KR20210006680A - Simultaneous Refrigeration and Defrost Operating System of Low Temperature Refrigeration Warehouse - Google Patents

Abstract

The present invention relates to a system for simultaneously operating refrigeration and defrosting of a low-temperature refrigeration warehouse. The operation system comprises a compressor (15), a condenser (17), an expansion valve (21, 27), and a plurality of evaporators (unit coolers) (23, 25). The operation system further comprises: frost accumulation detection sensors (S1, S2) mounted on the plurality of unit coolers (23, 25), respectively, to detect whether to defrost; a first and a second bypass pipe (P1, P2) to directly supply hot gas discharged from the compressor (15) to the corresponding unit coolers (23, 25) by bypassing the condenser (17) when frost accumulation of the unit coolers (23, 25) is detected; a first and a second bypass valve (V1, V2) arranged on the first and second bypass pipes (P1, P2); and a controller (C) to control the frost accumulation detection sensors (S1, S2), the bypass valves, and a solenoid valve to simultaneously carry out refrigeration and defrosting operation. The controller (C) opens the first bypass valve (V1) on the first bypass pipe (P1) to directly supply hot gas to the first unit cooler (23), and the second unit cooler (25) normally carries out refrigeration operation when defrosting work is carried out on the first unit cooler (23).

Description

Simultaneous Refrigeration and Defrost Operating System of Low Temperature Refrigeration Warehouse}

The present invention relates to a system for simultaneous refrigeration and defrost operation of a refrigeration warehouse, and more particularly, when a plurality of unit coolers are installed, a frost detection sensor is attached to each unit cooler, and a unit in which the frost detection sensor is operated It relates to a technology capable of simultaneously defrosting and refrigerating operation by directly supplying some refrigerant gas discharged from a compressor to a cooler to perform defrost, and a unit cooler in which a sensor does not operate normally operates.

In general, the refrigeration cycle consists of the processes of compression, condensation, expansion, and evaporation.

Compression compresses the evaporated refrigerant into a high temperature and high pressure state, condensation causes the compressed refrigerant to condense by dropping its temperature, and expansion expands the refrigerant as opposed to compression, making the temperature very low, making it easier to evaporate, and evaporation is the temperature. This is the process of lowering the temperature of the fluid by evaporating the refrigerant with the lowered value.

In more detail, the compressor compresses the refrigerant in a vapor state of low temperature and low pressure from the evaporator and converts it into a vapor refrigerant of high temperature and high pressure, and is installed in the outdoor unit. Therefore, it is easy to become a liquid state by releasing heat from the condenser, which is a post process, to the outside.

The condenser converts the high-temperature, high-pressure refrigerant in a vapor state into a liquid, and is installed in the outdoor unit. This is because the refrigerant needs to be liquefied so that the refrigerant can evaporate and take away heat from the evaporator.

The expansion valve expands the high-temperature, high-pressure liquid refrigerant that has become liquid in the condenser, that is, lowers the pressure to lower the evaporation temperature. This expansion valve is mounted on an outdoor unit or an indoor unit.

Then, the evaporator evaporates the refrigerant liquid to lower the ambient temperature. This evaporator is mounted in the indoor unit.

The refrigerant evaporated by the evaporator and converted into a low-temperature, low-pressure gaseous state is converted to a high-temperature, high-pressure refrigerant gas by returning to the compressor.

The refrigeration cycle is provided in various forms, an example of which is a form in which a plurality of unit coolers (evaporators) are connected to one outdoor unit.

That is, as shown in FIG. 1, as a structure in which a plurality of unit coolers 8 and 9 are arranged, the refrigerant gas discharged from the compressor 1 is condensed in the condenser 3 to become a refrigerant liquid, and the refrigerant liquid is a solenoid. It is supplied to the respective unit coolers 8 and 9 through the valve 5 and the expansion valve 7, evaporated, enters the compressor 1, and is compressed to form a refrigeration cycle.

In addition, the unit coolers 8 and 9 deteriorate refrigeration efficiency by adhering frost to the surface. That is, the unit coolers 8 and 9 cool the air, and since the air contains moisture, when moisture in the air condenses and freezes, it adheres in the form of frost.

In addition, as the frost grows and the thickness increases, the ventilation amount of the unit coolers 8 and 9 decreases and the thermal efficiency of the heat transfer tube decreases, so that the low temperature in the refrigerator cannot be maintained.

Therefore, in order to solve this problem, a defrost system is applied, and in the related art, defrost is performed using a defrost timer DT.

