JP2013053813A - Cooling apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cooling apparatus capable of reducing impact pressure to an expansion means by a liquid hammer phenomenon.SOLUTION: The cooling apparatus for cooling a freezer 50 includes: a refrigerant circuit in which a compressor 1, a condenser 2, an electromagnetic valve 3, an expansion valve 4, and an evaporator 5 are sequentially connected with a refrigerant pipe to allow a refrigerant to circulate therethrough; a heater 7 disposed in a refrigerant pipe on an upstream side of the electromagnetic valve 3 to heat the refrigerant in the refrigerant pipe; a liquid pipe temperature sensor 6 for detecting temperature of the refrigerant heated by the heater 7; and a control device 100 for controlling operation of the electromagnetic valve 3 and the heater 7. The electromagnetic valve 3, the expansion valve 4, the evaporator 5, and the heater 7 are disposed in the freezer 50. The control device 100 controls the heater 7 so that a detection temperature of the liquid pipe temperature sensor 6 will become temperature within a predetermined range having an upper limit value which is saturated liquid temperature of the refrigerant in the condenser 2 or below, when the compressor 1 is stopped and the electromagnetic valve 3 is closed.

Description

  The present invention relates to a cooling device including a refrigerant circuit for circulating a refrigerant.

  In a cooling device such as a unit cooler placed in a freezer / refrigerator (chamber), etc., when the operation of the device is stopped, or when the refrigerant circulation stops after reaching the cooling set temperature during operation, to the compressor at the time of restart In order to prevent liquid back-up, an electromagnetic valve is provided upstream of the expansion valve, the electromagnetic valve is closed before the compressor is stopped, and the refrigerant in the refrigerant flow path from the downstream of the electromagnetic valve to the compressor via the evaporator is predetermined. Compressor operation is stopped after pumping up to pressure (approximately atmospheric pressure) (pump down operation). Thereafter, during the re-cooling operation, the electromagnetic valve is opened, so that the high-pressure liquid refrigerant becomes a low pressure by the downstream expansion valve and is vaporized in the evaporator to perform heat exchange.

  However, since the solenoid valve and a part of the refrigerant pipe upstream of the solenoid valve are arranged in the freezer (hereinafter referred to as the inside of the warehouse), the refrigerant in the pipe is in a low temperature (for example, about −25 ° C.) inside the warehouse. The air is cooled to a considerably low temperature by the air (the liquid density is also high with excessive cooling). When the solenoid valve is opened in this state, the so-called liquid hammer phenomenon that the liquid refrigerant in a state of high pressure and excessive supercooling flows into the downstream of the solenoid valve in the low pressure state and collides with the expansion valve is promoted. It will be. This liquid hammer phenomenon causes problems such as generation of impact sound and breakage of the expansion valve.

  If the expansion valve breaks, the expansion stroke in the refrigeration cycle does not operate normally, causing a temperature rise in the storage, which may lead to a decrease in the quality of the contents. Further, when the refrigerant collides due to the impact of the liquid hammer, a very large abnormal sound and abnormal vibration are generated.

  Further, the impact pressure may be transmitted to the connection pipe and exceed the fatigue limit of the connection pipe, which may cause breakage of the connection pipe. When the connection pipe is broken, the refrigerant in the refrigerant circuit is released into the cabinet, the refrigerant in the refrigerant circuit becomes lean, and the quality of the stored items is reduced due to the temperature rise in the cabinet. In addition, refrigerated / freezer warehouses are designed to have a relatively high hermeticity in order to prevent the intrusion of outside air, and the refrigerant in the refrigerant pipe flows into the warehouse due to broken pipes, which lowers the oxygen density in the warehouse. To do. If there is work in the warehouse, it may become deficient and lead to an accident involving human life. Moreover, if the refrigerant in the refrigerant circuit is released into the atmosphere, global warming is promoted, which has a great influence from the viewpoint of protecting the global environment.

In recent years, for the purpose of pursuing energy saving, the purpose of preventing ozone layer destruction, and the purpose of preventing global warming, the refrigerant density tends to be increased like R410A, R404A, R32 and CO ₂ .
Since the impact pressure (liquid hammer pressure) due to the liquid hammer phenomenon increases in proportion to the density of the liquid refrigerant, the impact pressure increases as the liquid refrigerant density of the refrigerant increases as described above. For this reason, the liquid hammer phenomenon tends to become more prominent as the refrigerant density becomes higher. For example, when R404A and R410A are compared, the impact pressure of R410A is about 1.4 times that of R404A. For this reason, it is necessary not to generate an impact pressure that causes a failure of the equipment or an impact pressure that occurs until the pipe breaks.

  In order to prevent the liquid hammer phenomenon as described above, in the conventional cooling device, for example, an expansion valve to be used is an electronically controlled expansion valve, and an electromagnetic valve is disposed downstream of the electronic expansion valve. (For example, refer to Patent Document 1).

  Further, for example, the liquid hammer phenomenon is related to the density of the liquid refrigerant, and the impact pressure increases as the liquid density increases. For this reason, a method has been proposed in which control for reducing the liquid density is incorporated in the refrigeration apparatus in order to reduce the impact pressure (see, for example, Patent Document 2).

  In addition, for example, to reduce the liquid density, a heater is wound around the piping upstream of the solenoid valve, and the refrigerant is mixed with gas and liquid by heating the liquid refrigerant upstream of the solenoid valve before opening the solenoid valve. In order to reduce the collision pressure of the refrigerant against the expansion valve by reducing the liquid density in a two-phase separation state (see, for example, Patent Document 3).

