1. Experience in construction design of refrigeration system
The importance of piping design
1. When the system is operating normally, a small amount of oil will continue to leave the compressor with the exhaust, and the oil will return to the compressor when the system view is well designed;
2. If there is too much oil in the system, it will have a negative impact on the efficiency of the condenser and evaporator;
3. The oil returning to the compressor is less than the oil leaving the compressor, which eventually damages the compressor;
4. To refuel the compressor, the oil level can only be maintained for a short time;
5. Only the correct pipeline design can maintain a good oil balance in the system.
Suction line design
1. The horizontal suction pipeline should have a slope of more than 0.5% along the direction of refrigerant gas flow;
2. The cross-section of the horizontal suction pipeline must maintain the gas flow rate of not less than 3.6m/s;
3. In the vertical suction pipeline, the gas flow rate must not be less than 7.6-12m/s;
4. The gas flow rate greater than 12m/s cannot significantly improve the oil return, which will produce high noise and lead to a high pressure drop in the suction pipeline;
5. At the bottom of each vertical suction pipeline, a U-shaped oil return bend must be set up;
6. If the height of the vertical suction pipeline exceeds 5m, a U-shaped oil return bend must be set up for every additional 5m;
7. The length of the U-shaped oil return bend should be as short as possible to avoid gathering too much oil.
Evaporator suction line design
1. When the system does not adopt the evacuation cycle; At the outlet of each evaporator, a U-shaped interception bend should be provided. In order to prevent the liquid refrigerant from flowing into the compressor under the action of gravity during shutdown;
2. When the suction riser and the evaporator are connected, a section of horizontal pipe and interception bend should be left in the middle for the installation of the temperature sensing bag; Prevents malfunction of the expansion valve.
Exhaust line design
When the condenser is installed higher than the compressor, at the inlet pipe of the condenser, a U-bend is required to prevent the oil from returning to the exhaust side of the compressor during shutdown and also helps to prevent the liquid refrigerant from flowing from the condenser back to the compressor;
Liquid line design
1. There is usually no special restriction on the flow rate of refrigerant in the liquid pipeline, and when the solenoid valve is used, the flow rate of refrigerant should be less than 1.5m/s;
2. How to ensure that the refrigerant entering the expansion valve is a supercooled liquid;
3. When the pressure of the liquid refrigerant drops to its saturation pressure, a part of the refrigerant will flash into gas.
2. Common knowledge of refrigeration system
Hazards of refrigerant flash gases
1. Reduce the refrigeration capacity of the expansion valve;
2. It will corrode the valve pin and seat of the expansion valve, causing noise;
3. The liquid supply of the expansion valve to the evaporator is abnormal.
Filling volume and oil separator
1. In most refrigeration systems, the refueling capacity of the compressor is sufficient;
2. When the pipeline exceeds 20m, or there are many oil wells in the pipeline, or an oil separator is installed in the system, additional refrigeration oil needs to be replenished;
3. In some refrigeration systems, there is a risk of slow oil return, and when there are multiple evaporators or multiple condensers in parallel, it is recommended to install an oil separator.
Expansion valve/filter dried
1. Expansion valve or filter drier, according to the refrigerant used;
2. When selecting the filter drier, it is necessary to consider the water absorption capacity of the filter drier, the refrigeration capacity of the system and the charging capacity of the refrigerant of the system.
Operating voltage and number of starts
1. The working voltage should be within the specified range;
2. The number of starts cannot be more than 10-12 times/hour;
3. The running time after each start should not be less than 5 minutes to ensure the correct oil return and cooling of the motor, and the system design must ensure the minimum compressor running time.
evaporator
1. The selection of evaporator should match the load of the system and the cooling capacity of the compressor;
2. The heat exchange area is too large, the return gas temperature is high, and the evaporation temperature cannot be reduced;
3. The heat exchange area is too small, and the refrigerant cannot be fully evaporated, resulting in a return liquid.
condenser
1. The selection of the condenser should match the load and refrigeration capacity of the compressor;
2. Refer to the manufacturer's technical data;
3. The heat exchange area is too small, the refrigerant gas cannot be fully condensed, and the exhaust temperature and exhaust pressure increase.
