Abstract: Generally, the temperature and humidity of refrigerators change greatly with startup and shutdown. For better products, the temperature change range at different places at different times can be controlled to about 3℃, and the humidity change range will be larger. Some products reach a relative humidity below 50% when the compressor is running, but it may reach about 90% at shutdown. For products with special storage requirements, it cannot meet the needs. In order to achieve the storage effect of such items, water is used as the refrigerant to let the refrigerant pass through the heat exchanger. The temperature of the heat exchanger is near the dew point temperature, and PID technology is used to accurately control the speed of the compressor, the speed of the cooling fan, the temperature of the refrigerant, etc., so as to achieve accurate control of temperature and humidity.

Key words: PID, Refrigerant, Precise temperature and humidity control