In other words, the defrost timer DT performs defrost every predetermined time, and during defrost, the solenoid valve 5 disposed at the front end of the unit coolers 8 and 9 is turned off and the compressor 1 is stopped. After that, the defrost heater 4 is operated to perform a defrost operation on the unit coolers 8 and 9 by heat.

However, such a conventional defrost system, when operating by connecting a plurality of existing unit coolers to one outdoor unit, is unnecessary energy due to heater defrost operation simultaneously for each evaporator by a timer regardless of the large or small amount of frost damage on the unit cooler. In addition to waste, there is a problem that adversely affects the quality of the product due to the increase in the internal temperature of the heater due to the operation of the heater.

Patent application No. 10-2001-40573 (Name: air discharge structure of air conditioner outdoor unit)

Accordingly, the present invention has been proposed to solve the above problem, and the object of the present invention is to attach a frost detection sensor to each unit cooler and operate the frost detection sensor when a plurality of unit coolers are installed. Defrosting is performed by directly supplying some of the refrigerant gas discharged from the compressor to one unit cooler, and the unit cooler in which the sensor is not operated performs normal operation, thereby providing a technology capable of simultaneously defrosting and refrigerating operation.

The present invention has been proposed to solve the above problems, an embodiment of the present invention,

A system for simultaneous refrigeration and defrosting of a low-temperature freezer including a compressor 15, a condenser 17, expansion valves 21 and 27, and a plurality of evaporators (unit coolers 23, 25),

Each of the plurality of unit coolers (23, 25) is mounted to detect whether or not a defrost sensor (S1, S2) and;

When the unit coolers 23 and 25 detect frost, the hot gas discharged from the compressor 15 bypasses the condenser 17 and is directly supplied to the unit coolers 23 and 25. ,P2) and;

First and second bypass valves V1 and V2 disposed in the first and second bypass pipes P1 and P2; And

It includes a controller (C) that can simultaneously perform refrigeration and defrost operation by controlling the frost detection sensor (S1, S2), bypass valve, and solenoid valve,

When the controller (C) performs a defrosting operation on the first unit cooler (23), the first bypass valve (V1) on the first bypass pipe (P1) is opened so that the hot gas is transferred to the first unit cooler (23). ), and the second unit cooler 25 provides a simultaneous refrigeration and defrosting operation system of a low-temperature freezer that normally performs refrigeration operation.

Another embodiment of the present invention,

A system for simultaneous refrigeration and defrosting of a low-temperature freezer including a compressor 15, a condenser 17, expansion valves 21 and 27, and a plurality of evaporators (unit coolers 23, 25),

Each of the plurality of unit coolers (23, 25) is mounted to detect whether or not a defrost sensor (S1, S2) and;

A third bypass pipe (P3) for bypassing the condenser (17) of the hot gas discharged from the compressor (15) when the unit coolers (23, 25) detect frost;

A fourth bypass conduit (P4) bypassing the first expansion valves (21, 27) and the first solenoid valve (19) of the first unit cooler (23);

A fifth bypass conduit (P5) bypassing the second expansion valves (21, 27) and the second solenoid valve (24) of the second unit cooler (25);

Third to fifth bypass valves V3, V4 and V5 respectively disposed on the third to fifth bypass pipes P3, P4 and P5 to open and close the pipes; And

It includes a controller (C) that can simultaneously perform refrigeration and defrost operation by controlling the frost detection sensor (S1, S2), bypass valve, and solenoid valve,

The controller (C) opens the third bypass valve (V3) on the third bypass pipe (P3) when defrosting the first unit cooler (23) so that the hot gas is transferred to the liquid refrigerant pipe (L). Is supplied directly to the first unit cooler 23 through the fourth bypass conduit (P4), and the second unit cooler (25) simultaneously refrigerates and defrosts the low-temperature freezer that normally performs refrigeration operation. Provide a driving system.

As described above, the simultaneous refrigeration and defrost operation system of a low-temperature freezer according to the present invention has the following effects.

That is, when a plurality of unit coolers are installed, a frost detection sensor is attached to each unit cooler, and when any one of the plurality of unit coolers operates, some of the refrigerant gas discharged from the compressor is transferred to the condenser. By bypassing and supplying directly to the unit cooler to defrost, the remaining refrigerant gas discharged from the compressor is supplied to the unit cooler in which no defrost is detected through the condenser and solenoid valve, which are the normal paths, and the unit cooler continuously operates refrigeration. By doing so, defrost and refrigeration operation are possible at the same time, so that the compressor operation can be efficiently performed, the amount of heat generated from the heater defrost can be reduced, and the internal temperature of the chamber is kept constant, so that the quality of the product can be improved. .

