[Mechanical Equipment Technology Edition] Daily Question 201709023: Refrigeration Systems
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This post was last edited by YORK Industrial Refrigeration on 2017-9-25 at 09:32. Starting from now, in order to enhance communication among users, a 【Daily Question】 activity has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 wealth for active participation, 10-15 wealth for accurate answers. This question is valid for two days; no scoring will be given after that. Question: What are the common causes of low suction pressure in screw refrigeration compressors? I. First, start with the most obvious electrical components: 1. Check whether there are any faults in the sensors; 2. Verify if the alarms are functioning correctly; 3. Ensure that the load capacity is appropriate; 4. Examine the level of load. II. From a system perspective: 1. Refrigerant leakage (check for leaks); 2. The heat exchange efficiency of the evaporator: 2.1 Check the oil level (to determine if there is oil leakage that could affect heat exchange in the evaporator); 2.2 Issues related to the flow rate of the refrigerant pump; 2.3 Scaling problems in the evaporator; 2.4 Problems related to the concentration of the refrigerant; 3. Check for water in the refrigerant (which can cause blockages); 4. Examine the opening degree of the suction valve; 5. Issues with the expansion valve. http://bbs.hcbbs.com/data/attachment/forum/201709/22/080628uqt7vees7mohbobz.jpg ================================ Promotion: “Creative Ideas for Energy Savings” in the petrochemical industry – Phase 2 of this initiative is currently underway. http://bbs.hcbbs.com/thread-1666758-1-1.html (Source: Haichuan Chemical Industry Forum) “My Technical Upgrades” in the coal chemical industry, 2017: http://bbs.hcbbs.com/thread-1786290-1-1.html (Source: Haichuan Chemical Industry Forum)
Reasons: a. The evaporation temperature is too low, resulting in a large temperature difference for heat exchange； b. Insufficient system refrigerant ； c. Low opening degree of the liquid supply valve ； Excessive backflow line resistance ； d. The intake shut-off valve is partially open or faulty ； e. The intake filter is dirty or clogged with ice. Treatment 1) Overhaul the evaporator, increase the coolant flow rate, and reduce the compressor load. 2) Leak detection and refrigerant charging. 3) Increase the liquid supply and check the pipelines. 4) Open the intake valve or check the valve head. 5) Clean the filter screen and remove moisture.
Answer: (1) Insufficient or leaking refrigerant. (2) The flow rate of the refrigerant water is insufficient, resulting in less heat absorbed; this leads to poor evaporation of the refrigerant. Moreover, the vapor is supercooled and supersaturated, which facilitates wet compression. This is manifested by a decrease in the pressure difference between the inlet and outlet fluids of the unit, an increase in the temperature difference, a low suction temperature, and frosting at the suction port. (3) If the evaporator becomes clogged, heat exchange is impaired and the refrigerant cannot evaporate; the consequences are similar to those of a water shortage, with the difference being that the pressure difference between the inlet and outlet water increases, and frosting may also occur at the suction port. Therefore, the unit should be backwashed regularly. (4) Electrical faults cause false alarms. False alarms caused by moisture-induced short circuits or poor contacts in the low-voltage protection relay, damage to the unit’s electronic board, or communication failures. (5) Low-pressure faults can also occur when the machine is started to operate in conditions of low external temperatures and very low cooling water temperatures ； During unit operation, a low-pressure fault can also occur due to insufficient preheating, resulting in a low temperature of the refrigeration oil and inadequate separation of the refrigerant.
1. Contaminants in the liquid supply pipe, expansion valve, or filter of the refrigeration system, excessive restrictions on flow, a malfunctioning float valve, a low volume of ammonia circulation within the system, an insufficient height difference for liquid supply in the intercooler, or too small a pipe diameter – all of these can result in too low an intake pressure for the compressor. 2. Insufficient refrigerant charge or supply in the refrigeration system, as well as improper adjustment of the throttle valve, can all cause low suction pressure in the plastic molding machine. 3. If the evaporator piping is too long, or if too many compressors are used in parallel with an improperly designed suction manifold, this can also result in low suction pressure in the compressors. 4. An excessive oil content in the fluorocarbon system for easily soluble oils reduces the suction pressure. 5. Thick frosting on the warehouse evaporator or oil accumulation on its inner walls increases the thermal resistance, resulting in a lower suction pressure.
