JP5384124B2 - Refrigeration system, control device and control method thereof - Google Patents

Description

  The present invention relates to a refrigeration system used for a refrigeration / refrigeration showcase and the like, a control apparatus and a control method thereof, and more particularly, to a refrigeration system that switches operation stop of a compressor in accordance with a control target temperature.

  In general, in a refrigerated / refrigerated showcase used for food storage or display, the compressor is switched on / off according to the level of the internal temperature, and the switching operation follows the change in the internal temperature. By repeating, it controls to maintain the internal temperature at a constant temperature.

  The compressor is switched off when the internal temperature becomes equal to or higher than the specified on-set temperature, and the compressor is operated, and the internal temperature falls below the off-set temperature lower than the on-set temperature. This is done to stop the compressor operation. The temperature difference between the on-set temperature and the off-set temperature at this time is called a differential and is provided to avoid frequent on / off operation (hunting) of the compressor.

  In addition, the flow rate of the refrigerant circulating in the refrigeration cycle is adjusted for the purpose of stabilizing the cooling capacity at the time of cooling inside the cabinet and performing efficient operation, etc. As the flow rate adjusting valve, an electric expansion valve using a pulse motor or the like is frequently used. In a refrigeration cycle using an electric expansion valve, the refrigerant superheat degree of the evaporator is detected and compared with the set superheat degree, and the opening degree of the electric expansion valve is adjusted by PID control or the like according to the difference. The refrigerant flow control is performed.

  By the way, as described above, when switching on / off of the compressor, it is necessary to control the opening and closing of the electric expansion valve, and as one of the control methods at that time, for example, Patent Document 1 When stopping the compressor, fully open the opening of the electric expansion valve and fully open it after a predetermined time to balance the gas in the refrigeration cycle, and when starting the compressor, A technique for setting the valve opening to an initial opening (a preset reference opening) or a storage opening (an opening immediately before stopping the compressor) is described.

  The technique described in Patent Document 1 is intended for an air conditioner for room temperature adjustment, so that the electric expansion valve is fully opened to balance the gas. However, in a refrigerated / refrigerated showcase, In order to avoid the internal temperature from increasing, it is common not to take gas balance when the compressor is stopped. For this reason, when the above technology is applied to the control for a freezer / refrigerator showcase, the opening of the electric expansion valve is fully closed when the compressor is stopped, and the initial opening when the compressor is started. Alternatively, the memory opening is set.

No. 2-3093

  However, as described above, when the opening degree of the electric expansion valve is switched between the fully closed position and the initial opening degree (or the stored opening degree) in accordance with the on / off state of the compressor, the compressor is turned on / off. Each time switching off, the opening of the electric expansion valve is changed by a large operation amount.

  In addition, in a refrigeration / refrigeration showcase, the number of times the compressor is switched on / off is relatively large, and there are many cases where a severe switching operation is required, such as repeated on / off at intervals of about 5 minutes. In such a case, the number of times the compressor is switched on / off is 10 times or more per hour, and the driving frequency of the electric expansion valve is significantly increased.

  In addition, since the electric expansion valve is a mechanical part having a sliding part, the higher the drive frequency, the shorter the life of the sliding part due to wear of the sliding part. The durable life is the driving given to the pulse motor. Generally, it is defined by the number of pulses. For this reason, when the opening degree is changed as described above and the number of drive pulses applied to the pulse motor is greatly increased, the remaining number of pulses specified as the endurance life is rapidly consumed, and the electric expansion This will shorten the life of the valve. As a result, frequent replacement of the electric expansion valve is forced, resulting in a problem that the reliability of the freezing / refrigerating showcase is lowered.

  Therefore, the present invention has been made in view of the above problems, and even when the compressor is frequently switched on / off, the number of drive pulses of the drive signal for driving the electric expansion valve is large. The purpose is to extend the life of the electric expansion valve, and to improve the reliability of the refrigeration system itself.

In order to achieve the above object, the present invention is a refrigeration system in which a compressor, a condenser, an electric expansion valve, and an evaporator are sequentially connected, and the operation of the compressor is switched according to the temperature to be controlled. , disposed between the evaporator and the condenser, an electromagnetic valve for opening and closing the refrigerant flow path between them, when stopping the operation of the compressor, it is closed the solenoid valve, the solenoid valve In response to a signal for opening and closing the opening of the electric expansion valve is maintained at the opening when the operation of the compressor is stopped, and when the operation of the compressor is resumed, the electromagnetic valve is opened, The opening control of the electric expansion valve is started from the opening when the operation of the compressor is stopped in accordance with a signal for opening and closing the electromagnetic valve .