Migration of liquid refrigerants during shutdown
1. After the system shutdown and pressure equalization, the refrigerant condenses in the coldest part of the system;
2. The refrigerant in the system will condense into the compressor crankcase;
3. The refrigerant will be dissolved in the compressor oil, and the refrigerant in the oil is completely saturated;
4. When the compressor starts, the pressure decreases, and the refrigerant evaporates violently, forming oil foam;
5. Cause liquid or oil shock, damage valve plate and valve plate;
6. The oil is diluted by the refrigerant, and the lubrication capacity is greatly reduced.
Prevents migration of liquid refrigerants during shutdowns
1. Adopt gas-liquid separator for return gas pipeline;
2. Install the solenoid valve of the liquid supply pipeline;
3. Crankcase heater is adopted;
4. Turn on the heater 4 hours before the compressor starts.
Cleaning of the system
1. The system is not clean, which is one of the main factors affecting the life of the compressor;
2. When configuring the refrigeration system, it is very important to ensure the cleanliness of the system;
3. Factors that cause system pollution: oxides from brazing and electric welding, pipeline burrs and frustrations, flux and moisture from brazing, etc.;
4. Never drill holes in the pipeline after the installation is completed.
System pressure test
1. It is recommended to use pure dry nitrogen for pressure test;
2. The high-pressure side and the low-pressure side should not exceed the maximum allowable pressure;
System leak detection
1. Pure dry nitrogen and the refrigerant used must be used for leak detection;
2. Do not use oxygen, dry air or acetylene gas and other gases;
3. The pressure of leak detection should not exceed the test pressure.
The system evacuates to remove the moisture
1. The air and moisture in the system produce a high exhaust temperature, which increases the condensation pressure;
2. Cause mechanical and electrical failure of the compressor;
3. Vacuum pumps must be used to evacuate from both ends of the high and low pressure of the system at the same time;
4. The first evacuation is to close the suction and exhaust valves of the compressor;
5. First, a vacuum pump is used to pump to 1500 microns of Hg, and then refrigerant is added to the system through a drying device to destroy the vacuum state;
6. Repeat the above steps again;
7. Open the suction and exhaust valves of the compressor and vacuum the system to 500 microns of mercury;
8. Fill in the refrigerant and turn off the vacuum pump.
System evacuation precautions
1. The compressor must not be used as a vacuum pump to vacuum the system;
2. When the system is in a vacuum state, do not start and transport the compressor in any case, otherwise it will cause the compressor to burn out.
System check and startup
1. Check the electrical wiring to ensure that all are tightened and correct;
2. Observe the oil level of the compressor, the oil level should be higher in the middle of the oil mirror;
3. Dismantle or loosen the transport bracket under the compressor;
4. Check the high pressure and low pressure controller, compressor suction and exhaust valve, oil pressure safety controller, and other safety control devices;
5. Check whether the temperature controller is normal;
6. Mark the refrigerant used in the system;
7. Read the instructions and wiring diagrams and other information, and keep them properly for future reference.
System check and startup
1. The liquid refrigerant must be injected from the high-pressure side of the compressor;
2. Pay attention to the pressure of the system before and during the charging process;
3. Continue to charge until the system has enough refrigerant, do not overcharge;
4. When the system does not reach the normal operation state and the oil level is not kept in the center of the oil mirror, do not let the refrigeration device be in an unmanaged state.
System operation check
1. Check the suction and discharge pressure of the compressor;
2. Check the working condition of the sight glass and expansion valve;
3. Observe the oil level of the compressor crankcase;
4. Check the heat setting value of the thermostatic expansion valve and the position of the temperature sensing bag;
5. Check the voltage and current values of the compressor terminal;
6. Check whether the direction of the evaporator and condenser is correct;
7. Check whether the crankcase heater is normal;
8. Other items that need to be checked