1 is a view schematically showing a defrost operation system of a refrigerator warehouse according to the prior art.
2 is a diagram schematically showing an arrangement relationship between an outdoor unit and an indoor unit as a system for simultaneous refrigeration and defrost operation of a low-temperature freezer according to an embodiment of the present invention.
3 is a view showing an arrangement structure of a compressor, a condenser, an evaporator, and an expansion valve as a system for simultaneous operation of low-temperature refrigeration and defrosting shown in FIG. 2.
FIG. 4 is a diagram showing another embodiment of the simultaneous operation system for low temperature refrigeration and defrosting shown in FIG. 3.

Hereinafter, a system for simultaneously operating refrigeration and defrosting of a low-temperature freezer according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The refrigeration cycle applied to the refrigeration and defrost system of a low-temperature freezer proposed by the present invention consists of processes of compression, condensation, expansion, and evaporation.

The compression process compresses the refrigerant into a high temperature and high pressure state by compressing the refrigerant by the compressor 15 installed in the outdoor unit 10, and the condensation process condenses the compressed refrigerant by dropping the temperature by the condenser 17 of the outdoor unit 10. , The expansion process expands the refrigerant using the expansion valves 21 and 27, as opposed to compression, so that the temperature drops very low to make it easier to evaporate, and the evaporation process transfers the cooled refrigerant to the evaporator 23 of the indoor units 12 and 14. 25) to reduce the temperature of the fluid.

The system for simultaneous refrigeration and defrost operation of such a low-temperature freezer is applied in various forms, an example of which is applied to a refrigeration warehouse as shown in FIG. 2, and a plurality of unit coolers 23,25 in one outdoor unit 10 ) Is applied in a connected form.

That is, the system for simultaneous refrigeration and defrost operation of a low-temperature refrigeration warehouse proposed by the present invention includes, as shown in FIG. 3, a compressor 15 that is mounted on the outdoor unit 10 to compress the refrigerant into a high-temperature, high-pressure state; A condenser 17 mounted on the outdoor unit 10 and condensing the compressed refrigerant to lower the temperature to make a liquid phase; Expansion valves (21, 27) for expanding the refrigerant as opposed to compression to lower the temperature to a very low level to facilitate evaporation; A plurality of evaporators (23, 25; coolers) mounted on the indoor units (12, 14) and evaporating the refrigerant whose temperature has been lowered to lower the ambient temperature; A frost detection sensor (S1, S2) mounted on the plurality of unit coolers (23, 25) to detect whether or not to defrost;

When the unit coolers 23 and 25 detect frost, the hot gas discharged from the compressor 15 bypasses the condenser 17 and is directly supplied to the unit coolers 23 and 25. ,P2) and;

First and second bypass valves HSI (V1 and V2) disposed in the first and second bypass pipes P1 and P2; And

It includes a controller (C) capable of simultaneously performing refrigeration and defrosting operations by controlling the frost detection sensors S1 and S2, the bypass valve, and the solenoid valve.

To describe these systems in more detail,

The frost detection sensors S1 and S2 are mounted on the unit coolers 23 and 25, respectively, to sense whether frost is attached to the surface.

These red-eye detection sensors S1 and S2 are capable of various types of sensors, for example, a method of opposing an LED and a photodiode to each other and detecting that the light of the LED is blocked by frost.

Alternatively, when frost is applied to the surface of the crystal oscillator, a method of using a change in the resonant frequency is possible.

And, when frost is attached, by transmitting a signal to the controller C, the controller C recognizes that the frost is attached to the surfaces of the unit coolers 23 and 25, and switches to the defrost mode.

In addition, the bypass pipe conducts defrost by supplying the hot gas discharged to the compressor 15 to the unit coolers 23 and 25 requiring defrost.

One side of this bypass pipe is connected to a refrigerant pipe connecting the compressor 15 and the condenser 17, and the other side is connected to each of the plurality of unit coolers 23 and 25, for example, a first unit cooler ( It is connected by a first bypass pipe (P1) connected to 23) and a second bypass pipe (P2) connected to the second unit cooler (25).

That is, the first bypass pipe (P1) is connected to the refrigerant pipe connecting the compressor (15) and the condenser (17) on one side, the other side is connected to the first unit cooler (23), and a first bypass valve in the middle. (V1) is placed.

