The common phenomenon of cold storage is that the temperature of cold storage can't drop down and it drops slowly. Now, the reasons for the slow drop of cold storage temperature are simply analyzed:1, cold storage due to poor heat insulation or sealing performance, resulting in a large loss of cold energy.The poor thermal insulation performance is due to the insufficient insulation layer thickness of pipelines and warehouse insulation walls, and the poor thermal insulation and insulation effect, which is mainly caused by improper selection of insulation layer thickness in design or poor quality of insulation materials in construction. In addition, in the process of construction and use, the thermal insulation performance of thermal insulation materials may be destroyed, which may lead to the insulation layer being affected with moisture, deformation and even erosion, and its thermal insulation capacity will decrease, and the loss of cold storage capacity will increase, which will obviously slow down the temperature drop. Another important reason for the large cooling loss is the poor sealing performance of the warehouse, and more hot air invades the warehouse from the air leakage. Generally, if dew condensation occurs at the sealing strip of the warehouse door or the sealing part of the heat insulation wall of the cold storage, it means that the sealing is not tight. In addition, frequent opening and closing of the warehouse door or more people entering the warehouse together will also increase the cold loss of the warehouse. Try to avoid opening the warehouse door to prevent a lot of hot air from entering the warehouse. Of course, when the stock is frequently stocked or the stock quantity is too large, the heat load increases sharply, and it usually takes a long time to cool down to the specified temperature.2, the evaporator surface frost is too thick or too much dust, the heat transfer effect is reduced.Another important reason for the slow drop of the storage temperature is the low heat transfer efficiency of the evaporator, which is mainly caused by the thick frost layer or excessive dust accumulation on the evaporator surface. Because the surface temperature of evaporator in cold storage is mostly below 0℃, and the humidity in warehouse is relatively high, the moisture in the air is easy to frost or even freeze on the surface of evaporator, which affects the heat transfer effect of evaporator. In order to prevent the surface frost layer of evaporator from being too thick, it is necessary to defrost it regularly. Here are two simple defrosting methods: ① Stop the machine to defrost. That is, stop the compressor, open the warehouse door, let the warehouse temperature rise, and restart the compressor after the frost layer melts automatically. ② Frosting. After the goods in the warehouse are moved out, the surface of the evaporator tube is directly washed with tap water with high temperature to dissolve or fall off the frost layer. In addition to frosting too thick will lead to poor heat transfer effect of evaporator, the surface of evaporator is too thick due to long-term cleaning, and its heat transfer efficiency will also decrease obviously.3. There is more air or refrigeration oil in the evaporator, which reduces the heat transfer effect.Once more refrigeration oil is attached to the inner surface of the heat transfer tube of the evaporator, its heat transfer coefficient will decrease. Similarly, if there is more air in the heat transfer tube, the heat transfer area of the evaporator will decrease, its heat transfer efficiency will also decrease obviously, and the temperature drop rate of the warehouse will slow down accordingly. Therefore, in daily operation and maintenance, attention should be paid to timely removing the oil stain on the inner surface of the evaporator heat transfer tube and exhausting the air in the evaporator to improve the heat transfer efficiency of the evaporator.4. The throttle valve is improperly adjusted or blocked, and the refrigerant flow is too large or too small.Improper adjustment or blockage of the throttle valve will directly affect the refrigerant flow entering the evaporator. When the throttle valve is opened too much, the refrigerant flow will be too large, the evaporation pressure and temperature will also increase, and the temperature drop rate of the warehouse will slow down; At the same time, when the throttle valve is too small or blocked, the refrigerant flow will also decrease, the refrigeration capacity of the system will also decrease, and the temperature drop rate of the warehouse will also slow down. Generally, the refrigerant flow rate of throttle valve can be judged by observing evaporation pressure, evaporation temperature and frosting of suction pipe. Throttle blockage is an important factor affecting refrigerant flow, and the main causes of throttle blockage are ice blockage and dirty blockage. Ice blocking is due to the poor drying effect of the dryer, and the refrigerant contains moisture. When it flows through the throttle valve, the temperature drops below 0℃, and the moisture in the refrigerant forms ice and blocks the throttle valve hole. Dirty blockage is due to the accumulation of more dirt on the filter screen at the inlet of throttle valve, and the poor circulation of refrigerant leads to blockage.5. The amount of refrigeration in the system is insufficient and the refrigeration capacity is insufficient.There are two main reasons for the lack of refrigerant circulation. One is the lack of refrigerant charge. At this time, just add enough refrigerant. Another reason is that there is a lot of refrigerant leakage in the system. In this case, we should first find the leakage point, focus on checking the joints of various pipes and valves, and find out the leakage parts and