JP4767134B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a method for determining an operating frequency of a compressor in a refrigeration apparatus including an inverter compressor (variable speed compressor) having a variable operating frequency.

The conventional refrigeration system increases or decreases the operating frequency of the compressor based on the measured values of the refrigerant temperature, the suction pressure (low pressure) and the discharge pressure (high pressure) of the compressor, and the measured value and a preset threshold value. And the increase / decrease width of the operating frequency was determined. For example, there is a control method for reducing the operating frequency of the compressor when the discharge temperature of the refrigerant is equal to or higher than a set value and the compression ratio obtained from the suction pressure and the discharge pressure is equal to or higher than the set value (see Patent Document 1).
Japanese Patent Laid-Open No. 5-10608

  In conventional compressor operation control methods, control is performed by comparing measured values such as discharge temperature and suction pressure, and compression values calculated using the measured suction pressure and discharge pressure with threshold values. Since the zone control is performed, there is a problem that the controlled value becomes discontinuous.

  FIG. 3 shows an example in which the operation frequency control of the inverter compressor is performed so that the suction pressure of the compressor approaches the target value in the refrigeration apparatus equipped with the inverter compressor. The horizontal axis represents time, and the vertical axis represents the suction pressure. Zone control is performed in which four regions from region A to region D are set, and the boundary between region B and region C is set as a target value. This zone control will be described in detail.

  When the suction pressure exists in the region A, the suction pressure is very large as compared with the target value, and it is considered that the refrigerating capacity is insufficient. Therefore, the operating frequency of the compressor is greatly increased. When the suction pressure exists in the region B, the suction pressure is larger than the target value, and it is considered that the refrigerating capacity is insufficient. Therefore, the operating frequency of the compressor is increased small. Next, when the suction pressure exists in the region C, the suction pressure is smaller than the target value, and the refrigerating capacity is sufficient, so the operating frequency of the compressor is decreased. When the suction pressure exists in the region D, the suction pressure is very small compared to the target value, and the refrigerating capacity is excessive, so that the operating frequency of the compressor is greatly reduced.

  Thus, in order to control the operating frequency of the compressor, when the suction pressure is in the state A, the state A, and the state C, the control corresponding to the region C is performed. In the state A and the state A, the value of the suction pressure is the same, but the change in the suction pressure is the same control even though it is a downward tendency and an upward tendency and is opposite. Moreover, although the tendency of the suction pressure change is the same in the state A and the state C, the same control is performed although the value of the suction pressure is different. Further, in the state A and the state C, although the suction pressure value and the change tendency of the suction pressure are different, the same control is performed.

  As described above, in the conventional control method (zone control, etc.) for controlling the operation of the compressor by comparing the measured value or the calculated value obtained from the measured value with the threshold value, the state of the refrigeration apparatus is accurately grasped. It is difficult to control the operation of the compressor so that the necessary refrigeration capacity can be output efficiently.

The invention described in claim 1
In a refrigeration system equipped with a variable speed compressor with variable operating frequency,
A pressure detector and a temperature detector are provided on the suction side of the variable speed compressor,
The refrigerant outlet of the refrigeration apparatus comprises a second pressure detector and a second temperature detector,
The suction pressure when the refrigeration apparatus is most efficiently operated is set as the target suction pressure,
Set the evaporation temperature at the target suction pressure as the target suction temperature,
The refrigerant density at the target suction pressure and the target suction temperature is set as the target suction density,
Determine the predicted suction pressure that is the suction pressure after a predetermined time from the suction pressure detected by the pressure detector and the rate of change of the suction pressure,
Determining the suction refrigerant density, which is the density of the refrigerant sucked by the variable speed compressor, from the suction temperature detected by the temperature detector and the predicted suction pressure;
Determining the suction refrigerant volume, which is the volume of refrigerant that the variable speed compressor sucks per unit time from the current operating frequency of the variable speed compressor;
Determining the suction refrigerant mass that is the mass of the refrigerant that the variable speed compressor sucks per unit time from the suction refrigerant density and the suction refrigerant volume;
From the outlet pressure detected by the second pressure detector, the outlet temperature detected by the second temperature detector, the suction pressure, and the suction temperature, the refrigerant flowing out of the refrigeration apparatus and the Determine the enthalpy difference with the refrigerant flowing into the refrigeration system,
Determine the current refrigeration capacity of the refrigeration apparatus from the suction refrigerant mass and the enthalpy difference,
Determining a target enthalpy difference of the refrigeration apparatus from the outlet pressure, the outlet temperature, the target suction pressure, and the target suction temperature;
Determining a target suction refrigerant mass capable of obtaining a refrigeration capacity equal to the current refrigeration capacity from the refrigeration capacity and the target enthalpy difference;
From the target suction refrigerant mass and the target suction density, determine a target suction refrigerant volume capable of obtaining a refrigeration capacity equal to the current refrigeration capacity,
An operating frequency of the variable speed compressor is determined from the target suction refrigerant volume.