JP 2008-241238 A Japanese Patent No. 4476946 Japanese Patent Laid-Open No. 11-325654

The technique described in Patent Document 1 attempts to improve the liquid hammer phenomenon by using an electronic expansion valve.
However, the electronic expansion valve requires a control board in order to change the opening degree of the expansion valve. If the temperature of the space where the expansion valve is located is within the allowable temperature range of the control board, there is no problem, but the temperature of the freezer / refrigerated warehouse may be -25 ° C or lower. Placement in a refrigerated warehouse is impossible. For this reason, it is necessary to arrange a dedicated control board box near the electronic expansion valve. There is a problem in that the arrangement of the dedicated box causes an increase in box arrangement work and an increase in cost.

Further, in the technique described in Patent Document 2, the liquid hammer phenomenon is attempted to be improved by a method in which control for limiting the supercooling operation is mounted in order to reduce the liquid density.
However, by limiting the supercooling operation, the liquid refrigerant cannot be sufficiently subcooled, and the operation is performed at the expense of power consumption reduction and capacity increase. If a large amount of cooling load is put into the freezer (chamber) and the operation is performed at the sacrifice of capacity, the temperature inside the refrigerator will rise and the quality of the coolant will be reduced. There was a problem in that driving against energy saving would be carried out at the expense of reducing power consumption.

In the technique described in Patent Document 3, the refrigerant is constantly heated by an electric heater while the operation is stopped, thereby increasing the temperature of the refrigerant and reducing the liquid density to improve the liquid impact.
However, because the refrigerant is overheated to the two-layer separation zone, which is difficult to control by temperature detection, the temperature is not controlled, and energy is lost in the refrigeration cycle by always energizing when the refrigerant is stopped. There was a point.
In addition, there is a problem in that the cooling effect is reduced because the refrigerant not supercooled is sent to the evaporator.
Furthermore, since the expansion valve generally controls the flow path of the liquid refrigerant, the mechanical expansion valve has a problem that normal control cannot be performed when the two-phase separated refrigerant passes.

The present invention has been made to solve the above-described problems, and is capable of preventing the refrigerant from entering a two-phase state even when the refrigerant on the upstream side of the on-off valve is heated. Get the device.
Moreover, the cooling device which can reduce the impact pressure to the expansion | swelling means by a liquid hammer phenomenon is obtained.
Moreover, even when the refrigerant on the upstream side of the on-off valve is heated, a cooling device that can suppress a decrease in cooling capacity is obtained.

  A cooling device according to the present invention is a cooling device that cools a facility to be cooled, and includes a refrigerant circuit that sequentially connects a compressor, a condenser, an on-off valve, an expansion means, and an evaporator with a refrigerant pipe to circulate the refrigerant. A heating unit that is disposed in a refrigerant pipe upstream of the on-off valve and that heats the refrigerant in the refrigerant pipe, a temperature detecting unit that detects a temperature of the refrigerant heated by the heating unit, the on-off valve, and the Control means for controlling the operation of the heating means, the on-off valve, the expansion means, the evaporator, and the heating means are arranged in the cooled facility, and the control means is configured to stop the compressor. When the on-off valve is in a closed state, the heating means is set so that the temperature detected by the temperature detecting means is a temperature within a predetermined range in which the upper limit value is equal to or lower than the saturated liquid temperature of the refrigerant in the condenser. To control That.

  The present invention can prevent the refrigerant from entering a two-phase state even when the refrigerant on the upstream side of the on-off valve is heated. Moreover, the impact pressure on the expansion means due to the liquid hammer phenomenon can be reduced. Moreover, the fall of cooling capacity can be suppressed.

It is a refrigerant circuit figure of the cooling device concerning Embodiment 1 of the present invention. It is an illustration figure of the freezer in which the cooling device which concerns on Embodiment 1 of this invention is arrange | positioned. It is a figure which shows the installation range of the heater which concerns on Embodiment 1 of this invention. It is a figure which shows the example of installation of the heater which concerns on Embodiment 1 of this invention, and a liquid pipe temperature sensor. It is a figure which shows the example of installation of the liquid pipe | tube temperature sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the Ph diagram of the refrigerating cycle which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the relationship between the liquid hammer pressure and refrigerant | coolant temperature which concern on Embodiment 1 of this invention. It is a Ph diagram explaining the heater heating operation according to Embodiment 1 of the present invention. It is a flowchart of the heater control operation | movement which concerns on Embodiment 1 of this invention. It is a refrigerant circuit figure of the cooling device which concerns on Embodiment 2 of this invention. It is an illustration figure of the freezer in which the cooling device which concerns on Embodiment 3 of this invention is arrange | positioned.

Embodiment 1 FIG.
(overall structure)
FIG. 1 is a refrigerant circuit diagram of a cooling device according to Embodiment 1 of the present invention.
As shown in FIG. 1, the cooling device in the present embodiment includes a unit cooler 10, an outdoor unit 20, and a liquid refrigerant pipe 30 and a gas refrigerant pipe 40 that connect the unit cooler 10 and the outdoor unit 20. ing.
The “unit cooler 10” corresponds to the “load side unit” in the present invention.
The “outdoor unit 20” corresponds to the “heat source side unit” in the present invention.

The outdoor unit 20 includes the compressor 1. A condenser 2 is connected to the discharge side of the compressor 1 by a pipe to constitute a part of the refrigerant circuit. A blower 21 is provided in the vicinity of the condenser 2.
The compressor 1 is a compressor whose operating capacity can be varied. For example, the compressor 1 includes a positive displacement compressor driven by a motor controlled by an inverter.
The condenser 2 is constituted by, for example, a fin & tube type heat exchanger constituted by a heat transfer tube and a large number of fins.
The blower 21 is driven by a fan motor or the like, and can adjust the air volume by changing the motor rotation speed to adjust the air volume.

