Classification of screw chiller
A total of six different classifications can be made according to the air conditioning function, different refrigerants, condensation methods, the seal structure of the compressor, the structure of the evaporator, and the screw refrigeration compressor:
1. Divided into single cooling type and heat pump type according to air conditioning function.
2. According to the refrigerant used, it is divided into R134a and R22.
3, according to its condensation method is divided into water-cooled screw chiller and air-cooled screw chiller!
4. According to the seal structure of the compressor, it is divided into open type, semi-closed type and fully closed type.
5. Divided into ordinary type and full liquid type according to the structure of the evaporator
6. Classified according to different screw refrigeration compressors used in screw chiller. Screw refrigeration compressors are divided into two types: twin screw and single screw. The twin-screw refrigeration compressor has a pair of rotors with helical teeth that are coupled to each other and rotate in opposite directions. The single-screw refrigeration compressor has a rotor screw machined with 6 spiral grooves on the outer cylindrical surface. On the left and right sides of the butterfly and the rod, the identical planetary gears with 11 racks are installed vertically! A detailed understanding of the classification of screw chiller is undoubtedly a great help for friends who need to purchase screw chiller!
Second, the principle and application of screw chiller
螺杆式冷水机组的原理 1 Principle of screw chiller
The screw chiller is named as the screw chiller because of its key component-the compressor uses the screw type. The state of the unit from the evaporator is a gas refrigerant; after the compressor is adiabatically compressed, it becomes a high temperature and high pressure state. The compressed gas refrigerant is cooled and condensed in the condenser under constant pressure. After the condensation, it changes to a liquid refrigerant, which is then expanded to a low pressure by a throttle valve and becomes a gas-liquid mixture. Among them, the liquid refrigerant at low temperature and low pressure absorbs the heat of the material to be cooled in the evaporator and becomes a gaseous refrigerant again. Gaseous refrigerant re-enters the compressor through the pipeline and begins a new cycle. These are the four processes of the refrigeration cycle. It is also the main working principle of screw chiller.
螺杆式冷水机组应用 Application of 2 screw chiller
The power of screw chiller is relatively larger than that of scroll type. It is mainly used in central air-conditioning systems or large industrial refrigeration.
(1) Twin-screw refrigeration compressor
The twin screw refrigeration compressor is an energy-adjustable fuel injection compressor. Its three continuous processes of suction, compression, and exhaust are achieved by a periodic volume change when a pair of meshing male and female rotors in the body rotate. Generally, the male rotor is a driving rotor, and the female rotor is a driven rotor. Main components: double rotor, body, main bearing, shaft seal, balance piston and energy regulating device. The capacity is 15 ～ 100% stepless adjustment or two or three-stage adjustment. The hydraulic piston is used to increase or decrease the load. Conventional use: radial and axial are rolling bearings; open type is equipped with oil separator, oil storage tank and oil pump; closed type is used for differential pressure oil supply for lubrication, injection, cooling and drive piston piston capacity adjustment. Inspiratory process: the gas enters the interdental volume of the yin-yang rotor through the suction port. Compression process: When the rotor rotates, the volume between the male and female rotors 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
Compression is generated by the meshing of an active rotor and two star wheels. Its three continuous processes of suction, compression and exhaust are realized by the periodic volume change when the rotor and the star wheel rotate. The rotor has six teeth and the star wheel has eleven teeth. The main components are a rotor, two star wheels, a body, a main bearing, and an energy regulating device. The capacity can be adjusted steplessly from 10% to 100% and three or four stages. Inspiratory process: the gas enters the rotor slot through the intake port. As the rotor rotates, the star wheel enters into a state of meshing with the cogging of the rotor in turn, and the gas enters the compression cavity (the closed space formed by the curved surface of the rotor cogging, the inner cavity of the casing and the tooth surface of the star gear). Compression process: As the rotor rotates, the volume of the compression chamber is continuously reduced, and the gas is compressed until the leading edge of the compression chamber is turned to the exhaust port. Exhaust process: After the leading edge of the compression chamber is turned to the exhaust port and exhaust is started, a working cycle is completed. Due to the symmetrical arrangement of the star wheels, the compression occurs twice each time the cycle rotates, and the exhaust volume is correspondingly twice that of the above-mentioned one-cycle cycle.