The invention according to claim 2
In a refrigeration apparatus comprising at least one variable speed compressor with variable operating frequency and at least one constant speed compressor with constant operating frequency,
A pressure detector and a temperature detector on the suction side of the variable speed compressor and the constant speed compressor;
The refrigerant outlet of the refrigeration apparatus comprises a second pressure detector and a second temperature detector,
The suction pressure when the refrigeration apparatus is most efficiently operated is set as the target suction pressure,
Set the evaporation temperature at the target suction pressure as the target suction temperature,
The refrigerant density at the target suction pressure and the target suction temperature is set as the target suction density,
Determining the current total operating frequency of the entire refrigeration system from the current operating frequency of the variable speed compressor and the current operating number of the constant speed compressor;
Determine the predicted suction pressure that is the suction pressure after a predetermined time from the suction pressure detected by the pressure detector and the rate of change of the suction pressure,
Determining the suction refrigerant density, which is the density of the refrigerant sucked by the variable speed compressor, from the suction temperature detected by the temperature detector and the predicted suction pressure;
Determining the suction refrigerant volume, which is the volume of refrigerant that the refrigeration apparatus sucks per unit time from the total operating frequency of the entire refrigeration apparatus,
Determining the suction refrigerant mass that is the mass of the refrigerant that the refrigeration apparatus sucks per unit time from the suction refrigerant density and the suction refrigerant volume;
From the outlet pressure detected by the second pressure detector, the outlet temperature detected by the second temperature detector, the suction pressure, and the suction temperature, the refrigerant flowing out of the refrigeration apparatus and the Determine the enthalpy difference with the refrigerant flowing into the refrigeration system,
Determine the current refrigeration capacity of the refrigeration apparatus from the suction refrigerant mass and the enthalpy difference,
Determining a target enthalpy difference of the refrigeration apparatus from the outlet pressure, the outlet temperature, the target suction pressure, and the target suction temperature;
Determining a target suction refrigerant mass capable of obtaining a refrigeration capacity equal to the current refrigeration capacity from the refrigeration capacity and the target enthalpy difference;
From the target suction refrigerant mass and the target suction density, determine a target suction refrigerant volume capable of obtaining a refrigeration capacity equal to the current refrigeration capacity,
The operating frequency of the variable speed compressor and the number of operating constant speed compressors are determined from the target suction refrigerant volume.

  The present invention sets a target suction pressure in a refrigeration apparatus provided with an inverter compressor having a variable operating frequency, obtains a refrigerant enthalpy difference from a refrigerant temperature difference at the inlet and outlet of the refrigeration apparatus, and calculates the enthalpy difference and the current operating frequency. The operating frequency at which the refrigeration apparatus can output the refrigeration capacity required by the refrigeration cycle can be obtained from the suction pressure and the suction temperature. In addition, since the change speed of the suction pressure is taken into account when calculating the operation frequency, excessive or insufficient refrigeration capacity can be prevented and energy-saving operation can be performed.

  The present invention sets a target suction pressure in a refrigeration apparatus including at least one inverter compressor having a variable operating frequency and at least one constant speed compressor having a constant operating frequency, and sets the target suction pressure at the inlet / outlet of the refrigeration apparatus. Calculate the enthalpy difference of the refrigerant from the temperature difference, and the refrigeration system can output the refrigeration capacity required by the refrigeration cycle from this enthalpy difference, current operating frequency, number of units operated, suction pressure, and suction temperature. Can be requested. In addition, since the change speed of the suction pressure is taken into account when calculating the operating frequency and the number of operating units, excessive or insufficient refrigeration capacity can be prevented and energy saving operation can be performed.

  Hereinafter, the implementation method of this invention is demonstrated in detail using drawing.

  FIG. 1 is a refrigerant circuit diagram of a refrigeration apparatus equipped with one compressor to which the present invention is applied. This refrigeration apparatus includes an inverter scroll compressor (inverter compressor) 10 that can control the rotation speed by an inverter. In the present invention, the compressor is applicable to either a hermetic type or a semi-hermetic type regardless of the type of compression method such as a reciprocating type, a screw type, or a rotary type.

  In this embodiment, an HFC refrigerant is assumed as the refrigerant to be used, but the same effect can be obtained by using other refrigerants such as a CFC refrigerant, an HCFC refrigerant, and a natural refrigerant.

  The inverter compressor 10 sucks and compresses the low-temperature and low-pressure gaseous refrigerant and discharges it as a high-temperature and high-pressure refrigerant. The discharged high-temperature and high-pressure refrigerant flows into the oil separator 13. In the oil separator 13, the lubricating oil contained in the refrigerant is separated and stored.

  The separated lubricating oil flows into the strainer 27 through the service valve 26, and contaminants in the lubricating oil are removed by the strainer 27. The lubricating oil from which the contaminants have been removed is returned to the compressor 10 via the electromagnetic valve 28. At this time, the amount of lubricating oil in the compressor is measured by the float switch 23 installed in the compressor, and the electromagnetic valve 28 is opened and closed so that the amount of lubricating oil in the compressor becomes constant.

  In addition, when liquid refrigerant is included in the lubricating oil returned to the compressor, there is a possibility that the compression mechanism in the compressor may be insufficiently lubricated and become defective, so the pressure is reduced in the capillary tube 29 and the refrigerant is completely vaporized. Yes. By evaporating the refrigerant with the capillary tube 29, there is also an effect of cooling the lubricating oil.

  The refrigerant from which the lubricating oil has been removed in the oil separator 13 flows into the condenser 14, and the high-temperature and high-pressure refrigerant is cooled by the cooling fan 63 and condensed and liquefied. In this embodiment, an air-cooled condenser is used, but a water-cooled or evaporative condenser may be used. In this embodiment, an integrated refrigerator in which the condenser and the compressor are disposed in the same casing is assumed. However, the present invention is not limited to this, and the refrigerator and the condensing unit are separately provided. A separate installation type may be used.

  The refrigerant liquefied in the condenser 14 flows out of the condenser 14 and is stored in the receiver tank 15. The receiver tank 15 has a fusible plug 46 to prevent the refrigeration apparatus from being defective and the pressure and temperature inside the refrigerant circuit from becoming very high.