The unit cooler 10 includes a solenoid valve 3, an expansion valve 4, and an evaporator 5. In order from the liquid refrigerant pipe 30 connected to the unit cooler 10 to the gas refrigerant pipe 40, the solenoid valve 3, the expansion valve 4, and the evaporator 5 are connected in series to constitute a part of the refrigerant circuit. A blower 11 is provided in the vicinity of the evaporator 5.
Further, a heater 7 is provided which is disposed in the liquid refrigerant pipe 30 upstream of the electromagnetic valve 3 and heats the refrigerant in the liquid refrigerant pipe 30.
The “solenoid valve 3” corresponds to the “open / close valve” in the present invention.
The “expansion valve 4” corresponds to “expansion means” in the present invention.
The “heater 7” corresponds to the “heating means” in the present invention.

Further, the unit cooler 10 is provided with a liquid pipe temperature sensor 6 and an internal temperature sensor 8.
The liquid pipe temperature sensor 6 is provided between the electromagnetic valve 3 and the condenser 2 and measures the refrigerant temperature.
The internal temperature sensor 8 is provided in the unit cooler 10 and measures the temperature of internal air (hereinafter referred to as internal temperature) at which the evaporator 5 exchanges heat with the refrigerant.
The “liquid pipe temperature sensor 6” corresponds to “temperature detection means” in the present invention.
The “internal temperature sensor 8” corresponds to “second temperature detection means” in the present invention.

The expansion valve 4 is constituted by a mechanical expansion valve that opens and closes by a mechanical action, such as a temperature automatic expansion valve or a constant pressure expansion valve, and expands the refrigerant by decompressing it.
The evaporator 5 is comprised by the fin & tube type heat exchanger comprised with the heat exchanger tube and many fins, for example.
The blower 11 is driven by a fan motor or the like, and can adjust the air volume by changing the motor rotation speed, and can adjust the air volume.

The refrigerant circulating in the refrigerant circuit of this embodiment, for example, a refrigerant such as chlorofluorocarbon refrigerants (such as R404A · R410A) and natural refrigerant (CO _2, NH ₃₎ is used.

The control device 100 is constituted by a microcomputer, for example, and is arranged in the outdoor unit 20.
Measurement information from the liquid pipe temperature sensor 6 and the internal temperature sensor 8 is input to the control device 100. Further, the control device 100 includes a high pressure sensor (not shown) that measures the refrigerant pressure on the discharge side of the compressor 1, a low pressure sensor (not shown) that measures the refrigerant pressure on the suction side, and the degree of supercooling. Various measurement information necessary for operation control of the refrigeration cycle such as a temperature sensor (not shown) for measuring the outlet side temperature of the condenser 2 is input.
The control device 100 performs compression based on measurement information input from each sensor, various data received from the control device 100, operation details (operation mode, set temperature, etc.) instructed by a user from an operation device (not shown). The operation frequency of the machine 1, the rotational speed of the blower 21 (heat exchange capacity of the condenser 2), the rotational speed of the blower 11 (heat exchange capacity of the evaporator 5), the open / close state of the electromagnetic valve 3, and the like are controlled. Further, the control device 100 controls the heater 7 when the operation of the compressor 1 is stopped. Details will be described later.
“Control device 100” corresponds to “control means” in the present invention.

FIG. 2 is an exemplary view of a freezer in which the cooling device according to Embodiment 1 of the present invention is arranged.
As shown in FIG. 2, the unit cooler 10 is arrange | positioned inside the freezer 50 as a to-be-cooled installation.
In the evaporator 5 in the unit cooler 10, the air in the freezer 50 is cooled by exchanging heat between the low-temperature and low-pressure refrigerant and the air in the freezer 50. Details of the driving operation will be described later.
In the present embodiment, the case of the freezer 50 that is cooled to below the freezing point as the equipment to be cooled will be described, but the present invention is not limited to this, and the low temperature above the freezing point (for example, 5 ° C.). It is good also considering the refrigerator cooled to this temperature as a to-be-cooled installation. Moreover, it is good also as a to-be-cooled installation with comparatively big to-be-cooled spaces, such as a freezer warehouse (freezer room) and a refrigerator warehouse (refrigerated room).

(Installation position of heater 7)
FIG. 3 is a diagram showing an installation range of the heater according to Embodiment 1 of the present invention.
As shown in FIG. 3, the liquid refrigerant pipe 30 is connected to the electromagnetic valve 3 from the back side of the unit cooler 10 through, for example, an opening (not shown) formed in the freezer 50.
The heater 7 is disposed in the liquid refrigerant pipe 30 in the unit cooler 10 in the liquid refrigerant pipe 30 on the upstream side of the electromagnetic valve 3. In the example of FIG. 3, of the liquid refrigerant pipe 30 (700 mm) bent in an L shape in the unit cooler 10, a lateral portion (500 mm) having a long straight portion is set as a heater installation range. As described above, when the liquid refrigerant pipe 30 is bent in the unit cooler 10, the heater installation range is set to be a straight portion of the liquid refrigerant pipe 30. Thereby, construction at the time of installation of heater 7 can be made easy.
The installation range of the heater 7 is not limited to this, and the heater 7 may be disposed in the entire range of the liquid refrigerant pipe 30 in the unit cooler 10 in the liquid refrigerant pipe 30 on the upstream side of the electromagnetic valve 3.

