A low-pressure refrigerant liquid supply system and control method thereof

Abstract

The present invention discloses a low-pressure refrigerant liquid supply system and a control method thereof, which belongs to the technical field of steam compression cycle chilled water (heat pump) units, including a chilled water unit system and a bearing liquid supply system. The chilled water unit system includes a refrigerant pump, an evaporator, a condenser, a compressor, a power saver, a throttling mechanism, and a PLC control box. The bearing liquid supply system includes a first bearing lubrication liquid supply path from the condenser liquid collection bag to the compressor bearing and a second bearing lubrication liquid supply path from the condenser liquid collection bag to the compressor bearing. Through the design of the bearing liquid supply system, the influence of the vaporization of the refrigerant on the liquid supply of the refrigerant pump can be avoided as much as possible, the along-the-line / local resistance loss of the pipeline can be reduced, the cavitation margin before the refrigerant pump and the supercooling of the refrigerant can be guaranteed, the low-frequency operation of the refrigerant pump, the insulation of the bearing liquid supply pipeline and the exhaust of the pipeline after the refrigerant pump can effectively solve the adverse effects of pipeline vaporization on the liquid supply.

Description

Technical Field

[0001] The present invention relates to the technical field of steam compression cycle chillers (heat pumps), and in particular to a low-pressure refrigerant liquid supply system and a control method thereof. Background Art

[0002] At present, driven by the "dual carbon" policy, the country pays more and more attention to energy conservation and emission reduction, and the application of high-temperature heat pump units is becoming more common. Low-pressure refrigerants have been vigorously promoted and used in heat pump units due to their low saturation pressure and safer and more stable system design. The new generation of HFO low-pressure environmentally friendly refrigerants dominated by R1233zd (E) have been used by mainstream host manufacturers on the market.

[0003] Regarding the above-mentioned related technologies, the applicant found that in refrigeration and air-conditioning systems, technologies such as magnetic levitation, air levitation, and liquid floating bearings are more mature in the application of compressors. However, since the bearings, motors and other rotating parts of the compressor will generate heat during operation, a separate cooling system needs to be set up. During the startup stage, low condensing pressure operation stage, and shutdown stage, the low-pressure refrigerant unit cannot meet the liquid supply cooling needs due to the small system pressure difference. A separate refrigerant pump needs to be set up for forced liquid supply. Unlike the current medium and high pressure refrigerants, the low-pressure refrigerant is easy to vaporize, which puts higher requirements on the refrigerant pump liquid supply system. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a low-pressure refrigerant liquid supply system and a control method thereof, which can ensure efficient and stable operation of the unit throughout its life cycle by controlling the refrigerant pump.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A low-pressure refrigerant liquid supply system includes a chiller system and a bearing liquid supply system. The chiller system includes a refrigerant pump, an evaporator, a condenser, a compressor, a power economizer, a throttling mechanism, and a PLC control box. The bearing liquid supply system includes a first bearing lubrication liquid supply path from the condenser liquid collection bag to the compressor bearing and a second bearing lubrication liquid supply path from the condenser liquid collection bag to the compressor bearing.

[0007] By adopting the above technical scheme, the design of the bearing fluid supply system can avoid the influence of the vaporization of the refrigerant on the fluid supply of the refrigerant pump as much as possible, reduce the along-the-line / local resistance loss of the pipeline, ensure the cavitation margin before the refrigerant pump, and the subcooling of the refrigerant; the low-frequency operation of the refrigerant pump, the insulation of the bearing fluid supply pipeline, and the exhaust of the pipeline after the refrigerant pump can effectively solve the adverse effects of pipeline vaporization on the fluid supply. By controlling the bearing fluid supply system of the refrigerant pump, the efficient and stable operation of the chiller system throughout its life cycle is guaranteed.

[0008] Furthermore, a liquid bag is provided on the condenser, and a subcooler is provided in the condenser.

