Refrigeration equipment

Abstract

To provide a refrigeration system that can detect refrigerant shortages at an early stage. [Solution] The refrigeration system comprises a compressor configured to discharge refrigerant within a target discharge temperature range, a condenser, a receiver tank for storing the refrigerant discharged from the compressor, a subcooler arranged in parallel with the condenser for subcooling the refrigerant discharged from the receiver tank, an injection circuit which forms part of the refrigerant circuit and returns the liquid refrigerant in the receiver tank to the compressor, an electric valve provided in the injection circuit for reducing the pressure of the liquid refrigerant in the receiver tank, and a control device configured to control the valve opening of the electric valve according to the target discharge temperature range of the compressor, wherein the control device is configured to determine if there is a shortage of refrigerant in the refrigerant circuit, and the determination is made based on the determination condition that the valve opening remains above a predetermined threshold for a predetermined period of time.

Description

Technical Field

[0006] ,

[0001] The present invention relates to a refrigeration device.

Background Art

[0002] As a method for determining refrigerant shortage in a conventional refrigeration device, for example, a temperature difference between the inlet refrigerant temperature and the outlet refrigerant temperature of a subcooler is calculated, and when this temperature difference decreases from a set value, it is determined that there is a refrigerant shortage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0007] The refrigeration system of this disclosure allows for early detection of refrigerant shortages. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a refrigeration apparatus according to an embodiment of the present disclosure. [Figure 2A] This is a schematic diagram of a receiver tank according to an embodiment of the present disclosure. [Figure 2B] This is a schematic diagram of a receiver tank according to an embodiment of the present disclosure. [Figure 3] This is a flowchart of the refrigerant shortage detection process described in this disclosure. [Modes for carrying out the invention]

[0009] The refrigeration apparatus of this disclosure will be described below with reference to the drawings. While preferred embodiments of the refrigeration apparatus of this disclosure will be described below, the invention is not limited thereto, and various modifications and improvements are possible based on the knowledge of those skilled in the art.

[0010] Figure 1 is a schematic diagram of a refrigeration system 1 according to an embodiment. Figures 2A and 2B are schematic diagrams of a receiver tank according to an embodiment of this disclosure. The refrigeration system 1 according to an embodiment will be described using Figures 1, 2A, and 2B.

[0011] (Refrigeration device 1) The refrigeration system 1 comprises a compressor 14 configured to discharge refrigerant within a target discharge temperature range, an air-cooled condenser 20 as a condenser, a receiver tank 24 for storing refrigerant discharged from the compressor 14, an air-cooled subcooler 21 arranged in parallel with the air-cooled condenser 20 for subcooling the refrigerant discharged from the receiver tank 24, an injection circuit which forms part of the refrigerant circuit and returns the liquid refrigerant in the receiver tank 24 to the compressor, a liquid injection electric valve 36 provided in the injection circuit for reducing the pressure of the liquid refrigerant in the receiver tank 24, and a control device 4 configured to control the valve opening of the liquid injection electric valve 36 according to the target discharge temperature range of the compressor, wherein the control device 4 is configured to determine if there is a shortage of refrigerant in the refrigerant circuit.

[0012] (Inhalation temperature sensor 10) The intake temperature sensor is located upstream of the accumulator 12 and is configured to measure the temperature of the refrigerant supplied to the accumulator 12 in the refrigerant circuit.

[0013] (Low-pressure sensor 11) The low-pressure sensor 11 is located upstream of the accumulator 12 and is a sensor that detects the pressure of the refrigerant supplied to the accumulator 12 in the refrigerant circuit.

[0014] (Accumulator 12) The accumulator 12 is installed upstream of the compressor 14 and is a device that separates liquid refrigerant from gaseous refrigerant and sends only gaseous refrigerant to the compressor 14. This device prevents liquid refrigerant from flowing into the compressor 14, thereby preventing damage to the compressor 14.

[0015] (Strainer 13) The strainer 13 is installed upstream of the compressor 14 and is a filter device for removing foreign matter and impurities that have entered the refrigerant circuit.

[0016] (Compressor 14) The compressor 14 is located upstream of the oil separator 15 and downstream of the accumulator 12. The compressor 14 comprises, for example, an intake section, an injection refrigerant intake section, a compression chamber, a compression mechanism, and a discharge section. The intake section takes in low-pressure refrigerant and supplies it to the compression chamber. The injection refrigerant intake section takes in intermediate-pressure refrigerant from the injection circuit and supplies it to the intermediate stage of the compression chamber. The injection refrigerant intake section is in communication with the compression chamber and is mixed with the main flow refrigerant. The compression chamber provides a space to compress the intake refrigerant and raise it to the discharge pressure. The compression mechanism is a mechanism that performs physical action to compress the refrigerant and can be of reciprocating or rotary type. The discharge section sends the compressed, high-pressure refrigerant to the refrigerant circuit. The refrigerant discharged from the compressor 14 is supplied to the oil separator 15 located downstream. The compressor 14 may consist of a single compressor, or it may consist of multiple compressors arranged in parallel with the refrigerant circuit.

[0017] The compressor is configured to discharge the refrigerant within a target discharge temperature range. Here, the "target discharge temperature range" refers to a range of discharge temperatures that can be arbitrarily set when the compressor discharges the refrigerant. This range is set for the purpose of protecting the compressor. This prevents overheating and abnormal operation of the compressor, ensuring its reliability and durability.

[0018] The "target discharge temperature range" is determined by comprehensively considering factors such as the type of refrigerant, outside air temperature, refrigerant pressure, and saturation temperature of the refrigerant. The upper limit and lower limit are affected by many parameters such as the type of refrigerant, outside air temperature, pressure, and saturation temperature. If the upper limit is exceeded, the protection and efficiency of the refrigeration device 1 will be impaired, and if the lower limit is not reached, the cooling performance and energy efficiency will decrease. Therefore, these are set appropriately. The upper limit is set based on the safety of the refrigeration device 1 and the physical properties of the refrigerant. If the upper limit is exceeded, there is a possibility of changes in the state of the refrigerant and damage to the device. Each refrigerant has a critical temperature, and when this temperature is exceeded, the refrigerant can enter a supercritical state where there is no distinction between liquid and gas. The upper limit can be set based on this critical temperature. The upper limit is set based on different criteria depending on the refrigerant used. For example, when using CO2 refrigerant, the upper limit can be set based on its critical temperature. On the other hand, for refrigerants other than CO2, the upper limit can be set based on refrigerant characteristics and system conditions rather than the critical temperature. Since there is a limit to the temperature that the parts of the device can withstand, damage to the parts is a concern if the upper limit is exceeded. The lower limit is set to maintain the cooling performance of the refrigerant and improve the energy efficiency of the system. If the lower limit is not reached, the circulation of the refrigerant becomes insufficient and the efficiency of the refrigeration device 1 decreases. Each refrigerant has a saturation temperature under a specific pressure, and if this is not reached, the refrigerant may liquefy and heat exchange in the refrigerant circuit may become insufficient. Therefore, the lower limit can be set based on the saturation temperature of the refrigerant.

[0019] (Oil level switch 14A) The oil level switch 14A is a device that monitors the oil level in the compressor 14. Oil is important for the lubrication of the compressor 14. When the oil level is low, an abnormality is detected and safety measures such as stopping the operation of the compressor are taken. This prevents damage and failure of the compressor.