(Details of heater 7 and liquid tube temperature sensor 6)
FIG. 4 is a diagram showing an installation example of the heater and the liquid pipe temperature sensor according to Embodiment 1 of the present invention.
As shown in FIG. 4A, a heat insulating material 31 is provided around the liquid refrigerant pipe 30.
The heater 7 and the liquid pipe temperature sensor 6 are disposed on the liquid refrigerant pipe 30 side (the outer peripheral surface of the liquid refrigerant pipe 30) with respect to the heat insulating material 31. Thereby, the heat from the heater 7 is not interrupted by the heat insulating material 31, and the refrigerant temperature can be accurately measured by the liquid pipe temperature sensor 6.
For example, the heater 7 is formed in a circular arc shape corresponding to the outer shape of the liquid refrigerant pipe 30 and is disposed along the longitudinal direction of the liquid refrigerant pipe 30. The heater 7 is composed of, for example, an electric heater (aluminum heater or the like), and generates heat when electric power is supplied via the cable 7a.

  The liquid pipe temperature sensor 6 is disposed in the heater installation range of the liquid refrigerant pipe 30. For example, as shown in FIG. 4, the surface of the liquid refrigerant pipe 30 is disposed at a portion facing the heater 7. Thus, by arranging the liquid tube temperature sensor 6 in the heater installation range, the temperature of the refrigerant heated by the heater 7 is measured by the liquid tube temperature sensor 6. Further, by disposing the liquid pipe temperature sensor 6 at a position facing the heater 7, it is possible to accurately detect the refrigerant temperature while suppressing the heat from the heater 7 from being directly transmitted to the liquid pipe temperature sensor 6. .

  As shown in FIG. 4B, the liquid pipe temperature sensor 6 is configured by, for example, a thermistor, and is inserted into a cylindrical copper tube 32 connected to the outer peripheral surface of the liquid refrigerant pipe 30 by welding or the like. Is done. As described above, the copper tube 32 made of copper having high thermal conductivity is welded to the liquid refrigerant pipe 30 so that the liquid pipe temperature sensor 6 can be easily installed and the refrigerant temperature in the pipe is accurately measured. can do.

  In the example of FIG. 4 described above, the liquid tube temperature sensor 6 is configured by a thermistor and is installed by being inserted into the copper tube 32, but the present invention is not limited to this. For example, as shown in FIG. 5, a flat plate 33 made of, for example, copper may be welded to the liquid refrigerant pipe 30, and a thermostat 6a as a temperature detecting means may be bolted thereto.

(Driving operation)
Next, the operation of the cooling device will be described.
FIG. 6 is a diagram showing a Ph diagram of the refrigeration cycle according to Embodiment 1 of the present invention.
Hereinafter, the operation of the cooling operation for cooling the temperature in the freezer 50 to a predetermined target temperature will be described with reference to FIG.
In FIG. 6, the 410A refrigerant has a high pressure of 2.3 MPa, a low pressure of 0.15 MPa, a saturation temperature (condensation temperature) of the refrigerant in the condenser 2 of 40 ° C., and the degree of supercooling is set to 5K during normal operation. Shows the case. In addition, each numerical value is an example and is not limited to this.
Note that the target temperature in the freezer 50 is often kept at -25 ° C. or lower in a warehouse that cools frozen foods such as ice cream. When storing milk or dairy products, the warehouse is often kept at around 5 ° C. The target temperature can be changed depending on the contents to be cooled.

The control device 100 detects the temperature in the freezer 50 by the internal temperature sensor 8, and when the temperature in the freezer 50 exceeds the target temperature, the electromagnetic valve 3 is opened and the compressor 1 is driven. When the compressor 1 is driven, high-temperature and high-pressure gas refrigerant is discharged from the compressor 1 (point A in FIG. 6). The high-temperature and high-pressure gas refrigerant discharged from the compressor 1 flows into the condenser 2, exchanges heat with the ambient outdoor air in the condenser 2, condenses and liquefies, and becomes a high-pressure and low-temperature refrigerant (point B in FIG. 6). , Point C). The operation of the compressor 1 and the blower 21 is controlled so that this high-pressure and low-temperature refrigerant is supercooled to about 5K with respect to the saturation temperature (point C in FIG. 6).
The high-pressure and low-temperature liquid refrigerant that has flowed out of the condenser 2 is supplied to the liquid refrigerant pipe 30. The liquid refrigerant that has passed through the liquid refrigerant pipe 30 enters the unit cooler 10 and is throttled to a low pressure by the expansion valve 4 to become a gas-liquid two-phase refrigerant having a low pressure and a low dryness (point D in FIG. 6). Heat is exchanged with the internal air, and the air is evaporated and vaporized for cooling (point E in FIG. 6).
The gas refrigerant that has flowed out of the evaporator 5 passes through the gas refrigerant pipe 40 and is sucked into the compressor 1, and is discharged from the compressor 1 as a high-temperature and high-pressure gas refrigerant (point A in FIG. 6).
By such cooling operation, the internal temperature gradually decreases and approaches the target temperature.

When the temperature in the freezer 50 falls below the target temperature, the control device 100 closes the electromagnetic valve 3. The solenoid valve 3 operates in accordance with a control signal from the control device 100, blocks the refrigerant flow path of the liquid refrigerant pipe 30 and blocks the refrigerant.
Thereafter, when the suction pressure of the compressor 1 reaches a predetermined low pressure, the control device 100 sends a control signal for stopping the operation to the compressor 1, and the cooling operation is stopped when the compressor 1 stops.

When the refrigerant is shut off by the electromagnetic valve 3 and the cooling operation is stopped by stopping the compressor 1, the temperature in the freezer 50 gradually increases.
When the temperature in the freezer 50 increases by a certain value or more (for example, 3 ° C. to 5 ° C.), the solenoid valve 3 is opened again, the compressor 1 is driven, and the above-described operation is repeated.

