【HVAC Version】Daily Question 20180130
Thread Content
Discuss the fault analysis and countermeasures for lithium bromide refrigeration units. Answer: Failures in refrigeration units mainly stem from the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly determining the causes of various faults and applying appropriate troubleshooting methods requires not only theoretical knowledge in electrical and refrigeration technologies, but more importantly, practical skills. Only through extensive practice can one gain rich experience in repairing refrigeration equipment. With the development of screw chillers in recent years, their failure rate has **decreased** compared to the past. At the same time, the unit control system is also becoming increasingly sophisticated. The unit control systems of many manufacturers come equipped with a function for automatically detecting faults. In the event of any abnormal malfunction in the unit, the control system generates an alarm via sensors or other devices, and displays the alarm code or description on the unit’s operating interface for easy reference by maintenance personnel. If the unit’s alarm indicates that a system error is not the direct cause of the fault, it is necessary to check whether other components related to the alarm are functioning properly.
Discuss the fault analysis and countermeasures for lithium bromide refrigeration units. Answer: Failures in refrigeration units mainly stem from the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly determining the causes of various faults and applying appropriate troubleshooting methods requires not only theoretical knowledge in electrical and refrigeration technologies, but more importantly, practical skills. Only through extensive practice can one gain rich experience in repairing refrigeration equipment. With the development of screw chillers in recent years, their failure rate has **decreased** compared to the past. At the same time, the unit control system is also becoming increasingly sophisticated. The unit control systems of many manufacturers come equipped with a function for automatically detecting faults. In the event of any abnormal malfunction in the unit, the control system generates an alarm via sensors or other devices, and displays the alarm code or description on the unit’s operating interface for easy reference by maintenance personnel. If the unit’s alarm indicates that a system error is not the direct cause of the fault, it is necessary to check whether other components related to the alarm are functioning properly.
Answer: Failures in refrigeration units mainly stem from the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly determining the causes of various faults and applying appropriate troubleshooting methods requires not only theoretical knowledge in electrical and refrigeration technologies, but more importantly, practical skills. Only through extensive practice can one gain rich experience in repairing refrigeration equipment. With the development of screw chillers in recent years, their failure rate has **decreased** compared to the past. At the same time, the unit control system is also becoming increasingly sophisticated. The unit control systems of many manufacturers come equipped with a function for automatically detecting faults. In the event of any abnormal malfunction in the unit, the control system generates an alarm via sensors or other devices, and displays the alarm code or description on the unit’s operating interface for easy reference by maintenance personnel. If the unit’s alarm indicates that a system error is not the direct cause of the fault, it is necessary to check whether other components related to the alarm are functioning properly.
1. The refrigerant water in the lithium bromide unit is contaminated. The subjective judgment method for refrigerant water contamination is: a. Low cooling capacity ； b. When the unit is operating under light load conditions, there is an excessive amount of refrigerant flow ； c. Drop in absorber liquid level ； d. The extracted water sample is yellowish in color, with a density exceeding 1.04 kg/m³. The measure to take when the coolant water in a lithium bromide unit becomes contaminated is to reduce the steam pressure of the unit (if adjustment fails, other valves in the pipeline can be used for adjustment) ； Check the bypass valve of the strainer; if it is faulty, it must be replaced ； Adjust the solution circulation rate to appropriately lower the liquid level in the low-pressure generator ； Reduce cooling load ； Close the exhaust valve. The method for regenerating the coolant water in lithium bromide units is as follows: a. Keep the lithium bromide unit operating under normal conditions, so that the amount of coolant vapor generated in the generator is less than the amount of coolant water flowing through the bypass ； b. Open the bypass valve on the outlet pipe section of the evaporator pump, close the spray valve, so that the refrigerant water flows into the absorber ； c. When the water level is no longer visible in the sight glass, turn off the refrigerant pump of the bypass valve, and repeat steps a and b once more once there is water present. The above process can be repeated several times until the density of the sampled water is below 1.04 mg/m3. 2. Low cooling capacity: The reasons why the cooling capacity of the lithium bromide unit is lower than the design specifications are: a. Air leakage in the unit ； b. Poor pumping performance of the vacuum pump ； c. Refrigerant water pollution ； d. Inappropriate initial concentration of the solution ； e. Improper solution circulation rate ； f. Blockage of the heat transfer tube ports on the water side of the evaporator ； g. Low working steam pressure ； h. The cooling water volume and temperature do not meet the requirements ； i. Low dryness degree of the working steam ； j. Large error in measuring instruments ； k. The mass of the solution does not meet the standards. The measures to address the low cooling capacity of the unit are: a. Evacuate the system or perform leak detection under negative pressure ； b. Service the vacuum pump to improve its pumping capacity ； c. Eliminate factors causing refrigerant water contamination and regenerate the refrigerant water ； d. Adjust the concentration of the lithium bromide solution to meet the required level ； e. Adjust the solution circulation rate ； f. Stop the machine and open the water chamber cover for treatment ； g. When the required gas supply pressure cannot be achieved, a conversion of operating conditions can be performed ； h. Adjust the cooling water volume and temperature to meet the requirements ； i. Stop the machine, and install a gas-water separator in the steam pipe for adjustment ； j. Calibrate the instruments; improvements and cleaning are necessary due to installation issues and blockages ； k. The lithium bromide solution that does not meet the standards must be drained, used to flush the lithium bromide unit, and then a new solution that meets the quality requirements must be poured in.