[0020] (Discharge temperature sensor 14B) The discharge temperature sensor 14B is a sensor that measures the temperature of the refrigerant discharged from the compressor 14. The temperature detected by the discharge temperature sensor 14B is used to control the valve opening of the liquid injection electric valve 36. For example, if the temperature detected by the discharge temperature sensor 14B is high, that is, if the temperature of the refrigerant discharged from the compressor 14 is high, the valve opening of the liquid injection electric valve 36 is controlled to increase, thereby cooling the compressor 14. On the other hand, if the temperature detected by the discharge temperature sensor 14B is low, that is, if the temperature of the refrigerant discharged from the compressor 14 is low, the valve opening of the liquid injection electric valve 36 is controlled to decrease.

[0021] (High-pressure switch 14C) The high-pressure switch 14C is a safety device that activates when the pressure inside the compressor 14 becomes abnormally high. It is configured to stop the compressor 14 when the pressure exceeds a specified value.

[0022] (Oil separator 15) The oil separator 15 is installed downstream of the compressor 14 and is a device that separates the refrigerant and oil discharged from the compressor 14. By separating the oil discharged from the compressor 14 along with the refrigerant and returning it to the compressor 14 via the oil return pipe, it prevents the oil from flowing into the refrigerant circuit.

[0023] (Service valve 16) The service valve 16 is installed in the oil return piping and is used to replenish or drain oil during maintenance and inspection of the refrigeration system.

[0024] (Strainer 17) The strainer 17 is a filter device installed in the oil return piping that removes foreign matter and dirt mixed in with the oil.

[0025] (Solenoid valve 18) The solenoid valve 18 is installed in the oil return piping and is a valve that uses electromagnetic force to control the flow of oil.

[0026] (High-pressure sensor 19) The high-pressure sensor 19 is located downstream of the oil separator 15 and upstream of the air-cooled condenser 20, and is a sensor that detects the pressure of the high-pressure refrigerant compressed by the compressor 14.

[0027] (Air-cooled condenser 20) The air-cooled condenser 20 is located downstream of the oil separator 15 and upstream of the receiver tank 24, and is configured to cool the refrigerant with outside air, condensing it from a gaseous state to a liquid state.

[0028] (Air cooled supercooler 21) The air-cooled subcooler 21 is installed downstream of the receiver tank 24 and upstream of the economizer 26. It is configured to lower the temperature of the refrigerant by further cooling it with outside air after it has been liquefied in the air-cooled condenser 20.

[0029] (Fan 22 for air-cooled condenser) The fan 22 for the air-cooled condenser is a fan that blows outside air into the air-cooled condenser 20 and the air-cooled subcooler 21. The fan's speed and operation are adjusted according to the outside air temperature and the load on the refrigeration system.

[0030] (Outside air temperature sensor 23) The outside air temperature sensor 23 is a sensor that measures the outside air temperature around the refrigeration unit.

[0031] (Receiver Tank 24) The receiver tank 24 is located downstream of the air-cooled condenser 20 and upstream of the air-cooled subcooler 21. It is a tank for temporarily storing the refrigerant that has undergone the condensation process in the air-cooled condenser 20. It is used to stabilize the state of the refrigerant, adjust the flow rate of the refrigerant, and prevent refrigerant shortages or excesses in the refrigeration cycle.

[0032] (Refrigerant supply main pipe 24A) As shown in Figures 1, 2A, and 2B, the refrigerant supply main pipe 24A is connected to the outlet of the air-cooled condenser 20 and inserted into the receiver tank 24. It is the piping for supplying the liquid refrigerant, which has undergone the condensation process in the air-cooled condenser 20, to the receiver tank 24. The liquid refrigerant is supplied to the receiver tank 24 through the inlet of the refrigerant supply main pipe 24A.

[0033] (Refrigerant extraction main pipe 24B) The refrigerant extraction main pipe 24B is connected to the inlet of the air-cooled subcooler 21 and inserted into the receiver tank 24. It is the piping for extracting liquid refrigerant from the receiver tank 24. The liquid refrigerant is extracted through the refrigerant extraction main pipe 24B and supplied for the next process.

[0034] (Injection outlet piping 24C) The injection outlet pipe 24C is a pipe that forms part of the injection circuit for returning the liquid refrigerant in the receiver tank 24 to the compressor 14. Figure 2 is a diagram illustrating the injection outlet pipe 24C. As shown in Figures 2A and 2B, the injection outlet pipe 24C is inserted into the receiver tank 24 and is characterized by the height of its outlet (inlet). The height from the bottom of the receiver tank 24 to the outlet of the injection outlet pipe 24C is higher than the height from the bottom of the receiver tank 24 to the outlet (inlet) of the refrigerant outlet main pipe 24B. As shown in Figure 2A, if the liquid level of the liquid refrigerant is higher than the height to the outlets of both the refrigerant outlet main pipe 24B and the injection outlet pipe 24C, it is possible to extract liquid refrigerant from both the refrigerant outlet main pipe 24B and the injection outlet pipe 24C. On the other hand, as shown in Figure 2B, when the liquid refrigerant level drops to a level higher than the outlet of the main refrigerant extraction pipe 24B and equal to the outlet of the injection extraction pipe 24C, it becomes possible to extract liquid refrigerant from the main refrigerant extraction pipe 24B, but it becomes impossible to extract liquid refrigerant from the injection extraction pipe 24C. In other words, the amount of liquid refrigerant supplied to the injection circuit decreases, and the amount of refrigerant to return to the compressor 14 decreases (becomes insufficient). This makes it easier to detect the refrigerant shortage, which will be described later. Furthermore, if the liquid refrigerant level drops further, it becomes difficult to extract liquid refrigerant from the receiver tank 24, and the circulation of refrigerant in the refrigerant circuit stops.

[0035] (Injection outlet pipe temperature sensor 24D) The injection outlet pipe temperature sensor 24D is installed in the injection outlet pipe 24C and measures the temperature of the refrigerant in the injection outlet pipe 24C. The temperature measured by the injection outlet pipe temperature sensor 24D is transmitted to the control device 4 and used to detect refrigerant shortage. In one embodiment of the present invention, the injection outlet pipe temperature sensor 24D may not be installed.

[0036] (Refrigerant main pipe temperature sensor 24E) The refrigerant main pipe temperature sensor 24E is installed upstream of the inlet of the air-cooled subcooler 21 and is a sensor that detects the temperature of the refrigerant in the refrigerant main pipe 24B. The temperature measured by the refrigerant main pipe temperature sensor 24E is transmitted to the control device 4 and used to detect refrigerant shortage. In one embodiment of the present invention, the refrigerant main pipe temperature sensor 24E may not be installed.

[0037] (Liquid temperature detection temperature sensor 24F) The liquid temperature detection sensor 24F is located at the bottom of the receiver tank 24 and measures the temperature of the liquid refrigerant stored in the receiver tank 24. The temperature measured by the liquid temperature detection sensor 24F is transmitted to the control device 4 and used to detect refrigerant shortage. In one embodiment of the present invention, the liquid temperature detection sensor 24F may not be installed.

[0038] (Fusible plug 25) The fusible plug is located at the bottom of the receiver tank 24 and is a safety device. It is designed to release internal pressure when the temperature of the refrigerant liquid inside the receiver tank 24 rises abnormally. When the temperature exceeds a certain level, the fusible plug dissolves, and refrigerant is released to the outside to reduce the pressure.

[0039] (Economizer 26) The economizer 26 includes a first flow path located downstream of the air-cooled subcooler 21 and upstream of the liquid outlet, and a second flow path located downstream of the branching point of the injection circuit and upstream of the injection refrigerant suction section of the compressor 14. The economizer 26 is configured to exchange heat between the refrigerant flowing through the first flow path and the refrigerant flowing through the second flow path. The flow rate of the refrigerant flowing through the second flow path is controlled by a liquid injection solenoid valve 32.