[0009] By adopting the above technical solution, in order to maintain the stability of liquid supply, a liquid bag is separately arranged on the condenser to ensure sufficient supply of liquid refrigerant. In addition, a subcooler is provided inside the condenser. During the actual operation of the chiller system, the refrigerant in the liquid bag will have a subcooling degree of 2°C, which effectively prevents the refrigerant from vaporizing during the flow process.

[0010] Furthermore, the chiller system includes a hot gas bypass valve.

[0011] By adopting the above technical solution and the design of hot gas bypass as standard on the chiller system, the hot gas bypass valve is fully opened during the startup phase and slowly closed according to the set control cycle / control pulse after startup, thereby avoiding problems such as low evaporation pressure alarm, excessive loading of the compressor, and surging during the startup phase due to insufficient liquid supply.

[0012] A low-pressure refrigerant supply system control method, when the system pressure difference is greater than the set system pressure difference upper limit during the operation of the chiller system, after a set delay time, the compressor bearing lubrication supply adopts a first bearing lubrication supply path, and the second bearing lubrication supply path adopts a refrigerant pump for forced supply.

[0013] By adopting the above technical solution and controlling the bearing fluid supply system of the refrigerant pump, the efficient and stable operation of the chiller system throughout its life cycle is guaranteed.

[0014] Furthermore, the liquid level of the evaporator is monitored before the liquid is pumped, and if the liquid level of the evaporator is lower than the set value, the refrigerant pump stops running;

[0015] At the beginning of the pumping phase, the exhaust solenoid valve of the refrigerant pump opens to exhaust the gas. By monitoring whether the operating current of the refrigerant pump reaches the set threshold, the opening and closing of the exhaust solenoid valve is controlled.

[0016] During the pumping stage, the refrigerant pump operates at a low frequency.

[0017] By adopting the above technical solution, the vaporization of the refrigerant can be effectively avoided, the heat preservation of the liquid injection pipeline can be guaranteed, and the refrigerant can be prevented from absorbing heat and vaporizing when the ambient temperature is high.

[0018] Furthermore, during the pumping process, if the liquid level of the evaporator does not drop and the liquid level of the condenser does not increase within the set time interval, the refrigerant pump runs dry and is assigned a dry run count of +1. When the cumulative dry run count is greater than the set value, the chiller system is locked.

[0019] By adopting the above technical solution, the liquid level of the evaporator is monitored before liquid injection. In this way, the fault can be identified and monitored, and the liquid injection pipeline can be checked, which is convenient for further confirmation of the cause of the fault.

[0020] Further, after the injection is completed, the second bearing lubrication supply path is used to supply the bearing with fluid, and after the fluid supply differential is greater than the fluid supply differential set value before starting, and the refrigerant pump runs for a set time, the chiller system starts to run;

[0021] By adopting the above technical solution, after the chiller system is started, the opening of the first-stage liquid supply ball valve is controlled by setting the target value of the condenser liquid level gauge to ensure that the condenser has sufficient liquid refrigerant supply.

[0022] Furthermore, after the chiller system is started up, the system pressure difference is greater than the set system pressure difference upper limit, and after a delay of a set time, the compressor bearing fluid supply adopts the first bearing lubrication fluid supply path.

[0023] By adopting the above technical solution and using the first bearing lubrication supply path of the refrigerant pump, the efficient and stable operation of the chiller system throughout its life cycle is guaranteed.

[0024] Furthermore, during normal shutdown, fault shutdown or emergency shutdown, the second bearing lubrication supply path is used to supply fluid to the bearing.

[0025] By adopting the above technical solution and using the second bearing lubrication supply path of the refrigerant pump, the efficient and stable operation of the chiller system throughout its life cycle is guaranteed.

[0026] Furthermore, the CPU module in the PLC control box performs logical operations on the collected data and outputs relevant instructions to control the chiller system.