  As the discharge pressure of the compressor, this refrigeration apparatus measures the pressure in the receiver tank 15 and controls the compressor and the like. The receiver tank 15 is connected to a high pressure sensor 58 via a capillary tube 57, and the discharge pressure of the compressor is measured by the high pressure sensor 58. The receiver tank 15 is connected to a high pressure gauge 62 via capillary tubes 57 and 61 in order to observe the discharge pressure of the compressor as needed.

  In order to increase the refrigerating capacity of the liquid refrigerant, the liquid refrigerant stored in the receiver tank 15 is supercooled by the air cooling by the cooling fan 63 in the supercooler 16 again. In the present embodiment, the condenser 14 and the supercooler 16 are integrated, but the condenser and the supercooler may be provided separately.

  The supercooled liquid refrigerant flows into the filter dryer 17 through the service valve 48. The moisture in the refrigerant is removed by the filter dryer, and after the moisture indicator 18 confirms the amount of moisture, the liquid refrigerant flows out to an evaporator (not shown) such as a showcase installed in the store.

  In this embodiment, a liquid injection mechanism is used to cool the compressor. For this reason, a liquid injection circuit is provided from the receiver tank 15 to the compressor 10 via the service valve 34, the strainer 35, the electric valve 36, and the electromagnetic valve 37.

  The liquid refrigerant from which contaminants have been removed by the strainer 35 is decompressed by the motor-operated valve 36 to cool the compressor 10. The opening / closing degree of the electromagnetic valve and the opening / closing degree of the motor-operated valve are adjusted by the operating state of the compressor and the temperature of the compressor. When the discharge pressure of the compressor becomes very large, each compressor is urgently stopped by a high-pressure switch 52 provided in the compressor 10 via the capillary tube 51.

  Since the refrigerant that has been vaporized and cooled in the evaporator and has reached low temperature and low pressure may return to the refrigeration system including the liquid refrigerant (liquid back), the refrigerant and the gaseous refrigerant are allowed to flow into the accumulator 19 once and then the liquid refrigerant and the gaseous refrigerant are To separate. Possible causes of liquid back include expansion valve failure and clogging of the evaporator filter. The liquid back enters the case of the compressor 10 by the liquid back and compresses it. There is a possibility of insufficient lubrication due to a large amount of lubricating oil being discharged together when the refrigerant is discharged.

  In the accumulator 19, the liquid refrigerant is stored, and only the gaseous refrigerant flows out, and is sucked into the compressor 10 through the strainer 20. In this embodiment, since the refrigerant pressure returned from the evaporator is used as the suction pressure of the compressor, the inlet side of the accumulator 19 is connected to the low pressure sensor 59 by piping.

  Next, the operation control method of the inverter compressor 10 in the present embodiment will be described with reference to FIGS. 1 and 4. The operation control of the inverter compressor 10 is performed by inputting from each sensor to an arithmetic device (not shown), and calculating, storing, and outputting.

  First, the suction pressure LP of the inverter compressor 10 is measured by the low pressure sensor 59 (S10). This measurement is performed every predetermined time TS, and the suction pressure change rate GLP is calculated from the suction pressure PLP and the suction pressure LP before the predetermined time TS measured immediately before the current measurement using the following formula 1. (S11).

  Based on the current suction pressure LP and the change rate GLP of the suction pressure, a predicted suction pressure ELP at which the refrigeration apparatus is stabilized is calculated using Equation 2 below (S12). C1 is a constant that is adjusted according to the installation environment of the refrigeration apparatus.

  The suction gas temperature LT of the inverter compressor 10 is measured by a temperature sensor (not shown) (S13). From the predicted suction pressure ELP and the suction gas temperature LT, the density LD of the gas refrigerant on the suction side of the inverter compressor 10 is obtained from a previously stored table (S14). Note that the suction refrigerant density LD may be derived from a simple relational expression including the predicted suction pressure ELP and the suction gas temperature LT instead of using a table.

  In this embodiment, since the refrigeration apparatus is composed of only one inverter compressor, the volume LV of the refrigerant sucked by this inverter compressor can be obtained from the operating frequency (S15) of the inverter compressor (S18). The suction refrigerant mass LM is calculated from the suction refrigerant density LD and the suction refrigerant volume LV by using the following Equation 3 (S19).

  A target suction pressure TLP, which is a suction pressure when the refrigeration apparatus is most efficiently operated, is set by a prior test (S20). The evaporation temperature of the gas refrigerant at the target suction pressure TLP is set as the target suction temperature TLT (S21). A target suction density TLD, which is the density of the gas refrigerant at the target suction pressure TLP and the target suction temperature TLT, is obtained from a previously stored table (S22). The derivation of the target suction density TLD is not limited to a table, and a simple relational expression composed of the target suction pressure TLP and the target suction temperature TLT may be used.

  In order to maintain the current refrigeration capacity, it is necessary to operate the compressor so as to maintain the suction refrigerant mass LM. On the other hand, in order to operate the refrigeration apparatus in a state where the operation efficiency is good, it is necessary to operate the compressor so as to achieve the target suction density TLD. Therefore, the target suction volume TLV necessary to maintain the current suction refrigerant mass LM at the target suction density TLD is calculated from the suction refrigerant mass LM and the target suction density TLD using the following Equation 4 (S23).

  Since there is a fixed relationship between the operating frequency of the compressor and the suction volume, the target inverter compressor operating frequency TICF that can obtain the target suction volume TLV required by the refrigeration apparatus can be obtained (S24). The refrigeration capacity required by the refrigeration system can be obtained by controlling the operation of the inverter compressor so that the target inverter compressor operating frequency TICF is obtained.

