The so-called purification industry actually covers a wide range of areas. In addition to the hospital also includes pharmaceutical factories, laboratories, biology research institutes, hospitals in addition to the operating room there are laboratories, pharmacies, blood banks and so on, which need purification equipment, these are the areas that general central air-conditioning enterprises will ignore. At the same time, according to different places, the requirements of purification are different, including dehumidification, humidification, heating, air filtration and so on, to ensure temperature and humidity. For example, it is very difficult to control humidity to 70%, which depends on the machine; while temperature control must be at constant temperature, some important surgical moments require the temperature to be reduced from 20 degrees Celsius to 10 degrees Celsius, all of which need to be achieved by the unit. In addition, in the project of cleaning unit, the requirements for each link are very strict, such as controlling the air volume in the process of cleaning and dust removal, and so on. Most enterprises are difficult to meet the requirements.