The ultra-low temperature freezer or refrigerator is an essential instrument in biochemistry and molecular biology laboratories, and is mainly used for the preservation of biological samples or medicines. Ultra-low temperature refrigerators are often referred to as ultra-low temperature storage boxes and ultra-low temperature freezers. The temperature range of ultra-low temperature freezers is roughly from -60°C to -150°C. Ultra-low temperature freezers have a wide range of applications, such as biological research, metal processing, hospitals, and epidemic prevention systems.
 
Ultra-low temperature freezers can be used to store drugs, vaccines, enzymes, hormones, stem cells, platelets, semen, transplanted skin, and specimens drawn from the human body, plant seed genebanks, gene cloning libraries, and some important biological and chemical reagents, etc., as well as industry research and development. The medicine refrigerator is mainly used for refrigerated storage and transportation of medicines, biological preparations, vaccines and blood to facilitate real-time monitoring of temperature.
 
Ultra-low temperature freezers are different from general refrigerators, and they use a cascade refrigeration method. In ultra-low temperature freezers, there are usually two fully enclosed compressors that are used as high-temperature and low-temperature compressors. The condensing evaporator in the box mostly has a shell and tube structure, and the inside is a four-pipe threaded copper tube, which usually adopts a counter-current heat exchange method. In addition, the low-temperature working system of the freezer is also equipped with a related gas heat exchanger, which can perform the cool-heat  exchange of the low-pressure gas discharged from the evaporator with the high-pressure gas before entering the condensing evaporator. This design method reduces the heat load during the operation of the condensing evaporator, and can utilize the heat generated during the operation of the freezer to a large extent, so as to reduce the energy loss.
 
Generally, when investigating the performance of ultra-low temperature freezers or refrigerators, we should make a comprehensive consideration based on low cooling temperature, size, shape characteristics (horizontal or vertical), compressor noise, vibration amplitude, inside temperature uniformity, failure rate (especially compressor) and the types of optional accessories and in combination with our own use requirements and the space arrangement of the laboratories.