The basic thermodynamic theory of heat pumps originated from the Carnot cycle proposed by French engineer Carnot in 1824. In 1852, the British professor Thomson first proposed a heat pump idea, which was called a "heat multiplier" at that time. In the 1940s and 1960s, heat pump technology entered a period of rapid development, and various heat pump devices were used in schools, hospitals, offices and other places.

The application of heat pump technology to the drying industry has only been developed in the last century. In 1943, the German Sulze Company adopted heat pump technology for the first time when designing a dehumidification system for the basement; in 1950, the United States obtained a patent for heat pump drying technology; subsequently, heat pump drying technology spread around the world. In the 1970s, France installed nearly a thousand heat pump dryers to dry wood. By the 1980s, 3,000 wood processing plants used heat pump dryers. Japan has been studying heat pump drying technology since the 1960s. At present, 12% of the drying equipment adopts heat pump drying technology.

In recent years, researchers from the international community have made new progress in the research of heat pump drying technology. Akhilesh Singh conducted a simulation analysis on the low GWP refrigerants Re90, R600a, R32, R152a, R1234yf as R134a replacement refrigerants, and established a batch heat pump drying model. The results show that the SMER of R32 is better than R134a in terms of energy efficiency and two aspects. With an average SMER of 8% higher and the same input power, the efficiency of R152a is increased by 28.76% and the minimum energy efficiency time is the shortest. On the whole, R32 and R152a can produce better performance, especially R152a is more suitable for heat pump drying systems.

Domestic development status

The research of heat pump drying technology in my country started relatively late, but it is now in a leading position in the world. In 1985, the Shanghai Energy Institute began to develop my country's first heat pump wood dryer. In 1992, it began to develop heat pump grain seed dryers. From 1989 to 1993, Beijing Forestry University and Beijing Refrigerator Factory jointly developed the RCG series of dual-heat source wood dehumidification dryer products, which obtained national patents and were successfully marketed, with good social and economic benefits.

Around 2000, air energy drying technology was gradually developed and applied.