Detailed knowledge of screw chiller system

Detailed knowledge of screw chiller system

How to improve the service life of screw chillers and reduce the failure rate of screw chillers? This problem has been plagued by many friends, and it is also a relevant knowledge module they want to know very much. To solve this problem, you must have a more comprehensive understanding of screw chillers. Only the relevant knowledge of mechanical equipment and the understanding of its performance , Then the problem will be solved naturally. Today, the editor will explain in detail the classification, principle and application of screw chillers, common fault analysis, selection points and troubleshooting, and answer everyone’s doubts in all directions.

　　 1. Classification of screw chillers

　　 This article mainly focuses on the types of screw chillers! According to the air conditioner function, the different refrigerant, the condensation method, the sealing structure of the compressor, the structure of the evaporator, and the screw refrigeration compressor, there can be a total of six different categories. The six categories are listed in detail below. Information!

　　 1. According to the air conditioning function, it is divided into single cooling type and heat pump type.

　　 2. According to different refrigerants, it can be divided into R134a and R22.

　　3. According to its condensation method, it is divided into water-cooled screw chiller and air-cooled screw chiller!

　　4. According to the sealed structure of the compressor, it is divided into open type, semi-closed type and fully enclosed type.

　　 5. According to the structure of the evaporator, it is divided into ordinary type and full liquid type

　　 6. According to the different screw refrigeration compressors used in screw chillers. Screw refrigeration compressors are divided into twin screw and single screw. The twin-screw refrigeration compressor has a pair of rotors with helical teeth that gnaw together and rotate in opposite directions. The single-screw refrigeration compressor has a rotor screw with 6 spiral grooves on the outer cylindrical surface. The same planetary gears with 11 racks are installed vertically on the left and right sides of the butterfly and rod! A detailed understanding of the classification of screw chillers is undoubtedly a great help for friends who need to purchase screw chillers!

　　 2. The principle and application of screw chillers

　　1. Principle of screw chiller

　　 Screw chiller is named screw chiller because of its key component-the compressor adopts screw type. The state of the unit from the evaporator is gas refrigerant; after adiabatic compression by the compressor, it becomes a high temperature and high pressure state. The compressed gas refrigerant in the condenser is cooled and condensed at equal pressure, and then changes into a liquid refrigerant after condensation, and then expands to a low pressure through a throttle valve and becomes a gas-liquid mixture. Among them, the liquid refrigerant under low temperature and low pressure absorbs the heat of the substance to be cooled in the evaporator and becomes a gaseous refrigerant again. The gaseous refrigerant re-enters the compressor through the pipeline and starts a new cycle. These are the four processes of the refrigeration cycle. It is also the main working principle of screw chiller.

　　2, screw chiller application

　　The power of screw chiller is relatively larger than that of scroll type, which is mainly used in central air-conditioning system or large-scale industrial refrigeration

　　 (1) Twin-screw refrigeration compressor: Twin-screw refrigeration compressor is an energy-adjustable oil-injected compressor. Its three continuous processes of inhalation, compression, and exhaust are realized by the periodic volume changes produced by a pair of intermeshing female and male rotors in the body rotating. Generally, the male rotor is the active rotor and the female rotor is the driven rotor. Main components: double rotor, body, main bearing, shaft seal, balance piston and energy adjustment device. The capacity is 15～100% stepless adjustment or two or three-stage adjustment, adopting hydraulic piston increase and decrease load. Conventional use: both radial and axial bearings are rolling bearings; the open type is equipped with an oil separator, oil storage tank and an oil pump; the closed type provides differential pressure oil for lubrication, oil injection, cooling and piston movement that drives the slide valve capacity adjustment. Inhalation process: The gas enters the volume between the teeth of the yin and yang rotors through the inhalation ports. Compression process: When the rotor rotates, the volume between the female and male rotor teeth is connected (V-shaped space). Due to the mutual meshing of the teeth, the volume gradually decreases and the gas is compressed. Exhaust process: The compressed gas is moved to the exhaust port to complete a working cycle.

　　 (2) Single screw refrigeration compressor

　　 uses the meshing of an active rotor and two star wheels to produce compression. Its three continuous processes of suction, compression, and exhaust are realized by periodic volume changes when the rotor and star wheel rotate. The number of rotor teeth is six, and the star wheel is eleven teeth. The main components are a rotor, two star wheels, body, main bearing, and energy adjustment device. The capacity can be adjusted steplessly from 10%-100% and three- or four-stage adjustment. Inhalation process: The gas enters the rotor cogging through the inhalation port. With the rotation of the rotor, the star wheel enters the state of meshing with the rotor tooth slot in turn, and the gas enters the compression cavity (the enclosed space formed by the rotor tooth slot surface, the inner cavity of the casing and the star wheel tooth surface). Compression process: As the rotor rotates, the volume of the compression chamber decreases, and the gas is compressed until the front of the compression chamber turns to the exhaust port. Exhaust process: After the front of the compression chamber is turned to the exhaust port, the exhaust starts to complete a working cycle. Due to the symmetrical arrangement of the star wheel, the cycle will be compressed twice every time it rotates, and the displacement is correspondingly twice that of the aforementioned cycle.

