Zero-load operation system of steam compression water chilling unit and control method

Abstract

The invention discloses a steam compression water chilling unit zero-load operation system and a control method, and belongs to the technical field of water chilling units, the steam compression water chilling unit zero-load operation system comprises a water chilling unit system and a plate heat exchanger heat exchange system, the water chilling unit system comprises an evaporator, a condenser, a compressor, a power saver, a hot gas bypass valve, a throttling mechanism and a control box, the plate heat exchanger heat exchange system comprises a plate heat exchanger, a cold water bypass pipeline and a cooling water bypass pipeline. In the unit operation process, when the actual load requirement is larger than the maximum unloading capacity of a unit, the plate heat exchanger heat exchange system is not put into operation, and when the actual load requirement is smaller than the maximum unloading capacity of the unit or is close to the zero load requirement, the plate heat exchanger heat exchange system is put into operation. A plate heat exchanger heat exchange system for cold water and cooling water is additionally arranged, so that the unit can realize 0-100% load regulation on the premise of ensuring the outlet water temperature of the cold water, and zero-load stable operation is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of water chillers, and in particular to a zero-load operation system and a control method for a vapor compression water chiller. Background Art

[0002] At present, in the technical field of steam compression chiller operation, the mainstream brands on the market have been investigated. When the steam compression chiller is at low cooling water temperature, the lower limit of the unloading capacity is 20%, and when it is operating at high cooling water temperature, the minimum operating load must be higher than 20%. At present, many industrial and nuclear power projects require that the unit must have a load adjustment capacity of 0-100% under the premise of meeting the cold water outlet temperature. In order to meet the requirements of low-load operation, major host manufacturers will increase the unloading capacity of the unit by increasing the hot gas bypass.

[0003] With respect to the above-mentioned related technologies, the applicant found that the solution could not meet the requirements of the cold water outlet temperature. When the system operating pressure difference is low, for the compressors whose motors and lubricating oils require fluorine cooling, a separate refrigerant pump needs to be set up for forced liquid supply. The low pressure difference will cause insufficient liquid supply in the main liquid supply pipeline, and a separate refrigerant pump needs to be set up. Due to the easy vaporization of Freon, the refrigerant pump often suffers from dry grinding and damage, resulting in poor system operation stability. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a zero-load operation system and control method for a vapor compression chiller. By adding a plate heat exchanger system for cold water and cooling water, the unit can achieve 0%~100% load regulation and achieve stable zero-load operation while ensuring the outlet temperature of cold water.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: A zero-load operation system of a vapor compression chiller comprises a chiller system and a plate heat exchanger heat exchange system. The chiller system comprises an evaporator, a condenser, a compressor, a power economizer, a hot gas bypass valve, a throttling mechanism and a control box. The plate heat exchanger heat exchange system comprises a plate heat exchanger, a cold water bypass pipeline and a cooling water bypass pipeline.

[0006] Furthermore, an evaporation pressure sensor, a cold water inlet temperature sensor, a cold water outlet temperature sensor and a client cold water return temperature sensor are provided in the evaporator.

[0007] Furthermore, a condensing pressure sensor, a cooling water inlet temperature sensor and a cooling water outlet temperature sensor are provided in the condenser.

[0008] Furthermore, the throttling mechanism includes an electric regulating valve.

[0009] Furthermore, the cold water bypass pipeline includes a cold water manual ball valve, a cold water filter, a cold water on-site pressure gauge, a cold water soft connection, a bypass cold water pump and a cold water electric ball valve.

[0010] Furthermore, the cooling water bypass pipeline includes a cooling water manual ball valve, a cooling water filter, a cooling water on-site pressure gauge, a cooling water soft connection and a bypass cooling water pump.

