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How to control and reduce the operating cost of cold storage

作者:xuemei 点击:233 发布时间:2020-09-16

To control and reduce the operating cost of cold storage, we should focus on "oil, fluorine, water and electricity" in the operation and management of machinery and equipment; in the warehouse management, we should strictly control the "ice, frost, water, door and lamp"; in the quality management, we should adopt advanced technology and technology to improve the product quality.


Experts in the air conditioning refrigeration market point out that the evaporation pressure and temperature of the refrigeration system and the condensation pressure and temperature are the main parameters. It is an important basis for operation and adjustment. According to the actual conditions and system changes, continuously adjust and control the operation parameters to make it operate under the economic and reasonable parameters, which can ensure the safety of machinery and equipment and storage products, give full play to the equipment efficiency, and save water, electricity, oil, etc.


1. Prevent low evaporation temperature


A. If the temperature difference between evaporation temperature and warehouse temperature increases, the evaporation temperature will be too low, which will lead to the decrease of refrigeration coefficient and increase of energy consumption. It is estimated that if other conditions remain unchanged, the power consumption will be increased by 1 ~ 2% when the evaporation temperature decreases by 1 ℃. In addition, with the increase of temperature difference, the dehumidification capacity of the air cooler will increase and the humidity of the warehouse will decrease, which will lead to the increase of food dry consumption and the decline of food quality.


B. Evaporation temperature is usually used in China. The difference between evaporation temperature and storehouse temperature is generally 10 ℃, the evaporating temperature of fruit and vegetable cold storage is generally designed to be about - 10 ℃, that of frozen material cold storage room is - 28 ℃, and that of freezing room is - 33 ℃. In actual operation, the temperature difference of many fruit and vegetable storage warehouses is about 15 ℃. However, in developed countries such as Europe, the difference between evaporation temperature and warehouse temperature is generally 3 ~ 5 ℃.


C. Causes and solutions of low evaporation temperature


(1) Evaporator (air cooler) too small


There are problems in the design, or the actual storage varieties are different from the planned ones, and the heat load increases. For example, the cold storage for storing apples is used to store garlic sprouts. Because the harvesting time of garlic bolts in a production area is only a few days, it is impossible to achieve the same daily purchase amount as the apple, which is 5% - 15% of the storage capacity, but it will be full in 3-5 days. Therefore, if the temperature should be reduced to the appropriate level in time Storage temperature can only be achieved by reducing evaporation temperature. The evaporation area of evaporator should be increased or replaced.


(2) Excessive cooling capacity of compressor


After the reduction of warehouse load, the energy of compressor was not reduced in time. The compressor in the cold storage is matched according to the refrigeration system * heavy load, while the * heavy load of the fruit and vegetable cold storage occurs in the storage stage of the goods. Most of the time, the load of the compressor is less than 50%. When the storage end temperature drops to the appropriate storage temperature, the system load will be greatly reduced. If the larger machine is still turned on, the large horse drawn trolley will be formed, and the temperature difference will increase and the power consumption will increase.


According to the change of the warehouse load, the number of compressors should be reduced or the number of working cylinders should be reduced by energy regulating device.


(3) Evaporator not defrosted in time


The frosting of evaporator coil reduces the heat transfer coefficient, increases the thermal resistance, reduces the heat transfer effect, and reduces the refrigerant evaporation capacity. Under the condition of constant compressor energy, the evaporation pressure of the system will be reduced and the corresponding evaporation temperature will be reduced. Therefore, defrosting should be carried out in time.


(4) There is lubricating oil in the evaporator


The lubricating oil in the evaporator will form an oil film on the tube wall of the evaporation coil, which will also reduce the heat transfer coefficient, increase the thermal resistance, reduce the heat transfer effect, and reduce the amount of refrigerant evaporation, which will reduce the evaporation pressure and the corresponding evaporation temperature of the system. Therefore, it is necessary to timely drain the oil from the system and use hot ammonia to wash the lubricating oil out of the evaporator.


(5) Too small opening of expansion valve


If the expansion valve is opened too small, the liquid supply of the system is small. When the energy of the compressor remains unchanged, the evaporation pressure decreases, which leads to the decrease of evaporation temperature. The opening of expansion valve should be increased.

 

2. Prevent high condensation pressure


The increase of condensation pressure will lead to the increase of compression function, the reduction of refrigeration capacity, the decrease of refrigeration coefficient and the increase of energy consumption. It is estimated that if other conditions remain unchanged, the power consumption will increase by about 3% for every 1 ℃ increase of condensation temperature corresponding to condensation pressure. It is generally considered that the economical and reasonable condensation temperature is 3 ~ 5 ℃ higher than that of cooling water. Causes and solutions of condenser pressure rise:


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


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


(3) Insufficient cooling water flow. Increase the number of pumps 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 cooling tower. The cooling tower is installed outdoors. Due to the function of fan, a large number of dust, leaves, insects, etc. will enter the tower. If the time is long, the filler and pipeline of the cooling tower will be blocked. In addition, if the water distributor is used for a long time, the spray hole of the water distributor will also be blocked by debris or scale, which will affect the cooling Therefore, the cooling tower should 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 heat exchange area of condenser is reduced. Sufficient heat exchange area is an important guarantee for the heat transfer effect of condenser. Especially for the refrigeration system of the compressor condensing unit, because the condenser of this unit has the function of liquid reservoir, when the liquid level in the condenser is too high, the condensing effect of the condenser will be seriously affected. The condensing temperature and pressure will increase, and the power consumption of the refrigeration compressor will increase. Therefore, attention should be paid to the change of the liquid level during the operation, and the condensate liquid in the condenser should be discharged in time, Strictly control the feeding amount to ensure sufficient heat exchange area of condenser.


(6) The water distribution of condenser is not uniform. When the water distribution is not uniform, the water flow in some tubes is large, and the water flow in some tubes is small, which will reduce the heat transfer efficiency and increase the condensation temperature. A good water flow distribution should be that the water flows down the pipe wall in rotation. If the water flows down from the middle of the pipe, most of the water flow can not achieve the condensation effect. Therefore, when the water distributor distributes water unevenly, the water distributor should be replaced.


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


(8) There is air in the condenser. The air in the condenser increases the partial pressure and the total pressure in the system, and the air will form a gas layer on the surface of the condenser, resulting in additional thermal resistance, which reduces the heat transfer efficiency and increases the condensing pressure and temperature. Air should be released in time.


3. Prevent excessive exhaust temperature


If the exhaust temperature is too high, the lubrication of the compressor will be deteriorated, the friction force will be increased and the energy consumption will be increased; at the same time, the heat exchange between the refrigerant gas and the cylinder wall will be enhanced and the efficiency of the compressor will be reduced. Causes and solutions of high exhaust temperature:


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


(2) If the superheat of suction of compressor is too large, the insulation of suction pipe can be improved or the liquid supply of evaporator can be increased.


(3) The suction pressure is too low.