Ammonia/CO2 Cascade Refrigeration Systems

Scope of Application
Applicable to the case where there are strict requirements for ammonia charging volume.
The applicable CO2 evaporation temperature range of the NH3/CO2 cascade refrigeration system is -52℃~-25℃.
The load needs of quick freezing plants, freezing rooms, low temperature cold storage,etc. Can be met.
Applicable terminal evaporator forms:all forms such as air coolers, coils, IQF machines,etc.;
Applicable to the case with drastic load fluctuation;
Applicable to the case with large feeding height or large feeding resistance of the refrigerating circuit.

System Advantage:
Compared with a conventional ammonia refrigeration system, the ammonia/CO2 cascade refrigeration system has high overall efficiency and low operation cost;as the evaporation temperature decreases,the energy saving amplitude increases.The ammonia/CO2 cascade refrigeration system has higher COP than two compressors at<-35℃;the increase amplitude is increased as the evaporation temperature decreases.
The ammonia refrigerant charging volume of the ammonia/CO2 cascade refrigeration system is only about 10% of that of conventional ammonia pump feeding system.
Ammonia refrigerant is concentrated in the machine room and doesnt enter the personnel operation room, so the system safety is improved.
Because of using the pump feeding mode, the system also has the advantages of the ammonia pump feeding system and thus good stability.
Water defrosting or CO2 hot gas defrosting can be used in evaporator defrosting.
The cost of the operation and maintenance can be reduced by 60%.


System Disadvantages
There is still a small quantity of ammonia refrigerant in the machine room, there are secondary disaster risks.
High initial investment:
The CO2 cascade system is used mainly for quick freezing rooms and food quick-freezing plants. The initial investment in the CO2 cascade system is higher than that in a full-automatic two-compressor refrigeration system, the increase amplitude is different according to different requirements of the system(e.g. The impact of defrosting mode on the cost) and is generally 10%-20%.
The working pressure on the CO2 side is slightly higher than that of a conventional refrigerant.
Countermeasures:
Full-automatic operation of the refrigeration system:Reduce the risk of refrigeration system failure caused by human operation errors.
Active ammonia defense system:The same as the ammonia pump feeding refrigeration system.
The initial investment is high, the investment can be recovered depending upon the saved cost of operation and maintenance.
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