EP3015797A1

EP3015797A1 - Electromagnetic-valve control device for refrigerator, refrigerator, and method for controlling refrigerator

Info

Publication number: EP3015797A1
Application number: EP15191999.0A
Authority: EP
Inventors: Takeshi Takeda; Kenichi Murakami; Hitonobu SATO
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2014-10-31
Filing date: 2015-10-29
Publication date: 2016-05-04
Also published as: JP2016090103A

Abstract

A refrigerator (10) has a compressor (12), a gas cooler (14), an expansion valve (16), and an evaporator (18) connected in this order by a refrigerant pipe (20) and opens and closes an electromagnetic valve (26) provided in a bypass pipe (22) serving as a bypass section that connects the outlet side and the inlet side of the compressor (12). An electromagnetic-valve control device (30) opens the electromagnetic valve (26) if the pressure of a refrigerant at the outlet of the evaporator (18) during operation of the compressor (12) becomes lower than or equal to an ON threshold value set with reference to the triple point of the refrigerant. Accordingly, the electromagnetic-valve control device (30) can allow the refrigerator (10) to continue operating without having to stop the compressor (12) even when a physical quantity of the refrigerant approaches the triple point.

Description

{Technical Field}

The present invention relates to electromagnetic-valve control devices for refrigerators, refrigerators, and methods for controlling refrigerators.

{Background Art}

In a refrigerator that includes a compressor, a condenser, an expansion valve, and an evaporator, frost may form on the evaporator as the pressure at the low-pressure side decreases.
In such a case, when the refrigerant outlet temperature of the evaporator falls below, for example, 0°C, the frost adhered on the evaporator is removed by stopping the operation of the compressor and rotating a fan provided for the evaporator to continuously blow air thereto. However, once the compressor stops, temperature control is no longer performed.
PTL 1 discloses a method of preventing frost formation by suppressing a decrease in pressure at the low-pressure side by bypassing a portion of hot gas in the compressor toward the low-pressure side in a case where the refrigerant outlet pressure of the evaporator falls below a frost-formation-limit evaporation pressure.

{Citation List}

{Patent Literature}

[PTL 1] Publication of Japanese Patent No. 2792265 {Summary of Invention}

{Technical Problem}

As described above, PTL 1 discloses how to prevent frost formation without stopping the compressor.
A refrigerator that uses, for example, CO₂ as a refrigerant operates with the evaporation temperature set at a low temperature of, for example, -45°C so as to cool the atmosphere within, for example, a refrigerated showcase.
In this case, the pressure of the refrigerant is 0.83 MPa, which is close to the triple point (0.52 MPa, -56.6°C) at which the refrigerant solidifies (becomes dry ice). When performing a pump-down operation for leaving no refrigerant within the evaporator or when a physical quantity of the refrigerant reaches the triple point due to a load change, such as a load decrease, the refrigerant may solidify and be taken into the compressor. Therefore, in such a case, the compressor needs to be stopped for preventing the compressor from failing.
Accordingly, even when there is no frost formation, the compressor needs to be stopped if a physical quantity of the refrigerant may reach the triple point.
The present invention has been made in view of such circumstances and an object thereof is to provide an electromagnetic-valve control device for a refrigerator, a refrigerator, and a method for controlling a refrigerator that can allow the refrigerator to continue operating without having to stop the compressor even when a physical quantity of the refrigerant approaches the triple point.