[0027] By adopting the above technical solution, the automatic control of the chiller system is realized through the logical operation of the PLC control box.

[0028] In summary, compared with the prior art, the above technical solution has the following beneficial effects:

[0029] (1) The design of the bearing fluid supply system of the present application can minimize the impact of refrigerant vaporization on the refrigerant pump fluid supply, reduce the along-the-line / local resistance loss of the pipeline, ensure the cavitation margin before the refrigerant pump, and the subcooling of the refrigerant; the low-frequency operation of the refrigerant pump, the insulation of the bearing fluid supply pipeline, and the exhaust of the pipeline after the refrigerant pump can effectively solve the adverse effects of pipeline vaporization on the fluid supply. By controlling the bearing fluid supply system of the refrigerant pump, the efficient and stable operation of the chiller system throughout its life cycle is guaranteed;

[0030] (2) In order to maintain the stability of liquid supply, a liquid capsule is separately installed on the condenser to ensure sufficient supply of liquid refrigerant. In addition, a subcooler is installed inside the condenser. During the actual operation of the chiller system, the refrigerant in the liquid capsule will have a subcooling degree of more than 2°C, which effectively prevents the refrigerant from vaporizing during the flow process;

[0031] (3) By adopting the hot gas bypass design as standard on the chiller system, the hot gas bypass valve is fully opened during the startup phase and is slowly closed according to the set control cycle / control pulse after startup, avoiding problems such as low evaporation pressure alarm, excessive loading of the compressor, and surging during the startup phase due to insufficient liquid supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is an overall piping diagram of a refrigeration system of a low-pressure refrigerant liquid supply system in an embodiment of the present invention;

[0033] Figure 2 A refrigerant pump system piping diagram of a low-pressure refrigerant liquid supply system in an embodiment of the present invention;

[0034] Figure 3 A diagram of a pre-startup liquid injection pipeline for a low-pressure refrigerant liquid supply system in an embodiment of the present invention;

[0035] Figure 4 A bearing liquid supply pipeline diagram of a low-pressure refrigerant liquid supply system in an embodiment of the present invention;

[0036] Figure 5 A refrigerant pump liquid supply control logic diagram of a low-pressure refrigerant liquid supply system control method in an embodiment of the present invention;

[0037] Figure 6 The present invention is a control logic diagram of a liquid supply valve / hot gas bypass valve of a low-pressure refrigerant liquid supply system control method in an embodiment of the present invention.

[0038] Explanation of the reference numerals in the accompanying drawings: 1. Evaporator; 11. Evaporation pressure; 12. Evaporation liquid level; 2. Compressor; 21. Bearing supply pressure; 22. Bearing outlet pressure; 3. Condenser; 31. Condensation pressure; 32. Condensation liquid level; 4. Power economizer; 5. Primary supply ball valve; 6. Refrigerant pump; 7. Hot gas bypass valve; 8. Liquid pumping pipeline; 81. Sight glass; 82. Evaporator outlet valve; 83. First pump pre-filter; 84. First non-return valve; 85. Condenser inlet valve; 86. Exhaust solenoid valve; 87. Second non-return valve; 9. Bearing supply system; 91. Condenser outlet valve; 92. Second pump pre-filter; 93. Drying filter; 94. Fine filter; 95. Third non-return valve; 10. PLC control box. DETAILED DESCRIPTION

[0039] The principles and features of the present invention are described below in conjunction with all the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0040] The embodiment of the invention discloses a low-pressure refrigerant liquid supply system.

[0041] Reference Figures 1 to 4 A low-pressure refrigerant liquid supply system includes a chiller system and a bearing liquid supply system 9. The chiller system includes a refrigerant pump 6, an evaporator 1, a condenser 3, a compressor 2, a power saver 4, a throttling mechanism, and a PLC control box 10. The bearing liquid supply system 9 includes a first bearing lubrication liquid supply path from the condenser 3 liquid collection bag to the compressor 2 bearing and a second bearing lubrication liquid supply path from the condenser 3 liquid collection bag to the compressor 2 bearing.