[0011] A zero-load control method for a vapor compression chiller comprises the following steps: Step 1: The unit is started and running. If the cold water outlet temperature is greater than the set target value + the upper limit of the temperature difference, the unit is loaded. If the cold water outlet temperature is less than the set target value - the lower limit of the temperature difference, the unit is unloaded. Step 2: If the unit is in the load reduction stage, the control box calculates the minimum load that the unit can unload based on the compressor dynamic curve, and calculates the output cold water inlet and outlet temperature difference, and compares the calculated cold water inlet and outlet temperature difference with the actual operating temperature difference; Step 3: If the calculated temperature difference between the cold water inlet and outlet is ≥ the actual operating temperature difference, the plate heat exchanger heat exchange system is put into operation; if the calculated temperature difference between the cold water inlet and outlet is < the actual operating temperature difference, the plate heat exchanger heat exchange system is not put into operation.

[0012] Furthermore, after the plate heat exchanger heat exchange system is put into operation, If the bypass chilled water pump is maintained at the lower frequency limit of 25Hz, the unit will be given priority to reduce the load. If the unit has been reduced to the lower limit and the outlet water temperature of the chilled water is less than the set target value - the lower limit of the temperature difference, the bypass chilled water pump will be increased in frequency according to PID control; If the set target value - lower limit of temperature difference ≤ the outlet temperature of cold water ≤ the set target value + upper limit of temperature difference, the bypass cold water pump frequency is maintained; If the outlet temperature of the cold water is greater than the set target value + the upper limit of the temperature difference, the bypass cold water pump will reduce the frequency according to the PID control logic; When the frequency is reduced to 25Hz, and the calculated inlet and outlet water temperature difference on the cold water side outputted from the control box is less than the actual operating temperature difference, the control box outputs a signal to disable the heat exchange system of the plate heat exchanger, first shuts down the bypass cooling water pump and bypass cold water pump, and then closes the cold water electric ball valve.

[0013] Furthermore, if the unit is in the manual shutdown, fault shutdown, or water temperature suspension stage, in order to prevent cooling loss, the plate heat exchanger heat exchange system needs to be disabled, and the bypass chilled water pump and bypass cooling water pump must be turned off first, and then the chilled water electric ball valve must be closed.

[0014] In summary, compared with the prior art, the above technical solution has the following beneficial effects: (1) During the operation of the unit, when the actual load demand is greater than the maximum unloading capacity of the unit, the plate heat exchanger heat exchange system will not be put into operation. When the actual load demand is less than the maximum unloading capacity of the unit, or close to zero load demand, the plate heat exchanger heat exchange system will be put into operation. By adding the plate heat exchanger heat exchange system for cold water and cooling water, the unit can achieve 0%~100% load regulation and achieve stable operation at zero load while ensuring the cold water outlet temperature; (2) During the load regulation process, the unit will first reduce the operating load by reducing the suction volume, reducing the frequency and other load-reducing measures. When the unit's load output is still greater than the required load, the hot gas bypass valve will be opened to reduce the system operating pressure ratio, allowing the compressor to continue to unload until the unit reaches the limit low load of its own regulation. When the load demand is still less than the limit low load of the unit, the plate heat exchanger heat exchange system will be finally activated to further reduce the load, even to achieve zero load operation without stopping. By optimizing the regulation and control sequence, the unit can achieve the best energy-saving effect during the entire cycle of operation; (3) The selection of the plate heat exchanger should be combined with the actual unloading capacity of the compressor. The selection calculation should be carried out separately at high cooling water temperature and low cooling water temperature, and the larger value of the two should be taken. It is recommended to select a plate heat exchanger with a heat exchange margin of 1.2 times. After the plate heat exchanger model is determined, the corresponding bypass cold water pump and bypass cooling water pump should be matched. In order to increase the load adjustment capacity and ensure the cold water outlet temperature, the bypass cold water pump uses a variable frequency water pump, and a cold water electric ball valve is added to the outlet of the plate heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The system diagram of the water chiller of the present invention; Figure 2 This is a zero-load operation system diagram of the chiller of the present invention; Figure 3 This is a logic diagram of the zero-load control method for the vapor compression chiller of the present invention.