According to the present invention, when the operation of the compressor is stopped after the electromagnetic valve is provided between the condenser and the evaporator, the electromagnetic valve is closed and the motor is operated in accordance with a signal for opening and closing the electromagnetic valve. The opening of the expansion valve is maintained at the opening when the compressor operation is stopped, and when restarting the compressor operation, the electromagnetic valve is opened and the electric expansion is performed according to a signal for opening and closing the electromagnetic valve. Since the valve opening control is started from the opening when the compressor operation is stopped, the electric type when the compressor is stopped while preventing the rise in the internal temperature when the compressor operation is stopped. The fully closing operation of the expansion valve and the opening operation of the electric expansion valve when starting the compressor can be made unnecessary. For this reason, it is not necessary to greatly change the opening of the electric expansion valve each time the compressor is switched on / off, and the consumption of the number of drive pulses can be greatly reduced. Therefore, it is possible to extend the life of the electric expansion valve, and consequently improve the reliability of the refrigeration system.

Further, the present invention provides a refrigeration cycle in which a compressor, a condenser, an electric expansion valve, and an evaporator are sequentially connected, and is disposed between the condenser and the evaporator. A control device that controls an operation of a refrigeration system that switches operation stop of the compressor in accordance with a temperature to be controlled, the electromagnetic valve for stopping the operation of the compressor When closing the valve and maintaining the opening of the electric expansion valve at the opening when the operation of the compressor is stopped in response to a signal for opening and closing the electromagnetic valve, and when restarting the operation of the compressor The electromagnetic valve is opened, and the opening control of the electric expansion valve is started from the opening when the operation of the compressor is stopped in response to a signal for opening and closing the electromagnetic valve .

  According to the present invention, similarly to the above-described invention, even when the on / off of the compressor is frequently switched, the number of drive pulses of the drive signal for driving the electric expansion valve is prevented, It is possible to extend the life of the electric expansion valve and to improve the reliability of the refrigeration system itself.

In the control device for the refrigeration system, a first control unit that switches operation stop of the compressor according to a temperature to be controlled and outputs a signal for opening and closing the electromagnetic valve to control opening and closing of the electromagnetic valve; A second control unit that controls the opening degree of the electric expansion valve in accordance with the degree of refrigerant superheat of the evaporator, and the second control unit outputs an electromagnetic wave output from the first control unit. The open / close state of the electromagnetic valve is monitored based on a signal for opening / closing the valve, and the output of the drive signal for controlling the opening degree can be stopped in response to the electromagnetic valve being closed.

  In the control device for the refrigeration system, the first control unit operates the compressor when the control target temperature is equal to or higher than a first set value set to a predetermined temperature, and the control target The operation of the compressor can be stopped when the temperature becomes equal to or lower than a second set value lower than the first set value.

  In the control device for the freezing / refrigeration system, the freezing / refrigerating system may be used in a freezing / refrigerating showcase for keeping food items cold, and the temperature of the controlled object may be the internal temperature of the freezing / refrigerating showcase. it can.

Furthermore, the present invention provides a refrigeration cycle in which a compressor, a condenser, an electric expansion valve, and an evaporator are sequentially connected, and is disposed between the condenser and the evaporator. A control method for controlling an operation of a refrigerating and refrigeration system that switches operation stop of the compressor in accordance with a temperature to be controlled, the electromagnetic valve for stopping the operation of the compressor. When closing the valve and maintaining the opening of the electric expansion valve at the opening when the operation of the compressor is stopped in response to a signal for opening and closing the electromagnetic valve, and when restarting the operation of the compressor The electromagnetic valve is opened, and the opening control of the electric expansion valve is started from the opening when the operation of the compressor is stopped in response to a signal for opening and closing the electromagnetic valve .

  As described above, according to the present invention, even when the on / off of the compressor is frequently switched, the number of drive pulses of the drive signal for driving the electric expansion valve is prevented from being increased. It is possible to extend the life of the expansion valve, and to improve the reliability of the refrigeration system itself.

It is a block diagram which shows one Embodiment of the freezing / refrigeration system concerning this invention. It is a flowchart for demonstrating control operation | movement of the temperature control part shown in FIG. It is a flowchart for demonstrating control operation | movement of the superheat degree control part shown in FIG. It is a timing diagram which shows the operation example of the solenoid valve at the time of switching ON / OFF of a compressor and an electrically driven expansion valve.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the case where the freezing and refrigeration system according to the present invention is applied to a freezing and refrigeration showcase used for keeping food, displaying food, etc. will be described as an example.