repair them before charging enough refrigerant.6, compressor efficiency is low, refrigeration capacity can't meet the requirements of warehouse load.Due to the long-term operation of the compressor, the cylinder liner, piston ring and other parts are seriously worn, and the fitting clearance increases, so the sealing performance will decrease correspondingly, the gas transmission coefficient of the compressor will also decrease, and the refrigeration capacity will decrease. When the cooling capacity is less than the heat load of the warehouse, the temperature of the warehouse will drop slowly. The refrigeration capacity of the compressor can be roughly judged by observing the suction and discharge pressures of the compressor. If the refrigeration capacity of the compressor decreases, the common method is to replace the cylinder liner and piston ring of the compressor. If it still fails to work after replacement, other factors should be considered, and even the machine should be disassembled for maintenance and troubleshooting.Configuration of combined cold storage equipmentCombined cold storage is a kind of quick and simple cold storage equipment developed in recent years, which is to prefabricate various building components and heat insulation boards in a special factory and then assemble them on the construction site. At present, most small combined cold storages can be disassembled for the second time. Briefly introduce the categories of movable cold storage:Outdoor movable cold storage: large, medium and small combined cold storage are generally outdoor in design, which is different from indoor in that the outdoor type needs to be covered with external protective structure and foundation. The outer structure can prevent wind, rain and sun.Indoor movable cold storage: a small combined cold storage built indoors in an existing building.This paper analyzes the reasonable configuration of evaporator and refrigeration unit of combined cold storage equipment.1. The configuration of evaporator evaporation area of combined cold storage equipment is unreasonable;The evaporation area of evaporator in combined cold storage is far from the actual refrigeration technology requirements in configuration. According to the field observation of some combined cold storage, the evaporation area of its evaporator is only about 75% of what should be configured. As we know, the configuration of the evaporator in the combined cold storage should be calculated according to its design temperature requirements, and the evaporation area of the evaporator should be determined, and then the configuration should be carried out according to the refrigeration process requirements. If the evaporator is not configured reasonably according to the design requirements, blindly reducing the configuration area of the evaporator will greatly reduce the refrigeration coefficient per unit area of the evaporator of the combined cold storage, increase the refrigeration load and obviously reduce the energy efficiency ratio, which will lead to various unfavorable factors such as the slow temperature drop in the combined cold storage, the straight increase of the working coefficient of the refrigerator and the increase of the operating cost. Therefore, when designing and selecting the evaporator of the combined cold storage, the area of the evaporator should be selected according to the temperature difference of heat transfer.Second, the configuration of refrigeration unit of movable cold storage equipment is unreasonable:The refrigeration units configured on the combined cold storage produced by some manufacturers are not rationally configured according to the total refrigeration load designed and calculated by the storage and the insulation layer thickness of the enclosure structure of the combined cold storage, but the requirements of rapid cooling in the storage are met by increasing the number of refrigeration units. Take BZL-3×4 mobile cold storage as an example. The storage is 4m long, 3m wide and 2.7m high, with a net volume of 28.723m3. It is equipped with two 2F6.3 series refrigeration units and two independent serpentine smooth tube evaporators, and each unit and its independent evaporator form a complete refrigeration system for refrigeration operation. According to the machine load estimation and analysis of the cold storage, it can be known that the machine load of the movable cold storage is about 140(W/m3), and the actual total load is 4021.22(W)(3458.25kcal). According to the above data, a 2F6.3 series refrigeration unit (standard refrigeration capacity of 4000kcal/h) can also meet the refrigeration process requirements of the movable cold storage (up to-1,000 kcal/h).As we all know, in the refrigeration system, evaporation temperature and evaporation pressure are functionally related to each other, which are related to several conditions such as the temperature of the cooled object, refrigeration capacity, heat exchange area (mainly evaporator area) and compressor capacity. If one of these conditions changes, the evaporation temperature and evaporation pressure of the refrigeration system will change accordingly. In the BZL-3×4 combined cold storage, the evaporation area has not changed, but the capacity of the refrigerator has doubled, which makes the evaporation capacity of the evaporator in the movable cold storage incompatible with the suction capacity of the compressor (the evaporation capacity Vo is much smaller than the suction capacity Vh of the compressor), that is, V 0 < VH, the evaporation pressure Po and the evaporation temperature to drop sharply, the heat transfer temperature difference △t increases, and the cooling in the movable cold storage is difficult. Because the evaporation temperature is too low, the performance index of the compressor is poor.