In the cold chain distribution center storage system, the refrigeration system is divided into the following types by refrigerants:

1. Ammonia refrigeration system: ammonia refrigeration system is the most widely used in China at present. Ammonia is a kind of low combustible and high toxic refrigerant. although ammonia has large volume refrigerating capacity and more suitable physical properties as refrigerants and is environmentally friendly, it is known as the best refrigerant, but its use is restricted in China because of its safety problems.

2. Fluorine refrigeration system: after ammonia system is restricted in China, fluorine refrigeration system has been developed rapidly. Fluorine refrigerants are safer than ammonia refrigerants. However, fluorine refrigerants are synthetic, which destroy the environment to a certain extent, and the heat transfer efficiency is relatively low.

3. Carbon dioxide system: carbon dioxide, as a refrigerant, was mostly used in transportation refrigeration from the end of the 19th century to the 1930s, and was gradually eliminated because of the loss of refrigeration capacity of the system. At present, it has begun to be attached importance to because of technological progress.

4. About the safety of refrigerants: any refrigerants are safe when used correctly, and the incorrect use of any refrigerants can cause harm.