  FIG. 1 shows an embodiment of a refrigeration system according to the present invention. This system 1 includes a compressor 2, a condenser 3, a condenser fan 3a, an electromagnetic valve 4, and an electric expansion valve 5. And an evaporator 6, an evaporator fan 6 a, an inlet temperature sensor 7, an outlet temperature sensor 8, an interior temperature sensor 9, a temperature control unit 10, and a superheat degree control unit 11.

  The compressor 2, the condenser 3, the electromagnetic valve 4, the electric expansion valve 5 and the evaporator 6 are connected by a pipe 12, and the refrigerant circulates between them. Here, the flow rate of the refrigerant flowing through the pipe 12 is controlled by adjusting the valve opening degree of the electric expansion valve 5.

  The compressor 2 compresses the refrigerant in a low-pressure gas state supplied from the evaporator 6, converts the refrigerant into a high-pressure gas, and supplies it to the condenser 3 via the pipe 12.

  The condenser 3 condenses the high-pressure gaseous refrigerant supplied from the compressor 2, converts it into a high-pressure liquid refrigerant, takes away the heat of condensation, and releases the taken-out heat to the outside by the ventilation of the condenser fan 3a. .

  The electromagnetic valve 4 is a valve for opening and closing the refrigerant flow path 12 a between the condenser 3 and the evaporator 6, and is provided for switching whether or not the refrigerant flows into the evaporator 6. The solenoid valve 4 operates according to the solenoid valve drive signal SV output from the temperature control unit 10 and opens and closes according to the voltage level of the solenoid valve drive signal SV.

  The electric expansion valve 5 changes the high-pressure liquid refrigerant supplied from the condenser 3 to a low-pressure state. This electric expansion valve 5 incorporates a pulse motor (not shown) that is driven in accordance with an electric valve drive signal EV from the superheat degree control unit 11 and has a rotation angle corresponding to the number of pulses of the electric valve drive signal EV. Is adjusted to adjust the opening degree of the electric expansion valve 5.

  The evaporator 6 is provided to evaporate (vaporize) the refrigerant in a low-pressure liquid state, and the refrigerant takes heat of vaporization from the surroundings by being evaporated and is heated. At this time, the air around the evaporator 6 is cooled by the deprived heat, and the cooled air is discharged by the ventilation of the evaporator fan 6a, thereby adjusting the temperature inside the refrigerator / freezer showcase. Is called.

  The inlet temperature sensor 7, the outlet temperature sensor 8, and the interior temperature sensor 9 are respectively the temperature Tin of the refrigerant (liquid refrigerant) at the inlet of the evaporator 6, and the refrigerant (gas refrigerant) at the outlet of the evaporator 6. ) And the temperature Tis of the freezer / refrigerated showcase are detected. For example, a thermistor is generally used as the inlet temperature sensor 7 to the internal temperature sensor 9.

  The temperature control unit 10 is a control circuit for adjusting the temperature in the refrigerator / freezer showcase by controlling the operation of the compressor 2, for example, from a microcomputer and peripheral circuits (both not shown). Composed. The temperature control unit 10 compares the internal temperature Tis detected by the internal temperature sensor 9 with the on-set temperature Ton and the off-set temperature Toff set in advance, and the operation of the compressor 2 based on the results. Control the presence or absence. Note that the on set temperature Ton and the off set temperature Toff are the same as those in the prior art, and a temperature difference called differential is set between them.

  The temperature control unit 10 also has a function of controlling the opening and closing of the electromagnetic valve 4 in accordance with the operating state of the compressor 2, and the opening and closing control of the electromagnetic valve 4 is performed through an electromagnetic valve drive signal SV. This solenoid valve drive signal SV is set to a voltage level (for example, AC 200 V) that opens the solenoid valve 4 during the operation period of the compressor 2, while the solenoid valve 4 is closed during the stop period of the compressor 2. Is set to a voltage level (for example, 0 V).

  The superheat degree control unit 11 is a control circuit for controlling the valve opening degree of the electric expansion valve 5, and is composed of, for example, a microcomputer and a peripheral circuit, like the temperature control unit 10. The superheat degree control unit 11 controls the valve of the electric expansion valve 5 by PID control based on the superheat degree Tsh of the refrigerant in the evaporator 6 (detected temperature Tout of the outlet temperature sensor 8−detected temperature Tin of the inlet temperature sensor 7). The opening degree is obtained, and an electric valve drive signal EV corresponding to the obtained valve opening degree is output to the pulse motor of the electric expansion valve 5.