In addition, the second bypass pipe P2 is connected to the refrigerant pipe at one end and the second unit cooler 25 at the other end thereof, and a second bypass valve V2 is disposed in the middle.

Accordingly, by controlling the first and second bypass valves V1 and V2 by a signal from the controller C, opening and closing the first and second bypass pipes P1 and P2, the hot gas is selectively opened and It is supplied to the second unit cooler (23, 25).

For example, when defrost is required for the first unit cooler 23, the controller C discharges from the compressor 15 by opening the first bypass valve V1 on the first bypass pipe P1. The hot gas is supplied to the first unit cooler 23. At this time, the first solenoid valve 19 and the first suction gas solenoid valve 20 connected to the first unit cooler 23 are shut off.

In this way, by supplying the hot gas to the first unit cooler 23, a defrosting operation of dissolving the frost layer deposited on the surface of the first unit cooler 23 may be performed.

On the other hand, the second unit cooler 25 must continuously perform a normal refrigeration operation, and the second solenoid valve 24 and the second suction gas solenoid valve 26 connected to the second unit cooler 25 are open. By maintaining the state, the refrigerant liquid supplied from the condenser 17 is continuously supplied to the second unit cooler 25. At this time, the second bypass valve V2 on the second bypass pipe P2 is closed so that hot gas is not supplied to the second unit cooler 25.

In this way, the first unit cooler 23 performs a defrosting operation, and at the same time, the second unit cooler 25 performs a refrigeration operation.

Conversely, when defrost is required for the second unit cooler 25, the controller C opens the second bypass valve V2 on the second bypass pipe P2 so that the hot gas discharged from the compressor 15 is It is supplied to the second unit cooler (25).

At this time, the first bypass valve V1 on the first bypass pipe line P1 is closed so that hot gas is not supplied to the first unit cooler 23.

In addition, the second solenoid valve 24 and the second intake gas solenoid valve 26 connected to the second unit cooler 25 are shut off.

In this way, by supplying the hot gas to the second unit cooler 25, a defrosting operation of dissolving the frost layer deposited on the surface of the second unit cooler 25 may be performed.

On the other hand, since the first unit cooler 23 must continuously perform a normal refrigeration operation, the first solenoid valve 19 and the first suction gas solenoid valve 20 connected to the first unit cooler 23 are open. By maintaining the state, the refrigerant liquid supplied from the condenser 17 is continuously supplied to the first unit cooler 23. At this time, the first bypass valve V1 on the first bypass pipe line P1 is closed so that hot gas is not supplied to the first unit cooler 23.

In this way, the first unit cooler 23 may perform a refrigerating operation, and at the same time, the second unit cooler 25 may perform a defrosting operation.

As described above, in the simultaneous refrigeration and defrost operation system of a low-temperature freezer proposed by the present invention, a frost detection sensor (S1, S2) is attached to each of the plurality of unit coolers (23, 25), and any one of the frost detection is detected. When the sensors (S1, S2) operate, some of the refrigerant gas discharged from the compressor (15) is bypassed by the condenser (17) and directly supplied to the corresponding unit coolers (23, 25) to defrost. The remaining refrigerant gas discharged is supplied to the unit coolers 23 and 25 where no frost damage is detected through the condenser 17 and the solenoid valve, which are normal paths, and the unit coolers 23 and 25 are defrosted by continuously refrigerating operation. It relates to a technology capable of simultaneously operating and refrigerating.

Meanwhile, in FIG. 4, another embodiment of the present invention is shown.

In the embodiment shown in FIG. 3, the hot gas discharged from the compressor 15 during defrost operation is supplied to the unit coolers 23 and 25 through separate bypass pipes P1 and P2 to defrost,

In this embodiment, by arranging a plurality of bypass pipes (P3, P4, P5), hot gas is supplied to the unit coolers 23 and 25 through the existing liquid refrigerant pipe (L) and the bypass pipe to perform defrosting. There are differences that can be made.

