What is the difference between ammonia cooling system and refrigerant cooling system?
1. Refrigerant
Ammonia refrigerant is an environmentally friendly refrigerant, but its biggest feature is its toxicity and explosiveness; fluorine refrigerant has a damaging effect on the ozone layer, and its biggest advantage is the safety and reliability of use. Therefore, more than 95% of domestic refrigeration and air conditioning projects currently use it Fluorine is a refrigerant.
2. Compressor
2.1 Ammonia refrigeration unit
Ammonia refrigeration units generally use open piston compressors, open screw compressors or centrifugal compressors as the main refrigeration unit. The advantages and disadvantages of this type of open compressor are as follows:
2.1.1 Advantages:
The compressor is relatively separated from the motor, which makes the compressor applicable to a wider range.
The same compressor can adapt to different refrigerants. In addition to using halogenated hydrocarbon refrigerants, ammonia can also be used as refrigerant by changing the material of some parts.
Different capacity motors can be used according to different refrigerants and working conditions.
The cooling capacity of a single-head unit can reach about 2 million kcal. The cost is lower and the selling price is cheaper.
2.1.2 Disadvantages:
Shaft seals are required to seal the passage of refrigerant and oil leakage, which is also the object of frequent maintenance by users.
JB/T6906 "Screw Type Single-Stage Refrigeration Compressor" stipulates in Article 5.14: the oil leakage at the shaft seal when the open type machine is running should not be greater than 3ml/h. Since Freon and refrigeration oil are mutually soluble, the simultaneous leakage of Freon and refrigeration oil cannot be avoided during use, especially after 1000 hours of operation, due to the wear of the shaft seal, it will aggravate the leakage of Freon and refrigeration oil, and even affect the The user's normal use, thereby increasing the user's maintenance and operating costs. The equipped motor rotates at high speed, and the air flow noise formed by the cooling fan is large. In addition, the compressor itself is also noisy, which affects the environment. The noise of the open-type unit is generally above 85dB(A).
It is necessary to configure complex oil system components such as separate oil separators and oil coolers, which makes the unit bulky, inconvenient to use and maintain, heavy in weight and large in floor space.
low efficiency. Due to the need to use an external motor to drive the oil pump and use an ordinary low-efficiency motor, its efficiency is low, and the energy efficiency ratio under the nominal working condition of the air conditioner is generally not more than 3.9.
Because the single compressor type is generally used, once a fault occurs, the user will be unable to use it, especially for the cold source used in the production process, it will cause great loss to the user.
2.2 Fluorine refrigeration unit
Fluorine refrigeration units generally use semi-hermetic or fully-hermetic compressors, such as scroll compressors, piston compressors, screw compressors, and centrifugal compressors. The advantages and disadvantages of this type of semi-hermetic compressor are as follows:
2.2.1 Advantages:
Due to the semi-closed method and the integrated design of the motor and the compressor, the noise is low, the vibration is small, and there is no leakage of freon and refrigeration oil of the open-type unit, which reduces the maintenance and management costs of users, and does not cause leakage due to leakage. And affect the normal use of users.
Due to the semi-closed method, the motor and the compressor are integrated, and the built-in oil separator muffler greatly reduces the running noise. The difference between the open and semi-closed noise of the same cooling capacity is about 20dB(A).
Due to the built-in oil separator and the internal pressure difference oil supply method, the system has a simple structure, small size, light weight and few moving parts, which improves the reliability.
Due to the use of fluorine-resistant oil-resistant motor and internal pressure differential oil supply mode, there is no need to configure an external motor to drive the oil pump, which improves the energy efficiency ratio of operation. The energy efficiency ratio is generally greater than 4.1 under the nominal working condition of the air conditioner.
For occasions with higher requirements, the double-head or triple-head type can be used. Each refrigeration system is relatively independent. Once a system fails, other systems can work normally without causing too much impact on the production and working environment.
2.2.2 Disadvantages:
Since most of the semi-hermetic screw compressors currently used in China are imported from abroad, the cost price is relatively high. Due to the use of fluorine-resistant and oil-resistant special high-temperature-resistant motors, the cost is relatively high, which increases the material cost of the compressor. Therefore, the sales price of semi-hermetic compressors of the same grade is higher than that of open compressors.
The capacity of a single machine is small, and the current capacity of a single machine head generally does not exceed 1 million kcal.
3. Cooling system
3.1 Ammonia cooling system
3.1. Disadvantages:
Since ammonia is almost insoluble in mineral oil, oil will accumulate on the heat transfer surface of the pipes and heat exchangers of the ammonia refrigeration system, which will affect the heat transfer. The product is bulky.
When ammonia contains oil and water, it has a corrosive effect on copper and copper alloys (except phosphor bronze). Therefore, other copper and copper alloys are generally not allowed to be used in ammonia refrigerators, especially in heat exchangers, only iron pipes can be used as heat exchange. tube, less efficient and less reliable.
Ammonia is highly toxic and has a strong stimulating effect on human organs. When the volume fraction of ammonia vapor in the air reaches 0.5~0.6%, people will be poisoned if they stay in it for about half an hour; when the volume of ammonia vapor in the air reaches 0.5~0.6% When the score reaches 11~14%, it can be ignited (yellow flame), and if it reaches 16~18%, it will cause an explosion. Ammonia vapor has a polluting effect on food. Therefore, the ammonia machine should be ventilated so that the ammonia content does not exceed 0.02mg/L.
3.1.2 Advantages:
Ammonia is a natural refrigerant with 0 ODP and GWP. It has no effect on the atmospheric ozone layer and the greenhouse effect. It is an environmentally friendly refrigerant. cheap price.
3.2 Refrigerant Cooling System
3.2.1 Advantages:
It is miscible with refrigeration oil, no complicated oil is needed, and the structure is simple, small in size and beautiful in appearance.
R22 is a medium-temperature refrigerant, its boiling point is -40.8°C at room temperature, the condensation pressure is similar to that of ammonia, and the refrigerating capacity per unit volume is similar. The saturation pressure is higher at medium temperature and low pressure, so at lower temperatures, R22 is higher than ammonia. it is good.
R22 does not burn, does not explode, and has very little toxicity.
Freon chillers have strong versatility. At present, more than 95% of refrigeration units in the world use fluorine refrigerants.
3.2.2 Disadvantages:
At present, the commonly used refrigerant is R22, its ODP=0.05, and the GWP index is also high. It is a transitional refrigerant. my country's 1998 "National Plan" stipulates that R22 is completely banned from use in 2040 (prohibition of new production of R22 refrigeration equipment) , the price is more expensive.
4. Efficiency
Since ammonia refrigeration units generally use open units, their refrigeration efficiency is slightly lower than that of fluorine semi-hermetic refrigeration units with the same energy.
