JP4626520B2 - Showcase cooling system - Google Patents

Description

  The present invention relates to a showcase cooling system, and more particularly to a showcase cooling system that cools a plurality of showcases.

  FIG. 5 is a schematic configuration diagram showing a conventionally known showcase cooling system. Such a showcase cooling system 100 is installed in a store such as a supermarket or a convenience store. As shown in FIG. 5, the showcase cooling system 100 includes a plurality of showcases 110, 120, and 130 and a refrigerator 140, and the plurality of showcases 110, 120, and 130 and the refrigerator 140 are refrigerated. Configure the cycle. Further, the showcase cooling system 100 includes an integrated controller 150, and can comprehensively and rationally control the plurality of showcases 110, 120, and 130 and the refrigerator 140 described above.

  The plurality of showcases 110, 120, and 130 are juxtaposed in the store and constitute one group. Each showcase 110, 120, 130 includes a solenoid valve (not shown), a thermal expansion valve (not shown), an evaporator (not shown), a temperature sensor (not shown), and a showcase controller 111, respectively. , 121, 131. The solenoid valve controls opening and closing (on / off control) of the refrigerant flowing into the evaporator, and is connected to the showcase controllers 111, 121, and 131, respectively. The temperature sensor measures the internal temperature of the showcases 110, 120, 130, and is disposed in the vicinity of the air outlet of each showcase 110, 120, 130, and each showcase controller 111, 121, 131 is connected. The showcase controllers 111, 121, and 131 are for controlling the opening and closing of the solenoid valve based on the temperature acquired from the temperature sensor, and are connected to the general controller 150 (solenoid valve operating rate calculation unit).

  The refrigerator 140 includes a compressor 141, a condenser (not shown), an inverter 142, and a pressure sensor 143. The compressor 141 is driven and controlled by an inverter 142. The pressure sensor 143 measures the suction refrigerant pressure to the compressor 141 and is connected to the general controller 150 (rotation speed command calculation unit).

  The general controller 150 includes a solenoid valve operating rate calculation unit 151, a pressure set value calculation unit 152, and a rotation speed command calculation unit 153.

  The solenoid valve operating rate calculation unit 151 calculates the operating rate of the solenoid valve, and based on the solenoid valve opening / closing control information (on / off control information) acquired from the showcase controllers 111, 121, 131, the solenoid valve operating rate is calculated. Calculate the valve operating rate. Specifically, the operation rate of the solenoid valve is calculated every predetermined time by calculating the ratio of the ON time of the solenoid valve in the predetermined time every predetermined time.

  The pressure set value calculation unit 152 obtains a pressure set value serving as a control index for the compressor 141. The pressure set value is used to set the suction refrigerant pressure of the compressor 141, and is obtained based on the operating rate of the solenoid valve calculated by the solenoid valve operating rate calculator 151.

  Specifically, the pressure set value is obtained based on the control index shown in FIG. FIG. 6 is a diagram showing the correlation between the solenoid valve operating rate for obtaining the pressure set value and the pressure set value. As shown in FIG. 6, when the operation rate of the solenoid valve of at least one showcase 110, 120, 130 is 90% or more, it is determined that the refrigeration capacity of the refrigerator 140 is insufficient, and the current pressure setting While a value lower than the value by 0.01 Mpa is set as a new pressure set value, the operation rate of the solenoid valves of all the showcases 110, 120, and 130 is 90% or less and at least one showcase 110, 120 is used. , 130 is 40% or less, the refrigeration capacity of the refrigerator 140 is excessive, and a value increased by 0.01 Mpa from the current pressure setting value is set as a new pressure setting value. On the other hand, when the operation rate of the solenoid valves of all the showcases 110, 120, and 130 is 40% to 90%, the current pressure setting value is maintained assuming that the refrigerating capacity of the refrigerator 140 is appropriate.

  For example, based on solenoid valve opening / closing information (on / off information) acquired from the showcase controllers 111, 121, 131, the solenoid valve operating rates calculated by the solenoid valve operating rate calculator 151 are 50% and 95%, respectively. % And 45%, the solenoid valve operating rate of one showcase 120 is 95%. Therefore, the pressure setting value calculation unit 152 assumes that the refrigerating capacity of the refrigerator 140 is insufficient, A value obtained by lowering the pressure set value by 0.01 Mpa is set as a new pressure set value.