[0040] (Service valve 27) The service valve 27 is a valve used for charging and recovering refrigerant during maintenance of the refrigeration unit 1.

[0041] (Check joint 28) The check joint 28 is a connection port for measuring pressure and temperature within the refrigeration unit 1, and is used to attach measuring instruments during inspection and maintenance. This allows for checking the refrigerant pressure and temperature status and monitoring the system's condition.

[0042] (Filter dryer 29) The filter dryer 29 is a device that removes moisture and impurities contained in the refrigerant circuit.

[0043] (Moisture Indicator 30) The moisture indicator 30 is a device for monitoring the amount of moisture in the refrigerant. If there is too much moisture in the refrigerant circuit, the system's efficiency will decrease, and problems such as refrigerant freezing and corrosion can occur. The indicator is installed to prevent these issues.

[0044] (Ecom sensor 31) The Ecom sensor 31 is located downstream of the economizer 26 and is used to measure the temperature near the liquid outlet of the refrigeration device 1.

[0045] (Liquid injection solenoid valve 32) The liquid injection solenoid valve 32 is located downstream of the liquid injection electric valve 36 and upstream of the economizer 26, and is a variable-opening solenoid valve that adjusts the amount of refrigerant supplied to the economizer 26. The valve opening is controlled by an opening adjustment signal output by the control device 4. The liquid injection solenoid valve 32 may simply be a valve that opens and closes.

[0046] (Liquid injection solenoid valve 33) The liquid injection solenoid valve 33 is located downstream of the liquid injection electric valve 36 and upstream of the compressor 14. It is a variable-opening solenoid valve that adjusts the amount of refrigerant supplied to the compressor 14. The valve opening is controlled by an opening adjustment signal output by the control device 4. The liquid injection solenoid valve 33 may simply be a valve that opens and closes.

[0047] (Service valve 34) The service valve is used for charging and recovering refrigerant when performing maintenance or repairs on the refrigeration unit 1.

[0048] (Strainer 35) Strainer 35 is a filter device that removes foreign matter and dirt contained in the refrigerant circuit.

[0049] (Liquid injection electric valve 36) The liquid injection electric valve 36 is located downstream of the receiver tank 24 and upstream of the compressor 14, and is a variable-opening electric valve for adjusting the amount of refrigerant supplied to the compressor 14. Its valve opening is controlled according to an opening adjustment signal from the control device 4. The refrigerant flowing through the liquid injection electric valve 36 is divided into two paths: one leading to the economizer 26, which is equipped with a liquid injection solenoid valve 32, and the other leading to the compressor 14, which is equipped with a liquid injection solenoid valve 33. When both the liquid injection solenoid valve 32 and the liquid injection solenoid valve 33 are closed, the liquid injection electric valve 36 cannot supply refrigerant to the compressor 14. When either or both of the liquid injection solenoid valves 32 and 33 are open, the liquid injection electric valve 36 can supply refrigerant to the compressor 14 through either or both of these valves. The liquid injection solenoid valves 32 and 33 may be controlled in a reciprocal manner so that when one is closed, the other opens.

[0050] Note that the liquid injection solenoid valves 32 and 33 do not need to be provided. The flow rate of refrigerant to the compressor 14 may be controlled by the liquid injection electric valve 36 alone.

[0051] (Electrical box 37) The electrical box 37 is a box for housing the electrical control equipment and circuits of the refrigeration unit 1. It contains relays, contactors, control boards, etc., for controlling the operation of the refrigeration unit 1, and is configured to manage the operation of the entire refrigeration unit 1.

[0052] (Heat sink temperature sensor 37A) The heat sink temperature sensor 37A is attached to the heat sink of the electrical box 37 and measures the temperature of the heat sink. This sensor monitors whether the heat sink is functioning properly and whether the temperature is abnormally high, thereby preventing the heat sink from overheating.

[0053] (Electrical box temperature sensor 37B) The electrical box temperature sensor 37B is a sensor used to monitor the temperature inside the electrical box 37. It is used to prevent the temperature inside the electrical box 37 from rising and to manage the temperature inside the box.

[0054] (Refrigerator outlet temperature sensor 38) The refrigerator outlet temperature sensor 38 is installed downstream of the liquid outlet of the refrigeration unit 1 and measures the temperature near the liquid outlet of the refrigeration unit 1.

[0055] (Injection circuit) An injection circuit is a system that supplies refrigerant to the compressor 14 and returns it to the refrigerant circuit in order to cool the compressor 14 using the refrigerant. The injection circuit is provided to prevent the compressor from overheating while maintaining the operating efficiency of the compressor 14. This enables stable operation, especially under high load conditions and high-temperature environments, and improves the performance of the entire refrigeration cycle. The starting point of the injection circuit is the outlet of the injection outlet pipe 24C in the receiver tank 24, and the ending point is the outlet of the refrigerant supply main pipe 24A in the receiver tank 24. The piping and intervening devices that connect these starting and ending points constitute the injection circuit.

[0056] If there is insufficient refrigerant in the injection circuit, the compressor 14 will not be cooled sufficiently, and heat may be generated. This causes the temperature of the compressor 14 to rise, leading to decreased efficiency and accelerated wear of parts. In addition, the temperature of the lubricating oil will rise, reducing its lubrication effect and increasing friction inside the compressor 14. Furthermore, due to the refrigerant shortage, non-condensable gases may enter the injection circuit, reducing the cooling performance of the compressor 14. Therefore, the liquid injection electric valve 36 is controlled to open in order to suppress the rise in the discharge temperature of the compressor 14.

[0057] (Injection piping in an injection circuit) The injection piping in the injection circuit is for supplying refrigerant for liquid injection to the injection supply section of the compressor 14. Specifically, the injection piping is refrigerant piping that connects the injection outlet piping 24C of the receiver tank 24 to the injection inlet of the compressor 14.

[0058] (Detection of refrigerant shortage in the injection circuit) If there is insufficient refrigerant in the injection circuit, the compressor 14 will not be adequately cooled, potentially generating heat. This can cause the temperature of the compressor 14 to rise, leading to decreased efficiency and accelerated wear of components. Furthermore, the temperature of the lubricating oil will also rise, reducing its lubrication effect and increasing friction within the compressor. Additionally, the refrigerant shortage can cause non-condensable gases to enter the injection circuit, further reducing the cooling performance of the compressor 14. Therefore, a control system for detecting refrigerant shortage in the injection circuit will be described.

[0059] (Detection of refrigerant shortage 1: Refrigerant shortage detection based on the valve opening of the liquid injection electric valve 36) A refrigerant shortage is detected according to the valve opening of the liquid injection electric valve 36. When there is a refrigerant shortage, the refrigerant flow rate in the injection circuit decreases, and the cooling performance of the compressor 14 deteriorates, causing the valve opening of the liquid injection electric valve 36 to remain large for a long period of time. Therefore, if the valve opening of the liquid injection electric valve 36 remains above a predetermined threshold for a predetermined period of time or longer, a refrigerant shortage is detected.

[0060] (The "predetermined threshold" for the valve opening of the liquid injection electric valve 36) The "predetermined threshold" for the valve opening of the liquid injection electric valve 36 can be determined based on, for example, the temperature measured by the discharge temperature sensor 14B, the flow rate measured from the refrigerant flow sensor and pressure difference (pressure difference before and after compression), the pressure on the suction and discharge sides of the compressor 14 or the pressure in the injection circuit, the degree of subcooling calculated based on the liquid refrigerant temperature of the receiver tank 24 and economizer 26, the concentration of non-condensable gas, the operating current of the compressor 14, and pressure and temperature parameters corresponding to the load.