In more detail,

This embodiment is composed of a compressor 15, a condenser 17, expansion valves 21 and 27, and a plurality of unit coolers 23 and 25, as in the above-described embodiment, and a plurality of unit coolers 23 and 25 ), each of which is mounted on the frost detection sensor (S1, S2) for detecting whether or not defrost; A third bypass pipe (P3) for bypassing the condenser (17) of the hot gas discharged from the compressor (15) when the unit coolers (23, 25) detect frost; A fourth bypass conduit (P4) bypassing the first expansion valves (21, 27) and the first solenoid valve (19) of the first unit cooler (23); A fifth bypass conduit (P5) bypassing the second expansion valves (21, 27) and the second solenoid valve (24) of the second unit cooler (25); Third to fifth bypass valves V3, V4 and V5 respectively disposed on the third to fifth bypass pipes P3, P4 and P5 to open and close the pipes; And it includes a controller (C) capable of simultaneously performing refrigeration and defrost operation by controlling the frost detection sensors (S1, S2), bypass valve, and solenoid valve.

In the case of driving the refrigeration and defrosting system having such a structure, the hot gas discharged from the compressor 15 bypasses the condenser 17 through the third bypass conduit P3 and is connected to the outlet of the condenser 17. It is supplied to the tube (L). And, the hot gas supplied through the liquid refrigerant pipe (L) is supplied to the unit coolers (23, 25) through the fourth bypass pipe (P4) or the fifth bypass pipe (P5) to perform defrosting. I can.

At this time, the third bypass pipe (P3) is connected to the refrigerant pipe on the inlet side of the condenser (17) on one side, and to the liquid refrigerant pipe (L) on the outlet side of the condenser (17) by bypassing the condenser (17) on the other side. In the middle, a third bypass valve V3 is disposed.

In addition, the fourth bypass pipe (P4) is connected to the liquid refrigerant pipe (L) on one side, and bypasses the first solenoid valve (19) and the first expansion valves (21, 27) on the other side, The pass valve V4 is arranged.

And, the fifth bypass pipe (P5) is connected to the liquid refrigerant pipe (L) on one side, the other side bypasses the second solenoid valve 24 and the second expansion valves 21 and 27, and a fifth bypass in the middle. The pass valve V5 is arranged.

Therefore, by selectively controlling the third to fifth bypass valves V3, V4, and V5 according to a signal from the controller C to open and close the third to fifth bypass pipes P3, P4 and P5, hot gas Is selectively supplied to the first and second unit coolers 23 and 25.

To illustrate this process as an example,

When defrosting is required for the first unit cooler 23, the controller C opens the third bypass valve V3 on the third bypass pipe P3 so that the hot gas discharged from the compressor 15 is reduced to the condenser ( By bypassing 17), it is supplied to the liquid refrigerant pipe (L) at the outlet of the condenser (17).

In addition, the hot gas supplied through the liquid refrigerant pipe (L) is a fourth bypass pipe (P4) bypassing the first solenoid valve (19) and the first expansion valve (21) connected to the first unit cooler (23). By being supplied to the first unit cooler 23 through the defrosting operation can be performed. At this time, the first solenoid valve 19 and the first suction gas solenoid valve 20 connected to the first unit cooler 23 are shut off.

On the other hand, the second unit cooler 25 must continuously perform a normal refrigeration operation, and the second solenoid valve 24 connected to the second unit cooler 25 and the second suction gas solenoid valve 26 are By maintaining the open state, the refrigerant liquid supplied from the condenser 17 is continuously supplied to the second unit cooler 25.

In this way, the first unit cooler 23 performs a defrosting operation, and at the same time, the second unit cooler 25 performs a refrigeration operation.

Conversely, when defrosting is required in the second unit cooler 25, hot gas passes through the third bypass valve V3 on the third bypass pipe P3 to the liquid refrigerant pipe L at the outlet of the condenser 17. The supply process is the same.

Then, the hot gas supplied through the liquid refrigerant pipe (L) is a fifth bypass pipe (P5) bypassing the second solenoid valve 24 and the second expansion valve 27 connected to the second unit cooler 25. By being supplied to the second unit cooler 25 through the defrosting operation can be performed.

At this time, the second solenoid valve 24 and the second intake gas solenoid valve 26 connected to the second unit cooler 25 are shut off.

On the other hand, the first unit cooler 23 must continuously perform a normal refrigeration operation, and the first solenoid valve 19 connected to the first unit cooler 23 and the first suction gas solenoid valve 20 are By maintaining the open state, the refrigerant liquid supplied from the condenser 17 is continuously supplied to the third unit coolers 23 and 25.

In this way, the first unit cooler 23 may perform a refrigeration operation, and at the same time, the second unit cooler 25 may perform a defrost operation.