　　 Three, common failure analysis of screw chiller

In the process of using screw chillers, friends will find some common failures such as high pressure failure, low pressure failure, low valve temperature failure, compressor overheating failure, communication failure, etc. However, it is necessary to effectively solve these failures First link the main working principle of the screw chiller, and among them are the four processes of the refrigeration cycle. After adiabatic compression by the compressor, it becomes a high temperature and high pressure state. The compressed gas refrigerant in the condenser is cooled and condensed at equal pressure, and then changes into a liquid refrigerant after condensation, and then expands to a low pressure through a throttle valve and becomes a gas-liquid mixture. Among them, the liquid refrigerant under low temperature and low pressure absorbs the heat of the substance to be cooled in the evaporator and becomes a gaseous refrigerant again. The gaseous refrigerant re-enters the compressor through the pipeline and starts a new cycle. After understanding the main working principle of the screw chiller, let's analyze the common failures of the screw chiller.

1. High voltage failure

　　 The compressor discharge pressure is too high, causing the high pressure protection relay to operate. The compressor discharge pressure reflects the condensing pressure, the normal value should be 1.40~1.60MPa, and the protection value is set to 2.00MPa. If the pressure is too high for a long time, it will cause the compressor to run too much current, easily burn the motor, and easily cause damage to the compressor exhaust valve. Naturally, what should be done is to control the compressor exhaust pressure within a safe range. Inside!

2. Low voltage fault

　　 The suction pressure of the compressor is too low, causing the low-pressure protection relay to operate. The suction pressure of the compressor reflects the evaporation pressure, the normal value should be 0.40~0.60MPa, and the protection value is set to 0.20MPa. If the suction pressure is low, the return air volume will be small, and the refrigeration capacity will be insufficient, resulting in a waste of electric energy. For the return air cooling compressor motor, the heat dissipation is poor and the motor is easily damaged! The solution is the same as the high-pressure failure, try to keep the compressor in the normal pressure range.

　　3. Low valve temperature fault

　　 The outlet temperature of the expansion valve reflects the evaporation temperature, which is a factor that affects the heat exchange. Generally, the difference between it and the outlet temperature of the refrigerant water is 5.0~6.0℃. When a low valve temperature failure occurs, the compressor will stop, and when the valve temperature rises, it will automatically resume operation with a protection value of -2.0°C.

　　4. Compressor overheating failure

　　Thermistor is embedded in the compressor motor winding, the resistance is generally 1kΩ. When the winding is overheated, the resistance value will increase rapidly. When it exceeds 141kΩ, the thermal protection module SSM will act to cut off the operation of the unit. At the same time, the overheating fault will be displayed and the TH fault indicator will be on.

　　 5. Communication failure

The control of each module by the computer controller is realized through the communication line and the main interface board. The main cause of communication failure is poor contact or open circuit of the communication line, especially the interface is damp and oxidized to cause poor contact, and the unit electronic board or the main interface Board failure, improper selection of the address dial switch, and power failure can cause communication failure. The above five failure phenomena are common in z*, and understanding these failure phenomena, judgment capabilities, and solutions has an irreplaceable effect on prolonging the service life of the screw chiller!

　　 Fourth, the selection points of screw chillers and troubleshooting

　　 Product selection points

　　1. The main control parameters of the screw chiller are the refrigeration performance coefficient, rated refrigeration capacity, input power and refrigerant type, etc.

　　 2. The selection of chillers should be considered according to the cooling load and purpose. For refrigeration systems under low-load operating conditions for a long time, multi-head piston compressor units or screw compressor units should be selected for easy adjustment and energy saving.

　　 3. When selecting chillers, give priority to units with higher coefficient of performance. According to statistics, the average operating time of chillers at 100% load throughout the year accounts for less than 1/4 of the total operating time. 100%, 75%, 50%, 25% of the total operating time

　　The operating time ratio of the load is roughly 2.3%, 41.5%, 46.1%, and 10.1%. Therefore, when selecting chillers, priority should be given to models with a relatively flat efficiency curve. At the same time, the load adjustment range of the chiller should be considered when designing and selecting. Multi-head screw chillers have excellent partial load performance and can be selected according to actual conditions.

　　 4. When choosing a chiller, pay attention to the conditions of the nominal working condition. The actual cooling capacity of the chiller is related to the following factors:

　　A) Cold water outlet temperature and flow rate;

　　B) The inlet temperature, flow rate and fouling coefficient of the cooling water.

　　5. When choosing a chiller, pay attention to the normal operating range of this type of unit, mainly because the current limit of the main motor is the current value of the shaft power under the nominal operating condition

6. Attention should be paid in the design and selection: under the nominal working condition flow, the outlet temperature of the cold water should not exceed 15℃, and the outdoor dry bulb temperature of the air-cooled unit should not exceed 43℃. If it must exceed the above range, you should understand the compressor Whether the scope of use is allowed and whether the power of the main motor is sufficient.

The control of each module by the computer controller is realized through the communication line and the main interface board. The main cause of communication failure is poor contact or open circuit of the communication line, especially the interface is damp and oxidized to cause poor contact, and the unit electronic board or the main interface Board failure, improper selection of the address dial switch, and power failure can cause communication failure.