[0042] The design of the bearing fluid supply system 9 can minimize the impact of the vaporization of the refrigerant on the fluid supply of the refrigerant pump 6, reduce the along-the-line / local resistance loss of the pipeline, and ensure the cavitation margin before the refrigerant pump 6 and the subcooling of the refrigerant. The low-frequency operation of the refrigerant pump 6, the insulation of the bearing fluid supply pipeline, and the exhaust of the pipeline after the refrigerant pump 6 can effectively solve the adverse effects of pipeline vaporization on the fluid supply. By controlling the bearing fluid supply system 9 of the refrigerant pump 6, the efficient and stable operation of the chiller system in the entire life cycle is guaranteed.

[0043] According to the liquid supply requirements of the refrigerant pump 6, before the refrigerant pump 6 is started, a cavitation margin of 0.5m must be met in front of the refrigerant pump 6. When the system is designed, the center of the cylinder of the condenser 3 is more than 0.5m higher than the center of the cylinder of the evaporator 1.

[0044] During the startup phase of the chiller system, since the height difference between the center of the cylinder of condenser 3 and the center of the cylinder of evaporator 1 is more than 0.5m, during the standby phase of the chiller system, liquid refrigerant mainly exists in evaporator 1. Before startup, a refrigerant pump 6 is required to pump liquid into the liquid collection bag of condenser 3 to ensure that there is a sufficient supply of liquid refrigerant in condenser 3 before startup.

[0045] A liquid capsule is provided on the condenser 3, and a subcooler is provided inside the condenser 3. In order to maintain the stability of the liquid supply, a liquid capsule is separately provided on the condenser 3 to ensure sufficient supply of liquid refrigerant. In addition, a subcooler is provided inside the condenser 3. During the actual operation of the chiller system, the refrigerant in the liquid capsule will have a subcooling degree of more than 2°C, which effectively prevents the refrigerant from vaporizing during the flow process.

[0046] The chiller system includes a hot gas bypass valve 7. During the startup phase, due to the small pressure differential of the low-pressure refrigerant unit supply, insufficient refrigerant supply and low evaporation pressure 11 are prone to occur. By designing the hot gas bypass as standard on the chiller system, the hot gas bypass valve 7 is fully opened during the startup phase, and is slowly closed according to the set control cycle / control pulse after startup to avoid problems such as low evaporation pressure 11 alarm, excessive loading of the compressor 2, and surging during the startup phase due to insufficient liquid supply.

[0047] Reference Figure 1 Figure 4 A low-pressure refrigerant supply system control method, when the chiller system is in operation, the system pressure difference is greater than the set system pressure difference upper limit, after a delay setting time, the compressor 2 bearing lubrication supply path adopts the first bearing lubrication supply path, and the second bearing lubrication supply path adopts the refrigerant pump 6 for forced supply.

[0048] Before pumping, the evaporation liquid level 12 of the evaporator 1 is monitored. If the evaporation liquid level 12 of the evaporator 1 is lower than a set value, the refrigerant pump 6 stops running.

[0049] At the beginning of the pumping phase, the exhaust solenoid valve 86 of the refrigerant pump 6 is opened to exhaust the air. The opening and closing of the exhaust solenoid valve 86 is controlled by monitoring whether the operating current of the refrigerant pump 6 reaches a set threshold.

[0050] During the pumping phase, the refrigerant pump 6 operates at a low frequency.

[0051] During the pumping process, if within the set time interval, the evaporation liquid level 12 of the evaporator 1 does not drop and the condensation liquid level 32 of the condenser 3 does not increase, the refrigerant pump 6 runs dry and is assigned a dry run number +1. When the cumulative dry run number is greater than the set value, the chiller system is locked.