[0061] The injection circuit supplies refrigerant to suppress the discharge temperature of the compressor 14, so the discharge temperature can serve as an indicator. With respect to the temperature measured by the discharge temperature sensor 14B, if the refrigerant is insufficient, the cooling effect decreases and the discharge temperature rises, which affects the increase in valve opening. The valve opening can be adjusted in accordance with the rise in discharge temperature so as not to exceed the allowable discharge temperature range of the compressor 14, and a "predetermined threshold" can be determined.

[0062] Furthermore, a decrease in refrigerant flow rate reduces the compressor's cooling performance and increases the valve opening, thus the refrigerant flow rate affects the valve opening. Regarding the flow rate value measured from the refrigerant flow sensor or pressure difference (pressure difference before and after compression), when the flow rate decreases, the valve opening required to ensure the cooling effect can be calculated, and a "predetermined threshold" can be determined based on that value.

[0063] The pressure difference of the refrigerant affects the flow state and evaporation efficiency of the refrigerant. If the pressure is low, the evaporation of the refrigerant will be insufficient, and the cooling effect will decrease. Based on the pressure difference measured by the high-pressure sensor 19 and the low-pressure sensor 11 with respect to the pressure on the suction and discharge sides of the compressor 14 or the pressure in the injection circuit, the valve opening degree can be adjusted according to the refrigerant flow rate, and a "predetermined threshold" can be determined when the valve opening degree increases when the pressure difference exceeds a certain level.

[0064] Whether the refrigerant is in a subcooled state also affects the valve opening. When the refrigerant is insufficient, the subcooled state changes, and the valve opening tends to increase. The degree of subcooling is calculated based on the liquid refrigerant temperature of the receiver tank 24 and economizer 26. Since the valve opening of the liquid injection electric valve 36 increases when the degree of subcooling decreases, a "predetermined threshold" can be determined based on the relationship between the degree of subcooling and the valve opening.

[0065] When non-condensable gases are introduced during a refrigerant shortage, the refrigerant flow is obstructed, reducing cooling performance. The concentration of non-condensable gases in the injection circuit is detected, and the behavior of the valve opening when non-condensable gases are introduced is monitored. A "predetermined threshold" can be determined based on the detection of non-condensable gases and the resulting increase in valve opening.

[0066] The operating load of the compressor 14 also affects the valve opening when there is a refrigerant shortage. Higher loads require greater cooling performance, and the valve opening tends to increase. By monitoring the fluctuations in the valve opening in accordance with the operating current and load of the compressor 14, a "predetermined threshold" can be determined based on the valve opening required to obtain the cooling effect at maximum load.

[0067] ("Specified period") In order to determine the "predetermined period" for the liquid injection electric valve 36, it is necessary to understand the impact of refrigerant shortage on cooling performance and to determine whether the fluctuation in valve opening is temporary or a continuous condition due to refrigerant shortage. For this reason, the "predetermined period" can be determined based on, for example, the heat capacity and response time of the compressor 14, the rate of increase in discharge temperature, the refrigerant circulation rate, the type and physical properties of the refrigerant, the operating mode, the degree of non-condensable gas contamination, and the influence of the subcooler and economizer.

[0068] The heat capacity and response time of compressor 14 are parameters used to understand how long it takes for the entire system to be affected when the cooling performance of compressor 14 deteriorates. Regarding the heat capacity and internal temperature rise rate of the compressor, even if a refrigerant shortage occurs, the cooling performance of the compressor does not immediately deteriorate, so the time until the effects of the refrigerant shortage become apparent is estimated. By monitoring fluctuations in the internal temperature of the compressor and calculating the time until the effects of the refrigerant shortage become apparent based on the time it takes for the discharge temperature to significantly exceed the target temperature, a "predetermined period" can be determined.

[0069] Furthermore, the system response time in case of refrigerant shortage is determined based on the rate of increase in discharge temperature detected by the discharge temperature sensor 14B. When a refrigerant shortage occurs, the discharge temperature begins to rise, but the rate of this rise varies depending on the degree of refrigerant shortage. If the temperature rise is rapid, it is necessary to detect the refrigerant shortage in a short time. Based on the rate of increase in discharge temperature, the "predetermined period" can be adjusted, and if a rapid temperature rise is confirmed, it can be set to determine that there is a refrigerant shortage in a short time.

[0070] Furthermore, regarding the refrigerant circulation speed of the system, when a refrigerant shortage occurs, the system determines how quickly the shortage will affect the entire system, depending on the rate at which the refrigerant circulates throughout the system. By monitoring the refrigerant flow rate and circulation speed, the effects of a refrigerant shortage will appear quickly in systems with a high circulation speed, but the effects will appear later in systems with a slow circulation speed, requiring a longer time to make a determination. Considering the system's refrigerant circulation speed, the system may detect shortages quickly if the flow rate is high, and set a longer "specified period" if the flow rate is low.

[0071] Furthermore, the impact of refrigerant shortage on cooling performance and the duration of this impact vary depending on the type and characteristics of the refrigerant used, so the physical properties of the refrigerant must be considered. In the case of non-azeotropic mixed refrigerants (e.g., R448A), compositional changes may occur when refrigerant leaks, and the impact of these compositional changes on cooling performance differs. For example, azeotropic refrigerants do not undergo compositional changes, allowing for early detection of refrigerant shortages, but this may take longer with non-azeotropic refrigerants. Depending on the type of refrigerant, a "predetermined period" may be set considering the time it takes for cooling performance to deteriorate due to refrigerant shortages.

[0072] Furthermore, the impact of refrigerant shortage differs depending on the operating mode of the system (normal operation, overload operation, etc.), so the operating mode must be taken into consideration. Depending on the system load and compressor operating state during operation, refrigerant shortage will have an earlier impact during overload operation, so the time until refrigerant shortage is detected needs to be set to be shorter. However, during normal operation, the impact appears more gradually, so the "predetermined period" until detection can be set to be longer. In other words, the "predetermined period" can be dynamically adjusted according to the operating mode, making it possible to set a shorter "predetermined period" during overload operation and a longer "predetermined period" during normal operation.

[0073] Furthermore, if non-condensable gases are introduced when there is a refrigerant shortage, the physical properties of the refrigerant change, and the cooling performance deteriorates rapidly. Therefore, if the introduction of non-condensable gases is detected, it is necessary to quickly determine that there is a refrigerant shortage. In order to detect changes in temperature and pressure due to the introduction of non-condensable gases, the temperature changes detected in particular at the injection outlet pipe 24C are monitored, and the response speed when non-condensable gases are introduced is considered. If the introduction of non-condensable gases is confirmed, the system can be set to detect a refrigerant shortage within a short "predetermined period".

[0074] Furthermore, with respect to the subcooler and economizer, the impact of refrigerant shortage on refrigerant flow rate and temperature can be mitigated, which may extend the time until refrigerant shortage is detected. When the economizer 26 and air-cooled subcooler 21 are functioning in the system, the effects of refrigerant shortage appear with a delay, so the time until detection is set to be longer. In other words, the "predetermined period" can be determined based on the time until refrigerant shortage appears, taking into account the effects of the subcooler and economizer.