Claims (5)

A compressor (15), a condenser (17); As a system for simultaneous refrigeration and defrosting of a low-temperature refrigeration warehouse including expansion valves 21 and 27 and a plurality of evaporators (unit coolers 23 and 25),
A frost detection sensor (S1, S2) mounted on the plurality of unit coolers (23, 25) to detect whether or not to defrost;
When the unit coolers 23 and 25 detect frost, the hot gas discharged from the compressor 15 bypasses the condenser 17 and is directly supplied to the unit coolers 23 and 25. ,P2) and;
First and second bypass valves V1 and V2 disposed in the first and second bypass pipes P1 and P2; And
It includes a controller (C) that can simultaneously perform refrigeration and defrost operation by controlling the frost detection sensor (S1, S2), bypass valve, and solenoid valve,
When the controller (C) performs a defrosting operation on the first unit cooler (23), the first bypass valve (V1) on the first bypass pipe (P1) is opened so that the hot gas is transferred to the first unit cooler (23). ), and the second unit cooler 25 is a system for simultaneous refrigeration and defrost operation of a low-temperature freezer that performs a normal refrigeration operation. The method of claim 1,
One side of the bypass pipe is connected to a refrigerant pipe connecting the compressor 15 and the condenser 17, the other side is connected to the first unit cooler 23, and the first bypass valve V1 is disposed in the middle. 1 bypass pipe (P1), one side is connected to the refrigerant pipe, the other side is connected to the second unit cooler (25), and the second bypass pipe (P2) in which the second bypass valve (V2) is disposed is connected. By including, by controlling the first and second bypass valves V1 and V2 according to a signal from the controller C, opening and closing the first and second bypass pipes P1 and P2, the hot gas is selectively opened and Simultaneous refrigeration and defrosting operation system of low-temperature freezers supplied to the second unit cooler (23,25). A compressor (15), a condenser (17); As a system for simultaneous refrigeration and defrosting of a low-temperature refrigeration warehouse including expansion valves 21 and 27 and a plurality of evaporators (unit coolers 23 and 25),
A frost detection sensor (S1, S2) mounted on the plurality of unit coolers (23, 25) to detect whether or not to defrost;
A third bypass pipe (P3) for bypassing the condenser (17) of the hot gas discharged from the compressor (15) when the unit coolers (23, 25) detect frost;
A fourth bypass conduit (P4) bypassing the first expansion valve (21) and the first solenoid valve (19) of the first unit cooler (23);
A fifth bypass pipe (P5) bypassing the second expansion valve (27) and the second solenoid valve (24) of the second unit cooler (25);
Third to fifth bypass valves V3, V4 and V5 respectively disposed on the third to fifth bypass pipes P3, P4 and P5 to open and close the pipes; And
It includes a controller (C) that can simultaneously perform refrigeration and defrost operation by controlling the frost detection sensor (S1, S2), bypass valve, and solenoid valve,
The controller (C) opens the third bypass valve (V3) on the third bypass pipe (P3) when defrosting the first unit cooler (23) so that the hot gas is transferred to the liquid refrigerant pipe (L). Is supplied directly to the first unit cooler 23 through the fourth bypass conduit (P4), and the second unit cooler (25) simultaneously refrigerates and defrosts the low-temperature freezer that normally performs refrigeration operation. Driving system. The method of claim 3,
One side of the third bypass pipe (P3) is connected to the refrigerant pipe on the inlet side of the condenser (17), and the other side is connected to the liquid refrigerant pipe (L) at the outlet side of the condenser (17) bypassing the condenser (17), A third bypass valve (V3) is disposed in the middle,
The fourth bypass pipe (P4) has one side connected to the liquid refrigerant pipe (L), the other side bypasses the first solenoid valve 19 and the first expansion valve 21, and the fourth bypass valve (V4) in the middle. ) Is placed,
The fifth bypass pipe (P5) has one side connected to the liquid refrigerant pipe (L), the other side bypasses the second solenoid valve 24 and the second expansion valve 27, and the fifth bypass valve (V5) in the middle. ) Is placed
By selectively controlling the third to fifth bypass valves (V3, V4, V5) by a signal from the controller (C), the hot gas is selectively opened and closed by opening and closing the third to fifth bypass pipes (P3, P4, P5). A system for simultaneous refrigeration and defrosting of a low-temperature freezer that is supplied to the first and second unit coolers (23,25). The method according to any one of claims 1 or 3,
The frost detection sensor (S1, S2) is a system for simultaneous refrigeration and defrost operation of a low-temperature freezer, which is a method of opposing the LED and the photodiode and detecting that the light of the LED is blocked by frost.

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