example, Japanese Patent Laid-Open No. 192559/1990 as a device for defrosting in a binary cooling device. In this prior art, in a low temperature side unit of a binary cooling device, a hot gas bypass system is used to defrost using hot gas of a refrigeration cycle of the unit itself.

[0004]

According to this prior art, when frost grows and defrosting becomes necessary, hot gas bypass system is used to perform defrosting, and high temperature gas is absorbed in the heat absorbing side passage on the high temperature side of the cascade condenser. It is said that it is possible to prevent a decrease in the amount of hot gas by causing a refrigerant to flow to form a gas-filled state in which the liquid is not accumulated on the low temperature side. However, in this case, when the defrost cycle comes or a defrost command is generated, the defrost is performed based on the command regardless of the operating state before the defrost. This does not cause a problem in normal refrigeration operation, but the temperature inside the refrigerator is low immediately before defrosting, and the binary cooling device operates in a state where the pressure difference at the intermediate pressure is small, that is, the compression ratio is small. Since it is often in this operating state especially when the outside air temperature is low, when switching to defrost operation, the defrost capacity decreases and as a result, the defrost time becomes longer. There is.

An object of the present invention is, in a binary cooling device of this type, by positively increasing the pressure and temperature of the refrigerant of the low temperature side unit without depending on the operating state immediately before defrosting, and thereby the refrigeration cycle. After the heat is stored in the refrigerant, the defrosting is performed to shorten the time required for the defrosting.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a compressor 13,
A high temperature side unit 1 including a series refrigerant circuit including a condenser 14, a compressor 3n, a cascade condenser 4n, a pressure reducer 5n, and an evaporator 6n to form a refrigeration cycle, and a low pressure refrigerant that is a cooling side path of the cascade condenser 4n. The coil 40n includes at least one low temperature side unit 2n connected in parallel to the series refrigerant circuit of the high temperature side unit 1 via the expansion valves 10n in series, and each low temperature side unit 2n has its own A dual cooling device provided with a defrosting means 7n for defrosting the evaporator 6n by the refrigerant of the refrigeration cycle, the defrosting 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.
the refrigerant cutoff means 9n for cutting off the supply of the refrigerant from the high temperature side unit 1 to the n, and after the operation of the refrigerant cutoff means 9n,
Each low temperature unit 2n is provided with a defrost starting means 35n which operates the defrost means 7n in response to the temperature or pressure of the high-pressure refrigerant of the low temperature side unit 2n rising to the constant value. It is a former cooling device.

According to the present invention, the defrosting means 7n is used to discharge the gas discharged from the compressor 3n into the cascade condenser 4n.
It is a dual cooling device that bypasses the high-pressure refrigerant coil 41A and the pressure reducer 5n to perform hot gas bypass leading to the evaporator 6n.

According to the present invention, the defrosting means 7n causes the gas discharged from the compressor 3n to flow from the evaporator 6n to the pressure reducer 5n.
Through the high pressure refrigerant coil 41 of the cascade condenser 4n
It is a two-way cooling device that performs a reverse refrigeration cycle led to A.

According to the present invention, the defrosting means 7n is used to discharge the gas discharged from the compressor 3n into the cascade condenser 4n.
From the high pressure refrigerant coil 41A to the evaporator 6 through the pressure reducer 5n.
It is a two-way cooling device that carries out a normal refrigeration cycle led to n.

[0010]

According to the present invention, each low temperature side unit 2n is provided with the refrigerant blocking means 9n and the defrost starting means 35n in association with the defrost means 7n. Refrigerant shutoff means 9n
Prior to the start of defrosting, the refrigerant supply from the high temperature side unit 1 to the low pressure refrigerant coil 40n of the cascade condenser 4n is cut off. Since the supply of the low-pressure refrigerant is cut off in this manner, heat exchange between the high-pressure and low-pressure refrigerant in the cascade condenser 4n is no longer performed, so that the pressure and temperature of the high-pressure refrigerant of the refrigeration cycle of the low-temperature unit 2n rise. Then the heat is stored. When the pressure or temperature rises to the constant value, the defrost starting means 35n is activated and the defrosting by the defrost means 7n is started. As a result, the defrosting of the evaporator 6n is performed after securing the circulation amount of the refrigerant by the high-temperature refrigerant that has sufficiently accumulated heat and is gasified, so that the defrosting is completed in a short time.