  When the target inverter compressor operating frequency TICF exceeds the maximum value of the operating frequency at which the inverter compressor can be operated, the operation control is performed using the target inverter compressor operating frequency TICF as the maximum value. On the other hand, when the target inverter compressor operating frequency TICF is lower than the minimum value of the operating frequency at which the inverter compressor can be operated, the target inverter compressor operating frequency TICF is smaller than the predetermined value when the difference between the target inverter compressor operating frequency TICF and the minimum value is smaller than the predetermined value. The inverter compressor operating frequency TICF is set to the minimum value, and when the difference between the target inverter compressor operating frequency TICF and the minimum value is larger than a predetermined value, the inverter compressor is stopped to stop the inverter compressor. Prevents frequent repetition.

  FIG. 2 is a refrigerant circuit diagram of a refrigeration apparatus equipped with a plurality of compressors to which the present invention is applied. This refrigeration apparatus is composed of three compressors, 10 is an inverter scroll compressor (inverter compressor) whose rotation speed can be controlled by an inverter, and 11 and 12 are constant speed scroll compressors (constant constant) operated by commercial power. Fast compressor). In the present invention, these compressors are applicable to either a hermetic type or a semi-hermetic type regardless of the type of compression method such as a reciprocating type, a screw type, and a rotary type.

  In this embodiment, an HFC refrigerant is assumed as the refrigerant to be used, but the same effect can be obtained by using other refrigerants such as a CFC refrigerant, an HCFC refrigerant, and a natural refrigerant.

  The compressors 10, 11, and 12 are connected in parallel to both the discharge port and the suction port. Each compressor sucks and compresses a low-temperature and low-pressure gas refrigerant and discharges it as a high-temperature and high-pressure refrigerant. The discharged high-temperature and high-pressure refrigerant merges and flows into the oil separator 13. In the oil separator 13, the lubricating oil contained in the refrigerant is separated and stored.

  The separated lubricating oil flows into the strainer 27 through the service valve 26, and contaminants in the lubricating oil are removed by the strainer 27. The lubricating oil from which the contaminants have been removed branches and is returned to the compressors 10, 11, 12 via the solenoid valves 28, 30, 32. At this time, the amount of lubricating oil in each compressor is measured by the float switches 23, 24, 25 installed in each compressor, and the solenoid valves 28, 30 are set so that the amount of lubricating oil in each compressor becomes uniform. , 32 are opened and closed.

  In addition, when liquid refrigerant is included in the lubricating oil returned to the compressor, the compression mechanism in the compressor may be insufficiently lubricated and may be defective. Therefore, the pressure is reduced in the capillary tubes 29, 31, and 33, and the refrigerant is completely discharged. Vaporize. By evaporating the refrigerant with the capillary tubes 29, 31, 33, there is also an effect of cooling the lubricating oil.

  The refrigerant from which the lubricating oil has been removed in the oil separator 13 flows into the condenser 14, and the high-temperature and high-pressure refrigerant is cooled by the cooling fan 63 and condensed and liquefied. In this embodiment, an air-cooled condenser is used, but a water-cooled or evaporative condenser may be used. In this embodiment, an integrated refrigerator in which the condenser and the compressor are disposed in the same casing is assumed. However, the present invention is not limited to this, and the refrigerator and the condensing unit are separately provided. A separate installation type may be used.

  The refrigerant liquefied in the condenser 14 flows out of the condenser 14 and is stored in the receiver tank 15. The receiver tank 15 has a fusible plug 46 to prevent the refrigeration apparatus from being defective and the pressure and temperature inside the refrigerant circuit from becoming very high.

  As the discharge pressure of the compressor, this refrigeration apparatus measures the pressure in the receiver tank 15 and controls the compressor and the like. The receiver tank 15 is connected to a high pressure sensor 58 via a capillary tube 57, and the discharge pressure of the compressor is measured by the high pressure sensor 58. The receiver tank 15 is connected to a high pressure gauge 62 via capillary tubes 57 and 61 in order to observe the discharge pressure of the compressor as needed.

  In order to increase the refrigerating capacity of the liquid refrigerant, the liquid refrigerant stored in the receiver tank 15 is supercooled by the air cooling by the cooling fan 63 in the supercooler 16 again. In the present embodiment, the condenser 14 and the supercooler 16 are integrated, but may be provided separately.

  The supercooled liquid refrigerant flows into the filter dryer 17 through the service valve 48. The moisture in the refrigerant is removed by the filter dryer, and after the moisture indicator 18 confirms the amount of moisture, the liquid refrigerant flows out to an evaporator (not shown) such as a showcase installed in the store.

  In this embodiment, a liquid injection mechanism is used to cool the compressor. For this reason, from the receiver tank 15 to the compressors 10, 11, 12 via the service valves 34, 38, 42 and the strainers 35, 39, 43 and the motorized valves 36, 40, 44 and the electromagnetic valves 37, 41, 45, respectively. A liquid injection circuit is provided.

  The liquid refrigerant from which contaminants have been removed by the strainers 35, 39, 43 is decompressed by the motor-operated valves 36, 40, 44, and the compressors 10, 11, 12 are cooled. The opening / closing degree of the electromagnetic valve and the opening / closing degree of the motor-operated valve are adjusted by the operating state of the compressor and the temperature of the compressor. When the discharge pressure of the compressor becomes very large, each compressor is urgently stopped by the high pressure switches 52, 54, 56 provided in the compressors 10, 11, 12.

