Due to frost on the surface of the evaporator in the cold storage, it hinders the cold conduction and dissipation of the refrigeration evaporator (pipeline), which ultimately affects the refrigeration effect. When the thickness of the frost layer (ice layer) on the surface of the evaporator reaches a certain level, the refrigeration efficiency even drops below 30%, resulting in a large waste of electric energy and shortening the service life of the refrigeration system. Therefore, it is necessary to carry out cold storage defrosting operations within the appropriate cycle.
2
The purpose of defrosting
1. Improve the cooling efficiency of the system;
2. Ensure the quality of frozen products in the warehouse;
3. Save electric energy;
4. Extend the service life of the cold storage system.
3
Defrosting method
Cold storage defrosting methods: hot gas defrosting (hot fluorine defrosting, hot ammonia defrosting), water spray defrosting, electrical defrosting, mechanical (artificial) defrosting, etc.
1. Hot gas defrosting
Suitable for large, medium and small cold storage pipe defrosting:
The hot high-temperature gaseous refrigerant is directly entered into the evaporator without interception, and the temperature of the evaporator rises, which promotes the melting of the frost layer and the cold exhaust junction or then peeling off. Hot gas defrosting is economical and reliable, easy to maintain and manage, and its investment and construction are not difficult.
2. Spray water to defrost
Mostly used in large and medium-sized air cooler defrosting:
Regularly spray the evaporator with room temperature water to melt the frost layer. Although the defrosting effect is very good, it is more suitable for air coolers and is difficult to operate for evaporation coils. It is also possible to spray the evaporator with a solution with a higher freezing temperature, such as 5%~8% concentrated brine, to prevent frost formation.
3. Electric heating defrosting
Electric heating pipes are mostly used in small and medium-sized air coolers:
The electric heating wire is mostly used for electric heating and defrosting of aluminum pipes in medium and small cold storage, which is simple and easy to use for air coolers; However, for the case of aluminum pipe cold storage, the construction difficulty of aluminum fin installation heating wire is not small, and the failure rate in the future is relatively high, the maintenance and management are difficult, the economy is poor, and the safety factor is relatively low.
4. Mechanical manual defrosting
Small cold storage pipe defrosting is suitable for:
Manual defrosting of cold storage pipes is more economical, the original defrosting method. Artificial defrosting in larger cold stores is unrealistic, it is difficult to raise the head to operate, the physical energy consumption is too fast, the residence time in the warehouse is too long, which is harmful to health, the defrosting is not easy to be thorough, it may cause the evaporator to deform, and even smash the evaporator to cause leakage accidents.
4
Fluorine system defrost method selection
According to the different evaporators of the cold storage, choose a relatively suitable defrosting method. A small number of micro-small cold stores use the door to stop the warehouse and use air heat to naturally defrost. Some high-temperature warehouse air coolers choose to stop the refrigerator, turn on the fan of the air cooler separately, use the fan to circulate air to defrost, and do not use the electric heating pipe to achieve the purpose of energy saving.
1. Defrosting method of air cooler:
(1) There are electric heating pipe frosting and water frosting can be selected, areas with more convenient water can choose water frost coolers, and water shortage areas are biased to choose electric heating pipe frosting air coolers.
(2) Electric heating pipe defrosting is mostly used in small air cooler defrosting; Water flushing and frost coolers are generally installed in large air conditioning and refrigeration systems.
2. Defrosting method of steel row:
There are hot fluoride defrosting and manual defrosting options.
3. Defrosting method of aluminum pipe:
There are thermal fluoride defrosting and electrothermal defrosting options.
5
Cold storage defrosting time
Most cold storage defrosting is now controlled according to the defrosting temperature probe or defrosting time. The number of defrosting times, time, and defrosting stop temperature should be adjusted according to the quantity of goods stacked and the quality of the goods.
At the end of the defrosting time, then to the drip time, the fan is started. Be careful not to set the defrosting time too long, try to achieve a reasonable defrosting. (The defrosting cycle is generally based on the power delivery time or the compressor start-up time.) )
6
Analysis of the causes of excessive frost
There are many reasons for frost formation, such as evaporator structure, atmospheric environment (temperature, humidity), and air velocity. The effects on frost formation and air cooler performance are, in order:
1. The temperature difference between the inlet air and the cold storage air cooler;
2. The humidity of the inhaled air;
3. Fin spacing;
4. Inlet air flow rate.
When the storage temperature temperature is higher than 8 °C, the normal cold storage system hardly frosts; When the ambient temperature is -5°C~ 3°C and the relative humidity of the air is large, the air cooler is easy to frost; When the ambient temperature decreases, the frost rate decreases due to the decrease in the moisture content in the air.