(Liquid hammer phenomenon)
Next, the liquid hammer phenomenon due to the opening of the solenoid valve 3 in the cooling operation as described above will be described.

While the refrigerant circuit is shut off, some of the refrigerant in the liquid refrigerant pipe 30 upstream of the solenoid valve 3 is inside the freezer 50, so it is cooled to around the same temperature (for example, −25 ° C.) as the temperature inside the freezer 50. May be.
The refrigerant upstream of the solenoid valve 3 is a high-pressure refrigerant, and is in a state of being supercooled by about 5K with respect to the saturation temperature of the high-pressure pressure during normal operation.
However, the high-pressure liquid refrigerant cooled to substantially the same temperature as the temperature in the freezer 50 as described above has a higher degree of supercooling than during normal operation. For example, if the high-pressure saturation temperature of the refrigerant is around 40 ° C., the refrigerant cooled to −25 ° C. is in a state of being supercooled by as much as 65K.
For example, in the case of R410A refrigerant and a high pressure of 2.3 MPa (saturation temperature is about 40 ° C.), the liquid density at 35 ° C. is 1007 kg / m ³ , whereas the density at −25 ° C. is 1269 kg / m 2. For m ³ and 35 ° C., the density is as high as 26%.

  When the electromagnetic valve 3 is opened, such high-density refrigerant flows from the electromagnetic valve 3 into the refrigerant flow path at once. The high-density refrigerant flows into the expansion valve 4 and is dammed up here to cause a liquid hammer phenomenon.

The refrigerant that has flowed into the expansion valve 4 is in a state where it has no place to go and is suddenly blocked, and generates a very large impact pressure. Generally, the expansion valve 4 or the like may be broken by repeatedly applying an impact pressure exceeding 7 MPa, for example.
As described above, the inside temperature is lower than the target temperature, the solenoid valve 3 is closed, the number of times the valve is opened at or above the target temperature is, for example, 4 to 6 times per hour, and the product life is 35 for 10 years. It reaches 10,000 to 530,000 times.
By repeatedly applying such high impact pressure, the expansion valve 4 is greatly damaged, eventually the equipment does not operate normally, the expansion process during the refrigeration cycle does not operate normally, and the temperature of the refrigerator This may cause an increase in the quality of the contents.
In addition, due to a very large impact due to the liquid hammer phenomenon, a very large abnormal sound and abnormal vibration are generated when the refrigerant collides.

(Relationship between liquid hammer pressure and temperature)
The liquid hammer pressure generated by such a liquid hammer phenomenon has the following relationship.
ΔP = ρ ・ V ・ C
Here, ΔP is the liquid hammer pressure. ρ is the liquid density. V is a refrigerant moving speed. C is the speed of sound.
The liquid density ρ varies depending on the temperature and pressure of the refrigerant. The liquid density decreases as the temperature of the refrigerant increases. Moreover, since the temperature of a refrigerant | coolant rises when a pressure rises, a liquid density falls.

FIG. 7 is a diagram showing an example of the relationship between the liquid hammer pressure and the refrigerant temperature according to Embodiment 1 of the present invention.
In the example of FIG. 7, the relationship between the refrigerant temperature and the liquid hammer pressure at a high pressure of 2.3 MPa for the R410A refrigerant is shown.
As shown in FIG. 7, the liquid hammer pressure decreases as the refrigerant temperature increases. For example, at a temperature where the refrigerant temperature exceeds 30 ° C., the liquid hammer pressure is less than 7 MPa, which is the failure limit of the expansion valve 4. These numerical values are merely examples, and vary depending on the pipe length upstream of the solenoid valve 3 and the pipe inner diameter (refrigerant amount).
Thus, the liquid hammer pressure generated by the liquid hammer phenomenon can be reduced by heating the refrigerant and increasing the refrigerant temperature.

(Problems of overheating the refrigerant)
Although the liquid hammer pressure is reduced by raising the temperature of the refrigerant as described above, there are the following problems when the refrigerant is heated.
When a low-temperature and high-pressure liquid refrigerant (supercooled state) is heated, the temperature of the refrigerant rises as it is heated, and two-layer separation begins (boiling state) when the saturated liquid line is exceeded under the conditions (boiling state). There is no temperature rise. For this reason, since there is no change only by temperature detection, it becomes difficult to detect the enthalpy (converted) of the refrigerant.
As described above, heating the refrigerant to the two-phase refrigerant cannot perform heating control based on temperature detection, and performs wasteful heating, causing energy loss in the refrigeration cycle.
Moreover, if it heats too much, the vaporization degree of the refrigerant | coolant of the heater 7 vicinity will become excess, and the effect of shock absorption will fall.
Furthermore, since the expansion valve 4 generally controls the flow path of the liquid refrigerant, the mechanical expansion valve, in particular, cannot perform normal control when the two-phase separated refrigerant passes.

From the above, in the present embodiment, the refrigerant temperature upstream of the solenoid valve 3 is set to a temperature within a predetermined range in which the upper limit value is equal to or lower than the refrigerant saturation temperature (saturated liquid line) in the condenser 2. In addition, the heater 7 is controlled.
Further, the lower limit value of the predetermined range is that the impact pressure (liquid hammer pressure) due to the liquid hammer phenomenon generated in the expansion valve 4 when the electromagnetic valve 3 is opened is equal to or less than the predetermined value (destruction limit value of the expansion valve 4). Is set to a temperature (for example, 30 ° C.).
The heating operation of the heater 7 in this embodiment will be described with reference to FIG.