According to the present invention, the defrosting means 7n provides hot gas bypass. As this hot gas bypass system, a control valve such as a four-way switching valve 7n is 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, and the evaporator 6n, and the resistance pipeline. This is possible by providing a bypass circuit such as. Further, in the present invention, the defrosting means 7n performs a reverse refrigeration cycle or a normal refrigeration cycle. As the reverse refrigeration cycle system, the four-way switching valve 7n is used.
It is possible to adopt such a configuration that a control valve is provided. Further, as the normal refrigeration cycle method, it is possible to adopt a configuration in which the pressure reduction degree of the pressure reducer 5n is lowered, and in any case, a simple structure and a simple It is possible to switch between cooling and defrosting by operation.

[0012]

1 is a refrigeration circuit diagram according to a first embodiment of the present invention. In the illustrated embodiment, an outdoor unit 1 which is one high temperature unit installed outdoors or in a machine room,
It is provided with indoor units 2A, 2B, ... Which are a plurality of low temperature side units installed inside a refrigerator or the like. The outdoor unit 1 is provided with a compressor 13, a condenser 14, an accumulator 17, and a receiver 18 as main devices, and the receiver 18, the condenser 14, the compressor 13, and the accumulator 17 form a series refrigerant circuit. ,
This series refrigerant circuit includes a high pressure liquid line 25 and a low pressure gas line 26.
And 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 conduit provided with the capillary tube 20, and the intermediate pressure port and the suction port are unloaded. They are connected by a bypass line provided with a solenoid valve 21. On the other hand, the discharge port of the compressor 13 and the refrigerant inlet of the accumulator 17 are connected by a pipe line having a constant pressure expansion valve 22, and the discharge port and the suction port of the compressor 13 are connected by a pipe line having a solenoid 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, and the indoor units 2A, 2
The output level is adjusted according to the total cooling capacity of B, ... Further, in the outdoor unit 1, the pressure of the suction gas line of the compressor 13 is controlled to be constant by the valve opening adjusting action of the constant pressure expansion valve 22, the liquid refrigerant is decompressed by the capillary tube 16, and the suction of the compressor 13 is performed. The gas temperature is controlled to be constant.

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

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

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 and a drain pan heater 15A are connected in series by a pipe line, and when the four-way switching valve 7A is in defrost operation, the other switching port communicating with the high pressure side port and the low pressure liquid of the pressure reducer 5A. It is connected across the end of the distribution side.

The cascade condenser 4A is a high-pressure refrigerant coil 41A into which the high-temperature high-pressure refrigerant gas discharged from the compressor 3A is introduced during the cooling operation, and a low-pressure refrigerant which is a cooling-side passage into which the low-pressure refrigerant on the outdoor unit 1 side is introduced. Coil 40
A and A are formed by a heat exchanger that is capable of heat exchange. 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 series 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 not energized (off), and a second switching port that communicates with the pressure port by energization (on).
It has three ports, a switching port and a pressure port, which is connected to a pressure equalizing chamber that acts on the valve of the temperature-sensitive expansion valve 10A.
The switching port is branched and connected to the 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 the 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 provided in such a connection, the temperature-sensitive expansion valve 10A is held in a pressure equalizing operation state, the normal pressure reducing expansion function is exerted, and the three-way solenoid valve 9A is turned on. By doing so, a high pressure is applied to the pressure equalizing chamber and the valve is forcibly closed to operate as a refrigerant shutoff means.

In the indoor unit 2A, when the compressor 3A is driven, the high temperature high pressure gas refrigerant discharged from the compressor 3A exchanges heat with the low pressure refrigerant introduced into the low pressure refrigerant coil 40A in the cascade condenser 4A. After being condensed and liquefied, the temperature is reduced by the temperature-sensitive expansion valve 5A, and the low-pressure low-temperature liquid refrigerant is introduced to the evaporator 6A. And the evaporator 6A
At this time, heat is exchanged with the air inside the chamber which is circulated and blown by the evaporator fan 31A to evaporate and become a low-pressure gas refrigerant, which is sucked into the compressor 3A via the accumulator 8A. In this way, the cooling operation for cooling the air inside the refrigerator is performed by performing the circulation involving 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 in the valve opening operation, and the three-way solenoid valve 9A.
Is turned off. The flow state of the refrigerant is indicated by the solid arrow.