  Further, the superheat degree control unit 11 monitors the voltage level of the electromagnetic valve drive signal SV to detect the opening / closing of the electromagnetic valve 4, and the electric valve driving signal EV to the electric expansion valve 5 in accordance with the opening / closing of the electromagnetic valve 4. Also has a function of switching the presence or absence of the output.

  Next, the operation of the refrigeration system 1 having the above configuration will be described. Here, first, the control operation performed by the temperature control unit 10 will be described with reference to FIGS. 1 and 2. During the control operation, the temperature control unit 10 executes the routine shown in FIG. 2 every predetermined period (for example, 10 seconds) using a timer (not shown) or the like.

  When the process is started, as shown in FIG. 2, the temperature control unit 10 first takes in the internal temperature Tis detected by the internal temperature sensor 9 (step S1), and the internal temperature Tis is equal to or higher than the on-set temperature Ton. It is determined whether or not (step S2). At this time, for example, when the internal temperature Tis tends to increase and the internal temperature Tis is equal to or higher than the on-set temperature Ton (step S2: Yes), the compressor 2 is started (step S3). At the same time, the electromagnetic valve 4 is opened, and the refrigerant flow path 12a between the condenser 3 and the evaporator 6 is opened (step S4). As a result, cool air is discharged from the fan 6a for the evaporator 6 to cool the interior and lower the interior temperature Tis.

  Thereafter, when the internal temperature Tis gradually decreases and the detection temperature Tis of the internal temperature sensor 9 becomes lower than the on-set temperature Ton (step S2: No), the temperature Tis is equal to or lower than the off-set temperature Toff. It is determined whether or not it has reached (step S5). As a result, when the internal temperature Tis is higher than the off-set temperature Toff (step S5: No), the operation state (operating state) of the compressor 2 at that time is maintained, and the internal temperature Tis. Is continuously reduced (step S6). At this time, the solenoid valve 4 also maintains the open / closed state (open state) at that time, and continues to open the refrigerant flow path 12a (step S7).

  And when the internal temperature Tis falls sufficiently and the detection temperature Tis of the internal temperature sensor 9 becomes equal to or lower than the off set temperature Toff (step S5: Yes), the operation of the compressor 2 is stopped, The electromagnetic valve 4 is closed and the refrigerant flow path 12a is closed (steps S8 and S9). As a result, the internal cooling is stopped and the internal temperature Tis is gradually increased.

  Thereafter, the operations in steps S1 to S9 are repeated at 10 second intervals, and when the internal temperature Tis becomes equal to or higher than the on-set temperature Ton, the operation of the compressor 2 and the opening of the electromagnetic valve 4 are resumed. Reduce the temperature Tis.

  Next, the control operation performed by the superheat degree control unit 11 will be described with reference to FIGS. 1 and 3. The superheat degree control unit 11 operates in synchronization with the operation of the temperature control unit 10 and executes the routine shown in FIG. 3 at intervals of 10 seconds, for example, as with the temperature control unit 10.

  When the process is started, as shown in FIG. 3, the superheat degree control unit 11 first determines whether or not the electromagnetic valve 4 is opened with reference to the electromagnetic valve drive signal SV output from the temperature control unit 10. (Step S11). If the result of determination is that the solenoid valve 4 has been opened (step S11: Yes), the refrigerant temperature Tin at the inlet of the evaporator 6 and the refrigerant temperature Tout at the outlet are taken in (steps S12 and S13), respectively, and the current overheating The degree Tsh = Tout−Tin is calculated (step S14).

  Next, a deviation e (t) = Ts−Tsh between the set superheat degree (target value of the superheat degree Tsh) Ts and the current superheat degree Tsh is calculated (step S15), and a series of past deviation e, proportional band PB, Based on the integration time Ti and the differentiation time Td, the operation amount m (t) of the current valve opening is calculated by PID (proportional / integral / derivative) calculation according to the following equation (step S16). Here, Kp is a proportional gain.

  Thereby, the target opening degree of the valve that the electric expansion valve 5 should reach is derived, and the superheat degree control unit 11 sets the number of drive pulses so that the opening degree of the electric expansion valve 5 becomes the target opening degree. At the same time, an electric valve drive signal EV is output to the electric expansion valve 5 to increase or decrease the opening degree of the electric expansion valve 5 (step S17).

