Do cold storage maintenance, you must understand this knowledge!

Do cold storage maintenance, you must understand this knowledge!

1. "Three Preventions" of the Refrigeration System

　　 1. Prevent the evaporation temperature from being too low

　　 The increase in the temperature difference between the evaporating temperature and the warehouse temperature will make the evaporating temperature too low, which will lead to a decrease in the refrigeration coefficient and an increase in energy consumption. It is estimated that under other conditions unchanged, when the evaporation temperature drops by 1°C, it will consume 1 to 2% more electricity. In addition, the increase in temperature difference will increase the dehumidification capacity of the air cooler and reduce the humidity in the warehouse, which will increase the dry consumption of food and reduce the quality of food.

The difference between the evaporation temperature and the warehouse temperature is generally 10°C. The evaporation temperature of the fruit and vegetable cold storage is generally designed to be about -10°C, the freezing temperature is -28°C, and the freezing room is -33°C. In actual operation, many fruits and vegetables are stored The temperature difference of the library is about 15℃.

　　 Causes and solutions for the low evaporation temperature:

　　 The evaporator is too small, increase the evaporator area or replace the evaporator.

　　 The compressor cooling capacity is too large, and the number of compressors to be turned on should be reduced according to changes in the warehouse load.

　　 The evaporator was not defrosted in time, so it must be defrosted in time.

　　 The opening of the expansion valve is too small, and the opening degree of the expansion valve should be increased.

　　2, prevent the condensation pressure from being too high

　　 Prevent the condensing pressure from being too high and the condensing pressure will increase, which will increase the compression function, reduce the cooling capacity, decrease the refrigeration coefficient, and increase the energy consumption. It is generally considered that the economical and reasonable condensation temperature is 3 to 5°C higher than the outlet temperature of the cooling water. Causes and solutions for the increase in condenser pressure:

　　The condenser selected is too small. Replace or add condenser.

　　The number of condensers put into operation is small. Increase the number of operating units.

　　 The cooling water flow is insufficient. Increase the number of pumps and increase the water flow.

　　3. Prevent excessive exhaust temperature

　　 Excessive exhaust temperature will worsen the lubrication of the compressor, increase friction, and increase energy consumption; at the same time, excessive exhaust temperature will increase the heat exchange between the refrigerant gas and the cylinder wall, resulting in a decrease in compressor efficiency. Causes and solutions for excessive exhaust temperature:

　　 The compressor cylinder has poor cooling. Increase cooling water and improve cooling conditions.

　　 The compressor suction superheat is too high, improve the insulation of the suction pipe or increase the liquid supply of the evaporator.

　　 2. Maintenance of refrigeration system

　　 The refrigerant circulating in the system is required to be clean and free of impurities, but it is impossible to be completely clean in actual operation. This is related to the working conditions and the lack of cleanness of the refrigerant added to the system. The impurities that belong to the control include: lubricating oil, air, water, etc. The entry of these impurities into the refrigeration system is extremely detrimental to the work of the refrigeration device.

　　2.1 Lubricant

　　 The lubricating oil should have a proper viscosity. If the viscosity is too large, the flow resistance will be large and the friction work will increase; if the viscosity is too low, the friction surface cannot form an oil film, and the friction force will increase, and the friction work will increase. The viscosity of lubricating oil decreases with increasing temperature, which will cause deterioration of lubrication and increase of friction work. Therefore, when its temperature rises, it should be cooled in time or increase the cooling effect to reduce the oil temperature. When the lubricating oil and refrigerant dissolve each other, ensure smooth oil return, otherwise the compressor will be damaged due to lack of oil; at the same time, the evaporation pressure will drop due to too much oil in the refrigerant, which will eventually lead to a decrease in the refrigeration coefficient

　　2.2 water

　　The way water enters the system:

　　 The air was not evacuated during installation or maintenance, or the air was not fully evacuated.

　　 Evacuate the air during installation or maintenance and install a dryer.

　　 Enter from an unsealed place. Do not have leakage points, and avoid negative pressure operation.

　　There is water in the oil or refrigerant.

　　2.3 Air

When air enters the system, the pressure of the condensate in the system will increase, and the total pressure will increase. The air will also form a gas layer on the surface of the condenser, causing additional thermal resistance, reducing the heat transfer efficiency, and leading to an increase in the condensation pressure and temperature. For every 1kg/cm2 increase in condensing pressure, [this article source: Refrigeration Encyclopedia], power consumption increases by about 6.8%. In addition, the adiabatic index of air (K=1.41) lies in the refrigerant adiabatic index (ammonia k=1.28, freon 12k=1.13 freon 22k=1.18, causing the exhaust temperature to rise, and air should be discharged in time.

　　2.4 Remove dirt and frost on heat exchange equipment

　　 There are data statistics that 1.5mm scale on the water side of the condenser will cause the condensation temperature to rise by 2.8°C and increase the power consumption of the refrigeration device by about 9%. In addition, scaling will corrode the equipment and shorten the service life of the equipment. Therefore, the condenser should be cleaned frequently, and the thickness of the scale should not exceed 1mm at most.