{Solution to Problem}

In order to solve the aforementioned problems, an electromagnetic-valve control device for a refrigerator, a refrigerator, and a method for controlling a refrigerator according to the present invention employ the following solutions.
According to a first aspect of the present invention, there is provided an electromagnetic-valve control device for a refrigerator in which a compressor, a radiator, an expansion valve, and an evaporator are connected in this order by a refrigerant pipe and that opens and closes an electromagnetic valve provided in a bypass pipe serving as a bypass section that connects an outlet side and an inlet side of the compressor. The electromagnetic-valve control device opens the electromagnetic valve if a physical quantity of a refrigerant at an outlet of the evaporator during operation of the compressor becomes lower than or equal to a predetermined value set with reference to a triple point of the refrigerant.
The refrigerator according to this configuration includes the bypass pipe serving as a bypass section that connects the outlet side and the inlet side of the compressor.
Because the refrigerator cools the atmosphere of, for example, a refrigerated showcase, a physical quantity of the refrigerant during operation is close to the triple point at which the refrigerant solidifies. Therefore, the physical quantity of the refrigerant may reach the triple point due to, for example, a load change, possibly resulting in solidification of the refrigerant.
In this configuration, if the physical quantity of the refrigerant at the outlet of the evaporator during operation of the compressor becomes lower than or equal to the predetermined value set with reference to the triple point of the refrigerant, the electromagnetic valve provided in the bypass pipe is opened. Consequently, the bypass pipe causes a portion of high-temperature, high-pressure refrigerant discharged from the compressor to be extracted toward the inlet side of the compressor.
Specifically, due to the extraction through the bypass pipe, the physical quantity of the refrigerant to be taken into the compressor is prevented from reaching the triple point. Even if the refrigerant solidifies at the evaporator, the solidified refrigerant would not be taken into the compressor since the solidified refrigerant becomes vaporized by the extracted high-temperature, high-pressure refrigerant.
Accordingly, with this configuration, since a solidified refrigerant is prevented from being taken into the compressor, the refrigerator can continue operating without having to stop the compressor even when the physical quantity of the refrigerant approaches the triple point due to a load change.
In the first aspect, the electromagnetic-valve control device may include a switch that is disposed between the evaporator and the compressor and enters an ON state when the pressure of the refrigerant reaches a predetermined pressure. The electromagnetic valve may be opened when the switch is in the ON state.
According to this configuration, even when the pressure of the refrigerant decreases excessively, the refrigerant turned into a high-temperature, high-pressure state at the compressor can be quickly extracted toward the inlet side of the compressor with a simple configuration.
A refrigerator according to a second aspect of the present invention includes a bypass pipe serving as a bypass section that connects an outlet side and an inlet side of the compressor, an electromagnetic valve provided in the bypass pipe, and the aforementioned electromagnetic-valve control device.
According to a third aspect of the present invention, there is provided a method for controlling a refrigerator in which a compressor, a radiator, an expansion valve, and an evaporator are connected in this order by a refrigerant pipe and that opens and closes an electromagnetic valve provided in a bypass pipe serving as a bypass section that connects an outlet side and an inlet side of the compressor. The method includes opening the electromagnetic valve if a physical quantity of a refrigerant at an outlet of the evaporator during operation of the compressor becomes lower than or equal to a predetermined value set with reference to a triple point of the refrigerant.

{Advantageous Effects of Invention}

The present invention is advantageous in that it can allow the refrigerator to continue operating without having to stop the compressor even when the physical quantity of the refrigerant approaches the triple point.

{Brief Description of Drawings}

{Fig. 1} Fig. 1 is a circuit configuration diagram of a refrigerator according to an embodiment of the present invention.
{Fig. 2} Fig. 2 is a p-h diagram of CO₂.
{Fig. 3} Fig. 3 is a flowchart illustrating the flow of an electromagnetic-valve control process according to an embodiment of the present invention.

