One kind of cascade heat pump drying system and control method

The present invention relates to a cascade heat pump system and a control method for drying, heat pump drying the cascade system together constitute a high-temperature circuit and a low-level stage circuit using R134a refrigerant circuit in the high temperature stage, the low-temperature stage circuit using the refrigerant R744 . The present invention may cascade heat pump dryer system in accordance with the level of ambient temperature, high temperature operation of the control circuit and the low-level stage circuit, ensure that the system is working in a wide ambient temperature (-20 ℃ ~ 43 ℃) range to meet user requirements.