  Since the refrigerant that has been vaporized and cooled in the evaporator and has reached low temperature and low pressure may return to the refrigeration apparatus including the liquid refrigerant (liquid back), the refrigerant is once introduced into the accumulator 19 and separated in the accumulator 19. Possible causes of liquid back include expansion valve defects and clogged evaporator filters. Liquid refrigerant enters the cases of the compressors 10, 11, and 12 due to liquid back, and the compression mechanism is damaged by liquid compression. In addition, there is a possibility of insufficient lubrication due to a large amount of lubricating oil being discharged together when the liquid refrigerant is discharged.

  In the accumulator 19, the liquid refrigerant is stored, and only the gaseous refrigerant flows out, and is sucked into the compressors 10, 11, and 12 through the strainers 20, 21, and 22, respectively. In this embodiment, since the refrigerant pressure returned from the evaporator is used as the suction pressure of the compressor, the inlet side of the accumulator 19 is connected to the low pressure sensor 59 by piping.

  Next, the operation control method of the inverter compressor 10 and the constant speed compressors 11 and 12 in the present embodiment will be described with reference to FIGS. Operation control of the inverter compressor 10 and the constant speed compressors 11 and 12 is performed by inputting from each sensor to an arithmetic device (not shown), and calculating, storing, and outputting.

  First, the suction pressure LP of the inverter compressor 10 and the constant speed compressors 11 and 12 is measured by the low pressure sensor 59 (S10). This measurement is performed every predetermined time TS, and the suction pressure change rate GLP is calculated from the suction pressure PLP and the suction pressure LP before the predetermined time TS, which is measured immediately before the current measurement, using the formula 1. (S11).

  Based on the current suction pressure LP and the change rate GLP of the suction pressure, a predicted suction pressure ELP at which the refrigeration apparatus is stabilized is calculated using Equation 2 (S12). C1 is a constant that is adjusted according to the installation environment of the refrigeration apparatus.

  The suction gas temperature LT of the inverter compressor 10 and the constant speed compressors 11 and 12 is measured by a temperature sensor (not shown) (S13). From the predicted suction pressure ELP and the suction gas temperature LT, the density LD of the gas refrigerant on the suction side of the inverter compressor 10 and the constant speed compressors 11 and 12 is obtained from a previously stored table (S14). Note that the suction refrigerant density LD may be derived from a simple relational expression including the predicted suction pressure ELP and the suction gas temperature LT instead of using a table.

  In this embodiment, since a plurality of compressors are mounted, the operation control of the compressor is performed by calculating the operation frequency of the entire refrigeration apparatus. The total operating frequency SCF is calculated from the operating frequency ICF (S15) of the inverter compressor 10 and the operating number NC (S16) of the constant speed compressors 11 and 12 using the following formula (5) (S17).

  In the present embodiment, it is confirmed in a prior test that the discharge rate of the constant speed compressor at the power source frequency of 50 Hz is equal to the discharge rate of the inverter compressor at the operation frequency of 60 Hz. From this, the total operating frequency SCF of the entire refrigeration apparatus is calculated by converting the operating frequency of the constant speed compressor to 60 Hz and converting it to the operating frequency ICF of the inverter compressor.

  It has been confirmed in the above test that the discharge amount of the constant speed compressor is equal to the discharge amount of the inverter compressor at the operation frequency of 72 Hertz at the power source frequency of 60 Hertz. FIG. 8 shows the relationship between the total operating frequency SCF of the entire refrigeration apparatus calculated by this method and the low pressure when the refrigeration apparatus is in a steady state at the total operating frequency SCF.

  Unlike the conventional method, in this method, the low-pressure pressure decreases almost uniformly as the total operating frequency SCF increases, so it can be seen that the controllability of the refrigeration apparatus is good. Moreover, since there is no difference in tendency due to the difference in power supply frequency, there is no difference in performance due to the power supply frequency in the area where the refrigeration apparatus is installed.

  The volume LV of the refrigerant sucked by the compressor can be obtained from the obtained total operating frequency SCF (S18). From the suction refrigerant density LD and the suction refrigerant volume LV, the suction refrigerant mass LM is calculated using Equation 3 (S19).

  A target suction pressure TLP, which is a suction pressure when the refrigeration apparatus is most efficiently operated, is set by a prior test (S20). The evaporation temperature of the gas refrigerant at the target suction pressure TLP is set as the target suction temperature TLT (S21). A target suction density TLD, which is the density of the gas refrigerant at the target suction pressure TLP and the target suction temperature TLT, is obtained from a previously stored table (S22). The derivation of the target suction density TLD is not limited to a table, and a simple relational expression composed of the target suction pressure TLP and the target suction temperature TLT may be used.

  In order to maintain the current refrigeration capacity, it is necessary to operate the compressor so as to maintain the suction refrigerant mass LM. On the other hand, in order to operate the refrigeration apparatus in a state where the operation efficiency is good, it is necessary to operate the compressor so as to achieve the target suction density TLD. Therefore, the target suction volume TLV required to maintain the current suction refrigerant mass LM at the target suction density TLD is calculated from the suction refrigerant mass LM and the target suction density TLD using the above-described equation 4 (S23).

  Since there is a fixed relationship between the operating frequency of the compressor and the suction volume, the target total operating frequency TSCF that can obtain the target suction volume TLV required by the refrigeration apparatus can be obtained (S25). Since the operation cannot be performed when the target total operation frequency TSCF is larger than the maximum value of the total operation frequency of the refrigeration apparatus, the maximum value is replaced with the target total operation frequency TSCF. The operating frequency of the inverter compressor and the number of operating constant-speed compressors are determined from the obtained target total operating frequency TSCF (S26).

