Introduction of Common Refrigerants in Cold Storage Systems

At present, the commonly used refrigerants in cold storage systems are mainly divided into the following categories:

1. Ammonia

Ammonia is the most widely used medium pressure and medium temperature refrigerant, and it is also a very superior refrigerant. The focus is on improving safety. Generally, centralized refrigeration is used, and a dedicated computer room is set up. Ammonia is generally used in large refrigeration systems and cold storage with a volume of more than 10,000 tons.

Advantage:

Easy to obtain, low price, moderate pressure, large unit cooling capacity, high heat release coefficient, almost insoluble in oil, small flow resistance, easy to find when leaking.

Shortcoming:

It has a pungent odor, is poisonous, can burn and explode, and has a corrosive effect on copper and copper alloys.

2. Carbon Dioxide

From a technological point of view, carbon dioxide refrigeration uses a cascade system in the low-temperature field and is suitable for a cooling system in the high-temperature field. Since the cost of the cascade system is about 15% higher than that of traditional ammonia and freon, and the efficiency has no advantage, its efficiency can only exert its advantages when the temperature is below -40 degrees.

Advantage:

Carbon dioxide is a natural substance, which has no damaging effect on the atmospheric ozone layer and can reduce the greenhouse effect. It has a wide range of sources and is cheap. Carbon dioxide is safe, non-toxic, non-flammable, non-explosive, has good thermal stability, will not decompose harmful gases even at high temperatures, and will not damage the human body, food, and ecology when leaking.

Shortcoming:

cannot sustain life. If the concentration is too high, it will cause damage to people’s respiratory organs and even suffocation to death. Regardless of the subcritical cycle or the transcritical cycle, the operating pressure of the CO2 refrigeration system will be higher than that of the traditional refrigeration and air conditioning system, which brings many difficulties to the design of the system and components, and the manufacturing cost is relatively high.

3. Lithium Bromide

Lithium bromide is an efficient water vapor absorbent and air humidity regulator that can be used as an absorption refrigerant.

Advantage:

Powered by thermal energy, there is no need to consume a lot of electricity, and the requirements for thermal energy are not high. Except for the canned pump with low power, the whole refrigeration device has no other moving parts, with small vibration, low noise, and relatively quiet operation. The system uses lithium bromide solution as the working medium, and the refrigerator operates in a vacuum state, which is odorless, non-toxic, non-explosive, safe, and reliable. Wide range of cooling capacity. With the change of external load, the unit can perform step-less adjustment of cooling capacity within the range of 10% to 100%, and when the low load is adjusted, the thermal efficiency hardly decreases, the performance is stable, and it can well adapt to the requirements of variable loads. It has strong adaptability to changes in external conditions. Easy to install, easy to manufacture, easy to operate and maintain.

Shortcoming:

In the presence of air, lithium bromide solution is highly corrosive to ordinary carbon steel. This not only affects the life of the unit but also affects the performance and normal operation of the unit. Refrigerators operate under a vacuum, and the air is easily drawn in. Due to the direct use of heat energy, the heat exhaust load of the unit is relatively large, because the condensation and absorption process of the refrigerant vapor all need to be cooled. In addition, the water quality requirements for cooling water are relatively high. In places with poor water quality, special water quality treatment should be carried out when using it, otherwise, it will affect the normal performance of the unit.

4. Freon

Freon is a widely used refrigerant.

Advantage:

Most of them are colorless, have a weak odor, are non-flammable, non-explosive, and are safe refrigerants. Its technology is mature, its performance is stable, its degree of automation is high, and its management cost is low. The system pressure is moderate, the cooling capacity per unit volume is large, and the heat release coefficient is high. Freon and water are almost completely insoluble in each other. There are many types of Freon, which can be selected according to different working conditions. Its boiling point and freezing point are low, and its refrigeration performance is good.

Shortcoming:

The cooling capacity per unit volume is low, causing the greenhouse effect.

4.1. HCFC-R22

Advantage:

Colorless, weak odor, non-flammable, and non-explosive, is a safe refrigerant. The refrigeration capacity and saturation pressure per unit volume of R22 are higher than those of R12 and ammonia.

Shortcoming:

Due to its depleting effect on the ozone layer and high greenhouse effect value, it is listed as the second batch of restricted and banned refrigerants. R22 is not as chemically stable as R12 and is slightly more toxic than R12.

4.2. HFC-R404A

R404A is a mixture of HFC125, HFC-134a, and HFC-143. It is a chlorine-free non-azeotropic mixed refrigerant. It is a colorless gas at room temperature and a colorless and transparent liquid under its own pressure.

R404A is the closest to R-502, this refrigerant is suitable for all environments where R-502 can work normally.

Its ODP is 0, and it is an environmentally friendly refrigerant that does not destroy the atmospheric ozone layer.

R-404A is suitable for new commercial refrigeration equipment, transportation refrigeration equipment, or updated equipment at medium and low temperatures. It is mainly used to replace R22 and R502. It has the characteristics of cleanliness, low toxicity, non-combustibility, and good cooling effect. It is widely used in medium and low-temperature refrigeration systems.

4.3. HFC-R507

R507 is a chlorine-free azeotropic mixed refrigerant, which is a colorless gas at normal temperature and pressure and is a compressed liquefied gas stored in a steel cylinder. Its ODP is 0, so R507 is an environmentally friendly refrigerant that does not destroy the atmospheric ozone layer.

R507 is mainly used to replace R22 and R502. It has the characteristics of cleanliness, low toxicity, non-combustibility, and good refrigeration effect. It is widely used in medium and low-temperature refrigeration systems.