{Description of Embodiments}

An embodiment of an electromagnetic-valve control device for a refrigerator, a refrigerator, and a method for controlling a refrigerator will be described below with reference to the drawings.
Fig. 1 is a circuit configuration diagram of a refrigerator 10 according to this embodiment.
The refrigerator 10 according to this embodiment is a refrigeration cycle having a compressor 12, a gas cooler 14, an expansion valve 16, and an evaporator 18 connected in this order by a refrigerant pipe 20. The refrigeration cycle according to this embodiment uses, for example, CO₂ as a refrigerant.
Furthermore, the refrigerator 10 according to this embodiment includes a bypass pipe 22 serving as a bypass section that connects the outlet side and the inlet side of the compressor 12.
The compressor 12 takes in a refrigerant from the evaporator 18, compresses this refrigerant, and discharges the refrigerant toward the gas cooler 14.
The gas cooler 14 performs heat exchange between the high-temperature, high-pressure refrigerant discharged from the compressor 12 and outside air blown in by a gas cooler fan 15 so as to cause the refrigerant to dissipate heat.
The expansion valve 16 causes the refrigerant that has dissipated heat at the gas cooler 14 to adiabatically expand, so as to decompress the refrigerant.
The evaporator 18 performs heat exchange between the refrigerant decompressed at the expansion valve 16 and air blown in by an evaporator fan 19 so as to cause the refrigerant to absorb heat.
For example, the evaporator 18 is provided within a refrigerated showcase 24 that stores ice cream and performs heat exchange between the refrigerant and the atmosphere within the refrigerated showcase 24. Thus, the interior of the refrigerated showcase 24 is maintained at low temperature (e.g., an evaporation temperature of -45°C).
Accordingly, the refrigerator 10 forms a refrigeration cycle that cools the atmosphere within the refrigerated showcase 24.
The refrigerator 10 may be of a type that includes a plurality of evaporators 18 and a plurality of refrigerated showcases 24.
The bypass pipe 22 equipped between the outlet side and the inlet side of the compressor 12 is provided with an electromagnetic valve 26 and a throttle 28.
With regard to the bypass pipe 22, when the electromagnetic valve 26 opens, a portion of the high-temperature, high-pressure refrigerant discharged from the compressor 12 is extracted toward the inlet side of the compressor 12. The refrigerant traveling through the bypass pipe 22 is adjusted to a predetermined pressure by the throttle 28.
Open-close control of the electromagnetic valve 26 is performed by an electromagnetic-valve control device 30.
A low-pressure switch 32 that enters an ON state when the pressure of the refrigerant reaches a predetermined pressure is provided between the evaporator 18 and the compressor 12 and at the compressor 12 side relative to the refrigerant extraction position.
The low-pressure switch 32 enters an ON state when the pressure of the refrigerant between the evaporator 18 and the compressor 12 (referred to as "low pressure" hereinafter) becomes lower than or equal to a predetermined value (referred to as "ON threshold value" hereinafter) set with reference to the triple point of the refrigerant. Then, a signal indicating that the low-pressure switch 32 is in an ON state or an OFF state is output to the electromagnetic-valve control device 30.
The refrigerator 10 further includes a refrigerator control device 34 that controls the refrigerator 10.
The refrigerator control device 34 is composed of, for example, a central processing unit (CPU), a random access memory (RAM), a read-only memory (ROM), and a computer-readable storage medium. A series of processes for achieving various functions is stored in, for example, the storage medium in the form of a program. The CPU loads this program into, for example, the RAM and executes information processing and calculation so that the various functions are achieved. The program may be preinstalled in the ROM or another storage medium, may be provided by being stored in the computer-readable storage medium, or may be distributed via wired or wireless communication means. The computer-readable storage medium is, for example, a magnetic disk, a magneto-optical disk, a compact disc read-only memory (CD-ROM), a digital versatile disc read-only memory (DVD-ROM), or a semiconductor memory.
The refrigerator control device 34 performs various kinds of control, such as activating and stopping the compressor 12 and outputting a control command for the electromagnetic valve 26 to the electromagnetic-valve control device 30.
For example, before activating the compressor 12, the refrigerator control device 34 outputs a control command for opening the electromagnetic valve 26 to the electromagnetic-valve control device 30. As a result, the electromagnetic valve 26 in a closed state is opened by the electromagnetic-valve control device 30. When the electromagnetic valve 26 opens, the refrigerant at the outlet side of the compressor 12 is extracted toward the inlet side thereof via the bypass pipe 22. Since this balances out the outlet pressure and the inlet pressure of the compressor 12, the load on the compressor 12 at the time of activation decreases. When the activation of the compressor 12 is completed, the refrigerator control device 34 outputs a control command for closing the electromagnetic valve 26 to the electromagnetic-valve control device 30. Consequently, the electromagnetic-valve control device 30 closes the electromagnetic valve 26.
In order to cool the interior of the refrigerated showcase 24, the refrigerator 10 operates so that, for example, an evaporation temperature of -45°C and an evaporation pressure of 0.83 MPa are achieved.
Such physical quantities of the refrigerant are close to -56.6°C and 0.52 MPa, which correspond to the triple point where the refrigerant turns into its solid state (dry ice) (see the p-h diagram in Fig. 2). Therefore, if the load changes, such as when the load decreases, the physical quantities of the refrigerant may reach the triple point, possibly resulting in solidification of the refrigerant.
The refrigerator 10 according to this embodiment opens the electromagnetic valve 26 if a physical quantity of the refrigerant at the outlet of the evaporator 18 during operation of the compressor 12 becomes lower than or equal to a predetermined value set with reference to the triple point of the refrigerant.