  On the other hand, if the electromagnetic valve 4 is closed as a result of the determination in step S11 (step S11: No), no processing is executed and the opening degree of the electric expansion valve 5 is not changed.

  Next, operation examples of the electromagnetic valve 4 and the electric expansion valve 5 when the compressor 2 is switched on / off will be described with reference to FIGS.

  When the internal temperature Tis becomes equal to or higher than the on-set temperature Ton at the timing t1, the compressor 2 is started, the electromagnetic valve 4 is opened, and the refrigerant flow path 12a is opened. Further, in response to the opening of the solenoid valve 4, the opening adjustment of the electric expansion valve 5 based on the PID calculation is started, and the flow rate of the refrigerant circulating in the refrigeration cycle is adjusted. The operation of the compressor 2, the opening of the electromagnetic valve 4, and the opening adjustment of the electric expansion valve 5 are performed while the internal temperature Tis is equal to or lower than the on-set temperature Ton. It is executed continuously.

  Then, when the internal temperature decreases and the internal temperature Tis reaches the OFF set temperature Toff at timing t2, the operation of the compressor 2 is stopped, the electromagnetic valve 4 is closed, and the refrigerant flow path 12a is opened. Closed. Further, in response to the closing of the electromagnetic valve 4, the output of the electric valve drive signal EV to the electric expansion valve 5 is stopped (the number of drive pulses is zero), and the opening degree of the electric expansion valve 5 is increased. Adjustment is interrupted. As a result, the opening degree of the electric expansion valve 5 remains the same as the opening degree when the opening degree adjustment is stopped, and thereafter the state is maintained until the opening degree adjustment is resumed.

  Thereafter, when the internal temperature rises and the internal temperature Tis reaches the on-set temperature Ton again at timing t3, the operation of the compressor 2 is resumed and the electromagnetic valve 4 is opened. At this time, the adjustment of the opening degree of the electric expansion valve 5 is also resumed. However, the opening degree of the electric expansion valve 5 at the time of resumption is the opening degree when the adjustment of the opening degree is stopped (the opening degree at the timing t2). Therefore, the increase / decrease in the opening degree of the electric expansion valve 5 after restarting the operation of the compressor 2 is started from the opening degree when the opening degree adjustment is stopped.

  For this reason, the operation amount of the electric expansion valve 5 at the time described above is obtained by subtracting the opening when the opening adjustment is stopped from the target opening derived by the PID calculation, and is fully closed as in the prior art. The amount of operation of the electric expansion valve 5 can be remarkably reduced as compared with the case where the target opening degree is changed from this state. Therefore, the number of drive pulses of the electric valve drive signal EV can be kept small, and the consumption of the number of drive pulses accompanying the on / off switching of the compressor 2 can be greatly reduced.

  As described above, according to the present embodiment, when the operation of the compressor 2 is stopped after the electromagnetic valve 4 is provided between the condenser 3 and the evaporator 6, the electromagnetic valve 4 is closed and the electric motor is operated. The opening degree of the expansion valve 5 is maintained at the opening degree when the operation of the compressor 2 is stopped, and when the operation of the compressor 2 is resumed, the electromagnetic valve 4 is opened and the opening degree control of the electric expansion valve 5 is performed. Is started from the opening when the operation of the compressor 2 is stopped, so that the electric expansion valve when the compressor 2 is stopped while preventing the rise in the internal temperature when the operation of the compressor 2 is stopped 5 and the opening operation of the electric expansion valve 5 when the compressor 2 is started can be made unnecessary.

  For this reason, it is not necessary to largely change the opening degree of the electric expansion valve 5 each time the compressor 2 is switched on / off, and the consumption of the number of drive pulses can be greatly reduced. Therefore, it is possible to extend the life of the electric expansion valve 5 and to improve the reliability of the freezing / refrigerating showcase.

  In the above embodiment, the electromagnetic valve 4 is provided on the upstream side of the electric expansion valve 5 (between the condenser 3 and the electric expansion valve 5). If it is between the evaporators 6, it will not specifically limit, The electromagnetic valve 4 can also be provided in the downstream of the electric expansion valve 5 (between the electric expansion valve 5 and the evaporator 6).

  Moreover, in the said embodiment, although the temperature control part 10 and the superheat degree control part 11 were comprised as a separate control part for convenience of explanation, these can also be integrated and comprised from a single microcomputer. . In that case, transmission of information (solenoid valve drive signal SV) indicating opening / closing of the electromagnetic valve 4 from the temperature control unit 10 toward the superheat degree control unit 11 may be performed by internal processing of the microcomputer.