  The rotation speed command calculation unit 153 calculates a rotation speed that is a control index of the inverter 142 that controls the compressor 141. The rotational speed is calculated based on a deviation between the pressure set value obtained by the pressure set value calculation unit 152 and the suction refrigerant pressure of the compressor 141 measured by the pressure sensor 143.

  According to the showcase cooling system 100 described above, the solenoid valve operating rate calculating unit 151 calculates the operating rate of the solenoid valve, and the pressure set value calculating unit 152 obtains the pressure set value based on this operating rate. The compressor 141 is controlled by controlling the inverter 142 with the rotational speed calculated by the rotational speed command calculation unit 153 based on the deviation between the obtained pressure setting value and the suction refrigerant pressure of the compressor 141 measured by the pressure sensor 143. To drive.

  Therefore, according to the above-described showcase cooling system 100, it is possible to cope with changes in the environment such as the ambient temperature of the showcases 110, 120, and 130, and the power consumption of the refrigerator 140 is suppressed, thereby contributing to energy saving. (For example, refer to Patent Document 1).

Japanese Patent No. 3603497

  By the way, the above-described showcase cooling system 100 has a pressure setting value calculated by the pressure set value calculation unit 152 when one of the plurality of showcases 110, 120, and 130 has a high operation rate of the solenoid valve. The value will decrease, and the rotational speed calculated by the rotational speed command calculation unit 153 will increase. This means that if any one of the plurality of showcases 110, 120, and 130 has a high operation rate of the solenoid valve, the rotational speed of the compressor 141 increases, which is contrary to energy saving. Become.

  In view of the above circumstances, the present invention operates the solenoid valve of the showcase without increasing the rotational speed of the compressor when the operation rate of the solenoid valve of the specific showcase does not converge to a predetermined range. It is an object of the present invention to provide a showcase cooling system capable of converging the rate within a predetermined range and contributing to energy saving.

  In order to achieve the above object, the showcase cooling system according to claim 1 of the present invention controls the inflow of refrigerant to the evaporator by opening and closing control based on the deviation between the internal temperature and the set value. A plurality of showcases each equipped with a solenoid valve, and a refrigerator that constitutes the refrigeration cycle with the plurality of showcases, and the refrigeration is performed so that the operation rate of the solenoid valves of all the showcases converges within a predetermined range. In a showcase cooling system for controlling a machine, an electronic expansion valve is provided in each of the plurality of showcases, and when the operating rate of the solenoid valve of a specific showcase does not converge within a predetermined range, the solenoid valve of the showcase The opening degree of the electronic expansion valve of the showcase is controlled so that the operating rate of the display converges in a predetermined range.

  According to a second aspect of the present invention, there is provided a showcase cooling system comprising: an electromagnetic valve that controls opening and closing of a refrigerant liquid based on a deviation between an internal temperature and a set value thereof; A plurality of showcases each having a valve and a refrigerator constituting the plurality of showcases and the refrigeration cycle, and the refrigeration is performed so that the operation rate of the solenoid valves of all the showcases converges within a predetermined range. In the showcase cooling system that controls the machine, when the superheat degree is controlled so that the degree of superheat becomes a predetermined value, and the operation rate of the solenoid valve of a specific showcase does not converge to a predetermined range In addition, the opening degree of the electronic expansion valve of the showcase is controlled so that the operating rate of the solenoid valve of the showcase converges in a predetermined range in preference to the superheat degree control.

  In addition, the showcase cooling system according to claim 3 of the present invention, in claim 1 or 2, determines that the liquid back is present when the outlet pipe temperature of the evaporator is equal to or lower than the inlet pipe temperature, and opens the electronic expansion valve. It is characterized by priority control so that the degree becomes small.

  Further, in the showcase cooling system according to claim 4 of the present invention, in the case of determining the liquid back in claim 3, the opening degree of the electronic expansion valve is increased until the outlet piping temperature of the evaporator exceeds the inlet piping temperature. It is characterized by priority control so as to decrease.

  The showcase cooling system according to the present invention is provided with an electronic expansion valve in each of a plurality of showcases, and when the operation rate of the solenoid valve of a specific showcase does not converge to a predetermined range, Since the opening degree of the electronic expansion valve of the showcase is controlled so that the operation rate converges to a predetermined range, the operation rate of the solenoid valve of the showcase is set in advance without increasing the number of rotations of the compressor. It is possible to converge to a predetermined range and contribute to energy saving.

