Why should the cold room defrost?
- Improve the cooling efficiency of the system;
- Guarantee the quality of frozen products in the warehouse;
- Save electricity;
- Extend the service life of the cold storage system.
If the evaporator is frosted, it will affect the normal use of the cold storage, so the evaporator of the cold storage system should pay attention to maintenance,
Frosting of the evaporator will lead to an increase in thermal resistance and a decrease in the heat transfer coefficient. For the air cooler, the cross-sectional area of the air flow will decrease, resulting in an increase in the flow resistance and an increase in power consumption. So it should be defrosted in time.
How to defrost the cold storage? - 4 Defrosting Methods
- The defrosting methods of cold storage include hot gas defrosting (hot fluorine defrosting, hot ammonia defrosting), water spray defrosting, electrical defrosting, mechanical (manual) defrosting, etc.
1. Hot gas defrost
— suitable for defrosting of small, medium, and large cold storage pipes.
The high-temperature gaseous refrigerant on the discharge side of the compressor has directly flowed into the evaporator without interception, and the temperature of the evaporator will rise, causing the junction of the frosted layer and the cold row to melt or peel off.
- Advantages: The advantage of hot gas defrosting is energy saving. Because in the normal refrigeration cycle, the hot ammonia gas needs to be cooled with cooling water to make it liquefied. During the hot gas defrosting process, the frost acts as cooling water while being melted, and the evaporator becomes a condenser that needn’t cool water , and no electricity consumption when defrosting.
2. Water spray defrost
— mostly used in large and medium-sized air coolers for defrosting.
Use room temperature water spray to cool the evaporator to melt the frost layer. Although the defrosting effect of water spray is very good, it is only suitable for air coolers, and it is not easy to operate for evaporative coils. It is also possible to spray the evaporator with a solution with a higher freezing temperature such as 5% to 8% brine to prevent the formation of frost.
- Advantages and disadvantages: The advantages of water spray defrosting are that the defrosting operation is simple and easy to realize automatic control. The disadvantage is that the electricity and water consumption is large, and the defrosting cost is high.
3. Electric heating defrost
— Mostly used for medium and small air coolers.
Electric heating wires are mostly used for the electric heating and defrosting of aluminum tubes in small and medium-sized cold storage. It is relatively simple for air coolers; but in the case of cold storage with aluminum tubes, it is difficult to install heating wires on aluminum fins, and the failure rate in the future is also relatively high. It is difficult to maintain and manage, the economy is also poor, and the safety factor is relatively low.
4. Manual defrost
— It is more suitable for defrosting small cold storage pipes.
Manual defrosting of cold storage pipes is a relatively cost-effective defrosting method. However, it is unrealistic to use manual defrosting in large cold storage, it is difficult to operate with the head up, the physical energy consumption is too fast, and staying in the storage for too long is harmful to health. Moreover, the defrosting is not easy to complete, which may cause the evaporator to deform, or even smash the evaporator, resulting in a refrigerant leakage accident.
Compared with the above defrosting methods, hot gas defrosting is economical and reliable, easy to maintain and manage, and its investment and construction are not difficult.
Analysis of the causes of excessive frosting in the cold storage:
There are many reasons for the effect of frost, such as: evaporator structure, atmospheric environment (temperature, humidity) and air flow rate and so on.
The order of effect on frost formation and air cooler performance is:
- The temperature difference between the inlet air and the cold storage evaporator;
- Humidity of inhaled air;
- The distance between the fins;
- The velocity of the inlet air.
In addition, when the storage temperature is higher than 8 °C, the normal cold storage system is almost free of frost; when the ambient temperature is -5 °C ~ 3 °C and the relative air humidity is high, the air cooler is prone to frost; when the ambient temperature decreases, As the moisture content in the air decreases, the rate of frost formation decreases.
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