[0075] (Detection of refrigerant shortage 2: Refrigerant shortage detection based on control based on discharge temperature) The injection circuit is provided to control the discharge temperature of the compressor 14. When there is a shortage of refrigerant, non-condensable gases mix into the circuit, reducing the cooling performance of the compressor. As a result, the discharge temperature tends to rise. The discharge temperature sensor 14B is used to detect the temperature rise and adjust the valve opening of the liquid injection electric valve 36. When the discharge temperature exceeds a predetermined threshold temperature, the liquid injection electric valve 36 is opened. If there is a shortage of refrigerant, sufficient cooling effect cannot be obtained even if the valve opening reaches the upper limit, so the valve opening remains high. If the valve opening remains above the threshold for a certain period of time (e.g., 1 hour) or longer, the control device detects a refrigerant shortage.

[0076] The "predetermined threshold temperature" can be set based on the design allowable maximum discharge temperature of the compressor 14, the evaporation temperature of the refrigerant used, the type of refrigerant, the amount of non-condensable gas mixed in, and so on.

[0077] (Detection of refrigerant shortage 3: Detection of refrigerant shortage based on temperature difference) When a refrigerant shortage occurs, a temperature difference develops between the temperature inside the injection outlet pipe 24C and the saturation temperature. This temperature difference can be used to detect a refrigerant shortage early. The saturation temperature obtained from the pressure detected by the high-pressure sensor 19 is compared with the temperature of the injection outlet pipe temperature sensor 24D. If a large temperature difference occurs between the two, it is considered a sign of refrigerant leakage or refrigerant shortage, and a refrigerant shortage is detected.

[0078] (Detection of refrigerant shortage 4: Detection of refrigerant shortage due to refrigerant leak) For non-azeotropic mixed refrigerants such as R448A, compositional changes occur when refrigerant leaks, making it difficult to determine the degree of subcooling. Therefore, discharge temperature and pressure difference are used as the basis instead of the degree of subcooling. This allows for the detection of refrigerant shortage or leakage. During operation and shutdown, the difference between the injection outlet piping temperature and the saturation temperature is monitored, and if the difference exceeds a certain threshold, it is detected as a refrigerant leak. In addition, when a refrigerant leak is detected, the temperature and pressure profiles change due to changes in the refrigerant mixing characteristics. Therefore, by monitoring the pressure and temperature of the injection circuit, it is possible to detect a refrigerant shortage due to a refrigerant leak.

[0079] (Detection of refrigerant shortage 5: Detection of refrigerant shortage based on temperature difference) This section describes how to detect a refrigerant shortage by comparing data from the high-pressure sensor 19 and the injection outlet pipe temperature sensor 24D. When there is a refrigerant shortage, gasification progresses, creating a difference from the saturation temperature, which can be used to quickly identify the refrigerant shortage.

[0080] The control device 4 determines a refrigerant shortage in the refrigerant circuit based on the temperature difference between the refrigerant saturation temperature obtained from the pressure measured by the high-pressure sensor 19 and the refrigerant temperature measured by the injection outlet pipe temperature sensor 24D. This allows for a comparison between the refrigerant saturation temperature (liquid), which is estimated from the pressure measured by the high-pressure sensor 19, and the refrigerant temperature measured by the injection outlet pipe temperature sensor 24D. When gas is drawn out, a temperature difference is created between the refrigerant saturation temperature (liquid) and the refrigerant temperature in the injection outlet pipe 24C, allowing for earlier detection of a refrigerant shortage.

[0081] The high-pressure sensor 19 measures the pressure on the high-pressure side of the refrigerant circuit. Based on this measured pressure value, the saturation temperature of the refrigerant is calculated. The saturation temperature of the refrigerant is closely related to the pressure; the higher the pressure, the higher the saturation temperature (the temperature at which a liquid changes into a gas). The saturation temperature is an important indicator for determining whether the refrigerant exists as a liquid or is in the process of becoming a gas. When there is a sufficient supply of refrigerant, a saturation temperature corresponding to the pressure is obtained, but if there is a shortage of refrigerant, gasification progresses, causing the temperature and pressure to become unstable.

[0082] The injection outlet pipe temperature sensor 24D measures the temperature of the refrigerant flowing through the injection outlet pipe 24C. Liquid refrigerant is typically expected to flow through this pipe. When sufficient refrigerant is supplied, the temperature of this pipe approaches the saturation temperature based on the high-pressure side. However, if the refrigerant supply is insufficient and gasification progresses, gaseous refrigerant, rather than liquid, passes through the outlet pipe, resulting in a significant deviation of the refrigerant temperature in the pipe from the saturation temperature.

[0083] In the refrigerant shortage detection, the saturation temperature calculated from the pressure obtained by the high-pressure sensor 19 is compared with the refrigerant temperature in the injection outlet pipe 24C. During normal operation, when liquid refrigerant is flowing normally, the difference between the pressure-based saturation temperature and the temperature in the outlet pipe is small and practically the same. When there is a refrigerant shortage, as the refrigerant becomes insufficient and more gas flows, the temperature in the outlet pipe rises, creating a large temperature difference with the saturation temperature. By detecting this temperature difference, it is possible to determine that there is a refrigerant shortage.

[0084] When a refrigerant shortage occurs, the amount of liquid refrigerant in the receiver tank 24 and the refrigerant circuit decreases, and gas may pass through the extraction piping instead of liquid. The temperature changes of liquid and gaseous refrigerants are different. Liquid refrigerants maintain a temperature close to their saturation temperature due to pressure, while gaseous refrigerants are more likely to exhibit temperatures that deviate significantly from that temperature. As a result, as the refrigerant shortage progresses, a clear temperature difference will develop between the saturation temperature and the temperature of the extraction piping. This temperature difference can be an effective indicator for early detection of a refrigerant shortage.

[0085] Furthermore, if the above temperature difference exceeds a certain temperature difference, it may be determined that there is a refrigerant shortage. Here, the "certain temperature difference" may be determined according to the type of refrigerant, the saturation temperature based on the pressure measured by the high-pressure sensor, the refrigerant flow rate, the cooling load, etc.

[0086] Each refrigerant has its own unique saturation pressure-temperature characteristics. The saturation temperature at the same pressure and the gaseous and liquid properties differ depending on the type of refrigerant. Therefore, the "constant temperature difference" varies depending on the type of refrigerant. For example, refrigerants such as R410A and R134a have different saturation temperature characteristics even at the same pressure, so a "constant temperature difference" can be set accordingly for each.

[0087] Since the saturation temperature obtained from the pressure measured by the high-pressure sensor 19 is pressure-dependent, the saturation temperature changes when the pressure changes. Therefore, the "constant temperature difference" that occurs when there is a refrigerant shortage can be set considering the saturation temperature based on the measured pressure.

[0088] The refrigerant flow rate is also a factor that affects the temperature difference. When the refrigerant circulates through the circuit at an appropriate flow rate, the temperature difference remains stable. However, if the flow rate decreases due to a refrigerant shortage, heat exchange within the circuit becomes insufficient, which can lead to a larger temperature difference. A "constant temperature difference" can be determined by referring to data from a flow sensor that measures the refrigerant flow rate.

[0089] Furthermore, refrigerant shortage can be detected not only during operation but also when the system is stopped. When refrigeration unit 1 stops, the pressure inside refrigeration unit 1 does not fluctuate rapidly and settles into a stable state. Because the pressure fluctuation is small, the saturation temperature of the refrigerant is more stable, and therefore the temperature difference tends to become more constant compared to when the system is running. Since the temperature difference in this state is more susceptible to the effects of refrigerant shortage, it may be easier to detect refrigerant shortage without being affected by fluctuations during operation. Even when refrigeration unit 1 stops, residual heat in the refrigerant circuit and heat inflow from the outside may cause the refrigerant to partially gasify due to changes in its physical properties. If refrigerant shortage is progressing, the gasification may become more pronounced because there is a shortage of liquid refrigerant. As a result, a temperature difference occurs even when the system is stopped, making it possible to detect refrigerant shortage.