On the other hand, in the outdoor unit 1, when the compressor 13 is driven, the high-temperature high-pressure gas refrigerant discharged from the compressor 13 and the outside air circulated and blown by the condenser fan 32 in the condenser 14 and the heat. After being exchanged and condensed and liquefied, the pressure is reduced by the temperature-sensitive expansion valve 10A via the receiver 18 and the high-pressure liquid pipe 25 to become a low-pressure low-temperature liquid refrigerant, which is guided to the low-pressure refrigerant coil 40A, and the indoor unit 2A side high temperature and high pressure After exchanging heat with the gas refrigerant and evaporating, the low-pressure gas refrigerant becomes the low-pressure gas pipeline 26, the accumulator 17, and the compressor 1
Inhaled to 3. In this way, the circulation involving the condensation and evaporation of the refrigerant is performed, whereby each indoor unit 2A, 2B,
A refrigerating operation is performed in which the latent heat of condensation generated in ... Is released to the outside using a refrigerant as a medium. In this case, the temperature-sensitive expansion valve 10A
Controls the opening degree of the valve according to the temperature of the low-pressure gas refrigerant detected by the temperature sensing cylinder 39A, and performs control with a constant degree of superheat. The flow of the refrigerant is as shown by the solid arrow.

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

FIG. 2 is a flow diagram showing a mode of operation control in the first embodiment shown in FIG. In the first embodiment, each of the indoor units 2A, 2B, ... May perform cooling operation and defrosting operation individually, and some or all may be cooling operation, and some may be defrosting operation. , The output is adjusted on the outdoor unit 1 side according to the operating state at that time, and the indoor units 2A, 2B,
On the ... side, individual capacity control is performed by controlling the valve opening degree of the expansion valves 10A, 10B, .... For example, the outdoor unit 2A
In step m1, when cooling operation is performed and frost is formed on the evaporator 6A, the process shifts to step m2 and a defrosting detector or defrost timer (not shown) checks whether defrosting is necessary. Then, when the defrost start command is output, the process proceeds to the next step m3 to operate the refrigerant cutoff means. This refrigerant blocking means is performed as follows. That is, the three-way solenoid valve 9A
An ON output for energizing the electromagnetic coil is given to. 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 expansion valve 10A when it is turned on, so that the temperature expansion valve 10A is forcibly closed. Due to this valve closing, the cascade condenser 4A is
Since the supply of the low-pressure low-temperature liquid refrigerant to the low-pressure refrigerant coil 40A is cut off, the condensing pressure rises. About 10 seconds after the temperature-sensitive expansion valve 10A is closed, the defrost starting means realized by the high pressure switch 35 in step m4 is increased by about 10 seconds, 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 defrost operation is performed in the indoor unit 2A. In this case, the defrost operation is performed by stopping the evaporator fan 31A and setting the four-way switching valve 7A in the valve switching state shown by the broken line, and the refrigerant flows as shown by the broken line arrow. The hot gas exiting the compressor 3A is a check valve 27.
A, capillary tube 28A, drain pan heater 15
After passing through the hot gas bypass circuit consisting of A, the evaporator 6A
Flowing through the coil, heat-exchanges with the frost adhering to the coil for defrosting, then passes through the accumulator 8A,
Guided to the compressor 3A.

On the other hand, the refrigerant existing in the high-pressure refrigerant coil 41A of the cascade condenser 4A and in the pipe line connected to the inlet side of the temperature-sensitive expansion valve 5A is in a high-pressure gas state in which heat is accumulated as the condensing pressure increases. It is full and passes through the four-way switching valve 7A and the check valve 24A due to the pressure difference, then merges with the refrigerant that has passed through the evaporator 6A, and then is sucked into the compressor 3A through the accumulator 8A. As a result, defrosting is quickly performed by the refrigerant in the low temperature side refrigeration cycle in which sufficient heat is stored. In this case, since the refrigerant exists in a gas state on the high temperature refrigerant coil 41A side, a sufficient circulation amount of the refrigerant necessary for defrosting is secured.

When the defrost operation is performed and the defrost operation is checked in step m6 and the defrost operation command is output in accordance with the operation of the high pressure switch 38, the defrost operation is the original cooling operation. Returned to.

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

FIG. 3 shows the refrigeration circuit of the indoor unit 2A according to the second embodiment of the present invention. The second embodiment is similar to the first embodiment shown in FIG. 1, and corresponding members are designated by the same reference numerals. What should be noted in the second embodiment is that the two-way valve 42A is used instead of the three-way solenoid valve 9A in the first embodiment. A general-purpose electromagnetic valve 42A is used as the two-way valve 42A and is provided in the refrigerant pipe line in series with the temperature-sensitive expansion valve 10A. Then, the solenoid valve 42A is opened by the off operation during the normal cooling operation and closed by the on operation during the defrost operation, so that the same function as that of the three-way solenoid valve 9A can be exerted. The outdoor unit 1 has the same structure as that of the first embodiment, and therefore the illustration thereof is omitted.

Although not shown, instead of the example in which the temperature-sensitive expansion valve 10A and the solenoid valve 42A are connected in series, a structure using an electric expansion valve may be used. By adjusting according to the evaporation temperature and forcibly closing the valve during the defrost operation, it is possible to exhibit the same function as in the first and second embodiments.