[0016] Explanation of the reference numerals: 1. Evaporator; 11. Evaporation pressure sensor; 12. Cold water inlet temperature sensor; 13. Cold water outlet temperature sensor; 14. Client cold water return temperature sensor; 2. Compressor; 21. Guide vane; 3. Condenser; 31. Condensation pressure sensor; 32. Cooling water inlet temperature sensor; 33. Cooling water outlet temperature sensor; 4. Power economizer; 5. Hot gas bypass valve; 6. Electric regulating valve; 7. Control box; 8. Plate heat exchanger; 9. Cold water bypass pipeline; 91. Cold water manual ball valve; 92. Cold water filter; 93. Cold water local pressure gauge; 94. Cold water soft connection; 95. Bypass cold water pump; 96. Cold water electric ball valve; 10. Cooling water bypass pipeline; 101. Cooling water manual ball valve; 102. Cooling water filter; 103. Cooling water local pressure gauge; 104. Cooling water soft connection; 105. Bypass cooling water pump. DETAILED DESCRIPTION

[0017] 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.

[0018] In the current field of steam compression chiller operation technology, a survey of mainstream brands on the market shows that the lower limit of the unloading capacity of steam compression chillers is 20% when the cooling water temperature is low, and the minimum operating load is higher than 20% when the cooling water temperature is high. Currently, many industrial and nuclear power projects require that the unit must have a load adjustment capacity of 0-100% under the premise of meeting the cold water outlet temperature.

[0019] In order to meet the requirements of low-load operation, major host manufacturers will increase the unloading capacity of the unit by increasing the hot gas bypass method. First of all, this solution cannot meet the requirements of the cold water outlet temperature. In addition, when the system operating pressure difference is low, for the compressor 2 whose motor and lubricating oil need fluorine cooling, a separate refrigerant pump needs to be set up for forced liquid supply; low pressure difference will lead to insufficient liquid supply in the main liquid supply pipeline, and a separate refrigerant pump needs to be set up. Due to the easy vaporization of freon, the refrigerant pump often suffers from dry wear and damage, resulting in poor system operation stability; the variable frequency regulation method has a significant effect under low cooling water temperature conditions, but under high cooling water temperature conditions, the frequency reduction space is limited and the ability to adjust the load is poor.

[0020] In view of the above problems, an embodiment of the present invention discloses a zero-load operation system of a vapor compression chiller.

[0021] Reference Figure 1 and Figure 2A zero-load operation system of a vapor compression chiller includes a chiller system and a plate heat exchanger heat exchange system. The chiller system includes an evaporator 1, a condenser 3, a compressor 2, a power economizer 4, a hot gas bypass valve 5, a throttling mechanism and a control box 7. The operation of the chiller system is completed through the coordination of the evaporator 1, the condenser 3, the compressor 2, the power economizer 4, the throttling mechanism and the control box 7.

[0022] The evaporator 1 is provided with an evaporation pressure sensor 11, a cold water inlet temperature sensor 12, a cold water outlet temperature sensor 13 and a client cold water return temperature sensor 14. The condenser 3 is provided with a condensation pressure sensor 31, a cooling water inlet temperature sensor 32 and a cooling water outlet temperature sensor 33. The throttling mechanism includes an electric regulating valve 6. The evaporation pressure sensor 11 outputs an evaporation pressure value, the cold water inlet temperature sensor 12 outputs a cold water inlet temperature value, the cold water outlet temperature sensor 13 outputs a cold water outlet temperature value, the client cold water return temperature sensor 14 outputs a client cold water return temperature value, the condensation pressure sensor 31 outputs a condensation pressure value, the cooling water inlet temperature sensor 32 outputs a cooling water inlet temperature value, and the cooling water outlet temperature sensor 33 outputs a cooling water outlet temperature value.

[0023] The plate heat exchanger heat exchange system includes a plate heat exchanger 8, a cold water bypass pipeline 9 and a cooling water bypass pipeline 10. The cold water bypass pipeline 9 includes a cold water manual ball valve 91, a cold water filter 92, a cold water local pressure gauge 93, a cold water soft connection 94, a bypass cold water pump 95 and a cold water electric ball valve 96. The cooling water bypass pipeline 10 includes a cooling water manual ball valve 101, a cooling water filter 102, a cooling water local pressure gauge 103, a cooling water soft connection 104 and a bypass cooling water pump 105. The cold water bypass pipeline 9 and the cooling water bypass pipeline 10 can be integrated on the unit or placed in the customer's water system.

