Project Profile: Zhigao high temperature heat pump open close drying unit is used to dry 600 Jin watercress for 15 hours. When the moisture content is high in the early stage, the open drying mode is adopted to quickly heat up and remove most of the moisture, so as to avoid the mildew of vegetables caused by high moisture content and high humidity, and ensure the color and shape of vegetables remain unchanged, and improve the quality of dried vegetables. In the later stage, the closed-loop energy-saving mode is adopted to effectively ensure that the effective nutrients in vegetables are not damaged and lost. The quality of dried vegetables has been significantly improved compared with the previous sun drying and open-loop machine drying. The price of dried vegetables has increased by more than two times compared with the previous products, which greatly improves the economic benefits of users.