FIG. 4 shows a refrigeration circuit for 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. The same reference numerals are attached. It should be noted that the defrost operation in the indoor unit 2A is performed by the reverse refrigeration cycle in the third embodiment. Indoor unit 2
In A, a defrosting capillary tube 43 is provided in series in the high-pressure liquid pipe with respect to the temperature-sensitive expansion valve 5A, and a check valve 44 is connected in parallel with the capillary tube 43. A check valve 45 is provided in parallel with the valve 5A. Drain pan heater 15
The check valve 46 is connected in series to A, and the check valve 47 is connected in parallel to the 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 in the direction indicated by the solid arrow in FIG. 4, while in the defrost operation, the refrigerant flows in the arrow direction indicated by the broken line, and defrosting is performed by the reverse refrigeration cycle. Thus, the defrost operation by heat storage in the refrigerant is carried out as in the first embodiment. The outdoor unit 1 has the same structure as that of the first embodiment, and therefore its illustration is omitted.

FIG. 5 shows a refrigerating circuit of the indoor unit 2A according to the fourth embodiment of the present invention. The fourth embodiment is similar to the first embodiment shown in FIG. 1, and corresponding members are designated by the same reference numerals. In the illustrated fourth embodiment, the indoor unit 2A has a solenoid valve 48 for the temperature-sensitive expansion valve 5A.
It is noteworthy that the refrigerant pipe line that is provided by connecting the and the defrosting capillary tube 43 in series is connected in parallel. In the fourth embodiment, the refrigerant has a flow indicated by a solid line arrow in FIG. 5 during the cooling operation, and on the other hand, has a flow indicated by a broken line arrow during the defrost operation to perform defrosting by the normal refrigeration cycle. As in the example, the defrost operation is performed by storing heat in the refrigerant.

[0032]

As described above, according to the present invention, in the dual cooling device, when defrosting is performed, the supply of the refrigerant to the low pressure refrigerant coil 40n of the cascade condenser 4n is cut off, and the low temperature side unit 2n. The defrost operation can be performed with a high temperature refrigerant by increasing the refrigerant pressure of the refrigerant and allowing the defrost to start after the heat is sufficiently stored.Therefore, it depends on the cooling operation situation immediately before the defrost. In addition, the defrosting time can be shortened by sufficiently securing the defrosting ability. Further, in the invention of claim 2, at the time of defrosting, it is possible to prevent the refrigerant from staying in the high pressure refrigerant coil 41n of the cascade condenser 4n, and to increase the refrigerant circulation amount, so that the defrost time can be shortened.

[Brief description of drawings]

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

FIG. 2 is a flow diagram showing a mode of operation control of the first embodiment shown in FIG.

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

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

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

[Explanation 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

Claims (4)

[Claims] 1. A refrigeration cycle is formed by including a high temperature side unit 1 having a series refrigerant circuit including a compressor 13 and a condenser 14, a compressor 3n, a cascade condenser 4n, a pressure reducer 5n, and an evaporator 6n to form a cascade condenser. The low pressure refrigerant coil 40n, which is the cooling side path of 4n, is connected to the expansion valve 10n.
And at least one low temperature side unit 2n connected in parallel to the series refrigerant circuit of the high temperature side unit 1 via each of the above, and each low temperature side unit 2n is vaporized by the refrigerant of its own refrigeration cycle. A dual cooling device provided with a defrosting means 7n for defrosting the device 6n, which precedes the defrosting by the defrosting means 7n to the low pressure refrigerant coil 40n of the cascade condenser 4n in the corresponding low temperature side unit 2n. Of the refrigerant shutoff means 9n for shutting off the supply of the refrigerant from the high temperature side unit 1 and the temperature or pressure of the high pressure refrigerant of the low temperature side unit 2n rises to the constant value after the operation of the refrigerant shutoff means 9n. , Defrost starting means 35n for operating the defrost means 7n are provided in each low temperature side unit 2n. Apparatus. 2. The defrosting means 7n bypasses the discharge gas from the compressor 3n through the high pressure refrigerant coil 41A of the cascade condenser 4n and the decompressor 5n to perform hot gas bypassing to the evaporator 6n. The binary cooling device according to claim 1. 3. The defrosting means 7n carries out a reverse refrigeration cycle in which the discharge gas from the compressor 3n is guided from the evaporator 6n to the decompressor 5n to the high pressure refrigerant coil 41A of the cascade condenser 4n. Item 2. The dual cooling device according to item 1. 4. The defrosting means 7n performs a normal refrigeration cycle in which the discharge gas from the compressor 3n is guided 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.