(Heating operation of heater 7)
FIG. 8 is a Ph diagram illustrating the heater heating operation according to Embodiment 1 of the present invention.
FIG. 8A shows a state in which the liquid refrigerant is cooled to the internal temperature, and FIG. 8B shows heating by the heater 7.
In FIG. 8, the 410A refrigerant has a high pressure of 2.3 MPa, a low pressure of 0.15 MPa, a saturation temperature (condensation temperature) of the refrigerant in the condenser 2 of 40 ° C., and the degree of supercooling is set to 5K during normal operation. Shows the case. In addition, each numerical value is an example and is not limited to this.

  As shown in FIG. 8A, the high-pressure liquid refrigerant (point C ′ in FIG. 8A) cooled to substantially the same temperature (−25 ° C.) as the temperature in the freezer 50 has a supercooling degree of 65K. It will be in a state of attaching. If the cooling device is operated in this state, it cannot be sufficiently evaporated and vaporized in the evaporation step of the refrigeration cycle, and the two-phase refrigerant flows out of the evaporator 5. Such outflow of the two-phase refrigerant may cause liquid back to the compressor 1. For example, even when an accumulator (not shown) is provided to prevent liquid back, it is necessary to increase the capacity. Furthermore, the enthalpy of the high-temperature and high-pressure gas refrigerant discharged from the compressor 1 is reduced, and the efficiency (COP) is lowered.

As shown in FIG. 8 (b), in the present embodiment, by operating the heater 7, as a temperature within a predetermined range (30 ° C. or higher and lower than 40 ° C.), for example, the refrigerant temperature at which the degree of supercooling is 5K. Heat to 35 ° C.
By such heating, the liquid hammer pressure can be set to a predetermined value (impact limit value of the expansion valve 4) or less while maintaining the refrigerant in a liquid phase state. Moreover, the fall of driving | operation efficiency can be suppressed by setting a supercooling degree appropriately. Further, liquid back can be prevented without providing an accumulator or increasing the capacity of the accumulator.

  Next, details of the control operation of the heater 7 will be described with reference to FIG.

FIG. 9 is a flowchart of the heater control operation according to Embodiment 1 of the present invention.
Hereinafter, a description will be given based on each step of FIG.
(S1)
The control device 100 determines whether or not the temperature detected by the internal temperature sensor 8 (internal temperature) is equal to or higher than a predetermined temperature, the compressor 1 is stopped, and the electromagnetic valve 3 is closed. The control device 100 repeats the determination in step S1 until the condition is satisfied.
Here, the predetermined temperature is set to a temperature (for example, −25 ° C.) lower than a lower limit value of a predetermined range described later.

(S2)
When the condition of step S1 is satisfied, the control device 100 determines whether or not the temperature detected by the liquid tube temperature sensor 6 is a temperature within a predetermined range.
The upper limit value of the predetermined range is a value equal to or lower than the refrigerant saturation temperature (saturated liquid line) in the condenser 2. For example, in the case of R410A refrigerant and a high pressure of 2.3 MPa, a saturation temperature of 40 ° C. is set as the upper limit value.
The lower limit value of the predetermined range is a value at which the impact pressure (liquid hammer pressure ΔP) caused by the liquid hammer phenomenon generated in the expansion valve 4 when the electromagnetic valve 3 is opened is less than the predetermined value. For example, when the fracture limit of the expansion valve 4 is 7 MPa, the lower limit value is 30 ° C., which is the temperature at which the liquid hammer pressure ΔP becomes 7 MPa. These numerical values are merely examples, and vary depending on the pipe length upstream of the solenoid valve 3 and the pipe inner diameter (refrigerant amount).

(S3)
When the temperature detected by the liquid pipe temperature sensor 6 is not within the predetermined range, the control device 100 puts the electromagnetic valve 3 into the open prohibited state.
This open prohibition state means that the operation of opening the solenoid valve 3 is prohibited even when the temperature in the freezer 50 exceeds the target temperature and the cooling operation needs to be started in the cooling operation described above. It is a state to do. That is, when the refrigerant temperature upstream of the solenoid valve 3 is not within the predetermined range, the operation of opening the solenoid valve 3 is delayed.

(S4)
The control device 100 operates the heater 7 to start heating the refrigerant in the liquid refrigerant pipe 30 on the upstream side of the electromagnetic valve 3, and returns to step S1.
In this heating operation, as described above, feedback control for turning on / off the heater 7 may be performed so that the refrigerant has a predetermined degree of supercooling (5K). In other words, the control device 100 may perform on / off control of the heater 7 so that the temperature of the refrigerant detected by the liquid tube temperature sensor 6 becomes a predetermined temperature (35 ° C.).

(S5)
On the other hand, when the temperature detected by the liquid pipe temperature sensor 6 is a temperature within a predetermined range, the control device 100 makes the electromagnetic valve 3 openable.
This openable state is a state in which, in the above-described cooling operation, when the temperature in the freezer 50 exceeds the target temperature and the cooling operation needs to be started, an operation to open the solenoid valve 3 is possible. is there. That is, when the refrigerant temperature upstream of the electromagnetic valve 3 is within the predetermined range, an operation for opening the electromagnetic valve 3 is executed.

(S6)
The control device 100 stops the operation of the heater 7 and returns to step S1.
Thereafter, the above-described operation is repeatedly executed.

  In the above operation, in step S1, it is a condition that the temperature detected by the internal temperature sensor 8 is equal to or higher than a predetermined temperature. However, the present invention is not limited to this. In step S1, when the compressor 1 is in a stopped state and the solenoid valve 3 is in a closed state, the process may proceed to step S2 as satisfying the condition. Thus, regardless of the inside temperature, when the solenoid valve 3 is closed while the compressor 1 is stopped, the heater 7 is controlled so that the refrigerant temperature is in a predetermined range. Also good.

