Cold storage maintenance

1、 Three Prevention Measures for Refrigeration System

1. Prevent low evaporation temperature

If the temperature difference between the evaporation temperature and the warehouse temperature increases, the evaporation temperature will be too low, which will lead to a decrease in the refrigeration coefficient and an increase in energy consumption. It is estimated that, assuming all other conditions remain constant, for every 1 ℃ decrease in evaporation temperature, an additional 1-2% power consumption will be required. In addition, an increase in temperature difference can also cause coldfanThe increase in dehumidification capacity leads to a decrease in humidity in the warehouse, resulting in an increase in food dry consumption and a decrease in food quality.

The difference between evaporation temperature and warehouse temperature is generally 10 ℃. The evaporation temperature for fruit and vegetable cold storage is generally designed to be around -10 ℃, the freezing temperature for frozen goods is -28 ℃, and the freezing room is -33 ℃. However, in actual operation, the temperature difference in many fruit and vegetable storage warehouses is around 15 ℃.

Reasons and solutions for causing low evaporation temperature:

The evaporator is too small, and the evaporation area of the evaporator should be increased or replaced.

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

The evaporator was not defrosted in a timely manner, so it needs to be defrosted in a timely manner.

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

2. Prevent excessive condensation pressure

To prevent excessive condensation pressure, an increase in condensation pressure will lead to an increase in compression function, a decrease in refrigeration capacity, a decrease in refrigeration coefficient, and an increase in energy consumption. It is generally believed that a more economical and reasonable condensation temperature is 3-5 ℃ higher than the outlet temperature of cooling water. Reasons and solutions for causing an increase in condenser pressure:

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

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

Insufficient cooling water flow. Increase the number of running water pumps and increase the water flow rate.

3. Prevent excessive exhaust temperature

Excessive exhaust temperature can deteriorate the lubrication of the compressor, increase friction, and increase energy consumption; Meanwhile, excessive exhaust temperature can also enhance the heat exchange between refrigerant gas and cylinder wall, leading to a decrease in compressor efficiency. Reasons and solutions for causing high exhaust temperature:

Poor cooling of compressor cylinder. Increase cooling water and improve cooling conditions.

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

2、 Maintenance and upkeep 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, which is related to working conditions and insufficient cleanliness of the refrigerant added to the system. The impurities that belong to the control include lubricating oil, air, water, etc. These impurities entering the refrigeration system are extremely detrimental to the operation of the refrigeration device.

2.1 Lubricating oil

Lubricating oil should have an appropriate viscosity. If the viscosity is too high, the flow resistance will be high and the frictional work will increase; If the viscosity is too low, an oil film cannot be formed on the friction surface, and the friction force increases, the frictional work will also increase. The viscosity of lubricating oil decreases with increasing temperature, which will lead to deterioration of lubrication and increase in frictional work. Therefore, when its temperature rises, it should be cooled in a timely manner or the cooling effect should be improved to reduce the oil temperature. When lubricating oil and refrigerant dissolve into each other, smooth oil return should be ensured, otherwise it may cause compressor damage due to oil shortage; At the same time, excessive oil content in the refrigerant can cause a decrease in evaporation pressure, ultimately leading to a decrease in refrigeration coefficient

2.2 Water

The way water enters the system:

Failure to evacuate the air during installation or maintenance, or incomplete evacuation.

During installation or maintenance, evacuate the air and install a dryer.

Enter from an unsealed location. Do not have any leakage points and avoid negative pressure operation.

There is moisture in oil or refrigerant.

2.3 Air

Air entering the system will increase the pressure of condensed water in the system, leading to an increase in total pressure. The air will also form a gas layer on the surface of the condenser, generating additional thermal resistance and reducing heat transfer efficiency, resulting in an increase in condensation pressure and temperature. For every 1kg/cm2 increase in condensation pressure, the power consumption increases by about 6.8%. In addition, the adiabatic index of air (K=1.41) is determined by the adiabatic index of refrigerant (Freon 12k=1.13 Freon 22k=1.18), which causes an increase in exhaust temperature and requires timely discharge of air.

2.4 Remove dirt, frost, etc. from heat exchange equipment

According to statistics, a 1.5mm scale on the water side surface of the condenser can cause a 2.8 ℃ increase in condensation temperature and a 9% increase in power consumption of the refrigeration system. In addition, scaling can corrode equipment and shorten its service life. So it is necessary to regularly clean the condenser, and the maximum thickness of scale should not exceed 1mm.