  Furthermore, in the above-described embodiment, the solenoid valve drive signal SV is output to the superheat degree control unit 11 so that the open / close state of the solenoid valve 4 is transmitted to the superheat degree control unit 11, but the solenoid valve drive signal SV is not necessarily transmitted. There is no need to use it, and other signals may be output to the superheat degree control unit 11 as long as they indicate the open / closed state of the solenoid valve 4.

  In the above embodiment, the case where the opening degree of the electric expansion valve 5 is controlled by PID has been described as an example. However, the control method is P (proportional) control, PI (proportional integral) control, PD (proportional). Differentiation) control may be used.

DESCRIPTION OF SYMBOLS 1 Refrigeration / refrigeration system 2 Compressor 3 Condenser 3a Condenser fan 4 Electromagnetic valve 5 Electric expansion valve 6 Evaporator 6a Evaporator fan 7 Inlet temperature sensor 8 Outlet temperature sensor 9 Inside temperature sensor 10 Temperature control unit 11 Superheat control Part 12 Pipe 12a Refrigerant flow path

Claims (6)

A compressor, a condenser, an electric expansion valve, and an evaporator are sequentially connected, and is a refrigeration system that switches the operation stop of the compressor according to the temperature to be controlled,
An electromagnetic valve is disposed between the condenser and the evaporator, and opens and closes a refrigerant flow path therebetween.
When the operation of the compressor is stopped, the solenoid valve is closed, and the opening of the electric expansion valve is set to the opening when the operation of the compressor is stopped according to a signal for opening and closing the solenoid valve. When maintaining and resuming the operation of the compressor, when opening the solenoid valve and opening the solenoid valve according to a signal for opening and closing the solenoid valve, when the operation of the compressor is stopped A freezing and refrigeration system starting from the opening of A refrigeration cycle in which a compressor, a condenser, an electric expansion valve, and an evaporator are sequentially connected; and an electromagnetic valve that is disposed between the condenser and the evaporator and opens and closes a refrigerant flow path therebetween. A control device for controlling the operation of the refrigeration system that switches the operation stop of the compressor according to the control target temperature,
When the operation of the compressor is stopped, the solenoid valve is closed, and the opening of the electric expansion valve is set to the opening when the operation of the compressor is stopped according to a signal for opening and closing the solenoid valve. When maintaining and resuming the operation of the compressor, when opening the solenoid valve and opening the solenoid valve according to a signal for opening and closing the solenoid valve, when the operation of the compressor is stopped The control apparatus of the freezing and refrigeration system characterized by starting from the opening degree. A first control unit that switches the operation stop of the compressor according to a control target temperature, and outputs a signal for opening and closing the electromagnetic valve to control the opening and closing of the electromagnetic valve;
A second control unit that controls the opening degree of the electric expansion valve according to the refrigerant superheat degree of the evaporator,
The second control unit monitors an open / close state of the electromagnetic valve based on a signal for opening / closing the electromagnetic valve output from the first control unit , and controls the opening degree according to the electromagnetic valve being closed. 3. The control device for a refrigeration system according to claim 2, wherein the output of the drive signal for the operation is stopped.   The first control unit operates the compressor when the control target temperature is equal to or higher than a first set value set to a predetermined temperature, and the control target temperature is less than the first set value. The control device for the refrigeration system according to claim 3, wherein the operation of the compressor is stopped when the temperature becomes equal to or lower than a second set value which is low.   The freezing / refrigeration system is used in a freezing / refrigerating showcase for keeping foodstuffs cold, and the temperature of the controlled object is an internal temperature of the freezing / refrigerating showcase, 4. A control device for a refrigeration system according to 4. A refrigeration cycle in which a compressor, a condenser, an electric expansion valve, and an evaporator are sequentially connected; and an electromagnetic valve that is disposed between the condenser and the evaporator and opens and closes a refrigerant flow path therebetween. A control method for controlling the operation of the refrigeration system that switches the operation stop of the compressor according to the temperature to be controlled,
When the operation of the compressor is stopped, the solenoid valve is closed, and the opening of the electric expansion valve is set to the opening when the operation of the compressor is stopped according to a signal for opening and closing the solenoid valve. Maintain,
When the operation of the compressor is resumed, the opening when the operation of the compressor is stopped by opening the electromagnetic valve and controlling the opening of the electric expansion valve according to a signal for opening and closing the electromagnetic valve A control method for a refrigeration system characterized by starting from

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