To control and reduce the operating costs of cold storage, in the operation and management of machinery and equipment, we must focus on "oil, fluorine, water, and electricity"; in the management of warehouses, we must strictly control the five barriers of "ice, frost, water, door, and light" ;In quality management, mature technology and technology are adopted to improve product quality. Experts in the large air conditioning and refrigeration market pointed out that 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 the 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, equipment and stored products, give full play to equipment efficiency, and save money. Water, electricity, oil, etc.
1. Prevent the evaporation temperature from being too low
A. The increase of 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 cooling coefficient and an increase in energy consumption. It is estimated that when other conditions remain unchanged, when the evaporation temperature decreases by 1 °C, it will consume 1~2% more power. In addition, the increase in temperature difference will also increase the dehumidification capacity of the air cooler and reduce the humidity of the warehouse, which will increase the dry consumption of food and reduce the quality of food.
B. The evaporation temperature usually used in my country. The difference between the evaporation temperature and the temperature of the warehouse is generally 10 °C. The evaporation temperature of the fruit and vegetable cold storage is generally designed to be about -10 °C, the frozen storage room is -28 °C, and the freezing room is -33 °C. 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℃.
C. Reasons and solutions for low evaporation temperature
(1) There is a problem when the evaporator (cooler) is too small in design, or the actual storage variety is different from the planned storage variety, and the heat load increases. For example, the cold storage for apple storage is used to store garlic sprouts. The harvest period is only a few days. It is impossible to achieve the same daily purchase volume of apples as 5%-15% of the storage capacity, but it will be full in 3 to 5 days. Therefore, if the temperature should be lowered to a suitable storage in time. The temperature can only be achieved by lowering the evaporation temperature. The evaporation area of the evaporator should be increased or the evaporator should be replaced.
(2) The cooling capacity of the compressor is too large. After the load of the warehouse 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 during the storage stage of the goods. Most of the time, the load of the compressor is less than 50%. When the storage temperature drops to a suitable storage temperature, the system load is greatly reduced. If a large machine is still turned on, a large horse-drawn trolley will be formed, the temperature difference will increase, and the power consumption will increase. The number of compressors to be turned on should be reduced or the number of working cylinders should be reduced with an energy regulating device according to changes in warehouse load.
(3) The evaporator is not defrosted in time and the evaporator coil is frosted to reduce the heat transfer coefficient, increase the thermal resistance, reduce the heat transfer effect, and reduce the evaporation of the refrigerant. When the compressor energy remains unchanged, it will lead to The evaporation pressure of the system decreases, and the corresponding evaporation temperature decreases, so it is necessary to defrost in time.
(4) Lubricating oil in the evaporator The lubricating oil in the evaporator will form an oil film on the tube wall of the evaporating coil, which will also reduce the heat transfer coefficient, increase the thermal resistance, reduce the heat transfer effect, and cause the refrigerant to evaporate. If the amount of oil is reduced, the evaporation pressure of the system will be reduced, and the corresponding evaporation temperature will be reduced. Therefore, the oil should be drained to the system in time, and the lubricating oil in the evaporator should be brought out by hot ammonia flushing.
(5) The opening of the expansion valve is too small If the opening of the expansion valve is too small, the liquid supply of the system is small, and the evaporating pressure will decrease under the condition of the same compressor energy, resulting in a decrease in the evaporating temperature. The expansion valve opening should be increased.
2. Prevent the condensing pressure from being too high If the condensing pressure rises, the compression function will increase, the cooling capacity will decrease, the cooling coefficient will decrease, and the energy consumption will increase. It is estimated that when other conditions remain unchanged, the power consumption will increase by about 3% for every 1°C increase in the condensing temperature corresponding to the condensing pressure. It is generally considered that the more economical and reasonable condensing temperature is 3~5 °C higher than the outlet temperature of the cooling water. Causes and solutions for the increase in condenser pressure:
(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 running pumps and increase the water flow.
(4) The cooling water temperature is too high. Supplement low-temperature water (tap water or well water); use frost 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, which takes a long time. In addition, the nozzle holes of the water distributor will be blocked by debris or scale after a long time of use, which will affect the cooling effect. Therefore, 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 heat exchange area of the condenser is reduced. Sufficient heat exchange area is an important guarantee for the heat exchange effect of the condenser. Especially the refrigeration system using the compression condensing unit, because the condenser of this unit has the function of the liquid receiver, when the liquid level in the condenser is too high, the condensing effect of the condenser is seriously affected, and the condensing temperature and pressure 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 the refrigerant is added, the added amount should be strictly controlled to ensure sufficient heat exchange area of the condenser.
(6) The water distribution of the condenser 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. 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 effect of condensation. Therefore, when the water distribution of the water distributor is uneven, the water distributor should be replaced.
(7) There is scale on the condenser pipe. The scale on the condenser pipes leads to an increase in thermal resistance, a decrease in the heat transfer coefficient, a decrease in the heat exchange effect, and an increase in the 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, and the air also forms a gas layer on the surface of the condenser, resulting in additional thermal resistance, reducing the heat transfer efficiency, resulting in an increase in the condensation pressure and condensation temperature. Air should be released in time.
3. Prevent the exhaust temperature from being too high Excessive exhaust temperature will deteriorate the lubrication of the compressor, increase friction, and increase energy consumption; at the same time, excessive exhaust temperature will also cause the heat exchange between the refrigerant gas and the cylinder wall increase, resulting in a decrease in compressor efficiency. Causes and solutions for excessive exhaust temperature:
(1) Poor cooling of the compressor cylinder. Increase cooling water to improve cooling conditions.
(2) The suction superheat of the compressor is too large, improve the insulation of the suction pipe or increase the liquid supply of the evaporator.
(3) The suction pressure is too low.