[0090] (Detection of refrigerant shortage 6: Detection of refrigerant shortage based on temperature difference) By monitoring the difference between the refrigerant main outlet temperature and the injection outlet piping temperature, the refrigerant status can be understood, and refrigerant shortages can be detected early. As the gas begins to flow, the temperature difference becomes more pronounced, allowing for accurate and rapid determination of refrigerant shortages. The control device 4 is configured to determine refrigerant shortages in the refrigerant circuit based on the temperature difference between the refrigerant temperature measured by the refrigerant main outlet temperature sensor 24E in the receiver tank 24 and the refrigerant temperature measured by the injection outlet piping temperature sensor 24D. This allows for a comparison between the saturation temperature (liquid) detected by the refrigerant main outlet temperature and the injection outlet piping temperature. As gas is drawn out, a temperature difference is created between the saturation temperature (liquid) and the injection outlet piping temperature, allowing for earlier detection of a decrease in the amount of refrigerant.

[0091] More specifically, the refrigerant status is monitored based on the temperature difference measured by the refrigerant main pipe temperature sensor 24E and the injection pipe temperature sensor 24D in the receiver tank 24. The refrigerant main pipe temperature sensor 24E is installed at the outlet of the receiver tank 24 and measures the temperature of the liquid refrigerant flowing out of the tank. Normally, when the refrigerant is supplied properly, this temperature is close to the refrigerant's saturation temperature (liquid state). The injection pipe temperature sensor 24D monitors the temperature of the refrigerant flowing through the injection pipe. Under normal conditions, this temperature is also close to the saturation temperature because liquid refrigerant is flowing. However, when the refrigerant begins to run low, the amount of refrigerant supplied from the receiver tank decreases, and gaseous refrigerant begins to pass through the injection pipe. Since gaseous refrigerant is hotter than liquid refrigerant, a temperature difference is created between the main pipe temperature and the injection pipe temperature. This temperature difference acts as a trigger for detecting refrigerant shortage. The saturation temperature refers to the temperature when the refrigerant is in a liquid state. The saturation temperature is pressure-dependent and is determined based on the operating pressure of the refrigeration unit 1. When the refrigerant is in a liquid state, the refrigerant temperature will be close to the saturation temperature. By comparing the saturation temperature with the temperature of the injection outlet piping, it is possible to determine whether the refrigerant is liquid or gaseous. When gas begins to flow through the outlet piping, the difference between the saturation temperature and the piping temperature increases, which allows for earlier detection of refrigerant shortage.

[0092] When refrigerant becomes insufficient, the amount of refrigerant flowing from the receiver tank 24 to the injection outlet piping decreases, and the amount of gaseous refrigerant increases instead of liquid refrigerant. Gas has a lower energy transfer efficiency than liquid, resulting in reduced cooling performance. When gas begins to flow through the injection outlet piping, the temperature rises. This temperature change is a sign of refrigerant shortage. Because gas and liquid change temperature differently, the rise in the injection outlet piping temperature can create a clear temperature difference between it and the main pipe temperature. This temperature difference is a direct indicator of refrigerant shortage.

[0093] Furthermore, as described above (Detection of refrigerant shortage 5), a refrigerant shortage may be determined if the above temperature difference exceeds a certain temperature difference.

[0094] (Detection of refrigerant shortage 7: Detection of refrigerant shortage based on temperature difference) The control device 4 is configured to determine a refrigerant shortage in the refrigerant circuit based on the temperature difference between the refrigerant temperature measured by the liquid temperature detection sensor 24F and the refrigerant temperature measured by the injection outlet pipe temperature sensor 24D. This allows for a comparison between the saturation temperature (liquid) detected by the bottom temperature of the receiver tank 24 and the injection outlet pipe temperature. When gas is drawn out, a temperature difference is created between the saturation temperature (liquid) and the injection outlet pipe temperature, allowing for earlier detection of a decrease in the amount of refrigerant.

[0095] Under normal conditions, when there is sufficient refrigerant in the receiver tank 24, the temperature difference between the liquid temperature detection sensor 24F and the injection outlet pipe temperature sensor 24D is close to zero, indicating that the refrigerant in the injection circuit is circulating in a liquid state. When there is a refrigerant shortage, the refrigerant in the receiver tank 24 may gasify. As a result, the temperature of the refrigerant flowing through the injection outlet pipe rises, and a temperature difference appears. Based on this temperature difference, the control device 4 determines that there is a refrigerant shortage. Alternatively, as described above (detection of refrigerant shortage 5), a refrigerant shortage may be determined when the above temperature difference exceeds a certain temperature difference.

[0096] (Detection of refrigerant shortage 8: Detection of refrigerant shortage based on temperature difference) The control device 4 is configured to determine a refrigerant shortage in the refrigerant circuit based on the temperature difference between the saturation temperature obtained based on the pressure measured by the high-pressure sensor 19 and the temperature measured by the refrigerator outlet temperature sensor 38. The control device compares the ideal value of the saturation temperature (liquid) calculated by the high-pressure sensor 19 with the refrigerant liquid temperature measured by the refrigerator outlet temperature sensor 38, and if there is a temperature difference, it is determined that there is a change in the physical properties of the refrigerant due to a refrigerant shortage. Refrigerant leak detection can be performed not only during operation but also when stopped, allowing for earlier detection of a decrease in the amount of refrigerant.

[0097] When the refrigerant level is normal, the saturation temperature (liquid) calculated by the pressure sensor and the refrigerant temperature measured by the refrigerator outlet temperature sensor 38 can be approximately the same value. This indicates that sufficient refrigerant is being supplied. When there is a refrigerant shortage, as the refrigerant becomes insufficient and gasification progresses, the refrigerant temperature at the refrigerator outlet rises above the saturation temperature. This temperature difference indicates a refrigerant shortage.

[0098] The reason why a refrigerant shortage can be detected even when the refrigeration unit 1 is stopped is that even when the refrigeration unit 1 is stopped, the refrigerant inside may gradually gasify. In particular, when there is a refrigerant shortage, gasification is more likely to occur, and the temperature measured by the refrigeration unit outlet temperature sensor 38 rises. By utilizing this temperature difference, it is possible to detect refrigerant leaks or shortages early, even when the unit is stopped.

[0099] When refrigerant is insufficient, its properties can change. When a liquid refrigerant turns into a gas, its volume and thermal conductivity change, reducing its cooling performance. This makes it easier for the refrigerant temperature to deviate from its saturation temperature. If the refrigerant is not supplied sufficiently, the liquid refrigerant will disappear, the flow of gaseous refrigerant will increase, and as a result, the outlet temperature may rise. This temperature difference indicates a change in the refrigerant's properties and can serve as a clear indicator of refrigerant shortage.

[0100] Furthermore, as described above (Detection of refrigerant shortage 5), a refrigerant shortage may be determined if the above temperature difference exceeds a certain temperature difference.