Fault analysis and countermeasures for lithium bromide refrigeration units? Answer: The main fault is lithium bromide crystallization, and the primary causes are as follows: 1. Excessively low temperature at the cooling water inlet; it is necessary to control the temperature of the cooling water. 2. Accumulation of non-condensable gases. 3. Overloading of the refrigeration unit
Faults in refrigeration units mainly stem from two aspects: the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly identifying the causes of various faults and adopting appropriate troubleshooting methods involves not only theories in electrical and refrigeration technology
Faults in refrigeration units mainly stem from two aspects: the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly determining the causes of various faults and applying appropriate troubleshooting methods requires not only theoretical knowledge in electrical and refrigeration technologies, but more importantly, practical skills. Only through extensive practice can one gain rich experience in repairing refrigeration equipment. With the development of screw chillers in recent years, their failure rate has **decreased** compared to the past. At the same time, the unit control system is also becoming increasingly sophisticated. The unit control systems of many manufacturers come equipped with a function for automatically detecting faults. In the event of any abnormal malfunction in the unit, the control system generates an alarm via sensors or other devices, and displays the alarm code or description on the unit’s operating interface for easy reference by maintenance personnel. If the unit’s alarm indicates that a system error is not the direct cause of the fault, it is necessary to check whether other components related to the alarm are functioning properly.
1. Poor vacuum: A. Incomplete leak detection during debugging; B. Leaks occurring during operation; C. Weld leaks caused by corrosion; D. Decline in the performance of the vacuum pump; E. Insufficient vacuum level; F. Poor absorption by the unit; G. Abnormalities in the cooling water system.
2. Cooling capacity below the rated value: A. Poor vacuum level; B. Insufficient cooling water flow; C. Excessively high cooling water temperature; D. Measurement errors; E. Improper adjustment of the solution circulation volume; F. Too much or too little refrigerant water; G. Low or high overall concentration of the solution; H. Insufficient combustion volume; I. Reduced high-heat efficiency; J. Presence of slight crystallization; K. Contamination of the refrigerant water; L. Excessively low outlet temperature of the refrigerant water; M. Low cold load on the user side; N. Insufficient circulation volume; O. Substandard quality of the solution; P. High heat consumption due to hot water usage; Q. Blockages or scaling in the steel pipes; R. Blockage in the shield pump.
3. Uncontrolled high liquid level: A. Poor contact or disconnection of the high liquid level sensor; B. Faults in the liquid controller; C. Incorrect frequency setting of the frequency converter; D. Improper adjustment of the circulation volume; E. Insufficient filling volume of the solution; F. Blockage in the filter screen of the shield pump.
4. Excessive overheating or overpressure: A. Excessive combustion volume; B. Low solution circulation volume; C. Abnormalities in the cooling water system; D. Leaks in the high-pressure section; E. High concentration of the solution.