The predetermined value set with reference to the triple point of the refrigerant is between the aforementioned physical quantity of the refrigerant during operation and the triple point and is a physical quantity higher than the triple point. In this embodiment, this predetermined value is set as the ON threshold value at which the low-pressure switch 32 enters an ON state, and this ON threshold value is set to, for example, 0.68 MPa (the temperature of the refrigerant in this case is -50°C). The low-pressure switch 32 changes from an ON state to an OFF state when, for example, the refrigerant becomes 0.77 MPa (the temperature of the refrigerant in this case is -47°C) (referred to as "OFF threshold value" hereinafter).
Accordingly, the low-pressure switch 32 enters an OFF state at the OFF threshold value, which is a pressure value higher than the ON threshold value. When the low-pressure switch 32 enters an OFF state, the electromagnetic valve 26 closes.
Accordingly, when the refrigerant at the outlet of the evaporator 18 approaches the triple point due to, for example, a load change and the low pressure becomes lower than or equal to the ON threshold value, the electromagnetic-valve control device 30 opens the electromagnetic valve 26. With the electromagnetic valve 26 open, the bypass pipe 22 causes a portion of the high-temperature, high-pressure refrigerant discharged from the compressor 12 to be extracted toward the inlet side of the compressor 12.
Specifically, due to the extraction through the bypass pipe 22, the temperature and the pressure of the refrigerant to be taken into the compressor 12 increase, thus preventing the physical quantities of the refrigerant from reaching the triple point. Even if the refrigerant solidifies at the evaporator 18, the solidified refrigerant would not be taken into the compressor 12 since the solidified refrigerant becomes vaporized by the extracted high-temperature, high-pressure refrigerant.
Accordingly, in the refrigerator 10 according to this embodiment, even when a physical quantity of the refrigerant approaches the triple point due to a load change, the high-temperature, high-pressure refrigerant is extracted toward the inlet side of the compressor 12 so that a solidified refrigerant is prevented from being taken into the compressor 12, whereby the refrigerator 10 can continue operating without having to stop the compressor 12.
Fig. 3 is a flowchart illustrating the flow of an electromagnetic-valve control process according to this embodiment. The electromagnetic-valve control process is executed by the electromagnetic-valve control device 30 when the compressor 12 starts operating.
First, when the low-pressure switch 32 enters an ON state in step 100 as a result of the low pressure becoming lower than or equal to the ON threshold value, the process proceeds to step 102.
In step 102, the electromagnetic valve 26 is opened. Thus, a portion of high-temperature, high-pressure refrigerant discharged from the compressor 12 is extracted toward the inlet side of the compressor 12. As a result of this extraction, the temperature and the pressure of the refrigerant to be taken into the compressor 12 increase.
Subsequently, when the low-pressure switch 32 enters an OFF state in step 104 as a result of the low pressure increasing to the OFF threshold value or higher, the process proceeds to step 106.
Then, in step 106, the electromagnetic valve 26 is closed. Thus, the extraction toward the inlet side of the compressor 12 via the bypass pipe 22 stops. Then, the electromagnetic-valve control process is repeated while the compressor 12 is in operation.
As described above, the refrigerator 10 according to this embodiment has the compressor 12, the gas cooler 14, the expansion valve 16, and the evaporator 18 connected in this order by the refrigerant pipe 20 and opens and closes the electromagnetic valve 26 provided in the bypass pipe 22 serving as a bypass section that connects the outlet side and the inlet side of the compressor 12. The electromagnetic-valve control device 30 opens the electromagnetic valve 26 if the pressure of the refrigerant at the outlet of the evaporator 18 during operation of the compressor 12 becomes lower than or equal to the ON threshold value set with reference to the triple point of the refrigerant.
Accordingly, even when a physical quantity of the refrigerant in the evaporator 18 approaches the triple point due to a load change, the high-temperature, high-pressure refrigerant is extracted toward the inlet side of the compressor 12 so that the physical quantity of the refrigerant at the inlet of the compressor 12 would not reach the triple point. Therefore, since the refrigerator 10 according to this embodiment prevents a solidified refrigerant from being taken into the compressor 12, the refrigerator 10 can continue operating without having to stop the compressor 12.
Although the present invention has been described above with reference to the above embodiment, the technical scope of the present invention is not limited to the scope defined in the above embodiment. Various modifications and alterations may be added to the above embodiment so long as they do not depart from the scope of the invention, and embodiments with such modifications and alterations added thereto are included in the technical scope of the present invention. Moreover, the embodiments described above may be appropriately combined.
For example, although the open-close control of the electromagnetic valve 26 is performed based on pressure as a physical quantity of the refrigerant in the above embodiment, the present invention is not limited to this. The open-close control of the electromagnetic valve 26 may be performed based on temperature as a physical quantity of the refrigerant. In this case, for example, the ON threshold value for the electromagnetic valve 26 is set to -50°C, and the OFF threshold value for the electromagnetic valve 26 is set to -47°C.
Furthermore, although the electromagnetic-valve control device 30 is configured to perform the open-close control of the electromagnetic valve 26 in the above embodiment, the present invention is not limited to this. The refrigerator control device 34 may have the function of the electromagnetic-valve control device 30 such that the refrigerator control device 34 may be configured to perform the open-close control of the electromagnetic valve 26.
Furthermore, although the refrigerator 10 is of a single-stage compression type as an example in the above embodiment, the present invention is not limited to this. The refrigerator 10 may alternatively be of a two-stage compression type.
Furthermore, the flow of the electromagnetic-valve control process described in the above embodiment is merely an example. Unnecessary steps may be deleted, new steps may be added, or the processing order may be changed, so long as it does not depart from the scope of the present invention.