  Next, the operation control method of the compressor in consideration of the enthalpy of the refrigerant in the refrigeration apparatus in the refrigeration apparatus equipped with one inverter compressor will be described with reference to FIGS.

  The suction pressure LP of the inverter compressor 10 is measured by the low pressure sensor 59 (S30). This measurement is performed every predetermined time TS, and the suction pressure change rate GLP is calculated from the suction pressure PLP and the suction pressure LP before the predetermined time TS, which is measured immediately before the current measurement, using the formula 1. (S31).

  Based on the current suction pressure LP and the change rate GLP of the suction pressure, a predicted suction pressure ELP at which the refrigeration apparatus is stabilized is calculated using the above-described equation 2 (S32). C1 is a constant that is adjusted according to the installation environment of the refrigeration apparatus.

  The suction gas temperature LT of the inverter compressor 10 is measured by a temperature sensor (not shown) (S33). From the predicted suction pressure ELP and the suction gas temperature LT, the density LD of the gas refrigerant on the suction side of the inverter compressor 10 is obtained from a previously stored table (S34). Note that the suction refrigerant density LD may be derived from a simple relational expression including the predicted suction pressure ELP and the suction gas temperature LT instead of using a table.

  In this embodiment, since the refrigeration apparatus includes only one inverter compressor, the volume LV of the refrigerant sucked by the inverter compressor can be obtained from the operating frequency ICF (S35) of the inverter compressor (S38). From the suction refrigerant density LD and the suction refrigerant volume LV, the suction refrigerant mass LM is calculated by using Equation 3 (S39).

  The refrigerant temperature and the refrigerant pressure when the refrigerant flows out of the refrigeration apparatus, the refrigerant temperature and the refrigerant pressure when the refrigerant flows into the refrigeration apparatus are measured (S40), and the outlet and inlet of the refrigeration apparatus are obtained from the obtained refrigerant temperature and pressure. The refrigerant enthalpy difference H is obtained from a previously stored table (S41).

  The refrigerating capacity Q currently possessed by the refrigerating apparatus is calculated from the suction refrigerant mass LM and the refrigerating apparatus entrance / exit enthalpy difference H by using the following mathematical formula 6 (S42).

  The target suction pressure TLP, which is the suction pressure when the refrigeration apparatus is most efficiently operated, is set by a preliminary test (S43). The evaporation temperature of the gas refrigerant at the target suction pressure TLP is set as the target suction temperature TLT (S44). An enthalpy difference TH when the refrigeration apparatus is operated most efficiently is also set (S45).

  At the enthalpy difference TH necessary for operating the compressor most efficiently, the target suction refrigerant mass TLM necessary for maintaining the current refrigeration capacity Q is calculated using the following Equation 7 (S46).

  A target suction density TLD, which is the density of the gas refrigerant at the target suction pressure TLP and the target suction temperature TLT, is obtained from a previously stored table (S47). Note that the derivation of the target suction density TLD may be performed using a simple relational expression including the target suction pressure TLP and the target suction temperature TLT instead of using a table.

  In order to maintain the current refrigeration capacity, it is necessary to operate the compressor so that the target suction mass TLM can be maintained. On the other hand, in order to operate the refrigeration apparatus in a state where the operation efficiency is good, it is necessary to operate the compressor so as to achieve the target suction density TLD. Therefore, the target suction volume TLV necessary to maintain the current suction refrigerant mass TLM at the target suction density TLD is calculated from the suction refrigerant mass TLM and the target suction density TLD using the following formula 8 (S48).

  Since there is a fixed relationship between the operating frequency of the compressor and the suction volume, the target inverter compressor operating frequency TICF that can obtain the target suction volume TLV required by the refrigeration apparatus can be obtained (S49). The refrigeration capacity required by the refrigeration system can be obtained by controlling the operation of the inverter compressor so that the target inverter compressor operating frequency TICF is obtained.

  When the target inverter compressor operating frequency TICF exceeds the maximum value of the operating frequency at which the inverter compressor can be operated, the operation control is performed using the target inverter compressor operating frequency TICF as the maximum value. On the other hand, when the target inverter compressor operating frequency TICF is lower than the minimum value of the operating frequency at which the inverter compressor can be operated, the target inverter compressor operating frequency TICF is smaller than the predetermined value when the difference between the target inverter compressor operating frequency TICF and the minimum value is smaller than the predetermined value. The inverter compressor operating frequency TICF is set to the minimum value, and when the difference between the target inverter compressor operating frequency TICF and the minimum value is larger than a predetermined value, the inverter compressor is stopped to stop the inverter compressor. Prevents frequent repetition.

  Next, a compressor operation control method in consideration of the enthalpy of the refrigerant in the refrigeration apparatus in the refrigeration apparatus equipped with a plurality of inverter compressors and constant speed compressors will be described with reference to FIGS.

  The suction pressure LP of the inverter compressor 10 and the constant speed compressors 11 and 12 is measured by the low pressure sensor 59 (S30). This measurement is performed every predetermined time TS, and the suction pressure change rate GLP is calculated from the suction pressure PLP and the suction pressure LP before the predetermined time TS, which is measured immediately before the current measurement, using the formula 1. (S31).

  Based on the current suction pressure LP and the change rate GLP of the suction pressure, a predicted suction pressure ELP at which the refrigeration apparatus is stabilized is calculated using the above-described equation 2 (S32). C1 is a constant that is adjusted according to the installation environment of the refrigeration apparatus.