  In addition, the showcase cooling system according to the present invention controls the degree of superheat of the electronic expansion valve so that the degree of superheat becomes a predetermined value, and the operating rate of the solenoid valve of a specific showcase converges within a predetermined range. If not, the opening degree of the electronic expansion valve of the showcase is controlled so that the operating rate of the solenoid valve of the showcase converges to a predetermined range in preference to the superheat degree control. Without increasing the number, the operating rate of the solenoid valve of the showcase can be converged to a predetermined range, which can contribute to energy saving.

  In the showcase cooling system according to the present invention, when the outlet pipe temperature of the evaporator is equal to or lower than the inlet pipe temperature, it is determined as a liquid back, and priority control is performed so that the opening of the electronic expansion valve becomes small. The breakage of the refrigerator can be prevented.

  When it is determined that the liquid is back, priority control is performed so that the opening degree of the electronic expansion valve is reduced until the outlet pipe temperature of the evaporator exceeds the inlet pipe temperature, so that the opening degree of the electronic expansion valve may be excessively reduced. Absent.

  Exemplary embodiments of a showcase cooling system according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

  1 is a schematic configuration diagram showing a showcase cooling system according to an embodiment of the present invention, FIG. 2 is a diagram showing a refrigeration cycle of the showcase cooling system shown in FIG. 1, and FIG. 3 is a showcase cooling shown in FIG. 1 is a block diagram of a system.

  As shown in FIG. 1, the showcase cooling system includes a plurality of showcases 10, 20, and 30 and a refrigerator 40, and includes a plurality of showcases 10, 20, and 30 (electronic expansion valves 12, 22, and 32). The evaporators 13, 23, and 33) and the refrigerator 40 (the compressor 41 and the condenser 44) constitute a refrigeration cycle. Further, the showcase cooling system has an integrated controller 50, and comprehensively and rationally controls the plurality of showcases 10, 20, 30 and the refrigerator 40 described above.

  The plurality of showcases 10, 20, and 30 are arranged side by side in the store and constitute one group. As shown in FIGS. 2 and 3, the showcases 10, 20, and 30 are solenoid valves 11, 21, 31, electronic expansion valves 12, 22, 32, evaporators 13, 23, 33, and evaporator inlets, respectively. Piping temperature sensors 15, 25, 35, evaporator outlet piping temperature sensors 16, 26, 36, temperature sensors 17, 27, 37, and showcase controllers 18, 28, 38 are provided.

  The solenoid valves 11, 21, 31 perform opening / closing control (on / off control) of the refrigerant flowing into the evaporators 13, 23, 33, and are connected to the showcase controllers 18, 28, 38.

  The electronic expansion valves 12, 22, and 32 control the flow rate of the refrigerant flowing into the evaporators 13, 23, and 33 (control the opening degree), and are connected to the general controller 50 (electronic expansion valve controller 54). is there.

  The evaporators 13, 23, and 33 evaporate a low-temperature, constant-pressure liquid refrigerant, and cool the surrounding air with the heat of evaporation.

  The evaporator inlet pipe temperature sensors 15, 25, and 35 measure the inlet pipe temperature of the evaporators 13, 23, and 33, and are connected to the showcase controllers 18, 28, and 38, respectively. The evaporator outlet pipe temperature sensors 16, 26, and 36 measure the outlet pipe temperature of the evaporators 13, 23, and 33, and are connected to the showcase controllers 18, 28, and 38, respectively.

  The temperature sensors 17, 27, and 37 measure the internal temperature of the showcases 10, 20, and 30, and are disposed in the vicinity of the air outlet. Here, the reason why the vicinity of the air outlet is selected as the position for measuring the inside temperature of the showcases 10, 20, and 30 is influenced in part by the number of products stored in the showcases 10, 20, and 30. This is because the temperature change is the position where the temperature change appears most first.

  The showcase controllers 18, 28, and 38 control the solenoid valves 11, 21, and 31 and are connected to the general controller 50. The solenoid valves 11, 21, 31 are controlled to open / close the solenoid valves 11, 21, 31 based on the difference between the preset chamber temperature and the chamber temperature acquired from the temperature sensors 17, 27, 37 ( For example, when the acquired internal temperature is higher than the set internal temperature, the solenoid valves 11, 21 and 31 are opened (on control), and the acquired internal temperature is When the temperature is lower than the set internal temperature, the solenoid valves 11, 21 and 31 are closed (off control).