5. Sudden lack of solution in all areas simultaneously: A. Crystallization; B. Blockages in the refrigerant nozzles of the evaporator; C. Leaks in the lower tank
2. Cooling capacity below the rated value: A. Poor vacuum level; B. Insufficient cooling water flow; C. Excessively high cooling water temperature; D. Measurement errors; E. Improper adjustment of the solution circulation volume; F. Too much or too little refrigerant water; G. Low or high overall concentration of the solution; H. Insufficient combustion volume; I. Reduced high-heat efficiency; J. Presence of slight crystallization; K. Contamination of the refrigerant water; L. Excessively low outlet temperature of the refrigerant water; M. Low cold load on the user side; N. Insufficient circulation volume; O. Substandard quality of the solution; P. High heat consumption due to hot water usage; Q. Blockages or scaling in the steel pipes; R. Blockage in the shield pump.
3. Uncontrolled high liquid level: A. Poor contact or disconnection of the high liquid level sensor; B. Faults in the liquid controller; C. Incorrect frequency setting of the frequency converter; D. Improper adjustment of the circulation volume; E. Insufficient filling volume of the solution; F. Blockage in the filter screen of the shield pump.
4. Excessive overheating or overpressure: A. Excessive combustion volume; B. Low solution circulation volume; C. Abnormalities in the cooling water system; D. Leaks in the high-pressure section; E. High concentration of the solution.
5. Sudden lack of solution in all areas simultaneously: A. Crystallization; B. Blockages in the refrigerant nozzles of the evaporator; C. Leaks in the lower tank
Faults in refrigeration units mainly stem from two aspects: the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly determining the causes of various faults and applying appropriate troubleshooting methods requires not only theoretical knowledge in electrical and refrigeration technologies, but more importantly, practical skills. Only through extensive practice can one gain rich experience in repairing refrigeration equipment. With the development of screw chillers in recent years, their failure rate has **decreased** compared to the past. At the same time, the unit control system is also becoming increasingly sophisticated. The unit control systems of many manufacturers come equipped with a function for automatically detecting faults. In the event of any abnormal malfunction in the unit, the control system generates an alarm via sensors or other devices, and displays the alarm code or description on the unit’s operating interface for easy reference by maintenance personnel. If the unit’s alarm indicates that a system error is not the direct cause of the fault, it is necessary to check whether other components related to the alarm are functioning properly
Faults in refrigeration units mainly stem from two aspects: the electrical control system and the refrigeration system. Failures can prevent the unit from starting and operating properly, lead to a significant decrease in cooling capacity, or cause severe damage to the unit. Correctly identifying the causes of various faults and adopting appropriate troubleshooting methods involves not only theories in electrical and refrigeration technology
I. Causes of insufficient chilled water flow? 1. Clogged filters (in the chilled water system), resulting in an increased pressure difference between the inlet and outlet； ? 2. There is air at the water pump inlet, causing the pump to run dry (the pressure gauge at the pump outlet is unstable) ； ? 3. System valves are not opened, or the valve cores have come loose ； ? 4. Scaling of heat transfer tubes in the unit ； ? 5. Blockage of the unit’s heat transfer tubes ； ? 6. The water pump selected is too small, resulting in excessive system resistance. II. Reasons for the high inlet temperature of cooling water? 1. Uneven water supply to the cooling tower (insufficient water pressure), blockage in the water distribution tray ； ? 2. Relatively high ambient temperature ； ? 3. Insufficient air intake area ； ? 4. Incorrect selection of water tower ； ? 5. Incorrect fan rotation direction ； ? 6. Damage to the cooling tower fan drive mechanism (fan failure). III. Causes of cavitation in the solution pump
1. Insufficient amount of solution added to the unit ； ? 2. Poor vacuum level of the unit ； ? 3. The cooling water inlet temperature is too high ； ? 4. The cooling water flow rate is too low ； ? 5. No octanol has been added, or the amount of octanol is low ； ? 6. Refrigerant water pollution ； ? 7. Crystallization of the unit solution ； ? 8. Clogging of the absorber bladder filter (protects the pump). ? IV. Reasons for vacuum in the refrigerant pump ? 1. Low temperature at the cooling water inlet ； ? 2. The cooling water flow rate is too high ； ? 3. The cold water outlet temperature is too high ； ? 4. The refrigerant water spray valve is not properly adjusted ； ? 