Cold storage parallel units can be widely used in different industries such as food processing, quick freezing and refrigeration, medicine, chemical industry and military scientific research. Generally, compressors can use various refrigerants such as R22, R404A, R507A, 134a, etc. Depending on the application, the evaporation temperature can be from +10°C to -50°C.
Under the control of PLC or special controller, the parallel unit can always keep the compressor in the most efficient state by adjusting the number of compressors to match the changing cooling demand, so as to achieve the purpose of maximum energy saving.
Unit structure
1. Compressor
Semi-hermetic piston compressor: It is the most widely used and mature compressor at present. The refrigerant vapor enters from the suction port on the motor side, and flows through the coil, crankcase, and suction valve plate of the valve plate into the piston cylinder. It is then compressed in the piston cylinder, and when the exhaust valve plate on the valve plate opens, the gas is discharged to the high pressure side and flows to the oil separator or condenser.
The long-term shutdown of the piston compressor should keep the crankcase heater working for a period of time before starting up!
2, oil separator
It plays the role of separating the refrigerant oil and refrigerant gas in the exhaust gas.
Typically, each compressor has an oil separator. The high temperature and high pressure refrigerant vapor and refrigeration oil flow in from the oil inlet, the refrigeration oil is left at the bottom of the oil separator, and the refrigerant vapor and a very small amount of refrigeration oil flow out from the oil inlet and enter the condenser.
3. Liquid reservoir
It can ensure a stable refrigerant liquid flow to the end.
The accumulator is equipped with a liquid level indicator, which can observe the liquid level change and whether the refrigerant in the system is too much or too little according to the load.
4. Oil storage
Provides stable refrigeration oil for compressor operation.
The oil accumulator is equipped with an oil level indicator, which can be used to observe the oil level change and whether the refrigeration oil in the system is too much or too little according to the compressor on-off condition and the number of on-off stations.
If there is too much or too little refrigeration oil after the unit has been running normally for a period of time, the refrigeration oil can be released or supplemented through the angle valve on the oil accumulator.
5. Main valve parts
1) Solenoid valve: The solenoid valve coil is energized or de-energized to realize the automatic on-off of the pipeline.
Usually, the control system gives the on-off signal to realize automation.
2) Carbon steel globe valve: a valve that manually shuts off the pipeline, generally used for larger pipelines.
3) Ball valve: a valve that manually shuts off the pipeline, generally used for small copper pipelines.
4) Hand valve: a valve that manually shuts off the on-off of the pipeline, generally used for small copper pipelines, such as oil pipes.
5) Pressure gauge: Each unit is equipped with a set of pressure gauges, which are high pressure pressure gauge and low pressure pressure gauge respectively. Used to monitor system pressure and correct sensor pressure.
6. Control system
The common PLC (or single-chip microcomputer) of the parallel unit control system is equipped with a touch screen, a Chinese operation interface, and a touch keyboard, which has the advantages of simple operation, easy learning and use.
Multi-level authority can be set by touch key, which can control the start and stop of compressor and condensing fan, and can be forced to run, and has the function of delaying exit from forced state, which can effectively prevent the system from running in forced state for a long time. as a result of.
The parallel units and condensers all adopt the control method of cyclic start-up, energy adjustment and other function conversion, which can realize the uniform wear of each compressor. The start and stop of the compressor and the condensing fan are controlled by the computer, the system pressure is evenly adjusted, the pressure fluctuation of the refrigeration system is minimized, and the system works in the best state, thereby improving the working efficiency of the refrigeration system.
Through the touch screen, the running time and operation status of each compressor can be displayed, and the real-time curve and historical curve of the actual return steam pressure can be displayed, which is convenient for analyzing the cooling effect of the system.
The alarm status of the system can be displayed and recorded through the touch screen, and the control system is provided with upper and lower limit alarms for the return steam pressure, and real-time monitoring of the return steam pressure and supply liquid pressure is convenient for analyzing the operation of the refrigeration system, which is conducive to hidden dangers early detection and early prevention.
The parallel unit controller can also be networked to achieve remote monitoring and control according to customer needs.