(effect)
As described above, in the present embodiment, when the compressor 1 is stopped and the solenoid valve 3 is closed, the detected temperature of the liquid pipe temperature sensor 6 is set to the upper limit value of the refrigerant saturation temperature in the condenser 2. The heater 7 is controlled so that the temperature is within the predetermined range described below.
For this reason, even if it is a case where the refrigerant | coolant of the upstream of the solenoid valve 3 is heated, it can prevent that a refrigerant | coolant will be in a two-phase state. Therefore, heating control can be performed in the range of sensible heat rise in which the state of the refrigerant can be detected by temperature.
Therefore, the supercooling loss of the liquid refrigerant due to the heating of the heater 7 can be prevented, the energy loss in the refrigeration cycle can be suppressed, and the decrease in the cooling capacity can be suppressed. Thereby, the quality deterioration of the cooling thing in the freezer 50 can also be prevented.
Further, the vaporization degree of the refrigerant in the vicinity of the heater 7 does not become excessive, and the reduction of the liquid hammer phenomenon can be prevented from being reduced.
Further, it is not necessary to energize the heater 7 at all times, which can contribute to energy saving by reducing the power consumption of the heater 7.

Further, the heater 7 is controlled so that the refrigerant has a predetermined degree of supercooling (5K).
For this reason, the fall of efficiency can be reduced by sending the refrigerant | coolant of a suitable supercooling degree to the evaporator 5. FIG. Further, liquid back can be prevented without providing an accumulator or increasing the accumulator capacity.

In the present embodiment, the lower limit value of the predetermined range is a temperature at which the impact pressure due to the liquid hammer phenomenon generated in the expansion valve 4 becomes less than the predetermined value when the electromagnetic valve 3 is opened.
Thereby, the impact pressure to the expansion valve 4 due to the liquid hammer phenomenon can be reduced, and the destruction and deterioration of the expansion valve 4 due to the liquid hammer phenomenon can be suppressed.
In addition, the liquid hammer pressure can be suppressed to less than the breakage limit of the expansion valve 4.

In the present embodiment, the expansion valve 4 is constituted by a mechanical expansion valve that opens and closes the valve by a mechanical action. The expansion valve 4 is controlled by a heater 7 so that a liquid-phase refrigerant flows.
For this reason, it can suppress that a gaseous-phase refrigerant | coolant (two-phase refrigerant | coolant) passes through the expansion valve 4, and the abnormal operation | movement (malfunction) of the expansion valve 4 can be prevented.

In the present embodiment, after detecting that the internal temperature is equal to or higher than the predetermined temperature in step S1, control of energization to the heater 7 is started when the refrigerant temperature is not within the predetermined range. The present invention is not limited to this.
It is preferable that the temperature (temperature increase time) until the refrigerant temperature reaches the predetermined range after the internal temperature is detected as the predetermined temperature is as short as possible.
For this purpose, for example, based on the internal temperature detected by the internal temperature sensor 8 or based on the temperature change of the internal temperature, the time for the internal temperature to reach a predetermined temperature is predicted, and the internal temperature sensor 8 The energization of the heater 7 may be started in advance before the detected temperature reaches a predetermined temperature.

  Further, in order to suppress loss due to heat transfer from the refrigerant heated by the heater 7 to the refrigerant in the liquid refrigerant pipe 30 disposed outside the freezer 50, in the upstream portion of the heater installation range of the liquid refrigerant pipe 30, A check valve or the like may be provided.

Embodiment 2. FIG.
FIG. 10 is a refrigerant circuit diagram of the cooling device according to Embodiment 2 of the present invention.
As shown in FIG. 10, in the present embodiment, in addition to the configuration of the first embodiment (FIG. 1), in the refrigerant circuit of the third embodiment, the liquid refrigerant pipe 30 on the upstream side of the electromagnetic valve 3. Further, a pressure sensor 12 for detecting the pressure of the refrigerant heated by the heater 7 is provided.
Other configurations are the same as those in the first embodiment, and the same reference numerals are given to the same portions.

As described above, the liquid hammer pressure ΔP is proportional to the liquid density ρ. The liquid density ρ depends on the temperature and pressure of the refrigerant.
In the present embodiment, control device 100 determines the liquid density ρ of the refrigerant based on the detection results of liquid tube temperature sensor 6 and pressure sensor 12. For example, a relationship table of the temperature, pressure, and liquid density in the refrigerant type to be used is stored in advance, and the liquid density ρ is obtained by referring to this table.
In addition to the heating operation of the heater 7 of the first embodiment, the operation of the heater 7 is controlled so that the liquid hammer pressure ΔP calculated from the liquid density ρ does not exceed the destruction limit of the expansion valve 4.
When the liquid hammer pressure ΔP calculated from the liquid density ρ exceeds the destruction limit of the expansion valve 4, the electromagnetic valve 3 is prohibited from being opened.

  By such an operation, in addition to the effect of the first embodiment, it is possible to detect the refrigerant state in which the liquid hammer pressure ΔP exceeds the destruction limit of the expansion valve 4 with higher accuracy. Destruction, deterioration, etc. can be suppressed.

Embodiment 3 FIG.
In the third embodiment, a mode in which the liquid refrigerant pipe 30 that connects the unit cooler 10 and the outdoor unit 20 is arranged in the freezer 50 will be described.