5. The filter screen of the evaporator liquid bag is clogged. ? (Note: As can be seen from these two issues, either a too high or too low temperature of the cooling water, as well as an excessive or insufficient flow rate, can affect the operation of the unit; therefore, it is necessary to keep the temperature and pressure within the specified ranges.) 5. Reasons why the cold water outlet temperature does not reach the set value? 1. The cooling capacity of the unit is lower than the user’s heat load (the appropriate capacity was not selected) ； ? 2. Poor vacuum level of the unit ； ? 3. The solution circulation rate has not been adjusted to the optimal level ； ? 4. The coolant water spray valve is not properly adjusted ； ? 5. The hot water flow rate is too low ； ? 6. Insufficient amount of cooling water ； ? 7. The cooling water inlet temperature is too high ； ? 8. The amount of cold water is too high ； ? 9. The electric control valve is not fully open (or faulty, resulting in low hot water flow) ； ? 10. No octanol has been added, or the amount of octanol is low ； ? 11. Fouling or blockage of the heat transfer tubes ； ? 12. Refrigerant water pollution ； ? 13. Blockage of the absorber spray plates (poor absorption of refrigerant vapor) ? 14. Poor flow of refrigerant water spray. VI. Causes of abnormally high temperature in dilute solutions during unit operation? 1. Poor vacuum level of the unit ； ? 2. The cooling water volume is too low ； ? 3. The cooling water inlet temperature is too high ； ? 4. Blockage of the absorber trickle plate ； ? 5. Solute dissolution tube is open (the concentrated solution enters the absorber directly through the solute dissolution tube and mixes with the dilute solution) ； ? 6. Blockage or scaling of the heat transfer tubes in the absorber (preventing the circulating water from cooling down). ? Through the analysis of these six common problems, one should have a deeper understanding of some of the key parameters related to the operation of the unit. In addition to the effects of the three external systems mentioned earlier, the internal structure and circulation conditions also have a significant impact on the unit’s cooling efficiency; factors such as reduced amounts of octanol, poor vacuum levels, scaling, and blockages in the spray plates all play a role. The units we are using at present are already quite advanced and come equipped with many safety features, but scaling, corrosion of the pipelines inside the units, and losses of octanol are inevitable. Additionally, it is possible that the unit’s safety systems may fail, so it is very important to be familiar with some of the common faults that can occur in these units. ? Octanol was mentioned several times earlier; it is a surfactant that can improve the absorption efficiency of absorbers by enhancing their water-absorbing capacity ； On the other hand, it can improve the cooling efficiency of the condenser ； Ultimately, this achieves the goal of improving cooling efficiency; however, octanol is gradually lost as external vacuuming is applied, so the crew must replenish it appropriately during long periods of operation. The amount of n-octanol added is usually 0.1% to 0.3% of the weight of the solution; 0.3% is commonly used, which means that for 1 ton of solution, 3 kg of n-octanol is added. In addition to octanol, lithium chromate (Li2CrO4) is also added to the lithium bromide solution; lithium chromate acts as a corrosion inhibitor that slows down the corrosion of the equipment. The lithium bromide solution has a pH value of 9–10.5 upon injection, with a concentration of 50% ； When the pH value is greater than 10.5, HBr can be added; when the pH value is less than 9, LiOH can be added. It is important to focus on the analysis of common faults in such units, in order to gain a deeper understanding of the factors that affect them both externally and internally. The liquid components should be considered as information for general knowledge only. Other issues that need to be highlighted: Liu Suping and Wan Jie from Team 5 of the processing department have put forward some good suggestions, which we would like to share with everyone: ? 1. After the vacuum pump creates a vacuum, add an additional step: ? Open the vent valve on the left side of the oil separator, ? so as to create positive pressure inside the oil separator, and then close it. ? Avoid vacuum in the oil trap; after stopping the vacuum pump, ? the oil from the vacuum pump is drawn into the oil trap, ? which causes a false liquid level in the vacuum pump. ? Note: The upper and lower exhaust valves must be closed tightly. ? ? 