How to manage the refrigeration system of cold storage in summer

How to manage the refrigeration system of cold storage in summer

1. Reasonably adjust the operating parameters of the refrigeration system to improve equipment efficiency.

　　 The evaporating pressure and temperature of the refrigeration system and the condensing pressure and temperature are the main parameters. It is an important basis for operation and adjustment. According to actual conditions and system changes, the operating parameters are continuously adjusted and controlled to operate under economical and reasonable parameters, which can ensure the safety of machinery and storage products, give full play to equipment efficiency, and save Water, electricity, oil, etc.

　　 1. Prevent the evaporation temperature from being too low

　　(1) An increase in the temperature difference between the evaporation temperature and the warehouse temperature will make the evaporation 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 evaporating temperature drops by 1℃, it will consume 1~2% more electricity. In addition, the increase in temperature difference will also 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.

　　(2) The evaporation temperature commonly used in my country. 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 around -1010°C, the freezing room is -28°C, and the freezing room is -33°C. In actual operation, many fruit and vegetable storage rooms The temperature difference is about 15℃, while in developed countries such as Europe, the difference between the evaporation temperature and the warehouse temperature is generally 3~5℃

　　(3) Causes and solutions for low evaporation temperature

　　A, the evaporator (air cooler) is too small

There is a problem in the design, or the actual storage species is different from the planned storage species, and the heat load increases. For example, the cold storage intended to store apples is used to store garlic stalks. Since the harvest period of garlic stalks in a production area is only a few days, it cannot be done Like Apple, the daily purchase volume is 5%-15% of the storage capacity, but it will be full in 3~5 days. Therefore, if the temperature is to be brought down to a suitable storage temperature in time, it can only be achieved by reducing the evaporation temperature.

　　 The evaporation area of the evaporator should be increased or the evaporator should be replaced.

　　B, the compressor cooling capacity is too large

　　 After the warehouse load is reduced, the compressor energy is not reduced in time. The compressor of the cold storage is matched according to the large load of the refrigeration system z*, while the z* large load of the fruit and vegetable cold storage occurs during the cargo storage stage. Most of the other time, the compressor load is less than 50%. When the storage temperature drops to a suitable storage temperature, the system load is greatly reduced. If a larger machine is still turned on, a large horse-drawn cart is formed, the temperature difference increases, and the power consumption increases.

　　 The number of compressors to be turned on should be reduced or the number of working cylinders should be reduced with energy adjustment devices according to changes in the warehouse load.

　　C, the evaporator was not defrosted in time

The frosting of the evaporator coil reduces the heat transfer coefficient, increases the thermal resistance, reduces the heat transfer effect, and reduces the refrigerant evaporation. When the compressor energy remains unchanged, the evaporation pressure of the system will decrease, correspondingly The evaporation temperature is lowered, so defrost in time.

　　D, there is lubricating oil in the evaporator

The lubricating oil in the evaporator will form an oil film on the wall of the evaporator coil, which will also reduce the heat transfer coefficient, increase the thermal resistance, reduce the heat transfer effect, and reduce the evaporation of refrigerant, resulting in a decrease in the evaporation pressure of the system , The corresponding evaporation temperature is lowered, so the system should be drained in time, and hot ammonia should be used to flush out the lubricating oil in the evaporator.

　　E, the expansion valve is opened too small

　　 The opening of the expansion valve is too small, and the liquid supply of the system is small. When the compressor energy is unchanged, the evaporation pressure decreases, which leads to the decrease of the evaporation temperature.

　　 The opening degree of the expansion valve should be increased.

　　2, prevent the condensation pressure from being too high

　　 An increase in the condensing pressure will result in an increase in the compression function, a decrease in the cooling capacity, a decrease in the refrigeration coefficient, and an increase in energy consumption. It is estimated that under other conditions unchanged, the power consumption will increase by about 3% for every 1°C increase in the condensation temperature corresponding to the condensation pressure. It is generally considered that the more economical and reasonable condensation temperature is 3~5℃ higher than the outlet temperature of the cooling water. Causes and solutions for the increase in condenser pressure:

　　(1) The condenser selected is too small. Replace or add condenser.

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

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

　　 (4) The cooling water temperature is too high. Replenish low-temperature water (tap water or well water); use flushing water; ensure the cooling effect of the cooling tower. The cooling tower is installed outdoors. Due to the action of the fan, a large amount of dust, leaves, insects, etc. will enter the tower for a long time Otherwise, it will cause blockage of the cooling tower’s packing, pipes, etc. In addition, after a long time of use, the nozzle holes of the water distributor will also be blocked by debris or scale, which affects the cooling effect, so the cooling tower needs to be cleaned regularly to keep it clean. When the water temperature is close to the air wet bulb temperature, the cooling tower fan should be turned off to reduce power consumption.

　　(5) The condenser heat exchange area is reduced. Adequate heat exchange area is an important guarantee for the heat exchange effect of the condenser. Especially the refrigeration system using compression condensing unit, because the condenser of this unit also has the function of liquid reservoir, when the liquid level in the condenser is too high, it will seriously affect the condensing effect of the condenser, and the condensing temperature and pressure will increase. The power consumption of the refrigeration compressor increases. Therefore, attention should be paid to the change of the liquid level during operation, and the condensed liquid in the condenser should be discharged in time. When filling the refrigerant, strictly control the amount added to ensure sufficient heat exchange area of the condenser.

　　(6) The condenser has uneven water distribution. When the water distribution is uneven, the water flow rate z* in some pipes is large, and the water flow rate in some pipes is small, which will reduce the heat transfer efficiency and increase the condensation temperature. A good water flow distribution should be that the water flow rotates down the pipe wall. If the water flow flows down from the middle of the pipe, most of the water flow will not have the condensation effect. Therefore, when the water distributor is unevenly distributed, the water distributor should be replaced.

　　(7) There is scale on the condenser pipe. The scale on the condenser pipe causes the increase of thermal resistance, the decrease of heat transfer coefficient, the decrease of heat exchange effect, and the increase of condensation temperature. Improve water quality and descale in time.

　　(8) There is air in the condenser. The air in the condenser increases the partial pressure in the system and the total pressure. 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 condensation pressure and condensation temperature. The air should be released in time.

　　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 of excessive exhaust temperature and solutions:

　　 (1) Poor cooling of the compressor cylinder. Increase cooling water and improve cooling conditions.

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

　　(3) Inspiratory pressure is too low. The solution is the same as "to prevent the evaporation temperature from being too low".

　　(4) The condensing pressure is too high. The solution is the same as "to prevent the condensation pressure from being too high".

　　 2. Prevent impurities from entering the refrigeration system

　　 The refrigeration system is a sealed circulating system. The refrigerant circulating in the system must 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.

　　 So when using cold storage in summer, we must pay attention to the condition of the refrigeration equipment in the refrigeration system. Arrange the cold storage space reasonably. Save cold storage resources.