[0024] The selection of plate heat exchanger 8 should be combined with the actual unloading capacity of compressor 2. The selection calculation should be carried out at high cooling water temperature and low cooling water temperature respectively, and the larger value of the two should be taken. It is recommended to select plate heat exchanger 8 with 1.2 times the heat exchange margin. After the model of plate heat exchanger 8 is determined, the corresponding bypass cold water pump 95 and bypass cooling water pump 105 are matched. In order to increase the load adjustment capacity and ensure the cold water outlet temperature, the bypass cold water pump 95 adopts a variable frequency water pump, and a cold water electric ball valve 96 is added to the outlet of plate heat exchanger 8.

[0025] During the operation of the unit, when the actual load demand is greater than the maximum unloading capacity of the unit, the plate heat exchanger heat exchange system will not be put into operation. When the actual load demand is less than the maximum unloading capacity of the unit, or is close to zero load demand, the plate heat exchanger heat exchange system will be put into operation. By adding the plate heat exchanger heat exchange system for cold water and cooling water, the unit can achieve 0%~100% load regulation and achieve stable operation at zero load while ensuring the cold water outlet temperature.

[0026] During the load regulation process, the unit first reduces the operating load by reducing the suction volume, reducing the frequency and other load-reducing measures. When the unit's load output is still greater than the required load, the system operating pressure ratio is reduced by opening the hot gas bypass valve 5, allowing the compressor 2 to continue to unload until the unit reaches the limit low load of its own regulation. When the load demand is still less than the limit low load of the unit, the plate heat exchanger heat exchange system is finally enabled to further reduce the load, and even achieve zero load operation without stopping. By optimizing the regulation and control sequence, the unit is in the best energy-saving effect during the full cycle of operation.

[0027] The embodiment of the present invention discloses a zero-load control method for a vapor compression chiller, comprising the following steps: Step 1: The unit is started and running. If the cold water outlet temperature is greater than the set target value + the upper limit of the temperature difference, the unit is loaded. If the cold water outlet temperature is less than the set target value - the lower limit of the temperature difference, the unit is unloaded. Step 2: If the unit is in the load reduction stage, the control box 7 calculates the minimum load that the unit can unload according to the dynamic curve of the compressor 2, and calculates the output cold water inlet and outlet water temperature difference, and compares the calculated cold water inlet and outlet water temperature difference with the actual operating temperature difference; Step 3: If the calculated temperature difference between the cold water inlet and outlet is ≥ the actual operating temperature difference, the plate heat exchanger heat exchange system is put into operation; if the calculated temperature difference between the cold water inlet and outlet is < the actual operating temperature difference, the plate heat exchanger heat exchange system is not put into operation.

[0028] Step 4: After the plate heat exchanger heat exchange system is put into operation, if the bypass chilled water pump 95 is maintained at the lower frequency limit of 25Hz, the unit is given priority to reduce the load. If the unit has been reduced to the lower limit and the outlet water temperature of the cold water is less than the set target value - the lower limit of the temperature difference, the bypass chilled water pump 95 is frequency-increased according to the PID control; if the set target value - the lower limit of the temperature difference ≤ the outlet water temperature of the cold water ≤ the set target value + the upper limit of the temperature difference, the frequency of the bypass chilled water pump 95 is maintained; if the outlet water temperature of the cold water is greater than the set target value + the upper limit of the temperature difference, the bypass chilled water pump 95 is frequency-reduced according to the PID control logic.

[0029] When the frequency decreases to 25 Hz, and the calculated inlet and outlet water temperature difference on the cold water side outputted from the control box 7 is less than the actual operating temperature difference, the control box 7 outputs a signal to disable the heat exchange system of the plate heat exchanger, first shutting down the bypass cooling water pump 105 and the bypass cold water pump 95, and then shutting down the cold water electric ball valve 96.