[0052] After the injection is completed, the second bearing lubrication supply path is used to supply fluid to the bearing. After the fluid supply differential is greater than the fluid supply differential set value before startup and the refrigerant pump 6 runs for a set time, the chiller system starts to operate.

[0053] After the chiller system is started, the system pressure difference is greater than the set system pressure difference upper limit. After the delay setting time, the compressor 2 bearing fluid supply adopts the first bearing lubrication fluid supply path.

[0054] During normal shutdown, fault shutdown or emergency shutdown, the second bearing lubrication supply path is used to supply fluid to the bearing.

[0055] The CPU module in the PLC control box 10 performs logical operations on the collected data and outputs relevant instructions to control the chiller system.

[0056] The operating principle of a low-pressure refrigerant liquid supply system control method according to an embodiment of the present invention is:

[0057] Set the parameters as follows:

[0058] The upper limit of the liquid level of condenser 3 during the liquid pumping stage: Lc2;

[0059] The lower limit of the liquid level of condenser 3 during the liquid pumping stage: Lc1;

[0060] The lower limit of the liquid level of evaporator 1 during the liquid pumping stage: Le1;

[0061] The operation determination time of the refrigerant pump 6 during the liquid pumping phase: ΔT1;

[0062] Refrigerant pump 6 operating time before startup: ΔT2;

[0063] Refrigerant pump 6 operation time after shutdown: ΔT3;

[0064] The hydraulic pressure difference before starting is low: ΔP1;

[0065] After starting, the hydraulic pressure difference is low: ΔP2;

[0066] System pressure difference upper limit: ΔP3;

[0067] System pressure difference lower limit: ΔP4;

[0068] Condenser 3 liquid level control target value: Lc3;

[0069] Hot gas bypass valve 7 control period: ΔT4;

[0070] Hot gas bypass control pulse: ΔT5.

[0071] Note: Fluid supply differential = (bearing fluid supply pressure 21) - (bearing fluid outlet pressure 22)

[0072] System pressure difference = (condensing pressure 31) - (evaporating pressure 11)

[0073] Reference Figures 1 to 4 A low-pressure refrigerant liquid supply system control method is collaboratively completed by a falling film evaporator 1, a compressor 2, a condenser 3, a power economizer 4, a primary liquid supply ball valve 5, a refrigerant pump 6, a hot gas bypass valve 7, a liquid pumping pipeline 8, and a bearing liquid supply system 9.

[0074] Reference Figure 3 The liquid pumping pipeline 8 is composed of a sight glass 81, an evaporator liquid outlet valve 82, a first pump pre-filter 83, a first non-return valve 84, a condenser liquid inlet valve 85, an exhaust solenoid valve 86, and a second non-return valve 87.

[0075] Reference Figure 4The bearing liquid supply pipeline is composed of a condenser liquid outlet valve 91, a second pump pre-filter 92, a drying filter 93, a fine filter 94, a third one-way valve 95, a refrigerant pump 6, a first one-way valve 84, a sight glass 81, and a condenser liquid inlet valve 85. The drying filter 93, the fine filter 94, and the third one-way valve 95 constitute the first bearing liquid supply path. After the refrigerant completes lubrication and cooling in the bearing box, the refrigerant returns to the falling film evaporator 1.

[0076] Reference Figure 1 and Figure 5 After the chiller system receives the start-up command, the central processor of the PLC control box 10 will collect the liquid level LC of the condenser 3; if the liquid level of the condenser 3 is ≥Lc2, at this time, the evaporator liquid outlet valve 82 and the condenser liquid inlet valve 85 are in the fully closed position, and the condenser liquid outlet valve 91 is in the fully open position, and the refrigerant pump 6 operates at a high frequency.

