Table 4.

Summary of some heat pump assisted dryer (HPAD)/related work to HPAD in agricultural sector

HP assisted dryer/related work to HPAD	Application	Conclusion	References
HP dehumidifier assisted dryer	Grain	Mechanically feasible but not attractive economically due to low fuel prices prevailing at the time.	Flikke et al. (1957)
HP assisted dryer	Grain	Marginal energy saving but has some economic drawback (high capital cost), over drying and risk of spoilage due to mold growth.	Brook (1986)
HP assisted Dryer	Seed	Accelerated drying process without elevating the temperature, less expensive to operate than traditional natural gas fired systems and produces high quality seed.	Fritz et al. (1990)
HP assisted microwave dryer	Sliced carrot and whole root ginger	Higher product through put with low SMER.	Jia et al. (1993)
HP assisted fluidized bed dryer	Pharmaceutical products, fruits and vegetables	Low energy consumption due to high SMER and COP, and high products quality	Alves-Filho and Strommen (1996a, b, c)
Close loop solar assisted HP dryer	Material sensitive to the direct sunlight	Control temperature and humidity in the drying chamber. Since system deal with environmental changes.	Zafri et al. (2007)
Simulation model of HP assisted dryer	Garlic and white mulberry leaves	Applicable to drying herb, adaptable to examine effects of humidity and temperature of dried air to calculate the yield of the dried products with low deviation	Phoungchandang (2009)