[0030] If the unit is in the manual shutdown, fault shutdown, or water temperature pause stage, in order to prevent cooling loss, the plate heat exchanger heat exchange system needs to be disabled, first shut down the bypass cold water pump 95 and bypass cooling water pump 105, and then close the cold water electric ball valve 96.

[0031] The implementation principle of a zero-load operation system and control method of a vapor compression chiller according to an embodiment of the present invention is as follows: Reference Figure 3 , set the calculation parameters as follows: Target temperature Ts; Target temperature deviation graph; Deviation Td at target temperature; Calculate the cold water inlet and outlet temperature difference ΔTc; Bypass cooling water pump operating frequency lower limit F1; Bypass cooling water pump operating frequency upper limit F2.

[0032] In the early stage of design, the compressor 2 will be selected according to the unit operating conditions and cooling capacity. After the compressor 2 is selected, the dynamic operation curve data of the compressor 2 will be imported into the control module. During the actual operation, the control box 7 will calculate the minimum operating load percentage of the compressor 2 according to the operation curve, and output the calculated cold water inlet and outlet temperature difference ΔTc.

[0033] Calculate the cold water inlet and outlet temperature difference ΔTc = minimum operating load percentage (Designed cold water inlet temperature - Designed cold water outlet temperature) During the operation of the unit, the difference between the inlet and outlet temperatures of the cold water is not large (generally around 5°C), but the temperature of the cooling water varies greatly with the outdoor ambient temperature and the heat exchange capacity of the cooling tower during the annual refrigeration cycle. When the cooling water temperature is high, the logarithmic heat exchange temperature difference on the plate heat exchanger 8 side is large, and the heat exchange capacity is large. When the cooling water temperature is low, the logarithmic heat exchange temperature difference on the plate heat exchanger 8 side is small, and the heat exchange capacity is small. Therefore, the selection of the plate heat exchanger 8 should be carried out at high cooling water temperature and low cooling water temperature respectively in combination with the minimum unloading capacity of the compressor 2 at the water temperature. Finally, the plate heat exchanger 8 is selected based on the largest heat exchange area after calculation.

[0034] After the plate heat exchanger 8 is selected, the bypass cold water pump 95 and the bypass cooling water pump 105 are selected according to the parameters such as the inlet water pressure drop and flow rate of the plate heat exchanger 8. After the water pump is selected, the cold water filter 92 and the cooling water filter 102 are selected according to the requirements of filtering accuracy, pipe diameter, and local pressure drop.

[0035] In order to improve the load regulation capability of the plate heat exchanger heat exchange system, the bypass cooling water pump 95 uses a variable frequency water pump.

[0036] Load Regulation Process of the Unit After the unit is running, the control box 7 collects the evaporation pressure of the evaporation pressure sensor 11 and the condensation pressure of the condensation pressure sensor 31 in real time, and calculates the cold water inlet and outlet temperature difference ΔTc according to the compressor 2 curve.

[0037] The control box 7 collects the cold water outlet temperature of the cold water outlet temperature sensor 13 in real time. When the cold water outlet temperature is less than the target temperature Ts-the deviation under the target temperature Td and the calculated cold water inlet and outlet temperature difference ΔTc ≥ the client cold water return temperature-cold water outlet temperature, the plate heat exchanger heat exchange system is activated. Otherwise, the unit completes the load regulation of the unit by controlling the opening and closing of the guide vane 21 and the hot gas bypass valve 5.

[0038] The load regulation segmented control is as follows: after the control box 7 outputs the signal to enable the plate heat exchanger heat exchange system, the cold water electric ball valve 96 is opened. After it is fully opened, the bypass cold water pump 95 operates according to the set bypass cold water pump operating frequency lower limit F1, and the bypass cooling water pump 105 operates at full frequency.