Analysis of common faults of screw chiller
Aiming at the use of screw chiller units, some of the common fault problems that friends will have are high pressure faults, low pressure faults, low valve temperature faults, compressor overheating faults, communication faults, etc., but it is necessary to effectively solve these fault problems. The main working principle of the screw chiller is linked first, and among them, the four processes of the refrigeration cycle are the most important. After the compressor is adiabaticly compressed, it becomes a high temperature and high pressure state. The compressed gas refrigerant is cooled and condensed in the condenser under constant pressure. After the condensation, it changes to a liquid refrigerant, which is then expanded to a low pressure by a throttle valve and becomes a gas-liquid mixture. Among them, the liquid refrigerant at low temperature and low pressure absorbs the heat of the material to be cooled in the evaporator and becomes a gaseous refrigerant again. Gaseous refrigerant re-enters the compressor through the pipeline and begins a new cycle.
高压故障 1 high voltage fault
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 should be set to 2.00MPa. If the pressure is too high for a long period of time, it will cause the compressor to run too much current, burn the motor easily, and easily cause damage to the compressor's exhaust port valve. What should be done is to control the size of the compressor exhaust pressure within a safe range. Inside!
The compressor suction pressure is too low, causing the low-voltage protection relay to operate. The compressor suction pressure reflects the evaporation pressure. The normal value should be 0.40 ~ 0.60MPa, and the protection value should be set to 0.20MPa. If the suction pressure is low, the amount of return air is small and the cooling capacity is insufficient, resulting in a waste of electrical energy. Poor heat dissipation for the compressor motor of the return air cooling will easily damage the motor! The solution is the same as the high-pressure fault, try to keep the compressor within the normal pressure range.
低阀温故障 3 Low valve temperature failure
The expansion valve outlet temperature reflects the evaporation temperature, which is a factor that affects heat transfer. Generally, the temperature difference between the outlet temperature of the expansion valve and the refrigerant water is 5.0 ~ 6.0 ° C. When a low valve temperature fault occurs, the compressor will stop. When the valve temperature rises, it will automatically resume operation. The protection value is -2.0 ℃.
压缩机过热故障 4 Compressor overheating fault
The thermistor is embedded in the compressor motor winding, and 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 be activated to cut off the unit operation. At the same time, an overheating fault will be displayed and the TH fault indicator will be on.
通信故障 5 communication failure
The computer controller controls each module through the communication line and the main interface board. The main cause of the communication failure is the poor contact or disconnection of the communication line, especially the interface is affected by moisture and oxidation. In addition, the unit electronic board or the general interface Board failure, improper selection of address dial switch, power failure can cause communication failure. The above five kinds of failure phenomena are the most common, and understanding these failure phenomena, judgment ability, and solutions has an irreplaceable effect on extending the service life of screw chiller!
Fourth, the selection of screw chiller
1. The main control parameters of screw chiller are refrigeration performance coefficient, rated cooling capacity, input power and refrigerant type.
2. The selection of chiller should be considered according to the cooling load and application. For a refrigeration system with low load and long operating conditions, a multi-head piston compressor or screw compressor should be selected to facilitate adjustment and energy saving.
3. When selecting a chiller, priority should be given to the unit with a higher coefficient of performance. According to statistics, the operating time of general chillers under 100% load accounts for less than 1/4 of the total operating time. 100%, 75%, 50%, 25% of total operating time
The operating time ratio of the load is roughly 2.3%, 41.5%, 46.1%, and 10.1%. Therefore, when selecting a chiller, priority should be given to models with relatively flat efficiency curves. At the same time, the adjustment range of the chiller load should be considered in the design and selection. The multi-head screw chiller has excellent partial load performance and can be selected according to actual conditions.
4. When selecting a chiller, pay attention to the conditions of nominal working conditions. The actual chiller output is related to the following factors:
a) Cold water outlet temperature and flow;
b) Inflow temperature, flow rate and fouling factor of cooling water.
5. When selecting a chiller, pay attention to the normal working range of this type of unit, mainly because the current limit of the main motor is the current value of the shaft power under nominal conditions.
6. It should be noted in the design and selection: under nominal operating flow, the outlet temperature of cold water should not exceed 15 ° C, and the outdoor dry bulb temperature of air-cooled units should not exceed 43 ° C. If the above range must be exceeded, the compressor's Whether the range of use is allowed, and the power of the main motor is sufficient.
The computer controller controls each module through the communication line and the main interface board. The main cause of the communication failure is the poor contact or disconnection of the communication line, especially the interface is affected by moisture and oxidation. In addition, the unit electronic board or the general interface Board failure, improper selection of address dial switch, power failure can cause communication failure.