Heat source and drying process
High temperature drying heat pump dryer:
Heat source is ambient air. Fresh air is heated by condenser and the drying process is completed 
by exhaust the humidity air which heats the material, an open-loop air cycle heat pump dryer.
It is affected by the ambient temperature. Generally, the energy efficiency begins to gradually decrease when the ambient temperature is lower than 15 °C.
Dehumidification drying heat pump dryer:
Heat source is the released latent heat of wet air. The high temperature and 
high humidity air after drying materials is cooled and dehumidified by evaporator, and the latent heat released is absorbed. Then the dehumidified air is heated by condenser to complete the drying process of dry materials, that is, removing moisture from drying materials and dehumidifying wet air process, a closed-loop air cycle heat pump dryer.
The initial temperature of the material is low, and the pre-heating needs to consume auxiliary electric heating heat. In addition, it is basically not affected by the ambient temperature. The energy efficiency is subject to the internal temperature and humidity of the drying room. The greater the humidity is, the faster the moisture removing and the higher the energy efficiency.
Suitable ideal working conditions
High temperature drying heat pump dryer(open-loop)
Ambient temperature is not less than 15℃
Dehumidification drying heat pump dryer(closed-loop)
The dry bulb temperature is between 40 to 55℃ and Relative humidity is 50%~95% in the drying room.
Application case
High temperature drying heat pump dryer(open-loop)
- more than 65℃ temperature or high humidity more than 60% drying
- Need moisturizing and destroyed and deactivated enzyme activity process in initial drying process
- Drying little moisture martials
- Need rapid dehydration and shape
- Slow dehydration and long drying time
- Seasonal drying and high ambient temperature and low humidity
Dehumidification drying heat pump dryer(closed-loop)
- Drying below ambient temperature
- Drying temperature is higher than the ambient temperature not more than 10℃; The ambient humidity is bigger
- Ambient temperature is below 5 ℃
Application in drying flowers and materials containing volatile components
High temperature drying heat pump dryer(open-loop)
- No condensation water collection
- Volatile components such as aromatic hydrocarbons will be lost during exhaust
Dehumidification drying heat pump dryer(closed-loop)
- Closed drying with condensing water collection
- Minimized the loss of volatile components such as aromatic hydrocarbons
Pros and cons
High temperature drying heat pump dryer(open-loop)
- Maturity technology;
- Low production cost;
- Benefit price;
- Stable operation;
- Low failure rate
Dehumidification drying heat pump dryer(closed-loop)
- Complex operating conditions
- Precise control requirements