[0039] The bypass chilled water pump 95 keeps running according to the set bypass chilled water pump operating frequency lower limit F1. If the chilled water outlet temperature is less than the target temperature Ts-the target temperature lower deviation Td, if the compressor 2 is equipped with a variable frequency motor, the compressor 2 will be preferentially frequency-reduced. After the frequency drops to the lower limit, it is judged whether the opening of the guide vane 21 is greater than the dynamic surge limit setting value. If the judgment value is true, the unit will preferentially close the guide vane 21 to reduce the load. If the compressor 2 is equipped with a fixed frequency motor, the unit will preferentially close the guide vane 21 to reduce the load.

[0040] When the guide vane 21 is closed to the dynamic surge limit value, if the cold water outlet temperature is less than the target temperature Ts-the deviation under the target temperature Td, the unit opens the hot gas bypass valve 5 according to the set control cycle and pulse to reduce the load.

[0041] After the hot gas bypass valve 5 is fully opened, if the cold water outlet temperature is less than the target temperature Ts-the target temperature deviation Td, the bypass cold water pump 95 is frequency-increased according to the PID control logic to transfer the cold load of the unit to the cooling water side.

[0042] In the above low-load control operation process, the unit preferentially closes the guide vane 21 and opens the hot gas bypass valve 5 to reduce the load, so as to allow the unit to operate at the lowest load, reduce the power input of the motor, achieve energy saving, and try not to enable the plate heat exchanger heat exchange system to transfer the cold load.

[0043] If the target temperature Ts + target temperature upper deviation Tu < cold water outlet temperature, the bypass cold water pump 95 is frequency-reduced according to the PID control logic. If the above conditions are always met, the bypass cold water pump 95 is frequency-reduced to the bypass cold water pump operating frequency lower limit F1 and maintained. At this time, the cold water inlet and outlet temperature difference ΔTc is calculated < the client cold water return temperature - cold water outlet temperature. After the control box 7 outputs the signal to stop the plate heat exchanger heat exchange system, when the bypass cold water pump 95 and the bypass cooling water pump 105 stop, the cold water electric ball valve 96 is closed. The purpose of closing the cold water electric ball valve 96 when the plate heat exchanger heat exchange system is stopped is to prevent the loss of cooling capacity during the deactivation stage.

[0044] The plate heat exchanger heat exchange system is enabled, and the bypass cold water pump 95 operates according to the set bypass cold water pump operating frequency lower limit F1. After the bypass cooling water pump 105 operates at full frequency, if the target temperature Ts+target temperature upper deviation Tu<cold water outlet temperature, the guide vane 21 of the compressor 2 is opened according to the control cycle and pulse. When the target temperature Ts-target temperature lower deviation Td<cold water outlet temperature<target temperature Ts+target temperature upper deviation Tu, if the calculated cold water inlet and outlet temperature difference ΔTc<client cold water return temperature-cold water outlet temperature, the controller outputs a signal to disable the plate heat exchanger heat exchange system. When the bypass cold water pump 95 and the bypass cooling water pump 105 stop, the cold water electric ball valve 96 is closed. Otherwise, the plate heat exchanger heat exchange system maintains the current state.

[0045] After the plate heat exchanger heat exchange system is activated, if the target temperature Ts-target temperature lower deviation T<cold water outlet temperature<target temperature Ts+target temperature upper deviation Tu, the bypass cold water pump 95 maintains the lower frequency limit F1 operation.

[0046] During the manual shutdown / fault shutdown / water temperature pause stage of the unit, in order to avoid the loss of cooling capacity, after the motor is powered off, the plate heat exchanger heat exchange system needs to be disabled, and after the bypass cold water pump 95 and bypass cooling water pump 105 are stopped, the cold water electric ball valve 96 is closed.

[0047] In the above process, the control module in the control box 7 performs logical operations on the collected data and outputs relevant instructions to control the above process.