7. Protection device
The performance of the protection device directly affects whether the machine and system can work safely and stably.
It is recommended to choose those provided by world-renowned professional refrigeration accessories manufacturers.
1) Safety valve
It is generally set at the top of the pressure vessel (liquid accumulator, water-cooled condenser, evaporative condenser), and the opening pressure is 2.4MPa (350 PSIG).
2) Air release valve
It is generally installed on the top of the pressure vessel (liquid accumulator, water-cooled condenser, evaporative condenser), which can release harmful non-condensable gases in the system.
In addition, it is used as supplementary refrigerant and pressure measurement when overhauling the system.
Usually the valve should be closed, and the interface leading to the outside should be tightly sealed with a copper cap.
3) Liquid supply, return steam and oil filter
Liquid supply and return steam filter: It can efficiently remove the residual water, impurities and acidic substances in the system, and the filter element of the unit can be replaced.
4) Oil filter: Each half-sealed piston parallel unit is equipped with an oil filter, which can remove impurities in the oil circuit
5) Dual pressure controller
Before the unit is running, set the high and low pressure protection values. Ensure that a single compressor operates within a safe pressure range; when it operates beyond the safe range, it is recommended to manually reset it after the pressure is restored; it is strictly forbidden to reset and keep the compressor running without identifying the cause!
6) Crankcase heater
Each piston compressor has its own crankcase heater, which is used to drive off the refrigerant liquid in the crankcase refrigerated oil when the compressor is stopped.
7) Oil pressure differential switch (electronic oil pressure switch and mechanical oil pressure switch)
Each piston compressor is equipped with an oil differential switch to prevent the compressor from running for a long time when the oil pressure differential is too low (in some cases, lack of oil).
If the oil pressure difference is too low, the oil pressure difference switch will act and the compressor will stop. After confirming the cause of the low oil pressure difference and solving it, press the red button to reset.
8) Oil level controller
According to the oil level sensing part, the oil level of the compressor crankcase is sensed to control the opening and closing of the oil filling port and adjust the oil level of the compressor.
Electronic oil level controller: According to the oil level sensing component sensing the oil level of the compressor crankcase, it controls the opening and closing of the oil filling port and adjusts the oil level of the compressor.
9) SE-B2 protection device
Common BITZER piston compressors are equipped with a SE-B2 protection device, which provides motor/exhaust overheat protection, compressor start-stop frequency protection, and ensures that the compressor runs under safe working conditions.
Note: If the protection device of the compressor works, it means that the compressor is overloaded, lacks oil or is running under conditions that are not allowed to operate. The reason must be found out and eliminated in time, otherwise it may greatly reduce the life of the compressor and the unit. performance
10) Oil circulation
For common piston refrigeration compressor units using refrigerant R22, select suitable refrigeration oil. The lubricating oil of the compressor is supplied by an external container which is also used as an oil accumulator. The oil from the compressor exhaust is separated by the oil separator and then flows to the oil accumulator, oil filter, oil circuit solenoid valve, and oil level control. compressor, the cycle is steadily returned to the compressor crankcase.
8. Condenser part
The important heat exchange equipment in the refrigeration system, the heat is transferred from the high temperature and high pressure superheated refrigerant vapor to the condensing medium through the condenser, and the temperature of the refrigerant vapor also gradually drops to the saturation point and condenses into a liquid. Common condensing media are air and water. The condensing temperature is the temperature at which the refrigerant vapor condenses into a liquid.
1) Evaporative condenser
Evaporative condensers have the advantages of high heat transfer coefficient, large heat rejection, and wide application range.
When the ambient temperature is relatively low, the fan operation is stopped, and only the water pump can be turned on to condense the refrigerant with water alone.
When the temperature drops below freezing point, attention should be paid to the antifreeze problem of water.
When the system load is small, on the premise of ensuring that the condensing pressure is not too high, the evaporative cooling circulating pump can be stopped, and only air cooling can be used. The evaporative cooling inlet air deflector should be completely closed. The precautions when using the water pump are the same as those of the water-cooled condenser.