[0077] After the refrigerant pump 6 completes the refrigerant pump 6 running time before startup: ΔT2, if the hydraulic pressure difference ≥ the low hydraulic pressure difference before startup: ΔP1, the chiller system starts; otherwise, the refrigerant pump 6 is stopped, the evaporator liquid outlet valve 82, the condenser liquid inlet valve 85, and the condenser liquid outlet valve 91 are fully closed, and the chiller system fails to start.

[0078] After the chiller system is started, if the hydraulic pressure difference ≥ the hydraulic pressure difference after startup: ΔP2, the chiller system enters the operating state. Otherwise, the chiller system is shut down due to load reduction. The refrigerant pump 6 continues to operate for ΔT3, and then the chiller system enters the standby state. The evaporator liquid outlet valve 82, the condenser liquid inlet valve 85, and the condenser liquid outlet valve 91 are fully closed.

[0079] When the chiller system is in operation, if the system pressure difference is greater than the upper limit of the system pressure difference: ΔP3, the refrigerant pump 6 is turned off, otherwise, the refrigerant pump 6 continues to operate.

[0080] When the chiller system is in operation, if the system pressure difference is less than the lower limit of the system pressure difference: ΔP4, the refrigerant pump 6 starts.

[0081] When the outlet water temperature of the chiller system reaches the pause temperature or the system is shut down manually or due to a fault, the refrigerant pump 6 starts running. After the system is shut down continuously for a period of ΔT3, the chiller system enters the standby state, and the evaporator liquid outlet valve 82, the condenser liquid inlet valve 85, and the condenser liquid outlet valve 91 are fully closed.

[0082] After the chiller system receives the start-up command, the central processor of the PLC control box 10 will collect the liquid level LC of the condenser 3; if the liquid level of the condenser 3 is less than Lc2, the condenser liquid outlet valve 91 is fully closed, the evaporator liquid outlet valve 82, and the condenser liquid inlet valve 85 are in the fully open position, the refrigerant pump 6 operates at a low frequency, and the exhaust solenoid valve 86 is opened for exhaust. After the operating current of the refrigerant pump 6 reaches the set threshold, the exhaust solenoid valve 86 is closed.

[0083] During the pumping stage, if the evaporator 1 liquid level: Le does not decrease or the condenser 3 liquid level: Lc does not increase within the refrigerant pump 6 operation determination time: ΔT1, the refrigerant pump 6 is stopped and an alarm is output indicating that the refrigerant pump 6 pumping time is long. After the fault is reset, the pumping can be repeated. If the number of consecutive alarms is ≥5 times, the refrigerant pump 6 is locked and the refrigerant pump 6 and the pumping pipeline 8 need to be inspected and repaired to confirm the cause of the alarm.

[0084] Reference Figure 1 and Figure 6 If the liquid level of condenser 3 is greater than the upper limit of the liquid level of condenser 3 in the liquid pumping stage: Lc2, the control process is transferred. In order to ensure the smooth progress of the liquid supply process of the refrigerant pump 6, the cooperation of the first-level liquid supply ball valve 5 and the hot gas bypass valve 7 is required.

[0085] After the chiller system receives the start signal, the first-level liquid supply ball valve 5 is controlled according to the condenser 3 liquid level control target value: Lc3. When the actual liquid level of condenser 3 is ≤ the condenser 3 liquid level control target value: Lc3, the first-level liquid supply ball valve 5 is closed, otherwise it is opened.

[0086] Before the chiller system receives the start signal, the hot gas bypass valve 7 is in the fully open position. After receiving the start signal, the hot gas bypass valve 7 is slowly closed according to the set control cycle ΔT4 and control pulse ΔT5. This is mainly for low-pressure refrigerant chiller systems. During the startup phase, the system pressure difference is low. When the liquid supply is insufficient, it is easy to cause low evaporation pressure 11 alarm, too fast loading of compressor 2, surge during the startup phase and other related problems.