[0048] 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 zero-load operation system for a vapor compression chiller, characterized in that: The invention comprises a chiller system and a plate heat exchanger heat exchange system. The chiller system comprises an evaporator (1), a condenser (3), a compressor (2), a power economizer (4), a hot gas bypass valve (5), a throttling mechanism and a control box (7). The plate heat exchanger heat exchange system comprises a plate heat exchanger (8), a cold water bypass pipeline (9) and a cooling water bypass pipeline (10).

2. A zero-load operation system for a vapor compression chiller according to claim 1, characterized in that: The evaporator (1) is provided with an evaporation pressure sensor (11), a cold water inlet temperature sensor (12), a cold water outlet temperature sensor (13) and a client cold water return temperature sensor (14).

3. A zero-load operation system for a vapor compression chiller according to claim 1, characterized in that: The condenser (3) is provided with a condensation pressure sensor (31), a cooling water inlet temperature sensor (32) and a cooling water outlet temperature sensor (33).

4. A zero-load operation system for a vapor compression chiller according to claim 1, characterized in that: The throttling mechanism comprises an electric regulating valve (6).

5. A zero-load operation system for a vapor compression chiller according to claim 1, characterized in that: The cold water bypass pipeline (9) comprises a cold water manual ball valve (91), a cold water filter (92), a cold water local pressure gauge (93), a cold water soft connection (94), a bypass cold water pump (95) and a cold water electric ball valve (96).

6. A zero-load operation system for a vapor compression chiller according to claim 1, characterized in that: The cooling water bypass pipeline (10) comprises a cooling water manual ball valve (101), a cooling water filter (102), a cooling water local pressure gauge (103), a cooling water soft connection (104) and a bypass cooling water pump (105).

7. A zero-load control method for a vapor compression chiller according to any one of claims 1 to 6, characterized in that: The steps include: Step 1: The unit is started and running. If the cold water outlet temperature is greater than the set target value + the upper limit of the temperature difference, the unit is loaded. If the cold water outlet temperature is less than the set target value - the lower limit of the temperature difference, the unit is unloaded. Step 2: If the unit is in the load reduction stage, the control box (7) calculates the minimum load that the unit can unload itself according to the dynamic curve of the compressor (2), and calculates the output cold water inlet and outlet temperature difference, and compares the calculated cold water inlet and outlet temperature difference with the actual operating temperature difference; Step 3: If the calculated temperature difference between the cold water inlet and outlet is ≥ the actual operating temperature difference, the plate heat exchanger heat exchange system is put into operation; if the calculated temperature difference between the cold water inlet and outlet is < the actual operating temperature difference, the plate heat exchanger heat exchange system is not put into operation.

8. A zero-load control method for a vapor compression chiller according to claim 7, characterized in that: After the plate heat exchanger heat exchange system is put into operation, If the bypass chilled water pump (95) is maintained at the lower frequency limit of 25 Hz, the unit is given priority to reduce the load. If the unit has been reduced to the lower limit and the outlet water temperature of the chilled water is less than the set target value - the lower limit of the temperature difference, the bypass chilled water pump (95) is frequency-increased according to the PID control; If the set target value - the lower limit of the temperature difference ≤ the outlet temperature of the cold water ≤ the set target value + the upper limit of the temperature difference, the frequency of the bypass cold water pump (95) is maintained; If the outlet temperature of the cold water is greater than the set target value + the upper limit of the temperature difference, the bypass cold water pump (95) is frequency-reduced according to the PID control logic; When the frequency decreases to 25 Hz, and the calculated inlet and outlet water temperature difference on the cold water side outputted from the control box (7) is less than the actual operating temperature difference, the control box (7) outputs a signal to deactivate the heat exchange system of the plate heat exchanger, first shutting down the bypass cooling water pump (105) and the bypass cold water pump (95), and then shutting down the cold water electric ball valve (96).

9. A zero-load control method for a vapor compression chiller according to claim 7, characterized in that: If the unit is in the manual shutdown, fault shutdown, or water temperature pause stage, in order to prevent cooling loss, the plate heat exchanger heat exchange system needs to be stopped, and the bypass cold water pump (95) and bypass cooling water pump (105) are first turned off, and then the cold water electric ball valve (96) is closed.

Images