2. Issue regarding the need to close the butterfly valves before and after the automatic hot water control valve after the standby refrigeration unit is shut down: ? Considering the possibility that the automatic valve may not be airtight, hot water might still flow through the standby unit when the main unit is in operation, thereby heating the standby unit. Therefore, it is required that the butterfly valves before and after the automatic hot water valve be closed after the standby unit is shut down. 3. Regarding the requirements for circulating water temperature and pressure: ? Temperature: 20~31°C ? Pressure: 0.25~0.35 MPa ? There are no objections to the temperature; some people believe that the pressure should be ≥0.35 MPa ； In fact, applying pressure within a certain range helps to maintain a stable flow rate, which is beneficial for the unit. Additionally, there is negative pressure inside the unit; as long as the water supply is sufficient, a relatively lower pressure is also advantageous for the heat exchange tubes of the unit. Last year, control was carried out via the pump outlet, with the inlets and outlets of the refrigeration machine kept fully open. Requiring the same approach would also limit the suction volume of the pump, thereby preventing vacuum conditions from occurring. When it is put into use for the first time in summer, do not introduce the unit right away; instead, pass the water through the strainer first to remove impurities, and only after that bring in the unit. This is something that needs to be kept in mind. ? Questions regarding the automatic switching of frequency for water towers? When lithium bromide cooling water towers are in use, only one can be active at a time; if both are used simultaneously, the different pumping capacities of the pumps will result in an imbalance in the water volume between the two towers, causing one tower to run out of water while the other overflows. Therefore, when performing frequency conversion and automatic adjustment, it is done by having one tower in operation while the other is not; in other words, it is assumed that one tower is always at 100% (operational) while the other is at 0% (inactive). The so-called cascade control doesn’t really make much sense – it’s just a term used for description. After implementing cascade control, two-level (temperature control) automatic control can be achieved. For the second-level control, setting the circulation water temperature to automatic mode enables variable-frequency temperature control; ultimately, the temperature is regulated by controlling the fan speed. However, the fan speed cannot be too low, as this poses a risk of damaging the motor, so the minimum speed is set at 20% of the full-load speed. Feel free to ask more questions if you have any.
1. Insufficient amount of solution added to the unit ； ? 2. Poor vacuum level of the unit ； ? 3. The cooling water inlet temperature is too high ； ? 4. The cooling water flow rate is too low ； ? 5. No octanol has been added, or the amount of octanol is low ； ? 6. Refrigerant water pollution ； ? 7. Crystallization of the unit solution ； ? 8. Clogging of the absorber bladder filter (protects the pump). ? IV. Reasons for vacuum in the refrigerant pump ? 1. Low temperature at the cooling water inlet ； ? 2. The cooling water flow rate is too high ； ? 3. The cold water outlet temperature is too high ； ? 4. The refrigerant water spray valve is not properly adjusted ； ? 5. The filter screen of the evaporator liquid bag is clogged. ? (Note: As can be seen from these two issues, either a too high or too low temperature of the cooling water, as well as an excessive or insufficient flow rate, can affect the operation of the unit; therefore, it is necessary to keep the temperature and pressure within the specified ranges.) 5. Reasons why the cold water outlet temperature does not reach the set value? 1. The cooling capacity of the unit is lower than the user’s heat load (the appropriate capacity was not selected) ； ? 2. Poor vacuum level of the unit ； ? 3. The solution circulation rate has not been adjusted to the optimal level ； ? 4. The coolant water spray valve is not properly adjusted ； ? 5. The hot water flow rate is too low ； ? 6. Insufficient amount of cooling water ； ? 7. The cooling water inlet temperature is too high ； ? 8. The amount of cold water is too high ； ? 9. The electric control valve is not fully open (or faulty, resulting in low hot water flow) ； ? 10. No octanol has been added, or the amount of octanol is low ； ? 11. Fouling or blockage of the heat transfer tubes ； ? 12. Refrigerant water pollution ； ? 13. Blockage of the absorber spray plates (poor absorption of refrigerant vapor) ? 14. Poor flow of refrigerant water spray. VI. Causes of abnormally high temperature in dilute solutions during unit operation? 1. Poor vacuum level of the unit ； ? 2. The cooling water volume is too low ； ? 3. The cooling water inlet temperature is too high ； ? 4. Blockage of the absorber trickle plate ； ? 5. Solute dissolution tube is open (the concentrated solution enters the absorber directly through the solute dissolution tube and mixes with the dilute solution) ； ? 