  The showcase controllers 18, 28, and 38 are connected to a general controller 50 (solenoid valve operation rate calculation unit 51), and the general controller 50 acquires solenoid valve opening / closing control information (on / off control information). Is possible. Further, the integrated controller 50 can acquire the inlet piping temperature and the outlet piping temperature of the evaporators 13, 23, 33 from the showcase controllers 18, 28, 38.

  The refrigerator 40 includes a compressor 41, an inverter 42, a pressure sensor 43, a condenser 44, and an accumulator 45.

  The compressor 41 compresses the refrigerant gas evaporated in the evaporators 13, 23, and 33 to obtain a high-temperature and high-pressure refrigerant gas.

  The inverter 42 controls the drive of the compressor 41 and is connected to the general controller 50 (rotational speed command calculation unit 53).

  The pressure sensor 43 measures an inflow refrigerant pressure of the compressor 41, and is connected to the general controller 50 (rotational speed command calculation unit 53).

  The condenser 44 radiates heat under an equal pressure and condenses the refrigerant gas compressed by the compressor 41 to form a refrigerant liquid.

  The accumulator 45 is attached to the suction circuit. When the liquid refrigerant is supplied from the evaporators 13, 23, 33 to the compressor 41, the accumulator 45 may cause liquid compression and damage the compressor 41. The refrigerant gas (gaseous refrigerant) is separated and only the refrigerant gas (gaseous refrigerant) is sucked into the compressor 41.

  The general controller 50 includes a solenoid valve operating rate calculation unit 51, a pressure set value calculation unit 52, a rotation speed command calculation unit 53, and an electronic expansion valve controller 54.

  The solenoid valve operating rate calculator 51 calculates the operating rates of the solenoid valves 11, 21, 31, and the opening / closing control information (ON) of the solenoid valves 11, 21, 31 acquired from the showcase controllers 18, 28, 38. Based on the off control information), the operation rate of the solenoid valves 11, 21, 31 is calculated. Specifically, the operating rate of the electromagnetic valve is calculated for each predetermined time by calculating the ratio of the ON time of the electromagnetic valves 11, 21, 31 for the predetermined time for each predetermined time.

  The pressure set value calculation unit 52 obtains a pressure set value that serves as a control index for the compressor 41. The pressure set value is used to set the suction refrigerant pressure of the compressor 41 and is obtained based on the operation rates of the solenoid valves 11, 21, 31 calculated by the solenoid valve operation rate calculation unit 51.

  Specifically, the pressure set value is obtained in the same manner as the conventional showcase cooling system 100. That is, as shown in FIG. 6, when the operation rate of the solenoid valves 11, 21, 31 of at least one showcase 10, 20, 30 is 90% or more, the refrigerating capacity of the refrigerator 40 is insufficient. As a new pressure setting value, a value obtained by lowering the current pressure setting value by 0.01 Mpa is used. On the other hand, the operation rates of the solenoid valves 11, 21, 31 of all the showcases 10, 20, 30 are 90% or less. And when the operating rate of the solenoid valves 11, 21, 31 of at least one showcase 10, 20, 30 is 40% or less, it is determined that the refrigeration capacity of the refrigerator 40 is excessive, and the current pressure setting A value increased by 0.01 Mpa from the value is set as a new pressure setting value. On the other hand, when the operation rate of the solenoid valves 11, 21, 31 of all the showcases 10, 20, 30 is 40% to 90%, it is determined that the refrigeration capacity of the refrigerator 40 is appropriate and the current pressure setting value To maintain.

  The rotational speed command calculation unit 53 calculates a rotational speed that is a control index of the inverter 42 that controls the compressor 41. The rotational speed is calculated based on a deviation between the pressure set value calculated by the pressure set value calculation unit 52 and the suction refrigerant pressure measured by the pressure sensor 43.

  The electronic expansion valve controller 54 controls the degree of superheat of the electronic expansion valves 12, 22, and 32. Superheat degree control refers to control so that the difference between the inlet and outlet pipe temperatures of the evaporators 13, 23, and 33 is the same as the target value. In this embodiment, the evaporation obtained from the showcase controllers 18, 28, and 38 is used. Control is performed such that the difference (superheat degree) between the inlet pipe temperature and the outlet pipe temperature of the vessels 13, 23, and 33 becomes the same as a predetermined target value. Therefore, when the degree of superheat is larger than the target value, the opening degree of the electronic expansion valves 12, 22, and 32 is controlled to be larger, and when the degree of superheat is smaller than the target value, the electronic expansion valves 12, 22 are controlled. , 32 is controlled so that the opening degree becomes small.