[0101] (Detection and control of refrigerant shortage detection) The control device 4 performs the determination and control of refrigerant shortage detection. The control device 4 is configured to perform the determination and control of refrigerant shortage detection based on information detected by the suction temperature sensor 10, low-pressure sensor 11, discharge temperature sensor 14B, high-pressure sensor 19, outside air temperature sensor 23, injection outlet pipe temperature sensor 24D, refrigerant outlet main pipe temperature sensor 24E, and liquid temperature detection temperature sensor 24F installed in the refrigeration unit 1, as well as the valve opening of the electric valve, the operating status of the compressor 14, the operating status of the refrigeration unit 1, information on exclusion conditions, elapsed time for a predetermined period, information on error reset, and information on refrigerant shortage determination conditions. The control device 4 is configured to use the above information to perform on / off control of the power supply of the refrigeration unit 1, control of the valve opening of the electric valve, counter, error alarm, etc.

[0102] (Conditions for detecting refrigerant shortage) • Judgment condition 1: If the electric valve maintains a valve opening degree of "a predetermined threshold" or higher for a "predetermined period" or longer, it is determined that there is a refrigerant shortage.

[0103] • Judgment condition 2: In addition to condition 2, if the discharge temperature of compressor 14 reaches the "threshold temperature", it is determined that there is a refrigerant shortage, thereby more reliably detecting a refrigerant shortage.

[0104] Furthermore, the criteria for detecting a refrigerant shortage may consist of only criterion 1, or it may consist of both criterion 1 and criterion 2. In addition, other criteria besides criterion 1 and 2 (for example, the criterion based on the temperature difference described above) may be added.

[0105] (Exclusion conditions for refrigerant shortage detection) The exclusion conditions for detecting refrigerant shortage are, for example, the following exclusion conditions 1 to 6. If any one of exclusion conditions 1 to 6 is met, the control for determining refrigerant shortage may be disabled.

[0106] Exclusion condition 1: The time it takes for the refrigeration unit 1 to stabilize after being powered on is within a specified period (e.g., 24 hours).

[0107] Exclusion condition 2: The time elapsed since all abnormal stop switches in the refrigeration unit 1 were activated is within a specified period (e.g., 1 hour).

[0108] Exclusion condition 3: The time elapsed between the completion of defrosting operation by the refrigeration unit 1 and the restart of the compressor 14 is within a specified period (e.g., 30 minutes).

[0109] • Exclusion condition 4: The valve opening of the electric valve is controlled under fixed mode.

[0110] Exclusion condition 5: All compressors 14 are stopped.

[0111] Exclusion condition 6: The discharge temperature sensor 14B has detected an abnormality in any of the compressors 14.

[0112] If exclusion conditions 1 through 6 are not met, the control for determining refrigerant shortage detection will be initiated.

[0113] The exclusion conditions for detecting refrigerant shortage are not limited to the above exclusion conditions 1 to 6. Exclusion conditions may include, for example, when the cooling performance or the performance of the compressor 14 is temporarily significantly reduced in an environment where the outside temperature is extremely high or low, when the pressure sensor in the refrigerant circuit shows an abnormal value, when a significant pressure fluctuation occurs temporarily, or when the system is in a special operating state that deviates from normal operating conditions, such as maintenance mode or trial operation mode.

[0114] (Abnormal operation when refrigerant shortage is detected) If condition 1 is met, the first stage of error notification is issued, for example, "E91: Refrigerant shortage detected." In this case, the operation of refrigeration unit 1 does not stop.

[0115] If judgment condition 2 is met, a second-stage error alert is issued, for example, "E92: Refrigerant shortage alarm," and the compressor 14 is controlled in the same way as when there is an abnormal discharge temperature.

[0116] (Reset error / alarm) If the first stage error "E91" occurs, the error will be automatically cleared 23 hours after its occurrence. This is because it is preferable to detect refrigerant shortage once a day.

[0117] When the discharge temperature of compressor 14 returns to a predetermined range from the "threshold temperature" and the discharge temperature abnormality is resolved, the error is automatically cleared.

[0118] Figure 3 is a flowchart of the refrigerant shortage detection control. Except for step S1, the processes of each step shown in Figure 3 are performed by the control device 4.

[0119] (Step S1: Power ON) In step S1, the power to the refrigeration unit 1 is manually turned ON. This puts the refrigeration unit 1 into a state where the determination in step S2 is possible.

[0120] (Step S2: Does it meet the exclusion criteria?) In step S2, it is determined whether or not the exclusion conditions 1 to 6 are met. If the exclusion conditions 1 to 6 are not met, the process proceeds to step S3. If at least one of the exclusion conditions 1 to 6 is met, step S2 is repeated.

[0121] (Step S3: Is the valve opening at a "predetermined threshold"?) In step S3, it is determined whether the valve opening of the liquid injection electric valve 36 has reached a predetermined threshold. If it is determined that the valve opening has reached a predetermined threshold, the process proceeds to step S4. If it is determined that the valve opening has not reached a predetermined threshold, the process proceeds to step S14.

[0122] (Step S4: Counter +1) In step S4, "1 is added" to the current value of the counter. This is to track how many times the process in step S4 has occurred. If the counter exceeds the upper limit, the control device 4 may issue a refrigerant shortage warning as an error handling measure.

[0123] (Step S5: Has the "first predetermined period" elapsed?) In step S5, it is determined whether the valve opening has remained at a predetermined threshold for the first predetermined period. If it is determined that the first predetermined period has elapsed, the process proceeds to step S6. If it is determined that the first predetermined period has not elapsed, the process returns to step S3.

[0124] (Step S6: Refrigerant shortage detection alert issued) In step S6, the first stage of error notification is issued, for example, "E91: Refrigerant shortage detected". At this time, the operation of the refrigeration unit 1 is not stopped.

[0125] (Step S7: Has the discharge temperature reached the "threshold temperature"?) In step S7, it is determined whether the discharge temperature of the compressor 14 has reached the "threshold temperature". If it is determined that the "threshold temperature" has not been reached, the process proceeds to step S8. If it is determined that the "threshold temperature" has been reached, the process proceeds to step S12.

[0126] Here, "threshold temperature" refers to the temperature at which the discharge temperature of the compressor 14 exceeds the normal operating range and is considered abnormal. This temperature is set based on the specifications of the compressor 14, etc., and is a temperature that would not be reached under normal operating conditions. Specifically, it is set based on the limit point at which the compressor 14 and other related parts may be damaged, taking into account the type and properties of the refrigerant, the pressure and temperature inside the refrigeration system 1. If the "threshold temperature" is reached, the refrigeration system 1 is safely shut down in step S13 via step S12.

[0127] (Step S8: Is the valve opening at a "predetermined threshold"?) In step S8, it is determined whether the valve opening of the electric valve has reached a predetermined threshold. If it is determined that the predetermined threshold has been reached, the process proceeds to step S11. If it is determined that the predetermined threshold has not been reached, the process proceeds to step S9.

[0128] (Step S9: Counter +1) In step S9, "1 is added" to the current value of the counter. This is to track how many times the process in step S9 has occurred.

[0129] (Step S10: Has the "second predetermined period" elapsed?) In step S10, it is determined whether the valve opening has remained at a predetermined threshold for the second predetermined period. If it is determined that the second predetermined period has elapsed, the process proceeds to step S11. If it is determined that the second predetermined period has not elapsed, the process returns to step S7.

[0130] (Step S11: Reset) In step S11, the counter is reset and the process returns to step S2.

[0131] (Step S12: Refrigerant shortage alarm issued) In step S12, a refrigerant shortage alarm is issued. For example, as a second-stage error alarm, "E92: Refrigerant shortage alarm" is issued.

