Cold storage low pressure protection setting and troubleshooting | Method for distinguishing low evaporation pressure and false low pressure alarms
Low pressure protection, also known as evaporation pressure protection, is used to prevent the evaporation pressure from being too low, the evaporation temperature from falling below freezing point, the evaporator from frosting and freezing, and the compressor from operating in extremely low temperature and harsh conditions for a long time.
R404A low-temperature cold storage, with a conventional low pressure shutdown value of 0.05MPa (gauge pressure) and a low pressure reset value of 0.12MPa; The low pressure setting value of the medium high temperature preservation warehouse should be appropriately raised.
There are two types of low pressure protection for the Xitelide unit: mechanical pressure controller and electronic protection for pressure sensors. The electronic version has higher accuracy and supports delay and false alarm prevention. It is commonly used in foreign trade projects.
Low pressure alarm is divided into true low pressure and false low pressure: true low pressure is accompanied by a continuous decrease in storage temperature and insufficient liquid supply to the expansion valve; False low pressure is often caused by blockages in pressure pipelines and ice blockages in sensing capillaries.
Many beginners set the low pressure protection value too low during debugging, causing severe frosting and blockage of the evaporator before shutting it down, resulting in heat exchange failure of the evaporator and prolonged operation of the compressor beyond operating conditions.
The low-pressure differential pressure controller has a delay function, which delays for 30-60 seconds to avoid pressure fluctuations during startup and prevent false alarms and shutdowns due to startup shock.
Refrigerant leakage is the most common root cause of true low pressure: insufficient refrigerant quantity, continuous decrease in evaporation pressure, accompanied by insufficient cooling of the return pipe and weak cooling. Leak detection must be carried out before adding fluorine.
It is recommended to use main pressure sampling for low-voltage protection of parallel units, and each machine head should have independent low-voltage protection for dual protection to avoid single branch blockage and single machine dry burning.
For tropical export projects, do not blindly follow domestic low-pressure parameters. Instead, adjust the local refrigerant saturation pressure curve and adjust the pressure protection value in high-altitude areas.
After a low voltage alarm, do not repeatedly force a reset to power on. Multiple low voltage starts in a row can cause the evaporator to run out of liquid and dry, the exhaust temperature to soar, and accelerate the aging of the motor insulation.
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FAQ
1. What is the conventional low-pressure shutdown setting for R404A low-temperature storage? Shutdown at approximately 0.05MPa, reset to 0.12MPa (gauge pressure).
2. How long is the low-voltage protection delay usually set? 30-60 seconds, avoid transient fluctuations during startup.
3. Common causes of false low voltage alarms? Pressure capillary blockage, ice blockage, sensor malfunction.
Can continuous low voltage repeatedly force reset and startup? Not recommended, high exhaust temperature can damage the motor.
What are the low-pressure characteristics of refrigerant leakage? Low pressure, poor cooling, and no obvious supercooling in the return pipe.
6. What should be done for pressure protection parameters in high-altitude areas? Correction of pressure values is required.
How to do low-voltage sampling for parallel units? Main pipeline sampling+single machine independent low-voltage dual protection.