It may be because heat transfer in the evaporator is hindered, resulting in less heat absorption; this leads to insufficient evaporation of the refrigerant, low pressure, and low temperature as well. Check the evaporator fins for frost or water, or dust coverage, and ensure that the inlet pipes are not blocked
1. Contaminants in the liquid supply pipe, expansion valve, or filter of the refrigeration system, excessive restrictions on flow, a malfunctioning float valve, a low volume of ammonia circulation within the system, an insufficient height difference for liquid supply in the intercooler, or too small a pipe diameter – all of these can result in too low an intake pressure for the compressor. 2. Insufficient refrigerant charge or supply in the refrigeration system, as well as improper adjustment of the throttle valve, can all cause low suction pressure in the plastic molding machine. 3. If the evaporator piping is too long, or if too many compressors are used in parallel with an improperly designed suction manifold, this can also result in low suction pressure in the compressors. 4. An excessive oil content in the fluorocarbon system for easily soluble oils reduces the suction pressure. 5. Thick frosting on the warehouse evaporator or oil accumulation on its inner walls increases the thermal resistance, resulting in a lower suction pressure.
I’ll mention a few possible reasons for low suction pressure: 1. The inlet filter is clogged. 2. The inlet shut-off valve is faulty, or the process flow wasn’t checked carefully enough and the valve isn’t fully open, resulting in low inlet pressure. 3. The slide valve has failed or there’s a problem with the level load adjustment. 4. The worst one of all — faulty instrument readings, false signals! !
1. Contaminants in the liquid supply pipe, expansion valve, or filter of the refrigeration system, excessive restrictions on flow, a malfunctioning float valve, a low volume of ammonia circulation within the system, an insufficient height difference for liquid supply in the intercooler, or too small a pipe diameter – all of these can result in too low an intake pressure for the compressor. 2. Insufficient refrigerant charge or supply in the refrigeration system, as well as improper adjustment of the throttle valve, can all cause low suction pressure in the plastic molding machine. 3. If the evaporator piping is too long, or if too many compressors are used in parallel with an improperly designed suction manifold, this can also result in low suction pressure in the compressors. 4. An excessive oil content in the fluorocarbon system for easily soluble oils reduces the suction pressure. 5. Thick frosting on the warehouse evaporator or oil accumulation on its inner walls increases the thermal resistance, resulting in a lower suction pressure.
The pipeline is blocked, the expansion valve is damaged, the refrigerant flow decreases, the chilled water flow decreases, and the heat exchange efficiency of the evaporator is reduced
Answer: (1) Insufficient or leaking refrigerant. (2) The flow rate of the refrigerant water is insufficient, resulting in less heat absorbed; this leads to poor evaporation of the refrigerant. Moreover, the vapor is supercooled and supersaturated, which facilitates wet compression. This is manifested by a decrease in the pressure difference between the inlet and outlet fluids of the unit, an increase in the temperature difference, a low suction temperature, and frosting at the suction port. (3) If the evaporator becomes clogged, heat exchange is impaired and the refrigerant cannot evaporate; the consequences are similar to those of a water shortage, with the difference being that the pressure difference between the inlet and outlet water increases, and frosting may also occur at the suction port. Therefore, the unit should be backwashed regularly. (4) Electrical faults cause false alarms. False alarms caused by moisture-induced short circuits or poor contacts in the low-voltage protection relay, damage to the unit’s electronic board, or communication failures. (5) Low-pressure faults can also occur when the machine is started to operate in conditions of low external temperatures and very low cooling water temperatures ； During unit operation, a low-pressure fault can also occur due to insufficient preheating, resulting in a low temperature of the refrigeration oil and inadequate separation of the refrigerant.