[0132] (Step S13: Stop protection) In step S13, the refrigeration unit 1 is safely shut down. This measure automatically shuts down the refrigeration unit 1 if the discharge temperature of the compressor 14 exceeds a threshold temperature. This prevents further abnormal operation of the compressor 14 and the refrigeration unit 1.

[0133] (Step S14: No refrigerant shortage) In step S14, it is determined that there is no refrigerant shortage.

[0134] (Step S15: Normal operation) In step S15, the refrigerant shortage detection control is terminated. The refrigerant circulation rate is confirmed to be appropriate, and the detection process related to refrigerant shortage is completed. Once refrigerant shortage detection is complete, the refrigeration unit 1 returns to its normal operating mode (normal operation).

[0135] The "predetermined threshold" for the valve opening of the liquid injection electric valve 36 may be the maximum opening of the liquid injection electric valve 36, or, similar to the "predetermined threshold" mentioned above, it may be determined based on, for example, the temperature measured by the discharge temperature sensor 14B, the flow rate measured from the refrigerant flow sensor or pressure difference (pressure difference before and after compression), the pressure on the suction and discharge sides of the compressor 14 or the pressure in the injection circuit, the degree of subcooling calculated based on the liquid refrigerant temperature of the receiver tank 24 and economizer 26, the concentration of non-condensable gas, the operating current of the compressor 14, and pressure and temperature parameters corresponding to the load.

[0136] The "second predetermined period" for the liquid injection electric valve 36 in relation to the valve opening may be the maximum opening of the liquid injection electric valve 36, or, similar to the "predetermined threshold" mentioned above, it may be determined based on, for example, the temperature measured by the discharge temperature sensor 14B, the flow rate measured from the refrigerant flow rate sensor or pressure difference (pressure difference before and after compression), the pressure on the suction side and discharge side of the compressor 14 or the pressure in the injection circuit, the degree of subcooling calculated based on the liquid refrigerant temperature of the receiver tank 24 and economizer 26, the concentration of non-condensable gas, the operating current of the compressor 14, and pressure and temperature parameters corresponding to the load.

[0137] The "first predetermined period" may be, for example, one hour, or, as with the aforementioned "predetermined period," it may be determined based on, for example, the heat capacity and response time of the compressor 14, the rate at which the discharge temperature rises, the refrigerant circulation rate, the type and physical properties of the refrigerant, the operating mode, the degree of non-condensable gas contamination, and the influence of the subcooler and economizer.

[0138] The "second predetermined period" may be, for example, 23 hours, or, like the aforementioned "predetermined period," it may be determined based on, for example, the heat capacity and response time of the compressor 14, the rate at which the discharge temperature rises, the refrigerant circulation rate, the type and physical properties of the refrigerant, the operating mode, the degree of non-condensable gas contamination, and the influence of the subcooler and economizer.

[0139] Furthermore, the control device 4 may be controlled to increase the valve opening of the liquid injection electric valve 36 at predetermined intervals, regardless of the target discharge temperature range. Even when the target discharge temperature is low and the liquid injection electric valve 36 remains closed, refrigerant flows through the injection outlet piping 24C.Refrigerant determination can be made based on the refrigerant temperature at the time of flow.Even under conditions where the discharge temperature of the compressor 14 does not rise and refrigerant stops flowing through the injection outlet piping 24C, a decrease in the amount of refrigerant can be detected.

[0140] Regardless of the target discharge temperature, the system detects refrigerant shortages by periodically opening a valve to check the refrigerant flow and monitoring the temperature of the flowing refrigerant. This allows for early detection of refrigerant shortages even during low-load operation when the discharge temperature does not rise, or when the expansion valve is closed, by checking the refrigerant flow.

[0141] In Embodiment 1, as shown in Figures 1, 2A, and 2B, the starting point of the injection circuit was described as the outlet of the injection outlet pipe 24C in the receiver tank 24, but it is not limited to this. The starting point of the injection circuit may be, for example, a branching point from the refrigerant outlet main pipe 24B located downstream of the receiver tank 24 and upstream of the air-cooled subcooler 21. In other words, instead of taking the refrigerant stored in the receiver tank 24, the refrigerant may be taken in a flow path from the receiver tank 24 to the air-cooled subcooler 21. [Industrial applicability]

[0142] This invention is widely applicable to refrigeration equipment. [Explanation of Symbols]

[0143] 1. Refrigeration equipment 10. Intake temperature sensor 11. Low-pressure pressure sensor 12 Accumulators 13 Strainer 14 Compressors 14A Oil Level Switch 14B Discharge Temperature Sensor 14C High Pressure Switch 15 Oil Separator 16 Service valves 17 Strainer 18 Solenoid valve 19. High-pressure pressure sensor 20 Air-cooled condensers 21 Air-cooled subcooler 22 Fans for air-cooled condensers 23. Outdoor temperature sensor 24 Receiver Tank 24A Refrigerant supply main pipe 24B Refrigerant extraction main pipe 24C Injection Outlet Piping 24D Injection Outlet Pipe Temperature Sensor 24E Refrigerant Outlet Main Pipe Temperature Sensor 24F Liquid Temperature Detection Temperature Sensor 25 Fusible plug 26 Economizer 27 Service valve 28 Check joint 29 Filter Dryer 30 Moisture Indicator 31 Ecom Sensor 32 Liquid Injection Solenoid Valve 33 Liquid Injection Solenoid Valve 34 Service valves 35 Strainer 36 Liquid Injection Electric Valve 37 Electrical box 37A Heat sink temperature sensor 37B Electrical box temperature sensor 38. Refrigeration unit outlet temperature sensor

Claims

1. A compressor configured to form a refrigerant circuit through which the refrigerant circulates and to discharge the refrigerant within a target discharge temperature range, Condenser and, A receiver tank for storing the refrigerant discharged from the compressor, A subcooler is installed alongside the condenser to subcool the refrigerant discharged from the receiver tank, An injection circuit which constitutes part of the refrigerant circuit and returns the liquid refrigerant in the receiver tank to the compressor, An electric valve provided in the injection circuit for reducing the pressure of the liquid refrigerant in the receiver tank, The system includes a control device configured to control the valve opening degree of the electric valve according to the target discharge temperature range of the compressor, The control device is configured to determine whether there is a shortage of refrigerant in the refrigerant circuit. The refrigeration apparatus is characterized in that the determination is made based on the determination condition that the valve opening remains above a predetermined threshold for a predetermined period of time.

2. The refrigeration apparatus according to claim 1, characterized in that the control device is configured to set a lower limit of the target discharge temperature range when making the determination.

3. The receiver tank is A main pipe inserted into the receiver tank for supplying refrigerant to the subcooler, The receiver tank is inserted into the injection outlet piping that supplies refrigerant to the compressor, and the system comprises: The refrigeration apparatus according to claim 1, characterized in that the height from the bottom of the receiver tank to the inlet of the injection outlet piping is greater than the height from the bottom of the receiver tank to the inlet of the main pipe.

4. The refrigeration apparatus according to claim 1, characterized in that the injection circuit is branched from the refrigerant circuit located downstream of the receiver tank and downstream of the subcooler.

5. The refrigeration apparatus according to any one of claims 1 to 4, characterized in that the control device controls the valve opening of the electric valve to increase at predetermined intervals, regardless of the target discharge temperature range.

6. The injection circuit includes a branching point downstream of the electric valve, where it branches into a first flow path and a second flow path. The first flow path is equipped with a heat exchanger, The refrigeration apparatus according to claim 1, characterized in that the heat exchanger performs heat exchange between the refrigerant in the first flow path and the refrigerant from the subcooler.

Images