  The suction gas temperature LT of the inverter compressor 10 and the constant speed compressors 11 and 12 is measured by a temperature sensor (not shown) (S33). From the predicted suction pressure ELP and the suction gas temperature LT, the density LD of the gas refrigerant on the suction side of the inverter compressor 10 and the constant speed compressors 11 and 12 is obtained from a previously stored table (S34). Note that the suction refrigerant density LD may be derived from a simple relational expression including the predicted suction pressure ELP and the suction gas temperature LT instead of using a table.

  In this embodiment, since a plurality of compressors are mounted, the operation control of the compressor is performed by calculating the operation frequency of the entire refrigeration apparatus. The total operating frequency SCF is calculated from the operating frequency ICF (S35) of the inverter compressor 10 and the number of operating NCs (S36) of the constant speed compressors 11 and 12 using the formula 5 (S37).

  In the present embodiment, it is confirmed in a prior test that the discharge rate of the constant speed compressor at the power source frequency of 50 Hz is equal to the discharge rate of the inverter compressor at the operation frequency of 60 Hz. From this, the total operating frequency SCF of the entire refrigeration apparatus is calculated by converting the operating frequency of the constant speed compressor to 60 Hz and converting it to the operating frequency ICF of the inverter compressor.

  It has been confirmed in the above test that the discharge amount of the constant speed compressor is equal to the discharge amount of the inverter compressor at the operation frequency of 72 Hertz at the power source frequency of 60 Hertz. FIG. 8 shows the relationship between the total operating frequency SCF of the entire refrigeration apparatus calculated by this method and the low pressure when the refrigeration apparatus is in a steady state at the total operating frequency SCF.

  Unlike the conventional method, in this method, the low-pressure pressure decreases almost uniformly as the total operating frequency SCF increases, so it can be seen that the controllability of the refrigeration apparatus is good. Moreover, since there is no difference in tendency due to the difference in power supply frequency, there is no difference in performance due to the power supply frequency in the area where the refrigeration apparatus is installed.

  The volume LV of the refrigerant sucked by the compressor can be obtained from the obtained total operating frequency SCF (S38). From the suction refrigerant density LD and the suction refrigerant volume LV, the suction refrigerant mass LM is calculated by using Equation 3 (S39).

  The refrigerant temperature and the refrigerant pressure when the refrigerant flows out of the refrigeration apparatus, the refrigerant temperature and the refrigerant pressure when the refrigerant flows into the refrigeration apparatus are measured (S40), and the outlet and inlet of the refrigeration apparatus are obtained from the obtained refrigerant temperature and pressure. The refrigerant enthalpy difference H is obtained from a previously stored table (S41).

  The refrigerating capacity Q currently possessed by the refrigerating apparatus is calculated from the suction refrigerant mass LM and the refrigerating apparatus entrance / exit enthalpy difference H by using Equation 6 (S42).

  The target suction pressure TLP, which is the suction pressure when the refrigeration apparatus is most efficiently operated, is set by a preliminary test (S43). The evaporation temperature of the gas refrigerant at the target suction pressure TLP is set as the target suction temperature TLT (S44). An enthalpy difference TH when the refrigeration apparatus is operated most efficiently is also set (S45).

  At the enthalpy difference TH necessary for operating the compressor most efficiently, the target suction refrigerant mass TLM necessary for maintaining the current refrigeration capacity Q is calculated using the equation 7 (S46).

  A target suction density TLD, which is the density of the gas refrigerant at the target suction pressure TLP and the target suction temperature TLT, is obtained from a previously stored table (S47). Note that the derivation of the target suction density TLD may be performed using a simple relational expression including the target suction pressure TLP and the target suction temperature TLT instead of using a table.

  In order to maintain the current refrigeration capacity, it is necessary to operate the compressor so that the target suction mass TLM can be maintained. On the other hand, in order to operate the refrigeration apparatus in a state where the operation efficiency is good, it is necessary to operate the compressor so as to achieve the target suction density TLD. Therefore, the target suction volume TLV necessary for maintaining the current suction refrigerant mass TLM at the target suction density TLD is calculated from the suction refrigerant mass TLM and the target suction density TLD using the above equation 8 (S48).

  Since there is a fixed relationship between the operating frequency of the compressor and the suction volume, the target total operating frequency TSCF that can obtain the target suction volume TLV required by the refrigeration apparatus can be obtained (S50). Since the operation cannot be performed when the target total operation frequency TSCF is larger than the maximum value of the total operation frequency of the refrigeration apparatus, the maximum value is replaced with the target total operation frequency TSCF. From the obtained target total operation frequency TSCF, the operation frequency of the inverter compressor and the number of operating constant-speed compressors are determined (S51).

  In addition, when the operating frequency of the inverter compressor is smaller than a predetermined value, the starting and stopping of the constant speed compressor are frequently repeated by controlling so as not to increase the number of operating constant speed compressors. This can be prevented. Furthermore, it is possible to control whether to give priority to the refrigerating capacity or to give priority to energy saving operation by changing this value. Further, since the suction pressure LP varies with a certain range, it is desirable to use an average value within a predetermined time TS in order to stabilize the compressor operation control.

  In order to prevent large fluctuations in the target operating frequency and the target total operating frequency, the target operating frequency and the target total operating frequency obtained by the calculation, the average value of the current operating frequency and the total operating frequency are set as the new target operating frequency. Further, control may be performed so that the target total operation frequency is obtained.