FIG. 11 is an exemplary view of a freezer in which a cooling device according to Embodiment 3 of the present invention is arranged.
As shown in FIG. 11, the freezer 50 may not be able to install the unit cooler 10 at a suitable position depending on the facility conditions. In this case, the liquid refrigerant pipe 30 and the gas refrigerant pipe 40 may have to be routed in the freezer 50 for a long time.
In such a case, the second heater 9 for heating the refrigerant is provided in the liquid refrigerant pipe 30 disposed in the freezer 50 in the liquid refrigerant pipe 30 on the upstream side of the electromagnetic valve 3.

The second heater 9 is disposed, for example, by winding a heating wire around the liquid refrigerant pipe 30, and has a heat generation amount (watt density) per unit volume that is substantially the same as that of the heater 7.
It is not necessary to provide a sensor or the like for measuring the temperature of the refrigerant heated by the second heater 9.

The “second heater 9” corresponds to the “second heating means” in the present invention.
Other configurations are the same as those in the first embodiment, and the same reference numerals are given to the same portions.

  With such a configuration, the control device 100 according to the present embodiment performs control (parallel control) so that the operation state of the second heater 9 is the same as the operation state of the heater 7. That is, when the heater 7 is on, the second heater 9 is also on, and when the heater 7 is off, the second heater 9 is also off.

As described above, in the present embodiment, even when the liquid refrigerant pipe 30 that connects the unit cooler 10 and the outdoor unit 20 is disposed in the freezer 50, the refrigerant is heated by the second heater 9. And the same effects as those of the first embodiment can be obtained.
Further, since the heat generation amount (watt density) per unit volume is controlled so that the operation state of the second heater 9 configured substantially the same as the heater 7 is the same as the operation state of the heater 7, the second The refrigerant temperature can be set to a temperature within a predetermined range without measuring the temperature of the refrigerant heated by the heater 9. Therefore, the same effect as in the first embodiment can be obtained.

  DESCRIPTION OF SYMBOLS 1 Compressor, 2 Condenser, 3 Solenoid valve, 4 Expansion valve, 5 Evaporator, 6 Liquid pipe temperature sensor, 6a Thermostat, 7 Heater, 7a Cable, 8 Internal temperature sensor, 9 Second heater, 10 Unit cooler , 11 Blower, 12 Pressure sensor, 20 Outdoor unit, 21 Blower, 30 Liquid refrigerant piping, 31 Heat insulation material, 32 Copper tube, 33 Flat plate, 40 Gas refrigerant piping, 50 Freezer, 100 Control device.

Claims (8)

A cooling device for cooling a facility to be cooled,
A refrigerant circuit that sequentially connects the compressor, the condenser, the on-off valve, the expansion means, and the evaporator with refrigerant piping and circulates the refrigerant;
A heating unit that is disposed in a refrigerant pipe upstream of the on-off valve and heats the refrigerant in the refrigerant pipe;
Temperature detecting means for detecting the temperature of the refrigerant heated by the heating means;
Control means for controlling the operation of the on-off valve and the heating means,
The on-off valve, the expansion means, the evaporator, and the heating means are arranged in the cooled facility,
The control means includes
When the compressor is in a stopped state and the on-off valve is in a closed state,
The cooling device according to claim 1, wherein the heating unit is controlled so that a temperature detected by the temperature detection unit is a temperature within a predetermined range in which an upper limit value is equal to or lower than a saturated liquid temperature of the refrigerant in the condenser. The lower limit value of the predetermined range is
The cooling device according to claim 1, wherein when the on-off valve is in an open state, an impact pressure due to a liquid hammer phenomenon generated in the expansion means is a temperature that is a predetermined value or less. The control means includes
When the detected temperature of the temperature detecting means is not within the predetermined range, the operation of opening the on-off valve is prohibited,
3. The cooling device according to claim 1, wherein when the detected temperature of the temperature detecting means is a temperature within the predetermined range, an operation for opening the on-off valve is enabled. A second temperature detecting means for detecting the temperature of the air in the cooled facility;
The control means includes
When the detected temperature of the second temperature detection means is equal to or higher than a predetermined temperature, the compressor is stopped, and the on-off valve is closed, the heating means is operated,
The cooling device according to any one of claims 1 to 3, wherein when the temperature detected by the temperature detection means is a temperature within the predetermined range, the heating means is stopped. A second temperature detecting means for detecting the temperature of the air in the cooled facility;
The control means includes
When the detected temperature of the second temperature detection means is equal to or higher than a predetermined temperature, the compressor is stopped, and the on-off valve is closed, the heating means is operated,
2. When the temperature detected by the temperature detection means is a temperature within the predetermined range, the heating means is stopped, the on-off valve is opened, and the operation of the compressor is started. 4. The cooling device according to any one of 3. The on-off valve, the expansion means, and the evaporator are provided in a load side unit disposed in the cooled facility,
The compressor and the condenser are provided in a heat source side unit disposed outside the facility to be cooled,
The load side unit and the heat source side unit are connected by a refrigerant pipe constituting the refrigerant circuit,
The heating means is disposed in a refrigerant pipe in the load side unit among the refrigerant pipes on the upstream side of the on-off valve,
Among the refrigerant pipes on the upstream side of the on-off valve, the refrigerant pipes connecting the load side unit and the heat source side unit to the refrigerant pipes arranged in the cooled equipment, the refrigerant in the refrigerant pipes The cooling device according to any one of claims 1 to 5, further comprising a second heating means for heating the heater. The second heating means is configured so that a calorific value per unit volume is substantially equal to that of the heating means,
The control means includes
The cooling device according to claim 6, wherein an operation state of the second heating unit is controlled to be the same as an operation state of the heating unit. The expansion means is
The cooling device according to any one of claims 1 to 7, wherein the cooling device comprises a mechanical expansion valve that opens and closes the valve by a mechanical action.

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