1. Causes and solutions for low evaporation temperature
Reason 1: The evaporator (cooler) is too small
There are problems in the design, or the actual storage varieties are different from the planned storage varieties, and the heat load increases. For example, the cold storage intended to store apples is used to store garlic sprouts. Since the harvest period of garlic sprouts in a production area is only a few days, it is impossible to achieve the daily purchase volume of 5%-15% of the storage capacity like apples, but it must be filled in 3 to 5 days. Therefore, if the temperature is to be reduced to a suitable storage temperature in time, it can only be achieved by lowering the evaporation temperature.
Solution: The evaporation area of the evaporator should be increased or the evaporator should be replaced.
Reason 2: The cooling capacity of the compressor is too large
After the warehouse load is reduced, the energy of the compressor is not reduced in time. The compressor of the cold storage is matched according to the maximum load of the refrigeration system, and the maximum load of the fruit and vegetable cold storage occurs at the stage of goods entering the warehouse. Most of the other time, the load of the compressor is less than 50%. When the temperature drops to the appropriate storage temperature after the storage, the system load is greatly reduced. If the larger machine is still turned on, it will form a big horse pulling a small cart, the temperature difference will increase, and the power consumption will increase.
Solution: According to the change of the warehouse load, the number of compressors turned on should be reduced or the number of working cylinders should be reduced by using an energy regulating device.
Reason 3: The evaporator is not defrosted in time
The frosting of the evaporator coil reduces its heat transfer coefficient, increases thermal resistance, reduces the heat transfer effect, and reduces the evaporation amount of the refrigerant. Under the condition that the compressor energy remains unchanged, it will cause the evaporation pressure of the system to decrease, and the corresponding evaporation temperature will decrease, so it is necessary to defrost in time.
Solution: Defrost in time.
Reason 4: There is lubricating oil in the evaporator
The lubricating oil in the evaporator will form an oil film on the wall of the evaporating coil, which will also reduce the heat transfer coefficient, increase thermal resistance, reduce the heat transfer effect, reduce the evaporation amount of the refrigerant, and cause the evaporation pressure of the system to decrease, and the corresponding evaporation temperature to decrease.
Solution: Drain the system in time and use hot ammonia to defrost and bring out the lubricating oil in the evaporator.
Reason 5: Expansion valve is too small
The expansion valve is too small, the system liquid supply is small, and the evaporation pressure decreases when the compressor energy remains unchanged, resulting in a decrease in the evaporation temperature.
Solution: The expansion valve opening should be increased.
2. Causes and solutions for excessive condensation pressure
The condensation temperature is the temperature when the high-temperature and high-pressure gas refrigerant is cooled and condensed into a liquid under a certain pressure in the condenser. The condensation pressure is corresponding. The condensation pressure can be estimated from the exhaust pressure. In order to overcome the pressure drop, the exhaust pressure is always higher than the condensation pressure, which is generally equivalent to a saturated condensation temperature difference of 0.5℃.
The condensation temperature depends on the temperature of the cooling air. Under normal circumstances, the wind condensation temperature is 8~12℃ higher than the ambient temperature. If the condensation temperature is too high, the condensation pressure will also increase accordingly, the compression ratio will increase, the shaft work will increase, the gas transmission coefficient will decrease, the actual exhaust volume will decelerate sharply, and the cooling capacity will also decrease; in addition, the increase in condensation pressure will cause the exhaust pressure to increase, the exhaust temperature will also increase, and the power consumption will increase by about 3% for every 1℃ increase in the condensation temperature corresponding to the condensation pressure. The water condensation temperature is 3~5℃ higher than the outlet water temperature of the cooling water.
Causes and solutions for increased condenser pressure:
1. The condenser is too small. Replace or add condensers.
2. The number of condensers in operation is small. Increase the number of operating units.
3. Insufficient cooling water flow. Increase the number of water pumps in operation and increase the water flow.
4. The cooling water temperature is too high. Add low-temperature water (tap water or well water); use defrosting water; ensure the cooling effect of the cooling tower.
5. Clean the cooling tower regularly and keep it clean. When the water temperature is close to the wet bulb temperature of the air, the cooling tower fan should be turned off to reduce power consumption.
6. The heat exchange area of the condenser is reduced. When adding refrigerant, strictly control the amount added to ensure sufficient heat exchange area of the condenser.
7. The condenser water distribution is uneven. When the water distribution is uneven, the water flow in some pipes is the largest, and the water flow in some pipes is small, which will reduce the heat transfer efficiency and increase the condensation temperature.
8. There is scale on the condenser pipe. The scale on the condenser pipe increases the thermal resistance, reduces the heat transfer coefficient, reduces the heat exchange effect, and increases the condensation temperature. Improve the water quality and remove the scale in time.
9. 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, which will produce additional thermal resistance, reduce the heat transfer efficiency, and cause the condensation pressure and condensation temperature to increase. The air should be released in time.