It is a refrigerant circuit figure of the refrigerating device carrying one compressor. FIG. 3 is a refrigerant circuit diagram of a refrigeration apparatus equipped with a plurality of compressors. It is the figure which showed the example regarding the time change of suction pressure. It is a flowchart figure of the operation control to which this invention is applied in the refrigeration apparatus carrying one compressor. It is a flowchart figure of the operation control to which this invention is applied in the refrigeration apparatus carrying multiple compressors. It is a flowchart figure of the operation control which applied the invention of this application and considered enthalpy in the refrigerating device carrying one compressor. FIG. 7 is a flowchart of operation control in which the present invention is applied and enthalpy is taken into account in a refrigeration apparatus equipped with a plurality of compressors. It is a graph showing the relationship between a total operating frequency and low pressure pressure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inverter scroll compressor 11, 12 Constant speed scroll compressor 13 Oil separator 14 Condenser 15 Receiver tank 16 Subcooler 17 Filter dryer 18 Moisture indicator 19 Accumulator 20, 21, 22, 27, 35, 39, 43 Strainers 23, 24, 25 Float switch 26, 34, 38, 42, 47, 48 Service valve 28, 30, 32, 37, 41, 45 Solenoid valve 29, 31, 33, 49, 51, 53, 55, 57, 61 Capillary tube 36, 40, 44 Electric valve 46 Soluble plug 50 Low pressure switch 52, 54, 56 High pressure switch 58 High pressure sensor 59 Low pressure sensor 60 ECC board 62 High pressure gauge 63 Cooling fan

Claims (2)

In a refrigeration system equipped with a variable speed compressor with variable operating frequency,
A pressure detector and a temperature detector are provided on the suction side of the variable speed compressor,
The refrigerant outlet of the refrigeration apparatus comprises a second pressure detector and a second temperature detector,
The suction pressure when the refrigeration apparatus is most efficiently operated is set as the target suction pressure,
Set the evaporation temperature at the target suction pressure as the target suction temperature,
The refrigerant density at the target suction pressure and the target suction temperature is set as the target suction density,
Determine the predicted suction pressure that is the suction pressure after a predetermined time from the suction pressure detected by the pressure detector and the rate of change of the suction pressure,
Determining the suction refrigerant density, which is the density of the refrigerant sucked by the variable speed compressor, from the suction temperature detected by the temperature detector and the predicted suction pressure;
Determining the suction refrigerant volume, which is the volume of refrigerant that the variable speed compressor sucks per unit time from the current operating frequency of the variable speed compressor;
Determining the suction refrigerant mass that is the mass of the refrigerant that the variable speed compressor sucks per unit time from the suction refrigerant density and the suction refrigerant volume;
From the outlet pressure detected by the second pressure detector, the outlet temperature detected by the second temperature detector, the suction pressure, and the suction temperature, the refrigerant flowing out of the refrigeration apparatus and the Determine the enthalpy difference with the refrigerant flowing into the refrigeration system,
The current refrigeration capacity of the refrigeration apparatus is determined from the suction refrigerant mass and the enthalpy difference, and the target enthalpy of the refrigeration apparatus is determined from the outlet pressure, the outlet temperature, the target suction pressure, and the target suction temperature. Determine the difference,
Determining a target suction refrigerant mass capable of obtaining a refrigeration capacity equal to the current refrigeration capacity from the refrigeration capacity and the target enthalpy difference;
From the target suction refrigerant mass and the target suction density, determine a target suction refrigerant volume capable of obtaining a refrigeration capacity equal to the current refrigeration capacity,
The refrigeration apparatus, wherein an operating frequency of the variable speed compressor is determined from the target suction refrigerant volume. In a refrigeration apparatus comprising at least one variable speed compressor with variable operating frequency and at least one constant speed compressor with constant operating frequency,
A pressure detector and a temperature detector on the suction side of the variable speed compressor and the constant speed compressor;
The refrigerant outlet of the refrigeration apparatus comprises a second pressure detector and a second temperature detector,
The suction pressure when the refrigeration apparatus is most efficiently operated is set as the target suction pressure,
Set the evaporation temperature at the target suction pressure as the target suction temperature,
The refrigerant density at the target suction pressure and the target suction temperature is set as the target suction density,
Determining the current total operating frequency of the entire refrigeration system from the current operating frequency of the variable speed compressor and the current operating number of the constant speed compressor;
Determine the predicted suction pressure that is the suction pressure after a predetermined time from the suction pressure detected by the pressure detector and the rate of change of the suction pressure,
Determining the suction refrigerant density, which is the density of the refrigerant sucked by the variable speed compressor, from the suction temperature detected by the temperature detector and the predicted suction pressure;
Determining the suction refrigerant volume, which is the volume of refrigerant that the refrigeration apparatus sucks per unit time from the total operating frequency of the entire refrigeration apparatus,
Determining the suction refrigerant mass that is the mass of the refrigerant that the refrigeration apparatus sucks per unit time from the suction refrigerant density and the suction refrigerant volume;
From the outlet pressure detected by the second pressure detector, the outlet temperature detected by the second temperature detector, the suction pressure, and the suction temperature, the refrigerant flowing out of the refrigeration apparatus and the Determine the enthalpy difference with the refrigerant flowing into the refrigeration system,
Determine the current refrigeration capacity of the refrigeration apparatus from the suction refrigerant mass and the enthalpy difference,
Determining a target enthalpy difference of the refrigeration apparatus from the outlet pressure, the outlet temperature, the target suction pressure, and the target suction temperature;
Determining a target suction refrigerant mass capable of obtaining a refrigeration capacity equal to the current refrigeration capacity from the refrigeration capacity and the target enthalpy difference;
From the target suction refrigerant mass and the target suction density, determine a target suction refrigerant volume capable of obtaining a refrigeration capacity equal to the current refrigeration capacity,
The refrigeration apparatus characterized in that an operating frequency of the variable speed compressor and an operating number of the constant speed compressors are determined from the target suction refrigerant volume.