With the continuous development of refrigeration technology and the rapid expansion of cold storage capacity, how to maintain high-efficiency and low-energy refrigeration and freshness has become a bottleneck restricting the development of cold storage. This article puts forward rational suggestions for the construction of cold storage through technical measures on how to configure an appropriate heat exchange system, how to improve the refrigeration efficiency of the heat exchange system, and how to reduce the cold loss during the refrigeration process.
1. The impact of heat exchanger on the energy consumption of cold storage
1. When the evaporation temperature decreases, the compression ratio of compressor increases, and the energy consumption per unit cooling capacity increases. When the evaporation temperature decreases by 1°C, 3%-4% more power will be consumed. Therefore, minimizing the evaporation temperature difference and increasing the evaporation temperature not only saves power consumption, but also increases the relative humidity in the cold room.
2. As the condensation temperature increases, the compression ratio of the compressor increases. The condensation temperature is between 25℃-40℃. For every 1℃ increase, the power consumption increases by about 3.2%.
3, When the heat exchange surfaces of the condenser and the evaporator are covered with an oil layer, it will cause the condensation temperature to increase and the evaporation temperature to decrease, resulting in a reduction in cooling capacity and an increase in power consumption. When there is a 0.1mm thick oil layer on the inner surface of the condenser, the cooling capacity of the compressor will decrease by 16.6% and the power consumption will increase by 12.4%; when there is a 0.1mm thick oil layer on the inner surface of the evaporator, in order to maintain the determined low temperature Requirements, the evaporation temperature will drop by 2.5℃, and the power consumption will increase by 9.7%.
4. The air in the condenser will increase the condensation temperature. When the air pressure in the system reaches 0.2MPa, the power consumption will increase by 18% and the cooling capacity will decrease by 8%. Therefore, efforts should be made to prevent air from infiltrating into the system and the infiltrated air should be discharged in time. Air.
5. Regularly remove scale and clean the circulating pool to keep the condensed water clean. When the condenser scale is 1.5mm, power consumption will increase by 10%.
6. The surface of the evaporator is covered with a layer of frost, which reduces the heat transfer coefficient of . Especially when the outer surface of finned tube is frosted, it not only increases the heat transfer resistance, but also causes the air flow between the fins. It is difficult to reduce the heat transfer coefficient and heat dissipation area of the surface. When the indoor temperature is lower than 0°C and the temperature difference on both sides of the evaporator tube group is 10°C, the heat transfer coefficient of the evaporator after one month of operation is about 70 before frost.
7. The gas inhaled by the compressor allows a certain degree of superheat , but the superheat is too large. The specific volume of the inhaled gas increases, and its cooling capacity decreases and the relative power consumption increases.
Other energy-saving measures for refrigeration operation:
1. The compressor is one of the core components of the heat exchange system. When designing cold storage, the maximum load is often used to select the compressor. The number of compressors should be reasonably adjusted according to the load or the number of compressors should be reduced. The number of working cylinders matches the system load and the compressor cooling capacity to prevent the phenomenon of "big horse and small cart" and increase energy consumption. [Source: Refrigeration Encyclopedia] In the process of compressor selection and configuration, try to choose the "1+1" matching mode, that is, use a larger compressor with a small compressor or two with the same load. compressors so that they are in optimal operating condition rather than at full load.
2. The evaporative condenser has the characteristics of fast heat exchange, complete heat exchange, and no clogging of the spray device. It saves the investment of cooling tower and water pumps and circulating pools. The cooling water flow is only that of the water-cooled condenser. 1/10, significant energy saving effect. Medium and large cold storages should try to choose mainstream evaporative condensers, which can not only make full use of external natural conditions to achieve refrigerant refrigeration, but also have positive significance in reducing enterprise production costs.
3. The heat transfer amount of the envelope structure and insulation layer accounts for 20%-35% of the total heat load of the cold storage. Therefore, reducing the heat load of the envelope structure can achieve the purpose of energy saving.
4. The opening and closing of the cold storage door will cause a large loss of cooling capacity. Poor performance of the cold storage door may increase energy consumption by 15% or more.If the cold storage door is not closed in time, a large amount of hot air will enter the cold storage. The combination of hot and humid air will easily form frost on the surface of the air cooler and the evaporator. It will also break the balance of the cold storage temperature field and increase the burden on the refrigeration unit.
5. For the ammonia system, drain oil, air, defrost and remove scale regularly to maintain good heat transfer effect of the equipment and avoid too high condensation pressure and too low evaporation pressure.