  Further, the electronic expansion valve controller 54 generates a liquid back when the operation rate of the solenoid valves 11, 21, 31 is not improved despite the rotation speed command calculation unit 53 changing the rotation speed of the compressor 41. The opening degree of the electronic expansion valves 12, 22, and 32 is controlled within a range not to be used.

  That is, the showcases 10, 20, and 30 in which the operation rates of the electromagnetic valves 11, 21, and 31 are not improved are insufficient in the refrigerant flow rate (refrigeration capacity), so that the electronic expansion valve controller 54 has a large opening. The electronic expansion valves 12, 22, and 32 are controlled.

  The liquid back is a phenomenon in which the refrigerant remains in a liquid state and is sucked into the compressor 41, and the inlet pipe temperature of the evaporators 13, 23, 33 is equal to or higher than the outlet pipe temperature of the evaporators 13, 23, 33. In the case of inlet pipe temperature ≧ evaporator outlet pipe temperature), the electronic expansion valve controller 54 determines that the liquid is back. In this case, the electronic expansion valve controller 54 controls the electronic expansion valves 12, 22, and 32 so that the opening degree becomes small. Specifically, priority control is performed so that the opening degree of the electronic expansion valves 12, 22, and 32 is decreased until the outlet pipe temperature of the evaporators 13, 23, and 33 exceeds the inlet pipe temperature.

  For example, the solenoid valves 11, 21, 31 calculated by the solenoid valve operating rate calculator 51 based on the opening / closing information (ON / OFF information) of the solenoid valves 11, 21, 31 acquired from the showcase controllers 18, 28, 38. As shown in FIG. 4, if the operation rate is 50%, 95%, and 45%, the solenoid valve operation rate of one showcase 20 is 95%. Since the refrigerating capacity is insufficient, a value obtained by lowering the current pressure setting value by 0.01 Mpa is set as the pressure setting value.

  Then, the rotation speed calculated by the rotation speed command calculation unit 53 increases, and the rotation speed of the compressor 41 increases. For this reason, the refrigerating capacity becomes appropriate, and the operation rate of the electromagnetic valve 21 of the showcase 20 is improved.

  However, if the operating rate of the solenoid valve 21 of the showcase 20 is not improved despite the increase in the number of revolutions in this way, it is determined that the showcase 20 is affected by disturbance. In addition, as a disturbance, the case where the blowing air from the air conditioner indoor unit in a shop interferes with the air curtain of the showcase 20 is assumed.

  In this case, the electronic expansion valve controller 54 determines that the refrigerant flow rate (refrigeration capacity) of the showcase 20 is insufficient, and increases the valve opening degree of the electronic expansion valve 22 of the showcase 20. The refrigerant flow rate is controlled to increase.

  As a result, the shortage of refrigeration capacity of the showcase 20 is resolved, the operating rate of the solenoid valve 21 of the showcase 20 is improved, and the pressure set value calculation unit 52 does not lower the pressure set value more than necessary.

  As described above, according to the showcase cooling system, the electronic expansion valves 12, 22, and 32 are provided in the showcases 10, 20, and 30, respectively, and the operation rate of the electromagnetic valve 21 of the specific showcase 20 is within a predetermined range. Since the opening degree of the electronic expansion valve 22 of the showcase 20 is controlled so that the operation rate of the electromagnetic valve 21 of the showcase 20 converges to a predetermined range when the convergence does not occur, the rotation speed of the compressor 41 is controlled. Without increasing the operating rate of the solenoid valve 21 of the showcase 20 can be converged to a predetermined range, which can contribute to energy saving.

  In addition, when the operation rate of the solenoid valve 21 of a specific showcase 20 does not converge to a predetermined range, the operation rate of the solenoid valve 21 of the showcase 20 converges to a predetermined range in preference to superheat degree control. As described above, since the opening degree of the electronic expansion valve 22 of the showcase 20 is controlled, the operating rate of the electromagnetic valve 21 of the showcase 20 is set within a predetermined range without increasing the rotational speed of the compressor 41. Convergence can contribute to energy saving.