{Reference Signs List}

10: refrigerator
12: compressor
14: gas cooler
16: expansion valve
18: evaporator
20: refrigerant pipe
22: bypass pipe
26: electromagnetic valve
30: electromagnetic-valve control device
32: low-pressure switch
34: refrigerator control device

Claims

An electromagnetic-valve control device (30) for a refrigerator (10) in which a compressor (12), a radiator (14), an expansion valve (16), and an evaporator (18) are connected in this order by a refrigerant pipe (20) and configured to open and close an electromagnetic valve (26) provided in a bypass pipe (22) serving as a bypass section that connects an outlet side and an inlet side of the compressor (12),
wherein the electromagnetic-valve control device (30) is configured to open the electromagnetic valve (26) if a physical quantity of a refrigerant at an outlet of the evaporator (18) during operation of the compressor (12) becomes lower than or equal to a predetermined value set with reference to a triple point of the refrigerant.
The electromagnetic-valve control device (30) according to Claim 1, comprising:
a switch (32) that is disposed between the evaporator (18) and the compressor (12) and configured to enter an ON state when the pressure of the refrigerant reaches a predetermined pressure,

wherein the electromagnetic valve (26) is opened when the switch is in the ON state.
A refrigerator (10) comprising:
a bypass pipe (22) serving as a bypass section that connects an outlet side and an inlet side of a compressor (12);

an electromagnetic valve (26) provided in the bypass pipe (22); and

the electromagnetic-valve control device (30) according to Claim 1 or 2.
A method for controlling a refrigerator (10) in which a compressor (12), a radiator (14), an expansion valve (16), and an evaporator (18) are connected in this order by a refrigerant pipe (20) and that opens and closes an electromagnetic valve (26) provided in a bypass pipe (22) serving as a bypass section that connects an outlet side and an inlet side of the compressor (12), the method comprising:
opening the electromagnetic valve (26) if a physical quantity of a refrigerant at an outlet of the evaporator (18) during operation of the compressor (12) becomes lower than or equal to a predetermined value set with reference to a triple point of the refrigerant.