When using an evaporative condenser, it should be noted that the presence of non-condensable gases in the system will significantly reduce the heat exchange effect of evaporative condensation, resulting in high condensation pressure. low temperature system.
The pH of the circulating water should always be maintained between 6.5 and 8.
2) Air-cooled condenser
The air-cooled condenser has the advantages of convenient construction and only need to provide power for operation.
The wind condenser can be installed outdoors or on the roof, which reduces the occupation of the effective space and reduces the requirements for the user's installation site. During long-term operation, avoid placing sundries around the condenser so as not to affect the air circulation. Regularly check whether there are oil stains, deformation damage and other suspected leakage phenomena on the fins. Regularly use high-pressure water guns for flushing. Be sure to cut off the power and pay attention to safety when flushing.
Generally, the pressure-controlled condensing fan is used to start and stop. Because the condenser runs outdoors for a long time, dust, sundries, fluff, etc. easily flow through the coil and fins with the air, and adhere to the fins over time, and finally cause failure. Ventilation increases condensing pressure. Therefore, it is necessary to regularly check and keep the fins of the air-cooled condenser clean.
3) Water-cooled condenser
Horizontal shell and tube condenser: The advantages of horizontal shell and tube condenser are high heat transfer coefficient and less cooling water consumption. The upper side of the condenser end cover is equipped with a venting cock to release air when it is filled with water; the lower part is equipped with a water-draining cock to drain the water when the condenser is out of use in winter, so as to avoid freezing and cracking of the heat transfer tube.
Attention should be paid to the use of the water pump: when starting the water injection, the exhaust valve should be opened to remove the air accumulated in the pipe; a check valve should be installed on the pump outlet pipe to prevent backflow; the idling of the water pump will cause great damage to it. The cooling water flow should be ensured during use. When the cooling tower is running, ensuring the water quality of the cooling water system is an extremely important issue, and the normal operation of the water treatment instrument should be ensured.
9. Evaporator, expansion valve part
Evaporator is another heat exchange equipment in refrigeration equipment. For refrigeration system, it is a heat exchanger for refrigerant to absorb heat from outside the system.
In the evaporator, the liquid of the refrigerant boils at a lower temperature, converts it into vapor, and absorbs the heat of the object or medium being cooled. Therefore, the evaporator is a device that produces and outputs cold capacity in the refrigeration system. The evaporation temperature is the temperature at which the refrigerant liquid evaporates into a gas.
1) Air cooler
For example, the evaporator is installed in a channel, and the air outside the tube is transported by a fan, which is customarily called an air cooler (or a cooler).
The basic structure of the air-cooled finned evaporator is similar to that of the condenser. It consists of fan blades, fan motors, copper tubes, aluminum fins and defrosting elements. The main purpose of aluminum fins is to increase the heat exchange area of the evaporator.
When the evaporator operates at sub-freezing temperatures, ice and frost will condense between the coils and fins, and unless removed, the airflow through the coils will eventually be blocked.
Periodic defrost cycles are necessary in order for refrigeration equipment to operate continuously under conditions where frost is likely to build up.
2) Thermal expansion valve
A thermal expansion valve regulates the flow of refrigerant through the evaporator to maintain a preset temperature difference or degree of superheat between the evaporating refrigerant and the refrigerant vapor at the evaporator outlet. When the temperature of the refrigerant gas leaving the evaporator changes, the temperature bulb of the expansion valve senses its temperature and adjusts the flow of refrigerant through the expansion valve as needed.
3) Filter
End filter: installed after the end ball valve, to prevent particulate matter from flowing into the end solenoid valve and expansion valve and affecting the valve action.
4) Fan and end valve assembly
A. Liquid supply valve assembly
The liquid supply valve assembly is composed of a ball valve, a filter, and a solenoid valve expansion valve. The refrigerant enters the fan in this order, absorbs heat in the evaporator and evaporates into refrigerant vapor.
B. Return valve assembly
The return air pipeline and the return air shut-off valve return to the return air main pipe to the return air side of the unit. See the unit part for solenoid valve, ball valve and carbon steel globe valve.