  If the outlet pipe temperature of the evaporator is equal to or lower than the inlet pipe temperature (evaporator inlet pipe temperature ≧ evaporator outlet pipe temperature), it is determined that the liquid is back, and the opening degree of the electronic expansion valves 12, 22, 32 is Since priority control is performed so as to decrease, breakage of the refrigerator 40 (compressor 41) due to liquid back can be prevented.

  When it is determined that the liquid is back, priority control is performed so that the opening degree of the electronic expansion valves 12, 22, and 32 is decreased until the outlet pipe temperature of the evaporators 13, 23, and 33 exceeds the inlet pipe temperature. The opening degree is not excessively reduced.

  According to the above-described showcase cooling system, the integrated controller 50 has the electronic expansion valve controller 54. However, the showcase controllers 18, 28, and 38 of each showcase 10, 20, and 30 are electronic expansion valve controllers. 54 may be included.

  Moreover, although the refrigerator 40 shall be provided with the accumulator 45, the showcases 10, 20, and 30 may each have an accumulator.

  As described above, the showcase cooling system according to the present invention is useful for a showcase cooling system having a plurality of showcases, and is particularly suitable for a showcase cooling system that contributes to energy saving.

It is a schematic block diagram which shows the showcase cooling system concerning the Example of this invention. It is a figure which shows the refrigerating cycle of the showcase cooling system shown in FIG. It is a block diagram of the showcase cooling system shown in FIG. It is explanatory drawing for demonstrating an effect | action of the showcase cooling system shown in FIG. It is a schematic block diagram which shows the showcase cooling system conventionally known. It is a figure which shows the correlation of the solenoid valve operating rate for calculating | requiring a pressure setting value, and a pressure setting value.

Explanation of symbols

10, 20, 30 Showcase 11, 21, 31 Solenoid valve 12, 22, 32 Electronic expansion valve 13, 23, 33 Evaporator 15, 25, 35 Evaporator inlet piping temperature sensor 16, 26, 36 Evaporator outlet piping temperature Sensor 17, 27, 37 Temperature sensor 18, 28, 38 Showcase controller 40 Refrigerator 41 Compressor 42 Inverter 43 Pressure sensor 44 Condenser 45 Accumulator 50 General controller 51 Solenoid valve operating rate calculation unit 52 Pressure set value calculation unit 53 Rotation Number command calculation unit 54 Electronic expansion valve controller

Claims (4)

A plurality of showcases each provided with an electromagnetic valve that controls opening and closing of the refrigerant based on the deviation between the internal temperature and the set value to control the flow of refrigerant into the evaporator;
A plurality of showcases and a refrigerator constituting a refrigeration cycle,
In the showcase cooling system that controls the refrigerator so that the operation rate of the solenoid valves of all showcases converges to a predetermined range,
An electronic expansion valve is provided in each of the plurality of showcases,
When the operating rate of the solenoid valve of a particular showcase does not converge to a predetermined range, the electronic expansion valve of the showcase is opened so that the operating rate of the solenoid valve of the showcase converges to a predetermined range. Showcase cooling system characterized by controlling the degree. A plurality of showcases each provided with an electromagnetic valve for controlling the inflow of refrigerant liquid to the evaporator by opening and closing based on the deviation between the internal temperature and its set value, and an electronic expansion valve;
A plurality of showcases and a refrigerator constituting a refrigeration cycle,
In the showcase cooling system that controls the refrigerator so that the operation rate of the solenoid valves of all showcases converges to a predetermined range,
While controlling the degree of superheat of the electronic expansion valve so that the degree of superheat becomes a predetermined value,
When the operating rate of the solenoid valve of a particular showcase does not converge to a predetermined range, the showcase has a priority so that the operating rate of the solenoid valve of the showcase converges to a predetermined range. A showcase cooling system for controlling the opening of an electronic expansion valve of a case.   The showcase according to claim 1 or 2, wherein when the outlet piping temperature of the evaporator is equal to or lower than the inlet piping temperature, it is determined that the liquid is back, and priority control is performed so that the opening degree of the electronic expansion valve becomes small. Cooling system.   4. The showcase cooling system according to claim 3, wherein when the liquid back is determined, priority control is performed so that the opening degree of the electronic expansion valve is reduced until the outlet pipe temperature of the evaporator exceeds the inlet pipe temperature. .

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