6. Blockage or scaling of the heat transfer tubes in the absorber (preventing the circulating water from cooling down). ? Through the analysis of these six common problems, one should have a deeper understanding of some of the key parameters related to the operation of the unit. In addition to the effects of the three external systems mentioned earlier, the internal structure and circulation conditions also have a significant impact on the unit’s cooling efficiency; factors such as reduced amounts of octanol, poor vacuum levels, scaling, and blockages in the spray plates all play a role. The units we are using at present are already quite advanced and come equipped with many safety features, but scaling, corrosion of the pipelines inside the units, and losses of octanol are inevitable. Additionally, it is possible that the unit’s safety systems may fail, so it is very important to be familiar with some of the common faults that can occur in these units. ? Octanol was mentioned several times earlier; it is a surfactant that can improve the absorption efficiency of absorbers by enhancing their water-absorbing capacity ； On the other hand, it can improve the cooling efficiency of the condenser ； Ultimately, this achieves the goal of improving cooling efficiency; however, octanol is gradually lost as external vacuuming is applied, so the crew must replenish it appropriately during long periods of operation. The amount of n-octanol added is usually 0.1% to 0.3% of the weight of the solution; 0.3% is commonly used, which means that for 1 ton of solution, 3 kg of n-octanol is added. In addition to octanol, lithium chromate (Li2CrO4) is also added to the lithium bromide solution; lithium chromate acts as a corrosion inhibitor that slows down the corrosion of the equipment. The lithium bromide solution has a pH value of 9–10.5 upon injection, with a concentration of 50% ； When the pH value is greater than 10.5, HBr can be added; when the pH value is less than 9, LiOH can be added. It is important to focus on the analysis of common faults in such units, in order to gain a deeper understanding of the factors that affect them both externally and internally. The liquid components should be considered as information for general knowledge only. Other issues that need to be highlighted: Liu Suping and Wan Jie from Team 5 of the processing department have put forward some good suggestions, which we would like to share with everyone: ? 1. After the vacuum pump creates a vacuum, add an additional step: ? Open the vent valve on the left side of the oil separator, ? so as to create positive pressure inside the oil separator, and then close it. ? Avoid vacuum in the oil trap; after stopping the vacuum pump, ? the oil from the vacuum pump is drawn into the oil trap, ? which causes a false liquid level in the vacuum pump. ? Note: The upper and lower exhaust valves must be closed tightly. ? ? 2. Issue regarding the need to close the butterfly valves before and after the automatic hot water control valve after the standby refrigeration unit is shut down: ? Considering the possibility that the automatic valve may not be airtight, hot water might still flow through the standby unit when the main unit is in operation, thereby heating the standby unit. Therefore, it is required that the butterfly valves before and after the automatic hot water valve be closed after the standby unit is shut down. 3. Regarding the requirements for circulating water temperature and pressure: ? Temperature: 20~31°C ? Pressure: 0.25~0.35 MPa ? There are no objections to the temperature; some people believe that the pressure should be ≥0.35 MPa ； In fact, applying pressure within a certain range helps to maintain a stable flow rate, which is beneficial for the unit. Additionally, there is negative pressure inside the unit; as long as the water supply is sufficient, a relatively lower pressure is also advantageous for the heat exchange tubes of the unit. Last year, control was carried out via the pump outlet, with the inlets and outlets of the refrigeration machine kept fully open. Requiring the same approach would also limit the suction volume of the pump, thereby preventing vacuum conditions from occurring. When it is put into use for the first time in summer, do not introduce the unit right away; instead, pass the water through the strainer first to remove impurities, and only after that bring in the unit. This is something that needs to be kept in mind. ? Questions regarding the automatic switching of frequency for water towers? When lithium bromide cooling water towers are in use, only one can be active at a time; if both are used simultaneously, the different pumping capacities of the pumps will result in an imbalance in the water volume between the two towers, causing one tower to run out of water while the other overflows. Therefore, when performing frequency conversion and automatic adjustment, it is done by having one tower in operation while the other is not; in other words, it is assumed that one tower is always at 100% (operational) while the other is at 0% (inactive). The so-called cascade control doesn’t really make much sense – it’s just a term used for description. After implementing cascade control, two-level (temperature control) automatic control can be achieved. For the second-level control, setting the circulation water temperature to automatic mode enables variable-frequency temperature control; ultimately, the temperature is regulated by controlling the fan speed. However, the fan speed cannot be too low, as this poses a risk of damaging the motor, so the minimum speed is set at 20% of the full-load speed. Feel free to ask more questions if you have any.