Saffron Drying with a Heat-Pump Assisted Hybrid PV-Thermal Solar Dryer

Saffron is the most precious spice and Iran is its largest producer in the world. Saffron quality is profoundly affected by drying methods. The recent research works show that hybrid photovoltaic/thermal solar systems are more efficient in comparison with both individual photovoltaic and thermal systems. Meanwhile, heat pump dryers possess high energy efficiency. Furthermore, they are suitable for heat sensitive crops such as saffron. Therefore, in the present study, performance of a hybrid photovoltaic/thermal solar dryer equipped with a heat-pump system was considered for saffron drying, seeking high quality product and reduction in fossil fuels consumption. The effect of air mass flow rate at three levels (0.008, 0.012 and 0.016 kg/s), drying air temperature at three levels (40, 50 and 60 °C) and two different modes of the dryer (with and without heat-pump unit) on the operating parameters of the dryer was investigated. The results of the investigation showed that total drying time and energy consumption decreased as air flow rate and drying air temperature increased. Applying heat-pump with the dryer, led to a reduction in the drying time and energy consumption and an increase in electrical efficiency of the solar collector. The average of total energy consumption reduced by 33% when the dryer was equipped with heat - pump. Maximum values for electrical and thermal efficiency of the solar collector were found to be 10.8% and 25%, respectively. A maximum dryer efficiency of 72% and a maximum specific moisture extraction rate (SMER) of 1.16 were obtained at the air flow rate of 0.016 kg/s and the air temperature of 60 °C when using the heat-pump.