[0087] When the outlet water temperature of the chiller system reaches the pause temperature or the system is shut down manually or due to a fault, the hot gas bypass valve 7 opens at full speed, and the V4 valve closes at full speed to the minimum opening and maintains it. After the motor is powered off, the V4 valve closes at full speed.

[0088] After the chiller system enters the standby state, the first-stage liquid supply ball valve 5 is fully closed and the hot gas bypass valve 7 is fully opened to prepare for the next startup.

[0089] In the above process, the CPU module in the PLC control box 10 performs logical operations on the collected data and outputs relevant instructions to control the above process.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-pressure refrigerant liquid supply system control method, characterized in that: The invention comprises a chiller system and a bearing fluid supply system (9), wherein the chiller system comprises a refrigerant pump (6), an evaporator (1), a condenser (3), a compressor (2), a power saver (4), a throttling mechanism, a PLC control box (10) and a hot gas bypass valve (7), wherein the bearing fluid supply system (9) comprises a first bearing lubricating fluid supply path from a condenser (3) fluid collecting bag to a compressor (2) bearing, a second bearing lubricating fluid supply path from a condenser (3) fluid collecting bag to a compressor (2) bearing and a first-level fluid supply ball valve (5), wherein the center of the cylinder of the condenser (3) is more than 0.5 m higher than the center of the cylinder of the evaporator (1); When the chiller system is in operation and the system pressure difference is greater than the set upper limit of the system pressure difference, after a set delay time, the compressor (2) bearing lubrication liquid supply adopts the first bearing lubrication liquid supply path, and the second bearing lubrication liquid supply path adopts the refrigerant pump (6) for forced liquid supply; When the chiller system is in the standby stage, the liquid refrigerant mainly exists in the evaporator (1). Before starting, a refrigerant pump (6) is required to pump liquid into the liquid collecting bag of the condenser (3) to ensure that there is a sufficient amount of liquid refrigerant in the condenser (3) before starting. Before pumping, the liquid level of the evaporator (1) is monitored. If the liquid level of the evaporator (1) is lower than a set value, the refrigerant pump (6) stops running; At the start of the pumping phase, the exhaust solenoid valve (86) of the refrigerant pump (6) is opened to exhaust the gas, and the opening and closing of the exhaust solenoid valve (86) is controlled by monitoring whether the operating current of the refrigerant pump (6) reaches a set threshold value; During the pumping stage, the refrigerant pump (6) operates at a low frequency.

2. A low-pressure refrigerant liquid supply system control method according to claim 1, characterized in that: During the pumping process, if the liquid level of the evaporator (1) does not drop and the liquid level of the condenser (3) does not increase within a set time interval, the refrigerant pump (6) runs dry and is assigned a dry run count of +1. When the accumulated dry run count is greater than the set value, the chiller system is locked.

3. A low-pressure refrigerant liquid supply system control method according to claim 2, characterized in that: After the injection is completed, the second bearing lubrication supply path is used to supply fluid to the bearing. After the fluid supply differential is greater than the fluid supply differential set value before startup, and the refrigerant pump (6) runs for a set time, the chiller system starts to operate.

4. A low-pressure refrigerant liquid supply system control method according to claim 3, characterized in that: After the chiller system is started up, the system pressure difference is greater than the set system pressure difference upper limit, and after a delay of a set time, the compressor (2) bearing fluid supply adopts the first bearing lubrication fluid supply path.

5. A low-pressure refrigerant liquid supply system control method according to claim 1, characterized in that: During normal shutdown, fault shutdown or emergency shutdown, the second bearing lubrication supply path is used to supply fluid to the bearing.

6. A low-pressure refrigerant liquid supply system control method according to claim 1, characterized in that: The CPU module in the PLC control box (10) performs logic operations on the collected data and outputs relevant instructions to control the chiller system.

7. A low-pressure refrigerant liquid supply system control method according to claim 1, characterized in that: The condenser (3) is provided with a liquid bag, and the condenser (3) is provided with a subcooler.

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